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Cornell Waste Management Institute

Department of Crop and Soil Sciences
Cornell University
Ithaca, NY 14853
Phone 607-255-1187 - Email: cwmi@cornell.edu
Updated October 2007
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Murray B. McBride. 2007. Natural Attenuation of Trace Element Availability in Soils. R. Hamon, M. McLaughlin and E. Lombi, Editors. CRC Press. Boca Ratan. 113-136

Brian K. Richards, John F. McCarthy, Tammo S. Steenhuis, Anthony G. Hay, Yuniati Zevi and Annette Dathe. 2007. Journal of Soil and Water Conservation. 62(3):55A-56A.

ABSTRACT (Summary)
Algorithms to count the number colloids in microscope images allow quantitative descriptions of retention processes, and mathematical models are being developed to simulate colloid transport and retention processes.

Bojeong Kim, Murray B. McBride, Brian K. Richards and Tammo S. Steenhuis. 2007. Plant and Soil. 299:227-236

ABSTRACT
A long-term greenhouse column experiment using two soils of different textures amended with dewatered, composted and alkaline-stabilized sludges (biosolids) tested the effect of aging on trace metal solubility, mobility and crop uptake over 15 cropping cycles. Specifically, soil chemical properties and extractability of Cu, Zn and Mo were measured after each cropping cycle, and soybeans ( Glycine max (L.) Merr.) grown as the final crop were analyzed for those metal concentrations in the seeds. Significant Cu loss from the surface soil through leaching, and increased Zn extractability resulting from soil acidification were evident in the early cropping cycles shortly after sludge application, with the degree of Cu mobilization and soil acidification strongly dependent on the type of soil and sludge. Liming to counter acidification in later cycles enhanced Mo extractability and bioavailability substantially, with some sludge treatments producing soybean seeds with Mo concentrations up to 5 times greater than the control. Aging effects were difficult to discern for trace metals in this long-term study, since soil pH changes caused by sludge and liming amendments dominated metal solubility and crop uptake.

Keywords: aging, bioavailability, metal, mobility, sludge, soybeans

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Tammo S. Steenhuis, Annette Dathe, Yuniati Zevi, Jennifer L. Smith, Bin Gao, Stephen B. Shaw, Dilkushi DeAlwis, Samary Amaro-Garcia, Rosemarie Fehrman, M. Ekrem Cakmak, Ian C. Toevs, Benjamin M. Liu, Steven M. Beyer, John T. Crist, Anthony G. Hay, Brian K. Richards, David DiCarlo and John F. McCarthy. 2006. Biologia. 61 Suppl 19:S229-S233

ABSTRACT
Unsaturated soils are considered excellent filters for preventing the transport of pathogenic biocolloids to groundwater, but little is known about the actual mechanisms of biocolloid retention. To obtain a better understanding of these processes, a number of visualization experiments were performed and analyzed.

Keywords: colloid transport, colloid retention, microbial transport, microbial retention, partially-saturated soil, unsaturated porous media, pathogens

Murray B. McBride, K.A. Barrett, Bojeong. Kim, and Beverly Hale. 2006. Soil Science. 17(1): 21-28

ABSTRACT
Long-term changes in the solubility and bioavailability of heavy metals in soils, accumulated as the result of waste application, cannot be predicted without knowledge of the nature of metal retention in these soils. To test the theory that Fe- and Al-rich mineral phases in sewage sludge-amended soils can act as long-term sinks for heavy metals, soils were sampled from two field sites, each with a similar history of multiyear application of either high-Fe, high-Al, or high-Ca sludge (~25 years earlier) but with different textural characteristics. These soils were amended with Cd in the form of CdCl2 in the laboratory to determine Cd solubility as a function of total added Cd over the range of 0 to 20 mg/kg. The slopes of these linear solubility functions, used to determine the strength of Cd sorption, revealed that the high-Fe and high-Al sludge amendments did not improve the soils' affinity for Cd at either site. The high-Al sludge treatment decreased the affinity for Cd in the more coarse-textured soil. The high-Ca sludge amendment, conversely, increased the affinity for Cd, probably a result of the higher soil pH that has persisted since the sludge application. The results suggest that sludge Fe and Al may not be effective in binding Cd in all soils of humid-temperate climates.

Keywords: sewage sludge, biosolids, cadmium adsorption, soil

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Brock, E.H., Quirine M. Ketterings and Murray B. McBride. 2006. Soil Science. 171:388-399

ABSTRACT
Application of animal manure to meet the nitrogen (N) requirements or phosphorus (P) removal rates of agronomic crops can lead to accumulation of micronutrients in soil. The objective of this study was to determine the accumulation, depth distribution, and bioavailability of copper (Cu) and zinc (Zn) in fields amended with liquid dairy (Bos taurus) manure (DM) or solid poultry layer (Gallus domesticus) manure (PM) for up to 40 years using 109 fields of a case study farm in Southern New York. Soil total Zn contents in the plow layer (0-17.5 cm) increased with total P at a rate of 0.02 to 0.03 [mu]g Zn g-1 soil for each [mu]g P g-1 increase in total P. For Cu, the rate of increase was 10 times greater for DM fields (0.02 [mu]g Cu g-1) than that for PM fields (0.002 [mu]g Cu g-1). In the PM field with the longest manure history, Mehlich-3 extractable Zn levels were elevated (>10 mg Zn kg-1 soil) to a depth of 30 cm. For all other fields, Cu and Zn accumulated in the plow layer only. Leachate sampled from intact soil cores (50-cm depth) showed low dissolved Cu and Zn concentrations (<0.12 [mu]g Cu mL-1 and <0.21 [mu]g Zn mL-1) and plant bioavailability, expressed as 0.01 M CaCl2 extractable Cu and Zn of plow layer samples, also suggesting no risk of toxicity to most agronomic crops. Implementation of the P runoff index will discontinue manure application on high P fields and thus prevent buildup of Cu and Zn to concentrations of environmental concern

Ellen Z. Harrison, Summer Rayne Oakes, Matthew Hysell, and Anthony Hay. 2006. Science of the Total Environment. 367(2-3):481-497

ABSTRACT
Sewage sludges are residues resulting from the treatment of waste water released from various sources including homes, industries, medical facilities, street runoff and businesses. Sewage sludges contain nutrients and organic matter that can provide soil benefits and are widely used as soil amendments. They also, however, contain contaminants including metals, pathogens, and organic pollutants. Although current regulations require pathogen reduction and periodic monitoring for some metals prior to land application, there is no requirement to test sewage sludges for the presence of organic chemicals in the U. S. To help fill the gaps in knowledge regarding the presence and concentration of organic chemicals in sewage sludges, the peer-reviewed literature and official governmental reports were examined. Data were found for 516 organic compounds which were grouped into 15 classes. Concentrations were compared to EPA risk-based soil screening limits (SSLs) where available. For 6 of the 15 classes of chemicals identified, there were no SSLs. For the 79 reported chemicals which had SSLs, the maximum reported concentration of 86% exceeded at least one SSL. Eighty-three percent of the 516 chemicals were not on the EPA established list of priority pollutants and 80 percent were not on the EPA’s list of target compounds. Thus analyses targeting these lists will detect only a small fraction of the organic chemicals in sludges. Analysis of the reported data shows that more data has been collected for certain chemical classes such as pesticides, PAHs and PCBs than for others that may pose greater risk such as nitrosamines. The concentration in soil resulting from land application of sludge will be a function of initial concentration in the sludge and soil, the rate of application, management practices and losses. Even for chemicals that degrade readily, if present in high concentrations and applied repeatedly, the soil concentrations may be significantly elevated. The results of this work reinforce the need for a survey of organic chemical contaminants in sewage sludges and for further assessment of the risks they pose.

Keywords: sludge, biosolids, land application

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ABSTRACT
The transport of colloid-contaminant complexes and colloid-sized pathogens through soil to groundwater is of concern. Visualization and quantification of pore-scale colloid behavior will enable better description and simulation of retention mechanisms at individual surfaces, in contrast to breakthrough curves which only provide an integrated signal. We tested two procedures for quantifying colloid movement and retention as observed in pore-scale image sequences. After initial testing with static images, three series of images of synthetic microbead suspensions passing through unsaturated sand were examined. The region procedure (implemented in ImageJ) and the Boolean procedure (implemented in KS400) yielded nearly identical results for initial test images and for total colloid-covered areas in three image series. Because of electronic noise resulting in pixel-level brightness fluctuations the Boolean procedure tended to underestimate attached colloid counts and conversely overestimate mobile colloid counts. The region procedure had a smaller overestimation error of attached colloids. Reliable quantification of colloid retention at pore scale can be used to improve current understanding on the transport mechanisms of colloids in unsaturated porous media. For example, attachment counts at individual air/water meniscus/solid interface were well described by Langmuir isotherms.

Keywords: colloids, quantification, visualization

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Kim, Bojeong and Murray B. McBride. 2006. Environmental Pollution. 144:475-482.

ABSTRACT
Sequential extraction procedures are widely used to estimate the quantity of trace metals bound to different solid fractions in contaminated soils. However, reliability of speciation of trace metals by these procedures remains largely unexamined. In the present study, the selectivity of each extraction step was tested by observing the effect of reversing the extraction order in the procedure. Two different sequential extraction methods and their reversed modes were used for metal fractionation in sewage sludge-amended soils. Significantly increased amounts of extractable metals (Cd, Cu, Pb and Zn) were evident in the sludge-amended soils compared to control soil by all extraction schemes; however, the amounts of metals extracted by each step were strongly dependent on the order of extraction, the type of reagents and the nature of the individual metals. Caution is advised in deducing the forms of soil metals from sequential extraction results from metal-contaminated soils.

Keywords: sequential extraction, sludge-amended soil, extraction order, citrate-bicarbonate-dithionite extraction, sodium pyrophosphate

Murray B. McBride and Brian K. Richards. 2006. Working paper for NEC1001. Cornell University. 1-7.

ABSTRACT (Summary)
An increase in the total concentration and/or availability of trace elements is a typical consequence of applying wastes to soil. However, analyzing the concentrations of trace elements in soils is a complex process. A clear understanding of the intended purpose of the test results will help guide the choice of analytical approach to be used. In this article we first present some basic concepts regarding trace elements in soil and the general approaches that have historically been used in soil testing. We then describe advantages and limitations of differing chemical approaches used to determine the concentration and availability of trace elements in soils. The trend toward less chemically-aggressive tests is improving the correlation between test results and actual impacts of the elements in question. We discuss some of the practical difficulties associated with the analysis of trace levels of elements in the complex matrix that is soil.

Linda P. Wagenet, Ann T. Lemley, Deborah G. Grantham, Ellen Z. Harrison, Katrie Hillman, Kevin Mathers and Lee Hanle Younge. 2005. Journal of Extension. 43(2):10

ABSTRACT
We describe a program that evolved from Cooperative Extension educators' concern about declining attendance at face-to-face workshops on environmental issues. As a result, we developed an education program comprising six television programs; a radio series; Web-based materials; and information supplied to libraries. We randomly selected individuals to complete a written survey assessing their environmental knowledge and commitment pre- and post-broadcast. Our analyses indicate that watching the television programs did not predict significant changes in environmental knowledge or commitment. Our study findings do not strongly support the effectiveness of using local public television as an environmental education tool.

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Murray B. McBride. 2005. Communications in Soil Science and Plant Analysis. 36:2489-2501

ABSTRACT
Wastes applied to agricultural land can contain significant concentrations of bioavailable molybdenum (Mo). Because Mo uptake by forage crops could lead to hypocuprosis in ruminants, more knowledge is needed about which crops are most efficient in accumulating Mo. At an old sewage sludge-amended site, the concentrations of Mo, copper (Cu), and several other trace metals were measured in various grass species. Generally, the grasses grown on the sludge site contained higher Mo concentrations than the same species grown on a nearby control site. However, because Cu concentrations were also higher in the sludge-grown grasses, Cu:Mo ratios in the grasses were frequently higher on the sludge site. In contrast, all legumes tested (alfalfa, birdsfoot trefoil, red clover, pea), as well as canola and beets, had lower Cu:Mo ratios when grown on the sludge site. Sulfur concentrations in the two crops analyzed for this element (canola and pea) were higher on the sludge site than the control. It is concluded that Mo, Cu, and sulfur (S) bioavailability remains elevated in the soil several decades after sewage sludge application.

Keywords: molybdenum, copper, sulfur, sewage sludge, biosolids, forage legumes, grasses, heavy metal uptake, bioavailability, soils

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  • RISK PERCEPTION, RISK COMMUNICATION, AND STAKEHOLDER INVOLVEMENT FOR BIOSOLIDS MANAGEMENT AND RESEARCH

    • Ned Beecher, Ellen Z. Harrison, Nora Goldstein, Mary McDaniel, Patrick Field, and Lawrence Susskind. 2005. Journal of Environmental Quality. 34:122-128

    ABSTRACT
    An individual's perception of risk develops from his or her values, beliefs, and experiences. Social scientists have identified factors that affect perceptions of risk, such as whether the risk is knowable (uncertainty), voluntary (can the individual control exposure?), and equitable (how fairly is the risk distributed?). There are measurable differences in how technical experts and citizen stakeholders define and assess risk. Citizen knowledge and technical expertise are both relevant to assessing risk; thus, the 2002 National Research Council panel on biosolids recommended stakeholder involvement in biosolids risk assessments. A survey in 2002 identified some of the factors that influence an individual's perception of the risks involved in a neighbor's use of biosolids. Risk communication was developed to address the gap between experts and the public in knowledge of technical topics. Biosolids management and research may benefit from applications of current risk communication theory that emphasizes (i) two-way communications (dialogue); (ii) that the public has useful knowledge and concerns that need to be acknowledged; and (iii) that what may matter most is the credibility of the purveyor of information and the levels of trustworthiness, fairness, and respect that he or she (or the organization) demonstrates, which can require cultural change. Initial experiences in applying the dialogue and cultural change stages of risk communication theory—as well as consensus-building and joint fact-finding—to biosolids research suggest that future research outcomes can be made more useful to decision-makers and more credible to the broader public. Sharing control of the research process with diverse stakeholders can make research more focused, relevant, and widely understood.

    Kimberly Ann V. Zubris and Brian K. Richards. 2005. Environmental Pollution. 138:201-211

    ABSTRACT
    Synthetic fabric fibers have been proposed as indicators of past spreading of wastewater sludge. Synthetic fiber detectability was examined in sludges (dewatered, pelletized, composted, alkaline-stabilized) and in soils from experimental columns and field sites applied with those sludge products. Fibers (isolated by water extraction and examined using polarized light microscopy) were detectable in sludge products and in soil columns over 5 years after application, retaining characteristics observed in the applied sludge. Concentrations mirrored (within a factor of 2) predictions based on soil dilution. Fibers were detectable in field site soils up to 15 years after application, again retaining the characteristics seen in sludge products. Concentrations correlated with residual sludge metal concentration gradients in a well-characterized field site. Fibers found along preferential flow paths and/or in horizons largely below the mixed layer suggest some potential for translocation. Synthetic fibers were shown to be rapid and semi-quantitative indicators of past sludge application.

    Keywords: synthetic fabric fibers, sludge, soil contamination, biosolids, soil analysis, wastewater sludge

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  • ENVIRONMENTAL IMPACTS OF APPLYING MANURE, FERTILIZER, AND SEWAGE BIOSOLIDS ON A DAIRY FARM

    • Brian K. Richards, Brendan M. Schulte, Arik Heilig, Tammo S. Steenhuis, Murray B. McBride, Ellen Z. Harrison, and Philip Dickson. 2004. Journal of the American Water Resources Association. 40(4):1025-1042

    ABSTRACT
    Farms that once spread only manures are now also applying sewage biosolids (sludge) and/or other wastes such as those from food processing. The objective of this study was to monitor environmental impacts at a dairy farm applying these materials. Fields were selected representing recent waste applications of manure (M1, M2), sewage biosolids (B1, B2), or fertilizer only control (F1, F2), although most fields had historical biosolids applications. Fields representing each treatment were not experimental replicates because of varying applications and soil characteristics. Septage and food processing wastes were also applied. Soil percolates were collected with wick lysimeters. Runoff was sampled at seven stream sites. Test field soils and alfalfa (Medicago sativa) were analyzed for trace elements. Cumulative trace metal loadings were low, at most only 1 percent of USEPA Part 503 limits. Surface soil enrichment was most evident for Mo, P, and S. Alfalfa tissue showed no trends of concern. The B2 site had the greatest percolate concentrations for 6 of 13 elements. Percolate Cu was somewhat elevated at Sites M1, M2, B2, and F1. Percolate sodium was elevated on all M and B fields and sulfur was greatest at M2, B1, and B2. Soluble orthophosphate correlated with stream discharge during intensive monitoring of Stream Sites S1 (fertilizer) and S2 (biosolids). Peaks in S2 streamwater Mo lagged large runoff events by five days. Total streamwater export of Cu, Na, Mo, and soluble P were greater from the S2 biosolids subwatershed than from the S1 fertilizer subwatershed. Percolate concentrations exceeded corresponding streamwater concentrations in most cases.

    Keywords: nonpoint source pollution, sludge, waste/sewage treatment, runoff, percolate, farm management

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    Murray B. McBride, Brian K. Richards and Tammo S. Steenhuis. 2004. Plant and Soil. 262:71-84

    ABSTRACT
    In order to assess the potential impact of long-term sewage sludge application on soil health, the equivalent of about 25 years of agronomic applications of low-metal ('EQ') sewage sludge products were made to greenhouse soil columns. After a 6-year period of 'equilibration', during which time successive crops were grown with irrigation by simulated acid rain, the plant-available quantities of trace elements were estimated in the soils by extraction with 0.01 M CaCl2 at 90 °C, and measured directly by uptake into a crop of red clover (Trifolium pretense L.). Soil pH had a strong influence on the level of extractable and plant-available metals, and because the tested sludge products affected soil pH differently, pH was directly factored into the comparison of different sludge treatments with controls. CaCl2-extractable levels of several metals (Cu, Zn, Mo), sulfur and phosphorus were found to be higher in the soils amended with organic-rich sludge products than in the control soils. However, extractable Cd and Ni were not significantly elevated by the sludge amendments, presumably because of the low total loading of these metals. Copper, Zn and Mo applied in the form of sludge ash had low soil extractability, suggesting that these trace metals were trapped in high-temperature mineral phases formed during sludge incineration, and resisted subsequent weathering in the soil environment. Extractable soil metals in the alkaline-stabilized sludge treatment were also generally low. Phytotoxicity from the sludge metal loadings (Zn < 125, Cu < 135 kg/ha), was not clearly indicated as long as soil pH was maintained in the 6-7 range by lime amendment. Nevertheless, unexplained depressions in yield were noted with some of the sludge products applied, particularly the dewatered and composted materials. On limed soil columns, the most consistent effect of sludge product amendment on red clover composition was a marked increase in plant Mo.

    Keywords: biosolids, cadmium, copper, heavy metals, molybdenum, zinc

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    Shabnam Qureshi, Brian K. Richards, Tammo S. Steenhuis, Murray B. McBride, Philippe Baveye, Sylvie Dousset. 2004. Environmental Pollution. 132(1):61-71.

    ABSTRACT
    Leaching of sludge-borne trace elements has been observed in experimental and field studies. The role of microbial processes in the mobilization of trace elements from wastewater sludge is poorly defined. Our objectives were to determine trace element mobilization from sludge subjected to treatments representing microbial acidification, direct chemical acidification and no acidification, and to determine the readsorption potential of mobilized elements using calcareous sand. Triplicate columns (10-cm diameter) for incubation and leaching of sludge had a top layer of digested dewatered sludge (either untreated, acidified with H2SO4, or limed with CaCO3; all mixed with glass beads to prevent ponding) and a lower glass bead support bed. Glass beads in the sludge layer, support layer or both were replaced by calcareous sand in four treatments used for testing the readsorption potential of mobilized elements. Eight sequential 8-day incubation and leaching cycles were operated, each consisting of 7.6 d of incubation at 28 °C followed by 8 h of leaching with synthetic acid rain applied at 0.25 cm/h. Leachates were analyzed for trace elements, nitrate and pH, and sludge layer microbial respiration was measured. The largest trace element, nitrate and S losses occurred in treatments with the greatest pH depression and greatest microbial respiration rates. Cumulative leaching losses from both microbial acidification and direct acidification treatments were >90% of Zn and 64–80% of Cu and Ni. Preventing acidification with sludge layer lime or sand restricted leaching for all trace elements except Mo. Results suggested that the primary microbial role in the rapid leaching of trace elements was acidification, with results from direct acidification being nearly identical to microbial acidification. Microbial activity in the presence of materials that prevented acidification mobilized far lower concentrations of trace elements, with the exception of Mo. Trace elements mobilized by acidification were readsorbed by calcareous sand when present.

    Murray B. McBride and B. Hale. 2004. Soil Science, 169(7):505-514

    ABSTRACT
    Molybdenum (Mo) at elevated concentrations in nonacid soils is readily taken up into forages, particularly legumes, and can result in secondary copper deficiency or molybdenosis in ruminants. Because sewage sludge products are commonly higher in total and available Mo than soils, amendment of soils with sludges could cause health problems in livestock. To determine the long-term potential for sewage sludge amendments to raise forage Mo concentrations, alfalfa was grown on two controlled experimental sludge application sites at the University of Guelph, where three different sludge types (high Ca, high Al, high Fe) had last been applied 20 years earlier. Analysis of the alfalfa harvested from these two field sites, which had near-neutral soils of different texture, showed that more than about 5 kg ha-1 of cumulative Mo loading 20 years earlier could lower the forage Cu/Mo concentration ratio below 2/1, considered to be the lower limit to protect the health of grazing ruminants. The decreased Cu/Mo ratio was due to increases in alfalfa Mo concentrations, as alfalfa Cu was not significantly increased by the sludge amendments at either site. All six sludge treatments (three sludge types at two application rates) investigated at Elora and four of six treatments at Cambridge showed significant increases in alfalfa Mo relative to the controls. At Elora, the critical forage Cu/Mo ratio of 2 was reached with about 10 to 12 kg ha-1 total Mo applied historically from sludge, whereas this ratio was reached near 6 kg ha-1 total Mo applied at Cambridge. Soil analyses revealed that although CaCl2-extractable Mo was significantly increased in five of the six sewage sludge treatments at Elora and four of the six sludge treatments at Cambridge, most of the Mo applied in several sludge materials (particularly the high-Ca sludge) had been lost from the topsoil at both sites. Over all experimental plots at both sites, the alfalfa Mo concentration was correlated to readily extractable Mo (by 0.01 M CaCl2) in the soil. Total soil Mo and past Mo loading to soil were less reliable predictors of Mo concentration in alfalfa than the soil test for readily extractable Mo. The results revealed that residual plant-available Mo in sludge-amended soils can persist for decades with some types of sludge materials, but leaching losses of Mo may reduce the impact of residual Mo in soils. The need for stronger regulation and monitoring of Mo in waste materials intended for forage, pasture, and range land application is indicated.

    Keywords: biosolids, copper deficiency in ruminants, copper/molybdenum ratio, heavy metals, hypocuprosis

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    Murray B. McBride and J. Cherney. 2004. Communications in Soil Science and Plant Analysis, 35(3 & 4):517-535.

    ABSTRACT
    Farm application of sewage sludge products (biosolids) can potentially increase soil concentrations of macronutrients [especially phosphorus (P)], micronutrients [including sulfur (S), copper (Cu), zinc (Zn), molybdenum (Mo)] and heavy metals. In the present study, sampling and elemental analysis by ICP of soils and forages from 13 farms in Upstate New York that had applied sludge showed some elements to be significantly elevated (relative to controls) in the soils and crops of several farms. Specifically, total soil cadmium (Cd), chromium (Cr), Cu, vanadium (V), nickel (Ni), P, S, and Zn on several farms were significantly higher than the average for farms of this region, although the estimated soil loadings of regulated heavy metals from sludge application were no more than a few percent of the EPA 503 permitted loadings. For most elements, the higher soil concentrations did not result in significantly higher average forage concentrations. Nevertheless, the average forage S concentration was significantly increased on every farm that had applied sludge, most farms had significantly elevated average forage Zn, and three farms had significantly elevated average forage Mo contents. The highest forage Mo was found on several farms that had made a single application of an alkaline-stabilized sludge product. Forage Mo content was significantly correlated to two soil properties: pH and CaCl2-extractable Mo. Contrary to expectation, averaged over all farms, Mo contents of grass forages (2.4±1.9 mg/kg) were not generally lower than Mo contents of the forage legumes, alfalfa (2.0±2.2 mg/kg) and red clover (2.6±2.4 mg/kg). More intensive sampling of a single alkaline sludge-amended field revealed high variability in Mo content of alfalfa (0.67–7.4 mg/kg), soil pH, and CaCl2-extractable Mo in the soils. The alfalfa Cu/Mo ratio was strongly correlated to both soil pH and CaCl2-extractable Mo at the site of sampling. A laboratory experiment demonstrated that liming acidic (pH 5–6) sludge-amended soils to about pH 7 increased Mo solubility by about 10-fold, while having little effect on soluble S. It is concluded that, where sewage sludges are used as farm fertilizers, the greatest short-term risk to livestock is hypocuprosis induced by higher forage content of Mo and S.

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    Ellen Z. Harrison and Molly Moffe. 2003. Journal of the American Water Resources Association. 39(1):87-97.

    ABSTRACT
    Maintenance of the more than 24 million septic tanks in the US requires removal and disposal of septage. Disposal options include application to agricultural lands where the nutrients and organic matter can provide soil benefits. However, pathogens and contaminants are also contained in septage. An extensive search turned up very few data on septage quality, and those reveal high variability. The data used by USEPA in developing regulations had the lowest metal concentrations among the nine data sets that could be compared. Based on these data, EPA assumed that septage could be applied to agricultural land for more than 100 applications before reaching unacceptable cumulative loading of metals. They thus did not establish federal standards for metals in septage, and no monitoring is required under federal rules governing septage disposal. Analysis of the nine data sets we found showed that field site life would be reached in less than 100 applications for most septage and cumulative loading limits established by USEPA for sewage sludges will be exceeded in 16 applications for some septage as opposed to the 100 application estimate used by USEPA. Determination of acceptable cumulative loading depends on numerous technical and policy considerations. All septage sources reached the more restrictive loading limits such as those established by NYSDEC and the recommendations in Cornell publications in less than 100 applications. In one case the cumulative limit for copper was exceeded in a single application. These findings suggest additional data are needed on septage quality and that the federal and state agencies responsible for regulating application of septage to agricultural land should reassess their standards.

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    Keywords: septage, land application, Part 503 standards, site life, septic tank, septic waste, loading limits, cumulative limits

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    Shabnam Qureshi, Brian K. Richards, Murray B. McBride, Phillipe Baveye, and Tammo S. Steenhuis. 2003. Journal of Environmental Quality. 32:2067-2075

    ABSTRACT
    Due to geochemical processes, peat soils often have elevated concentrations of trace elements, which are gradually released following drainage for agriculture. Our objectives were to use incubation temperatures to vary microbial activity in two metalliferous peats (M7 acidic peat and M3 neutral peat) from the Elba, New York region, and to use periodic leaching to assess the extent of trace element release from these soils. Dried soils were mixed with glass beads to maintain aeration, moistened, and incubated at 4, 16, 28, and 37°C in 10-cm-diameter x 8-cm-tall columns. Five incubation-leaching cycles were performed, each consisting of 7.3 d of incubation (28 d for the final cycle) followed by 16 h of leaching with synthetic acid rain at 2.5 mm h-1 . Microbial activity was determined initially and after the final leaching by measuring C mineralization following glucose stimulation. Cumulative respiration results were ranked 28 > 16 > 4 > 37°C, with M7 acidic peat respiration values greater than M3 neutral peat at each temperature. Initial leachate pH levels were between 2 and 4, with acidification less pronounced and shorter-lived for the M3 peat. Leachate S, dissolved organic carbon (DOC), NO3-N, and trace elements declined with successive leachings (rebounding slightly in the final M3 leachate), with concentrations typically greater in the M7 leachate. Elemental losses followed the same general ranking (28 > 16 > 4 > 37°C); losses at 28°C were 15 to 22% for As, Cd, Ni, and Zn from the M7 peat; losses from M3 were comparable only for Cu (1%) and Ni (19%). The correlation of respiration with S, DOC, and trace elements losses indicates that microbial processes mediated the release of trace elements in both peat soils. Neutral M3 peat pH levels limited losses of most analytes.

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    TOXIC METALS IN SEWAGE SLUDGE-AMENDED SOILS: HAS PROMOTION OF BENEFICIAL USE DISCOUNTED THE RISKS?

    Murray B. McBride. 2003. Advances in Environmental Research. 8:5-19

    ABSTRACT
    Land application of contaminated waste products has been defended as beneficial use by some scientists and regulators, based on the premise that the behavior of any toxins accumulated in soils from this practice is reasonably well understood and will not have detrimental agronomic or environmental impacts into the foreseeable future. In this review, I use the case of toxic metals in sewage sludges applied to agricultural land to illustrate that metal behavior in soils and plant uptake is difficult to generalize because it is strongly dependent on the nature of the metal, sludge, soil properties and crop. Nevertheless, permitted agricultural loadings of toxic metals from sewage sludges are typically regulated using the sole criterion of total metal loading or concentrations in soils. Several critical generalizing assumptions about the behavior of sludge-borne metals in soil-crop systems, built into the US EPA risk assessment for metals, have tended to underestimate risks and are shown not to be well justified by published research. It is argued that, in the absence of a basic understanding of metal behavior in each specific situation, a more precautionary approach to toxic metal additions to soils is warranted.

    Keywords: heavy metals; sewage sludge; biosolids; US EPA; risk assessment; toxicity; agricultural crops; regulation; land application

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    ABSTRACT
    With the availability of sensitive multielement analytical capability, it is no longer essential to use chemically aggressive soil tests to extract measurable levels of most trace elements. However, the relative abilities of mild and aggressive extractants to assess metal bioavailability in soils have rarely been compared. A greenhouse experiment was carried out to compare a mild soil extractant (hot 0.01 M CaCl2) with an aggressive one (Mehlich 3) for predicting accumulation of trace metals by red clover (Trifolium pratense L.). Clover was grown on large columns of nonacid fine-textured and acid coarse-textured soils that had been amended several years earlier by a heavy application of sewage sludge products, and pH was subsequently adjusted using CaCO3 or H2 SO4. The soil extractants (CaCl2 and Mehlich 3) and clover tissue were analyzed for trace metals (As, Cd, Mo, Cu, Ni, Mn, Pb, and Zn) by axial-view ICP spectrophotometry. Linear regression analyses were performed to relate the concentration of each trace element in the red clover tissue to the concentration extracted from the soil. The results indicate that CaCl2 extraction is more reliable than Mehlich 3 extraction when evaluating plant availability of trace elements in soils with a wide range of properties (especially pH). The strongly acidic nature of the Mehlich 3 extractant caused large quantities of metals such as Zn, Cd, Cu, and Ni to be extracted from metal-contaminated soils even when the plant availability of these metals was low because of near-neutral soil pH or high clay and organic matter content. Conversely, in coarse-textured and acid soils containing lower total concentrations of metals, plant-available metals were often relatively high, yet Mehlich 3 frequently extracted smaller quantities of metals from these soils than from the near-neutral soils. We conclude that dilute CaCl2 is preferable to Mehlich 3 as a universal soil extractant for estimating short-term trace metal availability to crops. (Soil Science 2003;168:000-000)

    Keywords: Soil tests, heavy metals, uptake, bioavailability, trifolium pratense, sewage sludge, molybdenum, zinc.

    Ellen Z. Harrison and Summer Rayne Oakes. 2002. New Solutions, A Journal of Environmental and Occupational Health Policy. 12(4):387-408

    ABSTRACT
    The majority of US sewage sludges are disposed by application to land for use as a soil amendment. Class B sludges, containing a complex mix of chemical and biological contaminants, comprise the majority. Residents near land application sites report illness. Symptoms of more than 328 people involved in 39 incidents in 15 states are described. Investigation and tracking of the incidents by agencies is poor. Only one of 10 EPA regions provided substantial information on the incidents in their region. Investigations, when conducted, focused on compliance with regulations. No substantial health-related investigations were conducted by federal, state or local officials. A system for tracking and investigation is needed. Analysis of the limited data suggests that surface-applied Class B sludges present the greatest risk and should be eliminated. However, even under less risky application scenarios, the potential for off-site movement of chemicals, pathogens and biological agents suggest that their use should be eliminated.

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    Murray B. McBride. 2002. Soil Science. 167:62–67

    ABSTRACT
    Although it is well established that Cd uptake by crops is dependent on soil total Cd and soil pH, actual prediction of uptake based simultaneously on these two soil parameters has not generally been tested. In the present study, reanalyzing available data on the uptake of cadmium by lettuce, Swiss chard, and corn leaves from sewage-sludge- amended soils showed that an equation of general form:

    log (Cd)crop = a = b log (soil Cd) = c (soil pH)

    which includes the predictive factors of soil pH and total soil Cd only, was reasonably predictive of above-ground plant tissue Cd concentration, (Cd)crop, although the coefficients a, b, and c varied depending on the particular soil, climate, and crop type. Nevertheless, this equation allows a more direct comparison of Cd bioavailability in sewage-sludgetreated and uncontaminated soils because, in many experiments, soil pH is very different in the treated and control plots. After allowing for pH effects, the data fail to show consistently that Cd applied to soils in sewage sludge is less bioavailable than native Cd or Cd from other sources of contamination. The strongest evidence for a protective effect of sewage sludge in limiting Cd uptake by leafy crops was for low Cd loadings and nonacid soil conditions. Overall, however, long-term bioavailability depended primarily on the soil pH and Cd concentration in the soil. Although other factors, particularly soil organic matter content, soil texture, and mineralogy, probably affect the bioavailability of Cd in different soils, the lack of reported data sets including these soil parameters has hindered testing of their significance in controlling plant uptake.

    Keywords: Cadmium, bioavailability, sewage sludge, soil pH, crop uptake, Swiss chard, lettuce, corn.

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  • NONYLPHENOL IN ANAEROBICALLY DIGESTED SEWAGE SLUDGE FROM NEW YORK STATE

    • Scott W. Pryor, Anthony G. Hay, and Larry P. Walker. 2002. Environmental Science and Technology. 36:3678-3682

    ABSTRACT
    Nonylphenols (NPs) have been identified as xenoestrogens and have been found at high concentrations in Canadian and European biosolids. While nonylphenol polyethoxylates (NPEOs) are being phased out and regulated in several European countries, there is currently no regulation of these compounds in the United States, and little information is available concerning the presence of NPs in U.S. biosolids. Anaerobically digested sewage sludge from five wastewater treatment plants in central New York State was analyzed for the presence of NPs. Samples were taken from treatment plants in both small municipalities and larger metropolitan areas with a range of industrial inputs. Samples were extracted via Soxhlet apparatus and analyzed by GC/MS. The various isomers of NP were summed yielding total NP concentrations as high as 1840 mg/kg with a mean of 1500 mg/kg on a dry weight basis. These values are two to five times as high as previously reported concentrations for U.S. and Canadian biosolids from plants using similar treatment schemes.

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    Murray B. McBride, L.J. Evans. 2002. Canadian Journal of Soil Science. 82:323–333.

    ABSTRACT
    The long-term potential for sewage sludge amendments to alter forage trace metal concentrations was determined on bromegrass, which received no sludge application for 20 yr following annual application during 1973–1980 on a no-till randomized-plot experimental site. In addition, soils were analyzed for trace metals, both total and extractable (using hot 0.01 M CaCl2), by axial-view inductively coupled plasma spectrometry.

    For Cu, Ni, Zn and Cd, extractability from the soil (by CaCl2) as well as plant tissue concentrations were relatively low considering the high loadings of these particular metals, a fact attributable to the near-neutral pH and high organic matter content of these calcareous soils. However, total and extractable soil Mo remained elevated in the sewage-sludge-amended plots above the levels measured in the fertilized control plots some 20 yr after the last sewage sludge application. Mo bioaccumulated in the bromegrass more than the other trace metals investigated at this site. The Cu:Mo ratio in the forage, a measure of potential to induce Cu deficiency in grazing ruminants, was substantially depressed by most of the sewage sludge treatments. Comparison of the 2000 and 1980 bromegrass analyses suggests an increase in the long-term plant availability of Mo in soils amended with high-Fe and high-Al sludges. Conversely, there was a long-term decrease in Mo availability on the high-Ca sludge treatment, consistent with evidence that much of the Mo has been lost from the topsoil since sludge application. For Cu, Ni and Zn, plant availability appears to have decreased between 1980 and 2000, attributable in part to a calculated loss of substantial fractions of these metals from the topsoil.

    Bromegrass concentrations of Cu, Ni, Zn, Cd and Mo were strongly correlated to CaCl2-extractable and total metals in the soils, indicating the utility of 0.01 M CaCl2 in predicting plant availability. The chemical differences in the three sludge types applied at the site (high-Ca, high-Al, high-Fe) had little long-term impact on the extractability and phytoavailability of most trace metals remaining in the topsoil.

    Keywords: biosolids, molybdenum, copper, forage, cadmium, heavy metals

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  • THE ROLE OF MUNICIPALITIES IN REGULATING THE LAND APPLICATION OF SEWAGE SLUDGES AND SEPTAGE

    Ellen Z. Harrison and Malaika M. Eaton. 2001. Natural Resources Journal. 41(1):77-123

    ABSTRACT
    Application of sewage sludges to agricultural lands is increasing. This use represents an economical disposal option and provides the benefit of recycling the nutrients and organic matter sludges contain. The practice, however, raises a number of concerns. Although the combination of federal and state regulatory requirements is significant in forming the initial base for sewage sludge management decisions, local regulations also play a part in seeking to protect the health, safety, and welfare of citizens, who may object to land application. The primary legal constraints that localities face are constitutional Commerce Clause challenges and conflicts with right-to-farm statutes. The authority of a municipality varies from state to state. This article focuses on New York State, which has granted strong home rule to its municipalities. Examples of local ordinances and how they address particular concerns are described. Local ordinances vary widely in the issues and the level of detail they address. Issues addressed in local ordinances include human health risks, animal health risks, water quality, nuisance issues such as odor, liability and uncertainty, monitoring, and enforcement. They may impose restrictions on the type, amount, quality, or source of sludge. Some specify management practices, notification requirements, and additional monitoring beyond that required by federal or state rules. As a result of concern over the inability of state and federal agencies to provide consistent enforcement of rules due to staffing shortages, local ordinances frequently supply enforcement provisions. Local ordinances may also include fees to cover municipal costs.

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    • Murray B. McBride, Brian K. Richards, Tammo S. Steenhuis and G. Spiers. 2000. Journal of Environmental Quality. 29:848-854.

    ABSTRACT
    m (Mo) is a plant-available element in soils that can adversely affect the health of farm animals. There is a need for more information on its uptake into forage crops from waste materials, such as sewage sludge, applied to agricultural land. Field and greenhouse experiments with several crops grown on long-term sewage sludge-amended soils as well as soils recently amended with dewatered (DW) and alkaline-stabilized (ALK) sludges indicated that Mo supplied from sludge is readily taken up by legumes in particular. Excessive uptake into red clover (Trifolium pratense L.) (<30 mg/kg) was seen in a soil that had been heavily amended with sewage sludge 20 years earlier, where the soil contained about 3 mg Mo/kg soil, three times the background soil concentration. The greenhouse and field studies indicated that Mo can have a long residual availability in sludge-amended soils. The effect of sludge application was to decrease Cu to Mo ratios in legume forages, canola (Brassica napus var. napus) and soybeans [Glycine max (L.) Merr.] below the recommended limit of 2:1 for ruminant diets, a consequence of high bioavailability of Mo and low uptake of Cu added in sludge. Molybdenum uptake coefficients (UCs) for ALK sludge were higher than for DW sludge, presumably due to the grater solubility of Mo measured in the more alkaline sludges and soils. Based on these UCs, it is tentatively recommended that cummulative Mo loadings on forages grown on nonacid soils should not exceed 1.0 kg/ha from ALK sludge or 4.0 kg/ha from DW sludge.

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    Brian K. Richards, Tammo S. Steenhuis, John H. Peverly and Murray B. McBride. 2000. Environmental Pollution. 109(2):327-346.

    ABSTRACT
    The effect of sludge processing (digested dewatered, pelletized, alkaline-stabilized, composted, and incinerated), soil type, and initial soil pH on trace metal mobility was examined using undisturbed soil columns. Soils tested were Hudson silt loam (Glossaquic Hapludalf) and Arkport fine sandy loam (Lamellic Hapludalf), at initial pH levels of 5 and 7. Sludges were applied during four accelerated cropping cycles (215 t/ha cumulative application for dewatered sludge; equivalent rates for other sludges), followed by four post-application cycles. Also examined (with no sludge applications) were Hudson soil columns from a field site that received a heavy loading of sludge in 1978. Romaine (Lactuca sativa) and oats (Avena sativa) were planted in alternate cycles, with oats later replaced by red clover (Trifolium pratense). Soil columns were watered with synthetic acid rainwater, and percolates were analyzed for trace metals (ICP spectroscopy), electrical conductivity and pH.

    Percolate metal concentrations varied with sludge and soil treatments. Composted sludge and ash had the lowest overall metal mobilities. Dewatered and pelletized sludge had notable leaching of Ni, Cd and Zn in Arkport soils, especially at low pH. Alkaline-stabilized sludge had the widest range of percolate metals (relatively insensitive to soils) including Cu, Ni, B and Mo. Old site column percolate concentrations showed good agreement with previous field data. Little leaching of P was observed in all cases. Cumulative percolate metal losses for all treatments were low relative to total applied metals. Leachate and soil pH were substantially depressed in dewatered and pelletized sludge soil columns and increased for alkaline-stabilized and ash treatments.

    Keywords: sewage sludge, trace metals, preferential flow, metal mobility, leaching

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    Philippe Baveye , Murray B. McBride, David Bouldin, Thomas D. Hinesly , Mohamed S.A. Dahdoh and Mamdouh F. AbJel-sabour. 1999. The Science of the Total Environment. 227:13-28 (Elsevier Science)

    ABSTRACT
    Soil samples were collected at 15 cm increments to a depth of 75 cm from plots on a silt loam soil where until several years earlier and for 14 years anaerobically digested sewage sludge had been annually applied by furrow irrigation. The study protocol consisted of four replications of 6.1 by 12.2 m plots with 0 (T0), 1/4-maximum (T1), 1/2-maximum (T2) and maximum (T3) sludge application rates randomized within blocks. When sludge applications were terminated, maximum sludge-treated plots had received 765 Mg-1 had (dry weight equivalent) of sludge solids. Total soil concentrations of Cd, Cr. Cu, Ni, Pb and Zn had been significantly enhanced by all sludge application rates to a soil depth of 30 cm. Below the 30 cm depth, total soil Cd was increased to 75 cm, total Zn to 45 cm (T2 and T3 only), total Cr to 60 cm (T2 and T3 only), but total Cu, Pb, and Ni were not increased at depth. Despite the lack of significant increases in subsoil concentrations for some metals, mass balance calculations showed a relatively high proportion of all the above sludge-borne heavy metals to be unaccounted for in the soil profile for each application rate. Mass balance calculations of losses ranged from a high of 60 percent for Ni to a low of 36 percent for Cu and Pb. Similar losses were calculated from metal concentrations measured in soil samples taken at the time the sludge was applied. In soil surface samples (0 to 15 cm) from maximum sludge-treated plots, percentages of total metal concentration extracted with 4.0 M HNO3 ranged from a low of 31 for Zn to a high of 75 for Cu. Efficiency of metal extraction by HNO3 was inconsistent, depending on soil horizon and sludge treatment, so that evaluation of HNO3 -extractable metals is not a reliable method of estimating total metal retention in the profiles. In soil surface samples from maximum sludge-treated plots, the percentage of total metal contents extracted with DTPA ranged from a low of 0.03 for Cr to a high of 59 for Cd. The DTPA extractable levels of Cu, Ni, and Pb were higher in the subsoils of the sludge-treated soils, indicating that these metals had been redistributed from the surface layer to deeper zones in the profile of sludge-amended soil, despite the absence of elevated total concentrations of these three metals in the deeper subsoil.

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    Tammo S. Steenhuis, Murray B. McBride, Brian K. Richards, Ellen Z. Harrison. 1999. Environmental Science and Technology. 33(8):1171-1174

    ABSTRACT
    Recycling nutrients in wastewater sludge (biosolids) via land application is a desirable goal. However, potential movement of sludge-applied trace metals is of concern and an area of ongoing research. In this paper, we examine the first-order model used by the United States Environmental Protection Agency (US EPA) for predicting losses from the zone of incorporation as part of the risk assessment that undergirded the development of Part 503 regulations (1,2). We found that when empirical adsorption partition coefficients from the site are used as model inputs, the US EPA model for the incorporation zone is similar to that derived from preferential flow theory and simulates well the loss of metal from the surface soil layer at an orchard site where sludge was applied 15 years earlier.

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    Ellen Z. Harrison, Murray B. McBride and David R. Bouldin. 1999. Int. J. Environment and Pollution. 11(1):1-36

    ABSTRACT
    Current US federal regulations governing the land application of sewage sludges do not appear adequately protective of human health, agricultural productivity or ecological health. US standards are far less protective than those of many European countries and Canadian provinces. This is due to both policy choices such as a 'do no harm' philosophy applied in some northern European countries and also to many gaps and non-conservative assumptions in the risk assessment performed by US Environmental Protection Agency. The potential for widespread use of sludges on agricultural and residential land, the persistence of many of the pollutants, which may remain in soils for a very long time, and the difficulty of remediation support a cautious approach. Soil, water and crop characteristics in New York State and other areas of the northeastern US raise particular concerns. The authors do not suggest a prohibition of land application but, rather, significantly more restrictive use. Limiting cumulative additions of pollutants to prevent soils from exceeding recommended maximum contaminant levels can be achieved by application of clean sludges or by application of lesser amounts of less high quality sludges. Further investigation is needed to assess risks to ground and surface water and to establish standards for additional contaminants.

    Full Text. Int. J. Environment and Pollition journal is available in both hard copy and on-line PDF format. For more information and sample copy of IJEP, visit their web site at http://www.inderscience.com/.

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    David R. Bouldin. 1997. Soil Science Society of North Carolina Proceedings. Vol 40 .

    ABSTRACT
    The metals zinc and copper, among others elements, are essential to plant and animal life yet depress crop yields if added in excess. Maximum cumulative loads are estimates of the amount of a metal at which the depression in crop yields become unacceptable. The implications of such a limit is that a) the effects of previous additions persist and are additive to current applications and b) if cumulative additions lead to yield reductions, these yield reductions may persist even if additions of metals via sludges are stopped.

    Maximum cumulative loads of metals from application of sewage sludges to agricultural land differ by an order of magnitude among groups developing them. All use the same data yet arrive at different end points. In the following discussion the reasons for these differences are illustrated and several examples of alternative risk-based maximum cumulative loads are derived. As the probability of yield reductions approach zero, the maximum cumulative loads are 10 to 100 times less than the EPA 503 cumulative loads. These alternatives give farmers and others a perspective on how to develop a maximum cumulative load for their own situation if they are planning to landspread sludges and products containing sludges.

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    Vincent J. Camobreco, Brian K. Richards, Tammo S. Steenhuis, John H. Peverly, and Murray B. McBride. 1996. Soil Science. 161:740-750

    ABSTRACT
    When sewage sludge is applied to land for disposal or intended beneficial use, heavy metals accumulate in the soil. Because of the concern about the environmental danger that these sludge-borne metals could represent if mobilized, many studies have been undertaken in an attempt to clarify the different factors that contribute to metal solubility, plant uptake, and leachability. The objectives of this study were to determine if two independent factors-soluble organic chelators and preferential flow paths-enhance metal mobility through soil.

    Dilute solutions containing CdC12, ZnC12, CuCl2, and Pb(NO3)2 were applied to soil columns with a rainmaker, and leachate metals and chloride concentrations were measured. For four columns, the input metal concentrations (mg L-') were 7.25 Cd, 4.55 Zn, 3.51 Cu, and 13.85 Pb. In four other columns, the solution also contained dissolved organic matter so that the metals were organically complexed, and input metal concentrations (mg L-') were 6.30 Cd, 4.11 Zn, 3.19 Cu, and 12.55 Pb. For each treatment, two of the four soil columns were undisturbed and two wersub>e constructed from homogenized soils. The rate of continuous solution application was approximately 3 cm/day.

    The undisturbed soil columns treated with organically complexed metals had peak effluent concentrations, expressed as percent of influent, of 30, 26, 28, and 27% for Cd, Zn, Cu, and Pb, respectively. Peak effluent concentrations for undisturbed columns treated with metals in water were 30 and 23% of influent concentrations for Cd and Zn, but only 15 and 12% for Cu and Pb, respectively. However, the four homogenized soil columns retained all added metals, whether the metals were added in water or as organic complexes. The results indicate that previous laboratory metal leaching studies performed on homogeneous soils might have greatly underestimated metal mobility in the field and that preferential flow, both alone and in combination with organic-facilitated transport, can accelerate metal leaching through soils.

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    Brian K. Richards, John H. Peverly, Tammo S. Steenhuis and Barry N. Liebowitz. 1997. Journal of Environmental Quality. 26:782-788

    ABSTRACT
    Minimization of the concentration and mobility of trace metals is a primary concern when considering the land application of wastewater sludges. The effects of pelletization/drying, composting, incineration, and N-Viro chemical stabilization on composition and mobility of trace metals and P were compared. One day's production of dewatered digested sludge (Syracuse, NY) was used as the sole feedstock so that observed differences would solely be a result of the process used. Mobility was determined using the toxic characteristic leaching procedure (TCLP). Analyte concentrations were essentially constant during dewatered sludge production with mean values (mg kg-l TS) of 5.6 Cd, 10.7 Co, 130 Cr, 587 Cu, 49.7 Mo, 35.8 Ni, 26 880 P, 132 Pb, and 545 Zn. Concentrations in pellets were similar to dewatered sludge, but were reduced in composted sludge and N-Viro product by the addition of amendments. Incineration concentrated all analytes except Cd and Pb, which experienced volatilization losses. The mode of processing had widely ranging effects on mobilities. The TCLP-mobile fraction (percent of total) of analytes in dewatered sludge was <3% except Ni (7.1%), P (6.0%), and Zn (11.2%). Composting slightly increased Cd mobility, but reduced that of Ni and P. Pelletization increased the mobility of Cd (7.9%), Cu (3.8%), Ni (15.4%), and Zn (15%). The N-Viro process substantially increased mobilities of Cu (43%), Mo (50%), and Ni (24%) at elevated pH. Incineration increased mobilities of Cd and Mo, but reduced Ni, P, and Zn mobility. These results, with those of longer term in situ studies, can be used to guide the selection of sludge processes that minimize potential metal and P mobility.

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    Murray B. McBride, Brian K. Richards, Tammo S. Steenhuis, John J. Russo, and Sebastien Sauve. 1997. Soil Science. 162:487-500

    ABSTRACT
    The increased use of sewage sludge as a fertilizer, combined with reports that large fractions of sludge-borne heavy metals cannot be accounted for several years after land application, indicates that more detailed study of potential mobility of these metals in soils is needed. A field site that had received a single heavy application of municipal sewage sludge was re-investigated 15 years later to measure the degree to which toxic heavy metals as well as nutrient elements remained in the topsoil. Total elemental composition of soil samples collected recently at this site was measured by inductively coupled plasma (ICP) spectrometry analysis of acid digests as well as by neutron activation analysis (NAA). These two methods gave comparable results for most sludge-applied heavy metals, but not for those elements that reside largely in mineral lattice structures resistant to acid digestion.

    Based on elemental deficits calculated using soil chromium concentration as an indicator of the original sludge concentration in the soil, it is estimated that most of the sludge-applied Na, S, Ca, and Sr, about 40% of the Zn and Cu, and less than 30% of the Cd and P have been lost from the topsoil. There is limited evidence that about half of other heavy metals such as Hg, Ag, and Au has also been lost. The ICP analysis of water extracts of the soils shows present concentrations of water-soluble Cu, Zn, and Ni in the sludge-amended topsoil are more than 10 times higher than those in the control soil. Ion-selective electrode measurements confirm that a large fraction of soluble Cu appears to be in an organically complexed and mobile form, which leaches to shallow groundwater. To varying degrees, numerous other elements, including Cd, P, and S, have solubilities substantially higher than in the control soil after the 15-year period. Nevertheless, despite the fact that the elemental deficits are correlated to the distribution coefficients of the elements, the deficits can only be accounted for by leaching if those elements were more soluble in the soil immediately after sludge application than they are now. The Zn and Cd remaining in the topsoil (pH 6.5-7.0) after 15 years is plant-available, as indicated by excess uptake and severe phytotoxicity symptoms in vegetable crops.

    In summary, although the vertical metal concentration profiles failed to manifest substantial movement of most trace metals, it appears that large fractions of certain metals applied in the sludge amendment have redistributed and moved out of the soil surface by physical-chemical or biological processes and that there is potential for groundwater and surface water contamination.

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    David R. Bouldin. 1998. Crop and Soil Sciences. Cornell University.

    ABSTRACT
    The metals zinc and copper, among others elements, are essential to plant and animal life yet depress crop yields if added in excess. Maximum cumulative loads are estimates of the cumulative amount of a metal that cause an unacceptable risk of crop yield reduction (where cumulative load is the sum of all past metal additions). Cumulative loads are necessary because the effects of previous additions persist and are additive to current applications. An important consequence of the residual effects is that if cumulative loads cause yield reductions, these yield reductions will persist even if additions of metals via sludges are stopped.

    Maximum cumulative loads of metals from application of sewage sludges to agricultural land differ by an order of magnitude among groups developing the guidelines. All use the same data yet arrive at different maximum cumulative loads. In the following discussion the reasons for these differences with respect to Zinc are illustrated and several examples of alternative risk-based maximum cumulative loads are derived. These give farmers and others a perspective on how to develop a maximum cumulative load for their own situation if they are planning to landspread sludges and products containing sludges.

    The most important conclusion is that there is no unqualified estimate of the best maximum cumulative load and that any estimate of maximum cumulative load is subject to much uncertainty. The EPA maximum cumulative load has a high probability of leading to some yield reduction a substantial part of the time. The NEC-28 cumulative loads are on the order of one-tenth of the EPA cumulative loads and reflect a 10% yield reduction with a probability of 10 %. Even a cumulative load of 60 kg/ha of Zn (about 2% of the EPA maximum cumulative load of 2800 kg/ha) has a 1% probability of a 30 % yield reduction for the most sensitive crops. The only way to be certain of no adverse effects is not to use sludge.

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    Murray B. McBride. 1995. Journal of Environmental Quality, 26:5-18.

    ABSTRACT
    The new USE PA regulations for the use of sewage sludges will permit concentrations of particular toxic metals to increase locally on agricultural land by a factor of a hundred or more above present soil concentrations. Short-term field experiments have shown that the adsorptive properties of sludges themselves often prevent excessive uptake of many of these metals into crops, a protection attributable largely to the added organic matter. This protection cannot be considered to be permanent or effective for all toxic metals, as indicated by data from old sludged sites. Differences in degree of protection are evident for greenhouse and field experiments, largely attributable to different rooting patterns and degree of sludge mixing in these two situations. The USE PA reliance on field data for metal uptake by corn (Zea mays L.) has led to an underestimation of phytotoxicity thresholds applicable to a wider range of crops, in part because corn is able to root deeply and is metal-tolerant. Also, the decision to use 50% yield reduction and plant top (rather than root) concentrations of heavy metals as phytotoxicity indicators may have obscured incipient toxicity. Long-term field observations (several decades) often show that sludge-applied metals can remain sufficiently available, even in nonacid soils when total metal concentrations are below the proposed EPA limits, to harm sensitive crops and microbes. It is concluded that the ultimate impact of toxic metals from sewage sludges at levels approaching the proposed USE PA limits on various soil-crop systems is potentially harmful .

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    Brian K. Richards, Tammo S. Steenhuis, John H. Peverly, and Murray B. McBride. 1998. Environmental Pollution, 99:365-377

    ABSTRACT
    This study was undertaken to determine the present distribution and mobility of sludge-applied metals at an old land application site. Trace metals concentrations were determined for soils (using 4M HNO3 extracts), soil leachates (collected with passive wick lysimeters over a 2.5 year period), and plant tissue from a field site which received a heavy loading of wastewater sludge in 1978 and an adjacent control plot. Blue dye was used to indicate preferential percolate flowpaths in the sludge plot soil for sampling and comparison with bulk soil metals concentrations.

    After nearly 20 years, metals in the sludge plot leachate were found at significantly greater concentrations than in the control plot, exceeding drinking water standards for Cd, Ni, Zn, and B. Annual metals fluxes were only a fraction of the current soil metal contents, and do not account for the apparent substantial past metals losses determined in a related study. Elevated Cd, Cu and Ni levels were found in grass growing on the sludge plot.

    Despite heavy loadings, fine soil texture (silty clay loam) and evidence of past and ongoing metals leaching, examination of the bulk subsoil indicated no statistically significant increases in metals concentrations (even in a calcareous subsoil horizon with elevated pH) when comparing pooled sludge plot soil profiles with controls. Sampling of dyed preferential flow paths in the sludge plot detected only slight increases in several metals.

    Preferential flow and metal complexation with soluble organics apparently allow leaching without easily detectable readsorption in the subsoil. The lack of significant metal deposition in subsoil may not be reliable evidence for immobility of sludge-applied metals.

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    Murray B. McBride. 1998. Journal of Environmental Quality, 27:578-584.

    ABSTRACT
    The application of alkaline sludge products as liming agents to agricultural soils is now commonplace. Laboratory investigations of water extracts from two alkali-stabilized sludge products used in New York State reveals that 40 to 50% of the total Cu, 15 to 25% of the total Ni, and 11 to 13% of the Me dissolved out of the sludge product into water, whereas much smaller fractions of the Cd, Zn, Pb, Ag, and Hg were immediately water soluble. Speciation techniques, including differential pulse anodic stripping voltammetry (DPASV), electron spin resonance (ESR), and computer speciation calculate (MlNEQL+ ), indicated that the high solubility of Cu and Ni was a result of complexation with dissolved amides or amino acids in the alkaline (pH12) water extracts. Because of the high affinity of both Cu2+ and Ni2+ for N-ligands in amides, these metals were mobilized much more than Pb, Zn, or Cd. The low solubilities of Ag and Hg may indicate that they were present in the sludge product as the insoluble metallic or sulfide forms. Prolonged exposure of the alkaline extracts to air caused CO2 to gradually lower the solution pH to 8.1 forming a CaCO3, precipitate. However, the dissolved Cu and Ni concentrations did not diminish with pH, indicating that the metal-organic complexes were sufficiently stable at pH 8.1 to inhibit metal precipitation with the CaCO3. The results suggest potential for the transport of certain heavy metals from land-applied alkaline sludges into surface waters and shallow groundwater in some situations.

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    Murray B. McBride. 1998. Environmental Toxicology and Chemistry, 17(11):2274-2281.

    ABSTRACT
    Abstract-The use of sewage sludges as farm fertilizers, encouraged in recent years by changes in U.S. Environmental Protection Agency (U.S. EPA) policy, has raised concerns among some scientists regarding food safety and long-term soil productivity. The U.S. EPA risk assessment for entry into the human diet of three of the most toxic metals, cadmium (Cd), mercury (Hg), and lead (Pb), utilized uptake coefficients (UCs) to calculate the amount of each metal that could enter food crops from the soil. Each UC was calculated as the increment of metal concentration in the edible part of the crop per unit increase of metal loading to the soil. However, the final UC estimates employed in the risk assessment are biased toward low values by a number of factors. These include the use of geometric means to obtain single-point averages of UCs for each crop group evaluated, rather than using arithmetic means or probabilistic methods, a systematic analytical or contamination error apparent in the reported metal concentrations of the control crops, and the fact that most of the UC values were derived for soils with pH 6 or higher. For more than 50% of all the soil and cropping conditions represented in the risk assessment, the geometrically averaged Cd UC values used by the U.S. EPA underestimated the actual risk posed by uptake into crops. The UC values for Pb and Hg are uncertain because of analytical or contamination errors, and because of the few data available for a number of crops. These uncertainties and biases in the risk assessment would advise a more cautious approach to agricultural and home garden use of sewage sludge than is permitted by the U.S. EPA 503 rule.

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