Sludge, Sludge on the Range: Unresolved Science in the 503 Regulations.
(A paper presented at the AAAS Annual Meeting in Philadelphia, February 14, 1998 and at the 1998 California Plant and Soil Conference: Agricultural Challenges in an Urbanizing State, January 21-22, 1998. California Chapter of American Society of Agronomy and California Fertilizer Association.)
by
Albert G. Medvitz
P.O. Box 565
Rio Vista, CA 94571
email: amedvitz@wco.com
Abstract
The USEPA 40CFR part 503 regulations are problematic for the safe regulation of the land application of sewage sludge on grazing land. In several instances significant science is lacking about the long term (4 to 7 year) risks posed to livestock producers by using sewage sludge as an amendment to grazing !and. Both explicit and implicit assumptions in the 503 risk assessments and associated science compromise the conservative nature of the regulations in protecting the agricultural viability of livestock production enterprises.
Assumptions about animal exposure to the pollutants in sludge
In considering the potential dangers of sludge pollutants on livestock, the makers of the 503 sludge rule eliminated pollutants from consideration on the basis of estimates of toxicity, carcinogenic characteristics, and estimates of the exposure dose a highly exposed individual would likely encounter when exposed to sludge. This last probability was computed from a National Sewage Sludge Survey (NSSS) of publicly owned wastewater treatment works (POTWs). The survey, among other things, determined the prevalence and concentrations of pollutants in sludge produced by these works.
To determine allowable concentrations of pollutants to be applied and to be accumulated in the nation's soils, the rulemakers relied on the existing base of scientific research to assess the potency of pollutants and estimate the doses of these pollutants to which people and animals and plants in the environment would be exposed.
As is to be expected of the science of a complex material, the knowledge of toxicity and the environmental interactions of sludge borne pollutants is incomplete, as is the behavior and fate of these pollutants after they are land applied. Furthermore, the behavior of environmental organisms which govern their interactions with sludge (and hence doses of pollutants ingested, inhaled, or absorbed) vary widely depending on exposed species and environmental conditions or are poorly understood in themselves. To compensate the rulemakers relied heavily on simplifying assumptions and best-guess estimates about the interaction of pollutants with organisms in untested conditions. In some instances, they did not consider important but subtle long-term effects on breeding behavior and thus overlooked important potential deleterious outcomes of the use of sludge on agricultural lands.
In the case of sheep, sludge pollutant exposure is achieved through eating forage grown on sludge as well as ingesting soils while grazing. Estimates of soil ingestion by grazing animals vary from about 0.5% to as much as 24% of total diet depending on grazing conditions. When grazing lands are rich and fresh, animals are likely to consume little soil, when grazing conditions are such that forage is scarce, more soil is consumed. Soil ingestion also varies by species and animal and range management practices (1),(2). (Animals may also acquire pollutants from ephemeral streams and standing water from vernal pools on sludge amended ground, but this will not be discussed in this paper. )
The EPA considered domestic animal exposure to sludge pollutants in four of the fourteen pathways by which sludge borne pollutants and pathogens could be encountered in the environment (3). These are:
This paper considers these pathways, including pathways 4 and 5, only as they are relevant to livestock health and production.
In considering toxicity to animals which might feed on forages and ingest soil amended with sludge, the EPA eliminated from consideration organic pollutants, including dioxins and furans, and considered only 9 inorganic elements: Arsenic, Cadmium, Chromium, Copper, Lead, Molybdenum, Nickel, Selenium, and Zinc. (The consequences of this omission of important organic compounds will be discussed below). After identifying the pollutants to be considered the rulemakers then assessed them one by one. First they reviewed the literature to identify the most sensitive animal species for each pollutant (since sensitivity varies by species). Then, using the same literature, they estimated the maximum intake of each pollutant which would not cause a toxic effect to a highly exposed animal of the most sensitive species. In the case of animals ingesting sludge grown plants (pathway 6), after having estimated the maximum allowable intake level of the trace metal, the rulemakers then estimated how much forage animals ingest as well as the uptake of pollutants by plants grown in sludge amended soils. They also estimated background levels of pollutants in soils. From all of these estimates they calculated concentrations of pollutants in the soils which would produce concentrations in plant material such that animals eating these plants would consume trace metals below a level which would produce an observable adverse impact.
The process was similar for soil ingestion except it was not necessary to estimate pollutant uptake by plants. Rather, the EPA estimated levels of soil ingestion by grazing animals. The end result is an estimate of allowable concentrations of pollutants in sludge itself as well as maximum safe soil concentrations accumulating in the soil.
Problematic assumptions
Unfortunately, the 503 rules are compromised by several important assumptions. First, in calculating allowable concentrations of pollutants in sludge, the EPA rulemakers considered pollutants individually. But pollutants in sludge do not occur singly: they exist and act in concert with all of the pollutants found in the particular urban waste stream where the sludge is produced. In some instances, the rulemakers did consider the toxicity of interactions of pollutants (for example, in noting the interaction of zinc and copper) but did not develop risk assessment algorithms for interacting pollutants. In the particular instance of copper and zinc, high levels of both Zinc and Copper would do no damage (4). But the consequences of high concentrations of Cadmium and Zinc, in animal diets for example, are not considered. Cadmium also interacts with the metabolic action of Copper and inhibits the accumulation of Copper by the developing fetus (5). Nor do the EPA analyses consider the consequences of interactions between inorganic and organic pollutants.
The EPA also did not take into account the combined effects of animal ingestion of sludge amended soils at the same time as the effects of animals feeding on crops grown on these soils. In other words, they did not consider near endpoint conditions where animals might be grazing on forage produced with near maximum allowable soil concentrations of pollutants and ingesting newly applied sludge in the soil itself. The sum of the two pathways was not considered, nor were accumulated sludge concentrations considered in background estimates. Nor did they consider animal consumption of standing water on sludge amended lands. (This last consideration may be of considerable importance to California and other Western states where winter and spring wet seasons produce ephemeral streams and vernal pools on grazing land. Since little or no data exist about ingestion through surface water runoff from sludge amended lands. the problem is not considered in this paper.)
Soil ingestion estimates used in pathway 7 are inconsistent with assumptions made about sensitive species and conditions of sheep production in California. As noted above estimates of soil ingestion vary depending on grazing conditions. Even if one assumes the legitimacy of Fries(6) contention that estimates of soil ingestion are overstated, then soil ingestion rates will vary between near zero and 10% of animals daily diet. High end estimates would be particularly appropriate to sheep in California. Typical sheep grazing patterns in California are of flocks of sheep grazing the summer on cultivated fallow land or on post harvest stubble of a variety of crops, or on desert lands. Although precise data on levels of ingested soil are not available, it is not uncommon in ranch necropsies to find substantial residue of soil in sheep digestive systems. The upper estimates for soil ingestion seem not unreasonable for many California conditions.
It is worth noting that in developing pathway 7 the EPA estimates on soil ingestion violate it's own criteria of consideration of most sensitive species. In this pathway, soil ingestion was assumed to be 1.5 % of animal diets. The estimate is based on soil ingestion of cattle, not the most sensitive species for, say, Copper. Furthermore, the estimate is based on the geometric mean of data obtained from cattle grazing in rotation on sludge amended pasture, only one third of which is sludge amended. Thus, while sheep are clearly identified as the most sensitive species when ingesting Copper (7), data on soil ingestion by cattle were used to calculate ingestion rates rather than dryland grazing data appropriate to sheep. Given other estimates, this assumption leads to an underestimate of soil ingestion by a factor of 4 or 5 for the most sensitive species to Copper toxicity. Furthermore, the assumption that animals rotate through pastures of which only one third have been treated with sludge is based on observations of a particular set of management practices at a particular time and is arbitrary.
The 503 rules thus allow the concentration of pollutants in sludge to be a factor of 4 or 5 times the amount prescribed under the criteria of maximum usable with no observable toxic effects when pollutants are considered individually.
Limitations of the research base
More subtle faults with the 503 regulations emerge from the inadequacies of the research base available to adequately assess risks over time frames of more than a year or so. The overwhelming majority of research on sludge borne pollutants are experimental studies of a few months to a year of feeding animals sludge amended diets or grazing animals on pastures to which sludge has been applied. In the EPA discussion of toxic levels of Copper, for example, the relevant data are from observations made over one season (8). The majority of studies are concerned with the safety of animal products for human food The dependent variables in these studies are generally concentrations of pollutants in animal tissue which arise from ingestion of pollutants added to feed, ingestion of sludge, or forage grown on sludge in experimental diets. Except for a few instances, observations of animal breeding behavior and performance tend to be incidental asides.
For sheep, the production lifetime of a healthy ewe is on the order of seven years Yet there are very few long term studies of the effects of sludge borne pollutants on health and productivity of breeding flocks over this period of time In the early eighties Baxter et al conducted several studies on cattle, in which they studied pollutant accumulation in animal tissues One study examined such effects after nine months of grazing (9), the other compared tissue concentrations in a herd which grazed a sludge disposal site for approximately 6 years with concentrations of herd on a nearby cattle ranch (10)(11). In both studies, cattle were slaughtered and pollutants in tissues measured. In the longer more extensive study, significant increases in Cd in kidney tissues and decreases in liver Cu were noted as well as elevated levels of organics in fat tissue. Other than noting that the animals appear in good health with no apparent problems, the authors did not investigate effects on production or breeding effects. Also, while the "herd" had grazed the range for sometime, it is not clear how long individual sampled animals had been exposed to the sludge amended range.
In the early 1980's Hudgens, Hallford and others produced a series of studies of effects of a sludge amended diet on the productivity of breeding sheep. These ranged in length from a breeding season to four years and compared the effects of a control diet with those of a diet enhanced with cottonseed meal and another enhanced with 7% sewage solids (12) (13) (14) (15).
In these studies, the authors declare there are no significant or meaningful differences between experimental and control groups in terms of lambing and weaning performance(12), blood, milk and tissue elemental composition (15) reproductive performance (13), or adverse toxicological effects (14).
However the characteristics of the Los Cruces, New Mexico sludges used in these experiments are vastly different than the characteristics of sludges permitted under the 503 rules. Table one compares the concentrations of heavy metals in the long-term diet fed to ewes by Hudgens and Hallford (13) with concentrations in a diet from soil ingestion of land applied sludge with maximum concentrations of heavy metal pollutants permitted under the 503 regulations, assuming 7% soil ingestion in the animal diet. The table shows two conditions: maximum allowable concentrations applied to the soil surface and not incorporated, and maximum allowable soil concentrations. The comparison does not take into account ingestion of pollutants in forage. The differences in trace metal ingestion are readily apparent. For example, the Pb in the experimental diet is nearly a factor of 2 less than that which would arise if animals ingested 7% of their diet from soils with maximum allowable sludge pollutant concentrations. The experimental dietary Pb is a factor of 10 less than would be consumed if surface applied sludge with maximum permitted levels were ingested. Similar ratios apply to other elemental pollutants.
A further characteristic of the Hudgens and Hallford experiment compromises its relevance: the sludge was irradiated and presumably sterilized before being incorporated into the experiment. The 503 regulations do not require sterilization, but treatments to reduce pathogens are required for Class A sludges. Class B sludges, without additional pathogen treatment after wastewater treatment are allowed on grazing lands with a 30 day grazing restriction. The sterilization process in the Hudgens and Hallford experiment omits the possibility of observing effects on sheep from sludge borne pathogens, particularly if immune systems are stressed from elevated sludge exposure over five or six years.
Comparison of Metal Concentrations in Hudgens and Hallford Experimental Diet with Those in a Diet Composed of 7% Ingested Soil at Maximum 503 Concentrations.
| Pollutant | Maximum 503 concentration
allowed in applied sludge |
Maximum 503
|
Concentration in diet when soil with 503 maxima is 7% of diet (4) (mg/kg)
|
Concentration in sludge amended
diet in Hudgens and Hallford (2) | ||||||
| Arsenic | 75 |
41 |
25 |
5.25 |
1.8 |
not reported | ||||
| Cadmium | 85 |
39 |
24 |
6.2 |
2.0 |
0.5 | ||||
| Chromium | 3000 |
3000 |
1852 |
216 |
135 |
25.8 | ||||
| Copper | 4300 |
1500 |
926 |
307 |
71 |
26.4 | ||||
| Lead | 840 |
300 |
185 |
60 |
14 |
6.9 | ||||
| Mercury | 57 |
17 |
10.5 |
4 |
0.7 |
<0.04 | ||||
| Molybdenum(3) | 75 |
18 |
11 |
5 |
0.8 |
not reported | ||||
| Nickel | 420 |
420 |
259 |
31 |
20 |
2.7 | ||||
| Selenium | 100 |
100 |
62 |
7 |
4 |
not reported | ||||
| Zinc | 7500 |
2800 |
1728 |
547 |
143 |
55.6 | ||||
(1) calculated using soil density of 1.08 kg/liter of ayar clay soil from Montezuma Hills, a principal dryland agriculture area in California where sheep are rotated with small grains, assuming mixing to a depth of 15 cm. (6 in.)
(2) In addition to reporting values for tabulated pollutants, Hudgens and Hallford reported values for the following pollutants/nutrients (micrograms/gram): Ag (6.0), Ca (2014.0), Fe (601.7), K (5,066.3), Mg (1,045.7), Mn(35.8), Na (1,300), P(2,378.7).
(3) Since the publications of the 503 regulations, limits to Mo have been deleted from the rule pending EPA reconsideration. (16)
(4) Calculated adding background concentrations in basal (unamended diet), i.e. C tot = .07C sludge + .93C basal
Two other long term (3 year) studies by Bray et al (17) and Dowdy, Bray, et al (18) using goats and lambs show no or negligible effects on animals fed silage produced from sludge amended soils. Examination of the dietary concentrations in the studies show that' except for Zinc, they are even less than those reported in the New Mexico studies of Hudgens, Hallford and others cited above.
It should be emphasized at this point that these and the New Mexico studies of Hudgens, Hallford, and others do lend credence to the idea that sewage sludge with modestly elevated levels of pollutants may serve as a beneficial and safe soil amendment for California grazing lands. But the few studies investigating the long term effects of sludge on the breeding health of livestock do not lend credence to the 503 regulations as protecting the long term health of grazing animals.
The only study for cattle which I have found which at least in part addresses the issue was reported by Fitzgerald in 1980 (19). In this long term study of cattle and swine grazing on sludge amended soils, Fitzgerald reports that " In general, the calf crops have been from 90% to 95% in the control herd and 80 to 85% in the experimental herd." (19, p. 36). This difference, however may also be an experimental artifact in that the ratio of bulls to cows in the experimental herd was 1 to 30 but 1 to 20 in the control herd. Nevertheless, the observation warrants caution in the long term use of sludge on grazing land.
Organic Pollutants
The seriousness of the gaps in the research about the longer term effects of sludge borne pollutants on livestock is made more apparent by the lack of research on the impacts of organic pollutants. The EPA conducted initial screening of pollutants using a national survey of POTWs, the so called National Sewage Sludge Survey. Before conducting the survey, the rulemakers a priori eliminated significant organic pollutants on the basis that their use has been banned in the United States. As the National Research Council notes in its report on sludge, the exclusion was an error and the survey was flawed (20). Possible exposures are underestimated.
Despite the sludge survey issues, the EPA included selected organic pollutants in its analysis of pathways 4 and 5 which are about the accumulation of toxic substances in animal tissues as they effect humans who consume animals. In considering these pollutants, the EPA rulemakers did not include organic pollutants as having possible impacts on animals as evidenced by their absence from the relevant pathways (6 and 7). Furthermore, in considering the health impacts of organic pollutants they used the existing research base on the cancer causing character of these chemicals.
Again, organic pollutants, when they were considered, were considered individually and not in synergy with other organic or inorganic pollutants.
The research bias towards human carcinogens is important because it excludes other important effects of organic pollutants, most notably their effects as endocrine disrupters. Such effects may have important consequences for immune responses and reproduction in domestic food animals (21). Even in recent publications on organic pollutants in sludge, the research is directed to assessing the safety of human consumption of animal tissues and not the long breeding term viability of the animals (22).
The absence of research on the effects of both the organic and inorganic chemical species on long term breeding health of animal herds and flocks leaves open serious questions for producers about the protectiveness of the 503 regulations. Anyone close to the sheep and cattle production systems of this country knows that they have been operating under difficult economic circumstances for close to a decade. Further, they understand that lowered conception rates of a percentage point or two, increased abortion rates, earlier deaths of animals, or even modest shortening of breeding span could have a substantial economic and management impacts on livestock enterprises. They also know that such effects resulting from sludge applications would be hard to identify and trace.
The absence of research could be readily addressed by relatively modest experimental studies and epidemiological studies on the order of five to ten years where sludge has been used at the levels specified in the 503 regulations and where significant soil ingestion is likely to occur.
We must keep in mind that the issue is not whether or not sludge can be of benefit, but what are the conditions under which it can be used safely. In terms of breeding flocks of animals, the 503 rules are not based on a sufficiently firm scientific base to support trust in their use as a standard.
Other issues
This paper has focused on the problem of the lack of a sufficient research base on the long term effects of pollutants on breeding flocks to justify the USEPA 40CFR part 503 rules as a standard for the protection of livestock industries, particularly sheep production, in California. Besides concern for animals, the 503 regulations also must be analyzed in terms of the long term well being of range lands and on the ranchers ability to adapt his or her practices to changing crop production.
It should be noted that the research base on soil ecology usable to assess risks of the land application of sludge at the levels specified in the 503 regulations suffers a sparsity of data similar to that described above for breeding animals. McBride, Bouldin and others at Cornell question the EPA's risk assessment of phytotoxicity, partly as a result of data biased towards specific experimental species (23). Thus, for those who wish to pursue sludge use on grazing lands, caution and independent analysis should be used. Further research under specific conditions reflecting the diversity of our national environment and with crops and livestock produced under diverse, sometimes stressful, conditions needs to be accomplished before standards can be accepted with confidence.
References
1. Smith, S.R. (1996), Agricultural Recycling of Sewage Sludge and the Environment. CAB International p.. 90
2. Fries, George F. (1995), Transport of Organic Environmental Contaminants to Animal Products, Reviews of Environmental Contamination and Toxicology, vol. 41, p. 71-109. Fries suggests that high end estimates may substantially overestimate soil ingestion when plants are mature.
3. EPA (Prepared by Eastern Research Group)(1992), Technical Support Document for Land Application of Sewage Sludge, Vol. 1. USEPA, pp. 5-171 to 5-171; 5-172 to 5182; 5-183 to 5-191.
4. EPA (Prepared by Eastern Research Group)(1992), Ibid. p. 5-175
5. Campbell, J.K. and Mills, C.F. (1979) The Toxicity of Zinc to Pregnant Sheep. Environmental Research 20, p. 1.
6. Fries, George F. (1995), Ibid.
7. EPA (Prepared by Eastern Research Group)(1992), Ibid. p. 5-175, 176.
8. EPA (Prepared by Eastern Research Group)(1992), Ibid. p. 5-177.
9. Baxter, John C. et al (1982). Heavy Metal Retention in Cattle Tissues From Ingestion of Sewage Sludge. J. Environ. Qual. (11,4) p.616-620.
10. Baxter, et al (1983). Heavy Metals and Persistent Organics at a Sewage Sludge Disposal Site. J. Environ. Qual. 12: 311-316.
11. Baxter, J. C., et al (1983). Heavy Metal and Persistent Organics Content in Cattle Exposed to Sewage Sludge. J. Environ. Qual. (12,3) p. 316-319.
12. Hallford, D.M. et al (1982). Influence of Short Term Consumption of Sewage Solids on Productivity of Fall-Lambing Ewes and Performance of Their Offspring. J. Anim. Sci. (54,5) p. 922-932.
13. Hudgens, R.E. and Hallford, D.M., Effects of Long-Term Consumption of Sewage Solids on Reproductive Performance and Serum Progesterone and Estradiol-17beta in Mature Fine Wool Ewes. Theriogenology, Feb. 1983 (19,2) pp. 349-256.
14. Smith, G.S., et al (1985). Toxicological Effects of Gamma Irradiated Sewage Solids Fed as Seven Percent of Diet to Sheep for Four Years. J. Anim. Sci. (61 :4) p. 931941.
15. Swanson, D.W. et al (1984) Effects of Long-Term Consumption of Sewage Solids on Blood, Milk and Tissue Elemental Composition of Breeding Ewes. J. Anim. Sci. (59,2) p. 416-424.
16 EPA A Plain English Guide to the EPA Part 503 Biosolids Rule EPA, Sept. 1994, p 29.
17 Bray, B. J. et al (1985). Trace Metal Accumulations in Tissues of Goats Fed Silage Produced on Sewage Sludge-Amended Soil. J. Environ. Qual. (14,1) p. 114-118.
18. Dowdy, R.H., et al (1983a). Performance of Goats and Lambs Fed Silage Produced on Sludge-Amended Soil. J. Environ.. Qual. (12,4) p.467-472.
19. Fitzgerald, Paul R. (1980) An Evaluation of the Health of Livestock Exposed to Anaerobically Digested Sludge From A Large Community. in Proc. Nat. Conf. on Municipal and Industrial Sludge Utilization and Disposal/. Information Transfer, Inc. Silver Spring, Md. p 32-36.
20. NRC, Committee on the Use of Treated Municipal Wastewater Effluents and Sludge in the Production of Crops for Human Consumption( 1996). Use of Reclaimed Water and Sludge in Food Crop Production. National Academy Press. p.7
21. Fries, George F (1995). " A review of the Significance of Animal Food Products as Potential Pathways of Human Exposures to Dioxins". J. of Anim. Sci. 13: p. 1639 1650. p. 1641
22. Fries, George F. Ingestion of Sludge Applied Organic Chemicals By Animals, The Science of the Total Environment, 185(1996) p.93-108.
23. Harrison, Ellen Z. McBride, Murray B., Bouldin, David R (1997). Recommendations for Land Application of Sewage Sludges and an Appraisal of the US EPA's Part 503 Sludge Rules: Working Paper, August 1997. Cornell Waste Management Institute. p.28 ff.