Comments to US EPA regarding
Dioxin Standards for Land Applied Sewage Sludges
March 27, 2000
 
TO: Comment Clerk, Water Docket MC-4101
Environmental Protection Agency
401 M Street SW, Washington, DC 20460
Email OW-Docket@epamail.epa.gov
Re: Part 503 Sewage Sludge or Disposal Rule
Docket Number W-99-18
Please contact Ellen Harrison, EZH1@cornell.edu, 607 255-8576, 100 Rice Hall, Ithaca, NY 14853 with any questions and responses.
 
Submitted by the following Cornell University Researchers:
Ellen Z Harrison, Director, Cornell Waste Management Institute, Center for the Environment
Murray McBride, Professor, Department of Crop and Soil Science
James Gillett, Professor, Department of Natural Resources, Cornell University
Lois Levitan, Program Leader, Environmental Risk Analysis Program, Center for the Environment
Anthony Hay, Assistant Professor of Microbiology and Soil Ecotoxicology, Department of Microbiology
Peter Woodbury, Senior Research Specialist, Boyce Thompson Institute for Plant Research
David Bouldin, Professor Emeritus, Department of Crop and Soil Science
Table of contents:
 
Cancer is Not Most Sensitive End Point if 10-5 Risk is Used
A wide range of non-cancer effects are found (Brouwer, et al., 1998).
Non-cancer endpoints, especially developmental impacts through fetal and nursing infant exposures, are more sensitive end points than cancer where less than one-in-a-million cancer risk is used as cancer end point (data in US Dept. of Health and Human Services, ATSDR, 1998; WHO, 1998; Dr. Henry Anderson, Wisconsin Department of Health and Social Services, personal communication).
 
The immune system is a sensitive target for toxicity (US Dept. of Health and Human Services, ATSDR, 1998).
 
Developmental behavioral impacts were found at a does of 0.12 ppt/kg bw/day in rhesus monkeys and developmental effects are found to be among the most sensitive LOAEL in animals leading to a chronic oral MRL based on these effects (US Dept. of Health and Human Services, ATSDR, 1998).
 
Impact to Wildlife and Soil Organisms Not Assessed
Shrews may be at risk from TCDD and TCDF in land applied paper mill sludges (USEPA/Abt Assoc. , 1994).
 
Wildlife ingest significant quantities of soil (17% of diet for nine banded armadillo, 10% for woodcock, 9% wild turkey) (Beyer, et al, 1994) Whether this represents a risk due to sludge application is not clear.
 
Risks to predators including raptors higher on the food chain need to be assessed.

Not Protective of Farm Family
A dairy farm family in New York that uses sludge may well obtain all or nearly all of its meat and milk from animals exposed to sludge-amended pastures and forages. Since these are the primary dietary sources of dioxins and since diet is the primary non-occupational exposure route, this is a critical issue for the farm family. The RA does not take this potentially high level of exposure for the farm family into consideration. Using a point value of 10% beef from sludged sources is not protective of the family which raises its own meat and milk.
 
The farm family may also eat poultry and eggs from birds which free-range on sludged lands. They are also likely to inhale air that contains constituents volatilized from sludge and may drink water that has received sludge-leached inputs. Their diet may include vegetables grown on sludge-amended soils. Thus analysis of simultaneous exposure to multiple pathways is needed.
 
Land grant colleges and farm advisors must be aware of the risks to farm families since they advise farmers.
 
A revised risk assessment based on farm family health including prenatal and nursing exposure to infants of mothers residing on dairy farms is needed in which higher values are used for the percent of diet from sludged sources as well as simultaneous exposure from multiple pathways.
 
Not Protective of Children
Current levels of exposure to nursing infants exceeds the 4 pg TEQ/kg level TDI recommended by WHO (WHO, 1998) for nearly the entire population in Canada (Hoover, 1999) ­ and we would expect similar results for infants in the US.
 
Average daily intake of breast-fed infants on a body weight basis may be almost 1-2 orders of magnitude greater than that of an adult (WHO, 1998).
 
Sensitivity to toxicity of CDDs may be greater during the fetal/neonatal period than for adults and may have an impact on male reproductive system development (US Dept. of Health and Human Services, ATSDR, 1998).
 
Cognitive functioning in preschool children is negatively impacted by in utero exposure to PCBs and dioxins (Patandin, et al, 1999).
 
Birth weight and postnatal growth until 3 months of age were impacted by in utero exposure to PCBs and dioxins (Patandin, et al, 1998). Immune suppresive and delayed reproductive effects are also a concern.
 
A probabilistic risk evaluation of organochlorine exposure through breast milk showed that for a significant percentage of the population, PCBs and PCDD/PCDFs provide the greatest concern for non-cancer health effects from chemicals in breast milk (Hoover, 1999).

Grazing Animal Ingestion of Sludge
The pathways for animals ingesting forage and for animals ingesting soil need to be summed since a farmer using sludge would likely use it on pasture and on field crops. The amount of sludge ingested due not to uptake or soil ingestion but to ingestion of sludge adhering to plants needs to be included in the assessment.
 
The assumptions for amount of soil ingested by grazing animals result in a low estimated soil intake based on best management practices (1.5% of diet is value used in RA). Grazing cattle ingest from 1-18% of their dry matter intake as soils and sheep may ingest as much as 30% depending upon management and the seasonal supply of grass (Fries, 1996; Thornton and Abrahams, 1983). Other researchers use higher estimates such as 6% of diet as soil and point out the critical importance of assessing the amount of sludge ingested through material adhering to vegetation ­ and the lack of data on appropriate values for that variable (Wild, et al, 1994). Use of a probabilistic method for risk assessment would allow a more realistic range of values to be used for these key parameters.
 
Sludge applied to pastures is generally not incorporated into soils yet the risk assessment appears to assume that the sludge is tilled into the soil. This would have a significant bearing on the concentration of sludge-borne contaminants ingested.
 
The RA appears to assume zero dioxin ingestion by animals in yrs 2 and 3 when no sludge is assumed to be applied. It is not reasonable to assume that levels fall to zero in pasture and that there is no residual in the years following application.
 
Free range poultry eat soil and would bioaccumulate dioxins. Geese were found to consume 8% of their diet as soil and wild turkey 9% (Beyer, et al, 1994). Free range poultry might exhibit similar behavior. Chickens accumulate dioxins ­ animals foraging on soils containing low ppt PCDD/PCDF levels may bioaccumulate these compounds to unacceptable levels (Stephens et al, 1995). The risks to those consuming poultry should be assessed.
 
Monitoring
The rationale for exempting POTWs generating less than 1 MGD from testing is flawed. While the total quantity of sludge these plants contribute may be low, there is no reason to believe that the levels of dioxins in these sludges would be low. (This is an issue that could be investigated.) Since any particular farm may repeatedly apply sludge from a single POTW, the farm family, the particular land and ground and surface waters which flow from that land, and the meat and milk produced from that land could be contaminated at levels presenting a significant risk to those exposed. While the total number of people exposed will be limited due to low sludge volumes, the risk to those exposed, which may be substantially higher than presumed in this rationale, will not be known if no testing is done and that risk may be high. This is another example of how the sludge rules rely on concepts of "average" exposure which are not appropriate to protection of potentially highly exposed individuals.
 
The concept that monitoring frequency be reduced if low concentrations of dioxins (less than 10% of standard) are detected in sludge monitoring conducted in the first two years has merit. We have reservations, however, about the adequacy of the current level of knowledge regarding fluctuations in dioxin concentrations from a particular POTW from sample to sample and in knowledge about trends over time on which this concept is based. The data were not presented in the EPA documentation regarding the proposed rule. We believe that the amount of data is very sparse and does not allow the stated conclusions to be drawn. We would suggest that POTWs be required to collect data for 3 years and that an analysis then be performed on those data to assess the validity of the assumptions that there is little fluctuation and that levels are decreasing.
 
Background Exposure
A WHO panel recently completed reevaluation of PCB/PCDD/PCDF and determined that existing background exposures may be causing subtle effects at current intake levels of 2-6 pg TEQ/kg bw/day (WHO, 1998). Thus current exposure from background sources in an industrialized country like the US may already put us at risk.
 
This RA does not assume any background exposure and is only an assessment of incremental exposure from sludge application.
 
Risk Assessment Issues
A revised risk assessment using probabilistic methods which incorporates the various suggestions in these comments and which then calculates a daily intake that includes background intake from non-sludge sources is needed.
 
Realistic data and scenarios incorporating the variability and uncertainty should be used in a multi-media, multi-exposure probabilistic analysis of rather than persisting in use of out-dated point estimate risk assessment. EPA itself recognizes need to represent variability and uncertainty in risk assessments and the value of probabilistic tools such as Monte Carlo analysis. (US EPA Office of Research and Development, National Center for Environmental Assessment (NCEA). May 15, 1997. Policy for Use of Probabilistic Analysis in Risk Assessment at the US Environmental Protection Agency. 4pp. Available at: http://www.epa.gov/ncea/mcpolicy.htm. ;US EPA Risk Assessment Forum. March 1997. Guiding Principles for Monte Carlo Analysis. EPA/630/R-97/001. 35pp. http://www.epa.gov/oppefed1/ecorisk/backgrn.htm links to a down-loadable PDF file; Report of the Workshop on Selecting Input Distributions For Probabilistic Assessments. EPA/630/R-98/004. January 1999. National Center for Environmental Assessment.).
 
Using probabilistic methods to analyze impact of breast-feeding, Hoover showed that fat content in breast milk is a key variable. If an inappropriate single point value was used, results are skewed. (Hoover, 1999).
 
Uncertainty is great regarding dioxin toxicity due to very different responses of different species.
 
There are inadequate data on impacts on humans during fetal development and infancy (Hoover, 1999) (also inadequate data on wildlife for these same developmental impacts). Milk, a food in which bioaccumulated dioxins are shed and thus present in significant quantities is a primary food for infants and children. Over 95% bioavailability of most PCB, dioxin and furans from breast milk has been reported. (McLachlan, 1993; Hoover, 1999).
 
Most standards are developed based on adult models. Some research has tried to improve on this by incorporating pharmacokinetic adjustments for infants. "The breast-fed infant's intake of organochlorines has been found in general to exceed guidance values, raising the possibility that breast-feeding may pose health risks" (Hoover, 1999, p 528).
 
Use of different assumptions in the risk assessment process leads to different standards. Using a risk assessment process, the state of Wisconsin evaluated dioxin risks from paper sludge land application and derived a cancer-based standard of 1.2ppt in soil associated with a one-in-a-million risk and a value of 0.19ppt where grazing is allowed (Goldring, 1992). If the higher allowable cancer risk accepted by EPA in the sludge rules of one-in-ten-thousand were used, acceptable levels based on the Wisconsin assessment would be 19 ppt in soils where grazing is allowed. Our understanding of the RA is that 30 ppt TEQ in soil might result from the application of sludges containing 300 ppt under the assumptions used in the RA (Exhibit 3-7). Thus even based on cancer as an endpoint, using the Wisconsin risk assessment assumptions and methods would result in a lower standard, making the point that what assumptions are made is critical to the RA results. As stated above, however, cancer would not be the sensitive end point where risks greater that one-in-a-million are accepted.
 
Why was the application scenario changed from Round 1 TDS assumptions? The change in this and in other parameters such as soil ingestion rates which are changed from 200 to 400 mg/day (and the concomitant change in the assumption that what is ingested is not straight sludge but a sludge soil mixture [the concentration of sludge vs. soil is not clear in the RA and is important]) indicate that risk assessments are based on many uncertain assumptions which critically alter the outcomes. A number of the assumptions in the RA need to be more transparent.
 
Much greater explanation and clarity is needed regarding the assumptions used in the RA. A critical example about which we would seek clarification has to do with how soil concentrations were calculated. The algorithms in the RA document do not permit the reader to assess the actual assumptions made and values used. For example it is not clear how the many fold reduction in concentration from sludge to soil is projected. Various equations are displayed, but the justification for the values used are not clear. It is not clear whether soil incorporation into pasture is assumed, and if so to what depth. It is not clear what assumption is made regarding residual levels in years between applications and thus of cumulative soil levels. It is not clear how much of the dioxins is projected to leach, volatilize and degrade. It is not clear why 95th percentile was used for dairy fat consumption and mean was used for beef and lamb fat (Exhibit 3-12). What is the assumed proportion of sludge in the sludge/soil mixture used to calculate risks to children ingesting soil?
 
Soil concentrations resulting from application are a key variable. In fact soil concentration should be the regulated end point. The large reduction in concentration predicted in the risk assessment do not seem warranted nor do they seem to agree with the projections in the USEPA/Abt Associates document on risks to terrestrial wildlife from papermill sludges (USEPA/Abt Associates, 1994). Various studies show little or no loss of dioxins from soils (Orazio, et al. 1992; Hagenmaier, et al., 1992 b). Half-life in soil is a critical parameter and for TCDD estimates vary widely and are also very dependent on whether the material is in the surface soil or subsurface (estimates from 9 to 100 years in US Dept. of Health and Human Services, ATSDR, 1998).
 
No information is included on potential transformation to other toxic products.
 
TEFs are continuing to evolve, so their use is important but a source of uncertainty. The recent WHO consultation reevaluted them and recommends revisions that would result in an approximate 10% increase in TEQ calculations compared to using I-TEFs (WHO, 1998).
 
In regard to the groundwater pathway, the role of facilitated transport of dioxins bound to organic matter needs to be investigated. Sorption onto organic matter may give rise to the facilitated transport of these compounds into ground water (Nelson, et al 1998). This is a particular concern as complexation of hydrophobic chemicals with organic matter can also inhibit the ability of microorganisms to degrade these compounds even though they may still be available and therefore toxic to higher organisms (Rinella, 1993 #4).
 
There is a need to assess multiple simultaneous pathways for people ingesting soil, meat, dairy, vegetables, inhalation, drinking water.
 
Polybrominated biphenyls and dioxins seem to pose similar risks to dioxins and PCBs (Hornung et al, 1996; Helleday, et al, 1999, Weber and Greim, 1997; Henck, et al, 1994). They appear to be carcinogenic (Hoque, et al, 1998; Henderson, et al, 1995). They are detected in sludges (Hagenmaier, et al., 1992a). If they act in similar toxicologic or oncogenic mode to dioxins, they need to be factored into the risk assessment.
 
Many of the risk assessment assumptions questioned in our analysis of Round 1 (Harrison, et al 1999) also pertain to this assessment. For example, very low percent of watershed assumed to receive sludge (0.006%); relatively high cancer risk accepted; single point estimate of dietary intake not appropriate for the range of consumption patterns. The revised risk assessment should use a distribution rather than point estimates for such highly variable inputs.
Bioavailability is uncertain. While dioxins in breast-milk are very bioavailable, the potential for sludges to reduce bioavailability and the persistence of such an effect need to be assessed.

Risk Management Choices
A WHO panel recently completed reevaluation of PCB/PCDD/PCDF and determined that: 1) a revised TDI of 1 to 4 pg/km body weight is established with 4 considered a maximum for long-term exposure on a provisional basis and 1 as a goal; 2) existing background exposures may be causing subtle effects at current intake levels of 2-6 pg TEQ/kg bw/day; 3) efforts should be made to limit environmental releases to the extent feasible. (WHO, 1998; Brouwer, et al 1998). Thus in an industrialized country like the US, current exposure from background sources in an industrialized country like the US may already put us at risk of unknown nature and extent.
 
Schecter and Olson (1997) calculate that current dietary exposure to PCDDs and PCDFs results in approximately 30-300 excess cancers per million pop ­ and this does not include dioxin-like chemicals such as PCBs which might further increase the risk.
 
These standards do nothing to move towards the goal of minimizing exposure since more than 95% of US sludges tested fall within the proposed standards (Exhibit 3-1). The RA should include a more complete description of the distribution and pattern of dioxin levels in US sludges with a goal of better understanding sources exposure routes, relation to POTW processes, and especially how to reduce levels in sludges. It would appear to be incumbent on the regulated industries and regulatory community to move quickly to reduce the specific uncertainties of exposure and response in a way which expedites risk management of those sludges which may evoke adverse effects in non-cancer areas (learning, endocrine development, immune function) in particular segments of society and parts of potentially impacted ecosystems.
 
Given many of the uncertainties and concerns raised, it would be prudent to establish rules for exposure to dioxins that minimize exposure from land application. The current proposal not only does not accomplish that, but also offers no incentive for reaching a better understanding of critical processes, such as features of sludge and its uses which enhance or reduce bioavailability. Consideration should be given not only to setting a lower standard, but also to restricting uses in order to minimize exposure. Since meat and milk are the primary routes of significant exposure, consideration should be given to restricting use of sludges with more than very minimal dioxin levels on land used for grazing or growing forage crops.
 
Further Comments
EPA needs to continue to examine the sludge rules to both consider regulating additional contaminants and to reassess those already addressed. Additional contaminants not presently characterized and which are present at relatively high levels in sludges include surfactants (LAS and nonylphenol polyethoxylates) (Klopffer, 1996). The degradation of common nonionic surfactants such as nonylphenol polyethoxylates in POTWs leads to the accumulation of estrogenic nonylphenols in anaerobically digested sludge at levels as high as 4000mg/kg (Bennie, 1999). Although recent evidence suggests that nonylphenols spiked into uncontaminated sludge are degraded over several months, a significant portion of the nonylphenols in aged sludges is recalcitrant to biological transformation (Topp, 2000). In addition to persistence in the soil, the sorption of nonylphenols onto organic matter may give rise to the facilitated transport of these compounds into ground water (Nelson, et al, 1998,). Sludges were also found to contain potent polyaromatic EROD-induing compounds not presently being analyzed (Engwall et al, 1999). Poly brominated biphenyls used as flame retardants in the past need to be monitored and their risks assessed.
 
Changed assumptions in the dioxin RA from those in the TSD for Round 1 suggest a need to reassess the ingestion pathway for the round 1 pollutants since ingestion was limiting pathway for a number of pollutants.
 
Animal health risks posed by molybdenum are of critical concern particularly in states like NY where dairy is the major agricultural enterprise. Research in progress at Cornell suggests that even single applications of sludges can result in uptake of molybdenum into leguminous forages that may present a significant risk to ruminant herd health. Standards are needed to address this issue.
 
As recommended by the National Research Council, a new survey of sludge quality is needed with improved analytic methods and additional parameters.
 
There is a need for additional sludge research to address outstanding questions. A separate list of research needs follows:
 
Research Needs Pertaining to Land Application of Sewage Sludges
These are some areas in which additional research is needed. It is important to recognize that different soils, crops, sludges and sludge products will respond differently so that research results will vary depending on these and other variables. Research should be supported through an entity that is independent of the sludge stakeholders.
 
Sludge Quality and Variability
- Survey US sludges for additional contaminants (such as surfactants) and using improved analytic methods (as recommended by National Research Council)
- Analyze the temporal variability of quality and nutrient content of sludges from individual WWTPs. Quality varies significantly from sample to sample. Farmers and their advisors apply based on monitoring results not obtained from the particular sludge load being delivered and may thus over or under apply nutrients.
 
Nutrients
- At what rate does the N in selected sludges and sludge products become available as a plant nutrient?
- How variable over time is the N and P content and availability of N in sludge from particular treatment plants?
- What are the relationships between P availability and sewage treatment processes?
 
Groundwater Quality
- How much of trace metals applied in sludges and sludge products leaches through soils?
- What is the role in the movement of contaminants to groundwater of preferential flow through macropores?
- What is the role in the movement of contaminants to groundwater of facilitated transport by complexation of contaminants with organic matter?
- How much nitrogen applied in sludges, fertilizers and manures leaches through soils?
- Do pathogens applied in sludges leach through soils? Particularly viruses leaching from Class B sludges.
- What groundwater flow model will predict mobility of contaminants?
 
Crop Yield and Quality
- What are the yield responses of sensitive crops (like alfalfa) to sludge applied metals in long-term applications to acidic agricultural soils?
- What is the concentration of molybdenum and the Cu:Mo ratio in forage crops and pasture grown on agricultural soils in to which sludges have been added (both short and long term)? And what are the implications for dairy farms?
 
Surfactants
Although nonylphenol based surfactants have been phased out in Europe they are still widely used in the United States. A preliminary analysis of sludge from two upstate New York STPs shows nonylphenols to be present at concentrations of more than 1000mg/kg. These values can be compared to the temporary permissible limit of 50mg/kg nonylphenol allowed in land-applied sewage sludges in Denmark (Cavalli, 1999). At present there is neither monitoring nor regulation of nonylphenol concentrations in sludges in the United States. As application of nonylphenol contaminated sludges is a possible source of ground and surface water contamination as well as through direct exposure from soil ingestion, more work is needed to understand the fate of these compounds in agricultural settings.
 
Direct land application is not the only fate of nonylphenol contaminated sludges however. In New York state 57% of beneficial biosolids are either composted or heat dried (Rowland, 1998) before further use. Nonylphenols are volatile and significant atmospheric concentrations have recently been detected above STPs and rivers receiving nonylphenol inputs (Dachs, 1999). To date no work has been reported characterizing the fate of nonylphenols in high-temperature composting environments or during heat treatment. However, the elevated temperatures in these procedures, combined with the volatile nature of nonylphenols suggest a potential for localized atmospheric contamination during the treatment of contaminated sludge. More work therefore needs to be done to assess the fate of nonylphenols during processing of sludges.
 
- At what levels are surfactants and their metabolites present in sludges and in soils to which sludges have been applied?
- What is their fate when land applied?
- Are they volatilized during sludge composting and other treatment processes?
 
Aerosols and Health
- To what chemicals and pathogens are people exposed from aerosols and volatile emissions from land applications and sludge processing sites and what are the health risks associated with those exposures?

Pollution Prevention/Sludge Quality
- What are the sources that are responsible for concentrations of particular contaminants of concern in sludges?
- What can be done to reduce or eliminate the discharge of those pollutants into WWTP?

Testing and Monitoring
- What analytic methods will detect and quantify (if necessary) infective viruses and other pathogens?
- What analytic methods are appropriate for monitoring movement to groundwater?
- What analytic methods are appropriate for monitoring soils contaminants and their bioavailability?

Risk Assessment
- What is the impact on soil microbial system of long term sludge additions?
- What is the impact on wildlife exposed to sludge-treated systems?
- What are the likely exposures and impact of those exposures to the dairy farm family.
- Need to address multiple exposure pathways being experienced simultaneously (drinking water, breathing air, eating dairy, meat and vegetables, ingesting soil).
- Need to reassess direct ingestion risk since dioxin risk assessment uses 400mg/day ingestion rate and TSD used 200mg/day and since direct ingestion was the most limiting pathway for a number of the contaminants. Also need to evaluate the potential for acute toxicity from one-time high ingestion days.
- Need to apply probabilistic vs. deterministic methods of risk assessment.

Alternative Uses
- What other uses might be made of sludges that would pose fewer risks?
References Cited:
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Bennie, D. T. 1999. Review of the environmental occurence of alkylphenols and alkylphenol ethoxylates. Water Quality Research Journal of Canada. 34(1):79-122.
 
Beyer, W. N., E. E. Connor and S. Gerould. 1994. Estimates of Soil Ingestion by Wildlife. Journal of Wildlife Management. 58(2):375-382.
 
Brouwer, A., U. G. Ahlborg, F. X. R. van Leeuwen and M. M. Feeley. 1998. Report of the WHO Working Group on the Assessment of Health Risks for Human Infants from exposure to PCDDs, PCDFs and PCBs.
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Cavalli, L., and L. Vlatorta. 1999. Surfactants in sludge-amended soil. Tenside Surf. Det. 36(22-28).
 
Dachs, J., D. A. Van Ry, and S. J. Eisenreich. 1999. Occurence of estrgenic nonylphenols in the urban and coastal atmosphere of the lower Hudson river estuary. Environmental Science and Technology. 33(15):2676-2679.
 
Engwall, M., B. Brunstrom, C. Naf and K. Hjelm. 1999. Levels of dioxin-like compounds in sewage sludge determined with a bioassay based on EROD induction in chicken embryo liver cultures. Chemosphere. 38(10):2327-2343.
 
Fries, G.F. 1996. Ingestion of sludge applied organic chemicals by animals. Science of the Total Environment. 185:93-108.
 
Goldring, J. 1992. Assessment of Potential Human Health Impacts of Dioxin an Furan Contaminated Sludge Amended to Soils. Wisconsin Department of Health and Social Services.
 
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Hagenmaier, H., J. She and C. Lindig. 1992 b. Persistence of Polychlorinated Dibenzo-p-Dioxins and Polychlorinated Dibenzofurans in Contaminated Soil at Maulach and Rastatt in Southwest Germany. Chemosphere. 25(7-10):1449-1456.
 
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Hoover, S. M. 1999. Exposure to Persistent Organochlorines in Canadian Breast Milk: A Probabilistic Assessment. Risk Analysis. 19(4):527-545.
 
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Patandin, S., C. I. Lanting, P. G. H. Mulder, E. R. Boersma, P. J. J. Sauer and N. Weisglas-Kuperus. 1999. Effects of environmental exposure to polychlorinated biphenyls and dioxins on cognitive abilities in Dutch children at 42 months of age. Journal of Pediatrics. 134(1):33-41.
 
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Cornell Waste Management Institute
Cornell University
Ithaca, NY 14853
2000