Response to the “Scientific Peer Review of the Case for Caution”

May 20, 2002

Ellen Z. Harrison[i], Murray McBride[ii] and David Bouldin[iii]

Cornell University

A paper authored by Chrostowski, Foster and Preziosi of CPF Associates titled “Scientific Peer Review of the Case for Caution” was presented at the NY Water Environment Association meeting in February 2002. The authors of the Case for Caution, Ellen Harrison, Murray McBride and David Bouldin, are not developing a detailed rebuttal because we do not believe it will help to further the science or quiet the debate. We do, however, offer several comments below on the paper.

Two of the authors (Bouldin and McBride) and several of their colleagues at Cornell and in the northeast have been working on the questions regarding land spreading of sludges for over 25 years. Harrison has been involved in research and outreach regarding land application for the past 7 years. As faculty members of the College of Agriculture and Life Science at the Land Grant University for New York, part of our responsibility is to provide guidance and respond to questions from the agricultural community. Since 1975 we have received questions from farmers, Cooperative Extension personnel and the general public about the benefits and risks of the use of sludges on farms, gardens and play areas. Much of the information in the Case for Caution was derived from over 25 years of work to provide reasonable answers to the questions received.

1. Who funded the work?

We are grateful to the authors for raising questions about the source of funding for the Case for Caution. We agree that this is an important question and that readers should have information about the source of funding. Studies have shown that research findings are strongly influenced by the source of the funding for that work[iv]. It is regrettably not standard practice for researchers to identify the source of funding for their work except when so requested by the funder.

We are pleased to provide information on the source of funding for the Case for Caution and related research. Sources include the College of Agriculture and Life Sciences at Cornell, the Cornell University Agricultural Experiment Station, the US Department of Agriculture, the National Science Foundation and the NYS Energy Research and Development Authority (which provided support of research some years ago). There has been no funding for any of our sludge-related work from any source with a financial stake in the work or from any private sector source.

Several Cornell faculty members, including Bouldin and McBride, were co-authors along with 26 other faculty from 9 states of a publication providing guidance for the use of sewage sludges in the northeast that was the culmination of work by the Northeastern Soil Research Committee (Criteria and Recommendations for Land Application of Sludges in the Northeast, 1985, Pennsylvania State University, Bulletin 851). That committee was funded by USDA and the participating land grant universities in the NE.

It is interesting to note that the authors of the “peer review” provided their review at the request of Synagro Technologies, Inc., a firm whose business includes the land application of sewage sludges,

2. Peer review of the Case for Caution

The “peer review” criticizes the Case for Caution as not having been subject to independent peer review. The Case for Caution, while published as a working document by the Cornell Waste Management Institute (CWMI), was sent by CWMI to a number of scientists at Cornell and elsewhere for review. One reason to publish it as a working paper is to allow for revision and updating. A paper that is substantially identical to the Case for Caution appeared in the peer-reviewed journal, International Journal of Environment and Pollution[v]. It is unclear why the Synagro “peer review” chose to focus on the Case for Caution rather than the version that appeared in the peer-reviewed literature.

3. Different Assumptions

The “peer review” makes a number of assumptions with which the authors of the Case for Caution do not agree. We will not go through all of these, but provide several examples.

Calculations of the concentration of contaminants in soils that result from application of sludges rely on both the concentration of contaminants in the sludge and the amount of sludge applied. The authors of the “peer review” assume an application rate of 3 tons/acre while a rate of 10 tons/acre is the rate used by USEPA in its risk assessment for land application in agriculture. Experience in New York State suggests that 10 tons/acre is a reasonable figure. The low application rate used in the “peer review” results in lower calculated soil concentrations of contaminants.

The “peer review” also uses the “average value” for contaminant concentrations in sludges to calculate soil concentrations resulting from sludge application and the risks posed by those contaminants in soil. It is not clear what the relevance of this average value is to assessing the adequacy of the USEPA 503 sludge rules. We believe that the maximum concentration allowed under the rules (much higher than average values) is the appropriate value to use in assessing risks since sludges with these higher concentrations could be legally applied. Indeed, one of the concerns we have with the rules is that they provide no incentive for improving sludge quality since most sludges are already cleaner than those allowed under the rules.

The “peer review” suggests that nitrogen will limit the cumulative application of sludges. For Class A, EQ sludges, there is no limitation based on nitrogen or any other criteria.

Overall, an important reason there is disagreement about the US EPA 503 rules is the debate about what constitutes an acceptable risk. What level of crop yield reduction is considered acceptable, for example? How many additional cases of human disease are acceptable?

How to deal with uncertainty is another significant source of disagreement. Data on the concentrations of persistent bioaccumulative organic toxics in sludges is extremely limited. Past experience leads us to believe that a very cautious approach is called for when dealing with these fat-soluble chemicals and their potential introduction into milk and meat as well as the environment.

4. Risk Assessment Methods

The “peer review” criticizes many of the concerns with the risk assessment performed to develop the 503 rules raised in the Case for Caution. Rather than rehash those arguments here, we urge all interested persons to refer to the National Research Council report on biosolids that is expected to be released in June 2002. This report will review risk assessment issues as they pertain to the Part 503 rule.