Perceived
risks of dioxins:
Are proposed EPA sewage sludge regulations protecting animal agriculture?
Dr. Lynn Willett
Ohio State University
The US EPA
recently published 10-year study on dioxin which identifies
2,3,7,8-tetrachloro-p- dioxin, dioxin congeners and other dioxin-like compounds
as potent animal toxins as well as likely carcinogens.
Although the carcinogenic potential is controversial within the
scientific community, the report states these effects may be . . .occurring
in humans at general population background levels. According to the report, dioxins, by-products of combustion
and industrial chemical processes, enter the food chain primarily from
volatilization from soil to forage crops to milk, dairy and beef products, which
are identified as the source of 60-90% of human exposure.
Dioxins accumulate and are stored in fat tissues with clearance rates
ranging from a half-life of 58 days in lactating cattle to 7.1 years in humans.
US EPA
standards on the use and disposal of sewage sludge are codified in 40 CFR 503
which is expected to be finalized in December 2001.
Although sewage sludge as a soil amendment is favored for sustainable
agriculture, it is a potential source of dioxins, especially if co-mingled with
industrial waste and household chemicals. The
initially proposed standards would permit application of sewage sludge with less
than 300 part per trillion (ppt) of dioxin and require testing by Public
Operated Treatment Works (POTWs) treating more than 1 million gallons per day.
The OEPA sewage sludge regulations, being developed under Ohio
Administrative Code 3745-40, do not specify a tolerance limit for dioxins but
are expected to use the US EPA limit. The
OH 3745-40 requires testing for dioxins by POTWS treating more than 100,000
gallons per day.
The federal and state EPA sewage sludge regulations are not consistent with the findings of the EPA dioxin study. The US EPA regulations permit application of sewage sludge with dioxin levels significantly above the mean rural background level of 3.6 ppt which was identified as having potential toxic and/or carcinogenic effects. In addition, the study stated that At elevated chronic exposures of about 10 times background exposures, clearly adverse effects have been observed in both animals and humans. The National Sewage Sludge Survey indicates that about 90% of sewage sludge has dioxin levels between 3.6 and 300 ppt. Both regulations require records of sewage sludge application be kept only 5 years even though the half-life in soil is 25 to 100 years. If regulations change to meet the perceived risks stated in the dioxin study, soils receiving application of sludge with dioxin levels above background are at risk of being permanently taken out of production in the future.