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U.S. Department of Health and Human Services

Animal & Veterinary

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NAS Completes Review of EPA Dioxin Risk Assessment

by Jon F. Scheid, Editor
FDA Veterinarian Newsletter 2006 Volume XXI, No II

The National Academy of Sciences (NAS) on July 11 released its review of a dioxin risk assessment that the Environmental Protection Agency (EPA) has spent more than a decade developing, bringing the Federal government one step closer to finalizing the risk assessment on this complex and sometimes confusing issue.

EPA issued its first draft of the risk assessment in 1994. Developing the report has taken a long time because scientists needed to collect, evaluate, and accurately present the enormous amounts of sometimes inconclusive data available about dioxin.

Information about dioxin is still being developed, and some conclusions are controversial. To help resolve some of the critical questions surrounding the data and conclusions about dioxin, the NAS was asked to conduct an outside, expert review of the risk assessment. Scientists and policy makers consider an NAS review the “gold standard” for a thorough scientific evaluation.

In a summary of its findings, the NAS committee that reviewed the EPA draft risk assessment identified certain scientific underpinnings for the assessment that it said should be strengthened, and offered recommendations for additional review that it said would improve the assessment. The summary of the NAS committee report can be found at the following website http://darwin.nap.edu/open book.php?record_id=11688&page=8. The entire report can also be accessed from this site.

The term “dioxin” actually refers to a group of chemical compounds that share chemical structures and biological characteristics. Scientists have identified two forms as the most toxic (2,3,7,8-tetrachlorodibenzo-p-dioxin [TCDD], which is the most studied, and 1,2,3,7,8-pentachlorodibenzo-p-dioxin [PeCDD]) and use those two as a reference in determining the toxicity of other dioxins or mixtures of dioxin. The toxicity of other forms of dioxin is expressed as “toxicity equivalence,” or TEQ, to the most toxic forms of -dioxins.

Dioxins in high enough concentrations can cause adverse health effects in humans, including cancer. Scientists are also concerned, based on data from animal studies, that low level exposure in humans over long periods, or high levels at key times, might produce reproductive or developmental effects.

The EPA has issued regulations to limit the release of dioxin from significant sources in the United States, including municipal, medical, and hazardous waste incinerators and from cement kilns that burn hazardous waste. For water, EPA has issued regulations to reduce dioxin releases from pulp and paper facilities that rely on chlorine bleaching. These steps and others taken by the Federal government have curtailed known and quantifiable industrial dioxin emissions in the United States by 89 percent from 1987 levels.

Keeping food safe

Dioxins are found virtually everywhere in the world. Although dioxins are an environmental contaminant, most human exposure is through the diet. Scientists estimate that approximately 90 percent of human exposure is through dietary intake, primarily animal fats.

The Food and Drug Administration’s (FDA) Center for Veterinary Medicine (CVM) has a role in ensuring food and feed safety and has not waited for the final risk assessment report, but instead has already tried to address some of the dioxin issues. CVM has issued assignments each year since 2000 asking FDA’s field staff to collect samples of various complete feeds and feed ingredients and then test them to determine whether those feeds/feed ingredients could be contributing to dioxin in food produced from animals. The levels of dioxin CVM has found in these surveillance samples has generally been low.

In addition to determining background levels of dioxin, CVM has investigated any time high levels are found in feed or feed ingredients. CVM has taken action three times to reduce dioxin levels in the feed supply.

CVM issued a letter in 1997 to poultry and catfish producers and other users of clay products in feed asking them to stop using “ball clay” because of its high level of dioxins. Investigators found that ball clay from mines in Mississippi, Kentucky, and Tennessee had elevated dioxin concentrations. Some samples had dioxin at concentrations more than 100 times greater than that found in most topsoils.

Ball clay is a type of clay used mostly in the ceramic industry. It got its name by a practice of English miners to roll the clay into 30-50 lb. balls. The clay was used as a anti-caking agent in soybean meal.

In 2002, CVM worked with a mineral ingredient premix manufacturer who was recalling products found to contain high levels of dioxin. CVM determined the high temperature drying process the company used to produce its “protected” minerals was likely responsible for creating dioxin in the products, especially in mineral products containing high copper levels.

In 2003, CVM issued an alert to the feed industry warning against the use of mineral mixes and premixes that are byproducts or coproducts of industrial metal production. Earlier that year, FDA surveillance programs found elevated levels of dioxin in a feed product and traced the problem back to a zinc oxide product produced by a brass foundry.

CVM will continue to collect and analyze feed samples for dioxins and take appropriate actions to try to reduce dioxin levels in feed. Lower dioxin levels in feed should translate to lower dioxin levels in food of animal origin.

June, July