98 
 
Guidance for Industry 
 
Dioxin in Anti-Caking Agents Used in 
Animal Feed and Feed Ingredients 
This guidance supercedes guidance #98 of the same title, dated October 6, 1999 
 
 
 
This guidance is intended to notify members of the feed industry of recent finding regarding the 
presence of dioxin congeners that may be present in anti-caking agents and to offer general 
advice regarding the monitoring of these products.  This document has been revised in response 
to comments to the October 6, 1999 version. 
 
This guidance represents the agency's current thinking on the presence of dioxin congeners in 
anti-caking agents. It does not create or confer any rights for or on any person and does not 
operate to bind the Food and Drug Administration (FDA) or public.  An alternative approach 
may  be  used  if  such  approach  satisfies  the  requirements  of  the  applicable  statutes  and 
regulations. 
 
Comments  and  suggestions  regarding  this  guidance  document  should  be  submitted  to  the 
Division of Dockets Management (HFV-305), Food and Drug Administration, 5630 Fishers 
Lane, Room 1061, Rockville, MD 20852.  All comments should be identified with the Docket 
Number (99D-4201).   Additional information on the original guidance document dated October 
6, 1999 can be found in the Federal Register (Vol. 64, No. 199, October 15, 1999). Comments 
may be submitted at any time. 
 
For scientific questions regarding this guidance document, contact Randall Lovell, Center for 
Veterinary  Medicine  (HFV-222),  Food  and  Drug  Administration,  7519  Standish  Place, 
Rockville, MD 20855, 240-453-6857 e-mail: randall.lovell@fda.hhs.gov.  
 
 
U.S. Department of Health and Human Services 
Food and Drug Administration 
Center for Veterinary Medicine (CVM) 
April 12, 2000  Dioxin In Anti-Caking Agents Used in 
Animal Feed and Feed Ingredients 
 
 
Nearly two years ago, a multi-agency investigation tracked a previously unknown source of 
dioxins in our food supply back to a clay anti-caking agent, called ball clay, used in animal feeds 
and feed ingredients.  Together, industry and government moved swiftly to eliminate the use of 
ball clay in the animal feeds and thereby remove a source of dioxins in the human food chain. 
 
In an October 7, 1997, letter to members of the feed industry, we stated that the origin and scope 
of dioxins in clay deposits were unknown and, for this reason, mined clay products of all types 
should be used with caution in the production of animal feeds.  We advised companies offering 
anti-caking products for animal feed uses to assure that their products were not contaminated 
with dioxins. 
 
Many industry participants tested clay products used in animal feeds in 1998.  In particular, the 
American Feed Industry Association (AFIA) led a "Dioxin Task Force" that assembled dioxin 
data from a variety of sources and products.  Based on our experiences with ball clay, one dioxin 
congener, 2,3,7,8-tetrachlorodibenzodioxin (TCDD) was thought to be predominant.  
Consequently, TCDD was all that was reported by the Dioxin Task Force to the CVM in 
September 1998.  Fifty-nine, non-ball clay, clay product samples were reported to all be below 
the limit of detection for TCDD, with the detection limit in general being below 0.75 part per 
trillion (ppt) measured as TCDD. 
 
Also, in late 1998, FDA collected samples of clay and non-clay anti-caking products from feed 
and oilseed sites where they were being used.  The Environmental Protection Agency (EPA) 
subjected the samples to the complete analysis for all 17 dioxin and furan congeners of 
toxicological importance.  The results of this survey prompted FDA to share our findings and 
their implications for industry monitoring of clay and non-clay anti-caking products and our 
future plans. 
 
In brief, nine of fifteen samples of anti-caking, flow, and pelleting aid products were found to 
contain detectable dioxins varying from less than 1 ppt toxicity equivalents (part per trillion 
TEQ) to slightly over 20 ppt TEQ.  Unexpectedly, the primary dioxin congener contributing to 
the TEQ was 1,2,3,7,8-pentachlorodibenzodioxin (PeCDD).  Very little, if any TCDD was found 
in the samples. None of the samples appeared to be ball clay, but were identified as 
montmorillonite," "bentonite," "ground clay," and even "silicate" and "lime." 
 
FDA and EPA are continuing to investigate the sources of the more elevated samples; however, 
the information thus far indicates the need for increased caution in industry surveillance for 
dioxins in feed ingredients. 
 
First, there is now evidence that dioxins can be present in clay and non-clay anti-caking products 
other than ball clay. The current findings do not discount a natural origin for these residues. 
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Second, dioxin congeners other than TCDD, particularly PeCDD, may be present in important 
amounts. Therefore, analyses for dioxins should be for the entire congener group that contributes 
to the TEQ measurement, rather than just TCDD.  Persons retaining samples of clay extracts that 
were evaluated only for TCDD, for example, samples reported by the Dioxin Task Force, may 
wish to consider re-submitting the samples for a more thorough analysis. 
 
Third, the significance to public health of the relatively low concentrations of dioxins found in 
the latest samples is presently unclear.  On the one hand, these would seem to be small 
contributions of dioxin to the human food chain.  Most of the dioxin concentrations found in the 
positive samples were on the order of one-one thousandth of the highest concentrations found in 
ball clay.  On the other hand, the limited samples may not be representative of the full range of 
concentrations of dioxins that may be found in these products. 
 
Because dioxins were not detected in six of fifteen samples, it appears that dioxins can be 
minimized or avoided altogether in anti-caking agents.  All clay and non-clay anti-caking 
products for use in feeds or feed ingredients should be carefully monitored for dioxins, without 
regard to how remote or pristine the source.  We recommend that companies not use any clay or 
non-clay anti-caking products contaminated with dioxin in animal feed and feed ingredients.   
 
CVM plans to continue to sample regulated clay and non-clay anti-caking products for dioxins in 
conjunction with EPA and other government agencies.  Plans are also underway to sample other 
feed components for dioxin.  We will report back to you as new information becomes available. 
 
 
 
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