Exposure of laboratory animals to polychlorinated dibenzodioxins and polychlorinated dibenzofurans from commerical rodent chow.

Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDDs/PCDFs) are ubiquitous low level environmental contaminants. Present finding of PCDDs and PCDFs in the human food supply suggested that laboratory animals maintained under controlled conditions may also receive unwanted exposure to these compounds from food. In this study, a commercial rodent chow, Prolab-RMH 1000, was analyzed for the toxicologically active 2,3,7,8-substituted PCDDs and PCDFs. The results show that the feed had a total PCDD/F dioxin toxic equivalence (I-TEq) of 0.13 pg/kg (ppt) wet weight. OCDD was the most abundant congener present, followed by 1,2,3,4,6,7,8-HpCDD, with these congeners representing the 5th and 6th greatest contributors to the calculated TEq. Daily ingestion of I-TEqs for the rats is calculated to be 3.9-6.5 pg/kg/day, and 13.0-32.5 pg/kg/day for mice. It is therefore important to consider the potential for background exposure to PCDDs and PCDFs from the diet when conducting studies with laboratory animals. This is particularly important when sensitive responses, such as enzyme induction, immunotoxicity, and developmental/reproductive toxicity are being investigated at very low exposures to this class of compounds.