EXPOSURE OF LABORATORY-ANIMALS TO POLYCHLORINATED DIBENZODIOXINS AND POLYCHLORINATED DIBENZOFURANS FROM COMMERCIAL RODENT CHOW

Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDDs/PCDFs) are ubiquitous low level environmental contaminants. Present finding of PC DDs and PCDFs in the human food supply suggested that laboratory anima ls maintained under controlled conditions may also receive unwanted ex posure to these compounds from food. In this study, a commercial roden t 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) w et 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 g reatest 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/k g/day for mice. It is therefore important to consider the potential fo r 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 dev elopmental/reproductive toxicity are being investigated at very low ex posures to this class of compounds.