CARRY-OVER OF TOXICOLOGICALLY RELEVANT PO LYCHLORINATED DIBENZODIOXINAND FURAN CONGENERS INTO THE MILK OF LACTATING COWS

Approaches for determining the carry-over rate of polychlorinated dibe nzodioxin- and furan congeners are, in a simplified manner, possible b y comparing coherent data as regards feedingstuff and milk fat by assu ming a typical feed ration. Since, in this case, the rather variable b ioavailability of the toxic equivalents ingested enters unrecognised t he calculation and is mostly much worse compared with the measuring va lue after solvent extraction of the feedingstuffs for several hours th is method can only be approximately used for estimating the situation. Controlled experiments with individual lactating cows, kept under env ironmental conditions, are with high frequency considerably burdened w ith methodical error sources such as assumption of the balance of upta ke and excretion because of the lack of a defined supplementation begi nning and by extensive analyses of the matrices involved (feedingstuff and milk). For this reason carry-over trials on the relevant congener s of the PCDD/F-expositions originating from the environment were perf ormed. Using specially labelled congeners (13 C6, 37 Cl4) they show ex perimentally, besides the individual carry-over rate, also the kinetic s of depot buildup and excrection with the milk fat as a function of s upplementation time. With the pattern,, one cow = one congener'' a sub stance-optimized GC/MS measurement is feasible, which procures the ana lytics a great deal of reserves as to sensitivity and operation time. The individual carry-over rates of the congeners (cows orally suppleme nted on wheat starch: 50 and 100 ng/day) were < 1% for 2,3,7,8-TCDF, 3 6% for 2,3,7,8-TCDD, 15% for 1,2,3,7,8-PeCDD, 27% for 2,3,4,7,8-PeCDF, 10% for 1,2,3,4,7,8-Hx-CDF and 8% for 1,2,3,4,7,8-HxCDD. Hence, altog ether roughly 20% (19.2%) of the toxicologically relevant congeners pa sses into the milk fat. On the basis of this value it can formally be concluded, that for observing the background value of approximately 0. 6 pg i TE/g milk fat feedingstuffs must not be contaminated with quant ities exceeding 0.15 ng i TE/kg dry matter. Corresponding calculations can be done for the indiviudal congeners.