Dynamics of Dieldrin in Soil, Earthworms, and Song Thrushes

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Abstract
An experiment to study the passage of dieldrin from soil to earthworms to song thrushes (Turdus ericetorum) is reported. In contrast to some food chain studies there was a decrease in ppm at each step of the chain. A content of 25 ppm in the soil resulted in a range of 18.4 to 24.9 ppm in the earthworms after 20 days exposure. After 6 weeks of diets ranging from 0.32 to 5.69 ppm dieldrin, thrushes showed total body residues of 0.09 to 4.03 ppm. (All results expressed in terms of wet weight.) The pharmacodynamics of dieldrin was studied individually in 5 song thrushes. The average breakdown and accumulation of dieldrin per day increased with the dose rate as did the elimination up to an intake of 91 [mu]g/day after which it stabilized at 18-26 [mu]g/day. At the highest dose rate (381 [mu]g/day), 8.5% of the dieldrin consumed was accumulated, 84.2% was metabolized, and 7.2% was excreted as dieldrin. The bird at this dose rate died in 8 days. There appeared to be a loss of storage and organ fat, probably induced by the dieldrin, prior to death. The resultant reduction in liver size and increase in circulating dieldrin caused an increase in the liver and brain content from a calculated expectation of 7.77 and 3.12 ppm in a live bird fed at a dose rate of 381 jug/day to 17.94 and 16.88 ppm respectively at death. The bird fed 174 [mu]g/day and carrying 2.73 ppm in the liver and 1.05 ppm in the brain was in a more hazardous position than hitherto suspected with these levels as it bore a total body burden which could be lethal if all the fat were metabolized.