Decreasing half-life of dieldrin in egg yolk following a single oral administration of aldrin to laying hens

Laying hens were treated orally with a single dose of aldrin (AD) 1 mg/kg body weight. Concentrations (microgram/g) of AD or its epoxide (= dieldrin, DD) in the yolk of eggs laid for 21 days after AD treatment were determined by normal-phase high-performance liquid chromatography. The limits of determination were 0.02 microgram/g for AD and 0.03 microgram/g for DD, respectively. After AD treatment, although the low levels of AD (mean 0.02-0.03 microgram/g) were observed only during a three-day period (from 4th to 6th days), DD (mean 0.15 microgram/g) was found already on the 2nd day, indicating that the epoxidation of AD to DD in the hen's body is rapid. The highest level of DD (mean 0.40 microgram/g) was detected on the 6th day, and then DD levels decreased slowly and were detected up to the 21st day. In this decreasing phase, the half-life of DD in the yolk was estimated to be 25.6 days with a 95% confidence interval from 22.7 to 29.4 days.