Persistence and Changes in Bioavailability of Dieldrin, DDE, and Heptachlor Epoxide in Earthworms Over 45 Years

Abstract

The finding of dieldrin (88ng/g), DDE (52ng/g), and heptachlor epoxide (19ng/g) in earthworms from experimental plots after a single moderate application (9kg/ha) 45years earlier attests to the remarkable persistence of these compounds in soil and their continued uptake by soil organisms. Half-lives (with 95% confidence intervals) in earthworms, estimated from exponential decay equations, were as follows: dieldrin 4.9 (4.3-5.7) years, DDE 5.3 (4.7-6.1) years, and heptachlor epoxide 4.3 (3.8-4.9) years. These half-lives were not significantly different from those estimated after 20years. Concentration factors (dry weight earthworm tissue/dry weight soil) were initially high and decreased mainly during the first 11years after application. By the end of the study, average concentration factors were 1.5 (dieldrin), 4.0 (DDE), and 1.8 (heptachlor epoxide), respectively.