Use of Degradation Rates of DDT and Lindane Isomers for Determining the Timing of Release to Sediments of Greens Bayou: Houston Ship Channel, Texas

Abstract

Sediments collected from Greens Bayou, a tributary to the Houston Ship Channel, in Houston, Texas, were collected and analyzed in a laboratory study designed to determine anaerobic degradation rates for DDT and lindane isomers in the Bayou. This site-specific degradation data was then used to estimate the time period during which DDT and lindane were released to Greens Bayou from a former chemical manufacturing plant site. Initial DDT concentrations of 100–1,000 μg/kg degraded to nondetectable levels within 8 days. Initial lindane concentrations of 250–2,500 μg/kg degraded preferentially according to isomeric structure: Alpha BHC (α-BHC), Beta BHC (β-BHC), and Gamma BHC (γ-BHC) had half-lives ranging from 1–5 days. Delta BHC (Δ-BHC) had half-lives ranging from 22–30 days. It was concluded that any discharges of DDT or lindane prior to 1971 into Greens Bayou from the chemical manufacturing plant at sediment concentrations less than 2,500 μg/kg would have degraded long prior to 1983. Persistent DDT or lindane detected at significant levels in Greens Bayou sediments today could not have been deposited in sediments until many years after 1983 and must have been deposited at concentrations or loading levels high enough to have a toxic effect on the sediment's anaerobic degradation capacity.