PH11 Bioaccumulation and Biotransformation of POPs
Exhibit Hall
8:00 AM - Thursday, 13 November 2003
(PH120) Pesticide accumulation in soil-water microcosms evaluated with a negative exponential model.
Coveney, M1, Lowe, E1, Sepúlveda, M2, Marzolf, E1, Mace, L1, Bowen, P1, Conrow, R1, Gross, T2, 1 St. Johns River Water Management District, Palatka, FL, USA2 U.S.G.S. Florida Integrated Science Center, Gainesville, FL, USA
ABSTRACT- More than 670 piscivorous birds died on flooded farm fields adjacent to Lake Apopka, FL in 1998-99. Because organochlorine pesticide (OCP) toxicosis was a suspected cause, 700-L soil-water microcosms were established to measure accumulation of OCPs in mosquitofish (Gambusia holbrooki) and crayfish (Orconectes immunis) exposed to the highly organic soils (median TOC 39%). Ten different test soils and 3 blank soils were used in triplicate to present a range of TOC (2 – 48%) and OCPs. OCPs in organisms were measured at intervals up to 16 wk. As an alternative to selecting one time to represent OCP accumulation, we fit a negative exponential model to the time-course data. This approach is objective, uses all the data in parameter estimation, and provides both the equilibrium (accumulation) value and kinetic information (first-order rate constant k). Curve fitting was useful to analyze a subset of treatments where most values exceeded detection limits. In other cases, k values from successful model fits guided our choice of exposure times to average for accumulation. k represents the specific elimination rate, and our sample period (2 – 16 wk) could resolve k values in the range -0.01 to -0.1 d-1. In Gambusia, elimination rate for toxaphene exceeded that of DDE, and both k values varied little across the range of soil TOC and OCP levels (toxaphene -0.055 d-1 ± 0.008; DDE -0.027 d-1 ± 0.004; mean ± SD). Elimination rates for other analytes showed more variability.
Key words: organochlorine pesticide, lake apopka, accumulation rate, time-course