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TA2 Wildlife Toxicology
(172) Pesticide toxicosis in birds at Lake Apopka, Florida: remaining uncertainties.
Lowe, E1, Conrow, R1, Schell, J2, Coveney, M1, Marzolf, E1, Richter, S1, Gross, T3, Sepulveda, M3, 1 St. Johns River Water Management District, Palatka, FL, USA2 BBL Sciences, Tallahassee, FL, USA3 USGS, Gainesville, FL, USA
ABSTRACT- More than 670 birds, primarily piscivorous species, died on flooded farm fields adjacent to Lake Apopka, Florida in 1998-99. Tissue levels of organochlorine pesticides (OCPs), especially toxaphene, indicate that many of the birds died from pesticide toxicosis. A risk assessment prior to flooding the fields did not indicate a significant risk of acute toxicity from soil levels of OCPs. Forensic analyses based on additional data on concentrations of OCPs in soils and fish, on biota-sediment accumulation factors, and tissue levels of OCPs in dead birds also found no clear linkage between soil OCPs and acute toxicosis. Bioaccumulation studies were initiated to reduce uncertainties in accumulation factors from soils to fish and from fish to birds. Microcosm evaluations of accumulation factors for fish and crayfish did not find accumulation factors high enough to explain or predict acute mortality in piscivorous birds. Tissue concentrations of laboratory-raised great egrets fed contaminated fish (40% of diet) for 11 weeks at an average rate of approximately 300 ug toxaphene/kg/day were well below toxic levels and also were well below levels associated with the mortality event. Further evaluation of accumulation factors for fish and invertebrates is underway in quarter-acre mesocosms. A second bird feeding study also is underway to evaluate the potential for transfer of OCPs from adipose to other tissues during food deprivation.
Key words: organochlorine pesticides, lake apopka, tissue pesticide concentrations, birds
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