Shrnutí

Popis

The aquatic habitats of the Tensas River Basin in northeastern Louisiana have been heavily impacted by sediment and agrichemical runoff due to intensive drainage, extensive clearing of bottomland hardwoods, and agricultural production. Previous contaminant surveys in the Tensas River Basin documented elevated levels of organochlorine pesticides, particularly DDT and toxaphene, in fishes and sediments. Those pesticides were used in soybean and cotton farming throughout the basin from the 1940s to the 1970s. DDT and toxaphene have been consistently present in fishes collected from mainstem and backwater areas, including the Tensas River National Wildlife Refuge NWR. In the present study, fish and sediment samples were collected throughout the Tensas River watershed from 1991 through 1993. Sediments and fishes were analyzed for organochlorine pesticides to determine the potential sources, distribution, and fate of those pesticides in the watershed, and their impacts on fish and wildlife resources and NWR lands. Those analyses were also used to determine the potential hazard to consumers of fishes caught on the NWR. Analytical results indicate that concentrations of DDT, its metabolites, and toxaphene in fish tissues particularly from the mainstem approach or exceed levels of concern for fish and wildlife, including consumption by humans. Elevated sediment and fish tissue contaminant concentrations occur mainly in the rivers headwaters, and are of significant concern. Elevated organochlorine pesticide concentrations in the upper basin are thought to result from past actions, such as the disposal of contaminated soils, improper disposal of used pesticide containers, and improper cropdusting base operations, as well as nonpoint agricultural sources. Continued efforts by State and Federal agencies, in cooperation with private landowners, will be required to remove and remediate point sources of pesticide contamination, and to address nonpoint source contaminant loading.