USGS1984
Ninety-eight samples of 16 species of animals were collected at Lake Providence, 88 samples of 15 species at Lake Bruin, and 21 samples of 5 species at Lake St. John, Louisiana, between 15 July and 25 September 1980. Residues of 13 organochlorine compounds were identified in these samples. Substantial concentrations of many of these compounds throughout the food webs of all three lakes showed that the lakes act as sumps, accumulating residues from nearby agricultural land. DDT and its metabolites (DDE, TDE, and DDMU), toxaphene, and polychlorobiphenyls (PCBs) were the principal Organochlorine residues detected. With few exceptions, biomagnification of the principal residues was clearly illustrated. Tertiary consumers such as green-backed heron ( Butorides striatus ), snakes, spotted gar ( Lepisosteus oculatus ), and largemouth bass ( Micropterus salmoides ) contained the highest residues. Bluegill ( Lepomis macrochims ), blacktail shiner ( Notopis venustus ), yellow-crowned night-heron ( Nycticorax violaceus ), and other secondary consumers contained lower levels of residues. Primary consumers, crayfish ( Orconectes lancifer ) and threadfin shad ( Dorosoma petenense ), contained relatively low residue levels of most of the compounds. Frogs contained lower residue levels than expected based on their position in the food web. It is suggested that residue levels in immature green-backed herons and one or more of the longer-lived predators such as snakes, gars, or largemouth bass could be monitored to evaluate levels of Organochlorine chemical contaminants in aquatic habitats.