Screening for environmental contaminants and endocrine disruption in wildlife from the Lower Rio Grande Valley, Texas: an ecological and biomarker approach

Abstract

The Lower Rio Grande Valley (LRGV) of Texas is a ographics. unique area supporting as many as 700 vertebrate species, 86 of which are endangered. Wildlife species in the LRGV use small oxbow lakes and extended lengths of isolated river channels (bancos and resacas) or artificial reservoirs (settling basins) for aquatic habitat. Many of these water bodies receive pesticide drift, urban runoff, and industrial contaminants. Potentially endocrine-disrupting contaminants, such as phthalate esters and chlorinated pesticides, have been identified in water, sediment, and fish at these sites. The main objectives of this study were to determine the importance of the three aquatic site types to LRGV birds, and to determine if contaminants in organisms using these sites occurred at levels that had the potential to cause reproductive and endocrine-disrupting effects. Avian use of banjos, resacas, and settling basins was monitored during the spring and summer of 1997. Density of birds was greatest at bancos, followed by resacas, and settling basins. Reproductive success of green herons (Butorides virescens) was followed at two sites within the LRGV, and at a reference site west of the LRGV. Eggs were collected and analyzed for chlorinated contaminants. High levels of toxaphene were found. At one site, p,p'-DDE concentrations (range 6925-19377 ng/g) were above levels known to cause reproductive impairment in green herons. Reproductive success was normal at all sites, but sample sizes may have been too small to determine if problems existed. Male common carp (Cyprinus carpio) plasma was analyzed for biomarkers of endocrine disruption, and carcasses were analyzed for chlorinated contaminants. Contaminant values in carp were low. At one site male carp displayed reduced steroid hormone levels and depressed gonad size, potentially indicative of reproductive endocrine system impairment. No conclusion could be made about contaminant risks posed to wildlife by each site type because of small sample sizes. However, contaminants did follow a geographical distribution, with the highest concentrations of xenobiotics occurring at the eastern end of the study area. Wildlife using aquatic habitats in this area of the LRGV may be at risk for exposure to contaminants that have reproductive and/or endocrine-disrupting effects.