DDE mercury, and selenium in Biota, sediments, and water of the Rio Grande-Rio Bravo Basin, 1965-1995.

An assessment of contaminant stressors on biota of the Rio Grande was conducted to identify relevant contaminant issues, assess exposure and ecological effects, identify data gaps, and determine potential risks. Most contaminant data were from studies conducted during 1965-1995 in the Lower Rio Grande, on the Texas side of the river, within a 100-km boundary from Falcon Dam to the mouth. Contaminants most frequently reported were organochlorine compounds (OCs) and trace elements. The number of records for OCs and trace elements was at least twofold greater for fish than for birds, mammals, or reptiles. Of the OCs, p,p'-DDE was the most commonly reported. Among the trace elements, Hg was one of the most frequently reported; however, Se, As, Pb, Cu, and Zn were also common. The highest concentrations of OCs and trace elements were reported predominantly from Lower Rio Grande Valley locations, with approximately 68% of the highest values detected from Falcon Dam to the mouth of the river. Twenty-six (20%) of the locations with maximum concentrations corresponded to portions of Llano Grande Lake and the Arroyo Colorado. Recent analyses of birds and fish indicate that levels of DDE are currently much lower than in the 1970s or 1980s in Rio Grande wildlife. This apparent decline does not apply to Hg and Se levels in birds and fish, which have remained more or less constant, but may have increased over the years in some locations. Hg was of particular concern because of high levels found recently in addled eggs of aplomado falcons and in their potential prey. Hg was elevated in fish from the Big Bend area. Also, Se in fish sampled in 1993 and 1994 was near or above the threshold for potential effects in fish-eating wildlife. Future investigations should evaluate the potential impacts of Hg and Se on aquatic and terrestrial species from selected sites of concern.

Chlorinated hydrocarbons and biomarkers of exposure in wading birds and fish of the lower Rio Grande Valley, Texas.

During 1997 we evaluated reproductive success in colonial water birds nesting in the Lower Rio Grande Valley (LRGV), Texas, and correlated success with concentrations of contaminants in eggs. We also measured steroid hormones and gonadosomatic index (GSI) as biomarkers of endocrine effects in common carp (Cyprinus carpio). Nest and fledging success of green herons (Butorides virescens) and great egrets (Ardea alba) were similar to those found in other parts of North America; however, nesting success of black-crowned night-herons (Nycticorax nycticorax) was lower, very likely due to flooding of the nesting area. Except for DDE and toxaphene, all chlorinated pesticides in bird eggs were low and not of concern for negative effects on any of the three species. DDE was highest in green heron eggs and seemed to increase along a geographic gradient from west to east, with eggs from Falcon Reservoir containing low concentrations, and those at Los Indios containing the highest concentrations (approx. 11,000 ng/g WW), near or above the threshold for reproductive impairment. DDE levels in great egrets and black-crowned night-herons were below those that are associated with reproductive impairment. Mean DDE levels in carp at the JAS Farms site were above the threshold level suggested for predator protection. Toxaphene was detected in about 20% of the samples with high levels observed in green heron eggs from Los Indios (mean = 4,402 ng/g WW). These are the highest toxaphene levels reported in bird eggs in the LRGV. Toxaphene levels in fish ranged between 90 and 312 ng/g WW. In general, PCBs in bird eggs and fish tissue were low and at levels not of concern for reproductive effects. The greatest concentrations of testosterone and 11-ketotestosterone were detected in fish from the JAS Farms site, which also had the greatest concentrations of DDE. Increased androgen production and gonad development in fish at this site, relative to Pharr, could be possibly associated with endocrine disrupting effects of p,p'-DDE. DDE, toxaphene, PCBs, and hormones were highest in birds and fish from the eastern edge of the study area.