We collected, examined, and analyzed 368 fish of seven species from 10 sites in the Rio Grande Basin (RGB) during late 1997 and early 1998. Four sites were National Contaminant Biomonitoring Program (NCBP) stations where organochlorine and elemental contaminants in fish had been monitored from 1969 through 1986. The other six were USGS-National Stream Quality Accounting Network (NASQAN) stations where water quality is monitored. The objectives were to document temporal and geographic trends in the concentrations of accumulative organic and inorganic contaminants in RGB fish and the effects of contaminants on the fish; to continue testing the feasibility of incorporating biomarkers (that is, biochemical, histopathological, and other biological indicators of contaminant exposure or effects) into a monitoring program for large U.S. rivers; and to evaluate the compatibility of monitoring methods based on the analysis of fish with those used to monitor water by NASQAN. Common carp (Cyprinus carpio; carp) and black basses (Micropterus sp.; bass) were the targeted species; together, they represented 77% of the fish collected. Each fish was examined in the field for externally and internally visible gross lesions, selected organs were weighed to compute various ponderal and organosomatic indices, and samples of tissues and fluids were obtained and preserved for analysis of fish health and reproductive biomarkers. Composite samples of whole fish from each station were grouped by species and gender and analyzed by instrumental methods for persistent organic and inorganic contaminants and for dioxin-like activity (TCDD-EQ) using H4IIE rat hepatoma cell bioassay.
Overall, fish from stations in the lower RGB contained greater concentrations of some contaminants and appeared to be less healthy than those from sites in the central and upper parts of the basin, as indicated by general gradient of pesticide concentrations and biomarker responses from upstream to downstream. In the upper RGB, a minimal number of altered biomarkers and few or no elevated contaminant concentrations were noted. The exception was elevated concentrations [up to 0.46 ug/g wet-weight (ww)] of total mercury (Hg) in predatory species from Station 63 (Rio Grande at Elephant Butte Reservior, NM), a condition noted in the past.
Additional publication details
USGS Numbered Series
Biomonitoring of Environmental Status and Trends (BEST) Program: Environmental Contaminants and Their Effects on Fish in the Rio Grande Basin