Biological Effects of Selenium and other Contaminants Associated with Irrigation Drainage in the Salton Sea Area, California, 1992-1994.
The National Irrigation Water Quality Program (NIWQP) investigated contaminants associated with drainwater in the Salton Sea area from 1986-1990 and concluded that there was a risk to trust resources due to elevated levels of selenium, organochlorine pesticides, and possibly boron in the Salton Sea environment. The Salton Sea is a major inland nesting and wintering area with over 270 species of birds utilizing the Imperial valley as either permanent or seasonal habitat. It also supports four endangered species including the Yuma clapper rail, brown pelican, peregrine falcon, and the desert pupfish. This report describes the biological effects of environmental contaminants on several important fish and wildlife species.
Three studies were done:
1. Eggs were collected from nesting colonies of black-crowned night-herons, and great and snowy egrets to determine embryotoxicity of colonial waterbirds (fish eaters).
2. Black-necked stilt nests were monitored in May and June of 1993. The first egg laid was collected for contaminant analysis and nests were monitored at weekly intervals to determine the embryotoxicity and nesting proficiency of black-necked stilts.
3. Sailfin mollies were collected from 13 drains and samples were analyzed for metals and organochlorines to determine the contaminant body burdens of sailfin mollies which were used as a surrogate species for the endangered desert pupfish that inhabits agricultural drains.
Results and Discussion: A total of 35 great egret eggs, 24 snowy egret eggs, and 17 black-crowned nightheron eggs were collected. All the eggs were measured and the embryos removed and observed for gross deformities. The night-heron egg shells were 7-13 percent thinner than pre-DDT era night-heron eggs. Five embryos had some sign of deformity, but they did not have the deformities expected from selenium. The rate of embryo deformity observed in this study in great and snowy egret eggs was 29 percent. The selenium concentration was at a level of concern for toxicity in egrets and was in the range in which reproductive depression is expected. Nearly half of the egret eggs contained from 1.6 to 6 times the amount of DDE associated with reproductive effects in night-herons. Toxaphene (a persistent organochlorine pesticide), dieldrin and PCBs were also found at measurable, but non-hazardous quantifies. The levels of selenium in the black-necked stilt was at the Level of Concern for birds. Thirteen per cent of the black-necked stilts nests were affected by hatching failure which was a 4.5 percent reproductive depression when compared to stilts in selenium-normal environments. Since stilts are only a moderately sensitive species to selenium, it raises concerns about the potential for reproductive impairment in more sensitive species like ducks. The concentration of DDE in sailfin mollies was not hazardous to the fish themselves, but approached the threshold for protection of fish-eating birds. Their selenium concentrations were also at and in excess of the Level of Concern for dietary criteria, indicating that they present a risk to organisms that would consume them. Consequently, the federal and state endangered desert pupfish inhabiting agricultural drains are at risk of reproductive failure due to selenium concentration in the adult fishes sampled.
Conclusions: The amount of eggshell thinning observed in black-crowned night herons indicates that the species is likely to be experiencing reproductive depression related to egg failures. Resident species of birds in the Imperial valley are likely to experience reproductive impairment as a result of the DDE contamination. Reported declines in colonial nesting bird success at the Salton Sea is likely to be related to the high levels of multiple contaminants in these fish-eating birds. The reproductive depression in birds due to both selenium and DDE, hazards to the endangered pupfish, and levels of selenium in fish as a dietary food item have emerged as the most serious concerns for fish and wildlife resources in the Salton Sea area. Remediation efforts need to focus on reducing levels of selenium and DDE contamination of biota to below hazardous effects levels.
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