Reduced growth and survival of larval razorback sucker fed selenium-laden zooplankton

Four groups of larval razorback sucker, an endangered fish, were exposed to selenium-laden zooplankton and survival, growth, and whole-body residues were measured. Studies were conducted with 5, 10, 24, and 28-day-old larvae fed zooplankton collected from six sites adjacent to the Green River, Utah. Water where zooplankton were collected had selenium concentrations ranging from <0.4 to 78 microg/L, and concentrations in zooplankton ranged from 2.3 to 91 microg/g dry weight. Static renewal tests were conducted for 20 to 25 days using reference water with selenium concentrations of <1.1 microg/L. In all studies, 80-100% mortality occurred in 15-20 days. In the 28-day-old larvae, fish weight was significantly reduced 25% in larvae fed zooplankton containing 12 microg/g selenium. Whole-body concentrations of selenium ranged from 3.7 to 14.3 microg/g in fish fed zooplankton from the reference site (Sheppard Bottom pond 1) up to 94 microg/g in fish fed zooplankton from North Roadside Pond. Limited information prior to the studies suggested that the Sheppard pond 1 site was relatively clean and suitable as a reference treatment; however, the nearly complete mortality of larvae and elevated concentrations of selenium in larvae and selenium and other elements in zooplankton indicated that this site was contaminated with selenium and other elements. Selenium concentrations in whole-body larvae and in zooplankton from all sites were close to or greater than toxic thresholds where adverse effects occur in fish. Delayed mortality occurred in larvae fed the two highest selenium concentrations in zooplankton and was thought due to an interaction with other elements.     

Commentary: selenium study on endangered razorback sucker is flawed

The razorback sucker (Xyrauchen texanus) is listed as federally endangered throughout its range. A massive recovery effort by the Recovery Implementation Program for Endangered Fish Species in the Upper Colorado River Basin has focused its efforts in the upper Colorado River. The upper Colorado River basin also has two locations that have been identified by the National Irrigation Water Quality Program as having substantial selenium contamination. Selenium is toxic to fishes, affecting reproductive success. Thus, there is concern about potential effects of selenium on the endangered razorback sucker. Two sets of studies have investigated the effects of selenium on razorback suckers, but study results are conflicting. This commentary evaluates studies that claim selenium is not a problem for razorback sucker. We find that study bias was so pervasive that purported conclusions were unwarranted. Contaminated control water, older life stages of fish tested, lack of methodology for analysis of selenium in water, diet, or fish, use of rotifer food, low feeding rates, low growth rates of fish, and improper storage of site waters resulted in an apparent erroneous linkage of high selenium in whole-body residues with no adverse effects.     

Selenium impacts on razorback sucker, Colorado River, Colorado II. Eggs

Effects on hatching and development of fertilized eggs in adult razorback sucker (Xyrauchen texanus) exposed to selenium in flooded bottomland sites near Grand Junction, Colorado, were determined. After 9 months exposure, fish were collected and induced to spawn and eggs collected for inorganic element analyses. A 9-day egg study was conducted with five spawns from Horsethief ponds, six spawns from Adobe Creek channel, and four spawns from North Pond using a reference water and site waters. Selenium concentrations in eggs were 6.5 microg/g from Horsethief, 46 microg/g from Adobe Creek, 38 microg/g from North Pond, and 6.0 microg/g from brood stock. Eggs from young adults had a smaller diameter and higher moisture content than brood stock. There were no differences among the four sources in viability, survival, hatch, hatchability, or mortality of deformed embryos or larvae. Adobe Creek larvae had more deformed embryos in eggs held in site water than held in reference water. There were significant negative correlations between selenium concentrations in adult muscle plugs and percent hatch, egg diameter, and deformities in embryos. Results from this study suggest that selenium contamination in parts of the upper basin of the Colorado River should be a major concern to recovery efforts for endangered fish.     

Selenium impacts on razorback sucker, Colorado River, Colorado I. Adults

Adult razorback sucker (Xyrauchen texanus) were exposed to various selenium concentrations in ponds and isolated river channels of the Colorado River near Grand Junction, CO, to determine effects on their growth and residue accumulation over an 11-month period. Adults at Horsethief ponds were fed a commercial diet, whereas fish at Adobe Creek channel and North Pond foraged on natural food items. Selenium concentrations at Horsethief were 2.2 microg/L in water, 0.1-1.4 microg/g in sediment, and 2.3-3.1 microg/g in food organisms (1.1 microg/g in commercial fish food), at Adobe Creek were 3.8 microg/L in water, 0.5-2.1 microg/g in sediment, and 4-56 microg/g in food organisms, and at North Pond were 9.5 microg/L in water, 7-55 microg/g in sediment, and 20-81 microg/g in food organisms. The selenium concentrations in muscle plugs from adults at Adobe Creek (11.7 microg/g, SD = 0.4, n = 6) and North Pond (16.6 microg/g, SD = 1.0, n = 6) were greater than at Horsethief (4.5 microg/g, SD = 0.2, n = 6). During a depuration period adults from Adobe Creek and North Pond lost 1-2% of their selenium burden in 32 days and 14-19% in 66 days. Selenium accumulated in razorback sucker above toxic thresholds reported in other studies, yet those residues were less than those reported in muscle plugs of 40% of wild razorback sucker caught in the Green River, Utah.     

Selenium impacts on razorback sucker, Colorado: Colorado River III. Larvae

Razorback sucker (Xyrauchen texanus) larvae from adults exposed to selenium at three sites near Grand Junction, Colorado, for 9 months were used in a 30-day waterborne and dietary selenium study. Selenium concentrations in water averaged <1.6 microg/L from 24-Road, 0.9 microg/L from Horsethief, 5.5 microg/L from Adobe Creek, and 10.7 microg/L from the North Pond. Selenium in dietary items averaged 2.7 microg/g in brine shrimp, 5.6 microg/g in zooplankton from Horsethief east wetland, 20 microg/g in zooplankton from Adobe Creek, and 39 microg/g in zooplankton from North Pond. The lowest survival occurred in larvae fed zooplankton rather than brine shrimp. Survival of larvae at Adobe Creek and North Pond was lower in site water than in reference water. Survival of brood stock larvae was higher than Horsethief larvae even though they received the same water and dietary treatments. Arsenic concentrations in brine shrimp may have resulted in an antagonistic interaction with selenium and reduced adverse effects in larvae. Deformities in larvae from North Pond were similar to those reported for selenium-induced teratogenic deformities in other fish species. Selenium concentrations of 4.6 microg/g in food resulted in rapid mortality of larvae from Horsethief, Adobe Creek, and North Pond, and suggested that selenium toxicity in the Colorado River could limit recovery of this endangered fish.     

Selenium in eggs and milt of razorback sucker (Xyrauchen texanus) in the middle Green River,Utah

Eggs from three female and milt from five male endangered razorback suckers (Xyrauchen texanus) were collected from the Razorback Bar (about 20 km upstream of Ashley Creek) in the Green River of northeastern Utah. Eggs, but not milt, had concentrations of selenium that were above the range of selenium concentrations in control fish from laboratory studies or reference fish from field studies. The concentrations, however, were below those reported in selenium-exposed fish that had reproductive problems in laboratory studies or field investigations. Tests with three streamside spawned pairs of razorback suckers, which were sampled for eggs and milt in this study, resulted in no hatching of fertilized eggs. Concentrations of selenium in eggs and milt were significantly correlated with selenium concentrations in muscle plugs taken from the same fish, but egg and milt concentrations were not significantly different from muscle plugs. Selenium concentrations in eggs of razorback suckers in the Green River may be sufficiently elevated to cause reproductive problems that are contributing to the decline of this species in the upper Colorado River basin.     

Assessment of Exposure of Larval Razorback Sucker to Selenium in Natural Waters

This investigation evaluated effects of exposure of larval razorback sucker to waterborne and dietary selenium and other contaminants that occur in nursery habitats. Site waters were collected from three localities on the Colorado River near Grand Junction, CO; a total of five test waters (including control) were studied. Razorback sucker larvae were exposed to site-water contaminants via waterborne and dietary exposure using a laboratory food chain (algae, rotifer, razorback sucker). Fish were exposed for 28 days to site waters and food organisms cultured in site waters. Survival data were analyzed by inspection. Growth data were analyzed using analysis of variance to describe the response of fish in each site water and to describe the relative contribution of waterborne versus dietary exposure to constituents in site waters. Selenium concentrations in test-water treatments ranged from < 1 to 20.3 μg/L in water, < 0.702 to 21.8 μg/g in diet, and 2.34 to 42.0 μg/g in fish. Negative effects from dietary exposure to site-water constituents were detected, but the data suggest that they were caused by cocontaminants in the diet, not selenium exposure. Lack of detection of adverse effects from exposure does not imply that razorback sucker populations are not affected by increased environmental selenium concentrations. There are a variety of factors not included in this investigation that may influence sensitivity of razorback sucker populations to selenium. Received: 25 February 2001/Accepted: 18 June 2001     

Selenium concentrations in the razorback sucker (Xyrauchen texanus): Substitution of non-lethal muscle plugs for muscle tissue in contaminant assessment

A single muscle plug was collected from each of 25 live razorback suckers inhabiting the Colorado River basin and analyzed for selenium by instrumental neutron activation. Eight fish from Ashley Creek and three from Razorback Bar exhibited selenium concentrations exceeding 8 g/g, a level associated with reproductive failure in fish. Concentrations of selenium in eggs and milt were significantly correlated with selenium concentrations in muscle plugs and together indicate a possible explanation for the decline of this species in the Colorado River basin. Muscle plugs (<50mg) and muscle tissue (20 g) were collected from dorsal, anterior, and posterior areas of common carp, flannelmouth sucker, and an archived razorback sucker and analyzed for selenium. Concentrations of selenium in muscle plugs were significantly correlated with selenium concentrations in muscle tissue from the same location and fish (r=0.97). Coefficients of variation for selenium concentrations in each fish were <6.5% for muscle tissue, but ranged from 1.5 to 32.4% for muscle plugs. Increased variation in muscle plugs was attributed to lower selenium concentrations found in the anterior muscle plugs of flannelmouth suckers. Mean selenium concentrations in muscle plugs and tissue from dorsal and posterior areas and muscle tissue from the anterior area were not significantly different. The non-lethal collection of a muscle plug from dorsal and posterior areas of the razorback sucker and other fish species may provide an accurate assessment of selenium concentrations that exist in adjacent muscle tissue.     

Toxicity of inorganic contaminants, individually and in environmental mixtures, to three endangered fishes (Colorado squawfish, bonytail, and razorback sucker)

Two life stages of three federally-listed endangered fishes, Colorado squawfish (Ptychocheilus lucius), bonytail (Gila elegans), and razorback sucker (Xyrauchen texanus) were exposed to copper, selenate, selenite, and zinc individually, and to mixtures of nine inorganics in a reconstituted water that simulated the water quality of the middle Green River, Utah. The mixtures simulated environmental ratios of arsenate, boron, copper, molybdenum, selenate, selenite, uranium, vanadium, and zinc in two tributaries, Ashley Creek and Stewart Lake outlet, of the middle Green River. The rank order of toxicity of the individual inorganics, from most to least toxic, was: copper > zinc > selenite > selenate. Colorado squawfish larvae were more sensitive to all four inorganics and the two mixtures than the juveniles, whereas there was no consistent response between the two life stages for the other two species. There was no consistent difference in sensitivity to the inorganics among the three endangered fishes. Both mixtures exhibited either additive or greater than additive toxicity to these fishes. The primary toxic components in the mixtures, based on toxic units, were copper and zinc. Acute toxicity values were compared to measured environmental concentrations in the two tributaries to derive margins of uncertainty. Margins of uncertainty were low for both mixtures (9–22 for the Stewart Lake outlet mixture, and 12–32 for the Ashley Creek mixture), indicating that mixtures of inorganics derived from irrigation activities may pose a hazard to endangered fishes in the Green River.     

Selenium Concentrations in the Colorado Pikeminnow (Ptychocheilus lucius): Relationship with Flows in the Upper Colorado River

A Department of the Interior (DOI) irrigation drainwater study of the Uncompahgre Project area and the Grand Valley in western Colorado revealed high selenium concentrations in water, sediment, and biota samples. The lower Gunnison River and the Colorado River in the study area are designated critical habitat for the endangered Colorado pikeminnow (Ptychocheilus lucius) and razorback sucker (Xyrauchen texanus). Because of the endangered status of these fish, sacrificing individuals for tissue residue analysis has been avoided; consequently, little information existed regarding selenium tissue residues. In 1994, muscle plugs were collected from a total of 39 Colorado pikeminnow captured at various Colorado River sites in the Grand Valley for selenium residue analysis. The muscle plugs collected from 16 Colorado pikeminnow captured at Walter Walker State Wildlife Area (WWSWA) contained a mean selenium concentration of 17 μg/g dry weight, which was over twice the recommended toxic threshold guideline concentration of 8 μg/g dry weight in muscle tissue for freshwater fish. Because of elevated selenium concentrations in muscle plugs in 1994, a total of 52 muscle plugs were taken during 1995 from Colorado pikeminnow staging at WWSWA. Eleven of these plugs were from fish previously sampled in 1994. Selenium concentrations in 9 of the 11 recaptured fish were significantly lower in 1995 than in 1994. Reduced selenium in fish may in part be attributed to higher instream flows in 1995 and lower water selenium concentrations in the Colorado River in the Grand Valley. In 1996, muscle plugs were taken from 35 Colorado squawfish captured at WWSWA, and no difference in mean selenium concentrations were detected from those sampled in 1995. Colorado River flows during 1996 were intermediate to those measured in 1994 and 1995. Received: 21 June 1999/Accepted: 10 November 1999     

Hazard Evaluation of Inorganics, Singly and in Mixtures, to Flannelmouth SuckerCatostomus latipinnisin the San Juan River, New Mexico

Larval flannelmouth sucker (Catostomus latipinnis) were exposed to arsenate, boron, copper, molybdenum, selenate, selenite, uranium, vanadium, and zinc singly, and to five mixtures of five to nine inorganics. The exposures were conducted in reconstituted water representative of the San Juan River near Shiprock, New Mexico. The mixtures simulated environmental ratios reported for sites along the San Juan River (San Juan River backwater, Fruitland marsh, Hogback East Drain, Mancos River, and McElmo Creek). The rank order of the individual inorganics, from most to least toxic, was: copper > zinc > vanadium > selenite > selenate > arsenate > uranium > boron > molybdenum. All five mixtures exhibited additive toxicity to flannelmouth sucker. In a limited number of tests, 44-day-old and 13-day-old larvae exhibited no difference in sensitivity to three mixtures. Copper was the major toxic component in four mixtures (San Juan backwater, Hogback East Drain, Mancos River, and McElmo Creek), whereas zinc was the major toxic component in the Fruitland marsh mixture, which did not contain copper. The Hogback East Drain was the most toxic mixture tested. Comparison of 96-h LC₅₀values with reported environmental water concentrations from the San Juan River revealed low hazard ratios for arsenic, boron, molybdenum, selenate, selenite, uranium, and vanadium, moderate hazard ratios for zinc and the Fruitland marsh mixture, and high hazard ratios for copper at three sites and four environmental mixtures representing a San Juan backwater, Hogback East Drain, Mancos River, and McElmo Creek. The high hazard ratios suggest that inorganic contaminants could adversely affect larval flannelmouth sucker in the San Juan River at four sites receiving elevated inorganics.     

Concentrations of selenium in biota,sediments, and water at Cibola National Wildlife Refuge

Selenium contamination was studied at Cibola National Wildlife Refuge (Cibola NWR) in the lower Colorado River Valley, California and Arizona, USA. The objective was to determine whether local irrigation practices resulted in exposure of fish to toxic concentrations of selenium.Water, sediment, fish, and crayfish were collected from sites that received irrigation return flows and sites that did not. At sites receiving irrigation return flows, selenium was below concentrations that are toxic to fish. However, at two sites receiving water directly from the Colorado River, selenium was at the toxicity threshold for fish. Selenium concentrations were also elevated in crayfish from the sites where concentrations in sunfish were at the toxicity threshold.Further increases in selenium concentrations at sites that are already at the toxicity threshold could impair reproduction of sensitive species. Site-specific limnological conditions may play a role in accumulation of selenium to toxic concentrations, but major sources of selenium seem to be upstream in the Colorado River basin rather than from local agricultural practices. Selenium input to the Colorado River from irrigation projects, coal-fired power plants, and natural sources should be reduced to minimize the potential for selenium-induced toxicity in fish in backwaters along the lower Colorado River.     

Chronic Toxicity of Un-ionized Ammonia to Early Life-Stages of Endangered Colorado Pikeminnow (Ptychocheilus lucius) and Razorback Sucker (Xyrauchen texanus) Compared to the Surrogate Fathead Minnow (Pimephales promelas)

Ammonia-contaminated groundwater enters the Upper Colorado River from beneath the abandoned Moab Uranium Mill Tailings Pile near Moab, Utah. This reach of the Upper Colorado River was designated as critical habitat for four endangered fish species because it is one of the few existing areas with known spawning and rearing habitats. Un-ionized ammonia (NH₃) concentrations frequently exceed 1.00 mg/L in backwaters adjacent to the tailings pile, which exceeds the Utah 30-d average chronic water quality criterion for un-ionized ammonia (0.07 mg/L NH₃; temperature 20°C; pH 8.2) by a factor of more than 10. However, there is little published information regarding the sensitivity of endangered fishes to ammonia. We conducted 28-d static renewal studies with post-swim-up larvae to determine the relative sensitivity of Colorado pikeminnow (Ptychocheilus lucius), razorback sucker (Xyrauchen texanus), and the standard surrogate fathead minnow (Pimephales promelas) to NH₃. Chronic values (ChVs) for mortality and growth were determined as the geometric mean of the no observed effect concentration and the lowest observed effect concentration based on analysis of variance. The ChVs for growth of fathead minnow, Colorado pikeminnow, and razorback sucker were 0.43, 0.40, and 0.67 mg/L NH₃, respectively. The ChVs for mortality of fathead minnow, Colorado pikeminnow, and razorback sucker were 0.43, 0.70, and 0.67 mg/L NH₃, respectively. Therefore, the ChVs for mortality and growth were similar for fathead minnow and razorback sucker; however, the ChV for growth was lower than the ChV for mortality for Colorado pikeminnow. Maximum likelihood regression was used to calculate 28-d lethal concentrations (LCx) for each species. The 28-d LC50, LC20, and LC1 values for fathead minnow were 0.69, 0.42, and 0.13 mg/L NH₃, respectively. The 28-d LC50, LC20, and LC1 values for Colorado pikeminnow were 0.76, 0.61, and 0.38 mg/L NH₃, respectively. The 28-d LC50, LC20, and LC1 values for razorback sucker were 0.54, 0.38, and 0.25 mg/L NH₃, respectively. The fathead minnow, Colorado pikeminnow, and razorback sucker are relatively similar in sensitivity and rank at the 35th, 49th, and 31st percentiles, respectively, of the theoretical chronic fish sensitivity distributions for NH₃. The existing water quality criteria for NH₃, if met by remediation activities at the Moab site, would be protective of these endangered fishes even if fish sensitivity is based on the conservative LC1 value.     

Assessment of tolerant sunfish populations (Lepomis sp.) inhabiting selenium-laden coal ash effluents. 1. Hematological and population level assessment

Sunfish were collected from coal ash effluent-receiving streams and Ohio River watershed reference sites to assess the effects of exposure to low-level selenium concentrations. Selenium, copper, and arsenic concentrations were statistically higher in tissue samples from exposed fish than in reference fish. Leukopenia, lymphocytosis, and neutropenia were evident in exposed fish and were indicative of metal exposure and effect. White blood cell counts and percent lymphocyte values were significantly correlated with liver selenium concentrations. Plasma protein levels were significantly lower in exposed fish than in fish from the Ohio River, indicating that exposed fish may have been nutritionally stressed. Condition factors for fish from the ash pond-receiving streams were the same as, or lower than, those of fish from the reference sites. There was no evidence that the growth rate of fish in the receiving streams differed from that of fish in the reference streams. Despite liver selenium concentrations which exceeded reported toxicity thresholds and evidence of significant hematological changes, there were no significant differences in fish condition factors, liver-somatic indices, or length-weight regressions related to selenium.     

Assessment of Tolerant Sunfish Populations (Lepomis sp.) Inhabiting Selenium-Laden Coal Ash Effluents: 1. Hematological and Population Level Assessment

Sunfish were collected from coal ash effluent-receiving streams and Ohio River watershed reference sites to assess the effects of exposure to low-level selenium concentrations. Selenium, copper, and arsenic concentrations were statistically higher in tissue samples from exposed fish than in reference fish. Leukopenia, lymphocytosis, and neutropenia were evident in exposed fish and were indicative of metal exposure and effect. White blood cell counts and percent lymphocyte values were significantly correlated with liver selenium concentrations. Plasma protein levels were significantly lower in exposed fish than in fish from the Ohio River, indicating that exposed fish may have been nutritionally stressed. Condition factors for fish from the ash pond-receiving streams were the same as, or lower than, those of fish from the reference sites. There was no evidence that the growth rate of fish in the receiving streams differed from that of fish in the reference streams. Despite liver selenium concentrations which exceeded reported toxicity thresholds and evidence of significant hematological changes, there were no significant differences in fish condition factors, liver–somatic indices, or length–weight regressions related to selenium.     

Assessment of larval deformities and selenium accumulation in northern pike (Esox lucius) and white sucker (Catostomus commersoni) exposed to metal mining effluent

Uranium mining and milling operations in northern Saskatchewan (Canada) release effluents with elevated levels of certain trace metals and metalloids, including selenium. The goal of the present study was to evaluate the presence of selenium-induced deformities in northern pike (Esox lucius) and white sucker (Catostomus commersoni) larvae originating from adults collected downstream of a uranium mine. Eggs were fertilized in the field and incubated in the laboratory following a two-way (crossover) analysis-of-variance experimental design to discriminate effects from maternal transfer versus those from exposure to site water in the developing embryos. Selenium concentrations in northern pike and white sucker eggs (8.02 and 4.89 microg/g dry wt, respectively; mean +/- standard error throughout) from the exposure site were approximately two- to threefold higher than reference (2.35 +/- 0.20 and 1.94 +/- 0.25 microg/g dry wt, respectively). Among all evaluated deformities (skeletal curvatures, craniofacial deformities, fin deformities, and edema), only edema in white sucker fry from the exposure site was slightly elevated ( approximately 3%) compared to reference. The occurrence of edema, however, can be associated with factors other than selenium (e.g., other metals and organic compounds). Both fish species displayed strong linear relationships between the selenium concentrations in eggs and other tissues (muscle, liver, kidney, and bone), suggesting that selenium concentrations in eggs could be predicted from selenium concentrations in adult tissues. The lack of a clear, toxic response in the present study is in agreement with selenium thresholds for early life-stage deformities reported in other studies, with egg selenium concentrations in northern pike and white sucker collected at the exposure site being less than the 10 microg/g (dry wt) threshold associated with the presence of deformities.     

Selenium, Cadmium, Copper, and Zinc Concentrations in Sediments and Mullet (Mugil cephalus) from the Southern Basin of Lake Macquarie, NSW, Australia

Selenium, cadmium, copper, and zinc concentrations were measured in sediments and the tissues of mullet (Mugil cephalus) collected from the southern basin of Lake Macquarie, NSW, Australia. Trace metals in surficial sediments are enriched in trace metals relative to background concentrations (selenium, 3–19; cadmium, 14–42; copper, 1.5–3.6; zinc, 0.77–2.2 times background). Selenium, cadmium, and copper in Lake Macquarie mullet tissues are elevated compared to those in mullet collected from the Clyde River estuary, a relatively pristine location. Selenium and copper concentrations are also elevated compared to those reported in mullet tissues from other nonpolluted coastal environments. Zinc concentrations in Lake Macquarie mullet muscle tissues are significantly higher than those in muscle tissues of mullet from the Clyde River estuary, but mullet from both locations have similar zinc concentrations in other tissues. These results show that contamination of sediment with trace metals has resulted in elevated trace metals in the benthic feeding fish M. cephalus. Little of the variation of trace metal concentrations between fish was explained by variation in mass. Selenium concentrations in mullet are of concern in muscle tissues as they are above recommended acceptable limits for safe human consumption, while concentrations in tissues are at levels that may effect fish growth, reproduction, and survival. Copper concentrations in mullet tissues are also at levels that may reduce fish growth. Received: 11 September 1999/Accepted: 9 July 2000     

Elevated Levels of Metals and Organic Pollutants in Fish and Clams in the Cape Fear River Watershed

A study was performed in 2003 to 2004 to assess metal and organic contaminant concentrations at three areas in the lower Cape Fear River system, North Carolina, United States. Sites examined were Livingston Creek along the mainstem of the Cape Fear River near Riegelwood, Six Runs Creek in the Black River Basin, and Rockfish Creek in the Northeast Cape Fear River basin. The results of the investigation showed that levels of metals and organic pollutants in the sediments were lower than limits considered harmful to aquatic life. However, results of fish (adult bowfin) tissue analyses showed that concentrations of arsenic (As), cadmium (Cd), mercury (Hg), selenium (Se), and now-banned polychlorinated biphenyls (PCBs), and the pesticide dieldrin were higher than levels considered safe for human consumption by the United States Environmental Protection Agency and the North Carolina Health Director’s Office. Fish tissue concentrations of Hg, Se, and PCBs were also higher than concentrations determined by researchers to be detrimental either to the health of the fish themselves or their avian and mammalian predators. Due to the rural nature of two of the sites, increased concentrations of As, Cd, Se, and PCBs in fish tissue were unexpected. The likely reason the levels are increased in fish and some clams but not in sediments is that these pollutants are biomagnified in the food chain. These pollutants will also biomagnify in humans. In these rural areas there is subsistence fishing by low-income families; thus, increased fish tissue metals and toxicant concentrations may present a direct threat to human health.     

Bioaccumulation of selenium (Se) in the Cienega de Santa Clara wetland, Sonora, Mexico

The Cienega de Santa Clara, on the east side of the Colorado River delta, is a brackish wetland supported by agricultural drainage water from the United States that provides habitat for endangered fish and bird species. Bioaccumulation of selenium has created toxicity problems for wildlife in similar wetlands in the United States. This is the first selenium survey in the Cienega de Santa Clara. Ten sites were selected to collect water (dissolved), sediments (total), plants, invertebrates, and fish. Samples were collected from October 1996 to March 1997. Selenium was detected in all samples. Concentrations in water ranged from 5 to 19 microg/L and increased along a salinity gradient. Although water levels of selenium exceeded EPA criterion for protection of wildlife, levels in sediments (0.8-1.8 mg/kg), aquatic plants (0.03-0.17 mg/kg), and fish (2.5-5.1 mg/kg whole body, dry wt) did not exceed USFWS recommended levels. It is concluded from this study that the levels of selenium in water did not affect the overall health of the fish sampled. Therefore, it is important to maintain or improve the water quality entering this wetland to continue to have normal levels of Se in the food chain components.     

Selenium in aquatic organisms from subsurface agricultural drainage water,San Joaquin Valley,California

Concentrations of total selenium were high in 1983 in water, sediment, organic detritus, aquatic plants and invertebrates, and mosquitofish (Gambusia affinis) from Kesterson Reservoir (San Joaquin Valley, California) and the San Luis Drain. Selenium concentrations in biota from the Reservoir and Drain (referred to here collectively as Kesterson) exceeded 300 (g/g dry weight in some samples of algae, submerged rooted plants, chironomids, and mosquitofish, and were as high as 440 g/g dry weight in decomposing detritus. Overall, selenium concentrations in samples from Kesterson averaged about 100-fold higher than those from the Volta Wildlife Area (here termed Volta), a nearby site that does not receive subsurface drainage water. Selenium concentrations generally increased from water to sediment to plants to animals. Spatial (geographic) patterns were observed for selenium concentrations in samples from Kesterson, but not in those from Volta. Higher concentrations were usually measured in samples from the San Luis Drain than from the evaporation ponds that comprise Kesterson Reservoir. At Kesterson, concentrations were usually higher in August than in May. The elevated levels of selenium measured in forage organisms from Kesterson are probably toxic to sensitive consumer animals, and may explain recent observations of dead and deformed embryos in eggs of aquatic birds that nest at the Reservoir. The effects of the selenium on fish living in subsurface agricultural drainage water are still poorly understood.