Potential for Increased Bioavailability of Mercury in Selenium Contaminated Sites: Risk Assessment and Ecological Effects

EPA Grant Number: R830841
Title: Potential for Increased Bioavailability of Mercury in Selenium Contaminated Sites: Risk Assessment and Ecological Effects
Investigators: Trumble, John T.
Institution: University of California - Riverside
EPA Project Officer: Carleton, James N
Project Period: March 1, 2003 through February 28, 2005 (Extended to February 28, 2006)
Project Amount: $199,802
RFA: Superfund Minority Institutions Program: Hazardous Substance Research (2002) RFA Text |  Recipients Lists
Research Category: Hazardous Waste/Remediation , Land and Waste Management , Safer Chemicals


The long-term goal of this study is to test the hypothesis that selenium (Se) buffers the effects of mercury (Hg), thus allowing insects to attain higher levels of mercury in their bodies before toxic effects manifest. This general pattern has been documented for vertebrates, but not for insects. In addition, our preliminary data indicate that selenium is not biomagnified in predators, leading to the intriguing possibility that transfer of Hg would occur without the buffering effects of Se. The potential effects on ecosystem stability would be profound.

The objectives for the first year will include log-dose probit assessments of the toxicity and developmental/survivorship effects of mercury and selenium on common insects and their associated insect predators found in aquatic and terrestrial ecosystems. By recording the effects of Hg and Se independently and in combination on prey species, the ecological effects of these pollutants, and the bioavailability of each material will be determined for the critical organisms near the base of the food web. In addition, these studies will help determine if oral toxicity is more important than contact toxicity in the aquatic system. Using this baseline data, we can determine if the insect responses to these toxicants are antagonistic (where one material allows increased accumulation of the other without negative effects), additive (where the relative effects on development and survival are directly proportional to the contamination level), or synergistic (where the relative effects are greater than would be predicted by specific concentrations).

In the second year, we will quantify biotransfer of total Se, Se species, total mercury and inorganic and methyl mercury to the next trophic level, the predator species. In the terrestrial system, we will be able to study key forms of Se and mercury through diet studies. In the aquatic system, the experiments will focus on selenate pollution and both forms of mercury that are typically found in water contamination.


The hypothesis will be tested on two model insect systems that commonly occur in polluted aquatic or terrestrial ecosystems. For the aquatic system, a replicated complete block design with four replicates of 15-30 insects will elucidate mercury and selenium effects (independently and jointly, in the food (Euglena gracilis), in the water, and both concurrently) on an important filter feeding mosquito (Culex quinqeufaciatus, capable of transmitting encephalitis and West Nile Virus) and a common dragonfly predator (Sympatrum sp.) of the larvae. To provide data from a terrestrial system, we will similarly investigate a ubiquitous scavenger insect (Megaselia scalaris, which eats both plant and animal detritus) and a generalist predator (Podisius maculaventris). In the later system, either selenium, mercury, or both will be fed to the prey insect by incorporating the material in a commercially available diet. Predators will be fed contaminated prey. For each species we will measure survivorship, relative growth rate, and concentrations of mercury and selenium. Mercury in water, algae and insects will be measured using the standard cold vapor atomic absorption technique. Total selenium content of algal samples as well as insects will be determined at the University of California, Division of Agriculture and Natural Resources Lab at Davis using nitric/perchloric acid digestion of samples, and determination by vapor generation using inductively coupled argon plasma spectrometric analysis. Selenium and mercury speciation will be measured using X-ray absorption spectroscopy at Stanford University. Differences between treatments for all variables will be measured with either an ANOVA and Tukey's HSD test or using the nonparametric Kruskal-Wallis Test with post-hoc separations determined using the Mann-Whitney U test.

Expected Results:

Increased mercury accumulation in prey insects in selenium contaminated sites will likely lead to substantial negative effects on the predators, allowing populations of the prey insects to grow rapidly. Availability of prey insects with higher levels of mercury could lead to rapid accumulation in fish, birds, and mammals, or increased disease transmission (e.g., by increasing mosquito populations) that may present health risks for humans. Determination of mercury bioaccumulation in lower life forms will generate critical risk assessment data and provide the background for legislation designed to regulate the threshold mercury levels in surface water and soil in the presence of selenium. This is important because mercury and selenium co-occur at many Superfund sites, including a Native American Reservation, and in or near many agricultural areas where Hispanic farm workers live and work.

Publications and Presentations:

Publications have been submitted on this project: View all 15 publications for this project

Journal Articles:

Journal Articles have been submitted on this project: View all 4 journal articles for this project

Supplemental Keywords:

risk assessment, ecological effects, bioavailability, terrestrial habitat, aquatic habitat, western region, mining, agriculture, arthropod, selenium, mercury, RFA, Health, PHYSICAL ASPECTS, Scientific Discipline, ENVIRONMENTAL MANAGEMENT, INTERNATIONAL COOPERATION, Waste, Water, Ecosystem Protection/Environmental Exposure & Risk, POLLUTANTS/TOXICS, HUMAN HEALTH, Bioavailability, Exposure, Health Risk Assessment, Chemicals, Risk Assessments, chemical mixtures, Physical Processes, Environmental Monitoring, Ecological Risk Assessment, Ecology and Ecosystems, Risk Assessment, Mercury, health effects, aquatic ecosystem, chemical exposure, fate and transport, contaminated sites, animal model, hazardous waste, Selenium, human exposure, environmental toxicant, groundwater contamination, animal bioassays, dietary exposure, exposure assessment, heavy metals, bioaccumulation

Progress and Final Reports:

  • 2003 Progress Report
  • 2004 Progress Report
  • Final Report