Grantee Research Project Results

2003 Progress Report: 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: Hahn, Intaek
Project Period: March 1, 2003 through February 28, 2005 (Extended to February 28, 2006)
Project Period Covered by this Report: March 1, 2003 through February 28, 2004
Project Amount: $199,802
RFA: Superfund Minority Institutions Program: Hazardous Substance Research (2002) RFA Text |  Recipients Lists
Research Category: Hazardous Waste/Remediation , Safer Chemicals , Land and Waste Management

Objective:

The overall objective of this research project is to test the hypothesis that selenium (Se) buffers the effects of mercury, thus allowing insects to attain higher levels of mercury in their bodies before toxic effects are manifested. The specific objectives for Year 1 of the project include log-dose probit assessments of the toxicity and developmental/survivorship effects of mercury and Se on common insects and their associated insect predators found in aquatic and terrestrial ecosystems.

Progress Summary:

Investigation of the Toxicity of Se to Megaselia scalaris

The relative toxicities of ecologically relevant concentrations of sodium selenate, sodium selenite, seleno-L-methionine, and Se-(Methyl) selenocysteine hydrochloride to larvae were assessed in diet bioassays. The lethal concentration that killed 50 percent of the population was determined (LC50). With chronic exposure, selenocysteine was the most toxic of the Se species to the larvae (LC50 83 µg/g wet weight), followed by seleno-L-methionine (LC50 130 µg/g), selenate (LC50 258 µg/g), and selenite (LC50 392 µg/g). Significant decreases in larval survival relative to controls occurred at the lowest treatment tested (100 µg/g) for both selenate and selenite, at 100 µg/g for seleno-L-methionine, and 50 µg/g for selenocysteine. Thus, although all forms of Se are toxic, the organic forms occurring in plants are substantially more toxic. This work has led to the development of a new statistical technique for comparing LC50 values, which was presented at a meeting of the American Statistical Association.

Investigation of the Developmental Effects of Se on M. scalaris

Larval development time was significantly increased with exposure to selenate at 100 µg/g wet weight and above, selenite at 300 µg/g and above, and at 50 µg/g and 25 µg/g and above for seleno-L-methionine and selenocysteine, respectively. Pupal development was not affected by any of the Se treatments. Significant differences between male and female adult eclosion times were observed, with females eclosing later than males as Se concentrations increased. Ovipositing females did not discriminate between the highest treatment concentrations of any of the pollutants as compared to the controls, indicating a lack of avoidance behavior. Because most larval food sources are temporary, extending the developmental times and causing asynchrony between males and females will likely cause significant population disruption in these important detritivores.

Investigation of the Toxicity of Mercury to M. scalaris

The LC50 value for M. scalaris for methyl mercury (14 µg/g) was much lower than for any Se compound. Larval development time was increased significantly at only 10 µg/g, and puparial development time also was increased significantly at 20 µg/g. However, methyl mercury did not affect the developmental rate of the sexes differently. Thus, even extremely low levels of mercury will affect development and survival of this important detritivore.

Investigation of the Toxicity of Se and Mercury to Culex quinquefasciatis

For C. quinquefasciatis, we found an LC50 value of 11.8 µg/g for selenate in addition to delays in development, with a significantly different Growth Index value at the lowest level tested (2 µg/g). Mercury affected C. quinquefasciatis at a much lower concentration, with an LC50 value of 46.42 µg/kg, but did not cause any significant delays in developmental time.

The results from Year 1 of the project have provided dose-response relationships for Se and mercury for both M. scalaris and C. quinquefasciatis. In addition, the examination of the effects of Se and mercury on development time in M. scalaris and growth indices in C. quinquefasciatis provide alternative indices of toxicity that are more appropriate in chronic, low-dose situations. These findings allow for the quantification and comparison of lethal and nonlethal effects of these two pollutants on our test organisms.

Future Activities:

We will conduct experiments with M. scalaris and C. quinquefasciatis in Year 2 of the project to determine the joint toxicity of Se and mercury. In addition, we will test the effects of Se and mercury on a predator of C. quinquefasciatis in aquatic systems and a predator of M. scalaris in terrestrial systems. These studies will be conducted to contrast the aquatic versus terrestrial biomagnification of the test pollutants. Also, specifically in aquatic systems, we will measure predator species exposure to the toxicants through both dermal and oral exposure.

Journal Articles on this Report : 1 Displayed | Download in RIS Format

Publications Views

Other project views:	All 15 publications	5 publications in selected types	All 4 journal articles

Publications

Type	Citation	Project	Document Sources
Journal Article	Jensen PD, Arias M, Trumble JT. Developmental responses of a terrestrial insect detritivore, Megaselia scalaris (Loew) to four selenium species. Ecotoxicology 2005;14(3):313-322.	R830841 (2003) R830841 (2004) R830841 (Final)	Abstract from PubMed

Supplemental Keywords:

selenium, Se, sodium selenate, sodium selenite, selenocysteine, selenomethionine, methyl mercury, toxics, pollutants, entomology, ecotoxicology, Megaselia scalaris, Culex quinquefasciatis, LC50., Health, RFA, Ecosystem Protection/Environmental Exposure & Risk, Scientific Discipline, PHYSICAL ASPECTS, INTERNATIONAL COOPERATION, Waste, ENVIRONMENTAL MANAGEMENT, Water, POLLUTANTS/TOXICS, HUMAN HEALTH, Ecological Risk Assessment, Health Risk Assessment, Physical Processes, Mercury, Risk Assessments, chemical mixtures, Exposure, Bioavailability, Chemicals, Ecology and Ecosystems, Environmental Monitoring, Risk Assessment, health effects, heavy metals, dietary exposure, animal bioassays, Selenium, aquatic ecosystem, groundwater contamination, human exposure, animal model, chemical exposure, bioaccumulation, contaminated sites, fate and transport, hazardous waste, environmental toxicant, human health risk

Relevant Websites:

http://insects.ucr.edu/people/trumble.html Exit

Progress and Final Reports:

Original Abstract

2004 Progress Report

Final Report