Bioaccumulation of Platinum Group Metals in the Freshwater Mussel Elliptio Complanata

by Mays, Jason Warren

Abstract (Summary)
ABSTRACT MAYS, JASON WARREN. Bioaccumulation of Platinum Group Metals in the Freshwater Mussel Elliptio complanata. (Under the direction of Thomas J. Kwak and W. Gregory Cope). The use of catalytic converters for automobile exhaust purification has led to emission and environmental contamination by the platinum group metals (PGM) platinum (Pt), palladium (Pd), and rhodium (Rh). In this study, a total of 37 sites were sampled throughout central North Carolina and were chosen based on availability of the freshwater mussel Elliptio complanata, varied geographic distribution, land use patterns, and vehicle traffic density. At each site, a sample of sediment and three adult E. complanata were collected from within 50-150 m both upstream and downstream of the road crossing. Mussel tissue and sediment samples were analyzed for concentrations of Pt, cadmium (Cd) and mercury (Hg). Related stream and local variables investigated included sediment total organic carbon, water chemistry, and estimated vehicle traffic density at the bridge. Landscape variables included human population density, land use, and density of transportation infrastructure. Pt concentrations in mussel tissue ranged 0.09-1.98 ng/g dry weight and 0.06-1.86 ng/g dry weight in sediment among sites. A biota sediment accumulation factor for Pt, calculated as the mean [tissue]/[soil], was 3.2, compared to 87 and 88 for Hg and Cd, respectively. Pt contamination of mussels and sediment at highway crossing sites were not significantly correlated with the amount of traffic crossing the specific structure. Rather, multiple regression modeling indicated a significant relation between Pt concentration in mussels at a site and the human population of the watershed. A 28-d laboratory test was conducted with waterborne Pt and Pd to determine toxicity, bioaccumulation, and to assess several potential biomarkers of exposure to Pt and Pd. Test mussels were exposed to five concentrations of an equal mixture of Pt and Pd salts, ranging from 0.05 to 500 μg/L of each metal, in a static renewal test. The 500 µg/L concentration resulted in high mortality (4 of 9 dead by day 12) of test mussels; all individuals in each of the other test concentrations survived to the end of the test. There were nine replicate mussels per treatment concentration, allowing three mussels from each treatment to be sampled on days 7, 14 and 28. Tissue and hemolymph were assessed for concentrations of Pt, Pd, sodium (Na+), calcium (Ca2+), potassium (K+), and chloride (Cl-) concentrations. Na+,K+-ATPase activity was assessed in gill tissue as a potential biomarker of exposure. Tissue concentrations of Pt ranged from 0.10 ng/g dry weight in controls to 34,486 ng/g dry weight in the 500 µg/L treatment, and Pd ranged from 0.06 ng/g dry weight in controls to 34,404 ng/g dry weight in the 500 µg/L treatment. Concentrations of Pt in hemolymph ranged from 0.08 ng/mL in controls to 50.1 ng/mL in the 500 µg/L treatment, and Pd ranged from 0.06 ng/mL in controls to 12.2 ng/mL in the 500 µg/L treatment. On day 28, Na+,K+-ATPase activity displayed a logarithmic trend (y=0.489ln(x)+2.054; R2=0.73) of increasing activity with increasing PGM exposure concentration; however, activity was only significantly increased (P<0.05) at 5.0 µg/L and 50 µg/L concentrations. High variation and weak correlation of Na+,K+-ATPase activity with Pt and Pd exposure concentration indicate that it may not be a suitable biomarker of PGM exposure. Hemolymph Ca2+ concentrations were increased on day 7 at the 50 µg/L concentration. Hemolymph Na+ levels were decreased on day 28 at the 5.0 µg/L and 50 µg/L concentrations. Cl- and K+ levels were decreased at the 50 µg/L concentration. Tissue Pt and Pd concentrations in mussels exposed to the lowest test concentration (0.05 µg/L) displayed tissue concentrations of Pt that were approximately six times greater than the maximum tissue concentrations measured in stream-sampled mussels. Hemolymph ion measurement does not appear to be sensitive enough to serve as a biomarker of PGM exposure at environmentally relevant exposure concentrations. Results from this study will provide resource managers with information on this emerging group of contaminants needed to perform risk assessments for transportation impacts to natural systems and to develop conservation, protection, and mitigation plans for this critically imperiled faunal group.
Bibliographical Information:

Advisor:W. Gregory Cope; Thomas J. Kwak; Damian Shea

School:North Carolina State University

School Location:USA - North Carolina

Source Type:Master's Thesis

Keywords:fisheries and wildlife sciences


Date of Publication:04/15/2009

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