Effects of Polycyclic Aromatic Hydrocarbon Exposure on Three Life Stages of Freshwater Mussels (Bivalvia: Unionidae)

Abstract

Freshwater mussels (Bivalvia: Unionidae) are among the most threatened aquatic species in the world. One of the major issues implicated in this decline is water pollution. Polycyclic aromatic hydrocarbons (PAHs) are a suite of hydrophobic environmental pollutants common in terrestrial and aquatic ecosystems. These compounds are largely derived from petroleum related sources (e.g., gasoline, oil) and are of major concern from transportation-related runoff to aquatic systems due to the acute and chronic (e.g., mutagenic and carcinogenic) toxic properties of many members of this class. The effects of exposure to PAHs have been investigated in many species of bivalves; however, to date no comprehensive study of the effects of exposure to these compounds on all life stages of native freshwater mussels have been completed. The goals of this study therefore were to investigate the effects of exposure to PAHs on all life stages of freshwater mussels and to develop diagnostic tests that are rapid, accurate, inexpensive, and of minimal impact to the mussels. This study examined the acute (48 h) toxicity of PAHs to the glochidial (larval) and juvenile stages of mussels and the sub-acute (7 d) toxic effects on adult mussels. Additionally, the study examined the use of genetic damage as a biomarker of exposure of mussels to PAHs by utilizing the Comet assay to determine levels of DNA strand breakage following aqueous exposure. Finally, mussels were collected from areas of high and low environmental levels of PAHs and were analyzed to validate laboratory findings and to examine relations to previously obtained field PAH mussel, water and sediment measurements. We found that there were no acute toxic effects of PAHs on glochidia or juveniles of the two species of freshwater mussels examined, up to concentrations approaching water solubility, and well exceeding those commonly measured in the streams of North Carolina. Experiments with adult Elliptio complanata, both in the laboratory and from the field, indicated that genetic damage due to PAH exposure was likely present, however the results were highly variable and the potential for biological, ecological, and toxicological consequences were uncertain. Further development and improvement of assay methods may reduce this variation. Generally, mussels from streams with higher average daily traffic counts (ADTC) exhibited greater levels of genetic damage compared to mussels from streams with lower ADTC values. Data obtained from the laboratory study generally showed increasing DNA damage relative to increasing PAH concentration. Based on the data generated, however, PAHs are not likely contributing to acute toxicity of mussels in North Carolina streams, but the chronic, long-term pervasive effect of PAHs on native freshwater mussels remains uncertain.