Hg, As, Cd, and Pb in Water, Sediment, Mussel Tissue and Shells in the Kiamichi River Basin, Southeastern Oklahoma: Sources, Surface Water and Groundwater Quality, and Human Health Implications

Abstract:

The Kiamichi River (KR) of southeastern Oklahoma has a highly diverse freshwater-mussel population and is one of the most ecologically diverse rivers in Oklahoma. Studies show that the mussel population of the KR has declined by 60% since 2005, with three species listed as federally endangered, largely due to impoundment, sedimentation, and increasing droughts. The impact of toxic metals, including Hg, As, Pb, and Cd, to the health of the KR ecosystem, however, is not known. In this study, we analyzed Hg, As, Pb, and Cd in river water, sediment, and mussel tissue and shell using established EPA inductively-coupled plasma mass spectrometry (ICP-MS) methods. We found that tributary waters exceed the EPA criterion continuous concentration (CCC) for all four metals, and that the KR itself exceeds the EPA CCC for Pb and in sites near the Hugo Lake impoundment for Hg, too. Groundwater well sites exceeded EPA maximum contaminant levels (MCL) for all four metals. Importantly, As and Hg exceed the EPA human health criterion in all surface water samples. Exceeding EPA standards for these metals in particular means the river water poses risks to human health as well as to the aquatic life. Sites with a higher human influence index, which is the impact human activity has on the environment, also had the highest metal concentrations in water and sediment, implying human activity is increasing the metal content. The bioconcentration factor (BCF) and the bioaccumulation factor (BAF) both illustrate these metals are more readily incorporated into mussel tissue from water rather than sediment. Additionally, laser ablation (LA) ICP-MS results of mussel shell indicate an increase in these four metals during the 2010-2011 OK drought. Dissolved oxygen concentration is low during high-temperature drought conditions. The metabolism of the mussels increases to increase the rate of water flow into the mussel in order to extract more oxygen from the water. The increased rate of water flow into the mussel increases the amount of dissolved metals into the mussel body that can be incorporated into tissue and shell.