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Bottom Sediment as a Source of Organic Contaminants in Lake Mead, Nevada, USA
Citation:
Alvarez, D. A., M. R. Rosen, S. D. Perkins, W. L. Cranor, V. L. Schroeder, AND T. L. JONES-LEPP. Bottom Sediment as a Source of Organic Contaminants in Lake Mead, Nevada, USA. CHEMOSPHERE. Elsevier Science Ltd, New York, NY, 88(5):605-611, (2012).
Impact/Purpose:
In recent years, there has been an abundance of research determining the presence of synthetic organic compounds (SOCs) in environmental waters, especially those receiving treated effluents from municipal wastewater treatment plants (WWTPs). These studies generally focus on point source impacts and the lateral distribution of SOCs downstream of known point sources. Although the hydrodynamics within a flowing body of water (i.e., a stream or river) can be complex, it is generally intuitive that SOCs will continue to move downstream until they are removed by sorption or degradation.
Description:
Treated wastewater effluent from Las Vegas, Nevada and surrounding communities’ flow through Las Vegas Wash (LVW) into the Lake Mead National Recreational Area at Las Vegas Bay (LVB). Lake sediment is a likely sink for many hydrophobic synthetic organic compounds (SOCs); however, partitioning between the sediment and the overlying water could result in the sediment acting as a secondary contaminant source. Locating the chemical plumes may be important to understanding possible chemical stressors to aquatic organisms. Passive sampling devices (SPMDs and POCIS) were suspended in the LVB at depths of 3.0, 4.7, and 6.7 (lake bottom) meters in June of 2008 to determine the vertical distribution of SOCs in the water column. A custom sediment probe was used to also bury the samplers in the sediment at depths of 0-10, 10-20, and 20-30 cm. The greatest number of detections in samplers buried in the sediment was at the 0-10 cm depth. Concentrations of many hydrophobic SOCs were twice as high at the sediment-water interface than in the mid and upper water column. Many SOCs related to wastewater effluents, including fragrances, insect repellants, sun block agents, and phosphate flame retardants, were found at highest concentrations in the middle and upper water column. The total estrogenicity of chemicals, measured by the yeast estrogen screen, sampled in the middle of the water column was nearly twice as high as the upper column and nine times as high as those near the sediment-water interface. Declining water levels in the lake made it difficult to determine a clear gradient of chemicals as mixing of the water column was likely occurring. However, there is evidence to suggest that the water infiltrated into the sediment had a different chemical composition than the rest of the water column and could be a potential risk exposure to bottom-dwelling aquatic organisms.