Use of Passive Samplers for Detecting Spatial Distribution of Organic Contaminants In Lake Mead, Nevada, USA

Synthetic organic compounds (SOCs) pose a potential chronic or acute threat to the health of biota depending on the type of chemical. Approximately 650,000 m³/day of tertiary treated wastewater from the Las Vegas metropolitan area flows into Lake Mead through Las Vegas Wash (LVW), which enters into Las Vegas Bay (LVB). SOCs discharging into LVB can also originate from other sources including irrigated-urban runoff, storm-water runoff, subsurface inflow and accidental spills. SOCs have been found previously in bottom sediment, fish tissue and plasma, and the water column within LVB. Passive samplers were deployed in LVW, Lake Mead, and downstream of Hoover Dam, to determine the spatial distribution and potential sources of SOCs in Lake Mead. A commonly used musk fragrance, galaxolide, was found in LVB at a considerably higher concentration (up to 90 ng/L) compared to other compounds detected (generally <2 ng/L), followed by another musk fragrance, tonalide (9.5 ng/L). Both compounds were also detected downstream of but not above effluent outfalls in LVW (400 and 41 ng/L for galaxolide and tonalide, respectively). Galaxolide was detected at a concentration of 1.3 ng/L in Boulder Basin (approximately 20 km from the most upstream detection), but was not detected below Hoover Dam. The other compounds detected, many of which are legacy organochlorine compounds, were at much lower concentrations (<1 ng/L) but were detected at more sites including the site on the Colorado River below Hoover Dam. The spatial distribution of compounds detected indicates that the main source of SOCs is from LVW, but that other possible sources exist for organochlorine compounds downstream of Hoover Dam. Evidence of endocrine disruption in male fish has been observed at LVW, LVB, and below Hoover Dam including altered reproductive hormones, reduced gonadal development, and lower sperm quality possibly indicating exposure to estrogenic endocrine disrupting compounds.