Vickie L. Schroeder | Geology Reports

USGS2012

Bottom sediment as a source of organic contaminants in Lake Mead, Nevada, USA

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 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. There was 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.

Nevada↗

USGS2008

Investigation of organic chemicals potentially responsible for mortality and intersex in fish of the North Fork of the Shenandoah River, Virginia, during Spring of 2007

Declining fish health, fish exhibiting external lesions, incidences of intersex, and death, have been observed recently within the Potomac River basin. The basin receives surface runoff and direct inputs from agricultural, industrial, and other human activities. Two locations on the North Fork of the Shenandoah River were selected for study in an attempt to identify chemicals that may have contributed to the declining fish health. Two passive sampling devices, semipermeable membrane devices (SPMDs) and polar organic chemical integrative samplers (POCIS), were deployed during consecutive two-month periods during the spring and early summer of 2007 to measure select organic contaminants to which fish may have been exposed. This study determined that concentrations of persistent hydrophobic contaminants, such as polycyclic aromatic hydrocarbons (< picograms per liter), legacy pesticides (<10 picograms per liter), and polychlorinated biphenyls (<280 picograms per liter) were low and indicative of a largely agricultural area. Atrazine and simazine were the most commonly detected pesticides. Atrazine concentrations ranged from 68 to 170 nanograms per liter for the March to April study period and 320 to 650 nanograms per liter for the April to June study period. Few chemicals characteristic of wastewater treatment plant effluent or septic tank discharges were identified. In contrast, para-cresol, N,N-diethyltoluamide, and caffeine commonly were detected. Prescription pharmaceuticals including carbamazepine, venlafaxine, and 17a-ethynylestradiol were at low concentrations. Extracts from the passive samplers also were screened for the presence of estrogenic chemicals using the yeast estrogen screen. An estrogenic response was observed in POCIS samples from both sites, whereas SPMD samples exhibited little to no estrogenicity. This indicates that the chemicals producing the estrogenic response have a greater water solubility and are, therefore, less likely to bioaccumulate in fatty tissues of organisms.

Virginia↗