A survey on the temporal and spatial distribution of perchlorate in the Potomac River

Abstract

Samples of river water and treated drinking water were obtained from eight sites along the Potomac River between western Maryland and Washington DC. Samples were collected each month from October 2007 to September 2008 and analyzed for perchlorate by ion chromatography/mass spectrometry. Data on anions were also collected for seven of the twelve months. Data were analyzed to identify spatial and temporal patterns for the occurrence of perchlorate in the Potomac. Over the year of sampling, the largest monthly increase occurred from June to July, with levels then decreasing from July to September. Samples from the period between December and May had lower perchlorate concentrations, relative to the remainder of the study year. Spatially, higher levels of perchlorate were found at sites located in west-central Maryland, the eastern panhandle of West Virginia, and central northern Virginia, with levels decreasing slightly as the Potomac approaches Washington DC. Within the sampling boundaries, river (untreated) water perchlorate concentrations ranged from 0.03 μg L(-1) to 7.63 μg L(-1), averaged 0.67 ± 0.97 μg L(-1) over the year-long period and had a median value of 0.37 μg L(-1). There was no evidence that any of the existing drinking water treatment technologies at the sampling sites were effective in removing perchlorate. There were no correlations found between the presence of perchlorate and any of the anions or water quality parameters examined in the source water with the exception of a weak positive correlation with water temperature. Results from the summer (June-August) and fall (September-November) months sampled in this study were generally higher than from the winter and spring months (December-May). All but one of the locations had annual average perchlorate levels below 1 μg L(-1); however, 7 of the 8 sites sampled had river water perchlorate detections over 1 μg L(-1) and 5 of the 8 sites had treated water detections over this level.

Perchlorate in The Great Lakes: Isotopic Composition and Origin

“…The 36 Cl/Cl ratio of perchlorate in Lake Superior is higher than that reported previously for any other location. 35,36 Great Lakes perchlorate generally resembles that of indigenous natural perchlorate from the western USA in terms of δ 37 Cl values and 36 Cl/Cl ratios (Figure 3). The isotopic composition of indigenous natural perchlorate in groundwater appears to be fairly consistent over a wide portion of North America, including West Texas, New Mexico, and Oregon, [34][35][36]58 and similar isotopic composition is now also observed in perchlorate throughout the Great Lakes (Figures 2 and 3).…”

“…The apparent perchlorate removal in Lake Erie does not appear to cause significant isotope fractionation of oxygen and chlorine. In contrast, assuming Rayleigh-type fractionation according to the isotopic fractionation factors measured for microbial perchlorate reduction, 64 a 20% perchlorate reduction would cause about a 9‰ increase in δ 18 O and +3.5‰ increase in δ 37 Cl while a 30% reduction of perchlorate would increase the δ 18 O and δ 37 Cl values by about +14‰ and +5‰, respectively. However, complete biodegradation of perchlorate diffusing into the anaerobic sediments of Lake Erie (analogous to the "reactive microsites" model of Brandes and Devol (1997) 65 ) could be a plausible mechanism for perchlorate removal from Lake Erie without changing the isotopic composition of residual perchlorate.…”

“…Isotopic measurements enable researchers to distinguish between synthetic and natural perchlorate. Stable oxygen and chlorine isotope ratios in combination with the abundance of the radioactive isotope 36 Cl allow for routine discrimination of three major source types of perchlorate including synthetic perchlorate, Atacama perchlorate (from Chilean nitrate fertilizer), and indigenous natural perchlorate (which was first characterized in the Southern High Plains of Texas and New Mexico). ,,− Although perchlorate is a widespread surface water and groundwater contaminant across the US − ,, and has potentially adverse effects on human health, there is a limited amount of information about its natural cycle, including its natural formation mechanism(s), the relative importance of anthropogenic vs natural sources in groundwater and surface water, and the extent of its biodegradation in the environment.…”

“…For oxygen isotopes, a Faraday cup was used for 16 O and an electron multiplier for 17 O and 18 O, with data collection times of 1, 10, and 2 s per cycle, respectively, for a total of 100 cycles. Chlorine isotopes 35 Cl and 37 Cl were measured by Faraday cups with data collection times of 1 and 2 s per cycle, respectively, for a total of 20 cycles. Data are normalized to measurements of KClO 4 isotopic reference materials USGS37 and USGS38, 22 which were converted to TPAClO 4 (calibration data are given in Figure S2, Supporting Information).…”

Chlorine isotopic composition of perchlorate in human urine as a means of distinguishing among exposure sources

“…Perchlorate has been detected in surface water and groundwater across the United States 6-14 as well as in a wide range of food products including milk, infant formulas, fruits, and vegetables. 15-21 The primary routes of perchlorate exposure to humans appear to be through oral intake of food and drinking water.…”