Pesticides and Pesticide Degradates in Groundwater Used for Public Supply across the United States: Occurrence and Human-Health Context.

This is the first assessment of groundwater from public-supply wells across the United States to analyze for >100 pesticide degradates and to provide human-health context for degradates without benchmarks. Samples from 1204 wells in aquifers representing 70% of the volume pumped for drinking supply were analyzed for 109 pesticides (active ingredients) and 116 degradates. Among the 41% of wells where pesticide compounds were detected, nearly two-thirds contained compound mixtures and three-quarters contained degradates. Atrazine, hexazinone, prometon, tebuthiuron, four atrazine degradates, and one metolachlor degradate were each detected in >5% of wells. Detection frequencies were largest for aquifers with more shallow, unconfined wells producing modern-age groundwater. To screen for potential human-health concerns, benchmark quotients (BQs) were calculated by dividing concentrations by the human-health benchmark, when available. For degradates without benchmarks, estimated values (estimated benchmark quotients (BQE)) were first calculated by assuming equimolar toxicity to the most toxic parent; final analysis excluded degradates with likely overestimated toxicity. Six pesticide compounds and 1.6% of wells had concentrations approaching levels of potential concern (individual or summed BQ or BQE values >0.1), and none exceeded these levels (values >1). Therefore, although pesticide compounds occurred frequently, concentrations were low, even accounting for mixtures and degradates without benchmarks.

Hormones and Pharmaceuticals in Groundwater Used As a Source of Drinking Water Across the United States.

This is the first large-scale, systematic assessment of hormone and pharmaceutical occurrence in groundwater used for drinking across the United States. Samples from 1091 sites in Principal Aquifers representing 60% of the volume pumped for drinking-water supply had final data for 21 hormones and 103 pharmaceuticals. At least one compound was detected at 5.9% of 844 sites representing the resource used for public supply across the entirety of 15 Principal Aquifers, and at 11.3% of 247 sites representing the resource used for domestic supply over subareas of nine Principal Aquifers. Of 34 compounds detected, one plastics component (bisphenol A), three pharmaceuticals (carbamazepine, sulfamethoxazole, and meprobamate), and the caffeine degradate 1,7-dimethylxanthine were detected in more than 0.5% of samples. Hydrocortisone had a concentration greater than a human-health benchmark at 1 site. Compounds with high solubility and low Koc were most likely to be detected. Detections were most common in shallow wells with a component of recent recharge, particularly in crystalline-rock and mixed land-use settings. Results indicate vulnerability of groundwater used for drinking water in the U.S. to contamination by these compounds is generally limited, and exposure to these compounds at detected concentrations is unlikely to have adverse effects on human health.

Arsenic in private well water and birth outcomes in the United States.

BACKGROUND: Prenatal exposure to drinking water with arsenic concentrations >50 µg/L is associated with adverse birth outcomes, with inconclusive evidence for concentrations ≤50 µg/L. In a collaborative effort by public health experts, hydrologists, and geologists, we used published machine learning model estimates to characterize arsenic concentrations in private wells-federally unregulated for drinking water contaminants-and evaluated associations with birth outcomes throughout the conterminous U.S. METHODS: Using several machine learning models, including boosted regression trees (BRT) and random forest classification (RFC), developed from measured groundwater arsenic concentrations of ∼20,000 private wells, we characterized the probability that arsenic concentrations occurred within specific ranges in groundwater. Probabilistic model estimates and private well usage data were linked by county to all live birth certificates from 2016 (n = 3.6 million). We evaluated associations with gestational age and term birth weight using mixed-effects models, adjusted for potential confounders and incorporated random intercepts for spatial clustering. RESULTS: We generally observed inverse associations with term birth weight. For instance, when using BRT estimates, a 10-percentage point increase in the probability that private well arsenic concentrations exceeded 5 µg/L was associated with a -1.83 g (95% CI: -3.30, -0.38) lower term birth weight after adjusting for covariates. Similarly, a 10-percentage point increase in the probability that private well arsenic concentrations exceeded 10 µg/L was associated with a -2.79 g (95% CI: -4.99, -0.58) lower term birth weight. Associations with gestational age were null. CONCLUSION: In this largest epidemiologic study of arsenic and birth outcomes to date, we did not observe associations of modeled arsenic estimates in private wells with gestational age and found modest inverse associations with term birth weight. Study limitations may have obscured true associations, including measurement error stemming from a lack of individual-level information on primary water sources, water arsenic concentrations, and water consumption patterns.

Lithium in groundwater used for drinking-water supply in the United States.

Lithium concentrations in untreated groundwater from 1464 public-supply wells and 1676 domestic-supply wells distributed across 33 principal aquifers in the United States were evaluated for spatial variations and possible explanatory factors. Concentrations nationwide ranged from <1 to 396 µg/L (median of 8.1) for public supply wells and <1 to 1700 µg/L (median of 6 µg/L) for domestic supply wells. For context, lithium concentrations were compared to a Health Based Screening Level (HBSL, 10 µg/L) and a drinking-water only threshold (60 µg/L). These thresholds were exceeded in 45% and 9% of samples from public-supply wells and in 37% and 6% from domestic-supply wells, respectively. However, exceedances and median concentrations ranged broadly across geographic regions and principal aquifers. Concentrations were highest in arid regions and older groundwater, particularly in unconsolidated clastic aquifers and sandstones, and lowest in carbonate-rock aquifers, consistent with differences in lithium abundance among major lithologies and rock weathering extent. The median concentration for public-supply wells in the unconsolidated clastic High Plains aquifer (central United States) was 24.6 µg/L; 24% of the wells exceeded the drinking-water only threshold and 86% exceeded the HBSL. Other unconsolidated clastic aquifers in the arid West had exceedance rates comparable to the High Plains aquifer, whereas no public supply wells in the Biscayne aquifer (southern Florida) exceeded either threshold, and the highest concentration in that aquifer was 2.6 µg/L. Multiple lines of evidence indicate natural sources for the lithium concentrations; however, anthropogenic sources may be important in the future because of the rapid increase of lithium battery use and subsequent disposal. Geochemical models demonstrate that extensive evaporation, mineral dissolution, cation exchange, and mixing with geothermal waters or brines may account for the observed lithium and associated constituent concentrations, with the latter two processes as major contributing factors.

Incremental lifetime cancer risks computed for benzo[a]pyrene and two tobacco-specific N-nitrosamines in mainstream cigarette smoke compared with lung cancer risks derived from epidemiologic data.

The manner in which humans smoke cigarettes is an important determinant of smoking risks. Of the few investigators that have predicted cancer risks from smoking on a chemical-specific basis, most used mainstream cigarette smoke (MCS) carcinogen emissions obtained via machine smoking protocols that only approximate human smoking conditions. Here we use data of Djordjevic et al. [Djordjevic, M.V., Stellman, S.D., Zang, E., 2000. Doses of nicotine and lung carcinogens delivered to cigarette smokers. J. Natl. Cancer Inst. 92, 106-111] for MCS emissions of three carcinogens measured under human smoking conditions to compute probability distributions of incremental lifetime cancer risk (ILCR) values using Monte Carlo simulations. The three carcinogens considered are benzo[a]pyrene, N'-nitrosonornicotine (NNN), and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). Computed NNK ILCR values were compared with lifetime risks of lung cancer (ILCR(CMD)(obsSigma-lung)) derived from American Cancer Society Cancer Prevention Studies (CPS) I and II. Within the Monte Carlo simulation results, NNK was responsible for the greatest ILCR values for all cancer endpoints: median ILCR values for NNK were approximately 18-fold and 120-fold higher than medians for NNN and benzo[a]pyrene, respectively. For "regular" cigarettes, the NNK median ILCR for lung cancer was lower than ILCR(CMD)(obsSigma-lung) from CPS-I and II by >90-fold for men and >4-fold for women. Given what is known about chemical carcinogens in MCS, this study shows that there is a higher incidence of lung cancer from exposure to MCS than can be predicted with current risk assessment methods using available toxicity and emission data.

Calculated cancer risks for conventional and "potentially reduced exposure product" cigarettes.

Toxicant deliveries (by machine smoking) are compiled and associated cancer risks are calculated for 13 carcinogens from 26 brands of conventional cigarettes categorized as "regular" (R), "light" (Lt), or "ultralight" (ULt), and for a reference cigarette. Eight "potentially reduced exposure product" (PREP) cigarettes are also considered. Because agency-to-agency differences exist in the cancer slope factor (CSF) values adopted for some carcinogens, two CSF sets were used in the calculations: set I [U.S. Environmental Protection Agency (EPA)-accepted values plus California EPA-accepted values as needed to fill data gaps] and set II (vice versa). The potential effects of human smoking patterns on cigarette deliveries are considered. Acetaldehyde, 1,3-butadiene, and acrylonitrile are associated with the largest calculated cancer risks for all 26 brands of conventional cigarettes. The calculated risks are proportional to the smoking dose z (pack-years). Using CSF set I and z = 1 pack-year (7,300 cigarettes), the calculated brand-average incremental lifetime cancer risk ILCR(1)(acetaldehyde) values are R, 6 x 10(-5); Lt, 5 x 10(-5); and ULt, 3 x 10(-5) (cf. typical U.S. EPA risk benchmark of 10(-6)). These values are similar, especially given the tendency of smokers to "compensate" when smoking Lt and ULt cigarettes. ILCR(1)(subSigma-lung) is the brand-average per pack-year subtotal risk for the measured human lung carcinogens. Using CSF set I, the ILCR(1)(subSigma-lung) values for R, Lt, and ULt cigarettes account for

Occurrence and potential human-health relevance of volatile organic compounds in drinking water from domestic wells in the United States.

BACKGROUND: As the population and demand for safe drinking water from domestic wells increase, it is important to examine water quality and contaminant occurrence. A national assessment in 2006 by the U.S. Geological Survey reported findings for 55 volatile organic compounds (VOCs) based on 2,401 domestic wells sampled during 1985-2002. OBJECTIVES: We examined the occurrence of individual and multiple VOCs and assessed the potential human-health relevance of VOC concentrations. We also identified hydrogeologic and anthropogenic variables that influence the probability of VOC occurrence. METHODS: The domestic well samples were collected at the wellhead before treatment of water and analyzed for 55 VOCs. Results were used to examine VOC occurrence and identify associations of multiple explanatory variables using logistic regression analyses. We used a screening-level assessment to compare VOC concentrations to U.S. Environmental Protection Agency maximum contaminant levels (MCLs) and health-based screening levels. RESULTS: We detected VOCs in 65% of the samples; about one-half of these samples contained VOC mixtures. Frequently detected VOCs included chloroform, toluene, 1,2,4-trimethylbenzene, and perchloroethene. VOC concentrations generally were < 1 microg/L. One or more VOC concentrations were greater than MCLs in 1.2% of samples, including dibromochloropropane, 1,2-dichloropropane, and ethylene dibromide (fumigants); perchloroethene and trichloroethene (solvents); and 1,1-dichloroethene (organic synthesis compound). CONCLUSIONS: Drinking water supplied by domestic wells is vulnerable to low-level VOC contamination. About 1% of samples had concentrations of potential human-health concern. Identifying factors associated with VOC occurrence may aid in understanding the sources, transport, and fate of VOCs in groundwater.

Pesticides in groundwater of the United States: decadal-scale changes, 1993-2011.

The national occurrence of 83 pesticide compounds in groundwater of the United States and decadal-scale changes in concentrations for 35 compounds were assessed for the 20-year period from 1993-2011. Samples were collected from 1271 wells in 58 nationally distributed well networks. Networks consisted of shallow (mostly monitoring) wells in agricultural and urban land-use areas and deeper (mostly domestic and public supply) wells in major aquifers in mixed land-use areas. Wells were sampled once during 1993-2001 and once during 2002-2011. Pesticides were frequently detected (53% of all samples), but concentrations seldom exceeded human-health benchmarks (1.8% of all samples). The five most frequently detected pesticide compounds-atrazine, deethylatrazine, simazine, metolachlor, and prometon-each had statistically significant (p < 0.1) changes in concentrations between decades in one or more categories of well networks nationally aggregated by land use. For agricultural networks, concentrations of atrazine, metolachlor, and prometon decreased from the first decade to the second decade. For urban networks, deethylatrazine concentrations increased and prometon concentrations decreased. For major aquifers, concentrations of deethylatrazine and simazine increased. The directions of concentration changes for individual well networks generally were consistent with changes determined from nationally aggregated data. Altogether, 36 of the 58 individual well networks had statistically significant changes in concentrations of one or more pesticides between decades, with the majority of changes attributed to the five most frequently detected pesticide compounds. The magnitudes of median decadal-scale concentration changes were small-ranging from -0.09 to 0.03 µg/L-and were 35- to 230,000-fold less than human-health benchmarks.

Chemical mixtures in untreated water from public-supply wells in the U.S.--occurrence, composition, and potential toxicity.

Chemical mixtures are prevalent in groundwater used for public water supply, but little is known about their potential health effects. As part of a large-scale ambient groundwater study, we evaluated chemical mixtures across multiple chemical classes, and included more chemical contaminants than in previous studies of mixtures in public-supply wells. We (1) assessed the occurrence of chemical mixtures in untreated source-water samples from public-supply wells, (2) determined the composition of the most frequently occurring mixtures, and (3) characterized the potential toxicity of mixtures using a new screening approach. The U.S. Geological Survey collected one untreated water sample from each of 383 public wells distributed across 35 states, and analyzed the samples for as many as 91 chemical contaminants. Concentrations of mixture components were compared to individual human-health benchmarks; the potential toxicity of mixtures was characterized by addition of benchmark-normalized component concentrations. Most samples (84%) contained mixtures of two or more contaminants, each at concentrations greater than one-tenth of individual benchmarks. The chemical mixtures that most frequently occurred and had the greatest potential toxicity primarily were composed of trace elements (including arsenic, strontium, or uranium), radon, or nitrate. Herbicides, disinfection by-products, and solvents were the most common organic contaminants in mixtures. The sum of benchmark-normalized concentrations was greater than 1 for 58% of samples, suggesting that there could be potential for mixtures toxicity in more than half of the public-well samples. Our findings can be used to help set priorities for groundwater monitoring and suggest future research directions for drinking-water treatment studies and for toxicity assessments of chemical mixtures in water resources.

Health-based screening levels to evaluate U.S. Geological Survey ground water quality data.

Federal and state drinking-water standards and guidelines do not exist for many contaminants analyzed by the U.S. Geological Survey's National Water-Quality Assessment Program, limiting the ability to evaluate the potential human-health relevance of water-quality findings. Health-based screening levels (HBSLs) were developed collaboratively to supplement existing drinking-water standards and guidelines as part of a six-year, multi-agency pilot study. The pilot study focused on ground water samples collected prior to treatment or blending in areas of New Jersey where groundwater is the principal source of drinking water. This article describes how HBSLs were developed and demonstrates the use of HBSLs as a tool for evaluating water-quality data in a human-health context. HBSLs were calculated using standard U.S. Environmental Protection Agency (USEPA) methodologies and toxicity information. New HBSLs were calculated for 12 of 32 contaminants without existing USEPA drinking-water standards or guidelines, increasing the number of unregulated contaminants (those without maximum contaminant levels (MCLs)) with human-health benchmarks. Concentrations of 70 of the 78 detected contaminants with human-health benchmarks were less than MCLs or HBSLs, including all 12 contaminants with new HBSLs, suggesting that most contaminant concentrations were not of potential human-health concern. HBSLs were applied to a state-scale groundwater data set in this study, but HBSLs also may be applied to regional and national evaluations of water-quality data. HBSLs fulfill a critical need for federal, state, and local agencies, water utilities, and others who seek tools for evaluating the occurrence of contaminants without drinking-water standards or guidelines.