Drinking Water Maximum Contaminant Level Research Articles

Oxidative stress and genotoxicity in 1,4-dioxane liver toxicity as evidenced in a mouse model of glutathione deficiency

1,4-Dioxane (DX) is a synthetic chemical used as a stabilizer for industrial solvents. Recent occurrence data show widespread and significant contamination of drinking water with DX in the US. DX is classified by the International Agency for Research on Cancer as a group 2B carcinogen with the primary target organ being the liver in animal studies. Despite the exposure and cancer risk, US EPA has not established a drinking water Maximum Contaminant Level (MCL) for DX and a wide range of drinking water targets have been established across the US and by Health Canada. The DX carcinogenic mechanism remains unknown; this information gap contributes to the varied approaches to its regulation. Our recent mice study indicated alterations in oxidative stress response accompanying DNA damage as an early change by high dose DX (5000 ppm) in drinking water. Herein, we report a follow-up study, in which we used glutathione (GSH)-deficient glutamate-cysteine ligase modifier subunit (Gclm)-null mice to investigate the role of redox homeostasis in DX-induced liver cytotoxicity and genotoxicity. Gclm-null and wild-type mice were exposed to DX for one week (1000 mg/kg/day by oral gavage) or three months (5000 ppm in drinking water). Subchronic exposure of high dose DX caused mild liver cytotoxicity. DX induced assorted molecular changes in the liver including: (i) a compensatory nuclear factor erythroid 2-related factor 2 (NRF2) anti-oxidative response at the early stage (one week), (ii) progressive CYP2E1 induction, (iii) development of oxidative stress, as evidenced by persistent NRF2 induction, oxidation of GSH pool, and accumulation of the lipid peroxidation by-product 4-hydroxynonenal, and (iv) elevations in oxidative DNA damage and DNA repair response. These DX-elicited changes were exaggerated in GSH-deficient mice. Collectively, the current study provides additional evidence linking redox dysregulation to DX liver genotoxicity, implying oxidative stress as a candidate mechanism of DX liver carcinogenicity.

Environmental impacts of reclaimed asphalt pavement on leaching of metals into groundwater

To investigate the environmental impacts of reclaimed asphalt pavement (RAP) while it was freshly processed (i.e. hot mixed asphalt or HMA) and after being subjected to weathering, three RAP materials, namely north-RAP, central-RAP, south-RAP, from three plants and one fresh HMA loose mix sample (Fresh-HMA) throughout New Jersey, USA underwent four different weathering processes including: Ultraviolet (UV) and precipitation weathering on unbounded RAP, UV and precipitation weathering on compacted RAP, weathering by heat and moisture cycles, and groundwater flow-through leaching. Batch experiments were conducted to mimic releasing of trace elements in weak acidic leachate from landfills. North-RAP and central-RAP released levels of Pb greater than the United States Environmental Protection Agency (USEPA) primary drinking water maximum contaminant level (MCL) of 15 µg/L. Novel two-column experiments (a RAP column followed by a soil column) were conducted to investigate the release of trace elements from RAP and the attenuation effect of soil on potential pollutants. The results of these experiments showed that pollutants released from RAPs such as Mn and Ni were largely attenuated in the soil. The results suggest that RAP can be used as an unbound material in environments except those acidic (i.e., pH < 5 as in mines with sulfur-containing minerals and landfills with acidic environment).

Bioremediation Strategies Aimed at Stimulating Chlorinated Solvent Dehalogenation Can Lead to Microbially-Mediated Toluene Biogenesis.

In situ bioremediation practices that include subsurface addition of fermentable electron donors to stimulate reductive dechlorination by anaerobic bacteria have become widely employed to combat chlorinated solvent contamination in groundwater. At a contaminated site located near Baton Rouge, Louisiana (USA), toluene was transiently observed in groundwater at concentrations that sometimes far exceeded the US drinking water maximum contaminant level (MCL) of 1 mg/L after a fermentable substrate (agricultural feed grade cane molasses) was injected into the subsurface with the intent of providing electron donors for reductive dechlorination. Here, we present data that demonstrate that indigenous microorganisms can biologically produce toluene by converting phenylacetic acid, phenylalanine, phenyllactate, and phenylpyruvate to toluene. When grown in defined medium with phenylacetic acid at concentrations ≤350 mg/L, the molar ratio between toluene accumulated and phenylacetic acid supplied was highly correlated ( R2 ≥ 0.96) with a toluene yield exceeding 0.9:1. Experiments conducted using 13C labeled compounds (phenylacetic acid-2-13C and l-phenylalanine-3-13C) resulted in production of toluene-α-13C, confirming that toluene was synthesized from these precursors by two independently developed enrichment cultures. Results presented here suggest that monitoring of aromatic hydrocarbons is warranted during enhanced bioremediation activities where electron donors are introduced to stimulate anaerobic biotransformation of chlorinated solvents.

Trends in Drinking Water Nitrate Violations Across the United States.

Drinking water maximum contaminant levels (MCL) are established by the U.S. EPA to protect human health. Since 1975, U.S. public water suppliers have reported MCL violations to the national Safe Drinking Water Information System (SDWIS). This study assessed temporal and geographic trends for violations of the 10 mg nitrate-N L-1 MCL in the conterminous U.S. We found that the proportion of systems in violation for nitrate significantly increased from 0.28% to 0.42% of all systems between 1994 and 2009 and then decreased to 0.32% by 2016. The number of people served by systems in violation decreased from 1.5 million in 1997 to 200 000 in 2014. Periodic spikes in people served were often driven by just one large system in violation. On average, Nebraska and Delaware had the greatest proportion of systems in violation (2.7% and 2.4%, respectively), while Ohio and California had the greatest average annual number of people served by systems in violation (278 374 and 139 149 people, respectively). Even though surface water systems that serve more people have been improving over time, groundwater systems in violation and average duration of violations are increasing, indicating persistent nitrate problems in drinking water.

Soil nitrate accumulation and leaching to groundwater during the entire vegetable phase following conversion from paddy rice

Large amounts of farmland have been converted from traditional cereal cropping to intensive vegetable cropping in China, creating environmental risks. Previous studies utilized several methods of estimating nitrate accumulation in soil and leaching to groundwater under intensive vegetable cultivation, such as comparing intensive cropping to non-intensive cropping, or investigating the seasonal dynamics of soil nitrates in the short term, such as 1 or 2 years. This study tried to utilize a different method, considering the effects of total nitrogen (N) input during the whole vegetable cropping phase (up to 9 years) after conversion from traditional cereal cropping on soil and groundwater. A large-scale investigation was performed in the study area. Vegetable, soil, and groundwater samples were collected from 22 fields. Results showed that soil nitrate was significantly correlated with total N input from chemical fertilizer during the whole vegetable cropping phase, and groundwater nitrate was significantly correlated with soil nitrate. Nitrate concentration in 45 % of wells exceeded the drinking water maximum contaminant level, 10 mg L−1. These results suggest that soil nitrate accumulation in the area resulted from long-term application of large amounts of N chemical fertilizer, and not from manure. Furthermore, high irrigation levels caused the accumulated nitrate in soil to leach into the groundwater, resulting in nitrate contamination of the groundwater.

Analysis of trace neptunium in the vicinity of underground nuclear tests at the Nevada National Security Site

A high sensitivity analytical method for 237Np analysis was developed and applied to groundwater samples from the Nevada National Security Site (NNSS) using short-lived 239Np as a yield tracer and HR magnetic sector ICP-MS. The 237Np concentrations in the vicinity of the Almendro, Cambric, Dalhart, Cheshire, and Chancellor underground nuclear test locations range from <4 × 10−4 to 2.6 mBq/L (6 × 10−17–4.2 × 10−13 mol/L). All measured 237Np concentrations are well below the drinking water maximum contaminant level for alpha emitters identified by the U.S. EPA (560 mBq/L). Nevertheless, 237Np remains an important indicator for radionuclide transport rates at the NNSS. Retardation factor ratios were used to compare the mobility of 237Np to that of other radionuclides. The results suggest that 237Np is less mobile than tritium and other non-sorbing radionuclides (14C, 36Cl, 99Tc and 129I) as expected. Surprisingly, 237Np and plutonium (239,240Pu) retardation factors are very similar. It is possible that Np(IV) exists under mildly reducing groundwater conditions and exhibits a retardation behavior that is comparable to Pu(IV). Independent of the underlying process, 237Np is migrating downgradient from NNSS underground nuclear tests at very low but measureable concentrations.

The impact of recent advances in research on arsenic cancer risk assessment

Scientific debate surrounds the regulatory approach for evaluating carcinogenic risk of arsenic compounds. The arsenic ambient water quality criteria (AWQC), based on the assumption of a linear mode of action for skin cancer risk, results in an allowable limit of 0.018ppb in ambient waters; the drinking water Maximum Contaminant Level (MCL) was determined using a similar linear approach. Integration of results from recent studies investigating arsenic’s mode of action provide the basis for a change in the approach for conducting an arsenic cancer risk assessment. Results provide support for a concentration demonstrating a dose-dependent transition in response from those representing adaptive changes to those that may be key events in the development of cancer endpoints. While additional information is needed, integration of current research results provides insight for a new quantitative cancer risk assessment methodology as an alternative toxicologically-based dose response (BBDR) cancer modeling. Integration of the new experimental results, combined with epidemiological evidence, support a dose-dependent transition concentration of approximately 0.1μM arsenic. Some uncertainties remain; additional information from chronic in vitro studies underway is needed. Results to date also provide initial insight into variability in population response at low arsenic exposures.

Analysis of BTEX groundwater concentrations from surface spills associated with hydraulic fracturing operations

Concerns have arisen among the public regarding the potential for drinking-water contamination from the migration of methane gas and hazardous chemicals associated with hydraulic fracturing and horizontal drilling. However, little attention has been paid to the potential for groundwater contamination resulting from surface spills from storage and production facilities at active well sites. We performed a search for publically available data regarding groundwater contamination from spills at U.S. drilling sites. The Colorado Oil and Gas Conservation Commission (COGCC) database was selected for further analysis because it was the most detailed. The majority of spills were in Weld County, Colorado, which has the highest density of wells that used hydraulic fracturing for completion, many producing both methane gas and crude oil. We analyzed publically available data reported by operators to the COGCC regarding surface spills that impacted groundwater. From July 2010 to July 2011, we noted 77 reported surface spills impacting the groundwater in Weld County, which resulted in surface spills associated with less than 0.5% of the active wells. The reported data included groundwater samples that were analyzed for benzene, toluene, ethylbenzene, and xylene (BTEX) components of crude oil. For groundwater samples taken both within the spill excavation area and on the first reported date of sampling, the BTEX measurements exceeded National Drinking Water maximum contaminant levels (MCLs) in 90, 30, 12, and 8% of the samples, respectively. However, actions taken to remediate the spills were effective at reducing BTEX levels, with at least 84% of the spills reportedly achieving remediation as of May 2012. Our analysis demonstrates that surface spills are an important route of potential groundwater contamination from hydraulic fracturing activities and should be a focus of programs to protect groundwater. Implications: While benzene can occur naturally in groundwater sources, spills and migration of chemicals used for hydraulic fracturing activities have recently been thought to be a main source of benzene contamination in groundwater. However, there is little scientific literature to support that claim. Therefore, we accessed a publically available database and tracked the number of reported surface spills with potential groundwater impact over a 1-year period. Although the number of surface spills was minimal, our analysis provides scientific evidence that benzene can contaminate groundwater sources following surface spills at active well sites. Supplemental Materials: Supplemental materials are available for this paper. Go to the publisher's online edition of the Journal of the Air & Waste Management Association for an illustration of the average concentration of each BTEX chemical from pooled sample measurements, and various metrics from all 77 spills analyzed in this study.

Adapting water treatment design and operations to the impacts of global climate change

It is anticipated that global climate change will adversely impact source water quality in many areas of the United States and will therefore, potentially, impact the design and operation of current and future water treatment systems. The USEPA has initiated an effort called the Water Resources Adaptation Program (WRAP) which is intended to develop tools and techniques that can assess the impact of global climate change on urban drinking water and wastewater infrastructure. A three step approach for assessing climate change impacts on water treatment operation and design is being persude in this effort. The first step is the stochastic characterization of source water quality, the second step is the application of the USEPA Water Treatment Plant model and the third step is the application of cost algorithms to provide a metric that can be used to assess the coat impact of climate change. A model has been validated using data collected from Cincinnati’s Richard Miller Water Treatment Plant for the USEPA Information Collection Rule (ICR) database. An analysis of the water treatment processes in response to assumed perturbations in raw water quality identified TOC, pH, and bromide as the three most important parameters affecting performance of the Miller WTP. The Miller Plant was simulated using the EPA WTP model to examine the impact of these parameters on selected regulated water quality parameters. Uncertainty in influent water quality was analyzed to estimate the risk of violating drinking water maximum contaminant levels (MCLs).Water quality changes in the Ohio River were projected for 2050 using Monte Carlo simulation and the WTP model was used to evaluate the effects of water quality changes on design and operation. Results indicate that the existing Miller WTP might not meet Safe Drinking Water Act MCL requirements for certain extreme future conditions. However, it was found that the risk of MCL violations under future conditions could be controlled by enhancing existing WTP design and operation or by process retrofitting and modification.

Highly selectively monitoring heavy and transition metal ions by a fluorescent sensor based on dipeptide

Fluorescent sensor (DMH) based on dipeptide was efficiently synthesized in solid phase synthesis. The dipeptide sensor shows sensitive response to Ag(I), Hg(II), and Cu(II) among 14 metal ions in 100% aqueous solution. The fluorescent sensor differentiates three heavy metal ions by response type; turn on response to Ag(I), ratiometric response to Hg(II), and turn off detection of Cu(II). The detection limits of the sensor for Ag(I) and Cu(II) were much lower than the EPA's drinking water maximum contaminant levels (MCL). Specially, DMH penetrated live cells and detected intracellular Ag+ by turn on response. We described the fluorescent change, binding affinity, detection limit for the metal ions. The study of a heavy metal-responsive sensor based on dipeptide demonstrates its potential utility in the environment field.

Enhanced Particle Capture through Aluminum Hydroxide Addition to Pores in Sand Media

In this study, precipitation of Al(OH)3(am) was used to modify a sand filter medium by fluidized-bed pretreatment. A mixture of alum, sodium hydroxide, and tap water was applied to the filter bed in the last stage of the backwash cycle. The placement of Al(OH)3(am) in the filter pores was evaluated for both alum-treated raw water (contact filtration) and untreated raw water. The filter pretreated with Al(OH)3(am) achieved better than 99.98% removal of an untreated clay suspension, with a filter effluent turbidity below the detection limit of 0.01 NTU. Al(OH)3(am)-pretreated filters that were challenged with clay and humic acid achieved ≥99.8% turbidity removal efficiency for 14 h of operation in the contact filtration mode. Pretreatment with Al(OH)3(am) also enhanced turbidity removal efficiency (up to 99.8%) when the filter was challenged with clay and humic acid, even when the raw water was not coagulated. The aluminum concentration in the filter effluent of an Al(OH)3(am)-pretreated filter was below the EPA secondary drinking water maximum contaminant level (200 μg/L for aluminum) when the raw water pH was between 6 and 7; the pretreated filter had the best performance at pH 6.

Ratiometric and turn-on monitoring for heavy and transition metal ions in aqueous solution with a fluorescent peptide sensor

A novel fluorescent peptide sensor containing tryptophan (donor) and dansyl fluorophore (acceptor) was synthesized for monitoring heavy and transition metal (HTM) ions on the basis of metal ion binding motif (Cys-X-X-X-Cys). The peptide probe successfully exhibited a turn on and ratiometric response for several heavy metal ions such as Hg 2+, Cd 2+, Pb 2+, Zn 2+, and Ag + in aqueous solution. The enhancements of emission intensity were achieved in the presence of the HTM ions by fluorescent resonance energy transfer (FRET) and chelation enhanced fluorescence (CHEF) effects. The detection limits of the sensor for Cd 2+, Pb 2+, Zn 2+, and Ag + were lower than the EPA's drinking water maximum contaminant levels (MCL). We described the fluorescent enhancement, binding affinity, and detection limit of the peptide probe for HTM ions.

Uncertainty and Trend Analysis—Radium in Ground Water and Drinking Water

AbstractRadium activity measurements in water samples are encumbered by relatively large error bars, including for activity values near the regulatory drinking water maximum contaminant level of 5 pCi/L. The large error bars create uncertainty in the evaluation of temporal trends. This uncertainty is often the object of debate and disagreement in regulatory determinations, the design of remedial actions, and/or in litigation. The Mann‐Kendall nonparametric test is perhaps the most commonly used test for trend evaluation in environmental sciences. The test is simple and easy to apply by nonstatisticians and is recommended in several regulations and guidance documents. As typically applied, the Mann‐Kendall test does not consider the uncertainty related to error bars for individual data values. Ignoring this uncertainty can result in misleading conclusions on the presence or absence of trends. In this article, a procedure for trend analysis that accounts for error bars is described. For each data series analyzed, the procedure creates 1000 new data series by randomly assigning values that fall within the error bar around each data point. Trend analysis is then performed on the randomly created data series. The approach is applied to the evaluation of a radium data base containing analytical results from 137 locations (407 water samples) in Escambia County, Florida. The evaluation of the radium data base using the Mann‐Kendall test without accounting for the uncertainty reveals 10 significant trends at the 90% confidence level. Only two of these trends are supported by the data when the uncertainty from analytical error is accounted for.

Dietary Nitrate: Where Is the Risk?

Links between nitrate and health risk have been studied for > 50 years, resulting in a large body of research. As two book-length reviews of the issue (Addiscott 2005; L’hirondel and L’hirondel 2001) tried to show, none of the health claims against dietary nitrate have been substantiated. If there was not already an established maximum contaminant level (MCL) of 10 ppm for nitrate in drinking water in the United States [U.S. Environmental Protection Agency (EPA) 1991; World Health Organization (WHO) 1958], it would be extremely difficult, if not impossible, to justify one based on the extensive evidence gathered to date. The conclusion of Ward et al. (2005) in their article “Drinking-water Nitrate and Health—Recent Findings and Research Needs” (Ward et al. 2005) is somewhat different. Although they were not able to reasonably conclude that dietary nitrates elevate a single health risk, the authors insisted that possible risks “must be more thoroughly explored before changes to nitrate water quality standards are considered.” Why? Examining methemoglobinemia, cancer, reproductive, and other potential risks, Ward et al. (2005) presented the extensive body of research demonstrating only very slight negative, very slight positive, or no correlation (and usually all three). This is exactly what one would expect if there were no actual correlation. Yet instead of reexamining the MCL, Ward et al. recommended further searching for a justification of the 50-year-old regulation (WHO 1958). We would like to draw attention to a few key additional points. First, although the U.S. MCL for drinking water nitrate is 45 mg/L (U.S. EPA 1991), nitrate concentrations in vegetables may be > 50 times higher; vegetables often contain > 2,000–3,000 mg nitrate per kilogram. Yet nitrate-rich vegetables are good for health. Ward et al. (2005) seem aware of this point, as they stated that “intake of dietary nitrate is less likely to increase nitrosation, because of the presence of nitrosation inhibitors in vegetables.” However, they forgot the metabolism of nitrate in humans. Salivary nitrate (not dietary nitrate) is reduced to nitrite in the mouth. In fact, plasma nitrate is extracted by the salivary glands and secreted at high concentrations in saliva; in adults and children > 6 months of age, a fraction of this salivary nitrate is converted in the mouth to nitrite. Nitrite levels in saliva are maximal 20–60 min after nitrate intake. Also, because of the acidity of the gastric juice (Dang Vu et al. 1994), nitrite concentrations in gastric juice are extremely low; 15-fold to several hundredfold less than that of salivary nitrite. Regarding the cancer risks of nitrate, if drinking water with 10–20 ppm nitrate-nitrogen (nitrate-N) were toxic, vegetables (with their comparatively high nitrate levels) would likely also be toxic, in spite of the presence of reputed nitrosation inhibitors. Second, during the last 12 years, several works have indicated beneficial effects of nitrate due to its conversion in the body into nitrite (NO2−), nitric oxide, and diverse reactive compounds. The studies carried out since 1994 by the teams of Benjamin and Duncan are worth noting (Benjamin 2000; McKnight et al. 1999). Also, a meeting was held in Bethesda, Maryland, 8–9 September 2005 under the aegis of the National Institutes of Health and devoted to the “Role of Nitrite in Physiology, Pathophysiology and Therapeutics” (Gladwin et al. 2006). The current MCL for nitrates of the United States, Europe, and World Health Organization are all based on the flawed American Public Health Association survey from 1948 in which “special emphasis was placed on restricting the data to those [infantile methemoglobinemia cases] definitely associated with nitrate-contaminated water” (Walton 1951). This requirement ensured the inclusion of any suspected (although not proven) case of infantile methemoglobinemia where nitrate levels were even slightly above background (~2–5 ppm). A mere five suspected cases in that survey were reported at 10–20 ppm nitrate-N , and in some cases the water was tested months after the cyanotic episode. The societal costs of complying with the current MCL are growing, especially in rural communities least economically capable of shouldering the high costs per person of nitrate-ion removal. This economic burden imposed with questionable medical basis seems to have completely escaped Ward et al. (2005). Although we are not against continued study to ensure adequate protection of public health, it seems to us that more than enough evidence has been gathered to confidently say that nitrates are not the threat they were once thought to be. Raising the drinking water MCL for nitrates to 20 ppm nitrate-N to reflect the extensive body of research would relieve many small rural communities of a significant economic burden without adding appreciably to any known health risks.

Compositions of first flush and composite storm water runoff in small urban and rural watersheds, north-central Texas

The objective of this study was to evaluate chemical compositions of first flush and composite storm water runoff in four small, mixed land use watersheds in north-central Texas. The watersheds range from urban to rural, all discharging to a local lake providing aquatic habitat, recreation, flood control and drinking water. Automated devices near watershed outlets collected samples from seven storm events, from April 2001 to September 2003. Samples were analyzed for suspended solids, pesticides (diazinon, triazine and chlorpyrifos), nutrients (nitrogen and phosphorus), fecal coliforms and metals. Observed concentrations of most parameters were low relative to drinking water maximum contaminant levels (MCLs) and aquatic life criteria. Fecal coliforms and lead were detected in most samples, with highest lead concentrations in the most developed watershed, likely influenced by building material and automobile traffic. Pesticide concentrations were higher in an initial spring storm event following applications to control weeds and insects. Typical of urban runoff, most ammonia and phosphorus observations exceeded freshwater criteria for streams draining to lakes. Treated wastewater effluent accounted for the highest nitrogen and phosphorus observations. For most constituents, composite concentrations exceeded first flush concentrations, though differences were significant only for fecal coliforms.

Arsenic concentration variability in public water system wells in Minnesota, USA

There is significant random and systematic variability in As concentrations in numerous public water system wells in Minnesota. Arsenic concentrations fluctuate above and below the USA’s As drinking water Maximum Contaminant Level (MCL) of 10 μg/L. The average As concentration is commonly within one standard deviation of the MCL. Results of intensive sampling conducted over the course of approximately 1 year at 3 public water system wells is consistent with the analysis of historic As measurements. In some cases, significant As concentration variability was noted over a short period of time. In these wells, the As concentration was less than 10 μg/L shortly after pumping started, but the As concentration increased over time to a level exceeding 10 μg/L. In these wells, the As concentration decreased to below 10 μg/L again when pumping was briefly restarted after being stopped for 4 h. The As concentration variability is likely due to As adsorption reactions between Fe oxides in the well borehole and in the aquifer near the well borehole during periods when the pump is not in operation. When it is crucial to accurately determine true average As concentrations – for example, at one of the many wells that fluctuate above and below the regulatory As limit of 10 μg/L – it is worthwhile collecting samples frequently during pumping to more accurately determine the average As concentration. Determining a reliable average depends on the standard deviation (SD) of the measurements, with more measurements required if the SD is larger.

2004 National Atrazine Occurrence Monitoring Program Using the Abraxis ELISA Method

The goal of this project was to gain a better understanding of atrazine occurrence in the United States by surveying drinking water utilities' sources and finished water for atrazine on a weekly basis for seven months. Atrazine is a contaminant of interest because the United States Environmental Protection Agency (USEPA) has found short-term atrazine exposure above the drinking water maximum contaminant level (MCL) to potentially cause heart, lung, and kidney congestion, low blood pressure, muscle spasms, weight loss, and damage to the adrenal glands. Long-term exposure to atrazine concentrations above the drinking water MCL has been linked to weight loss, cardiovascular damage, retinal and muscle degeneration, and cancer. This survey effort improved upon previously conducted atrazine surveys through intensive, high frequency sampling (participating plants sampled their raw and finished water on a weekly basis for approximately seven months). Such an intensive effort allowed the authors to gain a better understanding of short-term atrazine occurrence and its variability in drinking water sources. This information can benefit the drinking water industry by facilitating (1) better atrazine occurrence management (i.e., awareness when plants may be more susceptible to atrazine), (2) more efficient atrazine control (e.g., effective treatment alternatives and more effective response to atrazine occurrence), and (3) treatment cost reduction (e.g., efficient atrazine control can result in substantial cost savings). Forty-seven drinking watertreatment plants located primarily in the Midwestern United States participated in the survey and sampled their raw and finished water on a weekly basis from March through October. Samples were analyzed using the Abraxis enzyme-linked immunosorbent assay (ELISA) test kit. Confirmation samples for quality assurance/quality control (QA/QC) purposes were analyzed using solid-phase extraction (SPE) followed by gas chromatography mass spectrophotometry (GC/MS). Several important conclusions can be drawn from this study including (1) surface waters were confirmed to be more vulnerable to atrazine contamination than groundwater sources, (2) peak atrazine concentrations corresponded well to precipitation/runoff events, and (3) atrazine occurrence tended to be uniform geographically when compared by river drainage basins. In addition, this project confirmed that the Abraxis atrazine ELISA test kit tended to have a positive bias (i.e., the measured ELISA concentration was higher than the actual concentration) in most measured samples. Finished samples tended to have more of a positive bias than raw water samples. Therefore, this bias may limit the effectiveness for ELISA for regulatory monitoring. There are many other applications for ELISA, however, including frequent monitoring for early detections of atrazine concentration changes that might trigger conventional analysis by GC/MS or be used for activated carbon dosing or other treatment operating controls.

Mobilization of Arsenite by Competitive Interaction with Silicic Acid

Due to the acute toxicity of As, mobilization of even a small fraction of As into surface and ground waters used as a source for drinking water represents a substantial risk to human health. Here we evaluate the mobilization of arsenite [As(III)] from the Fe‐(hydr)oxide mineral goethite (α‐FeOOH) through competitive displacement by silicic acid, a naturally occurring and ubiquitous inorganic ligand. The adsorption behaviors of silicic acid and As(III) on goethite were investigated at environmentally relevant pH (3–11). Single ion adsorption and zeta‐potential data were collected at silica concentrations characteristic of natural waters (3–30 mg L−1) and initial solution As(III) concentrations representative of high levels of contamination (3.75–7.5 mg L−1). Competitive adsorption scenarios with either Si or As(III) sorbed first to the goethite surface, followed by equilibration with the other sorbate, were also examined. No competitive displacement of either oxyanion was observed at total sorbate concentrations less than reactive surface site density, regardless of pH or addition scenario. However, at total sorbate concentrations greater than reactive surface site density, As(III) adsorption was reduced by 10 to 15% over the entire pH range regardless of addition scenario, resulting in aqueous concentrations well in excess of current (10 μg L−1) drinking water maximum contaminant levels. Surface complexation modeling of single ion adsorption and zeta‐potential data using the Charge Distribution Multisite Surface Complexation (CD‐MUSIC) model was used to calculate an appropriate set of surface adsorption equilibrium constants for As(III) and silicic acid adsorption, which was used to describe the competitive adsorption scenarios. Comparison of competitive adsorption data and CD‐MUSIC model predictions, at total sorbate concentration greater than reactive surface site density of goethite, suggest that silica is competitively displaced by As(III).

Environmental implications of low nitrogen use efficiency in excessively fertilized hot pepper (Capsicum frutescens L.) cropping systems

Abstract A randomized-block greenhouse plot experiment was conducted on N utilization efficiency and N losses in intensive hot pepper ( Capsicum frutescens L.) production systems typical of commercial practice in Shouguang, an important vegetable production area in Shandong province, northeast China. Crop yield and N utilization, soil mineral N dynamics and potential nitrate leaching losses were studied in control plots receiving no N fertilizer or organic manure and in experimental plots receiving 0, 600, 1200 or 1800 kg urea-N ha −1 plus a basal dressing of 15 t ha −1 air-dried poultry manure supplying 178 kg N ha −1 . Ammonia volatilization from the soil surface was monitored. A microplot was established in each of the plots receiving 1200 kg urea-N ha −1 (the local average commercial fertilizer N application rate), the urea applied to the microplot was labelled with 10 atom % 15 N tracer and residual soil 15 N and 15 N in harvested plant parts were determined. Previous intensive cropping led to a very high residual soil mineral N content (1117 kg N ha −1 ) before the experiment began and control plots gave a satisfactory mean fruit yield of 5.7 t DM ha −1 with no significant yield response to applied fertilizer and poultry manure. Only 10% of applied fertilizer N was recovered in the aboveground parts of the crop and about 52% was lost from the soil–plant system. Substantial nitrate leaching losses occurred using the two highest fertilizer N application rates but there was little NH 3 volatilization from the soil surface. In a survey of 94 wells in Shouguang, the NO 3 − –N concentrations in water used for drinking and irrigation were determined. Almost half of 94 local wells surveyed had NO 3 − –N concentrations above the USEPA public drinking water maximum contaminant level of 10 mg L −1 . The data indicate that N inputs for intensively managed vegetable crops in northeast China should be reduced urgently to maintain crop yields while avoiding serious long-term environmental damage.

Correction to “Benefit‐cost estimation for alternative drinking water maximum contaminant levels” by Patrick L. Gurian, Mitchell J. Small, John R. Lockwood, and Mark J. Schervish

Correction to “Benefit‐cost estimation for alternative drinking water maximum contaminant levels” by Patrick L. Gurian, Mitchell J. Small, John R. Lockwood, and Mark J. Schervish