Maximum Contaminant Level Research Articles (Page 1)

Field demonstration of in situ stabilization (ISS) of per- and polyfluoroalkyl substances in soil with remBind®.

Short communication: simultaneous removal of co-occurring contaminants reduces drinking water-attributed cancer risk: A United States case study.

Small rural water utilities in the Appalachia region of the US often experience extreme water loss while struggling to maintain water quality compliance. This study quantifies the impact of reducing water loss on distribution system water quality in Martin County, Kentucky. Hydraulic and water quality models were developed, calibrated, and validated using EPANET for chlorine residuals and KYPIPE for trihalomethane (TTHM) formation. The models evaluated water loss reduction scenarios ranging from the current 70% to the industry target of 15%. Results showed that lowering water loss increased residence times, causing chlorine residual declines of 22–68%, with one site falling to the 0.2 mg/L threshold. TTHM concentrations increased by 12–18% in winter–spring and 26–44% in summer–fall, with two sites exceeding the individual 0.080 mg/L maximum contaminant level. These novel findings indicate that reducing water loss can unintentionally degrade water quality, underscoring the need for integrated planning. Recommended mitigation strategies include seasonal operational adjustments, water source and TTHM precursor management, optimized tank management, targeted flushing, and phased infrastructure upgrades. The modeling framework developed offers potential for broader application in other rural systems facing similar challenges.

In this research project, supported by the Russian Ministry of Agriculture, we set out to compare the effectiveness of various sterilization regimens for blackcurrant lateral buds during introduction into in vitro sterile culture. The study was conducted using the facilities of the Agricultural Biotechnology Training and Production Laboratory of the Kostroma State Agricultural Academy (Russia). Lateral buds were harvested from lignified shoots of the Bryanskiy Agat, Vera, and Debryansk currant cultivars, obtained at the Federal Scientific Center of Horticulture in 2023. All varieties exhibited sufficiently high morphogenetic potential for in vitro cultivation. The determined optimal sterilizing agent was a 0.05 % solution of chlorhexidine gluconate (CHG) with a 10-min exposure. Meristem viability, depending on the pomological cultivar, ranged from 53.3 % to 66.7 %. The use of a 5.0 % sodium hypochlorite (SH) solution for exposures of 5, 10, and 15 min increased the viability of meristems from 53.3 to 73.3 %. The maximum contamination level was achieved with the combined use of both sterilizing agents (SH and CHG) under a 5-min exposure, ranging 50.0–70.0 %. The maximum number of morphogenically active meristems was obtained after sterilization with a 0.05 % solution (CHG) following an exposure of 10 and 15 min.

Globally, groundwater is a critical source of freshwater that supports drinking water, agriculture, and industry. Its protection is vital for long-term water safety and public health. In Lebanon, groundwater provides nearly half of the nation’s water supply; however, it faces significant challenges from unregulated extraction, poor infrastructure, and widespread contamination. The city of Tripoli is particularly vulnerable, where defective underground fuel storage tanks, unmanaged waste, and unrestricted well usage have led to alarming levels of toxins such as benzene, toluene, and xylene (BTX). Such conditions pose serious risks to both water sustainability and human health, emphasizing the critical need for regular monitoring and effective regulation. This study aims to investigate the presence of BTX in the groundwater of Tripoli, Lebanon, and to quantify their compound concentrations using gas chromatography–mass spectrometry. A total of 24 water samples were collected on multiple occasions from private wells during the winter, spring, and summer seasons and subsequently analyzed. Results indicated that BTX concentrations in many of the sampled wells, across most seasons, exceeded the maximum contaminant levels established by the United States Environmental Protection Agency for safe drinking water (0.005 ppm for benzene, 1 ppm for toluene, and 10 ppm for xylene), rendering the water unsuitable for drinking. The study revealed seasonal variations in BTX concentrations, with higher levels detected in spring and summer, and lower levels in winter, likely due to seasonal dilution effects from rainfall and infiltration. Among the BTX compounds, xylene exhibited the highest concentrations, followed by toluene, with benzene present at the lowest levels. The detection of BTX in the sampled groundwater clearly indicates pollution. Consequently, remediation measures are necessary to mitigate long-term health risks associated with these pollutants, and continuous monitoring of BTX levels is strongly recommended to effectively assess and manage groundwater pollution.

Characteristics of aqueous film forming foam (AFFF) sites impacted with per- and polyfluoroalkyl substances (PFAS): A 37-site study.

Abstract Nitrate contamination in shallow drinking water wells is an urgent and persistent concern for agricultural regions and disadvantaged communities worldwide. As viable options for the large‐scale removal of nitrates from groundwater remain elusive, greater emphasis has been placed on stakeholder‐based integrative approaches, yet few have been developed, and fewer evaluated for their effectiveness. The Central Valley in California is one of the most important intensive agricultural regions globally, where such a stakeholder‐based process (CV‐SALTS) has been initiated, and which is poised to serve as a model for controlling nitrate contamination elsewhere. Based on the Groundwater Ambient Monitoring and Assessment Program data for the 2000–2023 period, we develop a new data sufficiency metric, quantify the uncertainties associated with establishing nitrate concentrations and their changes in space and time, the impact of Confined Animal Feeding Operations (CAFOs), seasonal variability and drought on nitrate levels, and how they are addressed through CV‐SALTS policies. Our findings suggest that there remain substantial uncertainties associated with where nitrate concentrations are above safe levels, but that they predominantly intersect with environmental justice communities. Severe drought conditions and the proximity of CAFOS significantly elevated nitrate concentrations, but had previously not been sufficiently monitored or considered. A new data sufficiency metric based on nitrate variability, maximum contaminant level exceedance, and observation density can support stakeholder processes in prioritizing areas for additional monitoring and risk reduction. Our findings form the basis for recommended policy changes that are transferable to other regions.

Exposure to low levels of hexavalent chromium in drinking water alters diet-induced steatotic liver disease in male rats.

We report a machine learning (ML)-assisted liquid crystal (LC) droplet array platform for the detection of per- and polyfluoroalkyl substances (PFAS) in water. Our approach uses an autoencoder network to process thousands of images obtained from arrays of microscale droplets of thermotropic LCs. The latent space obtained using the autoencoder contains significant information that enables sensitive and selective detection of two amphiphilic PFAS [perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS)] at concentrations as low as parts-per-trillion (ppt) in ultrapure water, municipal tap water, and simulated river water containing dissolved organic matter. Despite the absence of visually discernible changes in the optical outputs of LC arrays at low PFAS concentrations, this approach accurately predicts their presence, even in water containing interfering molecules. We also demonstrate the use of transfer learning to differentiate between PFOA, PFOS, and PFOA/PFOS mixtures, showcasing the potential for practical environmental monitoring. This platform permits identification of PFOA and PFOS below the maximum contaminant levels (4 ppt) established by the U.S. Environmental Protection Agency. Our approach is compatible with automated printing, treatment, and high-throughput optical and ML analysis and could provide a basis for the development of low-cost sensors to monitor PFAS and other amphiphilic contaminants in real-world water samples.

1,2,3-Trichloropropane (1,2,3-TCP) is a suspected human carcinogen and a persistent emerging contaminant in groundwater and drinking water. 1,2,3-TCP was historically used as a solvent for cleaning and maintenance, paint and varnish removal, and degreasing, but its sources also include chemical manufacturing processes and application of soil fumigants. The California Department of Public Health (CDPH) has established a state maximum contaminant level (MCL) of 0.005µg/L for 1,2,3-TCP in drinking water and a public health goal (PHG) of only 0.0007µg/L. The primary research question addressed herein was whether aerobic or anaerobic cultures can potentially be applied for treatment of 1,2,3-TCP, and whether bacteria are capable of biodegrading 1,2,3-TCP to below the California MCL. During this study, we identified cultures capable of biodegrading 1,2,3-TCP via reductive dehalogenation as well as through aerobic cometabolic processes. Follow-on studies with organisms capable of aerobically degrading 1,2,3-TCP included kinetic modeling and assessment of concentrations of 1,2,3-TCP achievable via biodegradation. 1,2-Dichloropropane (1,2-DCP) is sometimes found co-mingled with 1,2,3-TCP, so studies also were conducted to quantify rates of 1,2-DCP biodegradation alone and when present together with 1,2,3-TCP. The dehalogenating consortium CPD-2, which was isolated from sewage sludge and includes Dehalococcoides, Dehalobacter and Dehalobium spp., biodegraded both 1,2,3-TCP and 1,2-DCP. Anaerobic 1,2,3-TCP degradation resulted in a transient production of 1,2-DCP followed by 1-chloropropane (1-CP), which accumulated nearly stoichiometrically and then slowly degraded, indicating complete dechlorination of 1,2,3-TCP by this mixed culture. Two different cometabolic pure cultures, Rhodococcus ruber ENV425 and Rhodococcus aetherivorans ENV493 degraded 1,2,3-TCP after growth on propane or isobutane. Importantly, both bacteria were capable of degrading 20µg/L of 1,2,3-TCP to < 0.005µg/L after growth on isobutane. Experiments conducted with ENV425 and ENV493 to quantify relevant kinetic parameters after growth on isobutane suggested that ENV425 facilitated more rapid 1,2,3-TCP degradation than ENV493. Both strains were observed to degrade 1,2-DCP much faster than 1,2,3-TCP when present individually or in mixtures. The data from this study suggest that cometabolic treatment of 1,2,3-TCP, or mixtures of 1,2-DCP and 1,2,3-TCP, is feasible and that relevant regulatory concentrations are achievable using this process. Similarly, anaerobic treatment may be possible at locations with higher concentrations or where 1,2,3-TCP occurs with other chlorinated solvents.

High absorbance of nitrate leads to surprising effects on hydroxyl radical formation during 222 nm UV treatment.

Aims: This study was conducted to evaluate the impact of coal mining activities on surface water quality around coal mining sites in Ankpa Local Government Area (LGA), Kogi State, Nigeria in June, 2024. Methodology: A total of 36 water samples (12 samples each from upstream, midstream and downstream) were collected using 1-liter plastic container, preserved in ice-chest and transported to the laboratory for analysis. Heavy metals (Aluminum – Al, Iron - Fe, Chromium - Cr, and Zinc - Zn) and microbial analysis were performed using standard laboratory procedures. Data collected was analyzed for descriptive statistics using GENSTAT Discovery Software. Results: Among the heavy metals analyzed, Al concentrations were within the lowest range (0.83 to 0.86 mg/L) but higher than secondary maximum contaminant level (SMCL). Conversely, the concentration of Fe across all sites were highest (6.55 to 6.61 mg/L). The chromium levels were within 1.85 to 1.95 mg/L which is higher than the WHO provisional guideline value of total chromium. Zinc levels across the sites were relatively stable (3.93 to 3.96 mg/L). Higher deposition of coliform were at the downstream while bacteria growth was only observed in the midstream. Salmonella spp, Shigella spp, and Enterobacter spp were recorded in all the sampling sites. At the upstream, the coliform count was 6.0 x 10⁵ CFU/ml, which was the lowest. At midstream, the coliform count was 4.0 x 10⁶ CFU/ml while downstream had values of 5.6 x 10⁶ CFU/ml. There was no bacterial growth at the upstream and downstream using nutrient agar and MacConkey agar. Conclusion: The findings underscore the need for regular water quality monitoring, environmental remediation efforts, and enhanced community engagement to mitigate the environmental and public health risks posed by coal mining activities in coal mining sites in Ankpa LGA, Kogi State, Nigeria.

This study investigated the levels and potential toxicity of polyaromatic hydrocarbons (PAHs) in underground water near a gas station within the Okinni locality, Osun State, Nigeria. Water samples from six locations were analysed with gas chromatography–mass spectrometry. Low-molecular-weight PAHs, naphthalene, acenaphthene and acenaphthylene were undetected. However, 3-ring PAHs (fluorene, phenanthrene and anthracene) were found across most sites, exceedingthe maximum contamination level of 0.0002 µg/mL set by the United States Environmental Protection Agency and the World Health Organization (0-0.005 µg/mL). High molecular weight PAHs also surpassed the Canadian Council of Ministers of the Environment's water quality guideline threshold (1.5 × 10−5 – 5.8 × 10−3 µg/mL). The health risk revealed average toxicity values ranging from 2.6 × 10−4 to 1.8 × 10−3 for adults and 6.06 × 10−4 to 4.18 × 10−3 for children, indicating potential carcinogenic health risks. Given that the values exceeded acceptable limits (1.0 × 10-6). There is an urgent need for attention from relevant authorities to protect public health. The risks would be largely subject to ingestion frequency, duration, and individual vulnerability, emphasizing the need for prompt action to safeguard the health of the populace. The findings suggest a possible unacceptable health risk from exposure to PAHs.

Chronic low-level uranium (U) exposure through drinking water is a public health risk in the United States. Nearly two-thirds of community water systems, serving 320 million people, have detectable U levels, with 2% exceeding the EPA's maximum contaminant level of 30 μg/L. Ingested U accumulates in kidneys and is nephrotoxic at high levels. Uranium binds to proximal tubule cells, causing injury and interfering with kidney function. Epidemiological studies suggest that even low-level (<30 μg/L) of U exposure could damage kidneys. Current biomarkers, like urinary U levels, fail to indicate tissue-specific concentrations and metabolic interactions in kidneys. Fractionation of 238U/235U may potentially serve as a biomarker for the metabolic interaction of U with organs. Our experiments with mice showed changes in U isotopic composition (238U/235U expressed as δ238U) in organs after administering 50 mg/L U via drinking water for 2, 7, and 14 days. We found 235U enrichment in kidneys and bones, the target organs, while urine was enriched in 238U. Our results provide evidence of isotopic fractionation resulting from U accumulation in kidneys. Urinary U isotopic composition may, thus, provide a sensitive, noninvasive measurement of renal U bioaccumulation that could aid early detection of nephrotoxicity and prevention of irreversible kidney damage.

Weathered uranium (U) rich sediment and mining and production activity could contribute to elevated concentrations of U in surface waters. In the San Juan River watershed in the Four Corners region of the United States, U-rich deposits are common in many geologic formations and, historically, U mining in the region was prevalent. The goal of this work was to identify potential sources of U to the San Juan River from ephemeral and perennial tributaries during monsoonal storms. Data show that most of the tributaries in the watershed have elevated U concentrations in surface-water samples, greater than the U.S. Environmental Protection Agency maximum contaminant level of 30 micrograms per liter (µg/L) for U. Although parts of the watershed have been mined for U, not all elevated concentrations were found in regions that drained from mined areas. The two highest total U concentrations in surface water in the region were from the Chinle Creek near Bluff watershed (362 µg/L) and Gallegos Canyon watershed (206 µg/L), the former having many U mines and the latter with none. The lack of an obvious effect from mining activity and U in the local geologic formations to the concentrations of U in the surface water suggests that another source could be the primary contributor of U to the San Juan River watershed.

Heavy metal contamination in soils poses serious threats to environmental and human health due to metal persistence and toxicity. In Senegal, particularly in the Niakhene region, soil pollution may result from agricultural practices, atmospheric deposition, and past land use. This study aims to determine the concentrations of heavy metals: Nickel (Ni), Arsenic (As), Zinc (Zn), Cesium (Cs), Palladium (Pd), and Tin (Sn) in agricultural soils and to assess their potential environmental and health risks. A total of 47 soil samples were collected at two depths (0–20 cm and 20–40 cm) and analyzed using energy-dispersive X-ray fluorescence (ED-XRF) spectroscopy, a non-destructive and accurate technique. The analysis revealed varying concentrations of heavy metals, with Zn ranging from 0.00 to 29.49 mg/kg, Ni from 20.02 to 47.30 mg/kg, and Arsenic (As) from 0.00 to 5.67 mg/kg. The study found that Cd, Cu, Pb, and Hg were not detectable in the samples. Comparative analysis with EU threshold limit values (TLVs) indicated that concentrations of most metals were within safe limits, although some samples approached the maximum contaminant levels (MCLs) for Nickel and Arsenic. The findings highlight the need for ongoing monitoring and potential remediation to manage soil contamination and protect environmental and human health. These findings highlight the importance of continuous soil monitoring in the region and support the implementation of appropriate soil management and pollution mitigation strategies to safeguard both environmental quality and public health.

Over 90% of the US population relies on community water supplies (CWS), which generally use chlorine for disinfection. Trihalomethanes are regulated disinfection byproducts associated with bladder cancer and adverse birth outcomes. Animal studies report trihalomethanes, especially brominated compounds, may damage kidney function, but epidemiologic research is limited. To evaluate long-term exposure to trihalomethanes in residential CWS and its association with chronic kidney disease (CKD) risk. The California Teachers Study (CTS) is an ongoing prospective cohort of female teachers and administrators enrolled between 1995 and 1996 with data linked to mortality and health care records. This cohort study analyzed CTS data from January 1, 2005, once CKD diagnostic coding was adopted, through December 31, 2018. Statistical analysis was conducted from July 2023 to December 2024. Residence time-weighted mean concentrations of 4 trihalomethanes, including 3 brominated trihalomethanes and chloroform, were calculated using annual measurements from CWS serving participants' homes from 1995 to 2005. Uranium and arsenic (potentially nephrotoxic metals, previously evaluated in the cohort) from CWS were included as part of a g-computation mixture analysis. Cases of moderate (stage 3) to end-stage CKD were identified with diagnostic codes or dialysis-related procedures. Mixed-effects multivariable-adjusted Cox proportional hazards regression models were used to estimate hazard ratios (HRs) and 95% CIs for CKD by exposure to trihalomethane levels (US maximum contaminant level of 80 μg/L). The study sample included 89 320 female participants (median age, 50 years [IQR, 43-61 years]) with 6242 CKD cases. Median concentrations were 5.5 μg/L (IQR, 0.5-24.1 μg/L; 95th percentile, 57.8 μg/L) for total trihalomethanes and 2.7 μg/L (IQR, 0.7-11.3 μg/L; 95th percentile, 30.0 μg/L) for brominated trihalomethanes. In flexible spline-based models, a clear exposure-response association was observed between trihalomethanes and CKD risk, with the highest risk for brominated trihalomethanes. The HRs for CKD risk associated with brominated trihalomethanes at the highest 2 exposure categories (75th percentile and at or above the 95th percentile) were 1.23 (95% CI, 1.13-1.33) and 1.43 (95% CI, 1.23-1.66), respectively (P < .001 for trend). Brominated trihalomethanes were the largest contributor (52.9%) to the association of the overall mixture with CKD risk, followed by uranium (35.4%), arsenic (6.2%), and chloroform (5.5%). In this prospective cohort study of California female teachers, exposure to trihalomethane concentrations less than 80 μg/L (US current standard) increased CKD risk, particularly brominated trihalomethanes, which are not separately regulated in community water. The findings may have public health implications given the widespread use of water chlorination and growing burden of CKD.

Techno-economic assessment of distributed wellhead RO water treatment for nitrate removal and salinity reduction: A field study in small disadvantaged communities.

Presence, distribution, and origin of radioisotopes in rock, soil, and groundwater in Central Mexico: implications of ionizing radiation for health.

Geospatial and socioeconomic factors of PFAS contamination in private drinking water wells: Insights for monitoring and management.