Maximum Contaminant Level Goal Research Articles

A graphene quantum dots based dual-modal fluorometric and visualized detection of copper ions

In this study, we present a dual-modal fluorometric and visualized detection method for Cu2+ ion, leveraging the synergistic properties of graphene quantum dots (GQDs) and Cu2+ ion catalyzed Fenton-like reaction. The Fenton-like reaction of Cu2+ ions and ascorbate generates highly reactive hydroxyl radical (·OH), which effectively disrupt the structure of GQDs, leading to fluorescence quenching. Under optimized conditions, the fluorescence quenching degree exhibited a linear correlation with Cu2+ concentration within the range of 40 to 2000 nM, enabling the detection of Cu2+ ions as low as 40 nM. Furthermore, we demonstrated the feasibility of semi-quantitative visual detection of Cu2+ ion concentrations in water using a portable ultraviolet instrument. The method achieved a minimum detectable concentration of Cu2+ ion as low as 10 μM, surpassing the maximum contaminant level goals of 20.47 μM set by the EPA and the guideline value of 31.47 μM recommended by the WHO. As such, this approach holds promise as a point-of-care testing (POCT) method for Cu2+ ion detection during copper pollution emergency events in water. Additionally, this method can be adapted for the detection of ascorbic acid. Our findings showcase the potential of this dual-modal detection approach, offering a sensitive, rapid, and efficient means for detecting Cu2+ ion, thereby contributing to environmental monitoring and public health applications.

Proposed Drinking Water Standards for PFAS

Proposed Drinking Water Standards for PFAS

Bottled water contaminant exposures and potential human effects

BackgroundBottled water (BW) consumption in the United States and globally has increased amidst heightened concern about environmental contaminant exposures and health risks in drinking water supplies, despite a paucity of directly comparable, environmentally-relevant contaminant exposure data for BW. This study provides insight into exposures and cumulative risks to human health from inorganic/organic/microbial contaminants in BW. MethodsBW from 30 total domestic US (23) and imported (7) sources, including purified tapwater (7) and spring water (23), were analyzed for 3 field parameters, 53 inorganics, 465 organics, 14 microbial metrics, and in vitro estrogen receptor (ER) bioactivity. Health-benchmark-weighted cumulative hazard indices and ratios of organic-contaminant in vitro exposure-activity cutoffs were assessed for detected regulated and unregulated inorganic and organic contaminants. Results48 inorganics and 45 organics were detected in sampled BW. No enforceable chemical quality standards were exceeded, but several inorganic and organic contaminants with maximum contaminant level goal(s) (MCLG) of zero (no known safe level of exposure to vulnerable sub-populations) were detected. Among these, arsenic, lead, and uranium were detected in 67 %, 17 %, and 57 % of BW, respectively, almost exclusively in spring-sourced samples not treated by advanced filtration. Organic MCLG exceedances included frequent detections of disinfection byproducts (DBP) in tapwater-sourced BW and sporadic detections of DBP and volatile organic chemicals in BW sourced from tapwater and springs. Precautionary health-based screening levels were exceeded frequently and attributed primarily to DBP in tapwater-sourced BW and co-occurring inorganic and organic contaminants in spring-sourced BW. ConclusionThe results indicate that simultaneous exposures to multiple drinking-water contaminants of potential human-health concern are common in BW. Improved understandings of human exposures based on more environmentally realistic and directly comparable point-of-use exposure characterizations, like this BW study, are essential to public health because drinking water is a biological necessity and, consequently, a high-vulnerability vector for human contaminant exposures.

An analysis of the use of the relative source contribution term in derivation of drinking water standards using perfluorooctanoic acid as an example.

The relative source contribution (RSC) term has long been used by the US Environmental Protection Agency (USEPA) and state regulatory agencies in setting criteria in water. The RSC reflects the proportion of the total daily intake of a chemical that can be derived from water when all other sources of exposure (e.g., food, air) are considered. This term is applied by the USEPA and state regulatory agencies when deriving ambient water quality criteria, maximum contaminant level goals, and drinking water health advisories for noncarcinogenic and threshold carcinogenic compounds. The value assigned to the RSC term affects the calculated criteria directly, with the allowable concentration in water decreasing with a decreasing RSC. A default RSC value of 20%-applied by regulatory entities in the USA for more than 40 years-assumes that 80% of an individual's exposure to a chemical's reference dose is from nonwater sources. Although the RSC is a chemical-specific parameter, there are few instances where a value other than the default of 20% has been approved and used. In 2000, USEPA outlined the process for developing chemical-specific RSC values, yet primary use of the default RSC value has continued since then. This article reviews USEPA's methodology for deriving chemical-specific RSC values and provides a case example using perfluorooctanoic acid (PFOA) to explore how the USEPA and state regulatory agencies are applying USEPA's guidance. The case study highlights inconsistent derivation of the RSC term, rooted in limitations in the current methodology. We suggest additional clarification of and more thoughtful use of the available data that may not meet USEPA's current adequacy requirements. We also recommend that the USEPA discuss recommendations for using biomonitoring data to set RSCs. Integr Environ Assess Manag 2023;19:605-612. © 2022 SETAC.

Pico-molar level detection of copper ion with extraordinarily high response by Ti-doped copper nitride fabricated via high power impulse magnetron sputtering

Various specific methods have been exercised in recent years to detect heavy metal ions in drinking water or body fluids for environmental as well as health safety. Likewise, development of a simple, fast, and robust method for copper ion (Cu2+) sensing is of paramount importance. Here, we demonstrate an effective Cu2+ sensor by exploiting the change in electrical conductivity of Ti-doped copper nitride (Cu3N) in presence of Cu2+ in solution. The Cu2+ sensor was fabricated with a Ti-doped Cu3N film deposited on indium-tin-oxide (ITO) coated quartz glass substrate by co-deposition method using high-power impulse magnetron sputtering (HiPIMS) and DC magnetron sputtering system simultaneously. DC sputtering power of Ti source was tuned from 0 W to 200 W with 50 W steps to achieve the Cu3N film with doping concentrations of 0, 0.19, 0.33, 0.87, and 1.6 at% respectively. Application of a diluted Cu2+ solution on the Ti-doped Cu3N film increases its electrical conductivity dramatically as manifested in the increase in current measured between two consecutive ITO electrodes beneath the thin film. The extraordinarily high copper sensitivity of the Ti-doped Cu3N film (1.6 at%) originated from the nitrogen-rich surfaces leads to detection of Cu2+ in water at as low as 8 pM concentration. The sensor exhibits not only high response but also a large linear dynamic range of 8 pM to 80 nM well below the maximum contaminant level goal for copper ion in drinking water. The high selectivity and reasonable cross-sensitivity of the sensor show potential commercialization in near future.

Thermal decomposition assisted one-step synthesis of high surface area NiCoP nanospheres for simultaneous sensing of Lead, Mercury and Cadmium ions in groundwater samples

Here we report a one-pot thermal decomposition assisted synthesis of nickel cobalt phosphide (NiCoP) hollow-nanospheres for simultaneous sensing of the Lead (Pb2+), Mercury (Hg2+) and Cadmium (Cd2+) ions in the groundwater samples. The as-fabricated sensor exhibits distinct peak potentials for Pb2+, Hg2+ and Cd2+ using anodic differential pulse stripping voltammetry technique. The peak separation ΔEP between PbHg and PbCd is 770 mV and 300 mV, respectively. The sensor exhibits an excellent selectivity, sensitivity and the limit of detection (LOD) of 1.59 nM, 2.52 nM and 1.70 nM for Pb2+, Hg2+ and Cd2+ ions, respectively which are below the prescribed maximum contaminant level goal (MCLG) values. The sensing ability of the sensor is attributed towards the high surface area of the as-synthesised NiCoP hollow nanospheres with the presence of orthorhombic plane Co2P as electrocatalytic active sites and the excellent conductivity. The sensor is successfully employed in the determination of heavy metal ions (HMIs) in groundwater samples with an excellent recovery percentage. This is the first report, on the successful demonstration of NiCoP as an active material for simultaneous detection of HMIs which can be effectively used for various environmental analysis.

Perchlorate: The Two-Decade Journey to a Proposed Rule

Perchlorate, a manufactured and naturally occurring chemical, was first detected in drinking water supplies in California in the 1980s. In the 1990s, perchlorate contamination (in the parts-per-billion range) was detected in drinking water supplies across the U.S. EPA began evaluating perchlorate for regulation in drinking water in 1998 and has spent 21 years issuing various proposals and findings on perchlorate, with a proposed (not final) drinking water regulation issued on June 26, 2019. The lack of a drinking water standard has had ramifications, including lack of trust in public drinking water resulting in economic hardship, particularly among Department of Defense personnel and other low-wealth communities, the states setting a patchwork of their own regulations on perchlorate, and lack of monitoring or clean-up of perchlorate in Department of Defense water systems. The reasons for EPA’s two-decade rulemaking process for perchlorate include the process EPA uses to determine regulatory feasibility under the Safe Drinking Water Act and the multi-year scientific review process. Key recommendations for shortening the process include amending the Safe Drinking Water Act and increasing transparency of the rulemaking process. List of Abbreviations: BMDL- Benchmark Dose Level; CCL- Contaminant Candidate List; DOD- Department of Defense; DWEL- Drinking Water Equivalent Level; EPA- Environmental Protection Agency; GAO- General Accountability Office; HRL- Health Reference Level; IRIS- Integrated Risk Information System; LOAEL- Lowest-Observed-Adverse-Effect Level; MCL- Maximum Contaminant Level; MCLG- Maximum Contaminant Level Goal; NOAEL- No-Observed-Adverse-Effect Level; NRC- National Research Council; RfD- Reference Dose; RSC- Relative Source Contribution; SAB-Science Advisory Board; SDWA- Safe Drinking Water Act

Development of an oral reference dose for the perfluorinated compound GenX

Ammonium 2,3,3,3‐tetrafluoro‐2‐(heptafluoropropoxy)‐propanoate, also known as GenX, is a processing aid used in the manufacture of fluoropolymers. GenX is one of several chemistries developed as an alternative to long‐chain poly‐fluoroalkyl substances, which tend to have long clearance half‐lives and are environmentally persistent. Unlike poly‐fluoroalkyl substances, GenX has more rapid clearance, but has been detected in US and international water sources. There are currently no federal drinking water standards for GenX in the USA; therefore, we developed a non‐cancer oral reference dose (RfD) for GenX based on available repeated dose studies. The review of the available data indicate that GenX is unlikely to be genotoxic. A combination of traditional frequentist benchmark dose models and Bayesian benchmark dose models were used derive relevant points of departure from mammalian toxicity studies. In addition, deterministic and probabilistic RfD values were developed using available tools and regulatory guidance. The two approaches resulted in a narrow range of RfD values for liver lesions observed in a 2‐year bioassay in rats (0.01–0.02 mg/kg/day). The probabilistic approach resulted in the lower, i.e., more conservative RfD. The probabilistic RfD of 0.01 mg/kg/day results in a maximum contaminant level goal of 70 ppb. It is anticipated that these values, along with the hazard identification and dose‐response modeling described herein, should be informative for risk assessors and regulators interested in setting health‐protective drinking water guideline values for GenX.

An evaluation of the USEPA Proposed Approaches for applying a biologically based dose-response model in a risk assessment for perchlorate in drinking water

The United States Environmental Protection Agency's (USEPA) 2017 report, “Draft Report: Proposed Approaches to Inform the Derivation of a Maximum Contaminant Level Goal for Perchlorate in Drinking Water”, proposes novel approaches for deriving a Maximum Contaminant Level Goal (MCLG) for perchlorate using a biologically-based dose-response (BBDR) model. The USEPA (2017) BBDR model extends previously peer-reviewed perchlorate models to describe the relationship between perchlorate exposure and thyroid hormone levels during early pregnancy. Our evaluation focuses on two key elements of the USEPA (2017) report: the plausibility of BBDR model revisions to describe control of thyroid hormone production in early pregnancy and the basis for linking BBDR model results to neurodevelopmental outcomes. While the USEPA (2017) BBDR model represents a valuable research tool, the lack of supporting data for many of the model assumptions and parameters calls into question the fitness of the extended BBDR model to support quantitative analyses for regulatory decisions on perchlorate in drinking water. Until more data can be developed to address uncertainties in the current BBDR model, USEPA should continue to rely on the RfD recommended by the NAS (USEPA, 2005) when considering further regulatory action.

Drinking water disinfection byproducts and risk of orofacial clefts in the National Birth Defects Prevention Study.

Maternal exposure to drinking water disinfection byproducts (DBP)s may contribute to orofacial cleft (OFC) development, but studies are sparse and beset with limitations. Population-based, maternal interview reports of drinking water filtration and consumption for 680 OFC cases (535 isolated) and 1826 controls were linked with DBP concentration data using maternal residential addresses and public water system monitoring data. Maternal individual-level exposures to trihalomethanes (THM)s and haloacetic acids (HAA)s (µg/L of water consumed) were estimated from reported consumption at home, work, and school. Compared to no exposure, associations with multisource maternal exposure <1/2 or ≥1/2 the Maximum Contaminant Levels (MCL)s for total THMs (TTHM)s and HAAs (HAA5) or Maximum Contaminant Level Goals (MCLG)s for individual THMs and HAAs (if non-zero) were estimated for all OFCs and isolated OFCs, cleft palate (CP), and cleft lip ± cleft palate (CL/P) using logistic regression analyses. Compared to controls, associations were near or below unity for maternal TTHM, HAA5, and individual THM exposures with all OFCs and isolated OFCs, CP, and CL/P. Associations also were near or below unity for individual HAAs with statistically significant, inverse associations observed with each OFC outcome group except CL/P. This study examined associations for maternal reports of drinking water filtration and consumption and maternal DBP exposure from drinking water with OFCs in offspring. Associations observed were near or below unity and mostly nonsignificant. Continued, improved research using maternal individual-level exposure data will be useful in better characterizing these associations.

Analysis of 2,4-D residues in soil profile using HYDRUS-1D model

ABSTRACT- Despite the benefits of herbicides, their persistence in soil can harm other plants in next rotations and contaminate ground water. The main purpose of this research is to simulate 2,4-dichlorophenoxyaceticacid(2,4-D) movement in silty clay loam soil using HYDRUS-1D model in a corn root zone. The maximum contaminant level goal, MCLG, of 2,4-D in water resources is 10 ppb. The 3.5 kg a.i ha-1 of 2,4-D was applied to the experimental field under two irrigation treatments including normal and deficit irrigation. The presence of 2,4-D along with soil water content was measured in soil profile at different depths during the growing season at 8, 13, 23, 30, 37 and 57 days after application. Both measured and simulated data showed that 2,4-D concentrations reduced from top to bottom of soil profile, maximum 40 cm in both irrigation treatments. The 2,4-D residues in normal and deficit irrigation were used for calibration and validation of HYDRUS-1D model, respectively. In general, total measured and simulated 2,4-D concentration in normal irrigation treatment were 68.94 and 64.96 mg kg-1and in deficit irrigation treatment were 74.3 and 74.0 mg kg-1, respectively. Statistical parameters including NRMSE, CRM and d were used for comparison of measured and simulated data. These parameters were 0.267, 0.77 and 0.846 for normal irrigation and 0.189, -0.02 and 0.937 for deficit regime, respectively. Therefore, the results showed a good agreement between measured values of herbicide residue and the values simulated using HYDRUS 1D model. The numerical simulations for deficit irrigation regime were more precise than normal irrigation because of less microbial activity due to less soil moisture. The numerical models could not simulate microbial activity with acceptable accuracy.

Spatially Averaged, Flow‐Weighted Concentrations – A More Relevant Regulatory Metric for Groundwater Cleanup

Spatially Averaged, Flow‐Weighted Concentrations – A More Relevant Regulatory Metric for Groundwater Cleanup

Fluorescence Chemosensory Determination of Cu2+ Using a New Rhodamine–Morpholine Conjugate

A new rhodamine-B carbonyl-morpholine derivative (denoted as RECM) was prepared by a two-step synthesis procedure. The employed method allowed a lactam ring development of rhodamine-B and ethylenediamine to demonstrate a facile amide bond formation. The obtained RECM was confirmed by 1H NMR, 13C NMR, and mass spectrometry analysis. RECM was formed to detect copper ion (Cu2+) due to its problematic toxicity features in aquatic ecosystems. It showed a high selectivity toward Cu2+ in comparison with some environmentally relevant alkali, alkaline earth, and transition metal cations at 50 µM in acetonitrile. Moreover, non-fluorescent RECM showed fluorescence intensity and UV-Vis absorbance increases in the presence of Cu2+ with high linear dependent coefficients (R2 = 0.964 and R2 = 0.982 respectively) as well as a color change from colorless to pink owing to the ring opening of the rhodamine spirolactam form. Binding capability experiments presented a clear 1:1 stoichiometry of RECM–Cu2+ complex with the binding constant (Ka) as 2.25 × 104 M−1. The calculation of limits of detection (LOD) was 0.21 µM based on the linear regression method, which is below the maximum contaminant level goal (MCLG) value of Cu2+ (1.3 ppm equals to 20.46 µM) in drinking water. These characteristics make the RECM a promising candidate for the real-time detection of toxic Cu2+ in environmental monitoring applications.

Ion Sensor Properties of Fluorescent Schiff Bases Carrying Dipicolylamine Groups. A Simple Spectrofluorimetric Method to Determine Cu (II) in Water Samples.

Four fluorescent Schiff bases carrying dipicolylamine groups were designed and synthesized to determine their ion sensor properties in partial aqueous solution. The corresponding amine compound and the aldehyde compounds such as 1-naphthaldehyde, 9-anthraldehyde, phenanthrene-9-carboxaldehyde and 1-pyrenecarboxaldehyde were used to prepare the new Schiff bases. The influence of many metal cations and anions on the spectroscopic properties of the ligands was investigated in ethanol-water (1:1) by means of emission spectrometry. From the spectrofluorimetric titrations, the complexation stoichiometry and complex stability constants of the ligands with Cd2+, Zn2+, Cu2+ and Hg2+ ions were determined. The ligands did not interact with the anions. However, the Schiff base derived from phenanthrene-9-carboxaldehyde showed sensitivity for Cu2+ among the tested metal ions. The phenanthrene-based Schiff base was used as analytical ligand for the simple and fast determination of Cu2+ ion in water samples. A modified standard addition method was used to eliminate matrix effect. The linear range was from 0.3mg/L to 3.8μg/L. Detection and quantification limits were 0.14 and 0.43mg/L, respectively. Maximum contaminant level goal (MCLG) for copper in drinking water according to EPA is 1.3mg/L. The proposed method has high sensitivity to determine copper in drinking waters.

Current Situation of Aqueous Arsenic Contamination in Pakistan, Focused on Sindh and Punjab Province, Pakistan: A Review

The arsenic contamination has seriously affected public health in Pakistan, especially in highly contaminated Sindh and Punjab provinces. Results of recent studies show that over 3% of the population in Punjab was exposed to arsenic contamination of over 50 ug/L in drinking water, and 20% of the population is exposed to over 10 ug/L, with the limited standard of WHO, same as the EPA also sets the maximum contaminant level goal (MCLG) for drinking water. The situation in Sindh province was worse than in Punjab province, as the results show that 16% and 36% of population exposed to arsenic contaminated water over 50 ug/L and 10 ug/L respectively. According to a study conducted and based on samples from 1,184 wells across the country that actually proved that the process of boiling or filtration was not helpful to remove As from groundwater. Recent medical studies have confirmed 40 cases of arsenicosis occurred in worst situation. The purpose of this paper is to make a review about the current situation of arsenic contamination and its effect in the Pakistan.

Determination of Cu2+ in Drinking Water Based on Electrochemiluminescence of Ru(phen)32+ and Cyclam

AbstractA convenient and simple electrochemiluminescence (ECL) method was employed to detect trace amounts of Cu2+ in drinking water. This method is based on the inhibitory effect of Cu2+ on the ECL of Ru(phen)32+ and 1,4,8,11‐tetraazacyclotetradecane (cyclam) system. ECL intensity of Ru(phen)32+ was considerably enhanced by the addition of cyclam because of the ECL reaction between them. The ECL intensity of Ru(phen)32+/cyclam system rapidy decreased with the addition Cu2+ because of the formation of chelate complex [Cu(cyclam)]2+. Good linear response (R2=0.9948) was obtained at Cu2+ concentration of 1.0×10−9−1.0×10−5 mol ⋅ L−1 at glassy carbon electrode in 0.1 mol ⋅ L−1 phosphate buffer (pH 9.0). Observed detection limit of 4.8×10−10 mol ⋅ L−1 satisfied the maximum contaminant level goal (MCLG) for Cu2+ set by the US Environmental Protection Agency (US EPA). Applicability of the proposed method was verified by the good reproducibility and stability of the method when applied to determine Cu2+ in tap water and simulated wastewater. Thus, a novel ECL detection method was developed for Cu2+ detection.

Public health risk assessment of groundwater contamination in Batman, Turkey

In this study, a comprehensive analysis of groundwater was performed to assess contamination and phenol content in Batman, Turkey, particularly in residential areas near agriculture, livestock and oil industry facilities. From these areas, where potentially contaminated groundwater used for drinking and irrigation threatens public health, 30 groundwater samples were collected and analyzed for heavy metal concentrations (Al, As, B, Ba, Ca, Cd, Cl, Co, Cr, Cu, Fe, Hg, Li, Mg, Mn, Mo, Na, Ni, NO3, P, Pb, phenol, S, Sb, Se, SO4, Sr, U, and Zn). Compared with the standards of the Environmental Protection Agency, Al, Fe, and Mn concentrations in groundwater exceeded secondary drinking water regulations, NO3 concentrations were high for maximum contaminant levels, and As, Pb, and U concentrations exceeded maximum contaminant level goals in all samples. Ni, Sb, and Se concentrations also exceeded limits set by the Turkish Standards Institution. Nearly all samples revealed concentrations of Se, Sb, Hg, and phenol due to nearby petroleum refineries, oil storage plants, and agricultural and livestock areas. The results obtained from this study indicate that the groundwater in Batman contains elements in concentrations that approach or exceed limits and thus threatens public health with increased blood cholesterol, decreased blood sugar, and circulatory problems.

Mode of action analysis for liver tumors from oral 1,4-dioxane exposures and evidence-based dose response assessment

1,4-Dioxane is found in consumer products and is used as a solvent in manufacturing. Studies in rodents show liver tumors to be consistently reported after chronic oral exposure. However, there were differences in the reporting of non-neoplastic lesions in the livers of rats and mice. In order to clarify these differences, a reread of mouse liver slides from the 1978 NCI bioassay on 1,4-dioxane in drinking water was conducted. This reread clearly identified dose-related non-neoplastic changes in the liver; specifically, a dose-related increase in the hypertrophic response of hepatocytes, followed by necrosis, inflammation and hyperplastic hepatocellular foci. 1,4-Dioxane does not cause point mutations, DNA repair, or initiation. However, it appears to promote tumors and stimulate DNA synthesis. Using EPA Guidelines (2005), the weight of the evidence suggests that 1,4-dioxane causes liver tumors in rats and mice through cytotoxicity followed by regenerative hyperplasia. Specific key events in this mode of action are identified. A Reference Dose (RfD) of 0.05mg/kgday is proposed to protect against regenerative liver hyperplasia based on a benchmark dose (BMD) approach. Based on this RfD, a maximum contaminant level goal of 350μg/L is proposed using a default relative source contribution for water of 20%.

A distance-dependent metal-enhanced fluorescence sensing platform based on molecular beacon design

A new metal-enhanced fluorescence (MEF) based platform was developed on the basis of distance-dependent fluorescence quenching-enhancement effect, which combined the easiness of Ag-thiol chemistry with the MEF property of noble-metal structures as well as the molecular beacon design. For the given sized AgNPs, the fluorescence enhancement factor was found to increase with a d6 dependency in agreement with fluorescence resonance energy transfer mechanism at shorter distance and decrease with a d−3 dependency in agreement with plasmonic enhancement mechanism at longer distance between the fluorophore and the AgNP surface. As a proof of concept, the platform was demonstrated by a sensitive detection of mercuric ions, using thymine-containing molecular beacon to tune silver nanoparticle (AgNP)-enhanced fluorescence. Mercuric ions were detected via formation of a thymine–mercuric–thymine structure to open the hairpin, facilitating fluorescence recovery and AgNP enhancement to yield a limit of detection of 1nM, which is well below the U.S. Environmental Protection Agency regulation of the Maximum Contaminant Level Goal (10nM) in drinking water. Since the AgNP functioned as not only a quencher to reduce the reagent blank signal but also an enhancement substrate to increase fluorescence of the open hairpin when target mercuric ions were present, the quenching-enhancement strategy can greatly improve the detection sensitivity and can in principle be a universal approach for various targets when combined with molecular beacon design.

Unknown Quantity: Regulating Radionuclides in Tap Water

Radioactivity surrounds us; each day we are exposed to a certain amount by virtue of being alive on planet Earth. Some of this exposure comes from radioactive substances (radionuclides) that occur naturally in a wide variety of geologic and soil formations. Occasionally these naturally occurring substances become more concentrated or accessible through human activities such as mining and nuclear energy production, resulting in greater potential for exposure than their original natural occurrence would suggest. Other radionuclides are artificially created. Residents in almost all parts of the United States live on lands that contain minor to substantial concentrations of radionuclides of one type or another.1 These substances often make their way into tap water, leading to exposures by ingestion, inhalation, or dermal pathways during showering or other contact with the water. Although radionuclides are widespread, there are large gaps in our knowledge about sources of these materials, their distribution, associated health risks, and mitigation measures. However, the information we do have suggests that current drinking water standards for radionuclides established by the U.S. Environmental Protection Agency (EPA) may not adequately protect health. The EPA is set to review these standards relatively soon, and the next two years are prime time for filling in numerous information gaps and doing other legwork to make sure the review is as well informed as possible.