Importance:Previous meta-analyses suggest that fluoride exposure is adversely associated with children's IQ scores. An individual's total fluoride exposure comes primarily from fluoride in drinking water, food, and beverages. Objective:To perform a systematic review and meta-analysis of epidemiological studies investigating children's IQ scores and prenatal or postnatal fluoride exposure. Data Sources:BIOSIS, Embase, PsycInfo, PubMed, Scopus, Web of Science, CNKI, and Wanfang, searched through October 2023. Study Selection:Studies reporting children's IQ scores, fluoride exposure, and effect sizes. Data Extraction and Synthesis:Data were extracted into the Health Assessment Workplace Collaborative system. Study quality was evaluated using the OHAT risk-of-bias tool. Pooled standardized mean differences (SMDs) and regression coefficients were estimated with random-effects models. Main Outcomes and Measures:Children's IQ scores. Results:Of 74 studies included (64 cross-sectional and 10 cohort studies), most were conducted in China (n = 45); other locations included Canada (n = 3), Denmark (n = 1), India (n = 12), Iran (n = 4), Mexico (n = 4), New Zealand (n = 1), Pakistan (n = 2), Spain (n = 1), and Taiwan (n = 1). Fifty-two studies were rated high risk of bias and 22 were rated low risk of bias. Sixty-four studies reported inverse associations between fluoride exposure measures and children's IQ. Analysis of 59 studies with group-level measures of fluoride in drinking water, dental fluorosis, or other measures of fluoride exposure (47 high risk of bias, 12 low risk of bias; n = 20 932 children) showed an inverse association between fluoride exposure and IQ (pooled SMD, -0.45; 95% CI, -0.57 to -0.33; P < .001). In 31 studies reporting fluoride measured in drinking water, a dose-response association was found between exposed and reference groups (SMD, -0.15; 95% CI, -0.20 to -0.11; P < .001), and associations remained inverse when exposed groups were restricted to less than 4 mg/L and less than 2 mg/L; however, the association was null at less than 1.5 mg/L. In analyses restricted to low risk-of-bias studies, the association remained inverse when exposure was restricted to less than 4 mg/L, less than 2 mg/L, and less than 1.5 mg/L fluoride in drinking water. In 20 studies reporting fluoride measured in urine, there was an inverse dose-response association (SMD, -0.15; 95% CI, -0.23 to -0.07; P < .001). Associations remained inverse when exposed groups were restricted to less than 4 mg/L, less than 2 mg/L, and less than 1.5 mg/L fluoride in urine; the associations held in analyses restricted to the low risk-of-bias studies. Analysis of 13 studies with individual-level measures found an IQ score decrease of 1.63 points (95% CI, -2.33 to -0.93; P < .001) per 1-mg/L increase in urinary fluoride. Among low risk-of-bias studies, there was an IQ score decrease of 1.14 points (95% CI, -1.68 to -0.61; P < .001). Associations remained inverse when stratified by risk of bias, sex, age, outcome assessment type, country, exposure timing, and exposure matrix. Conclusions and Relevance:This systematic review and meta-analysis found inverse associations and a dose-response association between fluoride measurements in urine and drinking water and children's IQ across the large multicountry epidemiological literature. There were limited data and uncertainty in the dose-response association between fluoride exposure and children's IQ when fluoride exposure was estimated by drinking water alone at concentrations less than 1.5 mg/L. These findings may inform future comprehensive public health risk-benefit assessments of fluoride exposures.

ImportancePrevious meta-analyses suggest that fluoride exposure is adversely associated with children’s IQ scores. An individual’s total fluoride exposure comes primarily from fluoride in drinking water, food, and beverages.ObjectiveTo perform a systematic review and meta-analysis of epidemiological studies investigating children’s IQ scores and prenatal or postnatal fluoride exposure.Data SourcesBIOSIS, Embase, PsycInfo, PubMed, Scopus, Web of Science, CNKI, and Wanfang, searched through October 2023.Study SelectionStudies reporting children’s IQ scores, fluoride exposure, and effect sizes.Data Extraction and SynthesisData were extracted into the Health Assessment Workplace Collaborative system. Study quality was evaluated using the OHAT risk-of-bias tool. Pooled standardized mean differences (SMDs) and regression coefficients were estimated with random-effects models.Main Outcomes and MeasuresChildren’s IQ scores.ResultsOf 74 studies included (64 cross-sectional and 10 cohort studies), most were conducted in China (n = 45); other locations included Canada (n = 3), Denmark (n = 1), India (n = 12), Iran (n = 4), Mexico (n = 4), New Zealand (n = 1), Pakistan (n = 2), Spain (n = 1), and Taiwan (n = 1). Fifty-two studies were rated high risk of bias and 22 were rated low risk of bias. Sixty-four studies reported inverse associations between fluoride exposure measures and children’s IQ. Analysis of 59 studies with group-level measures of fluoride in drinking water, dental fluorosis, or other measures of fluoride exposure (47 high risk of bias, 12 low risk of bias; n = 20 932 children) showed an inverse association between fluoride exposure and IQ (pooled SMD, −0.45; 95% CI, −0.57 to −0.33; P < .001). In 31 studies reporting fluoride measured in drinking water, a dose-response association was found between exposed and reference groups (SMD, −0.15; 95% CI, −0.20 to −0.11; P < .001), and associations remained inverse when exposed groups were restricted to less than 4 mg/L and less than 2 mg/L; however, the association was null at less than 1.5 mg/L. In analyses restricted to low risk-of-bias studies, the association remained inverse when exposure was restricted to less than 4 mg/L, less than 2 mg/L, and less than 1.5 mg/L fluoride in drinking water. In 20 studies reporting fluoride measured in urine, there was an inverse dose-response association (SMD, −0.15; 95% CI, −0.23 to −0.07; P < .001). Associations remained inverse when exposed groups were restricted to less than 4 mg/L, less than 2 mg/L, and less than 1.5 mg/L fluoride in urine; the associations held in analyses restricted to the low risk-of-bias studies. Analysis of 13 studies with individual-level measures found an IQ score decrease of 1.63 points (95% CI, −2.33 to −0.93; P < .001) per 1-mg/L increase in urinary fluoride. Among low risk-of-bias studies, there was an IQ score decrease of 1.14 points (95% CI, –1.68 to –0.61; P < .001). Associations remained inverse when stratified by risk of bias, sex, age, outcome assessment type, country, exposure timing, and exposure matrix.Conclusions and RelevanceThis systematic review and meta-analysis found inverse associations and a dose-response association between fluoride measurements in urine and drinking water and children’s IQ across the large multicountry epidemiological literature. There were limited data and uncertainty in the dose-response association between fluoride exposure and children’s IQ when fluoride exposure was estimated by drinking water alone at concentrations less than 1.5 mg/L. These findings may inform future comprehensive public health risk-benefit assessments of fluoride exposures.

Background: Jet fuels are a common chemical exposure in occupational settings involving aircraft. Jet fuels are heterogeneous mixtures of aromatic and aliphatic hydrocarbons, as well as non-hydrocarbon performance additives. Several components of jet fuels have been linked to adverse health outcomes. The “Sergeant First Class Heath Robinson Honoring Our Promise to Address Comprehensive Toxins Act of 2022” required the U.S. Department of Veterans Affairs (VA) to develop a report to Congress on the health effects of jet fuels used in the military. Objectives: This investigation assessed the epidemiologic evidence of the health effects associated with occupational exposure to jet fuels in military and non-military settings using robust and reproducible systematic review methods. Methods: Two scientific databases (PubMed and EBSCOhost), 17 gray literature sources and five review articles were searched for relevant, primary epidemiologic studies through May, 2024. Risk of bias and strength of evidence were evaluated according to the U.S. Environmental Protection Agency’s (EPA) Integrated Risk Information System (IRIS) assessment framework for systematic reviews and evidence synthesis. Results: Twenty-eight studies met the inclusion criteria, including 18 studies in military settings and 10 studies in non-military occupational settings. It was determined that there was slight evidence of associations between jet fuel exposure and neurologic, cognitive and behavioral, respiratory, and cancer outcomes. For all other health outcome categories, the available evidence of jet fuels effect on humans was considered indeterminate. Discussion: To our knowledge, this is the first systematic review of epidemiologic evidence on the health effects of occupational jet fuel exposure. Available data were sparse for multiple health outcomes, and most studies tended to be of lower quality. Future work will include expanding the scope of the review to integrate toxicological and mechanistic evidence.

•Systematic review conducted of coliphage levels in treated wastewater effluents.•Insights into technologies influencing viral inactivation in wastewater treatment.•Density of coliphages in influent was significantly higher than in treated effluent.•Combined chlorine might not effectively inactivate viruses in wastewater.

Recreational water quality guidelines protect the public from health risks associated with water recreation by helping to prevent unacceptable concentrations of pathogenic organisms in ambient water. However, illness risk is associated with both the concentration of pathogens in the water and the degree of contact with those pathogens. Different recreational activities can result in different levels of contact with ambient water containing water-borne pathogens. We conducted a systematic literature review and meta-analysis to evaluate risks of illness associated with different recreational activities and different levels of contact to ambient surface waters. We screened 8,618 potentially relevant studies for quantitative measures of risk using inclusion/exclusion criteria established in advance. We categorized recreational activities as swimming, sports-related contact, minimal contact, and sand contact. We combined relative risks using a random effects meta-analysis for adverse health outcome categories representing gastrointestinal illness, respiratory illness, skin, eye, ear, nose, throat, and cold/flu illness. We identified 92 studies meeting our inclusion criteria. Pooled risk estimates indicate significant elevation of gastrointestinal illness with the recreational activity categories swimming (2.19, 95% CI: 1.82, 2.63) and sports-related contact (2.69, 95% CI: 1.04, 6.92), and nonsignificant elevation of gastrointestinal illness with minimal contact (1.27, 95% CI: 0.74, 2.16). We also found a significant elevation of respiratory illness with swimming (1.78, 95% CI: 1.38, 2.29) and sports-related contact (1.49, 95% CI: 1.00, 2.24), and no elevation of respiratory illness with minimal contact (0.90, 95% CI: 0.71, 1.14). This study suggests that exposures associated with different types of recreational activities are important characteristics of the exposure pathway when assessing illness risk associated with recreation in ambient surface waters.

Formulation and Protocol for the Inorganic Arsenic (iAs) IRIS Assessment (Poster 1) Janice S. Lee1, Ila Cote1, Tom Luben1, Ellen Kirrane1, Ryan Jones1, Jeff Gift1, J. Allen Davis2, Ingrid Druwe1, Audrey Turley3, Michelle Cawley3, Robyn Blain3, Sorina Eftim3, Kris Thayer1 1 EPA, Office or Research and Development, National Center for Environmental Assessment – Research Triangle Park, 2 EPA, Office or Research and Development, National Center for Environmental Assessment – Cincinnati, 3 ICF International

Increasing interest in recycling water for potable purposes makes understanding the risks associated with potential acute microbial hazards important. We compared risks from de facto reuse, indirect potable reuse (IPR), and direct potable reuse (DPR) scenarios using a previously published quantitative microbial risk assessment methodology and literature review results. The de facto reuse simulation results are compared to a Cryptosporidium spp. database collected for the Long Term 2 Enhanced Surface Water Treatment Rule's information collection rule (ICR) and to a literature review of norovirus (NoV) densities in ambient surface waters. The de facto simulation results with a treated wastewater effluent contribution of 1% in surface waters and a residence time of 30 days most closely match the ICR dataset. The de facto simulations also suggest that using NoV monitoring data from surface waters may overestimate microbial risks, compared to NoV data from raw sewage coupled with wastewater treatment reduction estimates. The predicted risks from IPR and DPR are consistently lower than those for the de facto reuse scenarios assuming the AWTFs are operating within design specifications. These analyses provide insight into the microbial risks associated with various potable reuse scenarios and highlight the need to carefully consider drinking water treatment choices when wastewater effluent is a component of any drinking water supply.

Coliphage have been proposed as indicators of fecal contamination in recreational waters because they better reflect the persistence of pathogenic viruses in the environment and through wastewater treatment than traditional fecal indicator bacteria. Herein, we conducted a systematic literature search of peer-reviewed publications to identify coliphage density data (somatic and male-specific, or MSC) in raw wastewater and ambient waters. The literature review inclusion criteria included scope, study quality, and data availability. A non-parametric two-stage bootstrap analysis was used to estimate the coliphage distributions in raw wastewater and account for geographic region and season. Additionally, two statistical methodologies were explored for developing coliphage density distributions in ambient waters, to account for the nondetects in the datasets. In raw wastewater, the analysis resulted in seasonal density distributions of somatic coliphage (SC) (mean 6.5 log(10) plaque forming units (PFU)/L; 95% confidence interval (CI): 6.2-6.8) and MSC (mean 5.9 log(10) PFU/L; 95% CI: 5.5-6.1). In ambient waters, 49% of MSC samples were nondetects, compared with less than 5% for SC. Overall distributional estimates of ambient densities of coliphage were statistically higher for SC than for MSC (mean 3.4 and 1.0 log(10) PFU/L, respectively). Distributions of coliphage in raw wastewater and ambient water will be useful for future microbial risk assessments. Published by Elsevier Ltd.

Purpose of Review With the increasing interest in recycling water for potable reuse purposes, it is important to understand the microbial risks associated with potable reuse. This review focuses on potable reuse systems that use high-level treatment and de facto reuse scenarios that include a quantifiable wastewater effluent component. Recent Findings In this article, we summarize the published human health studies related to potable reuse, including both epidemiology studies and quantitative microbial risk assessments (QMRA). Overall, there have been relatively few health-based studies evaluating the microbial risks associated with potable reuse. Several microbial risk assessments focused on risks associated with unplanned (or de facto) reuse, while others evaluated planned potable reuse, such as indirect potable reuse (IPR) or direct potable reuse (DPR). Summary The reported QMRA-based risks for planned potable reuse varied substantially, indicating there is a need for risk assessors to use consistent input parameters and transparent assumptions, so that risk results are easily translated across studies. However, the current results overall indicate that predicted risks associated with planned potable reuse scenarios may be lower than those for de facto reuse scenarios. Overall, there is a clear need to carefully consider water treatment train choices when wastewater is a component of the drinking water supply (whether de facto, IPR, or DPR). More data from full-scale water treatment facilities would be helpful to quantify levels of viruses in raw sewage and reductions across unit treatment processes for both culturable and molecular detection methods .

Assessing the risk of bias (RoB) of individual studies is a critical part in determining the certainty of a body of evidence from non-randomized studies (NRS) that evaluate potential health effects due to environmental exposures. The recently released RoB in NRS of Interventions (ROBINS-I) instrument has undergone careful development for health interventions. Using the fundamental design of ROBINS-I, which includes evaluating RoB against an ideal target trial, we explored developing a version of the instrument to evaluate RoB in exposure studies. During three sequential rounds of assessment, two or three raters (evaluators) independently applied ROBINS-I to studies from two systematic reviews and one case-study protocol that evaluated the relationship between environmental exposures and health outcomes. Feedback from raters, methodologists, and topic-specific experts informed important modifications to tailor the instrument to exposure studies. We identified the following areas of distinction for the modified instrument: terminology, formulation of the ideal target randomized experiment, guidance for cross-sectional studies and exposure assessment (both quality of measurement method and concern for potential exposure misclassification), and evaluation of issues related to study sensitivity. Using the target experiment approach significantly impacts the process for how environmental and occupational health studies are considered in the Grading of Recommendations Assessment, Development and Evaluation (GRADE) evidence-synthesis framework.

Blood lead levels (BLLs) have decreased over the last several decades but lead exposure remains a risk and the relationship between socioeconomic status, lead, and neurodevelopment is not well-understood. Differences in the distributions of sociodemographic characteristics between children with higher and lower BLLs may account for the nonlinear concentration-response (C-R) relationship observed between BLL and cognitive effects in multiple studies. Specifically, adjustment for sociodemographic characteristics may be an over-adjustment leading to an underestimate of the association at the upper end of the distribution. We analyzed data from the US cohorts examined in the pooled analysis of Lanphear et al. 2005. Like the original analysis, we analyzed relationships of BLL and sociodemographic factors with child IQ using fixed effects multivariable generalized linear regression, and stratified the dataset into children with peak BLLs < 7.5 and ≥ 7.5 µg/dL. Unlike the original analysis we considered the interaction between concurrent BLL and sociodemographic factors and estimated the cumulative impact of BLL and sociodemographic characteristics across the distribution of IQ using quantile regression. The correlation of concurrent BLL with sociodemographic characteristics was generally stronger in the high peak blood lead group, potentially reducing our ability to distinguish the independent effect of blood lead from the effect sociodemographic factors at the upper end of the distribution. The cumulative effect of BLL and sociodemographic factors was largest at the upper end of the IQ distribution in the low peak BLL group suggesting the importance of considering baseline IQ. Overall, this analysis suggests that distribution of sociodemographic factors across the range of BLLs may explain, in part, the attenuation of the C-R relationship at higher BLLs. Disclaimer: Views expressed in abstract are those of authors and do not represent views/policies of the US EPA.

Understanding pathogen risks is a critically important consideration in the design of water treatment, particularly for potable reuse projects. As an extension to our published microbial risk assessment methodology to estimate infection risks associated with Direct Potable Reuse (DPR) treatment train unit process combinations, herein, we (1) provide an updated compilation of pathogen density data in raw wastewater and dose-response models; (2) conduct a series of sensitivity analyses to consider potential risk implications using updated data; (3) evaluate the risks associated with log credit allocations in the United States; and (4) identify reference pathogen reductions needed to consistently meet currently applied benchmark risk levels. Sensitivity analyses illustrated changes in cumulative annual risks estimates, the significance of which depends on the pathogen group driving the risk for a given treatment train. For example, updates to norovirus (NoV) raw wastewater values and use of a NoV dose-response approach, capturing the full range of uncertainty, increased risks associated with one of the treatment trains evaluated, but not the other. Additionally, compared to traditional log-credit allocation approaches, our results indicate that the risk methodology provides more nuanced information about how consistently public health benchmarks are achieved. Our results indicate that viruses need to be reduced by 14 logs or more to consistently achieve currently applied benchmark levels of protection associated with DPR. The refined methodology, updated model inputs, and log credit allocation comparisons will be useful to regulators considering DPR projects and design engineers as they consider which unit treatment processes should be employed for particular projects.

The objective of this paper is to explain how to apply, interpret, and present the results of a new instrument to assess the risk of bias (RoB) in non-randomized studies (NRS) dealing with effects of environmental exposures on health outcomes. This instrument is modeled on the Risk Of Bias In Non-randomized Studies of Interventions (ROBINS-I) instrument. The RoB instrument for NRS of exposures assesses RoB along a standardized comparison to a randomized target experiment, instead of the study-design directed RoB approach. We provide specific guidance for the integral steps of developing a research question and target experiment, distinguishing issues of indirectness from RoB, making individual-study judgments, and performing and interpreting sensitivity analyses for RoB judgments across a body of evidence. Also, we present an approach for integrating the RoB assessments within the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) framework to assess the certainty of the evidence in the systematic review. Finally, we guide the reader through an overall assessment to support the rating of all domains that determine the certainty of a body of evidence using the GRADE approach.

Human noroviruses (NoV) are a leading cause of recreational waterborne illnesses and responsible for the majority of viral-associated gastrointestinal illnesses nationwide. We conducted a systematic literature review of published peer-reviewed publications to identify NoV density data in wastewater influent, and provided an approach for developing pathogen density distributions, using the NoV data. Literature review inclusion criteria included scope, study quality, and data availability. A non-parametric bootstrap statistical model was used to estimate the NoV distribution in wastewater influent. The approach used accounts for heterogeneity in study-specific distribution curves, sampling locations, and sampling season and provides a comprehensive representation of the data. Study results illustrate that pooling all of the available NoV data together in a meta-analysis provides a more comprehensive understanding of the technical literature than what could be appreciated from individual studies. The studies included in this analysis indicate a high density of NoV in wastewater influent (overall mean = 4.6 log10 genome copies (GC)/liter (L)), with a higher density of NoV genogroup (G) II (overall mean = 4.9 log10 GC/L) than for GI (overall mean = 4.4 log10 GC/L for GI). The bootstrapping approach was also used to account for differences in seasonal and geographical occurrences of NoV GI and GII. The methods presented are reproducible and can be used to develop QMRA-ready density distributions for other viral pathogens in wastewater influent, effluent, and ambient waters. To our knowledge, our results are the first to quantitatively characterize seasonal and geographic differences, which could be particularly useful for future risk assessments.

Increased risks of lung and bladder cancer have been observed in populations exposed to high levels of inorganic arsenic. However, studies at lower exposures (i.e., less than 100 μg/l in water) have shown inconsistent results. We therefore conducted an ecological analysis of the association between historical drinking water arsenic concentrations and lung and bladder cancer incidence in U.S. counties. We used drinking water arsenic concentrations measured by the U.S. Geological Survey and state agencies in the 1980s and 1990s as proxies for historical exposures in counties where public groundwater systems and private wells are important sources of drinking water. Relationships between arsenic levels and cancer incidence in 2006–2010 were explored by Poisson regression analyses, adjusted for groundwater dependence and important demographic covariates. The median and 95th percentile county mean arsenic concentrations were 1.5 and 15.4 μg/l, respectively. Water arsenic concentrations were significant and positively associated with female and male bladder cancer, and with female lung cancer. Our findings support an association between low water arsenic concentrations and lung and bladder cancer incidence in the United States. However, the limitations of the ecological study design suggest caution in interpreting these results.

We conducted a supplemental water quality monitoring study and quantitative microbial risk assessment (QMRA) to complement the United States environmental protection agency's (U.S. EPA) National Epidemiological and Environmental Assessment of Recreational water study at Boqueron beach in Puerto Rico to estimate the gastrointestinal (GI) illness levels associated with recreational water exposures. The previously reported epidemiological study had sufficient statistical power to detect an average illness rate of approximately 17 swimming associated GI illnesses per 1000 recreation events or greater, and found no consistent relationships between water quality measured by fecal indicator organisms (FIO) and swimming-associated illnesses (U.S. EPA, 2010a). The QMRA incorporated monitoring data for pathogens and fecal indicators collected during the epidemiological study period and calculated average swimming-associated illness levels that were approximately two GI illnesses per 1000 recreation events. To our knowledge, this is the first time that a comprehensive water quality monitoring program and QMRA analysis has been conducted in parallel with a recreational water epidemiological study. The QMRA results were consistent with the low rate of reported illnesses during the 2009 epidemiological study (i.e. <17 GI illnesses per 1000 recreation events) and provide additional context for understanding the epidemiological results. The results illustrate that coupling QMRA with an epidemiological study at a single study site provides a unique ability to understand human health illnesses especially under conditions where water quality, as measured by traditional FIO is good and/or average illness rates are lower than can be quantified via epidemiological methods alone. (C) 2015 Elsevier B.V. All rights reserved.

Introduction: The Risk Of Bias in Non-randomized Studies – of Interventions (ROBINS-I) tool evaluates internal validity (risk of bias) in non-randomized studies of interventions in comparison to an ideal (hypothetical) randomized trial. The use of ROBINS-I in studies dealing with exposures or interventions in environmental health has not yet been explored. This study evaluated the usability and applicability of ROBINS-I in studies of environmental health (EH) exposure. Methods: Three researchers in sequential rounds applied ROBINS-I to three systematic reviews of EH exposures: bisphenol-A and obesity; perfluorooctanoic acid and birth weight; and polybrominated diphenyl ethers and thyroid function. We began by providing instructions for application of ROBINS-I to EH studies, including possible confounders and co-exposures specific to the exposures considered in the three reviews. For the first two rounds of testing, two reviewers independently applied ROBINS-I and provided feedback on usability of the tool. Barriers and facilitators to the appropriateness of ROBINS-I for environmental health were identified and modifications made to the tool, as necessary. For the third round of testing, three reviewers independently applied the tool and came to consensus on item-level and overall study risk of bias. Results: Suggested modifications ranged from syntax and wording to conceptual changes to the tool. The term "intervention" was replaced with "exposure" throughout the document. Additional instructions were provided to address assessment of cross-sectional studies. Fields to collect information on measurement of exposures and outcomes of interest was added to the project protocol. Additional granularity was added to the measurement of interventions/exposure domain. Conclusion: Modifications made to the risk of bias tool to tailor it to studies of EH exposure increased understanding and application of the tool, as well as consistency in responses.

We simulate the influence of multiple sources of enterococci (ENT) as faecal indicator bacteria (FIB) in recreational water bodies on potential human health risk by considering waters impacted by human and animal sources, human and non-pathogenic sources, and animal and non-pathogenic sources. We illustrate that risks vary with the proportion of culturable ENT in water bodies derived from these sources and estimate corresponding ENT densities that yield the same level of health protection that the recreational water quality criteria in the United States seeks (benchmark risk). The benchmark risk is based on epidemiological studies conducted in water bodies predominantly impacted by human faecal sources. The key result is that the risks from mixed sources are driven predominantly by the proportion of the contamination source with the greatest ability to cause human infection (potency), not necessarily the greatest source(s) of FIB. Predicted risks from exposures to mixtures comprised of approximately 30% ENT from human sources were up to 50% lower than the risks expected from purely human sources when contamination is recent and ENT levels are at the current water quality criteria levels (35 CFU 100 mL-1). For human/non-pathogenic, human/gull, human/pig, and human/chicken faecal mixtures with relatively low human contribution, the predicted culturable enterococci densities that correspond to the benchmark risk are substantially greater than the current water quality criteria values. These findings are important because they highlight the potential applicability of site specific water quality criteria for waters that are predominantly un-impacted by human sources.