Systematic evidence map (SEM) template: Report format and methods used for the US EPA Integrated Risk Information System (IRIS) program, Provisional Peer Reviewed Toxicity Value (PPRTV) program, and other "fit for purpose" literature-based human health analyses.

BACKGROUND: Systematic evidence maps (SEMs) are gaining visibility in environmental health for their utility to serve as problem formulation tools and assist in decision-making, especially for priority setting. SEMs are now routinely prepared as part of the assessment development process for the US Environmental Protection Agency (EPA) Integrated Risk Information System (IRIS) and Provisional Peer Reviewed Toxicity Value (PPRTV) assessments. SEMs can also be prepared to explore the available literature for an individual chemical or groups of chemicals of emerging interest. OBJECTIVES: This document describes the typical methods used to produce SEMs for the IRIS and PPRTV Programs, as well as "fit for purpose" applications using a variety of examples drawn from existing analyses. It is intended to serve as an example base template that can be adapted as needed for the specific SEM. The presented methods include workflows intended to facilitate rapid production. The Populations, Exposures, Comparators and Outcomes (PECO) criteria are typically kept broad to identify mammalian animal bioassay and epidemiological studies that could be informative for human hazard identification. In addition, a variety of supplemental content is tracked, e.g., studies presenting information on in vitro model systems, non-mammalian model systems, exposure-level-only studies in humans, pharmacokinetic models, and absorption, distribution, metabolism, and excretion (ADME). The availability of New Approach Methods (NAMs) evidence is also tracked (e.g., high throughput, transcriptomic, in silico, etc.). Genotoxicity studies may be considered as PECO relevant or supplemental material, depending on the topic and context of the review. Standard systematic review practices (e.g., two independent reviewers per record) and specialized software applications are used to search and screen the literature and may include the use of machine learning software. Mammalian bioassay and epidemiological studies that meet the PECO criteria after full-text review are briefly summarized using structured web-based extraction forms with respect to study design and health system(s) assessed. Extracted data is available in interactive visual formats and can be downloaded in open access formats. Methods for conducting study evaluation are also presented which is conducted on a case-by-case basis, depending on the usage of the SEM.

Occurrence and distribution of hexavalent chromium in groundwater from North Carolina, USA.

Hexavalent chromium (Cr(VI)) is a groundwater contaminant that is potentially harmful to human health. Understanding the occurrence of Cr(VI) in groundwater resources is critical for evaluating its risks to human health. Here we report a large dataset (n = 1362) of Cr(VI) and total chromium (CrT) concentrations in public, private, and monitoring wells from different aquifers across North Carolina. These water quality data come from new and previous measurements conducted at Duke University, as well as data reported by the U.S. Environmental Protection Agency, the N.C. Department of Environmental Quality, and the U.S. Geological Survey. The data confirm that Cr(VI) is the predominant species of dissolved Cr and that groundwater from aquifers in the Piedmont region contain significantly higher concentrations than groundwater from the coastal plain. Though there is only one exceedance of the U.S. EPA Maximum Contaminant Level (100 µg/L for CrT) in the dataset, over half of all wells measured for Cr(VI) (470 out of 865) in the dataset exceeded the N.C. Health Advisory Level of 0.07 µg/L. Using information from this dataset, we explore three different approaches to predicting Cr(VI) in groundwater: (1) CrT concentrations as a proxy for Cr(VI); (2) Exceedance probabilities of health goals for groundwater from aquifers located in specific geologic areas; and (3) Censored linear regression using commonly measured field parameters (pH, electrical conductivity, dissolved oxygen) with relationships to Cr(VI) as regressors. Combining these approaches, we have identified several areas in the Piedmont region where Cr(VI) in drinking water wells is expected to be higher than the advisory level, which coincide with large population groundwater reliant populations. While this study focuses on N.C., the wide-spread occurrence of Cr(VI) in groundwater at concentrations above health guidelines in aquifers of the Piedmont region could pose high human health risks to large populations in the eastern U.S.