Updated arsenic toxicity values shift risk estimates in Eskişehir water study

Updated arsenic toxicity values substantially changed the health-risk interpretation of unchanged drinking-water samples in a basin-fed system influenced by geothermal activity, according to a study of 42 municipal, spring, and river-water samples from ten districts in Eskişehir Province, Türkiye. Arsenic exceeded the World Health Organization and Turkish national TS266 guideline value of 10 micrograms per liter in nearly one-third of the samples, yet the Water Quality Index classified almost all samples as “Excellent” under the same guideline values. When the researchers applied arsenic toxicity values from the January 2025 U.S. Environmental Protection Agency IRIS update, the Hazard Index and modeled cancer risk rose above acceptable thresholds at most sites. The legacy 1995 arsenic values flagged far fewer locations using the identical measured concentrations.

The contrast arose because the study evaluated the same water chemistry against two different toxicological bases. The drinking-water guideline and the toxicological reference values are revised independently, so compliance with a concentration guideline does not necessarily provide a current assessment of health risk. The authors do not characterize the arsenic guideline as flawed. Instead, their results show a structural disconnect between regulatory compliance and contemporary toxicological evidence, demonstrating that a water supply can meet guideline-based quality classifications while producing substantially different risk estimates after arsenic toxicity information is updated.

Trace-element measurements showed that arsenic was the principal contributor to cumulative risk in this system. The researchers quantified 17 elements by inductively coupled plasma mass spectrometry, then assessed health risk deterministically and probabilistically. Arsenic concentrations were correlated with antimony, lithium, and boron, a pattern consistent with a shared geogenic source rather than treatment-related contamination. Municipal and spring samples also had broadly similar trace-element profiles. These observations connect arsenic exposure to the basin’s geothermally influenced geology, although the supplied findings do not establish the precise contribution of any individual geological or treatment process.

Monte Carlo simulation indicated that the difference between the updated and legacy arsenic values was robust to uncertainty in exposure parameters. In other words, varying modeled exposure conditions did not remove the divergence: the revised arsenic toxicity inputs continued to produce higher risk classifications than the older values for the same samples. The result supports the conclusion that updated toxicological information, rather than a change in water quality, drove the reclassification. It also shows why a health-risk assessment based only on a regulatory guideline may not capture the implications of newer dose-response information.

The study is a focused environmental-health assessment rather than a nationwide survey or a clinical investigation. It covers one basin-fed drinking-water system, 42 samples and ten districts in Eskişehir, and its modeled results should not automatically be generalized to other aquifers, cities or water-source types. The reported outcomes are estimates derived from measured water chemistry and toxicological inputs, not observations of diagnosed illness among residents. Even with those limits, the case study has implications beyond arsenic: it demonstrates that unchanged samples can receive a different health-risk interpretation when reference values are revised, and that cumulative assessment of multiple trace elements may reveal risks not apparent from a guideline exceedance count alone.

Subject of Research: Arsenic-based health-risk reassessment of a geothermally influenced drinking-water basin in Eskişehir, Türkiye

Article Title: Updated arsenic toxicity values substantially alter health-risk interpretation in a regulation-compliant, geothermally influenced basin-fed drinking-water system

Article References: Çetinkaya, S., Benkli, A. B., & Erdem, O. (2026). Updated arsenic toxicity values substantially alter health-risk interpretation in a regulation-compliant, geothermally influenced basin-fed drinking-water system. Environmental Geochemistry and Health, 48(16), Article 652. https://doi.org/10.1007/s10653-026-03489-x

Image Credits: AI Generated

DOI: 10.1007/s10653-026-03489-x

Keywords: arsenic, drinking water, health risk, Eskişehir, toxicology, ICP-MS, Monte Carlo simulation, geogenic contamination, Hazard Index, water quality, Updated, toxicity