Mercury, often the headline concern in seafood safety, was below the limit of detection in 87.9 percent of all determinations. Every detected value in the five focal species complied with the maximum levels set under European Union regulation 2023/915, meaning that for the species most commonly landed at Sur, mercury does not currently appear to pose a compliance concern. Lead told a similar story in commercial muscle tissue, where it was entirely undetected — with one notable exception among benthic feeders, discussed below.

Cadmium, by contrast, showed a striking and statistically robust pattern of tissue partitioning. Concentrations in liver and kidney exceeded those in gill and muscle by roughly an order of magnitude across seven species examined. In the liver, where only three samples were available, the difference was confirmed statistically by a Kruskal–Wallis test (H = 25.15, p = 1.44 × 10⁻⁵).

The authors interpret this gradient as consistent with metallothionein-mediated sequestration: metal-binding proteins in the liver and kidneys actively capture and store cadmium, keeping concentrations in edible muscle comparatively low. Sur sits within an upwelling-influenced system, a setting the study links to this accumulation behaviour. The clearest compliance failure involved lead in two goatfish composite samples, which exceeded the EU maximum level of 0.300 mg/kg, with one composite measuring 0.327 mg/kg.

Goatfish are obligate benthic feeders, foraging directly on or in sediments, and the study attributes the exceedance to this sediment exposure rather than to widespread contamination of the water column. Cadmium also exceeded screening thresholds in Indian scad during accredited composite screening. The most consequential part of the assessment concerns arsenic, evaluated using the US EPA IRIS 2025 oral reference dose for inorganic arsenic of 6 × 10⁻⁵ mg/kg-day.

Because the inorganic fraction of arsenic in the sampled tissues was not measured directly, the researchers applied a precautionary assumption that 10 percent of measured arsenic is in the inorganic form. Under this scenario, Hazard Index values ranged from 0.96 in Indian mackerel to 7.28 in pharaoh cuttlefish, exceeding the threshold of 1.0 in four of the five focal species. Even at the more lenient 4 percent inorganic fraction recommended in US EPA guidance, three species still exceeded 1.0, indicating that the risk signal is not an artefact of an extreme assumption.

Carcinogenic risk estimates compounded the concern. Using the revised cancer slope factor of 32 per mg/kg-day, all five focal species exceeded the conventional carcinogenic risk threshold of 1 × 10⁻⁴, and the authors report that this conclusion held robustly across the published range of inorganic arsenic fractions. In other words, whether one assumes a conservative or a moderate conversion of total arsenic to its inorganic form, the calculated lifetime cancer risk remains above the regulatory benchmark.

Arsenic was the principal contributor to the Hazard Index in four of the five species, making speciation analysis — the direct chemical measurement of inorganic versus organic arsenic — the study’s declared primary research priority. The authors are careful about what these numbers do and do not mean. Hazard Indices and cancer slope calculations are model-based screening tools built on conservative assumptions, not measurements of actual harm to consumers, and the inorganic fraction in fish tissue was assumed rather than measured.

The liver and kidney cadmium findings rest on small sample numbers in some tissues, and the goatfish lead exceedance came from composite samples rather than individual fish. Nevertheless, as a baseline, the study establishes reference points against which future monitoring of the Ash Sharqiyah coast can be judged, and it identifies cuttlefish — a species whose Hazard Index reached 7.28 under the precautionary scenario — as the clearest candidate for follow-up arsenic speciation work. For a fishery that had never been systematically characterised, the overall picture is one of reassurance on mercury and lead in the main commercial species, a well-characterised biology-driven cadmium gradient that keeps the metal out of muscle, and a genuine, assumption-dependent open question around arsenic.

The study’s authors frame their dataset as the foundation for evidence-based monitoring on the Omani coast, with arsenic speciation now the single most valuable next measurement for converting precautionary screening estimates into a definitive assessment of consumer safety.

Subject of Research: Potentially toxic element contamination and human health risk assessment in commercially important fish from the Sur coastal waters, Oman

Article Title: Baseline assessment of potentially toxic elements in commercially important fish species from the coastal waters of Sur, Sultanate of Oman: tissue distribution and human health risk assessment

Article References: Al Alawi, M., Al Farsi, M., Al Wahibi, H., Samuel, S. D. P., Alalwiya, A. H., Al Muhaijri, N. R., Al Jafaari, H. S. A., Faltas, A. F. L., & Sudhakar, M. S. (2026). Baseline assessment of potentially toxic elements in commercially important fish species from the coastal waters of Sur, Sultanate of Oman: tissue distribution and human health risk assessment. Environmental Monitoring and Assessment, 198(11), Article 1257. https://doi.org/10.1007/s10661-026-16106-2

Image Credits: AI Generated

DOI: 10.1007/s10661-026-16106-2

Keywords: heavy metals, arsenic, cadmium, lead, mercury, seafood safety, Oman, fishery monitoring, risk assessment, tissue distribution, Environmental Monitoring and Assessment, baseline