Toxic Metals in Southwestern Atlantic Fish Pose Greater Risk Than Thought, 30-Year Review Finds

A sweeping review of three decades of research has found that commercially important marine fish along the coasts of Brazil, Uruguay, and Argentina carry measurable burdens of potentially toxic elements, and that updated toxicological criteria dramatically change how dangerous eating those fish may be. The analysis, published in Frontiers in Ocean Sustainability, is the first comprehensive and integrative evaluation of trace element contamination in the muscle tissue of coastal fish species from the Southwestern Atlantic Ocean, drawing on 97 studies published over the past 30 years.

The research team examined fourteen elements in the muscle of commercially harvested coastal species: arsenic, cadmium, chromium, copper, mercury, manganese, molybdenum, nickel, lead, rubidium, selenium, strontium, vanadium, and zinc. Several of the fish species considered, including the mullet Mugil liza, the whitemouth croaker Micropogonias furnieri, the Brazilian codling Urophycis brasiliensis, the silverside Odontesthes argentinensis, and the striped weakfish Cynoscion guatucupa, are transboundary resources that migrate across national jurisdictions and hold high ecological and economic value for the region. That mobility makes them both valuable commodities and useful sentinels of contamination, since their tissues integrate pollutant exposure across broad stretches of coastline.

The geographic picture that emerges from the review is strikingly uneven. Research on trace elements in Southwestern Atlantic marine fish has expanded substantially over the past three decades, but the expansion has been lopsided: the overwhelming majority of the 97 studies reviewed were conducted in Brazil, while Uruguay and large areas of the Argentine coast remained poorly represented. This concentration means that risk assessments for entire fishing grounds and shared stocks rest on a thin and geographically skewed evidence base, leaving substantial blind spots in a region subject to increasing anthropogenic pressures from industry, urbanization, and intensive agriculture.

Methodologically, the field has matured in important ways. The review documents the increasing use of multi-element ICP-based analytical techniques, which allow laboratories to quantify many elements simultaneously in a single sample, along with direct arsenic speciation, the process of chemically distinguishing toxic inorganic arsenic from the far less harmful organic forms that dominate most fish tissue. Quantitative human health risk assessment has also become standard practice, replacing simple comparisons of measured concentrations against maximum permissible limits with formal calculations of exposure relative to toxicological reference values.

To assess the hazards associated with fish consumption, the authors applied a harmonized framework using three established metrics: Target Hazard Quotients, which compare estimated daily intake of each element with its oral reference dose; the Hazard Index, which sums those quotients across elements to capture cumulative non-carcinogenic risk; and Carcinogenic Risk, which estimates the probability of developing cancer over a lifetime of exposure. Risk was evaluated for the general population and, where consumption data allowed, for fishing communities, whose diets typically include far more locally caught fish than average.

The most consequential finding of the review concerns arsenic, and it hinges on a technical distinction that most consumers never hear about. Total arsenic concentrations in seafood are dominated by organic compounds such as arsenobetaine, which are essentially non-toxic and rapidly excreted. Inorganic arsenic, by contrast, is a well-established carcinogen, and only its concentration should drive cancer risk estimates. Because many older studies reported only total arsenic, the authors critically re-evaluated the subset of studies with measured inorganic arsenic levels and recalculated the associated risks using the updated Oral Reference Dose and Cancer Slope Factors established in 2025 by the United States Environmental Protection Agency’s Integrated Risk Information System.

The result of that recalculation is the review’s headline statistic. When the older studies with measured inorganic arsenic were re-evaluated using the updated USEPA-IRIS Cancer Slope Factors, the proportion of cases with a Carcinogenic Risk exceeding the conventional threshold of one in ten thousand rose from 2 percent to 46 percent. In other words, applying the most current toxicological criteria transformed what had appeared to be a negligible cancer risk into a potentially significant one for nearly half of the re-evaluated cases. The authors emphasize that this does not mean the fish became more contaminated between studies; rather, the risk classification itself is highly sensitive to updated toxicological reference values, and older assessments built on superseded criteria may systematically understate the hazard.

The sensitivity of risk estimates to reference values is a lesson that extends well beyond the Southwestern Atlantic. Toxicological benchmarks such as reference doses and cancer slope factors are periodically revised as new epidemiological and toxicological evidence accumulates, and the 2025 IRIS updates reflect the latest evaluation of inorganic arsenic’s potency. A monitoring program that was fully compliant when it was designed can therefore become outdated without any change in the environment it measures. The review argues that regional seafood-safety frameworks need mechanisms for routinely recalculating risk with current criteria, rather than treating a single historical assessment as definitive.

Beyond arsenic, the review identifies a catalogue of gaps that currently limit the reliability of health risk estimates for the region. Geographic and taxonomic coverage remain incomplete, particularly for Uruguay and the Argentine coast and for the transboundary stocks that cross them. Population-specific fish consumption data are outdated or missing, which matters because exposure calculations depend directly on how much fish people eat and which species they choose. Vulnerable and high-consumption groups, including fishing communities and coastal populations that rely heavily on local catches, are underrepresented in existing assessments. Analytical harmonization across laboratories and studies is limited, and direct determination of inorganic arsenic is still the exception rather than the rule, forcing many risk assessments to rely on uncertain conversion assumptions from total arsenic measurements.

The authors position their synthesis as a regional framework for improving seafood-safety assessment, monitoring strategies, and evidence-based fisheries and public-health policies. For the Southwestern Atlantic, whose coastal zones face mounting anthropogenic pressure, the practical implications are concrete: expand monitoring into underrepresented countries and fishing grounds, prioritize direct arsenic speciation in routine analyses, update consumption surveys for the populations that actually eat the fish, and build periodic recalculations of risk into regulatory practice. For consumers, the review does not issue a simple warning against eating fish, which remains an important source of protein, selenium, and omega-3 fatty acids. Instead, it shows that the safety of the region’s seafood cannot be judged by contamination measurements alone; the verdict depends on which chemical forms of each element are present, which toxicological criteria are applied, and whose eating habits are assumed. As updated reference values ripple through the risk assessment community, the review suggests that many historical reassurances about the region’s fish may need to be revisited, and that the true margin of safety for heavy fish consumers is narrower than three decades of older studies implied.

Subject of Research: Toxic trace element contamination and human health risk from marine fish consumption in the Southwestern Atlantic Ocean

Article Title: Critical review of toxic trace elements and human health risk in marine fishes of the Southwestern Atlantic Ocean

Article References: Thompson, G., & Volpedo, A. (2026). Critical review of toxic trace elements and human health risk in marine fishes of the Southwestern Atlantic Ocean. Frontiers in Ocean Sustainability, 4, Article 1971894. https://doi.org/10.3389/focsu.2026.1971894

Image Credits: AI Generated

DOI: 10.3389/focsu.2026.1971894

Keywords: trace elements, marine fish, Southwestern Atlantic Ocean, inorganic arsenic, human health risk, carcinogenic risk, seafood safety, USEPA IRIS, Brazil, Argentina, Uruguay, fish consumption