Striped marlin shows higher modeled dietary risk from mercury in Gulf of California

Sport-caught striped marlin from the southern Gulf of California yielded higher modeled non-carcinogenic risk estimates than dolphinfish under the study’s consumption assumptions, according to an observational assessment of 151 fish. Hazard-index estimates exceeded 1 for 82.8% of children, 45.3% of women of childbearing age and 32.8% of men evaluated for striped marlin consumption, while all dolphinfish estimates remained below 1. Mercury, rather than arsenic or selenium, was the dominant contributor to both species’ risk estimates.

These are screening calculations, not evidence that consumption causes illness, and they depend on treating total mercury as a methylmercury surrogate and assuming that inorganic arsenic accounts for 10% of total arsenic. The researchers sampled muscle and liver from 86 dolphinfish, Coryphaena hippurus, and 65 striped marlin, Kajikia audax, collected during sport-fishing trips off Cabo San Lucas, Mexico, in 2018 and 2019. The sample comprised 40 male and 46 female dolphinfish, with a mean fork length of 81.2 ± 14.7 centimeters and mean weight of 4.7 ± 2.8 kilograms.

It included 32 male and 33 female striped marlin, whose mean lower-jaw fork length was 183.4 ± 19.4 centimeters and mean weight 31.9 ± 10.7 kilograms. Fish were selected because striped marlin commonly occur in the area and the Gulf of California receives contaminants from mining, intensive agriculture, shrimp aquaculture, fisheries and urban activity, according to the study. Tissue preparation and elemental analysis were designed to measure mercury, arsenic and selenium in both species and both tissues.

Muscle and liver samples were frozen at −19°C, freeze-dried at −48°C and 133 × 10−3 mbar for 48 hours, and ground with an agate mortar. Portions weighing 0.25 grams underwent overnight acid addition and three-hour digestion in capped vessels at 120°C. Total mercury was measured by cold-vapor atomic absorption spectrophotometry, total arsenic by hydride-generation atomic absorption spectrophotometry and selenium by graphite-furnace atomic absorption spectrophotometry. Duplicate samples, high-purity reagents, ultrapure water and certified reference materials were used for quality control, with reference-material recoveries of 94–96% for mercury, 92–95% for selenium and 98–102% for arsenic.

All reported concentrations were converted from dry weight to micrograms per gram of wet weight. Median concentrations in dolphinfish muscle were 0.08 micrograms per gram wet weight for mercury, 0.81 for arsenic and 0.20 for selenium. Its liver medians were 0.09 micrograms per gram for mercury, 2.40 for arsenic and 0.27 for selenium.

In striped marlin muscle, the corresponding medians were 0.29 micrograms per gram for mercury, 0.591 for arsenic and 0.27 for selenium; liver medians were 0.12 for mercury, 1.50 for arsenic and 0.23 micrograms per gram for selenium. Arsenic had the highest median concentration in every species-and-tissue combination, but the modeled risk rankings differed because the assessment incorporated element-specific oral reference doses and the assumed inorganic fraction of total arsenic. Element concentrations generally increased with fish size in significant associations identified by Spearman rank correlation and Bonferroni correction.

Mercury in both muscle and liver was positively associated with length and weight in both species, with correlation coefficients of 0.408–0.461 in dolphinfish and 0.463–0.551 in striped marlin. Dolphinfish length and weight were also positively associated with arsenic in muscle and liver, with coefficients of 0.429–0.461. In striped marlin, weight was positively associated with arsenic and selenium in muscle, at 0.497 and 0.435, respectively, but no significant relationships linked those elements to body size in liver.

Selenium in dolphinfish muscle was not significantly associated with size. The researchers did not directly measure fish age, so the observed size relationships do not by themselves establish that larger fish had experienced longer exposure. Comparisons between the 2018 and 2019 sampling periods found no statistically significant differences in elemental concentrations within the compared tissues of either species.

The researchers therefore pooled the two years for the dietary assessment. That finding covers only the sampled years and does not establish that contaminant levels remained stable over longer periods. The catch also had a size profile that may limit generalization: sampled dolphinfish were adults, apparently reflecting the tendency of sport-fishing tournaments to target larger fish, whereas most sampled striped marlin were below reported lower-jaw fork lengths at first maturity.

For the dietary calculations, researchers used estimated per-capita consumption rates in northwestern Mexico of 4.1 grams per day for dolphinfish and 21.9 grams per day for striped marlin. Exposure was estimated for three consumer groups: children weighing 30 kilograms, women of childbearing age weighing 65 kilograms and men weighing 75 kilograms. The assessment used oral reference doses of 0.0003 milligrams per kilogram of body weight per day for arsenic, 0.0001 for mercury expressed as methylmercury and 0.0005 for selenium.

For every species and consumer group, the hazard quotient for mercury was greater than that for selenium, which in turn was greater than the arsenic hazard quotient. Mercury accounted for more than 93% of the combined hazard index for dolphinfish: 93.2% for children, 93.26% for women of childbearing age and 93.43% for men. In striped marlin, its contribution was approximately 97.6% in each group, reaching 97.57% for children and women of childbearing age and 97.56% for men.

The different hazard-index results for the two species therefore emerged from the combined influence of measured concentrations, species-specific consumption rates and consumer body weights, rather than from a simple comparison of total mercury concentrations. All hazard-index values associated with dolphinfish were below 1. For striped marlin, 53 of 64 samples exceeded 1 in the children’s scenario, 29 of 64 did so for women of childbearing age and 21 of 64 for men.

The study describes these proportions as estimates for the specified groups and consumption assumptions, not observed clinical outcomes. The hazard index is a screening approach and does not establish that harm will occur. The analysis also did not characterize exposure from every fish species in a consumer’s diet, and its population-wide consumption rates may not capture differences associated with socioeconomic status.

Although fishing-dependent households may consume fish at higher rates, the study did not directly quantify those variations. The absence of direct chemical speciation also limited the assessment: methylmercury was not measured separately, and inorganic arsenic was represented by an assumed share of total arsenic rather than direct measurement. The researchers also calculated a selenium health-benefit value, or HBVSe, using the molar concentrations of selenium and mercury.

All values were positive in muscle and liver from both species, indicating a molar excess of selenium over mercury. Mean HBVSe values were 2.51 in dolphinfish muscle and 2.99 in striped marlin muscle; values were higher in liver. The authors interpreted the pattern as indicating potential selenium–mercury antagonism, in which selenium may mitigate effects associated with mercury.

This toxicological model does not directly show that selenium cancels dietary mercury risk in people, and the positive values coexist with the screening estimates in which mercury remains the principal source of potential risk. By measuring mercury, arsenic and selenium simultaneously in the muscle and liver of both species, the study expands a regional evidence base in which monitoring has been uneven and arsenic data are particularly limited. The results show that the highest measured median concentrations were for arsenic, while the modeled risk estimates were driven chiefly by mercury.

For people who consume fish frequently, the study supports continued monitoring and dietary risk assessment, particularly for children and women of childbearing age, as well as broader consideration of consumers with elevated fish-consumption rates. It does not establish that the sampled fish are broadly unsafe to eat, identify an actual clinical effect or resolve the uncertainties created by assumed chemical speciation, limited dietary data and a sport-fishing sample. Direct measurement of mercury and arsenic species, more representative sampling and more detailed information about individual consumption would be needed for a more precise assessment of exposure.

Subject of Research: Dietary mercury, arsenic and selenium risk assessment in Gulf of California dolphinfish and striped marlin

Article Title: Health risk assessment associated with Hg, As, and Se in the dolphinfish Coryphaena hippurus and the striped marlin Kajikia audax from the southern Gulf of California

Article References: Ruelas-Inzunza, J., Arriaga-Flores, Y. K., Sánchez-Osuna, K. G., Gil-Manrique, B., Escobar-Sánchez, O., Spanopoulos-Zarco, P., & Vega-Sánchez, B. (2026). Health risk assessment associated with Hg, As, and Se in the dolphinfish Coryphaena hippurus and the striped marlin Kajikia audax from the southern Gulf of California. Frontiers in Marine Science, 13, Article 1950335. https://doi.org/10.3389/fmars.2026.1950335

Image Credits: AI Generated

DOI: 10.3389/fmars.2026.1950335

Keywords: dolphinfish, striped marlin, mercury, arsenic, selenium, dietary risk assessment, hazard index, Gulf of California, marine fish, food contaminants, Health, risk