Shellfish Safety: Checking Mercury and Selenium Levels

Jenn Hoskins
16th March, 2024

Shellfish Safety: Checking Mercury and Selenium Levels

Image Source: Natural Science News, 2024

Key Findings

  • Study in Southeast India found shellfish have safe levels of selenium and mercury
  • Selenium in shellfish can help protect against mercury toxicity
  • All shellfish types studied had more selenium than mercury, indicating low health risks
Seafood, particularly shellfish, is a staple in many diets around the world, prized for its nutritional value. However, the presence of trace metals like mercury (Hg) and selenium (Se) in seafood has raised concerns about potential health risks. A recent study by researchers at the Tamil Nadu Dr. J. Jayalalithaa Fisheries University (TNJFU)[1] has shed light on these concerns by examining the concentrations of Se and Hg in shellfish from the Gulf of Mannar (GoM) coast in Southeast India, and assessing the associated health risks. Mercury is a toxic element that can have harmful effects on the nervous system, particularly in children and fetuses. Selenium, on the other hand, is an essential nutrient that plays a critical role in maintaining proper thyroid function and antioxidant defenses. Interestingly, selenium can also mitigate mercury toxicity. The balance between these two elements in seafood is, therefore, a critical factor in determining its safety for consumption. The TNJFU study investigated the levels of Se and Hg in various shellfish species, including shrimp, crab, cephalopods, and bamboo shark. The results showed that Se concentrations varied across species but remained within safe limits, while Hg levels were consistently below the maximum residual limits set by food safety authorities. This is reassuring news for seafood lovers, as it suggests that shellfish from the GoM coast can be consumed without exceeding the recommended daily intake of Se or the upper limit of Hg. A notable aspect of the study was the finding that the Se:Hg molar ratio in all shellfish samples was greater than 1, indicating an abundance of selenium relative to mercury. This is significant because a higher Se:Hg ratio has been associated with reduced mercury toxicity. Previous research has suggested that selenium's protective effects against mercury may be due to the formation of a Se-Hg complex that is less harmful[2][3]. In this context, the high Se:Hg ratios observed in the GoM shellfish provide a measure of safety against mercury's potential adverse health effects. The study also found that Se levels in shellfish negatively correlated with the trophic level and size of the organisms, while Hg levels showed a positive correlation. This means that larger, higher-trophic-level species like sharks tend to accumulate more mercury and less selenium. Despite this, the health risks associated with mercury in these shellfish were still deemed negligible, as indicated by target hazard quotients and hazard indexes below 1 for all age groups. These findings from the GoM coast are consistent with other studies conducted in different parts of the world. For instance, research in Brazil[4] highlighted the bioaccumulation of trace metals in fish, emphasizing the need for continuous monitoring of these substances in aquatic food sources. Similarly, studies on wild mammals[3] and fish from East Kolkata Wetlands[5] have contributed to our understanding of metal toxicity and its impact on food safety. In conclusion, the TNJFU study offers valuable insights into the safety of shellfish consumption in Southeast India. By analyzing the levels of Se and Hg, the research provides evidence that the shellfish in this region are safe to eat, with Se concentrations that meet dietary needs without exceeding safe limits for mercury exposure. This research not only contributes to the local context but also complements global efforts to ensure the safety of seafood consumption. It serves as a reminder of the importance of monitoring and managing environmental contaminants to protect public health and maintain the integrity of our food systems.

NutritionHealthMarine Biology


Main Study

1) Biomonitoring of mercury and selenium in commercially important shellfish: Distribution pattern, health benefit assessment and consumption advisories.

Published 14th March, 2024

Related Studies

2) Mercury and selenium co-ingestion assessment via rice consumption using an in-vitro method: Bioaccessibility and interactions.

3) Selenium and mercury concentrations, Se:Hg molar ratios and their effect on the antioxidant system in wild mammals.

4) Bioaccumulation and health risk assessment of trace metal contamination in the musculature of the trahira fish (Hoplias malabaricus) from two neotropical rivers in southeastern Brazil.

5) Health risk assessment and metal contamination in fish, water and soil sediments in the East Kolkata Wetlands, India, Ramsar site.

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