Bioavailability and adverse health effects of Hg from foods on humans: A critical review

Mercury (Hg) is a potent neurotoxin that poses a health threat to the global population. Mercury exposure occurs via multiple pathways, whereas dietary exposure is the dominant route in the general human population, including fish, seafood, and rice consumption. Microorganisms may convert Mercury-containing compounds may be transformed into methylmercury (MeHg) by microorganisms in the environment. MeHg poses a severe hazard to human health through bioaccumulation and biomagnification through the food chain. MeHg exposure adversely affects neurodevelopment, leading to reduce cognitive function. Besides MeHg exposure may also impair the immune system and reproductive system. Approximately 20 million people worldwide are at risk from Hg exposure. Due to the bioconcentration and amplification of Hg, as well as the genotoxic and carcinogenic potential, it is essential to study the health risks and detrimental effects of human Hg exposure through dietary intake. Dietary consumption of Hg-polluted foods may trigger health risks. The majority of existing studies assessed health risks based on total heavy metals, leading to overestimating risks as not all heavy metals are available for human gastrointestinal absorption. Hence, bioaccessible heavy metals have been commonly employed since they refer to the largest dissolved fraction of heavy metals that are available for human absorption. However, the existing assessment models based on total or bioaccessible heavy metals were recently pointed out to overestimate their risks, due to lacking biotic components and ignoring the physiological function of humans, so exploring accurate assessment methods based on bioavailability referring to the percentage of heavy metals absorbed into the human body are considered to be more scientific and precise. In the present review, we collected the existing literature on dietary Hg exposure and summarized the exposure pathways, bioavailability/bioaccessibility of Hg in humans, as well as the pollution sources and the toxic effects of Hg exposure in humans. This study aims to assess the health risks of Hg exposure through the oral intake route in humans, and proposes existing research gaps and future development directions, while providing an effective theoretical basis for implementing the Minamata Convention. The results show that existing studies on food Hg are centered on seafood, rice, mushrooms, vegetables, and breast milk. Interestingly, the Hg bioavailability/bioaccessibility was independent of total Hg concentration, while Hg/selenium ratios, nutrition, cooking methods, and food composition altered the effective state of Hg. Notably, Hg exposure has large negative health impacts-even at low concentrations on humans. The toxicity of Hg to human health mainly includes the nervous system, immune system, and reproductive system. Although each Hg species possesses distinct physicochemical properties and may exert distinct biological effects, however, most Hg compounds are toxic. Further investigation on the behavior of Hg compounds and their interactions with the human body should be carried out to broaden the knowledge and to improve measures against Hg toxicity. Secondly, other possible Hg-polluted foods should be explored to investigate their interactions with Hg behaviors and underlying mechanisms. Thirdly, it is necessary to establish personalized assessment models to accurately assess the health risks. In addition, the effective monitoring, prevention, and remediation measures should also be developed for Hg pollution monitor to reduce the human health risks of dietary Hg exposure.