In Vivo Mercury (De)Methylation Metabolism in Cephalopods under Different pCO2 Scenarios

Demethylation by Reactive Oxygen Species Lowers Methylmercury Accumulation in Rice

It is a paradox that the accumulation of neurotoxic methylmercury (MeHg) in rice is generally low despite efficient MeHg production in paddies and absorption by rice plants. Because rice-paddy systems are conducive to reactive oxygen species (ROS) generation and ROS have recently been revealed to efficiently demethylate MeHg absorbed in autotrophs, we propose that ROS, generated in soils and plants, are significant yet overlooked drivers that lower MeHg accumulation in rice. ROS-mediated demethylation in both soils and rice plants is estimated to have reduced rice MeHg by 84%, highlighting the importance of these overlooked drivers in safeguarding global rice consumers.

Ecotoxicology of cephalopod early life phases: review and perspectives

The present review provides the first analysis and synthesis of the available scientific information on the effects of anthropogenic contaminants on cephalopod embryos, paralarvae, and juveniles. We evaluated 46 articles published between 1970 and 2023 that focused on trace elements (69%), pharmaceutical compounds (11%), persistent organic compounds (11%), and plastics (9%). To date, the greatest scientific effort has originated from Europe and Asia (France [57%], China [9%], Italy [7%], and Spain [4%]), with few reports available from the rest of the world. Most studies focused on species of economic importance (cuttlefish [69%], octopuses [18%], and squid [13%]), with few reports on species of low commercial value or that reside in remote habitats such as nautiluses. Although 28 contaminants have been evaluated, cadmium, copper, zinc, fluoxetine (FLX), polycyclic aromatic hydrocarbons (PAHs), organophosphorus compounds, and tributyltin (TBT) were the only contaminants associated with adverse effects on various biological, physiological, and ethological processes during early life phases. Despite these advances, the present review demonstrates the crucial need for ecotoxicology studies that focus on (i) embryotoxicology and the interactions among toxic agents during the early stages of cephalopod development, (ii) survival and recruitment, and (iii) species that inhabit coastal and oceanic environments that have not yet been the focus of previous studies, especially those in countries with few published records. With this information, critical areas can be identified, marine biodiversity monitoring programs can be developed, and effective conservation strategies can be created that include measures to mitigate marine pollution.

Organ-specific mercury stable isotopes, speciation and particle measurements reveal methylmercury detoxification processes in Atlantic Bluefin Tuna

Identifying metabolism and detoxification mechanisms of Hg in biota has important implications for biomonitoring, ecotoxicology, and food safety. Compared to marine mammals and waterbirds, detoxification of MeHg in fish is understudied. Here, we investigated Hg detoxification in Atlantic bluefin tuna Thunnus thynnus using organ-specific Hg and Se speciation data, stable Hg isotope signatures, and Hg and Se particle measurements in multiple tissues. Our results provide evidence for in vivo demethylation and biomineralization of HgSe particles, particularly in spleen and kidney. We observed a maximum range of 1.83‰ for δ202Hg between spleen and lean muscle, whereas Δ199Hg values were similar across all tissues. Mean percent methylmercury ranged from 8% in spleen to 90% in lean muscle. The particulate masses of Hg and Se were higher in spleen and kidney (Hg: 61% and 59%, Se: 12% and 6%, respectively) compared to muscle (Hg: 2%, Se: 0.05%). Our data supports the hypothesis of an organ-specific, two-step detoxification of methylmercury in wild marine fish, consisting of demethylation and biomineralization, like reported for waterbirds. While mass dependent fractionation signatures were highly organ specific, stable mass independent fractionation signatures across all tissues make them potential candidates for source apportionment studies of Hg using ABFT.

Mercury transformations in algae, plants, and animals: The occurrence, mechanisms, and gaps

Mercury (Hg) is a global pollutant showing potent toxicity to living organisms. The transformations of Hg are critical to global Hg cycling and Hg exposure risks, considering Hg mobilities and toxicities vary depending on Hg speciation. Though currently well understood in ambient environments, Hg transformations are inadequately explored in non-microbial organisms. The primary drivers of in vivo Hg transformations are far from clear, and the impacts of these processes on global Hg cycling and Hg associated health risks are not well understood. This hinders a comprehensive understanding of global Hg cycling and the effective mitigation of Hg exposure risks. Here, we focused on Hg transformations in non-microbial organisms, particularly algae, plants, and animals. The process of Hg oxidation/reduction and methylation/demethylation in organisms were reviewed since these processes are the key transformations between the dominant Hg species, i.e., elemental Hg (Hg0), divalent inorganic Hg (IHgII), and methylmercury (MeHg). By summarizing the current knowledge of Hg transformations in organisms, we proposed the potential yet overlooked drivers of these processes, along with potential challenges that hinder a full understanding of in vivo Hg transformations. Knowledge summarized in this review would help achieve a comprehensive understanding of the fate and toxicity of Hg in organisms, providing a basis for predicting Hg cycles and mitigating human exposure.

Challenges and strategies for preventing intestinal damage associated to mercury dietary exposure

Food represents the major risk factor for exposure to mercury in most human populations. Therefore, passage through the gastrointestinal tract plays a fundamental role in its entry into the organism. Despite the intense research carried out on the toxicity of Hg, the effects at the intestinal level have received increased attention only recently. In this review we first provide a critical appraisal of the recent advances on the toxic effects of Hg at the intestinal epithelium. Next, dietary strategies aimed to diminish Hg bioavailability or modulate the epithelial and microbiota responses will be revised. Food components and additives, including probiotics, will be considered. Finally, limitations of current approaches to tackle this problem and future lines of research will be discussed.