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.

Simple and rapid formic acid sample treatment for the isolation of HgSe nanoparticles from animal tissues.

The present work explores for the first time the potential of formic acid on the extraction of tiemannite (HgSe) nanoparticles from seabird tissues, in particular giant petrels. Mercury (Hg) is considered one of the top ten chemicals of major public health concern. However, the fate and metabolic pathways of Hg in living organisms remain unknown. Methylmercury (MeHg), largely produced by microbial activity in the aquatic ecosystems is biomagnified in the trophic web. HgSe is considered the end-product of MeHg demethylation in biota and an increasing number of studies focuses on the characterization of this solid compound to understand its biomineralization. In this study, a conventional enzymatic treatment is compared with a simpler and environmentally friendly extraction by using formic acid (5 mL of = 50 % formic acid) as exclusive reagent. The analyses by spICP-MS of the resulting extracts from a variety of seabird biological tissues (liver, kidneys, brain, muscle) reveal comparable results by both extraction approaches in terms of nanoparticles stability and extraction efficiency. Therefore, the results included in this work demonstrate the good performance of employing organic acid as simple, cost effective and green procedure to extract HgSe nanoparticles from animal tissues. Moreover, an alternative consisting of a classical enzymatic procedure but with ultrasonic assistance reducing the extraction time from 12 h to 2 min is also described for the first time. The sample processing methodologies developed, combined with spICP-MS, have emerged as powerful tools for the rapid screening and quantification of HgSe nanoparticles in animal tissues. Finally, this combination allowed us to identify the possible occurrence of Cd particles and As particles associated with HgSe NPs in seabirds.

Presence of nano-sized mercury-containing particles in seafoods, and an estimate of dietary exposure.

The toxicity of nano-sized particles of mercury (NP-Hg), which are thought to be generated during the detoxification of methyl mercury (MeHg), may differ from that of MeHg, elemental Hg (Hg0), and inorganic Hg (I-Hg). From a human health perspective, it is important to evaluate the presence of NP-Hg in seafoods. We investigated the in vivo formation of NP-Hg in fish and shellfish, which are the main sources of Hg exposure in humans. NP-Hg was measured in 90 fish samples with single-particle inductively coupled plasma mass spectrometry (spICP-MS) after enzyme degradation with pancreatin and lipase. In addition to NP-Hg, total Hg (T-Hg), MeHg, and selenium (Se) concentrations were evaluated. Transient Hg signals were detected as nanoparticles from almost all samples by using spICP-MS. Higher particle number concentrations (CPN) were observed in the tuna-swordfish group than in the shellfish group (17.7 × 107 vs. 1.2 × 106 particles/g, respectively). Although the CPN and maximum particle mass increased significantly with increasing T-Hg concentration, the increase in CPN was greater than those in maximum particle mass. Assuming that the NP-Hg detected was HgSe (tiemannite) and spherical based on previous reports, the maximum particle diameter was estimated to be 89 nm. The mean dietary exposures to NP-Hg, T-Hg, and MeHg were estimated to be 0.067, 5.75, and 5.32 µg/person per day, respectively. Generation of NP-Hg was inferred to be widespread in marine animals, with a preferential increase in the number of particles rather than an increase in particle size. The mean dietary exposure to NP-Hg in Japanese people was estimated to be 1.2 ng/kg body weight (BW) per day. Compared to PTWI of 4 µg/kg BW per week (0.57 µg/kg BW per day) derived by JECFA (2011), the health risk from redissolved I-Hg from NP-Hg is small.

First finding of tiemannite, HgSe, in human bladder stones: An electron microprobe study.

Human bladder stones, surgically removed from a 4 years old boy, were studied by X-ray diffraction (XRD) and by electron microprobe analyses (EPMA). XRD data show that the bladder stones are mainly composed of struvite with minor apatite. Tiny particles, <10 µm in size, composed of mercury (Hg) and selenium (Se) were found using scanning electron microscopy (SEM) and quantitative analysis by wave-length dispersive system (WDS). On the basis of their composition, the particles consist of tiemannite, a rare mineral with the ideal formula HgSe. The young patient was not exposed to relevant mercury contamination and has no teeth fillings of amalgam. Although this observation is not conclusive, we suggest that Hg was introduced as methylmercury by food. The discovered tiemannite can be classified as endogenous mineral, i.e., directly precipitated from the same fluids that formed the host bladder stones. This assumption is supported by the fact that tiemannite and struvite can crystallize at the same temperature and pH values. As proposed for the formation of tiemannite previously reported in the liver of cetaceans, we suggest that the tiemannite in the human body represents a probable product of demethylation of Hg. In this contribution, we suggest that Hg and Se were initially collected by urine in the human body and finally precipitated to form tiemannite under appropriate chemical-physical conditions together with the formation of the host bladder stone. This observation suggests that the precipitation and accumulation of metals, including Hg and Se, in the human body can be considered a physiological response to eliminate part of these trace elements, thus enabling detoxification.