Internal dynamics of inorganic and methylmercury in a marine fish: Insights from mercury stable isotopes

Internal Dynamics and Metabolism of Mercury in Biota: A Review of Insights from Mercury Stable Isotopes

“…Lee et al (2020) 113 recently showed positive shifts in δ 202 Hg in the liver from the isotopic mixing line between the tissues without synthetic Hg exposure (control) and the iHg diet, whereas the isotopic compositions of the muscle and kidney fell on the mixing line. 113 A similar tissue-specific pattern has been reported from other fish feeding experiments with a high iHg diet. 89 , 119 Because the fish were exposed to an iHg diet and little MeHg exists in the body to be demethylated, Lee et al (2020) 113 refuted the possibility that the observed MDF in the fish liver was caused by in vivo demethylation.…”

“… 107 , 108 Prior studies have shown that a large fraction of iHg from dietary uptake accumulates in the intestinal villi and epithelial surfaces of the intestine, which is then excreted as feces and urine. 110 − 113 The preferential bioaccumulation and slow excretion of MeHg lead to much more efficient trophic transfer and biomagnification of MeHg than iHg in aquatic food webs. The potential methylation of iHg and demethylation of MeHg and the main locations for these processes in fish are still under debate.…”

“…For instance, much slower isotopic equilibration (∼1000 days) was observed in the muscle tissues of adult Pacific Bluefin Tuna fed natural squid and sardine diets (∼0.1 μg/g) compared to rapidly growing juvenile fish (∼60 days; zebrafish and flatfish) exposed to MeHg spiked food pellets (0.4 to 1.6 μg/g). 89 , 113 , 120 Therefore, tissues of fish with a faster growth rate (e.g., small fish, during early life stages) or/and high levels of MeHg exposure would reflect their short-term MeHg sources better than those of large-body fish or/and low levels of MeHg exposure.…”

“…In contrast to MeHg, fish exposed to a diet containing considerable proportions of iHg (30–100%) exhibited much slower isotopic turnover and incomplete equilibration to the iHg diet, due to the efficient excretion of iHg in most tissues. 89 , 113 , 119 Intestine was the only tissue type that showed complete isotopic equilibration to the diet because iHg cannot cross the intestinal barrier and thus accumulate in the epithelial surface and intestinal villi. 110 This suggests the potential utility of the intestine for characterizing the isotopic compositions of iHg sources in the environment.…”

“… 110 This suggests the potential utility of the intestine for characterizing the isotopic compositions of iHg sources in the environment. 113 …”