In Vivo Mercury Methylation and Demethylation in Freshwater Tilapia Quantified by Mercury Stable Isotopes

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Original languageEnglish
Pages (from-to)7949-7957
Journal / PublicationEnvironmental Science and Technology
Issue number14
Online published10 Jun 2013
Publication statusPublished - 16 Jul 2013
Externally publishedYes


In vivo methylation and demethylation processes were simultaneously investigated in freshwater tilapia after dietary exposure to mercury (198Hg(II) and methyl200Hg). During one month dietary exposure followed by two month depuration, both MeHg and THg increased continuously in muscle tissues but decreased in liver during depuration, indicating the inter-organ transportation of MeHg from liver toward muscle. Direct evidence of in vivo net methylation process in freshwater tilapia was observed. Specifically, 0.67-1.60% of the ingested Hg198(II) was converted into Me198Hg and deposited in fish muscle at the end of depuration. The methylation potential in terms of methylated fraction was elevated at higher temperature and decreased at higher dosage. However, no direct evidence of MeHg demethylation was observed. In contrast to some previous reports of dose-dependent demethylation, the percentage of MeHg in the liver decreased significantly with increasing THg concentrations, likely due to the faster inter-organ MeHg transportation from liver toward muscle. Our study demonstrates the important role of organ- and species-specific biodynamics in understanding mercury transformation and speciation in fish. The observed in vivo methylation process in tilapia was slow, suggesting that the high %MeHg in fish should be mainly derived from MeHg ingestion instead of in vivo transformation. © 2013 American Chemical Society.