Methylmercury speciation in fish muscle by HPLC-ICP-MS following enzymatic hydrolysis

Abstract

Monomethylmercury (MeHg + and its complexes; hereafter referred to as MeHg) in the intracellular environment is known to be predominantly bonded to thiol-containing biomolecules, but the actual identities of these target biomolecules remain unknown. While binding with glutathione acts as a detoxification mechanism for MeHg, binding with L -cysteine is thought to be the main pathway of MeHg transport across the blood-brain barrier. Here we report a HPLC-ICP-MS method that is capable of separating and analyzing MeHg-cysteine complexes (MeHgCys; charges are neglected for simplicity) and MeHg-glutathione complexes (MeHgGlu), as well as MeHgX (X ¼ H 2 O, OH À , or Cl À ) and inorganic HgX, with detection limits at the sub-micromolar levels. The method was successfully applied for the determination of MeHg speciation in a dogfish muscle sample after enzymatic hydrolysis with trypsin, and provided the first analytical evidence for the presence and dominance of MeHgCys in fish muscle.

Speciation of methylmercury in rice grown from a mercury mining area

“…Enzymatic hydrolysis was used to extract various MeHg species from the uncooked and cooked white rice samples based on a procedure developed for MeHg speciation analysis for fish muscle (Lemes and Wang, 2009). Several enzymes including trypsin, pepsin, protease K, chymotrypsin, a-amylase were tested for optimal performance with respect to the recovery of the Hg T and MeHg T concentrations and the preservation of MeHg speciation.…”

“…Approximate 1 mL of the supernatant was taken for Hg T measurement. Aliquots of supernatant from the uncooked rice sample and cooked rice sample were diluted with ultrapure water to minimize the matrix interference with the speciation analysis (Lemes and Wang, 2009). The diluted sample was adjusted to pH ¼ 5 with a 4 M acetic acid (Lemes and Wang, 2009) before being injected for MeHg speciation analysis.…”

“…Harris et al (2003) provided the first analytical evidence for the dominance of MeHgethiol complexes in fish muscle based on synchrotron-aided X-ray absorption spectroscopy. By using high performance liquid chromatography e inductively coupled plasma mass spectrometry (HPLC-ICP-MS), Lemes and Wang (2009) was the first to report that MeHg in a dogfish muscle was present almost exclusively as CH 3 Hg-L-cysteinate. Here we report the first study on the speciation of MeHg in rice grains grown from a rice paddy near a Hg mine, and the effect of cooking on MeHg speciation in rice.…”

“…CH 3 Hg-L-cysteinate (CH 3 HgCys) and CH 3 Hg-L-glutathionate (CH 3 HgGlu) were synthesized according to Lemes and Wang (2009). The mixed working solutions of various concentrations were made by stepwise dilution from the stock solution and adjusted to pH 5 before being analyzed.…”

Mercury contamination in aquatic ecosystems under a changing environment: Implications for the Three Gorges Reservoir

“…As a result, there is virtually no free Hg 2+ ions (or more accurately, the aquo complexes Hg(H 2 O) x 2+ ) in environmental or biological media. Instead, Hg(II) speciation is dominated by its complexes with dissolved organic carbon (primarily via its sulfhydral function groups) in freshwaters, with chloride in estuarine and marine waters, with sulfide and thiols in anoxic waters [15], and with thiols and thiol-containing proteins in biological systems [16]. Any changes in the type and concentration of these complexing ligands, therefore, will result in major changes in the speciation and bioavailability of Hg.…”