Determinations of methylmercury and mercury methylation/demethylation rate constants in environmental samples using isotope dilution/tracing methods by automatic ethylation-purge and trap-GC-ICP-MS.

BACKGROUND

Mercury (Hg), especially methylmercury (MeHg) as a most toxic format of Hg in the environment, has been paid widely concern due to its high bioaccumulative capability and great risk to humans. Great efforts have been made to develop ethylation-purge and trap-gas chromatography-inductively coupled plasma mass spectrometry system for MeHg analysis and Hg biogeochemical cycling investigation. However, the generally manual operation limits the analytical efficiency, and the lack of applications in the real environmental samples restricts the future study. There is a great need for a rapid and accurate method to determine MeHg and Hg methylation/demethylation processes in environmental samples.

RESULTS

Herein, an automatic ethylation-purge and trap-GC-ICP-MS system based on isotope dilution method for MeHg analysis was developed. The results showed that the limit of detection of the developed method was 0.01 ng L, the MeHg can be analyzed within 6 min with a relative standard deviation of 4.3 %. The accuracy of this proposed method was verified by the satisfying recoveries of certified reference materials (99.0 ± 0.35 % in ECM-CC580, sediment; 98.0 ± 0.67 % in DORM-4, Fish protein). In addition, comparable concentrations of MeHg in natural water were measured using both of the developed and classical distillation methods. Subsequently, the developed method was adapted for measuring concentrations of MeHg in the water, sediment, and fish muscle collected from the coastal and freshwater systems. Finally, the photic demethylation and biotic methylation/demethylation rate constants in natural surface water and sediment were determined using isotope dilution/tracing methods by automatic ethylation-purge and trap-GC-ICP-MS.

SIGNIFICANCE AND NOVELTY

The developed automatic ethylation-purge and trap-GC-ICP-MS system is promising for accurate and convenient MeHg analysis and Hg biogeochemical cycling investigation in real environmental samples with isotope dilution and tracing methods.