ICP-MS/MS as a tool to study abiotic methylation of inorganic mercury reacting with VOCs

Abstract

Methylmercury (CH₃Hg) is one of the most widespread toxic contaminants. Although the formation of CH₃Hg in aqueous environments has been widely investigated, little information is available on direct anthropogenic or natural emissions of CH₃Hg to the atmosphere. In this work, ICP-MS/MS was chosen as a tool to study abiotic methylation of inorganic mercury reacting with VOCs in a gas environment for the first time. We found that the gaseous Hg⁺ ions were transformed to the more toxic CH₃Hg⁺ ions instantaneously when colliding with some VOCs. Several VOCs, e.g., methyl iodide (CH₃I), methylbenzene, acetic acid and ethyl acetate, exhibited good methylation of Hg⁺ ions with productivities of 1.77%, 1.28%, 1.35% and 1.18%, respectively. Four isotope peaks of CH₃¹⁹⁹Hg (M = 214), CH₃²⁰⁰Hg (M = 215), CH₃²⁰¹Hg (M = 216) and CH₃²⁰²Hg (M = 217) were identified when Hg⁺ ions collided with CH₃I, and the methyl group in CH₃Hg⁺ was validated by the source of CD₃I, indicating that CH₃Hg⁺ ions were formed. This study reveals that the abiotic methylation of Hg⁺ ions could occur when in contact with the VOCs in the atmosphere, leading to secondary environmental pollution.