The Existence of Airborne Mercury Nanoparticles

Avik J Ghoshdastidar,Parisa A Ariya

doi:10.1038/s41598-019-47086-8

Abstract

Mercury is an important global toxic contaminant of concern that causes cognitive and neuromuscular damage in humans. It is ubiquitous in the environment and can travel in the air, in water, or adsorb to soils, snow, ice and sediment. Two significant factors that influence the fate of atmospheric mercury, its introduction to aquatic and terrestrial environments, and its bioaccumulation and biomagnification in biotic systems are the chemical species or forms that mercury exists as (elemental, oxidized or organic) and its physical phase (solid, liquid/aqueous, or gaseous). In this work, we show that previously unknown mercury-containing nanoparticles exist in the air using high-resolution scanning transmission electron microscopy imaging (HR-STEM). Deploying an urban-air field campaign near a mercury point source, we provide further evidence for mercury nanoparticles and determine the extent to which these particles contain two long suspected forms of oxidized mercury (mercuric bromide and mercuric chloride) using mercury mass spectrometry (Hg-MS). Using optical particle sizers, we also conclude that the conventional method of measuring gaseous oxidized mercury worldwide can trap up to 95% of nanoparticulate mercuric halides leading to erroneous measurements. Finally, we estimate airborne mercury aerosols may contribute to half of the oxidized mercury measured in wintertime Montréal urban air using Hg-MS. These emerging mercury-containing nanoparticle contaminants will influence mercury deposition, speciation and other atmospheric and aquatic biogeochemical mercury processes including the bioavailability of oxidized mercury to biota and its transformation to neurotoxic organic mercury.

Highlights

Mercury has no known beneficial function in the body and can cross both the blood-brain and placental barriers, with known adverse neuromuscular and developmental health effects[1,2,3]
Despite some higher concentration mass spectrometry measurements of mercuric chloride and mercuric bromide, we found these measurements to be comparable with concurrent manual denuder measurements of gaseous oxidized mercury[33], and with previous GOM and mercuric halide measurements taken at the site[10]
Analyzing TEM grids adhered to the micro-orifice uniform deposit impactor (MOUDI) stages, we find mercury and silver by EDS in an HR-STEM image of a 10 nm mercury nanoparticle sampled in ambient air at the site (Fig. 4)

Summary

Introduction

Mercury has no known beneficial function in the body and can cross both the blood-brain and placental barriers, with known adverse neuromuscular and developmental health effects[1,2,3]. It is introduced into the environment through natural and anthropogenic processes, with gaseous elemental mercury spending upwards of a year in the atmosphere travelling far from its source of origin[4,5]. Anthropogenic point sources can emit oxidized mercury or mercury present as an inorganic compound These emissions feature higher proportions of oxidized mercury than what is generally found in the atmosphere, as gaseous elemental mercury typically comprises 90% of total atmospheric mercury or greater[6]. With absolute detection limits in the picograms, gaseous Hg0 has been measured accurately, and in short time-resolution even in the most remote locations for decades

Methods

Results

Conclusion