Proof of concept for a passive sampler for monitoring of gaseous elemental mercury in artisanal gold mining

Elias de Barros Santos,Stacy Ferlin,Paleah Moher,Alexandre Guimarães Brolo,Kevin Telmer,Italo Odone Mazali,Anne Hélène Fostier

doi:10.1038/s41598-017-16713-7

Abstract

Mercury emissions from artisanal gold mining operations occurring in roughly 80 developing countries are a major workplace health hazard for millions of people as well as the largest contributor to global mercury pollution. There are no portable, cheap, and rapid methods able to inform workers or health practitioners of mercury exposure on site in remote locations. In this work, a proof of concept for a miniaturized mercury sampler, prepared by the direct reduction of gold into the porous nanostructures of Vycor glass (PVG), is introduced. Mercury retention on the PVG/Au sampler induces significant color changes, due to the formation of Au-Hg amalgam that affects the surface plasmon resonance characteristics of the material. The color change can potentially be quantified by the analysis of pictures obtained with a cell phone camera rapidly and onsite. Laboratory experiments showed the viability of using PVG/Au as passive sampler for monitoring of Hg°. PVG/Au samplers were then deployed in an artisanal and small-scale gold mining (ASGM) operations in Burkina Faso and it was able to indicate personal mercury exposures. The amount of mercury quantified in the samplers for all miners was higher than the current personal exposure limit set by the US Occupational Safety & Health Administration (OSHA).

Highlights

Mercury is naturally present in the Earth’s biogeochemical system and it can be released to the atmosphere as gaseous elemental mercury (GEM, Hg°) from natural sources, such as volcanic and geological activities[1,2], and from anthropogenic sources, such as artisanal and small-scale gold mining (ASGM), coal burning, cement production, and primary production of non-ferrous metals and chlor-alkali[3,4,5]
Gold is impregnated in a solid matrix of the porous Vycor glass (PVG), the red color, due to the collective excitation of conducting electrons in gold nanostructures called surface plasmon resonance (SPR), is similar to what is observed in colloidal suspensions of gold nanostrucutres[34,35]
Results from laboratory experiments showed that the monitoring of mercury by the passive PVG/Au sampler can be realized by either UV-vis spectroscopy or by analyzing the color channels of photos of the samplers

Summary

Introduction

Mercury is naturally present in the Earth’s biogeochemical system and it can be released to the atmosphere as gaseous elemental mercury (GEM, Hg°) from natural sources, such as volcanic and geological activities[1,2], and from anthropogenic sources, such as artisanal and small-scale gold mining (ASGM), coal burning, cement production, and primary production of non-ferrous metals and chlor-alkali[3,4,5]. The trap typically consists of a mercury absorbent material (e.g. gold or active carbon compounds) This type of sampler is expensive and impractical. McNicholas et al reported a very sensitive Hg° sensor based in gold nanoparticles deposited on carbon nanotubes, and a detection limit of 2 ppb in air was achieved[29]. This new generation of mercury sensors still require regeneration steps, which often contributes to the increase of complexity and costs. Such materials become impractical for large scale field applications In this context, the purpose of this work was to demonstrate a proof of concept for a low-cost and sensitive Hg° vapor sampler.

Objectives

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Results

Conclusion