A synthesis of mercury research in the Southern Hemisphere, part 2: Anthropogenic perturbations

Abstract

Environmental mercury (Hg) contamination is a global concern requiring action at national scales. Scientific understanding and regulatory policies are underpinned by global extrapolation of Northern Hemisphere Hg data, despite historical, political, and socioeconomic differences between the hemispheres that impact Hg sources and sinks. In this paper, we explore the primary anthropogenic perturbations to Hg emission and mobilization processes that differ between hemispheres and synthesize current understanding of the implications for Hg cycling. In the Southern Hemisphere (SH), lower historical production of Hg and other metals implies lower present-day legacy emissions, but the extent of the difference remains uncertain. More use of fire and higher deforestation rates drive re-mobilization of terrestrial Hg, while also removing vegetation that would otherwise provide a sink for atmospheric Hg. Prevalent Hg use in artisanal and small-scale gold mining is a dominant source of Hg inputs to the environment in tropical regions. Meanwhile, coal-fired power stations continue to be a significant Hg emission source and industrial production of non-ferrous metals is a large and growing contributor. Major uncertainties remain, hindering scientific understanding and effective policy formulation, and we argue for an urgent need to prioritize research activities in under-sampled regions of the SH.

Deforestation as an Anthropogenic Driver of Mercury Pollution

“…While the Amazon region overall remains a net Hg sink in BAU, the removed vegetation leads to decreased Hg 0 deposition in the Amazon (change from HIST: −105 Mg year –1 ; 95% CI: −53 to −152 Mg year –1 ) and enhanced Hg 0 emissions from soils (+35 Mg year –1 ; 95% CI: 28–275 Mg year –1 ). For the Amazon policy scenarios, we have also considered the impact that fire-mediated forest clearing , has on biomass burning emissions of Hg, which are 15 Mg year –1 (95% CI: 10–17 Mg year –1 ) larger in BAU than HIST. The BAU scenario shows atmospheric Hg 0 concentrations increasing up to 0.3 ng m –3 (+50%) within the Amazon region (Figure S11); this would be a detectable change in Hg 0 , comparable to the 0.5 ng m –3 (−30%) decrease between 1995 and 2015 in North American Hg 0 observations .…”

Environmental contamination and climate change in Antarctic ecosystems: an updated overview

“…In all the samples with an accentuated metal deposition, the value of the ratio [Hg ng g −1 ]/[OC%] is usually >11. 75 Emissions of Hg 0 are increasing in some Southern Hemisphere countries 76 and global warming will likely reduce the sea-ice cover in some Antarctic coastal areas; thus, concern is growing about Antarctica's potential role as the ultimate sink of Hg. Furthermore, studies on the metal cycling between air and snow in the Antarctic Plateau 77,78 and the Hg accumulation pattern in cryptogams collected along the Reeves Glacier 79 indicate that coastal ecosystems also receive Hg 0 via katabatic winds (i.e., the cold and dense air masses sliding down-slope from the Antarctic Plateau towards the sea).…”

Mercury in Fish and Human Hair and Estimated Dietary Intake in a Riverside Community of the Madeira River Basin in the Brazilian Amazon

“…Currently, artisanal and small-scale gold mining (ASGM) is the main anthropogenic source of Hg in tropical regions [ 5 ], especially in the Amazon. In Brazil, it is estimated that 10 to 50 t of Hg derived from ASGM is emitted into aquatic and terrestrial ecosystems per year [ 6 ].…”

“…Additionally, natural Hg concentrations are relatively high in the Brazilian Amazon due to rock weathering and continuous atmospheric deposition [ 11 ]. Increasing deforestation and large-scale forest fires in the region intensify the remobilization of Hg 2+ retained in terrestrial ecosystems and, consequently, its transport to aquatic ecosystems [ 5 , 12 ].…”