Drawing on the most recent research, an international team including a researcher from the Institut méditerranéen d'océanographie (MIO/PYTHÉAS, CNRS / Université de Toulon / IRD / AMU) has produced a new global assessment of the mercury budget for the United Nations. Human activities are estimated to have led to an increase in mercury concentrations in the atmosphere of around 450 % compared with natural levels (prevailing before 1450) and to an average increase of 300 % in mercury deposits in the oceans and soils.
Every 5 years, a scientific committee produces the UNEP Global mercury assessment for the United Nations. This document reports all the current scientific knowledge on the mercury cycle for use by political decision-makers. Thanks to these reports, the Minamata Convention was signed by 128 countries in 2013 and came into force last year.
MIO researcher Lars-Eric Heimburger had the honour of participating in the 2018 edition, which will be published very shortly. The scientists chose to reproduce the chapter "Updated global and oceanic mercury budgets for the United Nations global mercury assessment 2018" in the journal "Environmental science and technology", published on 18 September 2018. This article reviews the literature on global mercury emissions and presents revised global and oceanic mercury budgets.
The researchers first assessed two competing scenarios for the impacts of silver mining in South America from the 16th to the late 19th century, which they believed could be the largest human source of atmospheric mercury in history. Taking into account the geochemistry of silver ore and historical documents on the use of mercury, they showed that comparing these scenarios with the characteristics of atmospheric mercury in environmental archives provides strong support for a scenario of low mining emissions.
Updated global mercury budget showing anthropogenic impact on the mercury cycle since pre-anthropogenic times (before 1450). Ranges (where appropriate) are given in brackets after the most likely values. Mass units in kilotonnes (kt), flux in kilotonnes per year (kt/yr).
Based on this scenario of low emissions from these mines and on other published work, the researchers re-estimated the global mercury budget. The result indicates that human activities have increased atmospheric mercury concentrations by around 450 % compared with natural levels (prevailing before 1450). Current anthropogenic atmospheric emissions are 2.5 ± 0.5 kt/year.
This increase in atmospheric mercury concentrations has resulted in an average increase in mercury deposition of 300 % and an increase in mercury concentration in surface marine waters of 230 % and in deeper marine waters of 12 to 25 %. The overall increase in mercury in organic surface soils (15 %) is small due to the large mass of natural mercury already present as a result of rock weathering, but this figure varies from region to region.
Finally, the researchers formulated specific research recommendations to reduce uncertainties, in particular through a better understanding of the fundamental processes of the mercury cycle and through the continuous improvement of emission inventories from major natural and anthropogenic sources. In particular, a better understanding of natural inputs such as hydrothermal sources is advocated.
Source(s) :
Outridge P, R Mason, F Wang, S Guerrero, LE Heimbürger-Boavida. Updated global and oceanic mercury budgets for the United Nations Global Mercury Assessment 2018. ES&T 52 (20): 11466-11477. doi.org/10.1021/acs.est.8b01246
Contact(s) :
- Lars-Eric Heimbürger, MIO/ PYTHÉAS
lars-eric.heimburger@mio.osupytheas.fr, 04 86 09 06 14