Global source of mercury from commercial products and its biogeochemical cycling

Mercury (Hg) poses a significant global threat to humans and wildlife in the form of methylmercury, a neurotoxin. Soil and ice core records indicate that atmospheric Hg deposition has tripled globally over the last 200 years due to human activity (such as coal combustion). Current atmospheric emissions inventories for Hg only take into account processes that directly release Hg into the atmosphere. Estimates of the amount of Hg mined for use in commercial products (e.g., electrical apparatus, fungicides, dental amalgams) since 1850 exceed direct emissions during the same period. The Hg contained in products will eventually enter the environment during manufacturing, usage, and disposal, via wastewater, direct land application, incineration and leaching from solid waste treatment. Once introduced into mobile surface reservoirs like the atmosphere, terrestrial and aquatic environments, Hg can exchange rapidly between them. The slow transfer of Hg from the surface to deeper, long-lived reservoirs means that anthropogenic perturbations like this will leave a lasting legacy. Thus, Hg-containing products have the potential to be a major, previously unrecognized contribution to the global rise in environmental mercury over the last 150 years.

To investigate this problem, we quantify the flow of mined Hg through specific product pools to its entry into the environment for 1850 to the present, using a substance flow analysis approach. We implement the time-dependent Hg source from products into an existing eight-compartment, fully coupled global model framework of the biogeochemical cycle of Hg. Reservoirs include the atmosphere, ocean pools, terrestrial pools, and the large mineral reservoir of Hg, to which we add surface freshwater and landfill compartments. We examine the resulting accumulation and distribution of total Hg among the different geochemical reservoirs and calculate anthropogenic enrichment factors for each reservoir. We compare these results to those obtained without including the product Hg source and to current estimates of the global Hg budget in the literature. We calculate trends in atmospheric Hg content to test whether including Hg in products improves our ability to reproduce observed declining atmospheric Hg concentrations in the face of increasing direct emissions.