By Roberta Attanasio, IEAM Blog Editor
In October 2013, the brought renewed attention to a major global pollution problem known to result in the contamination of seafood and, subsequently, in a variety of health problems in people that consume it. Designed to limit mercury use and emissions internationally, the Convention is only a first step in limiting mercury pollution.
Meanwhile, more research is needed to fully understand the worldwide impact of mercury on different ecosystems. Although the global cycle of mercury has been characterized to a certain extent, and the mechanisms leading to the transformation of inorganic mercury to the highly toxic form of methylmercury is well understood, there are still a lot of unknowns related to the regional and local characteristics of mercury deposition and its effects on specific ecosystems.
Since the time of the , and especially during the last two decades, most people have been aware of the danger lurking in our oceans, particularly in seafood. For example, pregnant women are advised to avoid fish known to contain high levels of methylmercury, to prevent the development of major neurological disorders in the unborn fetus.
However, despite all the emphasis placed on the presence of mercury in waterways and, therefore, in fish consumed by large segments of the human population, mercury can be found in other places and in amounts that adversely affect the environment, including soil, wildlife, and so on.
In 2012, the published a report that highlights elevated mercury concentrations in several songbird species and bats, a group of animals largely ignored in mercury research. According to the report, “mercury concentrations in this animal group are significant enough to cause physiological and reproductive harm, creating a major paradigm shift in ecotoxicological research, assessment, monitoring, management, and policy.”
Fortunately, there is now more interest on “largely ignored” mercury-polluted ecosystems. Two recently published studies focus on the montane environment and how altitude influences mercury concentrations.
Hua Zhang and collaborators examined topsoil samples along an elevational gradient transect on Mt. Leigong in subtropical southwestern China. The , published November 25, 2013, show for the first time that the content of mercury derived from the atmosphere distinctly increases with altitude. The authors provide potential mechanisms for this so-called altitudinal magnification effect or “mountain trapping effect” (see figure below, from Zhang et al. 2013, Scientific Reports 3:3322).
Potential mechanisms for mercury magnification in montane soils, by Hua Zhang and Jonas Sommar, licensed under
But how does mercury present at higher altitude affect the forest floor and fauna? The answer comes from a new study published in Environmental Toxicology and Chemistry, by Jason Townsend and colleagues and titled “” (December 3, 2013). The study focuses on a high-elevation ecosystem of the northeastern United States – the Catskill Mountains.
The investigators found that elevation and the ecological and climatic changes that occur along elevational gradients have a major influence not only on the environmental concentrations of mercury but also on the bioaccumulation of mercury in montane wildlife – birds and salamanders. Indeed, results from the study show that montane animal species bioaccumulate higher concentrations of mercury than their lower elevation counterparts.
Importantly, the study shows that most mercury in terrestrial birds and salamanders is present as methylmercury, the biologically available, highly neurotoxic form of mercury found in fish and known to move efficiently through food webs. Thus, atmospheric (ionic) mercury can be converted to methylmercury in forested, terrestrial sites well removed from permanent bodies of water.
It’s time to accept the idea that mercury contamination is not limited to seafood – and it’s time to carry out further studies to accurately assess the extent of the problem in terrestrial ecosystems.