Global mercury assimilation by vegetation
by | VIEW 141
The serious problem of the environmental toxicity of mercury has led to a series of initiatives by national and international organizations that deal with environmental protection and public health, committed to its progressive elimination from production cycles in all its forms.
In 2013 these efforts materialized in the Minamata Convention on Mercury, an international agreement signed by more than one hundred countries that provides for the gradual introduction of a series of containment measures, leading to a total ban on certain devices in 2020, including batteries, fluorescent lamps and cosmetics.
The European Union is in turn committed to the same objective, having in 2005 established a program in several points which indicated a series of measures aimed at the progressive reduction of the use of mercury in all its forms.
Fish consumption is the most important cause of exposure to mercury ingestion in animals and humans. Some large fish, such as blue tuna and swordfish, may contain high levels of the metal due to the phenomenon of bioaccumulation, as a result of the fact that they are fish at the top of the marine food chain; a large consumption of these fish products can lead to mercury poisoning.
The FDA recommends that certain categories of people, namely young children, nursing mothers and women who may become pregnant, consume no more than 340 grams of low-mercury seafood per week; in the case of fish with a higher mercury content, such as albacore tuna, and in the case of fish caught amateur in waters not considered safe, the maximum weekly consumption is halved; in addition, large fish such as shark and swordfish should be avoided.
Researchers from the Global Mercury Assimilation by Vegetation study, published on the Environmental science & technology, told: "Assimilation of mercury (Hg) by vegetation represents one of the largest global environmental Hg mass fluxes.
We estimate Hg assimilation by vegetation globally via a bottom -up scaling approach using tissue Hg concentrations synthesized from a comprehensive database multiplied by respective annual biomass production (NPP). As global annual NPP is close to annual vegetation die-off, Hg mass associated with global NPP approximates the transfer of Hg from plants to soils, which represents an estimate of vegetation-mediated atmospheric deposition.
Annual vegetation assimilation of Hg from combined atmospheric and soil uptake is estimated at 3062 ± 607 Mg yr-1, which is composed of 2491 ± 551 Mg yr-1 from aboveground tissue uptake and 571 ± 253 Mg yr-1 from root uptake.
Assimilation of atmospheric Hg amounts to 2422 ± 483 Mg yr-1 when considering aboveground tis sues only. Atmospheric assimilation increases to 2705 ± 504 Mg yr-1 when considering that root Hg may be partially derived from prior foliar uptake and transported internally to roots.
Estimated atmospheric Hg assimilation by vegetation is 54-137% larger than the current model and litterfall estimates, largely because of the inclusion of lichens, mosses, and woody tissues in deposition and all global biomes.
Belowground, about 50% of root Hg was taken up from soils with currently unknown ecological and biogeochemical consequences."