Plants, terrestrial mercury

Mercury (Hg) contamination is widespread in water, in surficial soils and sediments, and in the tissues of plants and animals in ecosystems around the globe. Once deposited to terrestrial and aquatic ecosystems, some inoiganic mercury is transformed into methylmercury (MeHg), a highly toxic compoimd that bioaccumulates efficiently in food webs (Wiener et al. 2003). As a result of the toxicity of MeHg to wildlife and humans, many nations are interested in reducing environmental mercury contamination and associated biotic exposure (UNEP 2002). 

Terrestrial plants function as conduits for the transport of elemental mercury from the geosphere to the atmosphere (Leonard et al. 1998a). Estimated mercury emissions from plants in the Carson River Drainage Basin of Nevada over the growing season (0.5 mg Hg/m2) add to the soil mercury... 

Most bore waters include high concentrations of at least one of the following chemical contaminants (Table 1) lithium (Li), boron (B as H3BO3), arsenic (As), hydrogen sulphide (H2S), mercury (Hg), and sometimes ammonia (NH3). If released into a river or lake, these contaminants can potentially damage aquatic life, terrestrial plants, and/or human health. The disposal of highly saline bore waters can also have an adverse effect on water quality. 

There appears to be a potential for deposition of elemental mercury via plant-leaf uptake. Lindberg et al. (1992) indicated that forest canopies could accumulate elemental mercury vapor, via gas exchange, at the leaf surface followed by mercury assimilation in the leaf interior during the daylight hours. However, Hanson etal. (1995) indicated that this would only occur when air concentrations of elemental mercury were above an equilibrium level for the local forest ecosystem. Therefore, dry foliar surfaces in terrestrial forest landscapes may not be a net sink for atmospheric elemental mercury, but rather a dynamic exchange surface that can function as a source or sink dependent on several factors. 

Lenka M, Panda KK and Panda BB (1992) Monitoring and Assessment of Mercury Pollution in the Vicinity of a Chloralkali Plant. IV. Bioconcentration of Mercury in In Situ Aquatic and Terrestrial Plants at Ganjam, India. Arch Environ Contam Toxicol 22 195-202. 

Significant sublethal effects of mercury include an increased frequency of cancers, birth defects, and chromosomal aberrations in laboratory animals and wildlife. Adverse sublethal effects of mercurials also include growth inhibition, abnormal reproduction, histopathology, high mercury accumulations and persistence, and disrupted biochemistry, metabolism, and behavior. These - and other aspects of exposure to various mercurials by living organisms - are documented and discussed for representative species of bacteria and other microorganisms, aquatic and terrestrial plants and invertebrates, fishes, amphibians, birds, and mammals. 

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