Plant uptake, mercury

CLEA SGV = Contaminated land exposure assessment soil guideline values. The values given are the minimum values and relate to use of land as Allotments or Residential with plant uptake. See page 22. Relates to Cr(VI) and inorganic mercury. 

Lindberg SE, Jackson DR, Huckabee JW, Janzen SA, Levin MJ and Lund JR (1979) Atmospheric Emission and Plant Uptake of Mercury from Agricultural Soils near the Almaden Mercury Mine. J Environ Qual 8 572—578. 

Mosbaek H, Tjell JC and Sevel T (1988) Plant Uptake of Mercury in Background Areas. Chemo-sphere 17 1227-1236. 

While mercury is now a general urban contaminant, and urban soils can be expected to contain about five or six times as much total mercury as uncontaminated rural soils, little is known about the effect this level of contamination has on plant uptake. According to Goldwater [323], the concentration of mercury in foods does not appear to have changed substantially over the past 30 years, and... 

Gilmour and Miller [324] have studied the fate of a mercurous-mercuric fungicide (calochlor) added to turf grass and to bare soil and found that about half of the total mercury added was lost in 57 days. Plant uptake, however, did not account for this loss and these authors concluded that it was mainly due to... 

Leonard, T.L., G.E. Taylor, Jr., M.S. Gustin, and G.C.J. Fernandez. 1998a. Mercury and plants in contaminated soils 1. Uptake, partitioning, and emission to the atmosphere. Environ. Toxicol. Chem. 17 2063-2071. 

Sanders et al. (1983) have also shown that the effects of Cu(II) on the growth of crab larvae and on their metallothionein with copper chelate buffer systems must be interpreted on the basis of free Cu ion activity. The data obtained reveal predictable relations between [Cu ] in seawater and processes at the cellular and organismic levels. Similarly, the uptake of metal ions by plants (e.g., of aluminum) is usually related to free metal-ion activity. Others have shown that the chelation of a variety of metals reduces the toxicity of metals to organisms for example, a reduction in the uptake of mercury by fish in the presence of EDTA and cysteine a reduction in copper and/or zinc toxicity to... 

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. 

As mercury is not very phytotoxic in normally occurring concentrations (plants may possess a type of protection mechanism), little is known about mercury uptake and metabolism in plants. 

Not much is known about mercury uptake and metabolism in wild plant species. However, accumulation of the metal has been observed in mushrooms and aquatic plants (Kabata-Pendias and Pendias, 1984). Most studies of agricultural crops, with Hg loads far greater than those encountered in normal conditions, demonstrate the tendency for mercury to accumulate in the roots (Steinnes, 1995). 

Beauford, W., Barber, J., Barringer, A.R., 1977. Uptake and distribution of mercury within higher plants. Physiol. Plant 39, 261-265. 

Clearly, effects which have to be studied are the extent to which the enhanced levels in the contaminated soils now characteristic of urban areas, lead to increased trace-element levels in plants grown for human or animal consumption, the extent to which increased trace-element uptake can lead to phytotoxic effects and the possibility of toxic effects on livestock and human beings. The possible consequences of the permanent presence of enhanced levels of elements such as cadmium and mercury in food chains are so far-reaching and unpredictable that there is everything to be said for preventing the development of such a situation. 

The ability of plants to restrict their uptake of copper, lead and mercury from contaminated soil is also limited and, since contamination of the soil with most trace elements appears to be cumulative and largely irreversible, a point will eventually be reached when contaminant levels of these elements will render land permanently unsuitable for grazing or for growth of crops. 

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