Mercury Concentrations in Plants and Animals

An elevated concentration of mercury (i.e., 1.0 mg/kg FW), usually as methylmercury, in any biological sample is often associated with proximity to human use of mercury. The elimination of mercury point-source 

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Standards imposed to the industrial waste streams charged in heavy metals are more and more drastic in accordance with the updated knowledges of the toxicity of mercury, cadmium, lead, chromium... when they enter the human food chain after accumulating in plants and animals (Forster Wittmann, 1983). Nowadays, the use of biosorbents (Volesky, 1990) is more and more considered to complete conventional (physical and chemical) methods of removal that have shown their limits and/or are prohibitively expensive for metal concentrations typically below 100 mg.l-i. 

Mercury concentrations in field collections of selected species of plants and animals... 

Table 5.6 Mercury Concentrations in Field Collections of Selected Species of Plants and Animals (Values shown are in mg total Hg/kg fresh weight [FW], or dry weight [DW].)... 

It turns out that most of these compounds have similar characteristics that contribute to their toxicity to both humans and other species of plants and animals. First, the compounds are environmentally persistent. Many of the early pesticides, and certainly the metals, do not break down in the environment or do so only very slowly. If persistent chemicals are released continually to the environment, the levels tend to rise ever higher. This means they are available to cause harm to other organisms, often not even the target of the pesticide. Second, the early pesticides were broad acting and toxic to many species, not just the target species. These poisons often killed beneficial insects or plants. Third, many of these compounds would bioaccumulate or concentrate in species as they moved up the food chain. The chlorinated pesticides accumulate in the fat of animals. Animals that consumed other animals accumulated more and more of these pesticides. Most species could not metabolize or break down the compounds. Lead accumulates in bone and methyl mercury in muscle. And finally, because of their persistence in the environment and accumulation in various species, the persistent toxicants spread around the world even to places that never used them. Animals at the top of the food chain, such as polar bears and beluga whales, routinely have fat PCB levels greater that 6 ppm. 

Heat Transfer The movement and dispersion of heat by conduction, convection, or radiation. Heavy Metals High-density metallic elements generally toxic to plant and animal life in low concentrations (e.g. mercury, chromium, cadmium, arsenic, and lead). 

Although these cations and anions are indispensable, excessive amounts of them are toxic, so that it is important that their concentrations are regulated, either by mechanisms existing in the animal or by externally imposed controls. There are also several kinds of metal ions found in Nature which do not appear to serve any useful biological function but which are highly toxic if they are absorbed into the body. These include arsenic and the environmental pollutants lead, cadmium and mercury ions. Most of the remaining metals occur as inert species such as the aluminosilicates and titanium dioxide that are poorly absorbed, if at all, by plants and animals, or are present in only trace amounts and have little physiological effect. 

Mercury accumulation in soils tends to correlate with the organic matter level. The highest natural Hg concentrations have been reported in peaty and waterlogged soils. Toxicity to organisms is usually attributable to soil conditions that favor the production of volatile forms of Hg evidently, Hg cations interact strongly enough with humus and clays to limit availability of this form to plants and animals. 

The term heavy metals covers a wide range of elements, such as copper, lead, mercury, cadmium, manganese, zinc, etc. These are naturally present in the environment at low concentrations. Some heavy metals are indispensable for plant and animal growth in very small quantities (trace elements), but become toxic at higher doses. Besides the fact that all heavy metal sulfides are insoluble, their chemical properties are dissimilar. Copper is treated separately in winemaking in view... 

Minamata Disease is defined as neuropathy arising from intake of fish and shellfish containing high concentrations of methylmer-cury. The outbreak is dependent on factors that include mercury concentrations in water, bioconcentration and biomagnification of mercuric compounds by aquatic plants and animals, and continuous daily intake of mercury-contaminated fish in large quantities. Minamata Disease patients have neurological symptoms that include paresthesia, visual field... 

Mercury concentrations in world-wide field collections of plants and animals are documented factors known to modify mercury accumulations and their significance are discussed. 

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