Mercury food chain

Exposure. The exposure of humans and animals to mercury from the general environment occurs mainly by inhalation and ingestion of terrestrial and aquatic food chain items. Pish generally rank the highest (10—300 ng/g) in food chain concentrations of mercury. Swordfish and pike may frequently exceed 1 p.g/g (27). Most of the mercury in fish is methyl mercury [593-74-8]. Worldwide, the estimated average intake of total dietary mercury is 5—10 p-g/d in Europe, Russia, and Canada, 20 pg/d in the United States, and 40—80 pg/d in Japan (27). 

Some metals used as metallic coatings are considered nontoxic, such as aluminum, magnesium, iron, tin, indium, molybdenum, tungsten, titanium, tantalum, niobium, bismuth, and the precious metals such as gold, platinum, rhodium, and palladium. However, some of the most important poUutants are metallic contaminants of these metals. Metals that can be bioconcentrated to harmful levels, especially in predators at the top of the food chain, such as mercury, cadmium, and lead are especially problematic. Other metals such as silver, copper, nickel, zinc, and chromium in the hexavalent oxidation state are highly toxic to aquatic Hfe (37,57—60). 

There are concerns that land application of sludge will result in an increase of pathogenic bacteria, viruses, parasites, chemicals and metals in drinking water reservoirs, aquifers, and the food chain. This raises additional concerns of cumulative effects of metals in cropped soils. Research shows that if metals such as zinc, copper, lead, nickel, mercury, and cadmium are allowed to build up in soils due to many applications of sludges over the years, they could be released at... 

Apart from CH3 Hg+, other forms of R-Hg+ have been found in the natural environment, which originate from anthropogenic sources but are not known to be generated from inorganic mercury. These forms have been found in terrestrial and aquatic food chains. A major source has been fungicides, in which the R group is phenyl, alkoxy-alkyl, or higher alkyl (ethyl, propyl, etc.). These forms behave in a similar manner... 

Mercury, tin, lead, arsenic, and antimony form toxic lipophilic organometallic compounds, which have a potential for bioaccumulation/bioconcentration in food chains. Apart from anthropogenic organometallic compounds, methyl derivatives of mercury and arsenic are biosynthesized from inorganic precursors in the natural environment. 

There is a vast range of aqueous organic pollutants with a wide toxicity profile. Some, e.g. polychlorinated biphenyls, certain herbicides, fungicides and pesticides, and organo-mercury compounds, are persistent and may bioaccumulate in the food chain. Trace contaminants such as sodium chloride, iron and phenols (especially if chlorinated) may also impart a taste to water. Typical consent levels for industrial discharges are provided in Table 13.10. 

Heavy metals may also be concentrated in passage up the food chain. Other pollutants, e.g. fungicides, pesticides, biocides, polychlorinated biphenyls or organic mercury compounds, are persistent and can therefore also bioaccumulate. 

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. 

Bodaly RA, St. Louis VL, Paterson MJ, Fudge RJP, Hall BD, Rosenberg DM, Rudd JWM. 1997. Bioaccumulation of mercury in the aquatic food chain in newly flooded areas. In Sigel A, Sigel H, editors, Metal ions in biological systems, Vol. 34 Mercury and its effects on environment and biology. New York (NY) Marcel Dekker Inc., p. 259-287. 

Herrin RT, Lathrop RC, Gorski PR, Andren AW. 1998. Hypolimnetic methylmercury and its uptake by plankton during fall destratification a key entry point of mercury into lake food chains Linmol Oceanogr 43 1476-1486. 

Monteiro LR, Furness RW. 1997. Accelerated increase in mercury contamination in North Atlantic mesopelagic food chains as indicated by time series of seabird feathers. Environ Toxicol Chem 16 2489-2493. 

Sulfide ores usually contain small amounts of mercury, arsenic, selenium, and tellurium, and these impurities volatilize during the ore treatment. All the volatilized impurities, with the exception of mercury, are collected in the dust recovery systems. On account of its being present in low concentrations, mercury is not removed by such a system and passes out with the exit gases. The problem of mercury contamination is particularly pertinent to zinc plants since the sulfidic ores of zinc contain traces of mercury (20-300 ppm). The mercury traces in zinc sulfide concentrates volatilize during roasting and contaminate the sulfuric acid that is made from the sulfur dioxide produced. If the acid is then used to produce phosphatic fertilizers, this may lead to mercury entering the food chain as a contaminant. Several processes have been developed for the removal of mercury, but these are not yet widely adopted. 

When the mercury-containing equipment is improperly disposed of on land, the mercury will eventually leachate out from the waste equipment. Once released into the environment, mercury remains there indefinitely, contaminating the soil, sediment, and groundwater. This contamination eventually enters the food chain, exposing local populations to mercury s harmful effects.2... 

The release of mercury into the environment, its introduction in the biogeochemical cycle, and its concentrated propagation along the food chain due to changes in climate are a worldwide concern. The problem of mercury in the society is not new, it has long been considered as toxic element of concern owing to its mobility,... 

Methylmercury can be bioconcentrated in organisms and biomagnified through food chains, returning mercury directly to man and other upper trophic level consumers in concentrated form... 

Mercury point sources and rates of particle scavenging are key factors in atmospheric transport rates to sites of methylation and subsequent entry into the marine food chain (Rolfhus and Fitzgerald 1995). Airborne soot particles transport mercury into the marine environment either as nuclei for raindrop formation or by direct deposition on water (Rawson etal. 1995). In early 1990, both dimethylmercury and monomethylmercury were found in the subthermocline waters of the equatorial Pacific Ocean the formation of these alkylmercury species in the low oxygen zone suggests that Hg2+ is the most likely substrate (Mason and Fitzgerald 1991 Figure 5.1). 

High concentrations of methyknercury in subthermocline low-oxygen seawater were significantly and positively correlated with median daytime depth (<200 m to >300 m) of eight species of pelagic fishes mean total mercury concentrations in whole fishes ranged between 57 and 377 jjg/kg DW. The enhanced mercury accumulations in the marine mesopelagic compartment is attributable to diet and ultimately to water chemistry that controls mercury speciation and uptake at the base of the food chain (Monteiro et al. 1996). 

Huckabee, J.W., D.M. Lucas, and J.M. Baird. 1981. Occurrence of methylated mercury in a terrestrial food chain. Environ. Res. 26 174-181. 

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