Mercury water contamination level

Inza, B., F. Ribeyre, R. Maury-Brachet, and A. Boudou. 1997. Tissue distribution of inorganic mercury, methylmercury and cadmium in the Asiatic clam (Corbicula fluminea) in relation to the contamination levels of the water column and sediment. Chemosphere 35 2817-2836. 

McLEAN That s certainly the case. I think that much of the data on the mercury concentrations in atmospheric precipitation are too high. As far as the oceans are concerned, I think oceanographers are the leaders in analytical methodology and contamination control for the determination of mercury in water. The levels of mercury which they are finding in the oceans are now much lower (vAtI-IO ng/liter) than what were being quoted five years ago. 

From 1969 to 1972, over 3,500 fish from New York State lakes and streams were collected and analyzed for mercury content (Eisenbud et al., 1978 Boulton and Hetling, 1972). Less than ten percent of these fish lad mercury levels above 1.0 mg Ife/Kg body weight, the present Lfriited States Food and Drug Administration "actionable level" for commercially caught fish. A sizable proportion of these fish were collected from Onondaga Lake, near Syracuse, New York, a body of water contaminated by discharges frcm a chlor-alkali plant. 

Bottom sediments constitute a principal sink for aqueous mercury. Concentrations of 1-10 /Ag Hg/g generally have been observed in sediments from contaminated waters, and levels up to 1(X) /itg/g or more have been reported in various instances (22). Though bottom sediments sequester a substantial fraction of the mercury that enters aquatic ecosystems, sediment-accumulated mercury may be remobilized back into the water. Jemelov (105) showed that fish exposed to bottom sediment, which contained inorganic mercury at 100 fig/g, accumulated methylmercury to 3 /xg/g after treatment for 15 days. Birge et al. (22) demonstrated that mercury released from bottom sediments accumulated to appreciable concentrations in fish eggs and produced significant frequencies of embryonic and larval mortality. 

US EPA. Maximum contaminant level for mercury, http //water.epa.gov/drink/contaminants/ basicinformation/mercury.cfin [accessed on 20.05.15]. 

By law, the maximum contamination level of lead in drinking water is 0.05 ppm. This number corresponds to 0.05 milligrams of lead per liter of water. That s pretty dilute. But mercury is regulated at the 0.002 ppm level. Sometimes, even this unit isn t sensitive enough, so environmentalists have resorted to the parts per billion (ppb) or parts per trillion (ppt) concentration units. Some neurotoxins are deadly at the parts per billion level. 

Because there are few major natural sources of mercury and since most inorganic compounds of this element are relatively insoluble, it was assumed for some time that mercury was not a serious water pollutant. However, in 1970, alarming mercury levels were discovered in fish in Lake Saint Clair located between Michigan and Ontario, Canada. A subsequent survey by the U.S. Federal Water Quality Administration revealed a number of other waters contaminated with mercury. It was found that several chemical plants, particularly caustic chemical manufacturing operations for the production of chlorine and sodium hydroxide, were each releasing up to 14 or more kilograms of mercury in wastewaters each day. 

It has been stated [413] that in Clay Lake, which lies within this water system, the mercury concentration is about twenty times as great as that found in relatively uncontaminated waters in the area. D Itri and D Itri [414] have reported that where mercury is a fresh-water contaminant, populations (such as the 0jibway Indians of Ontario) which depend on fish or shellfish as a major food source, carry clinically dangerous levels of mercury in the blood. 

Some advanced industrial nations have established strict guidelines for water supply facilities to protect their citizens from the adverse effects of toxicity and hazardous materials. Some countries have set up maximum contaminant levels (MCLs) beyond which the drinking water is considered unhealthy. The MCL established by the United States for lead is 0.05 mg/L and for cadmium is 0.01 mg/L. The United States has not defined an MCL for nickel. Specific detailed on adverse effects of lead, cadmium, mercury, nickel, and their compounds are well documented in the U.S. Environmental Protection Agency list. This list contains the Toxic Release Inventory (TRI) for chemicals, and the list is updated every five years. 

Industries are constantly dumping heavy metal ions into lakes, rivers and reservoirs, thereby polluting them. Heavy metals are broadly defined as materials whose density is above 5 g/cm (Barakat 2011). Conmion heavy metals present in aqueous streams include chromium, mercury, lead and cadmium (Bailey et al. 1999). Table 2.1 (Kumiawan et al. 2006a) shown below describes the maximum contaminant level of heavy metals in surface water and their toxicides. 

Sodium selenite has also been incorporated into styrene—butadiene mbber and used in a pellet form which results in the slow release of selenium into water. These pellets have been placed in lakes in Sweden which have fish contaminated with mercury owing to high levels of that element in the water. The selenium released by the pellets reacts with mercury to form insoluble, heavy mercury selenide which setties to the lake bottom and removes mercury from the ecosystem (126). 

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. 

Although the rate of mercury input to the ocean s surface waters has increased as a result of anthropogenic activities, it is not clear that the relatively high MMHg concentrations now seen in the larger fish, e.g., tuna, shark, and swordfish, are the result of pollution. Measurements of mercury levels in preserved fish collected over the past 100 years have proven inconclusive due to small sample sizes and contamination effects. 

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