Mercury persistence

Mercury is a toxic substance that, through human and natural activities, cycles through the atmosphere, hydrosphere, and ecosphere affecting the health of both humans and wildlife. It enters the environment naturally through erosion, fire, and volcanic processes, as well as a result of human industrial practices. The human activities such as combustion, smelting, and mining have elevated global mercury levels to approximately three times those found before industrialization. Once released, mercury persists in the environment where it circulates between air, water, sediments, and biota in various forms. Mercury is present everywhere in the environment. The level of Hg in air varies from 0.5 ng/m3 to 10 ig/m3. 

Air-poUutant effects on neural and sensory functions in humans vary widely. Odorous pollutants cause only minor annoyance yet, if persistent, they can lead to irritation, emotional upset, anorexia, and mental depression. Carbon monoxide can cause death secondary to the depression of the respiratory centers of the central nervous system. Short of death, repeated and prolonged exposure to carbon monoxide can alter sensory protection, temporal perception, and higher mental functions. Lipid-soluble aerosols can enter the body and be absorbed in the lipids of the central nervous system. Once there, their effects may persist long after the initial contact has been removed. Examples of agents of long-term chronic effects are organic phosphate pesticides and aerosols carrying the metals lead, mercury, and cadmium. 

Thus, there is not a great deal of difference between the three classes in acute toxicity all are highly toxic. However, methyl mercury is more persistent than the other two types, and so has the greater potential to cause chronic toxicity. The latter point is important when considering the possibility of sublethal effects. 

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. 

Mercury and its compoimds Toxic or persistent organic compounds of Si... 

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. 

The trend from heavy metal and phenolic based biocides, e.g. mercury and pentachlorophenol types, to more environmentally acceptable but less persistent organic types, requires more attention to plant hygiene (Figure 6, Briggs, 1980). 

In addition to the chemicals included on the other lists, the CDC also included heavy metals such as arsenic, lead, and mercury volatile solvents such as benzene, chloroform, and bromoform decomposition products such as dioxins and furans polychlorinated biphenyls (PCBs) flammable industrial gases and liquids such as gasoline and propane explosives and oxidizers and all persistent and nonpersistent pesticides. Agents included in this volume are limited to those that are most likely to pose an acute toxicity hazard. 

Barrett, R.T., J.U. Skaare, and G.W. Gabrielsen. 1996. Recent changes in levels of persistent organochlorines and mercury in eggs of seabirds from the Barents Sea. Environ. Pollut. 92 13-18. 

Jernelov, A. 1969. Conversion of mercury compounds. Pages 68-74 in M.W. Miller and G.G. Berg (eds.). Chemical Fallout, Current Research on Persistent Pesticides. Chas. C Thomas, Springfield, IL. 

Norheim, G. and B. Kjos-Hanssen. 1934. Persistent chlorinated hydrocarbons and mercury in birds caught off the west coast of Spitsbergen. Environ. Pollut. 33A 143-152. 

Norheim, G., L. Some, and G. Holt. 1982. Mercury and persistent chlorinated hydrocarbons in Antarctic birds from Bouvetoya and Dronning Maud Land. Environ. Pollut. 28A 233-240. 

Froslie, A., G. Holt, and G. Norheim. 1986. Mercury and persistent hydrocarbons in owls Strigiformes and birds of prey Falconiformes collected in Norway during the period 1965-1983. Environ. Pollut. 11B 91-108. 

Commenting ona January 5,1999 proposal, environmental groups in early April called again on EPA to lower its proposed Toxic Release Inventory (TRI) reporting threshold to zero for certain chemicals. The chemicals include mercury, dioxins, and lead. Currently facilities are only required to report chemical releases if they manufacture or process at least 25,000 pounds or otherwise use 10,000 pounds annually of a fisted TRI chemical. The environmental advocates argued that any releases of chemicals considered to be persistent, bioaccumulative and toxic should be reported as a threat to public health. This abstract includes all the information contained in the original article. 

Mercury and its compounds are toxic and persistent and have a marked ability to... 

Notable progress has been made over the past three decades in reducing some forms of marine pollution, such as oil, radioactive substances, heavy metals (with the exception of mercury), and some of the persistent organic pollutants, such as DDT and... 

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. 

Mercury Metal - persistent - bioaccumulates - contaminates many species of fish. Widely used in industrial processes. Causes developmental neurotoxicity -children most susceptible... 

Probably the greatest concern in the workplaces is solvent exposure from cleaning agents or chemical processes. Farmers and pesticide workers can also be exposed to compounds clearly designed to affect the nervous system. The outdoor environment can contain elevated levels of a number of persistent chemicals that can adversely affect the nervous system, such as lead, mercury, and chlorinated pesticides. 

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