Chronic toxicity, mercury

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. 

Scheuhammer AM. 1987. The chronic toxicity of aluminum, cadmium, mercury, and lead in birds a review. Environ Pollut 46 263-295. 

Chronic toxicity studies provide information on the long-term health effects of chemical substances. Adverse health effects in exposed animals and subsequent severe damage are known to occur after repeated exposure to low doses over a period of time. The slow accumulation of mercury or lead in the body or after a long latency period from exposure to chemical carcinogens is an example. Chronic or prolonged periods of exposure to chemical substances may also cause adverse effects on the reproduction and behavior of animals and humans. The symptoms caused after chronic exposure usually differ from those observed in acute poisoning from the same chemical. In fact, when exposed to low concentrations of chemical substances, as is the case with chronic toxicity studies, the industrial worker and common public are unaware of the exposure. 

Weihe P, Grandjean P, Debes F, et al Health implications for Faroe Islanders of heavy metals and PCBs from pilot whales. Sci Total Environ 186 141-148,1996 West I, Lim J Mercury poisoning among workers in California s mercury mills a preliminary report. J Occup Med 10 697-701,1968 White RF, Feldman RG, Travers PH Neurobehavioral effects of toxicity due to metals, solvents and insecticides. Clin Neuropharmacol 13 392-412,1990 Williamson AM, Teo RKC, Sanderson J Occupational mercury exposure and its consequences for behavior. Int Arch Occup Environ Health 50 273-286,1982 Yang Y-J, Huang C-C, Shih T-S, et al Chronic elemental mercury intoxication clinical and field studies in lampsocket manufacturers. Occup Environ Med 51 267-270, 1994... 

Mitsumoei K, Hieano M, Ueda H, Maita K and Shieasu Y (1990) Chronic toxicity and carcinogenicity of methyl mercury chloride in B6C3F1 mice. Fundam Appl Toxicol 14 179-190. 

Rice DC (1989) Brain and tissue levels of mercury after chronic methyl mercury exposure in the monkey. ] Toxicol Environ Health 27 189-198. Roberts MC, Seawright AA and Ng JC (1979) Chronic phenylmercuric acetate toxicity in a horse. Vet Hum Toxicol 21 321-32. 

Poisons can be acute (with immediate effect, e.g., hydrogen cyanide (HCN)) or chronic (referring to the systemic damage done after repeated exposure to low concentrations over long periods of time, e.g., heavy metals like mercury, lead, cadmium and also vinyl chloride). The chemicals most often associated with chronic toxicity are also carcinogens (e.g., benzene, cadmium compounds), which are problematic because when, if at all, the... 

Heavy metal ions are perhaps the most common of all water pollutants. The heavy metals include such frequendy encountered elements as lead and mercury, as well as many less common ones like cadmium, chromium, nickel, and copper. These metals can, at times, be acutely toxic, causing immediate symptoms, but often they are chronically toxic in very small quantities. Chronic toxicity is characterized by nagging symptoms that lessen normal body functions. Inadequate disposal of wastes from mining or industrial activities causes these metals to find their way into water supplies. In addition, some farming activities and the disposal of household wastes can contribute to the presence of heavy metals in our water supplies. 

There have been relatively few reports of chronic toxicity from laboratory work and most of these are now historical case smdies from times when chemists had little understanding of risks from chemicals. Perhaps one of the most significant concerns, at least from past experience, has been for mercury, because it is very toxic by inhalation and readily vaporizes. 

The chronic toxicity of preservatives that are administered in the eye is a constant source of concern and is often reported benzalkonium chloride and thiomersal would eventually cause epithehal damage and phenylmercuiic compounds cause mercury deposition in the lens. However, so far these preservatives have not been banned for that reason. Recent investigations even show that benzalkonium is not toxic for the cornea [47]. 

F. I Toxicity varies among different species and with different forms of mercury. Chronic methyl mercury toxicosis results from continued exposure to dosages of 0.2-5.0 mgAg body weight. 

Mount, E. L Chronic toxicity of methyl mercury chloride to fathead minnow. Testimony in the matter of proposed toxic effluent standards for Aldrin-Dieldrin et al. Fed. Water Pol. Control Agency (307), Docket 1, Exhibit 4 (1974). 

Accumulations of mercury in the body affect the nervous system and cause brain damage. One form of chronic mercury poisoning, "hatter s disease," was fairly common in the nineteenth century. Mercury compounds were used to convert fur to felt for making hats. Many hat makers of the time worked in hot, cramped spaces and used these compounds without special precautions. The hatters inadvertently ingested or inhaled the toxic mercury compounds while they worked. 

Galen, a physician whose views outUved him by about a thousand years, died about 200 AD. He beUeved that mercurials were toxic, and did not use any mercury compound therapeutically. However, as a result of Arabian influence, the therapeutic uses of mercury were slowly recognized by Western Europe. In the thirteenth century mercury ointments were prescribed for treating chronic diseases of the skin. Mercury and its compounds, such as mercurous chloride, mercuric oxide, mercuric chloride, and mercuric sulfide, were used widely from the fifteenth to the nineteenth centuries, and to some extent in the twentieth century. During the first half of the twentieth century, the primary therapeutic uses of mercury included bactericidal preparations, such as mercuric chloride, mercuric oxycyanide, and mercuric oxide and diuretics, such as aryl HgX (Novasural) and mercurated ahyl derivatives (14). 

Thain, J.E. 1984. Effects of mercury on the prosobranch mollusc Crepidula fornicata acute lethal toxicity and effects on growth and reproduction of chronic exposure. Mar. Environ. Res. 12 285-309. 

Ingestion Toxicity Data are available for the acute (single-dose) ingestion/oral toxicity of many toxic materials (National Institute for Occupational Safety and Health, Registry of Toxic Effects of Chemical Substances, 1983 Lewis, Sax s Dangerous Properties of Industrial Materials, 9th ed., 1996). However, very few data are available for prolonged ingestion or periodic doses of toxic materials. It is likely that metabolic processes would operate to increase the total burden required for toxic effects for such chronic exposures, except for some materials (such as mercury and lead) which apparently can accumulate in the body. 

Methyl and ethyl mercury compounds have similar toxicological properties, and there is no sharp demarcation between acute and chronic poisoning. Once a toxic dose has been absorbed and retained for a period of time, functional disturbances and damage occur. The latency period for a single toxic dose may vary from one to several weeks longer latency periods on the order of years have been reported for chronic exposures. ... 

Mercury was used to cure the felt used in hats, and workers developed the characteristic signs of mercury vapor toxicity. Acute exposure to high concentrations of mercury vapor causes respiratory distress, which can be fatal. The symptoms of chronic exposure to mercury vapor include personality changes such as excitability, depression, memory loss, fine motor tremor that can become progressively worse, gingivitis, and hallucination. There is some mercury inhalation exposure from dental amalgam, but for most people there are no health-related effects. Metallic mercury is very poorly absorbed from the intestine, thus it is much better to swallow the mercury from a thermometer than inhale it (see chapter on mercury). 

C. The symptoms are characteristic of a person chronically exposed to vapors released from elemental mercury. Since the dental technician may handle elemental mercury, including mishandling, the symptoms presented may occur. While the technician may be exposed to solvent vapors released from dental adhesives, the symptoms are not characteristic of this type of exposure. Fluoride toxicity would not be expected because these are not symptoms associated with fluoride ingestion, and the patient and not the technician would be most likely exposed to quantities high enough to cause any symptoms. The technician has little exposure to li-docaine, and the symptoms are not typical of lido-caine toxicity. 

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