Mercury, methyl

Mercury leaves the body mostly through the urine and feces. One of the worst-known cases of mercury poisoning occurred at Minamata, Japan, when methylmercury compounds formed during the manufacture of a paint solvent were discharged into Minamata Bay. Local people who ate a large amount of fish began 

TABLE 3-10 Environmental and Occupational Exposure to Mercury in Humans 

TABLE 3.11 Average Daily Retention of Total Mercury and Mercury Compounds in the General Population 

Children at Risk Very young children are more sensitive to mercury than adults are. Mercury in the mother s body passes to the fetus and can pass to a nursing infant through breast milk. However, the benefits of breast-feeding may be greater than the possible adverse effects of mercury in breast milk.90 

---

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). 

Benzoxazolinone [59-49-4] M 135.1, m 137-139 , 142-143 (corrected), b 121-213 /17mm, 335-337 /760mni. It can be purified by recrystn from aqueous Me2CO then by distn at atm pressure then in a vacuum. The methyl mercury salt recryst from aq EtOH has m 156-158°. [J Am Chem Soc 67 905 1945.]... 

Mercury in fish has been found in waters in the United States and Canada. Mercury in the waters is converted into methyl mercury by aquatic vegetation. Small fish consume such vegetation and in turn are eaten by larger fish and eventually by humans food with more than 0.5 ppm of mercury (0.5 mg/kg) cannot be sold in the United States for human consumption. 

Mercury is emitted from the mercury cell process from ventilation systems and by-product streams. Control techniques include (1) condensation, (2) mist elimination, (3) chemical scrubbing, (4) activated carbon adsorption, and (5) molecular sieve absorption. Several mercury cell (chloralkali) plants in Japan have been converted to diaphragm cells to eliminate the poisonous levels of methyl mercury found in fish (9). 

Organic S A Methyl mercury Bacterial activity on inorganic mercury Pesticides... 

FIGURE 5.51 Dose-response relationships for methyl mercury.(Used with permission.)... 

FAS is normally characterized by growth retardation, anomalies of the head and face, and psychomotor dysfunctions. Excessive consumption of ethyl alcohol may lead to malformations of the heart, extremities, and kidneys. Since consumption of ethyl alcohol is socially acceptable and prevalent even in pregnant women, the risks associated with the use of ethyl alcohol are remarkable. However, it should be kept in mind that there are several chemical compounds in tlie occupational environment that may also cause malformations even at low doses. The oc-cupationally-important known human teratogens include methyl mercury, ethyl alcohol, PCB compounds, tobacco smoke, lead, TCDD, 2,4,5- F, carbon monoxide, nitrogen dioxide, gasoline, and fluoride. 

Self-Test 13.8A In 1972 grain treated with methyl mercury was released for human consumption in Iraq, resulting in 459 deaths. The half-life of methyl mercury in body tissues is 70. d. How many days are required for the amount of methyl mercury to drop to 10.% of the original value after ingestion ... 

The next eight chapters will be devoted to the ecotoxicology of groups of compounds that have caused concern on account of their real or perceived environmental effects and have been studied both in the laboratory and in the field. These are predominantly compounds produced by humans. However, a few of them, for example, methyl mercury, methyl arsenic, and polycyclic aromatic hydrocarbons (PAHs), are also naturally occurring. In this latter case, there can be difficulty in distinguishing between human and natural sources of harmful chemicals. 

The solubility of organomercury compounds depends primarily on the nature of the X group nitrates and sulfates tend to be salt-like and relatively water-soluble, whereas chlorides are covalent, nonpolar compounds of low water solubility. Methyl mercury compounds tend to be more volatile than other organomercury compounds. 

Apart from the release of human-made organomercurial compounds, methyl mercury can also be generated from inorganic mercury in the environment as indicated in the following equation ... 

It is difficult to establish to what extent methyl mercury residues found in the environment arise from natural as opposed to human sources. There is no doubt, however, that natural generation of methyl mercury makes a significant contribution to these residues. Samples of Tuna fish caught in the late 18th century, before the synthesis of organomercury compounds by humans, contain significant quantities of methyl mercury. 

As noted earlier, diverse forms of organomercury are released into the environment as a consequence of human activity. Methyl mercury presents a particular case. As a product of the chemical industry, it may be released directly into the environment, or it may be synthesized in the environment from inorganic mercury which, in turn, is released into the environment as a consequence of both natural processes (e.g., weathering of minerals) and human activity (mining, factory effluents, etc.). 

In a report from the U.S. EPA (1980), fish contained between 10,000 and 100,000 times the concentration of methyl mercury present in ambient water. In a study of methyl mercury in fish from different oceans, higher levels were reported in predators than in nonpredators (see Table 8.2). Taken overall, these data suggest that predators have some four- to eightfold higher levels of methyl mercury than do nonpredators, and it appears that there is marked bioaccumulation with transfer from prey to predator. 

In a laboratory study (Borg et al. 1970), bioaccumulation of methyl mercury was studied in the goshawk (Accipiter gentilis). The details are shown in Table 8.3 below. 

Thus, chickens bioaccumulated methyl mercury to about twice the level in their food, whereas goshawks bioaccumulated methyl mercury to about four times the level present in the chicken upon which they were fed. The period of exposure was similar... 

FIGURE 8.3 Environmental fate of methyl mercury (adapted from Crosby 1998). 

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. 

Another major incident concerning methyl mercury was the severe pollution of Minamata bay in Japan (see Box 8.1). Here fish, fish-eating and scavenging birds, and humans feeding upon fish all died from organomercury poisoning. There may have been localized declines of marine species in this area due to methyl mercury, but there is no clear evidence of this. 

---