The environmental metals of greatest concern are lead, mercury, arsenic, and cadmium. In the past, lead paint was available for use in homes, and lead pipes and/or lead solder delivered water to some homes. As a result, people can be exposed to lead on a daily basis; this exposure is a major pediatric concern. Mercury similarly is a contaminant of our environment; human beings are exposed to mercury in the fish they eat as well as in the amalgam fillings in their teeth. | Thallium sulfate is very hazardous. Because thallium is not selectively toxic for rodents and many people have been poisoned by thallium, its use is now strictly regulated in many countries. Acute poisoning is accompanied by gastrointestinal irritation, motor paralysis, and death from respiratory failure. Sublethal doses taken over a period of time redden the skin and cause alopecia, characteristic signs of thallium poisoning. Pathological changes include perivascular cuffing and degenerative changes in the brain, liver, and kidney. Neurological symptoms are prominent and include tremors, leg pains, paresthesias of the hands and feet, and polyneuritis, especially in the legs. Psychoses, delirium, convulsions, and other types of encephalopathy also may be noted. Treatment of thallium intoxication involves the oral administration of ferric ferrocyanide (Prussian blue), hemodialysis, and forced diuresis. Prussian blue binds thallium in the intestine and enhances its fecal excretion. Administration of systemic chelating agents should be avoided, because they may increase uptake of thallium into the brain (
