U Man Defines Mercury Danger

The 0.5 parts per million safe level for mercury set by the U. S. Food and Drug Administration (FDA) does not mean 0.6 parts per million is dangerous, says Dr. Rolf Hartung, associate professor of environmental and industrial health at the University. But while the boundary area where negative effects on humans become apparent is about 5.0 parts per million, ' giving a 10-fold safety factor, that "is not much when we consider our ignorance about long-term effects of mercury on man and on the fetus and genetic material," he adds. The U-M professor say s some fish in Lake St. Clair, from which it is now forbidden to remove fish because of mercury pollution, have leveks as high as 7.0 parts per million, or 2.0 parts per million above the level where damage to the human nervous system begins. However, the average for Lake St. Clair fish is only about 2 I parts per million, he adds. Hartung says scientists do I not really know how long it I will take to clear Lake St. Clair of mercury contamination. While flushing time for the lake is about one year, this applies only to water replacement and does not include bottom sediment replacement I where the contaminating influence begins. Mercury can only be diluted, never destroyed, and I "some specialists claim that I in 100 years, 50 per cent of the mercury in one contaminated lake in Sweden will be removed," he notes. Interestingly, the fish living in mercury-infested waters seem to be able to tolerate the level of metal they are absorbing, but, Hartung worries, "it is dubious whether man can take them." Scientists distinguish between two kinds of mercury - inorganic and organic. The poisoning caused by inorganic mercury vapor or salt, though serious, can be cured w i t h drugs. The true crisis centers around methyl mercury, an . organic material of high toxicity synthesized by nature as well as man. "Methyl mercury combines readily with proteins and enzymes in the bod y," explains Hartung, "and destroys, first, their function and, second, the cell tissue. If they are brain cells, they do not grow back." , Clinical symptoms of mercury poisoning in its early stages include numbness of fingers and toes, irritability, and personality and behavioral changes. Though the poisoning can usually be controlled if arrested early, these first symptoms are difficult to diagnose since they involve subtle changes. In any case, treatment is palliative only, since no known "cure" exists. The more obvious symptoms such as paralysis and distorted senses, including "tunnel visión," do not j pear until poisoning has j gressed considerably. Late stages of poisoning a r e K marked by mental aberration, ■ coma and finally death. The I stronger symptoms are j I reversible and cannot even I be arrested to any great deI gree. To date, there are no identiI fied cases on record of merI cury poisoning from fish Icaught in Lake St. Clair. Luilll II... - m.T-„- - M