Nexus - 0208 - New Times Magazine-pages

Page Content (OCR)

200ppm phenylmercury acetate (PMA) in the can, with external paints containing up to 2000ppm of PMA.” Mercury enters the food chain from agricultural sprays and industrial effluents. Mercury may even enter our body directly from cosmetics and tattoos. Incredible as it may seem, the cosmet- ic industry continues to use mercurials with phenylmercuric acetate and mercurous chloride still being added to face creams as antisep- tics. For many years authorities were little concerned about the man made mercury contribution to the environment believing that dis- persed low levels were harmless.” These views are illustrated by the attitude of authorities investigating the Minamata disaster in Japan. observed to dance, scream incessantly and often fling them- selves in the sea. Three years later a six year old girl was taken to a pediatric clinic and diagnosed to have a sever nervous disorder. Soon after, a number of other patients with similar symptoms were admitted to a local hospital. When medical staff at the Minamata Health centre examined records for the region it was realised that at least 30 other people had suffered from the same symptoms with the first victim dating back to December 1953. By 1973 over 850 Minamata disease victims had been identified."* The poisoning was eventually traced to fish, most likely contaminated by the waste discharge into Minamata bay by a large chemical-fertiliser factory. P. and F. D'Ttri comment that: Although up to 2010ppm of mercury (wet weight) were collected from the mud near the factory's drainage outlet .., this element was not initially given a high priority, because the patients did not display the familiar symptoms of inorganic mercury poisoning such as loose teeth, sore gums, and tremors.” It was not until February 1969, thirteen years after investigations were begun, that the poisoning agent was identified as methyl mer- cury. This extremely toxic compound was discharged together with mercury catalyst in the waste from vinyl chloride manufac- ture. In the meantime, Swedish scientists had shown that organ- isms in marine bottom sediments could also convert inorganic mer- cury into the highly toxic, readily absorbed, methyl mercury.” Mercury is often classified as either organic or inorganic. Among the organomercurials, as the former class is called, alkylmercurials are regarded as the group of compounds most dan- gerous to living organisms. Widely used a fungicides, alkylmer- cury has been indicted in a number of incidents as the cause of untold human suffering and deaths. One major catastrophe occurred in 1972 in Iraq when seed grain treated with methylmer- cury, an alkylmercurial salt, was inadvertently ground into flour for bread, rather than being used merely for planting. Five hundred people died of mercury poisoning and in excess of six thousand people were hospitalised for the same ailment.” Catastrophes such as these prompted renewed interest into mer- cury toxicity and industrial mercury exposure.” The mechanism of mercury poisoning is now known to involve the oxidation to mercuric ion which can occur in biological envi- [: 1953, along Minamata Bay on Kyushu Island, cats were 18¢NEXUS ronments, Within cells, mercuric ions act as potent nonspecific enzyme inhibitors and denaturants of protein and thereby interfere with cellular metabolism and function. Mercuric ion can also alter membrane function and transport, including the release and uptake of neurotransmitters in the brain. It appears that mercury preferen- tially accumulates in specific cell types in the brain.” The kidney is also a target organ for inorganic mercury toxicity.” In 1980, B.A. Schetz, Director of Toxicological Research at Dow Chemical Company cautioned: There are such things as teratogens - substances that cause harm to a developing organism at levels that are not harmful to the adult. Mercury and thalidomide, two of the most potent teratogens that have been studied, are only that - they do not cause harm to either male or female adults at the same exposure level that will harm a fetus.” R.L. Rawls, writing for Chemical and Engineering News also reported that Monsanto, another giant U.S. chemical company: identifies mercury and two or three other compounds as posing particular hazards to the fetus in the work environ- ment™ This sinister aspect of mercury toxicity highlights the need to assess the total environmental contribution of mercury to living organisms even instances that may be initially considered as small or insignificant. cury level in the environment. Mercury occurs in the envi- ronment at minute background levels or in small localised concentrated ore deposits, making it one of the least abundant met- als. For example, the concentration in sea water is only SOppm, or 0.05 parts per billion In mercury ore deposits the metal is com- monly found as the sulphide and less commonly as the monovalent chloride. These ores are highly insoluble. It seems that nature has limited the toxic impact of environmen- tal mercury on living organisms by providing mechanisms for bio- logical systems to cope with the extremely low background levels. Protection of the human organism involves the production of the small detoxifying proteins called metallothionines which bind heavy metals such as mercury, cadmium and lead with high affini- 6 A t this point it seems appropriate to consider the natural mer- On the other hand, Man, via industrial processes and agriculture continues to disseminate mercury in the environment, substantially elevating the background levels in the food chain. For example, mercury levels of 0.1mg per kg or 100ppb were found in Australian Supermarket potatoes” not to mention the high levels now current- ly found in fish.* The form of the mercury also seems to be important. The mer- cury poisoning catastrophes recorded in past and recent histories involved man made mercury compounds or concentrated mercury salts. A further clue is perhaps obtained from the observations of H.A. Davey and J.C. Van Moort who studied the phenomenon of mer- cury being deposited from the gasses emitted from the thermal JUNE-JULY 1992 SOURCES OF MERCURY POISONING MERCURY LEVELS IN NATURE - ARE THEY A CLUE?