Human Health Effects of the Chernobyl Disaster
Increased Incidence of Thyroid Cancer
The release of radioactivity from the famous explosion at the fission nuclear power reactor at Chernobyl eight years ago has resulted in a substantial increase in the incidence of thyroid cancer in children in the immediate area but no great increase in the incidence of childhood leukemia, tumors, or genetic defects. In the region of the Belarus republic closest to Chernobyl, the childhood thyroid cancer rate has reached over 100 cases per million children, compared to less than 3 per million in most countries. More than 500 children in Belarus and Ukraine have been diagnosed with this disease. The likely cause of the cancers is radioactivity from the isotope 131-I and perhaps 133-I released during the explosion (1).
Lead Pollution
Analysis of snow in the Greenland ice sheet indicates rather high levels of lead pollution in air from 500 BC to AD 300 and AD 1000-1500. The earliest lead pollution was associated with mining in Greece and then mining by the Romans, especially in Spain. The later pollution was due mainly to lead and silver smelting in Germany (2).
Detrimental Effect of Lead upon IQ in Australia
Studies of children in Port Pirie, Australia have produced further evidence of the detrimental effect of lead upon IQ. The cumulative exposure to lead of the children from birth to age seven years was determined by analyzing for the element in their baby teeth (3).
Ozone Hole Phenomena
The Antarctic
The Antarctic ozone hole appeared earlier than usual in 1994; it was as large and as severe as the holes in 1992 and 1993. The region of severe depletion covered about 24 million square kilometers, which is approximately the size of North America (4).
The Role of Nitric Acid
Our knowledge of the role of nitric acid in the formation of ozone holes over polar areas has recently been improved by a joint publication from researchers in Scotland and the United States. Using data obtained by satellite, Santee and coworkers discovered that the nitric acid trihydrate (NAT) crystals, HNO33H2O, which first form when the lower stratosphere cools in the dark polar winter over Antarctica, can grow large enough and last long enough to sediment. Thus, they partially denitrify this region of the atmosphere for several months. (Because the so-called type II crystals that form at even lower temperatures are even larger, they experience fallout from the lower stratosphere even faster.)
In contrast, the reduction in gas-phase HNO3 concentrations in the Arctic lower stratosphere during the 1992-1993 winter was "less intense, more localized, and more transient", indicating no significant denitrification. For that reason, no Arctic ozone hole was formed. Once significant sunlight appeared (required before chlorine can participate in catalytic cycles that destroy ozone), the nitric acid photolyzed to NO2, which combined with chlorine monoxide to deactivate the chlorine. The increased cooling of the Arctic lower stratosphere in future winters could be sufficient to intensify the loss of nitric acid and thereby lead to greater depletions of Arctic ozone (5).
Stratospheric Ozone Depletion in Nonpolar Regions
The Role of the Halogens
S. Solomon and coworkers have recently speculated that iodine, as well as its fellow halogens, chlorine and bromine, may play a role in stratospheric ozone depletion. Biogenic processes in the ocean release methyl iodide to the atmosphere, where most of it is destroyed in a few days. However, tropical thunderclouds could transport some of it to the lower stratosphere before it is destroyed. In combination with chlorine and bromine oxides, IO and I could participate in cycles that destroy ozone. Chlorine and bromine alone cannot account for all the ozone destruction observed over nonpolar regions in the low stratosphere (6).
Cycles that Remove Ozone
Experimental measurements of free radical concentrations in May, 1993 between 15 oN and 60 oN indicate that the OH/HOO reaction chain is responsible for 30-50% of the ozone loss in the low stratosphere. Chains involving nitrogen radicals are less important in this region than previously thought. Almost one-third of the loss is due to cycles involving halogens, including that initiated by collision of ClO with Br.
Equally important is the following cycle, reminiscent of the "dimer" mechanism that operates in ozone holes, for the 2O3 --> 3O2 process.
- Cl + O3 --> ClO + O2
- OH + O3 --> HOO + O2
- ClO + HOO --> HOCl + O2
- HOCl + sunlight --> OH + Cl
The same mechanism with bromine replacing chlorine is also important. The greatest removal rate for ozone at these latitudes should occur in spring and fall, when ozone production is minimal. Although the sunlight then is not sufficient to dissociate much O2, it is adequate to drive the free radical processes (7).
The feasibility of A. Y. Wong's scheme to reduce stratospheric ozone destruction due to reactions involving chlorine has been questioned. The scheme involves the introduction of electrons into the stratosphere, which would allow the conversion of chlorine to chloride ion and its hydrates and potentially the subsequent removal of the chloride ions. A. A. Viggiano and colleagues have noted that chloride ions react quickly after their formation (to reform chlorine radicals) and never amount to more than a tiny fraction of the anions present. The dominant ions are NO3- and CO3-. Viggiano et al. also note the very large energy requirements for the electron production and for removal of the 2.4 X 10^9 kg of chlorine from the stratosphere (8).
Pesticides and Dioxin
Great Lakes
The herbicide atrazine and its metabolite, in which the nitrogen-based ethyl group is removed, were found in all 490 samples of water from the Great Lakes in a 1990-1992 study. Highest concentrations of atrazine were found in Lakes Ontario and Erie (70-110 parts per trillion (ppt)), with lower levels (20-35 ppt) in Lakes Huron and Michigan. It was estimated that the Great Lakes may contain more than 600,000 kg of the herbicide and that its residence time there is in years. Atrazine concentrations in rivers that flow into these lakes can exceed 20,000 ppt (i.e., 20 ppb) (9).
There are about 600 basic ingredients in the 34,000 pesticides registered with the U.S. EPA. Approximately 75% of all U.S. cropland and 70% of livestock are treated with pesticides. In 1991, 495 million pounds of herbicides, 175 million pounds of insecticides, 75 million pounds of fungicides, and 72 million pounds of other pesticides were used; this accounted for three-quarters of all pesticide use in the United States (10).
Environmental Estrogens
DDT and its metabolite DDE, as well as methoxychlor, dieldrin, kepone, and some PCB's are thought to be environmental estrogens. These synthetic compounds are found in the environment and mimic the action of the sex hormone estrogen because they can bind to the estrogen receptor in cells. Some scientists are worried that they can disrupt the hormone balance in human eggs and fetuses, thus causing reproductive abnormalities. Examples of reproductive problems caused by such chemicals have already been observed in wildlife, such as alligators in Florida. They may also play a role in inducing cancer in humans (11).
The U.S. EPA has issued a 2000-page draft of its reassessment of the health risks of dioxins. The report reaffirms their 1985 conclusion that it is a probable cause of cancer in humans. Even trace amounts of dioxins may also disrupt regulatory hormones, produce reproductive and immune-system disorders, and lead to abnormal fetal development. Although waste combustion produces 95% of all known dioxin emissions in the United States, about half its source is unknown. Dioxin levels in the environment were small until about 1930, peaked about 1970, and have declined since then. Human body burdens of dioxins may also have declined. The Toxic Equivalent intake of dioxins and furans of Americans is currently about 111 pg, leading to a body fat concentration of about 40 ppt (12).
Lithium Battery Advances
Rechargeable Power Source
Recent advances in lithium ion battery technology may allow these devices to become the rechargeable power source of choice in electric cars of the future. Due to their high voltage, they can store a large amount of energy per given mass or volume of battery. In the past, however, such batteries have been somewhat impractical because they had to be hermetically sealed and required nonaqueous electrolytes due to lithium's violent reaction with water. In the newly developed battery, the electrolyte is water that already contains a high concentration of Li+ ions; elemental lithium (present as LiMn2O4 in one electrode) is unreactive in this medium unless an external connection to the other electrode is made (13).
Air-Pollution Control for Power Plants
A process called SNOX, which removes both NOx and SO2 from the flue gases produced by coal-fired power plants, has been developed and demonstrated. The nitrogen oxides are first reduced to N2. The resulting gas is then heated and catalytically oxidized to sulfur trioxide, which is then hydrated to sulfuric acid. More than 90% of the NOx and SO2 were removed from the flue gases in the demonstration held at an Ohio Edison plant (14).
Literature Cited
- Williams, D. Nature 1994, 371, 556.
- Emsley, J. New Scientist 1994, (Oct 1), 14.
- McMichael, A. J. American Journal of Epidemiology 1994, 140, 489-499.
- Chemical and Engineering News 1994, (Oct 10), 5.
- Santee, M. L. Science 1995, 267, 849-852.
- Chemical and Engineering News 1994, (Nov 14). Solomon, S. Journal of Geophysical Research 1994, 99, 20491-20499.
- Wennberg, P. O. Science 1994, 266, 398-404.
- Viggiano, A. A. Science 1995, 267, 82-84. Summary in Chemistry and
- Engineering News 1995, (Jan 9), 23.
- Schottler, S. P.; Eisenreich, S. J. Environmental Science and Technology 1994, 28, 2228-2232.
- Lang, L. Environmental Health Perspectives 1993, 101, 578-583.
- Chemical and Engineering News 1994, (Jan 31), 19.
- Chemical and Engineering News 1994, (Sept 19).
- Glanz, J. Science 1994, 264, 1084; Li, W. Science 1994, 264, 1115-1118.
- Durrani, S. M. Environmental Science and Technology 1994, 28, 88A-90A.
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