environmental chemistry update
edited by COLIN BAIRD Univerrity of Western Ontario London. ON, Canada N6A5B7
R guide for instructors and their students to recent research developments in aspects of environmental problems that have a strong chemical connection Human Health Effects of the Chernobyl Disaster Increased Incidence of Thyroid Cancer
The release of radioactivity from the famous explosion a t the fission nuclear vower reactor a t Chernobvl eight .. "vears :igo has resulted 111 a sutrst;inti;il inrrwn. in thr incidence ofthwuid cancer in cluldrell in t h ~inlin(,di;irt. . a r w hut 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 i n most countries. More than 500 children in Belarus and Ukraine have been diagnosed with this disease. The likel cause of the cancers is ' and perhaps 1 3 3 ~reradioactivity from the isotope 131 leased during the explosion (11. 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 i n Spain. The later pollution was due mainly to lead and silver smelting in Germany (21. Detrimental Effect of Lead upon lQ 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 (31. Ozone Hole Phenomena The Antarctic
The Antarctic ozone hole appeared earlier than usual in 1994; i t was as large and a s severe a s 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 (41. 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
Rbout the Ruthor... Colin Baird is author of the textbook Environmental ChemisFreeman: New York, and of the alticle 'lntroducing Atmospheric Reactions: A Systematic Approach for Students" in thls Journal 1995, 72,153.
and coworkers discovered that the nitric acid trihydrate (NATj crystals, HN03.3Hz0, 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 I1 crystals that form a t even lower temperatures are even larger, they experience fallout from the lower stratosphere even faster.) In contrast, the reduction i n gas-phase HN03 concentrations in the Arctic lower stratosphere during the 19921993 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 ~hotolvzedto NO?. . which combined with chlorine morloxid(! 11,dw~ctiv:~t(~ the chlurine. The inrrcaicd rooling of the Arctic lowrr str;~to.inhwrin future w n t e r s could he sufficient to intensify t h h 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 recentlv- sveculated that . iodine, as well a s its fellow halogens, chlorine and bromine, may . play . . a role i n stratosvheric ozone deoletion. Bioeenic processes in the ocean release methyl iodide to the a&osphere, where most of i t is destroyed in a few days. However, tropical thunderclouds could transport some of i t to the lower stratosphere before i t is destroyed. In combination with chlorine and bromine oxides, I 0 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 OWHOO 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 C10 with Br. Equally important is the following cycle, reminiscent of the "dimer" mechanism that operates in ozone holes, for the 203 + 302 process.
try, 1995; W. H.
C10 + HOO + HOCI + 0, HOCI +sunlight 4 OH + C1
684
Journal of Chemical Education
The same mechanism with bromine replacing chlorine i s also important. The greatest removal rate for ozone a t these latitudes should occur i n s w i n e and fall, when ozone production is minimal. ~ l t h o u the ~ h sunlight then is not sufficient to dissociate much Oz, i t is adequate to drive the free radical processes (7). The feasibility of A. Y. Won& scheme to reduce stratosphrric ozone dt:atruct~ondue to reactions inwdvlng chlorme has Ix!en queit~oncd. The scheme invol\w the m~roductionof 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 NOi and COi . Vimiano et al. -also note the very large energy requirements for the electron nroduction and for removal of the 2.4 x 10' k "e of chlorine from ihe stratosphere (8). Pesticides and Dioxin Great Lakes The herbicide atrazine and its metabolite, i n which the nitrogen-based ethyl group is removed, were found i n all 490 samples of water from the Great Lakes in a 1990-1992 studv. Hiehest concentrations of atrazine were found in ~ a k & 0;ario and Erie (70-110 parts per trillion (pptj), with lower levels (20-35 ppt) i n Lakes Huron and Michigan. It was estimated that the Great Lakes may contain more than 600.000 ke 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 nnt (i.e.. . .. 20 pph) (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).
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The U S . EPA h a s issued a 2000-page draft of its reassessment of the health risks of dioxins. The report reaffirms their 1985 conclusion that i t 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. oeaked about 1970. and have declined since then. ~ u m a n ' i o dburdens ~ of dioxins mav also have declined. The Toxic Eauivalent 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 a s LiMnz04 in one electrode) i s unreactive i n this medium unless a n external connection to the other electrode is made (13). Air-Pollution Control for Power Plants A process called SNOX, which removes both NOx and SOz from t h e flue gases produced by coal-fired power plants, has been developed and demonstrated. The nitrogen oxides are first reduced to Nz.The resultinggas i s 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 i n the demonstration held a t an Ohio Edison plant (14). Literature Cited
Environmental Estrogens DDT and its metabolite DDE, as well a s methoxychlor, dieldrin, kepone, and some PCB's a r e thought to be environmental estrogens. These synthetic compounds a r e 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 causine renroductive abnormalities. Examnles of reproductive pro61ems caused by such chemicals have alreadv been observed i n wildlife. such a s allieators in Florida. They may also play a role i n inducing cancer i n humans (11).
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1. Willisms. D. Nntum 1994.371. 556. 2. Emsley J.Nru Scieatin 1994.106 11, 14. 3. MeMichael. A. J.Amrrimn Journal nfEpidm?iolog). 1994. I&. 489-499. 4. Chemiml and Enxinenng News 1994. lOct 101.5. 5 . Santce. M. L.Scimce 1995,287,849-852. 6. Chemical a > i d E , t ~ r t e e r i i i r N ~1994. u s tNou 14,.Solornon.S.Jolournn1 ofCOOph.y~Icd Research 1994.99.20491-20499. 7. Wennberg. P. 0.Scienm 1994.266.39W04. 8. Vi&ano. A. A. Scierice 1995,267, 82-84, Summary in Charnialv ond Engineering News 1995,(Jan 91.23. 9. Schottler, S. P:Eisenreieh. S. d. Enuimi~rnentalScierrcr and T~elrhoiagv1394.28,
2228-2232.
10. Lane. L. E m i m n m e a t d H d t h Pwsurdioes
1993.101.578-583.
Volume 72 Number 8 August 1995
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