juvenile brook trout, after exposure to 50 mg/l. of lime-neutralized iron suspensions were not directly (toxicologically) affected, but the attrition rate seemed dependent on adverse physical conditions. In applying the results of the present study to nature, it must be remembered that the chemical characteristics of a particular water body have a major influence in determining which iron species predominate. This experiment simulated an aquatic environment with neutral pH and a high oxygen content, especially familiar to shallow, fast-flowing streams where aeration is maximized. Under these conditions, ferric hydroxide floc formation would most likely eliminate food sources and would cause fish to avoid this stretch of water. In contrast, a slightly acidic water with low oxygen content often contains large quantities of dissolved Fez+. Fish present in this environment would be exposed to the insidious deposition of iron on their gills and on the perivitelline membrane covering their eggs.
Acknowledgments The authors wish to acknowledge the help and cooperation obtained from the Pennsylvania Fish Commission, particlarly from the following branches: Benner Spring Fish Research Station a t Bellefonte and the State Fish
Hatchery in Tionesta. Special thanks are extended t o Dr. E. J. Smith who contributed to the completion of this paper by supplying data on long-term tests with coho salmon.
Literature Cited (1) Baker, R. A., Wilshire, A. G., Enuiron. Sci. Technol. 4, 401
(1970). ( 2 ) Mount, D. I., Brungs, W. A,, W a t e r Res., 1 , 2 1 (1967). (3) Sykora, J. L., et al., ibid., 6,935 (1972). (4) Jones, J. R. E., J . Ewp. Biol. (Brit.) 24,110 (1947). (5) Sprague, J. B., J . W a t e r Pollut. Control Fed., 36,990 (1964). ( 6 ) Shelford, V. E., Allee, W. C., J . E x p . Zool., 14,207 (1913). (7) Smith, E. J., “Effect of Lime Neutralized Iron Hydroxide Suspensions on Selected Species of North American Fish”, Doctoral Dissertation, Univ. of Pittsburgh, Grad. School of Public Health, Pittsburgh, Pa., 1973. (8) Siegel, S., “Nonparametic Statistics for the Behavioral Sciences’’, McGraw-Hill, New York, N.Y., 1956. (9) Sprague, J . B., Drury, D. E., “Avoidance Reactions of Salmonid Fish to Representative Pollutants”, “Advances in Water Pollution Research”, pp 169-79, Pergamon Press, Oxford, 1969. (10) Sokal, R. S., Rohlf, F. J., “Biometry”, W. H. Freeman, San Francisco, Calf., 1969.
Received f o r reuiew September 18, 1975. Accepted September 17, 1975.
Evaluating Environmental Impacts of Stack Gas Desulfurization Processes Chiou-shuang J. Yan Drexel University, Philadelphia, Pa. 19 104
The environmental impacts of the five most advanced and promising stack gas desulfurization processes, namely, limestone slurry scrubbing, lime slurry scrubbing, magnesia slurry scrubbing-regeneration to H2S04, sodium solutionSO2 reduction to sulfur, and catalytic oxidation have been examined. In these desulfurization processes, various kinds of pollutants/wastes are formed; the lime slurry scrubbing generates the greatest quantity while the catalytic oxidation the least. From this information, an attempt was made to assess the external costs of these control processes which could serve as an additional criterion for selecting control processes. The limestone slurry scrubbing process is the best choice when operating cost is the sole criterion. However, given the marketability of the resultant sulfuric acid, the catalytic oxidation process emerges as the best process when external costs are added to the operating cost.
In controlling pollution of all kinds, two apparently important facts are often neglected: Removal of a particular pollutant from a particular source and location may merely result in transforming that substance into different forms of pollutants in different locations; and, as first suggested by Leontief ( I ) , the activity of pollution control itself requires inputs of various kinds, and the production of those inputs in turn may generate additional pollutants. In some cases, although it is possible to recycle part of the residuals from consumption and production activities into useful products, economic considerations and physical limitations often lead to conversion of one form of pollutant into another form. In our ecological system, most pol54
Environmental Science & Technology
lutants can, in principle, be removed from water and air streams by use of appropriate equipments, chemicals, and utilities, but what is left must be disposed of in solid form. As previously asserted by Ayres and Kneese ( 2 ) , Kohn ( 3 ) , and Russel ( 4 ) , the interrelations among the various waste streams call for an integrated approach to the environmental control, rather than handling pollution control as separate and isolated problems of disposing gas, liquid, and solid wastes. As an example, this study attempts to incorporate environmental interrelations in evaluating five specific air pollution control alternatives.
Five Stack Gas Desulfurization Processes to B e Evaluated As coal becomes more and more important as a power plant fuel in this time of energy shortage, and the combustion of high-sulfur content Eastern coal would impair air quality, efforts have been made to devise efficient processes to control SO:! emission. Besides desulfurization before combustion, stack gas desulfurization is considered the most promising method that could also be applicable to all other fossil fuels. In this method, the sulfur-bearing fossil fuels are burned and the resulting pollutants, such as SO:! and particulates in the stack gases, are removed by physical and chemical means. Of the many stack gas desulfurization processes being developed, the following five processes are most promising: Limestone slurry, lime slurry, magnesia slurry-regeneration to sulfuric acid, sodium solution scrubbing-SO2 reduction to sulfur, and catalytic oxidation--80% sulfuric acid. In their recent study, McGlarmery and Torstrick ( 5 ) have compared in detail the control costs of these five processes designed for 90% SO:! removal from 500-MW new coal-fired power plants burning fuels containing 3.5% sul-
Table I. Annual Input-Output of Stack Gas Desulfurization Processesa Input
Uti - . I ities Steam, M Ib Water, M gal Electricity, M KWH Fuel oil, M gal Natural gas,-M scf Heat credit, M M Btu Chemicals Limestone, M tons Lime, M tons MgO, M tons Coke, M tons Soda ash, M tons Catalyst, M lit. output Wastes CaSOJCaSO,, M tons By-products H,SO , M tons Na,Sd,, M tons Sulfur, M tons
Limestone slurry
492 800 250 300 78 740
Lime slurry
490 000 241 900 74 100
Magnesia slurry
440 2 207 71 5
-
-
175
-
156.4
156.4
-
81.2 -
Calculations of PollutantslWastes Generated f r o m t h e Five Processes In the pollution control systems, the major origins of pollutantdwastes can be classified into two categories: Primary Sources. These include the incomplete conversion of the pollutants to be removed and the undesirable by-products formed in the reaction and regeneration steps. The output rows of Table I list the undesirable by-products from the primary sources of the five control processes. Following the method of McGlarmery and Torstrick, NazS04 from the sodium solution process is treated as a salable byproduct although its marketability is questionable. The annual production and the apparent consumption of Na2S04 in 1972 are about 1,364,000 tons, of which 660,000 tons are by-products from various processes (6). The sodium solution process for each 500-MW power plant will generate 13,000 tons of Nazi304 per year resulting in the vast excess supply since the number of the potential desulfurization plants is estimated to be 200 units. Sulfur and H2S04 are also treated as salable by-products although their marketability is also subject t o great uncertainty ( 7 ) . I t should be noted that for limestone slurry and lime slurry processes, the possible water pollutants from the leaching of CaS03, CaS04, and incomplete closed loop operations are not included. Secondary Sources. These include the pollutants generated from production of inputs, such as various chemicals and utilities necessary for control processes. The utility re-
0.134 1.086 0.763
-
1.800
-
110.400b -
a C a p a c i t y : 500MW; f u e l : coal; SO, r e m o v a l : 90%; s u l f u r c o n t e n t o f t h e f u e l : 3.5%.
fur. However, except for the on-site disposal of calcium solids, the costs of disposing transformed pollutants, undesirable by-products, and the indirect pollutants generated from production of inputs are not accounted for. If the purpose of a control process is to eliminate a particular pollutant from our environment without adverse external effect, the cost must include not only the direct operating cost but also the indirect external cost of correcting the adverse effects. The inclusion of these indirect external costs will aid us in choosing the best system for our society as a whole. For assessing these indirect costs, we will, first of all, analyze through material balance tables the overall environmental impacts of the above five control processes described briefly in the appendix.
987 000
509.5 62 900
-
Catalytic oxidation
179 000 312 000 90 440
2 137 800 9 953 400 74 190
000
500 060 356
20 300 -
Sodium solution SO, reduction
100% H,SO,.
0.134 9.300
13.000 32.700 c 8 0 % H,SO,.
Table II. Pollutant Generating Factors for Utilitiesa
Electricity, lb/100 kwh Steam, IbJM Ib Fuel, Ib/M.Btu Gaseous fuel Liquid fuel Solid fuel Cooling water, Ib/M gal Process water, Ib/M gal
Particulate
SO,
NO,
2 2
3 3
.7 .7
1 2 2
-
.4 .7 1.4
-
3 5 -
Solid
-
-
-
.35 .35
a From ( 8 , 9 ) .
quirements for each process listed in Table I are also based on McGlarmery and Torstrick. The pollution factors of utility production are listed in Table I1 (8, 9). Note that these factors are for the existing facilities and are much higher than the New Source Performance Standards. Multiplying these factors with utility requirements in Table I, we obtain pollutants generated in Table 111. The input rows of Table I also show the major chemicals used in each process. Production of these chemicals in turn requires utilities and raw materials which are estimated from the literature (10, 11).Following the procedure for estimating pollutants generated from the primary sources, the factors for each of these chemicals are obtained in Table IV. The pollutants generated from production of each chemical are then calculated by multiplying these factors by the quantities of chemicals required (Table 111). The total pollutants/wastes produced by each process as calculated above do not include more remote indirect sources such as pollutants generated from transportation of materials, production of equipments, and indirect inputs. In addition, all processes are assumed to be equally reliable, and the pollutants emitted during the down-time of these processes are not included.
Results a n d Conclusions The pollutants/wastes generating characteristics of the five processes are summarized as follows: Volume 10, Number 1, January 1976
55
Limestone Slurry Process. A great quantity of CaS03/ Cas04 wastes, as much as four times the weight of the sulfur removed, is produced. In some cases, these wastes were reported to have poor settling characteristics in the ponds which could lead to difficulty in reclaiming the land for subsequent uses. In addition, potential runoff could occur leading to significant water pollution problems. Lime Slurry Process. The characteristics and problems
Table II I A. PollutantsWastes Generation-Limestone Slurry Scrubbing,a Tonslyear
Primary source CaSO,/CaSO, Secondary source Utility Steam Water Electricity Chemical Limestone Total
Particulate
SO,
NO,
Solid
Water soluble
-
-
-
156 400
b
493 787
740 1181
173 275
-
-
nil 1280
nil
nil
-
1921
448
156444
-
44
-
of lime slurry process are basically the same as the limestone slurry process, except that, in addition, about 3000 tons of particulates are produced in the course of lime production from limestone. Of course, these particulates could be generated off-site. Magnesia Slurry Process. This process operates with the same principle as the lime slurry process, except that the by-products, MgSOJMgS04, are regenerated, eliminating the great quantities of solid wastes. The regeneration step which requires process water and fuels results in somewhat higher SO2 and NO, production than those from the lime slurry process. Since magnesia is regenerated for reuse, particulates generated from manufacturing magnesia are small in quantity. Sodium Solution Process. Although it is considered as a regenerative process, this process generates a great amount of Na2S04 by-product. As mentioned above, Na2S04 may have to be treated as a waste rather than a byproduct due to its excess supply. In addition, this process uses great quantities of steam and water resulting in the generation of the largest quantities of airborne pollutants among the five processes. Catalytic Oxidation Process. This process is not only the cleanest process producing hardly any direct pollutants but also is the least energy intensive. The heat from the
a Capacity, 5 0 0 W. f u e l coal, SO r e m o v a l 90%; s u l f u r c o n t e n t e s t i m a t e b f o ? l e a c h i n g ' o f CaSO,/CaSO, and o f t h e fuel, 3.5%. t h a t in t h e purge stream.
pN6t
Table III B. PollutantdWastes Generation-Lime Scrubbing,a Tonslyear
Table Ill D. Pollutants/WastesGeneration-Sodium Solution Scrubbing-SO, Reduction to Sulfur/ Tonslyear
Slurry
Particulate
Water
Primary source Ca S0,/Ca SO Secondary source Utility Steam Water Electricity Chemical Lime Total
Particulate
SO,
NO,
Solid
uble
-
-
-
156 400
b
490
735
172
-
-
-
741
SOI-
-
-
1112
-
259
42
-
-
431
156442
45 _ -3 0_ ~ _ _ _ _ _ 4276
1847
-
-
b a C a p a c i t y 500 W. f u e l coal. SO r e m o v a l 90%; s u l f u r c o n t e n t o f t h e f u e l , 2.5%. pN6t estirnateb f o ? legching'of CaSO,/CaSO, and t h a t i n t h e purge stream.
Table III C. PollutantsWastes Generation-Magnesia Slurry-Regeneration to H,SO,,a Tonslyear Particulate
SO,
NO,
Solid
SO,
NO,
Water soluble
Solid
Primary source - (32 7 0 0 ) b Sulfur (13 0OO)b Na,SO, Secondary source Utility Steam 2 138 3 2 0 7 749 1742 Water Electricity 742 1 1 1 3 260 Natural gas 255 102 Heat credit - 6 3 -95 -22 Chemical Lime 5 560 Soda ash Antioxidation C C C C c catalyst __ -Total 3 077 4 225 1 089 2 302 a C a p a c i t y 5 0 0 W . f u e l : coal, SO r e m o v a l : 90%. s u l f u r c o n t e n t o f t h e f u e l : 5.5%. y T r k a t e d as saiablg b y - p r o d u c t . b a t a n o t available.
Table III E. Pollutants/Wastes Generation-Catalytic Oxidation,a Tonslyear
Primary source H,SO, Secondary source Utility Steam 440 660 154 Water Electricity 711 1 0 6 7 249 Fuel oil 791 1 1 8 7 277 Heat credit -20 -30 -7 Chemical 41 MgO Lime 5 Coke nil nil nil C C C Catalyst -~ --_ Total 1 9 6 8 2 8 8 4 673
Secondary source Uti I ity Steam 179 269 63 .Water Electricity 904 1356 316 Heat credit -987 -1 481 -345 Chemica I C C c Catalyst _ _ ~ Total 96 144 34
a C a p a c i t y 5 0 0 W; f u e l , c o a l ; S O r e m o v a l , 90%. s u l f u r c o n t e n t of t h e f u e l , i . 5 % . y T r e a t e d as salabl2 b y - p r o d u c t . c b a t a n o t available.
a C a p a c i t y , 500 W . f u e l c o a l . SO r e m o v a l 90%. s u l f u r c o n t e n t of t h e f u e l , 3.5%. yTrkated'as saiablk b y - p r o d h c t . C b a t a n o t available.
56
Environmental Science & Technology
Primary source HZSO,
Particulate
SO,
NO,
-
-
-
Solid
Water soluble
-
(109 9OO)b
-
-
-
-
55 c -
55
-
C
-
Table IV. Pollutant Generating Factors for Chemicals.0 Lb/Ton Particulate
Solidb
-
120
75
-
nil nil
nil
Soda ash Lime Limestone Coke Magnesia
nil
-
75
a F r o m References 10, 1 1 . A s s u m i n g c r u d e t r o n a c o n t a i n i n g 6% of insolubles, such as b e n t o n i t e a n d shale, i s d i r e c t l y used in t h e process.
Table V. National Emission of Pollutants and Annual Damage Costs0 E m i s s i o n level w i t h o u t further c o n t r o l 1 000 tons/year
Part icu I ate
36 280 46 850 26 690
sox NO, a For
Annaul damage cost,b dollardyear
8 180 13 780
Average damage cost, dollarslton
225 294
c
c
I n c l u d i n g damages t o h e a l t h , 1 9 7 7 . F r o m Reference 9. residential p r o p e r t y , m a t e r i a l s a n d vegetation. N o t available.
exothermic reaction is used to minimize the energy requirements and the generation of pollutants/wastes. No byproduct other than sulfuric acid is produced. Table VI lists the various pollutants/wastes generated by each process. Note that these pollutants/wastes are generated while removing 41,344 tons of sulfur or 82,688 tons of SO2 from the air. In this table, C a s 0 3 and Cas04 are considered as wastes while sulfur, H2S04, and Na2S04 are treated as useful by-products. Of the five processes, in terms of physical volume, catalytic oxidation produces the least amounts of pollutants/ wastes followed by magnesia slurry while lime slurry produces the largest quantities of pollutants/wastes. However, since the pollutantslwastes mix of these processes are dif-
Table VI. Annual Control Costs-External
Pol I u tan t s/wastes, to ns/yea r Particulate
so* N0,
Solid Water soluble cost External cost 1 000 dollars/ year Particulate
so*
N0, Solid Total Operating costc 1 000 dollars/ year Total cost 1 000 dollars/ year a Capacity, 500
ferent, quantitative comparison cannot be made without assigning a proper weight for each pollutant. In the absence of more ideal data, the damage costs per ton derived from the EPA data are used as weights in calculating the external costs of the five processes (Table V). Due to lack of data, the linear relationship between emission level and damage cost is assumed. Since the degree of damage is likely to increase a t an increasing rate with the emission level, the use of the average damage costs may lead to underestimation of the true external costs. As data on NO, and solid wastes are not available, their damage costs are somewhat arbitrarily assumed to be $294 (same as SO,) and $3.00 per ton respectively. I t should be noted that the damage cost of solid wastes depends a great deal on local conditions such as population density and the availability of open space. Given the damage costs of each pollutant and waste, the external costs for each process are calculated in Table VI. Together with the direct costs calculated by McGlarmery and Torstrick, we arrive a t the overall costs of the five processes (also in Table VI). Of the three regeneration processes, catalytic oxidation is obviously the best choice both from the point of view of pollutants/wastes generation and the annual operating cost. Of the two throw-away processes, limestone slurry is better than lime slurry for lower annual cost and less pollutantslwastes generation. The choice between catalytic oxidation with lower pollutant generation and limestone slurry with lower operating cost is harder to make. If the above external cost is added to the operating cost, catalytic oxidation emerges as the best choice. However, as the total costs of these two processes are quite close, and for limestone slurry the cost figure is very sensitive to the weight assigned t o solid wastes, careful re-examination is desired for final decision. Many aspects of damage caused by environmental pollution are not yet explored or fully understood today. T o the extent that this paper depends on the rather crude data on damage costs, ignores local conditions, and leaves out the more remote environmental repercussions, care must be exercised in applying or interpreting the results. I t should be noted that the main purpose of this paper is to direct attention to the need for an integrated environmental control
and Operating Costs0
Limestone
Lime
1280 1921 448 156 444
4 276 1847 43 1 156 442
b
b
Magnesia
Sodium
Catalytic oxidation
1968 2 884 673 386
3 077 4 225 1089
2 202
96 144 34 55
692 1242 320
22 42 9
b
288 565 132 469 1454
962 543 127 313 1945
443 848 198 1 1490
2 261
73
7 703
8 102
9 211
11 602
8 874
9 157
10 047
10 701
13 863
8 947
M W ; f u e l , c o a l ; SO, r e m o v a l , 9 0 % ; s u l f u r c o n t e n t o f t h e f u e l , 3.5%.
7
-
Data n o t available. C A f t e r M c G l a r m e r y a n d T o r s t r i c k .
Volume 10, Number 1, January 1976 57
system. Although a segmental control system may be a practical necessity, external costs of various pollutants, in addition to direct operating costs, must be imputed in evaluating control strategies, schemes, and processes. APPENDIX
Brief Description of the Five S t a c k Gas Desulfurization Processes All process data represent the state of technology in late 1973. Limestone S l u r r y Scrubbing. Stack gas is washed with a recirculating slurry (pH of 5.8-6.4) of limestone and reacted calcium salts in water using a two-stage scrubber system for particulates and SO2 removal. Limestone feed is wet ground prior to addition to the scrubber effluent hold tank. Calcium sulfite and sulfate salts are withdrawn to a disposal area for discard. Lime S l u r r y Scrubbing. Stack gas is washed with a recirculating slurry (pH of 6.0-8.0) of calcined limestone (lime) and reacted calcium salts in water using a two-stage venturi scrubbing. Lime is purchased from “across the fence” calcination operation, slaked, and added to both circulation streams. Calcium sulfite and sulfate are withdrawn to a disposal area for discard. Magnesia S l u r r y Scrubbing-Regeneration to HzS04. Stack gas is washed using a two-stage venturi scrubbing. Water is utilized for removal of particulates, and a recirculating slurry (pH 7.5-8.5) of magnesia (MgO) is utilized for removal of S 0 2 . Makeup magnesia is slaked and added to cover only handling losses since sulfates formed are reduced during regeneration. Slurry from the SO2 scrubber is dewatered, dried, calcined, and recycled, during which concentrated SO2 is evolved to a contact sulfuric acid plant producing 98% acid. Sodium Solution Scrubbing-SO2 Reduction to Sulfur. Stack gas is washed with water in a venturi scrubber for removal of particulates and then washed in a valve tray scrubber with a recirculating solution of sodium salts in water for SO2 removal. Makeup sodium carbonate is added to cover losses due to handling and oxidation of sodium sulfite to sulfate. Sodium sulfate crystals are purged from
the system, dried, and sold. Water is evaporated from the scrubbing solution to crystallize and thermally decompose sodium bisulfite, driving off concentrated SO1. The resulting sodium sulfite is recycled to the scrubber, and the SO2 is reacted with methane for reduction to elemental sulfur. Catalytic Oxidation. Stack gas is first cleaned of particulates by a high-temperature electrostatic precipitator. Then the SO2 is catalytically converted to SOs, and available excess heat is recovered. The SO3 reacts with moisture in the stack gas to form H2S04 mist which is scrubbed in a packed tower using a recirculating acid stream to yield 80% acid. The mist is removed by a Brink mist eliminator, and the clean 254’F gas is exhausted to the stack.
Acknowledgment I am indebted to T. Y. Yan of Mobil Research and Development Corp. for his help in constructing the material balance tables and A. M. Chung of Drexel University for his valuable suggestions. Literature Cited (1) Leontief, W., Reo. Econ. Stat., 52,262-71 (Aug. 1970). (2) Ayres, R. U., Kneese, A. V., A m . Econ. Reu., 59,282-97 (1969).
(3) Kahn, R. E., Proc. 1970 Soc.-Stat. Sec., Am. Stat. Assoc., pp 207-14. (4) Russel, C. S., A m . Econ. Reu., 63,236-43 (1973). (5) McGlarmery, G. C., Torstrick, R. L., “Cost Comparison of Flue Gas Desulfurization Systems,” Fuel Gas Desulfurization Symposium, Atlanta, Ga., Nov. 1974. (6) Stanford Research Institute, Chemical Economics Handbook, Menlo Park, Calif., 1974. (7) Sulfur Oxide Control Technology Assessment Panel on Projected Utilization of Stack Gas Cleaning Systems by SteamElectric Plants, “Final Report,” ASTD 1569, April 1973. (8) Jenkins, R. E., McCutchen, G. D., Environ. Sci. Technol., 6, 884-8 (1972). (9) Environmental Protection Agency, “The Economics of Clean Air,” Annual Report of the Administrator of the EPA to the Congress of the U.S., March 1972. (10) Faith, W. I., Keyes, D. B., Clark, R. L., “Industrial Chemicals”, 3rd ed., John Wiley, New York, N.Y., 1965. (11) Kirk, R. E., Othmer, D. F., Encyclopedia of Chemical Technology, 2nd ed., 1964, ibid.
Received for review January 29, 1975. Accepted August 27, 1975. This work was supported by a grant from Drerel C’niuersity.
Atmospheric Oxidation of Chlorinated Ethylenes Bruce W. Gay, Jr.*, Philip L. Hanst, Joseph J. Bufalini, and Richard C. Noonan Environmental Protection Agency, Environmental Science Research Laboratory, Atmospheric Chemistry and Physics Division, Research Triangle Park. N.C. 277 11
Chlorinated ethylenes are released into the air in great quantities. The US.Tariff Commission gives the following 1974 U.S. production figures: vinyl chloride, 2.5 X lo9 kg; trichloroethylene, 2.0 X lo8 kg, and tetrachloroethylene, 3.3 X lo8 kg. The vinyl chloride monomer produced is largely converted to polyvinyl chloride, but it has been estimated that approximately 6% of the monomer is lost to the air during processing, corresponding to 1.5 X lo8 kg in 1974. The 1974 production of all halogenated organic compounds in the United States was more than five billion kilograms (11.
These halogenated organic compounds do not occur naturally in the environment, and therefore much attention is being given to their effects on human health and welfare. 58
Environmental Science 8 Technology
The fully halogenated compounds, such as trichlorofluoromethane and dichlorodifluoromethane, are chemically unreactive and have not been implicated in any direct effects on human health. Their lack of reactivity, however, allows them to remain in the atmosphere long enough to reach the stratosphere, where a detrimental interaction with stratospheric ozone may be taking place (2, 3 ) . The halogenated ethylenes seem to be sufficiently reactive for them to be fully photooxidized in the troposphere. While this reactivity may be a desirable property from the point of view of stratospheric effects, it apparently is associated with direct effects on human health. Vinyl chloride has recently received notoriety by being linked to angiosarcoma, a rare type of cancer in the human liver. Exposures
