Atal-Ayub Nagar - still drinking poison
Yet another Carbide factory fire - Atal Ayub Nagar residents left homeless and traumatised: Echoes of the 1984 Union Carbide disaster in 2001
SUMMARY OF THE GREENPEACE REPORT
Greenpeace Research Laboratories, Exeter 1999 Executive summary
The Union Carbide India Ltd (UCIL) pesticide plant in Bhopal, which used to manufacture (among other products) the pesticide Sevin (carbaryl) gained world-wide recognition as a result of the tragic chemical disaster on the night of 2-3rd December 1984.
The accident, involving a massive release of methylisocyanate (MIC) gas resulted in the death or injury of many thousands of people in the surrounding residential areas. A number of studies, conducted in the after-math of the accident understandably focused on the long-term consequences of acute exposure to MIC. Very little attention was paid then to the state of the UCIL site and immediate surroundings with respect to contaminants other than MIC, which may have been present not only as a result of the accident, but also the routine operation of the plant. This remains the case today. As legal processes continue to try to establish liability and compensation following the 1984 disaster responsibility for the contamination which remains on and around the site remains unaddressed. Given the nature of the processes at the plant, and the chemicals handled, it is possible that residents of the communities surrounding the former UCIL site may still be exposed to hazardous chemicals on a daily basis.
In order to gain an insight into the nature and severity of chemical contamination of the former UCIL site and its surroundings, samples of solid wastes, soils and groundwaters from within and surrounding the site were collected by Greenpeace International in May 1999. Samples were returned to the Greenpeace Research Laboratories, based in the University of Exeter, UK., for analysis of heavy metals and organic contaminants. Sludges and soils were collected at locations both within the plant boundary (adjacent to former formulation plant and waste disposal sites) and in an area to the north of the plant at which solar evaporation ponds (SEPS) were formerly located.
Groundwater samples were collected from drinking water wells to the north and south of the former UCIL site in order to determine the extent of aquifer contamination with volatile organic compounds.
The results of this survey indicate general contamination of the site and immediate surroundings with chemicals arising either from routine processes during the operation of the plant, spillages and accidents. or continued and ongoing release of chemicals front materials which remain dumped or stored on site. Within this overall contamination some locations sampled indicated the presence of "hot-spots" of severe contamination with heavy metals and/or persistent organic pollutants.
1. Samples collected in the vicinity of the former Sevin (carbaryl) formulation plant contained elevated levels of mercury and/or organochlorine compounds. For example: -
i)Sample IT9012, collected from a drain directly beneath the plant, contained free mercury at over 12% of the overall weight of the sample (between 20000 and 6 million times higher than might be expected as background). Chromium, copper, nickel and lead were also present at elevated levels. The toxic organochlorines hexachloroethane and hexachlorobutadiene (HCBD), common constituents in solid wastes arising from the chlorinated chemicals industry. were also found. HCBD is a potent kidney toxin. Although insufficient information exists to evaluate fully its carcinogenicity, the USEPA list HBCD as a possible human carcinogen.
ii)Sample IT9013 collected from a ditch adjacent to the Sevin plant, contained a complex mixture of organochlorines, including several isomers of' hexachlorocyclohexane (HCH also known as benzene hexachloride, BHC), numerous chlorinated benzenes and DDT. The presence of HCH isomers provides further confirmation of the formulation of Sevin/BHC pesticide mixtures, indicated by the presence of containers labelled as such still present on site. Similarly, the presence of chlorinated benzenes suggests their former use or manufacture on site, perhaps predating Sevin production. The reason for the appearance of DDT and metabolites remains unclear as there is no record of it being manufactured or used on site.
2. Samples of solid waste/soil collected from the south-east corner of the plant. the former location of acid waste neutralisation pits, revealed significant, though patchy, contamination. Sample IT9015 from this area also showed mercury levels elevated above background, although much lower than in IT9012. This sample also contained numerous organic contaminants. Including 11 identifiable organochlorines with a similar profile (HCH, chlorinated benzenes, DDE) to the sludge sample from the ditch (IT9013). In addition, several other organochlorine compounds were detected which could not be fully identified.
3. Samples of soil collected from the location of the old solar evaporation ponds (SEPS) appeared less contaminated overall although only a small proportion (as low as 20%) of the organic compounds isolated could be identified to any degree of reliability. This greatly limits any assessment of the nature and extent of contamination in these materials.
4. Volatile organochlorine compounds (VOCs), including chloroform (trichloromethane), carbon tetrachloride (tetrachloromethane) and chlorinated benzenes were detectable in groundwater collected from all three wells close to the northern boundary of the former UCIL plant. Lower, though still significantly elevated, levels were found in samples of groundwater accessed immediately to the south of the boundary and from a well in the south east corner of the site itself. No organochlorine contaminants were reported above detection limits in water drawn from wells further north, adjacent to the SEPS or further south from the plant.
i)Samples IT9030 and IT9032, collected from wells adjacent to the northern plant boundary contained highly elevated concentrations of carbon tetrachloride (ca 3.4 and 1.7 mg/l respectively) and chloroform (2.59 and 0. I mg/l respectively). Both these compounds were used as solvents in the Sevin manufacturing process. As the wells sampled lie upstream from the flow of groundwater in this area, the presence of these contaminants probably reflects long-term contamination of the aquifer from routine use of spillages on site. Despite warning signs not to drink the water these wells remain accessible and in continued use by the local residents.
ii)Chlorobenzenes were also detectable in these samples. IT9030 containing over2.8 mg/i of 1.2-dichlorobenzene. Trichlorobenzenes, rarely reported in drinking water at levels in excess of I ug/l, were present at elevated levels in all three samples north of the boundary, as well as in the wells on and to the south of the boundary. Sample IT9030 again contained the highest concentrations, at approximately 180 ug/l.
iii)Of 10 VOCs found for which WHO guidelines have been established, 8 were present at concentrations above those limits in IT9030. In the case of carbon tetrachloride, concentrations in IT9030 were more than1700 times above the WHO limit for drinking water.
5. In total, the survey conducted by Greenpeace International has demonstrated substantial and, in some locations, severe contamination of land and drinking water supplies with heavy metals and persistent organic contaminants both within and surrounding the former UCFL pesticide formulation plant. There is an urgent need for a more detailed and extensive survey if the full extent of ongoing contamination from the plant is to be determined.
6. It is also essential that steps are taken to reduce and, as far as possible, eliminate further exposure of communities surrounding the contaminated site to hazardous chemicals. Contaminated wastes and soils must be safely collected and securely contained until such time as they can be effectively treated. Such treatment must entail the complete removal and isolation of toxic heavy metals from the materials and complete destruction of all hazardous organic constituents. The treatment process selected for this purpose must operate in a closed loop configuration, such that there are no releases of the chemicals or their hazardous by-products to the environment.
7. For contaminated groundwater. the ultimate goal should be the remediation of the aquifers. This may be achieved in part, by state of the art filtration technology which traps both volatile and semi-volatile organic contaminants, allowing their isolation, storage and treatment. In the short term, however, the priority. and responsibility of the Government, must be to provide clean water to the communities and to prevent access to contaminated wells. Urgent action must also be taken to prevent further contamination of aquifers through proper containment of chemicals and contaminated materials both on and surrounding the site.
8. The financial and legal responsibility for the clean-up operation must be borne by the former and/or current owners of the former UCIL site and the Government of India.
Between 1977 and 1984, Union Carbide India Limited (UCIL), located within a working class neighbourhood in Bhopal, was licensed by the Madhya Pradesh Government to manufacture phosgene, monomethylamine (MMA), methylisocyanate(MIC) and the pesticide carbaryl, also known as Sevin (Behl et al, 1978, UCC 1985, Singh & Ghosh 1987).
Phosgene was manufactured by reacting chlorine, brought to the plant by tanker, and carbon monoxide, produced from petroleum coke and oxygen in an adjacent production facility within the plant (Behl et al, 1978, UCC 1985). The MMA, also brought in by tanker, was combined with phosgene, in the presence of chloroform (used as a solvent throughout the process) to produce methyl carbomoyl chloride (MCC) and hydrogen chloride gas (HCl). HCl was then separated from the MCC so that it could be broken down into MIC and HCl. The MIC was then collected and transferred to stainless steel storage tanks, whilst the HCl, along with residues of MCC, chloroform, and other unwanted by-products (eg carbon tetrachloride, MMA, dimethylallophanoyl chloride, ammonium chloride, dimethyl urea, trimethlbiuret and cyanuric acid) were collected and recycled back through the processes (Behl et al. 1978, UCC 1985).
MIC was manufactured primarily to make the pesticide carbaryl (Sevin) as well as smaller quantities of aldicarb (Temic) and butlyphenyl methylcarbamate, all destined for the Indian market (MacKenzie, 1984). Carbyl; was produced by reacting MIC with a slight excess of alpha-napthopl, in the presence of carbon tetrachloride (NERRI 1990), and once made it was sold as the pesticide Sevin. However based on verbal information supplued by ex-workers, and the presence of sacks of hexachlorocyclohexane (lindane) next to the Sevin plant, it is possible that Sevin-lindane formulations were also being manufactured on site.
The reaction described above, once of interest only to the few, are now some of the most widely studied, scrutinised and publicised due to the occurrence of the world's worst industrial disaster.
With the disaster in mind, in May 1999, Greenpeace International, along with Bhopal-based NGOs Bhopal Group for Information and Action and Bhopal Gas Peeedit Mahila Udyog Sanghatana carried out an investigation of the former UCIL site. Samples of soil were collected both from areas once used for waste disposal, and around the former Sevin plant, where a ruptured and leaking storage tank was found. Groundwater samples were also collected form a number of private wells located amongst the shanty settlements of Bhopal. The aim of the sampling program was to identify organic pollutants and heavy metal contaminants present in and around the former UCIL site.
Addressing the problem: the need for an internationally verified survey and decontamination programme for the former UCIL plant and surrounding area.
The results of this investigation demonstrate extensive and, in some areas, severe chemical contamination of the environment surrounding the former Union Carbide plant. Analysis of water samples drawn from wells serving he local community has also confirmed the contamination of groundwater reserves with chemicals arising either from previous or ongoing activities and/ir incidents. As a result of the ubiquitous presence of contaminants, the exposure of the communities surrounding the plants to complex mixtures of hazardous chemicals continues on a daily basis. Though less acute than the exposure which took place as a result of the 1984 MIC release, long-ten-n chronic exposure to mixtures of toxic synthetic chemicals and heavy metals is also likely to have serious consequences for the health and survival of the local population.
This open, but largely undocumented, contamination must be urgently and effectively addressed such that the communities of Bhopal are no longer exposed to this legacy of pollution. In order to do this safely and effectively, an effective and fully verified decontamination programme must be undertaken:-
1. Survey and inventory
The study conducted by Greenpeace has highlighted the nature and severity of the problems surrounding the former UCIL production facility. However, a more extensive survey will be necessary in order that the full extent of contamination of soils, sediments and groundwater may be determined and documented.
* The survey should firstly produce an inventory of all accumulations, contained or otherwise. of industrial wastes both within and beyond the plant boundaries.
* Secondly, further samples of topsoil and subsoil, sediments from surface watercourses and groundwater should be analysed in order to gain further information on the geographical extent and complexity of contamination with hazardous organic chemicals and heavy metals.
This survey should be initiated as rapidly as possible, employing internationally accepted techniques and appropriately accredited laboratories. However the completion of all aspects of the survey should not be seen as a prerequisite for the initiation of programmes to contain and treat those materials (as outlined further below) which are clearly heavily contaminated.
2. Containment of industrial wastes
On the basis of the information obtained in the survey, all accumulations of industrial wastes, particularly those lying beyond the plant boundaries, must be safely and properly contained. Containment must be fully enclosed, above ground and effected in a manner which constitutes safe storage, permits controlled access to the wastes, and which is fully documented, such that any of the wastes may be retrieved for further treatment at any time. The efficacy of containment must also be verified at suitable intervals.
Note that containment is an interim measure only, to prevent continued exposure of humans and wildlife to these contaminated materials and the spread of such contaminants to other environmental media. It must not be viewed as a final solution.
3. Containment of contaminated environmental media
Furthermore, any soils which are found to contain level of hazardous contaminants significantly above background must be removed (to a depth at which levels of complex contaminants are equivalent to background levels) and properly contained as above. This removal and containment process should start with the most heavily contaminated sites chronic first.
4. Complete destruction or recovery of hazardous constituents
For contaminated solid materials covered by 2 and 3 above, the goal must then be the complete destruction or recovery of all hazardous constituents in a process which ensures that there are no releases to the environment of the hazardous chemicals (or their products of incomplete destruction) during or after treatment.
For persistent organic compounds, the goal must be 100% conversion non-hazardous final products; for heavy metals, the goal is 100% recovery in a form, which can be isolated fully from the matrix and contained separately. The technology used must have the capability to re-introduce any waste streams containing residual quantities of hazardous chemicals (above limits of detection using internationally accepted techniques and suitably accredited laboratories) for further processing, thereby facilitating total contaminant removal.
5. Decontamination of groundwater
For contaminated groundwater aquifers, above ground containment prior to treatment is not an option. In those cases in which groundwater is determined to contain levels of hazardous substances above background concentrations, the priority must be to ensure that further consumption by humans and livestock is prevented. Pumping equipment should be removed or deactivated and wells capped to prevent access. Alternative water supplies must then be made available as necessary. The responsibility for these public health protection measures must lie with the Government of India.
Wherever possible, efforts should be made to remove contaminants as rapidly and effectively as possible from those aquifers affected. A review of available approaches and technology will be essential in this regard. Filtration through activated charcoal, commonly employed for groundwater clean up, may effectively remove semi-volatile contaminants, although more volatile compounds (including the halomethanes) may simply escape to the atmosphere. Techniques employing rapid semi-permeable membrane filtration, with extraction into vegetable oil (e.g. Zander et al. 1992), may be effective in removing both volatile and semi-volatile contaminants. In any case, all wastes streams generated, which are likely to contain high concentrations of hazardous chemicals, should then be properly contained until such time that they may be decontaminated according to the criteria outlined in 4 above.
6. Avoidance of further contamination
Every effort must be made to ensure that the inventorying, containment and/or treatment of any of the contaminated material does not lead to more widespread contamination of the surrounding environment. Workers employed in handling such materials must be properly trained, fully aware of the hazards and safety procedures relating to each material and provided with appropriate protective clothing and other necessary safety equipment in order to minimise or eliminate direct exposure.
7. Responsibility for the decontamination programme
The financial, operational and legal responsibility for the decontamination of the site and the surrounding community, in a manner consistent with the criteria set out above, must be home by the former and/or current owner(s)/operator(s) of the production facility. Legal action against the responsible party must be taken if that party fails to implement a full and effective decontamination programme.
8. Oversight and verification
All components of the decontamination programme, from the survey and design phases through to completion, should be subject to oversight by independent international experts. The effectiveness of any clean-up measures employed must similarly be subject to independent verification using state of the art sampling and analytical techniques.
Alloway, B.J.(1990). Heavy metals in soils. John Wiley and Sons Inc., New York
ATSDR (1996). Toxicological profile for hexachloroethane (update). Agency for Toxic Substances and Disease Registry, Atlanta, GA. US Department of Health and Human Services.
ATSDR (1997). ARSDR's Toxicological profiles on CD ROM. Agency for Toxic Substances and Disease Registry, U.S. Public Health Service, CRC Publishers.
Behl, V.K., Iyer, C.R., Choudhary. S.P. and Khanna, S. (1978). 0peration Manual. Part I. Methyl isocyanate unit. Reviewed by Ballal, K.D. October, 1978. Union Carbide India Limited. Agricultural Products Division, Bhopal, India. 136pp.
Bhandari, N.R., Syal, A.K., Kambo, I., Nair. A., Beohar. V., Saxena, N.C., Dabke, A.T., Agarwal, S.S. and Saxena, B.N. (1990). Pregnancy outcome in women exposed to toxic gas in Bhopal. Indian J. Med Res. [B] 92: 28-33
Bryant, J.G.(1993). Chlorinated benzenes. IN: Kroschwitz. J.L. & Howe-Grant, (Eds). The Kirk-Othmer Encyclopedia of Chemical Technology, Fourth Edition Publ. Wiley-Interscience, N.Y. Volume 6: 87-100
Budavari, S.M., O'Neil, J., Smith A., and Heckleman P.E. [Eds] (1989). The Merck index: an encyclopaedia of chemicals, drugs and biologicals. 11th Edn Merck and Co, Inc., New Jersey, USA.
Burston, M.W., Nazari, M.M., Bishop, P.K. & Lerner, D.N. (1993). Pollution if groundwater in the Coventry region (UK) by chlorinated hydrocarbon solvents. Journal of Hydrology 149, 1-4: 137-161
Butler, E.C. & Hayes, K.F (1998). Effects of solution composition and pH on the reductive dechlorination of hexachloroethane by iron sulfide. Environmental Science and Technology 32, 9: 1 276-1284 CRC (1969) Handbook of chemistry and physics. A Ready reference book of chemical and physical data. Weast, R.C. [Ed] Pub. By The Chemical Rubber Co. library of Congress Card No. 13-11056.
Cullinan, P., Acquilla, S.D. and Dhara, V,R. (1996). Long term morbidity in survivors of the 1984 Bhopal gas leak. National Medical Journal of India 9, 1: 5-10
Cullinan, P., Acquilla, S.D. and Dhara, V.R. (on behalf of the International Medical Commission on Bhopal) (1997). Respiratory morbidity 10 years after the Union Carbide gas leak at Bhopal: a cross sectional survey. British Medical Journal 314: 338-343 D'Silva, T.D.J., Lopes, A., Jones, R.L., Singhawangcha, S. and Chan, J.K. (1986). Studies of methyl isocyanate chemistry in the Bhopal incident. J. Org. Chem. 51: 3781-3788
DHHS (1998). Report on carcinogens. Summary. 8th Edition. US Department of Health and Human Services, 1998, 252pp.
Dikshith, T.S.S., Raizada, R.B., Kumar, S.N., Srivastava, M.K., Kulshrestha, S.K. & Adholia. U.N. (1990) Residues of DDT and HCH in major sources of drinking water in Bhopal, India. Bull. Environ. Contam. Toxicol. 45: 389-393
Edwards I.R., Ferry D.H., Temple W.A. (1991). Fungicides and related compounds. In: Handbook of pesticide toxicology, [Ed] W.J.Hayes, Jr and E.R.Laws, Jr. Academic Press, Inc. Vol.3. Classes of pesticides, pp. 1409-1470.
EEC (1979). Council Directive 80/68/EEC of 17 December 1979 on the protection of groundwater against pollution caused by certain dangerous substances (OJ 1, 20, 26.1.1980, P. 43)
Freiria-Gandara, M.J., Lorenzo-Feffeira, R.A., Alvarez-Devesa. A. & Bermejo, F.(1992). Occurrence of halogenated hydrocarbons in the water supply of different cities of Galicia (Spain). Environmental Technology 13: 437-447.
Gupta, B.N., Rastogi, S.K., Chandra, H., Mathur, N., Mahendra, P.N., Pangtey, B.S., Kumar, S., Kumar, P., Seth, R.K., Dwivedi, R.S. and Ray, PK. (1988). Effect of exposure to toxic gas on the population of Bhopal: part I-epidemiological, clinical, radiological and behavioural studies. Indian Journal of Experimental Biology 26: 149-160
Hashsham, S.A., Scholze, R. & freedman, D.L (1995). Cobalamin-enhanced anaerobic biotransformation of carbon tetrachloride. Environmental Science and Technology 29, 11: 2856-2863
Howard, P. H. (1989). Handbook of environmental fate and exposure for organic chemicals. Volume 1: Large production and priority pollutants. Lewis Publishers, Inc., USA
Howard, P.H., Boethling, R.S., Jarvis, W.F., Meylan, W.M. and Michalenko, E.M.[Eds] (1991). Handbook of Environmental Degradation Rates. Lewis Publishers, Inc., USA
Hughes, J.B. & Parkin, G.F. (1996a). Concentration effects on chlorinated aliphatic transformation kinetics.
Journal of Environmental Engineering 122, 2: 92-98
Hughes, J.B. & Parkin, G.F. (1996b). Individual biotransformation rates in chlorinated aliphatic mixtures. Journal of Environmental Engineering 122, 2: 99-106
Indian Council of Medical Research (1985). Health effects of exposure to toxic gas at Bhopal: an update on ICMR sponsored researches, New Delhi
Kennicutt, M.C., Green, R.H., Montagna, P. and Roscigno, P.I., (1996). Gulf of Mexico Offshore Operations Monitoring Experiment (GOOMEX), Phase 1: sublethal responses to contaminant exposure introduction and overview. Can. J. Fish. Aquat. Sci. 53: 2540-2553
Kumar, S. (1994). Independent assessment of Bhopal. The Lancet 343: 283-284 acids. US Patent No.2 903 479. Patented Sept. 8, 1959. US Patent Office
Lerner, D.N., Gosk, E., Bourg, A.C.M., Bishop, P.K., Burston, M.W.. Mouvet, C., Egranges, P., &
Jakobsen, R. (1993). Postscript - summary of the Coventry groundwater investigation and implications for the future. Journal of Hydrology 149(1-4): 257-272
Loran, M.M. & Olsen, I,. (1999). Degradation of 1,1,2,2-tetrachloroethane in a freshwater tidal wetland: field and laboratory evidence. Environmental Science and Technology 33(2): 227-234
MacKenzie, D.(1984). The chemistry behind Bhopal's tragedy. New Scientist I 104: 1434; 3-4
MacKenzie, D.(1985a). Uncharted pipe could explain Bhopal disaster. New Scientist 106, 1451:4
MacKenzie, D.(1985b). Bhopal: Carbide insists it was sabotage. New Scientist 198: 1482: 15
Miller, P.L., Vasudevan, D., Gschwend, P.M. & Roberts, A.L. (1998). Transformation of hexachloroethane in sulfidic natural water. Environmental Science and Technology 32, 9: 1269-1275
Milne, R. (1988). "Act of sabotage" killed thousands at Bhopal. New Scientist 118, 1613: 28
NEERI (1990). Assessment of pollution damage due to Solar Evaporation Ponds at UCIL, Bhopal. Published by National Environmental Engineering Research Institute, Nagpur-440 020, Madhya Pradesh Pradushan Niwaran Mandal, Bhopal, 1990.
Overton, E.B. (1994). Toxicity of petroleum. In: Basic Environmental Toxicology. Cockerhain & Shane [Eds], Chapter 5: 133-156
Rastogi, S.K., Gupta, B.N., Husain, T., Kumar, A., Chandra, S. and Ray, PK. (1988). Effect of exposure to toxic gas on the population of Bhopal: part II-respiratory impairment. Indian Journal of Experimental Biology 26: 149-160
Rivett, M.O., Feenstra. S., Cherry, J.A. (1994), Transport of a dissolved-phase plume from a residual solvent source in a sand aquifer, Journal of Hydrology, 159 (1-4): 27-41.
Saxena, A.K., Singh, K.P., Nagle, S.L., B. N. Ray Srivastav, R.K., Tewari, S.P., and Singh, R. (1988). Effect of exposure to toxic gas part IV-immunological and chromosomal studies. Indian Journal of Experimental Biology 26: 173-176
Singh, M.P. and Ghosh, S. (1987). Bhopal gas tragedy: model simulation of the dispersion scenario. Journal of Hazardous Materials 17: 1-22
Snedecor, G (1993). Hexachloroethane, Chlorocarbons, -hydrocarbons (CHC'=CCl2)- In: Kirk-Othmer Encyclopedia of Chemical Technology. (Eds] Jacqueline 1, Kroschwits; Mary Howe-Grant. Fourth edition, Vol. 6. John Wiley & Sons, Inc. pp.29-31
Sriramachari, S. and Chandra, H. (1997). The lessons of Bhopal [toxic] MIC gas disaster, scope for expanding global biomonitoring and environmental specimen banking. Chemosphere 34. 9/10: 22372250
Suzuki T., Yaguchi K., Nishima T., Suga T. (1996). Degradation of terbutol in soils from turfgrass and drainage basins on golf-courses. Journal of Agricultural And Food Chemistry 44, 6: 1599-1602
Suzuki T., Yaguchi K., Ohnishi K., Suga T. (1995). Identification of degradation products of terbutol in environmental water from golf-courses. Journal of Agricultural and Food Chemistry 43, 6: 1 71 2-1717.
UCC (1985). Bhopal methyl isocyanate incident investigation team report, Danbury, Connecticut. US. Union Carbide Corporation, March 1995
US EPA (1986). Factsheets for regulated chemicals: Hexachlorobutadiene. Office of Environmental Health Hazard Assessment. US Environmental Protection Agency
US EPA (1988). Reviews of environmental contamination and toxicology. Vol. 106, Environmental Protection Agency, Office of Drinking Water Health Advisories, Springer-Verlag New York Inc. ISSN 0179-5953: 21-35
US EPA (1999), Current drinking water standards. National primary and secondary drinking water regulations. Office of Ground Water and Drinking Water. US Environmental Protection Agency
Wallace. L.A. (1997) Human exposure and body burden for chloroform and other trihalomethanes. Critical Reviews in Environmental Science and Technologv 27(2): 113-194. WHO (1989).Mercury Environmental Health Criteria 86-ISBN92415 600
WHO (1993) Guidelines for drinking water quality. Vol. I. Recommendations. Second Edition, ISBN 92 4 154460 0
Williams G.M., Weishurger J.H. (1996). Chemical carcinogens. In Toxicology: the basic science of poisons. Klaasen C.D., Arnbur M.O. and Doull J. [Eds], MacMillan Publishing Co,. New York: 99-73.
Zander, A.K., Chen, J.-S., and Semmens, M.J. (1992). Removal of hexachlorocyclohexane isomers from water by membrane extraction into oil. Water Research 26, 2: 129-137