The Bhopal disaster
- Causes
The Bhopal disaster, was an industrial accident that occurred on the night of the night of the 2-3 of December at a pesticide plant in Bhopal India .[1] The company that owned the plant was the Union Carbide India Limited (UCIL), a subsidiary of the American company Union Carbide Cooperation (UCC).Over 500,000 people were exposed to methyl isocyanate gas (MIC) and other chemicals leading to the instant death of more than 3,800 people and causing significant health problems to thousands of people who lived around the plant.
The manufacturing process employed in the plant had the chemical methylamine reacting with phosgene to produce MIC; this was then reacted with 1-naphthol to produce carbaryl the final product. The demand for pesticides however reduced in the 80’s due to famine in India which lead to the stockpiling of MIC at the plant. [2]
There were many factors that lead to this terrible industrial disaster include; the storage of the unused MIC in very huge tanks that were filled to levels higher than required, lack of maintenance of the plant which lead to the failure of safety systems. The decrease in the demand of pesticides pushed UCIL to near bankruptcy, to mitigate against this most of the companies safety systems were switched off so as to reduce costs, most notably the switching off of the MIC refrigeration tank which would have reduced the severity of the accident. To make matters worse there was a slum near the plant and there were no disaster management plans.[3][2]
Before the disaster there were other minor accidents within the plant, like the leakage of phosgene,chlorine and carbon monoxide gasses in 1982,1983 and 1984 which injured some workers. Coupled with poor safety practices such as undersized safety equipment and dependence on manual operations, it is believed that there were toxic gases in the atmosphere before the accident though in small concentrations.[2]
The gasses released include methyl isocayanate (C2H3NO),phosgene(CCl2O), hydrogen cyanide(HCN), carbon monoxide(CO), hydrogen chloride(HCL), oxides of nitrogen, monomethyl amine (CH5N)and carbon dioxide(CO2).[2]
The 30 metric tons was way above the threshold limit value of 0.02 ppm, this extremely high exposure level is what caused the very high death toll. Air was not the only thing that was affected, water bodies like rivers were affected as fish was declared unsafe to eat this was due to MIC’s high reactivity with water.[5]
After the disaster there has been evidence of contamination of both the soil and ground water caused by the leaching of heavy metals and other chemicals like chloroform, trichloroethene, tetrachloroethene, and dichlorobenzene at 600 times higher than the safe limits of 5ppb in water. [6]This is from the plant which has since been abandoned without proper rehabilitation.
B) HEALTH EFFECTS
The gasses released into the atmosphere that night include methyl isocayanate (C2H3NO),phosgene(CCl2O), hydrogen cyanide(HCN), carbon monoxide(CO), hydrogen chloride(HCL), oxides of nitrogen, monomethyl amine (CH5N)and carbon dioxide(CO2).[2] The residents of Bhopal got the toxic exposure via the lungs whose area is 100 m2 and the damp surface containing 300 million alveoli absorbed these gasses.
The safe exposure level for MIC is 0.02 ppm in an 8 hour span, in Bhopal 30 metric tonnes were released in the span of one hour, MIC is a very strong irritant and is very toxic to the skin, eyes and the membranes of the respiratory tract. This is because it is very reactive with water and when inhaled, the mucous tissues corrode almost immediately. It is caused by the MIC vapour being hydrolysed to produce hydrocyanic acid which is highly corrosive to mucous membranes especially in the lungs. This occurs almost immediately at concentrations of 50ppm which is the same range as that of the gas cloud that enveloped Bhopal for several hours. This explains the high mortality levels in that accident.[7][8]
Another cause was chemical asphyxiants present in the gases released such as carbon monoxide and hydrogen cyanide. These gasses bond with haemoglobin in the blood leading to the formation of carboxyhaemoglobin which replaces oxygen in the blood. The central nervous system is affected as follows; lack of vigilance, slowed reactions and responses, reduced co-ordination, mental performance, dexterity. The stillbirth rate was 300% and neonatal mortality (death as an infant) was about 200% right after the tragedy. [5]
The ocular side effects included chemosis, redness, watering, ulcers and photophobia. The respiratory problems include distress, pulmonary edema, pneumonitis and pneumothorax. Gastrointestinal illnesses such as persistent diarrhea, anorexia, persistent abdominal pain were also reported. At the psychological level neuroses, anxiety states, adjustment reactions were reported. [9]
The long term health effects of the disaster include ocular problems such as persistent watering of the eyes, corneal opacities and chronic conjunctivitis. The respiratory illnesses include obstructive and restrictive airway disease, decreased lung function, pulmonary fibrosis and bronchial asthma. In the reproductive area there is an increased rate of pregnancy loss, increased infant mortality due to fatal deformities and decreased placental and fetal weight. Exposure to MIC has also lead to genetic problems which chromosomal abnormalities that lead to the birth of deformed babies whose mortality rate is very high. Neurobehavioral problems have also been reported they include poor learning abilities and lack of psychomotor skills which has led to a lot of mentally ill children. Recent news also indicate that third generation children of the survivors are also showing debilitating deformities. [9][10]
REFERENCES
- Broughton, E. "the Bhopal disaster and its aftermath: a review". Environmental health, 2005, 6.
- Eckerman, I. The bhopal saga—causes and consequences of the world's largest industrial disaster, 2005.
3. D'Silva, Themistocles . The Black Box of Bhopal: A Closer Look at the World's Deadliest Industrial Disaster. Victoria, B.C.: Trafford,2006.
4. Kalelkar, A . Investigation of large-magnitude incidents: Bhopal as a case study. (pdf) London: the institution of chemical engineers conference on preventing major chemical accidents,1998.
5. Misra UK, Kalita J: A study of cognitive functions in methyl-iso-cyanate victims one year after bhopal accident. Neurotoxicology 1997, 18(2):381-386.
6. Sharma DC: Bhopal: 20 Years On. Lancet,2005.
7. Kimmerle, G. and Eben, A.Toxicity of methyl isocyanate and how to determine its quality in air.Archives of Toxicology, 20, 235–241,1964.
8. Klaassen, C.D. (ed). Casarett and Doull's Toxicology. The Basic Science of Poisons. 6th ed. New York, NY: McGraw-Hill, 2001.
9. Dhara VR, Dhara R: The Union Carbide disaster in Bhopal: a review of health effects.
Arch Environ Health,2002.
10. Mangla B: Long-term effects of methyl isocyanate. Lancet,1989.
