Malathion’s Risk Assessment.
zs that are involved in the management of any risk. Risk assessment is done by determining the qualitative and quantitative value of the potential threat. In a qualitative risk assessment two factors of the risk have to be calculated. The first element of the risk ‘R’ that should be calculated is ‘p’ , which is the probability of the risk ever occurring. The second factor of ‘R’ that should be calculated is loss ‘L’. This is the loss that may occur if the risk occurs. Method of risk assessment differs depending on the subject of analysis.
Hazard identification
Malathion is an organophosphate insecticide that easily degrades in the environment. Malathion is not only harmful to pesticides and mosquitoes but it can also kill beneficial, harmless insects. The pesticide can also affect animals such as birds and aquatic animals that feed on insects. If the pesticide is left on hardened surfaces and chlorinated water it increases malaoxon a product of malathion’s degradation which could be harmful.
Dose response analysis
Malathion has low toxicity, however; its ingestion leads to metabolization of malaoxon which is more toxic. The United States EPA classifies malathion as pesticide with suggestive evidence of causing cancer. However, it states that malathion is not potentially carcinogenic. Research by the department of preventive medicine shows that new-born babies exposed to malathion on the second trisemester of pregnancy are commonly observed to have gastrointestinal problems (Department of Preventative Medicine, 1992). Malathion can cause kidney damage and leukemia. The pesticide can also delete genes from a DNA molecule. Oral administration of technical grade malathion to rats in the long term is observed to increase cases of neoplastic hepatocellular lesions after an 18 months dosing. The doses were administered at 1500mg/kg/day. These tumors were as a result suppression of acetycholinesterase and hepatic toxicity rather than the direct effect of malathion (Moeller & Rider, 1962). Two year feeding (oncogenic) of a rat estimated the systemic NOAEL at 100 ppm (5mg/kg/day) and the Systemic LEL at 1000 ppm (50 mg/kg/day). The 1000ppm dosage was observed to decrease the weight and brain cholinesterase (American Cyanamid Co., 1980)
Exposure assessment
Malathion degrades quickly in about six hours and the risk of exposure is high in the first day. Degradation in soil may vary depending on the soil conditions. Inhalation exposure is highest in the first few hours of spraying after which exposure only occurs through contact and ingestion of contaminated food. Reduced out-door activities and closure of houses during the spraying program could reduce exposure greatly. Respiratory exposure that occurs in the first few hours of application can greatly be reduced by night time applications. Dermal exposure by contact with surfaces applied with the pesticide is bound to be the highest.
Risk characterization
According to Moeller and rider the reference dose for chronic oral exposure (Rfd) is 16 mg/day (0.23 mg/kg/day) .This is the no adverse effect level (NOAEL) for humans. This was experimentally proved with red blood cell cholinesterase activity being used as an indicator of the toxicity levels of threshold.After assessing the dangers of malathion and resultant exposure I would declare the pesticide less dangerous if used carefully, and therefore; I would vote for its use. According to research the no adverse effect level (NOAEL) lies at 16mg a day. There is very little chance that an individual could get exposed to 16mg of malathion in a single day. The exception could be if the victim directly ingested the pesticide. A lot of exposure to the chemical occurs in the first six hours after which exposure by inhalation diminishes to zero. Other forms of exposure such as through contact or ingestion may persist for some time as the pesticide gradually degrades in the soil or sprayed surfaces. Similarly, the observed threshold that causes harm to rodents (1500mg/kg/day) is not likely to cause harm because the exposure is not likely to persist for long enough to cause harm to other animals. Proper sensitization of the general population on how to reduce chances of exposure should suffice in taking care of the possible minimal exposure that may occur. Spraying could possibly be done at night so that the pesticide is given enough time to degrade before people go out for their daily activities. This should greatly reduce respiratory exposure.
References
Moeller, H.C. and J.A. Rider. (1962). Plasma and red blood cell cholinesterase activity as indications of the threshold of incipient toxicity of ethyl-p- nitrophenyl thionobenzenephosphorate (EPN) and malathion in human beings. Toxicol. Application. Pharmacol. 4: 123-130.
American Cyanamid Company. (1980). MR ID Number. 00110562; HED Document. Number. 002504. Available from EPA. Write to FOI, EPA, Washington, DC20460.
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