Environmental science concepts and applications

Environmental Science

The City and the Problem

Hazard identification Does exposure to substance cause increased likelihood of adverse health effect such as cancer or birth defects?

According to the Agency for Toxic Substances and Disease Registry, exposure to the pesticide Malathion is hazardous to human health but the substance has relatively low toxicity to humans, other mammals, and birds compared with other insecticides. Although intentional exposure to pregnant women would hardly be recommended, it should be noted that genetic toxicology studies indicate that Malathion do not cause gene mutations in bacteria. In contrast, according to the CDC (Center for Disease Control) West Nile Fact Sheet, in a small number of cases, West Nile Virus has been spread during breastfeeding and even during pregnancy from mother to baby.

Mild exposure to both West Nile Virus and the insecticide designed to prevent it by killing the carrier mosquitoes can cause headaches, nausea and vomiting, and general weakness. 80% of those exposed to West Nile show no symptoms at all, but 1 in 150 can sustain permanent neurological damage. High doses of Malathion include hypertension, pallor, abdominal pain, sweating, blurred vision, poor concentration, confusion, and memory loss. Thus, as serious as these symptoms may be, the consequences of contracting West Nile virus can be far more severe, although there is also a greater likelihood the individual will show no symptoms at all if he or she is bitten by an infected mosquito.

Step 2. Dose-response assessment. What is relationship between amount of exposure (dose) and seriousness of adverse health effect? A person exposed to a low dose may have no symptoms, whereas a high dose may result in illness.

In a test study of Malathion, a single exposure to 10% Malathion (95% pure) induced contact sensitization in almost half the participants and 0.1 and 0.01% concentrations of 99.3% Malathion evoked positive responses in previously sensitized participants. Higher doses thus result in more severe symptoms, and a greater likelihood of the individual showing severe symptoms. In contrast, the response of the individual to West Nile is not based upon degree of exposure, but more due to the state of the person's health or sensitivity to the virus. This tends to suggest that, given the unpredictability of the response to West Nile, it would be better to apply the insecticide.

Critics allege that as many as 90 cases of Malathion-related illnesses could result proposed application program with as many as four fatalities, compared with one individual out of 150 sustaining permanent neurological damage. But the ability to guard one's self against a spraying entirely is more realistic than a multiplying insect population.

Step 3. Exposure assessment How much, how often, and how long are humans exposed to substance in question? Where humans live relative to emissions is also considered.

While it is possible that certain individuals might be exposed to higher doses of the pesticide than is desirable, the idea expressed by opponents of the spraying, that monetary resources proposed for pesticide application could be better spent on educational efforts to avoid exposure to the mosquitoes themselves rather than on the application of Malathion seems unrealistic, as even the most cautious individual can hardly guarantee that he or she can avoid exposure to West Nile virus-causing mosquitoes. Although proximity to the spraying of humans may be an issue, refuge during the spraying is possible, while it is impossible to entirely avoid exposure to insects throughout the summer. In contrast, when insecticide is sprayed, individuals can be specifically instructed to take cover during those times, and if necessary shelter could be provided to those individuals with inadequate housing, such as migrant workers.

Step 4. Risk characterization. What is probability of individual or population having adverse health effect? Risk characterization evaluates data from dose-response assessment and exposure assessment (steps 2 and 3). Risk characterization indicates that Mexican-Americans, many of which are agricultural workers, are more vulnerable to pesticide exposure than other groups.

Although it is argued that the poor or uneducated would not follow the safety precautions required by the Malathion application program, this is also true of individuals who fail to take precautions against West Nile. Uninformed residents, for example, could be outside during aerial spraying, or they could handle or eat matter that contains residues from application of the pesticide -- but the poor might be even more apt to spend long hours working outside, where mosquitoes breed, and are unable to afford to mend screens, use insecticide or have adequate long-term shelter to protect themselves against the insects.