Illinois Pesticide Applicator Practice Test

Why is pesticide breakdown much slower in groundwater?

1. High temperature and light conditions

2. Presence of bacteria

3. Low oxygen and light conditions

4. High mineral content

The correct answer is: Low oxygen and light conditions

Pesticide breakdown happens more slowly in groundwater primarily due to low oxygen and light conditions. In most groundwater environments, there is limited light penetration and low levels of dissolved oxygen, which significantly impacts the degradation processes that rely on aerobic organisms and photolytic reactions. Aerobic degradation, which typically breaks down pesticides in the presence of oxygen, is hindered in anaerobic conditions found in deeper groundwater. Additionally, the lack of light limits photodegradation, a process in which sunlight helps break down chemical compounds. Therefore, the combination of low oxygen levels and absence of light in groundwater contributes to the slower breakdown of pesticides compared to surface environments where these factors are more favorable for degradation. This understanding is crucial for pesticide management, particularly in protecting water supplies and assessing the potential risks associated with pesticide usage in agricultural practices.