QAL Laws & Regulation Practice Exam

What causes leaching of pesticides into groundwater?

1. Pesticides applied sporadically

2. Persistent pesticides applied to the soil

3. Heavy application of non-persistent pesticides

4. Pesticides mixed with organic matter

The correct answer is: Persistent pesticides applied to the soil

The leaching of pesticides into groundwater primarily occurs when persistent pesticides are applied to the soil. Persistent pesticides are designed to remain in the environment for extended periods, which increases their likelihood of being transported through soil and into groundwater systems. These chemicals can withstand degradation and retain their potency much longer than non-persistent ones. As rainwater or irrigation water permeates the soil, it can carry these persistent compounds downward, leading to contamination of groundwater sources. In contrast, options discussing sporadic application, heavy application of non-persistent pesticides, or mixing pesticides with organic matter don't significantly contribute to groundwater contamination to the same extent as persistent pesticides. Sporadic application may limit exposure, non-persistent pesticides break down relatively quickly, and while organic matter can affect pesticide retention, it generally helps mitigate leaching rather than promote it. Thus, the characteristics of persistent pesticides and their behavior in the environment make them the most significant contributors to groundwater leaching.