QAL Laws & Regulation Practice Exam

Under which soil conditions are pesticides most likely to leach?

1. A heavy clay soil, low in organic material

2. A sandy soil, high in organic material

3. A sandy soil, low in organic material, where groundwater is shallow

4. A clay soil, high in organic material, where groundwater is deep

The correct answer is: A sandy soil, low in organic material, where groundwater is shallow

Pesticides are most likely to leach through soil that has specific characteristics facilitating the movement of chemicals down through the soil profile and eventually into groundwater. In this scenario, sandy soil is pertinent because it has larger pore spaces compared to clay, allowing for quicker water movement. When this sandy soil is low in organic material, there is less capacity for the soil to adsorb the pesticides, making it easier for them to move downwards. The presence of shallow groundwater further exacerbates the situation; if the groundwater table is near the surface, there is a higher potential for pesticides to reach it as they leach through the sandy soil. In contrast, heavy clay soils generally retain water and have smaller pore spaces, making leaching less likely. High organic material in any soil type usually contributes to pesticide adsorption and retention, which also diminishes leaching potential. Therefore, the combination of sandy soil, low organic content, and shallow groundwater creates an environment where leaching of pesticides is maximized, making this choice the most appropriate under the given conditions.