What is the term for the downward movement of pesticides in the soil?

• A. Bioconcentration
• B. Leaching
• C. Photodecomposition
• D. Volatilization

Answer: (B)

Leaching is the downward movement of pesticides through the soil with percolating water. When a pesticide is water-soluble and not strongly held by soil particles, water can transport it down the soil profile, potentially reaching deeper layers or groundwater. Factors that influence this include how soluble the chemical is, how strongly it adsorbs to soil (soil texture and organic matter affect this), the amount and rate of rainfall or irrigation, and how quickly the pesticide degrades in soil. This concept is distinct from bioconcentration (build-up in living organisms), photodecomposition (degradation by sunlight), and volatilization (evaporation into the air). Leaching is a key concern because it can move pesticides beyond the root zone or into groundwater.