What is leaching?

• A. Water vaporization
• B. Movement through air
• C. Pesticide degradation
• D. Movement through soil

Answer: (D)

Leaching is the downward movement of water-soluble substances through soil with percolating water. When a pesticide dissolves in infiltrating water, gravity pulls it down from the surface and root zone into deeper soil layers, and it may eventually reach groundwater if conditions allow. This is different from evaporation (water turning to vapor), movement through air (volatile transport), or chemical degradation (breaking down the pesticide rather than moving it). Leaching depends on how soluble the chemical is, how strongly it binds to soil particles, soil texture and organic matter, and how much rainfall or irrigation occurs. Highly soluble pesticides in sandy, low-organic-matter soils with heavy rainfall are more prone to leaching, whereas ones that bind tightly to soil stay put more often.