Each pesticide has unique properties that determine reactivity. The environmental media also determines how fast pesticides break down. Those that persist can travel long distances in the atmosphere. In water, breakdown is usually by hydrolysis, often mediated by pH. In aquatic systems, pesticide break down by microorganisms in sediments may also be important. The predominant pathway in soil is microbial degradation, although for some pesticides chemical degradation is important.
Pesticides are also susceptible to photolysis on soil and foliar surfaces.
Metabolic reactions are catalyzed by enzymes. Environmental conditions can influence reaction rate and therefore how fast pesticides break down. For air, these conditions include temperature, moisture, sunlight intensity, and free radicals. For water, conditions include temperature, pH, sunlight intensity, and sediment microbial activity. For soil, conditions include temperature, soil type, organic matter, moisture, pH, aeration, and microbial activity.