Reported 96-hour LC50 values indicate very high toxicity for aquatic invertebrates such as Daphnia spp. The rate of degradation increases with temperature and with exposure to sunlight. Due to its low residence time and soil binding affinity, it is not expected to be significantly mobile. 4-Nitrophenol, a breakdown product of methyl parathion, does not adsorb well to soil particles and may contaminate groundwater. Some volatilization of applied methyl parathion may occur.
Degradation is faster in the presence of sediments, and is faster in fresh water than in salt water.
Pure methyl parathion is a colorless crystalline solid. Please refer to the pesticide product labeling.