Abstract: Based on grain storage ecology, the degradation behavior of grain protectant, malathion was studied in climate chambers simulating three typical storage environments of grain, namely 75% relative humidity at 30 ℃(adverse conditions), 60% relative humidity at 20 ℃(mild conditions) and cold (4～10 ℃) (low-temperature conditions) . And test grains were wheat, corn and paddy rice. The results showed that half-lifes of malathion in grains tested are 24.8 , 14.5 and 14.7 w respectively in mild conditions, 17.4 , 8.2 and 6.6 w respectively in adverse conditions, and 62.4 , 25.7 and 43.9 w respectively in low-temperature conditions. And the persistence of malathion is observably influenced by storage conditions such as moisture and temperature and type of grain stored. It is noted that especially for low-temperature conditions, the amounts of malathion residue are high in test grains , and degradation rate is slow.

Key words: grain storage, malathion, degradation, residue