Persistence of Malathion in the Environment Hydrolysis of malathion is a major route of degradation in aquatic systems, and increases with increasing alkalinity and temperature. Microbial activity and interaction with sediments may increase degradation and are important in estuarine environments, although high concentrations of malathion are toxic to microbes. Malathion is readily converted to malaoxon in the environment under the influence of oxygen and light. Malaoxon is 40 times more acutely toxic than malathion but malaoxon breaks down much more quickly. In soil, breakdown is quicker than in waters and is fastest in high moisture, high alkalinity soils.
Microbial activity is predominate in soils.
Most malathion residues are found in plants with high lipid contents. Malathion does not bioconcentrate in aquatic organisms because it has such a short half-life. Fathead Minnows 8.6 ppm Goldfish 10.7 ppm Mechanism of Toxicity to Animals Malathion can easily enter the body through ingestion, inhalation, and absorption through the skin. Malathion is toxic due to the presence of the carboxy ester group which is readily hydrolyzed by mammalian carboxyesterase in the liver. Both chemicals can be hydrolyzed at the ester linkage, yielding alkyl phosphates and leaving groups, of low toxicity.