AWWA WQTC58815

Malathion is an insecticide used to control mosquitoes, flies, lice and other household pests. It is also used to kill insects on fruits, vegetables and ornamentals. It is an organophosphate compound and is part of several commercial insecticides. Because of its solubility in water (130 ppm), malathion can be found in surface and groundwaters as a result of runoff from its various uses. In soil, it degrades rapidly depending on soil type and environmental conditions. The half-life in soil is typically 1-25 days, in air is 1.5 days and in natural waters is less than a week. Ultraviolet (UV) light has received considerable attention recently as a way to provide disinfection for small systems. Unfortunately the dose of UV required to destroy pesticides is often too large to be feasible for small water systems. However, UV in concert with UV sensitizers is capable of producing hydroxyl radicals, which can greatly reduce the required UV dose to destroy pesticides. Hydroxyl radicals are strong oxidants, even stronger than ozone. The objectives of this study were to: evaluate degradation of malathion with UV light; and, evaluate hydrogen peroxide, Fe (II), and Fe (III) as possible sensitizers. Solutions with malathion were placed into a petri dish with or without the desired sensitizer. Samples were exposed to different doses of UV light by varying the time. The light source was a 1 kw medium pressure UV lamp from Calgon Carbon. The UV with just water required a dose of 1320 mJ/cm² to degrade 85% of the malathion (16mg/L). With UV and 0.1 % H₂O₂, a dose of 323 mJ/cm² was required for complete degradation. The UV/Fe²⁺/ H₂O₂ solution degraded greater than 90% of the malathion at a dose of 65 mJ/cm², while the UV/ Fe ³⁺/ H₂O₂ degraded greater than 90% of the malathion at a UV dose of 77 mJ/cm². In the presence of sensitizers, such as iron and hydrogen peroxide, the UV dose was drastically reduced and is in the range that is currently being used to kill pathogens in drinking water. In the presence of these sensitizers it is feasible to use UV to destroy malathion. Includes 8 references, table, figures.