AWWA WQTC58815

Malathion is an insecticide used to control mosquitoes, flies, lice and otherhousehold pests. It is also used to kill insects on fruits, vegetables and ornamentals. It isan organophosphate compound and is part of several commercial insecticides. Becauseof its solubility in water (130 ppm), malathion can be found in surface and groundwatersas a result of runoff from its various uses. In soil, it degrades rapidly depending on soiltype and environmental conditions. The half-life in soil is typically 1-25 days, in air is1.5 days and in natural waters is less than a week. Ultraviolet (UV) light has received considerable attention recently as a way to providedisinfection for small systems. Unfortunately the dose of UV required to destroypesticides is often too large to be feasible for small water systems. However, UV inconcert with UV sensitizers is capable of producing hydroxyl radicals, which can greatlyreduce 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 withUV 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 desiredsensitizer. 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 themalathion (16mg/L). With UV and 0.1 % H₂O₂, a dose of 323 mJ/cm² was required forcomplete degradation. The UV/Fe²⁺/ H₂O₂ solution degraded greater than 90% of themalathion 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 dosewas drastically reduced and is in the range that is currently being used to kill pathogens indrinking water. In the presence of these sensitizers it is feasible to use UV to destroy malathion. Includes 8 references, table, figures.

Product Details

Edition:

Vol. - No.

Published:

11/02/2003

Number of Pages:

9

File Size:

1 file , 280 KB