Organoarsenicals added to animal feed are excreted mostly unchanged and are present in manure. Land-application of organoarsenical-contaminated manure represents an important mechanism for arsenic introduction to environmental systems. In this study, direct photolysis at 254 nm of four organoarsenicals (i.e. arsanilic acid, carbarsone, nitarsone, and roxarsone) was investigated using a batch-recycle UV reactor system. Organoarsenical speciation affected the apparent molar absorptivity, which generally ranged from 4�103 to 3�104 M-1cm-1 across the pH 2-12 range, and the rate of photolysis. Specific values of the quantum yield at 254 nm were lowest for the doubly anionic form of nitarsone (~10-4 mol/Einstein) and highest for the fully deprotonated form of roxarsone (~10-3 mol/Einstein). The corresponding fluence-based pseudo-first order rate constants ranged from approximately 2�10-5 to 3�10-4 cm2/mJ; these parameters were used to model the apparent reaction kinetics as a function of pH. With these kinetics, 90% transformation of organoarsenicals in water at pH 7 would be achieved for UV doses on the order of 13�52 J/cm2. The effects of nitrate, phosphate, and dissolved organic matter extracted from chicken litter on photolytic transformation of organoarsenicals were also studied. The bulk reaction kinetics for organoarsenical transformation were affected by the presence of dissolved organic matter; however, nitrate and phosphate did not significantly alter the transformation kinetics of organoarsenicals by UV254nm.

Photolysis of organoarsenicals in agricultural waste

247th National Meeting (2014)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.