Degradation of parathion and the reduction of acute toxicity in TiO₂ photocatalysis

Photocatalytic degradation of methyl parathion was done using a circulating TiO₂/UV and TiO₂/solar reactor. Indoor experimental results showed that, under the photocatalysis conditions, parathion was more effectively degraded than under the photolysis and TiO₂ only conditions. Parathion (38μM) was completely degraded under photocatalysis within 90min, and more than 80% TOC decrease after 150 minutes. The main ionic byproducts during the photocatalysis were measured, and almost complete nitrogen recovery was achieved as mainly NO₃⁻ NO₂⁻, and NH₄⁺, and 80% of sulfur as recovered as SO₄²⁻. Organic intermediates such as nitrophenol and methyl paraoxon were also identified during the photocatalysis of parathion, and these were further degraded after 90 minutes. Microtox bioassay using Vibrio fischeri was used in evaluating the toxicity of solutions treated by photocatalysis and photolysis of parathion. The results showed that the acute toxicity expressed as EC₅₀ almost reduced after 90min under the photocatalysis condition whereas only 40% reduction of toxicity as EC₅₀ was achieved in photolysis condition. The outdoor results using a TiO₂/solar system were similar to the TiO₂ indoor system, indicating the possibility of applying TiO₂/solar system for the treatment of parathion-contaminated water.