Decomposition byproducts induced by gamma radiation and their toxicity: the case of 2-nitrophenol

The induced degradation and detoxification of 2-nitrophenol (2-NP) in aqueous media by gamma irradiation were carefully evaluated in this study. Gamma radiation at absorbed doses as low as 20 kGy was able to degrade 2-NP to reach a removal of at least 85% across the investigated range of concentration (50-150 ppm). 2-NP breaks down to aromatic-based compounds with increasing number of byproducts upon increasing the radiation treatment from the absorbed dose of 50% decomposition (D₅₀) to the absorbed dose of 90% decomposition (D₉₀), after which no byproducts could be detected, indicating the formation of undetectable aliphatic hydrocarbons, insoluble, or volatile byproducts. Toxicology studies showed that the degradation of 2-NP under absorbed doses up to D₉₀ resulted in a more toxic byproduct than the parent compound, and a remarkable reduction in the toxicity was observed with the irradiated samples with absorbed doses above D₉₀. Varying the pH of the media to acidic or basic conditions did not significantly alter the degradation behavior of 2-NP. However, a notable improvement of the detoxification was associated with the samples of acidic pH. Adding 0.5% of H₂O₂ to 2-NP solutions had a positive effect by reducing D₉₀ by a factor of nine and diminishing the toxicity by twofolds.