Biomimetic degradability of linear perfluorooctanesulfonate (L-PFOS): Degradation products and pathways

The reductive degradability and decomposition pathways of linear perfluorooctanesulfonate (L-PFOS) were investigated in a biomimetic system consisting of Ti(III)-citrate and Vitamin B₁₂. Biomimetic degradation of L-PFOS could well be described by a first-order exponential decay model. Accompanied by the release of fluoride ion, technical PFOS could not only be transformed to perfluorocarboxylates (PFCAs) and perfluoroalkylsulfonates (PFSAs) with perfluoroalkyl carbon chain length < C8 (thereafter referred as carbon-chain-shortened degradation products), but also be transformed to PFCAs with perfluoroalkyl carbon chain length ≥ C8 (thereafter referred as carbon-chain-lengthened degradation products). Perfluorohexanesulfonate and perfluorotetradecanoate were the most abundant carbon-chain-shortened and -lengthened degradation products of technical PFOS, respectively. Based on the various degradation products detected during biomimetic reduction of linear [1,2,3,4-¹³C₄]-PFOS, the degradation pathways of L-PFOS were proposed as follows: L-PFOS was first reduced to C₈F₁₇• radical by cleavage of C-S bond, and then transformed to PFOA through hydrolysis. However, the carbon-chain-shortened products were not generated through the sequential chain-shortening via C₈F₁₇• radicals and/or L-PFOS, while the carbon-chain-lengthened products were not formed via C₈F₁₇• radicals by stepwise addition of CF₂ moiety. In fact, C₈F₁₇• radical and/or L-PFOS were further reduced to form C_nF_2n+1• (n = 1, 2, 3, 4) radicals, and these radicals were chain-lengthened by stepwise addition of C₄F₈ moiety and eventually transformed to various degradation products via hydrolysis (PFCAs) or combination reaction with sulfonyl hydroxide (PFSAs). All carbon-chain-lengthened chemicals were first reported as the degradation products during the decomposition of L-PFOS, while carbon-chain-shortened compounds were first identified as the biomimetic reduction products of L-PFOS.

Characteristics and products of the reductive degradation of 3-nitro-1,2,4-triazol-5-one (NTO) and 2,4-dinitroanisole (DNAN) in a Fe-Cu bimetal system

It has been shown previously that, under acidic conditions, 3-nitro-1,2,4-triazol-5-one (NTO) and 2,4-dinitroanisole (DNAN) degrade in the presence of iron/copper bimetal particles; the reactions can be modeled by pseudo-first-order kinetics. This study investigates the reaction mechanisms of the degradation processes under different conditions. Batch studies were conducted using laboratory-prepared solutions and an industrial insensitive munition-laden (IMX) wastewater. The influence of parameters such as initial pH of the solution, copper/iron (Fe-Cu) contact, and solid/liquid ratio were systematically investigated to assess their impact on the reaction kinetics. These parameters were subsequently incorporated into pseudo-first-order decomposition models for NTO and DNAN. The activation energies for the degradation reactions were 27.40 and 30.57 kJ mol^-1, respectively. Degradation intermediates and products were identified. A nitro-to-amino pathway, which ultimately may lead to partial mineralization, is postulated. The amino intermediate, aminonitroanisole, was detected during DNAN degradation, but for NTO, aminotiazolone is suggested. Additionally, urea was identified as a degradation product of NTO.