Synthesis And Environmental Fate Of Nitro Nonylphenol Isomers

Nonylphenol (NP) occurs ubiquitously as endocrine-disrupting micropollutants in the environment. The main source of NP in the environment is the degradation of nonylphenol polyethoxylates originated from wastewater treatment plants. Sludge application as the biosolid fertilizer can release large amounts of NP into soil. Many studies have paid attention to the degradation of NP in agricultural soils and sediments. Degradation of NP in soil and soil/sewage sludge mixture has been found to form a novel metabolite with a nitro-group at the ortho-position of the aromatic ring of NP molecule, i.e., nitro-nonylphenol (nitro-NP). Since a high proportion of nitro-metabolite of NP is produced, nitration of NP can be considered as an important metabolism in nature environment. Some studies have showed that nitro-NP has less toxicity and oestrogenic potency than its parent compound NP. However, the knowledge of the environmental fate and toxicity is limited. Nitro-NP belongs to the nitro-aromatic compound and may have similar toxicity and degradation behavior to those of other nitro-aromatic compounds. Nitro-NP has the nonyl chain and therefore has also isomers like NP. The isomers may have different degradation and estrogenic activity. Here, using four nitro-NP isomers and14C-nitro-NP111, we studied the isomer-specific degradation and fate in an agriculture soil and a nitrifying activated sludge where the nitro-NP occurs during the degradation of NP.Using the Friedel-Crafts alkylation, four para-nonylphenol isomers containing a quaternary a carbon (NP111, NP112, NP38, NP65) and a14C-labelled NP isomer (14C-NP111) were firstly synthesized from phenol and four branched nonanols. The four NP isomers are the major components of technical NP. Then the four nitro-NP isomers (nitro-NP111, nitro-NP112, nitro-NP38, nitro-NP65) and a14C-labelled nitro-NP isomer (14C-nitro-NP111) was synthesized by nitration of the corresponding NP isomers using nitric acid. The four branched NP isomers and14C-nitro-NP can be applied to studies on the environmental fate and risk assessment of nitro-NP isomers.We studied the fate of the four nitro-NP isomers during the incubation for266days in an oxic rice paddy soil. The degradation kinetic of the isomers was fitted to the availability-adjusted first-order kinetic model. The degradation rates of nitro-NP isomers were different among the isomers, in the same order of their parent NP isomers with the same structure of the alkyl chain. However, nitro-NP isomers had smaller degradation rates and therefore are more recalcitrant than their parent NP isomers in the soil. We also used the14C-nitro-NP111to study the course of mineralization and formation of bound residues. The mineralization of nitro-NP111was only8.5%over the whole incubation. The mineralization rate (0.03%per d) of nitro-NP111was lower than its parent compound NP111(0.09%per d). About40%of the applied radioactivity was transformed into the bound residues, owing to microbial activity. Bound residues were mainly in the form of physico-chemical enclosure. One metabolite of14C-nitro-NP111was detected in the active soil, which was more polar than nitro-NP111. The chemical structure of the metabolite is still unclear. Our study indicates that the formation of nitro metabolite may not be an effective pathway to reduce the environmental risk, but nitration may be an important metabolism of nonylphenol in many environments. The main metabolite M1increased quickly in initial four days and thereafter kept stable. However, M1in extractable radioactivity kept increasing. It can be conferred that nitro-NP bound to extracelluler polymer substances or was assimilated by microbes.For the study of nitro-NP isomers fate in nitrifying activated sludge, we set four treatments (sterilized group, ammonia-oxidizing group, inhibition group, and trophic medium group) to study the degradation of nitro-NP isomers by different microbial communities. After incubation for36days under oxic conditions, the degradation data were fitted to the first-order model. The degradation rates were different among different isomers, like the degradation of nitro-NP isomers in the soil. The degradation difference among treatment groups was significant, indicating that the microbial community could affect the degradation of nitro-NP isomers. The14C-nitro-NP111was applied to study the fate and metabolism of nitro-NP in nitrifying activated sludge. In trophic group, about70%of the applied radioactivity was transformed into non-extractable residues, owing to the high microbial activity in this treatment. In other groups, the14C-recovery was low, which might be owing to volatilization of nitro-NP. Several metabolites of nitro-NP were detected in different treatment groups.In summary, we studied the isomer-specific degradation and fate of nitro-NP isomers in agriculture soil and nitrifying activated sludge. The study demonstrated that nitro-NP was more persistent than NP in agriculture soil and bound residues were mainly in the form of physico-chemical enclosure that could release into soil when the environmental conditions change. Like NP isomers, degradation of nitro-NP isomers in the soil was also isomer-specific that implicated the risk assessment of nitro-NP should consider the specific fate of different isomers. The different microbial communities can metabolite nitro-NP by the different pathways and nitro-NP was maily metabolited by.heterotrophic bacteria in nitrifying activated sludge. The metabolism and bound-residue formation of nitro-NP in different environments should be investigated for a better understanding of the environmental risk of nitro-NP. The microbial community should be investigated to understand the metabolism and to provide the basis for bioremediation of nitro-NP contaminated sites.