Fate Of Nonylphenol(Including Isomers) In Soil-Wheat System With Long-Term Reclaimed Water Irrigation

Nonylphenol?NP?is one of the environmental endocrine disruptors?EDCs?in reclaimed water with high detection frequency and concentration.In this paper,the distribution and accumulation of NP and its 12 isomers in soil-wheat system were studied through field barrel experiment.The changes of NP forms in soil with biodegradation process was studied by ¹⁴C batch experiment in laboratory.The relationship between the half lives and the structure of NP isomers was also studied by batch experiment.The main conclusions are as follows:?1?Based on the NP concentration in the reclaimed water of the study area,the pollution load of different irrigation years?50,100,150,200 and 300 years?of the reclaimed water was simulated.The human health risk of exposuring to NP in wheat grains by ingestion was 10^-9 orders of magnitude,and the risk values were low.The BCF of NP in different tissues of wheat at maturity stage was BCF_root>BCF_leaf>BCF_stem>BCF_grain.The half-life of NP in natural conditions was 75.25-128.11 days,and the NP residue in soil-wheat system during the maturity period only accounted for 10%-28% of the initial addition.?2?The distribution of NP 12 isomers in soil and wheat is specific.The higher the concentration of NP isomers,the easier they accumulate in the soil bottom.The isomers with higher concentration in different soil depth and tissues of wheat at maturity stage were NP3 and NP11,and the isomers with the lowest concentration were NP8.NP4,NP5 and NP10 were easy to accumulate in wheat roots,while in stems,leaves and grains,NP2 and NP4 were easy to accumulate.?3?During the biodegradation of NP in soil,the recovery of ¹⁴C was 70-92%.¹⁴C labeled biodegradation experiments showed that after 34 days,the proportion of bound ¹⁴C increased from 65.43%to 90.53%in the unsterilized soil and NP mainly existed in the soil as bound residual;¹⁴CO₂ form accounting for 21.07%of the total ¹⁴C;methanol extractable parts accounting for 3.07%;and DI water extractable parts accounting for 0.78%,respectively.The DI water extractable parts was the lowest,indicating that NP was not easy to be utilized by plants,which was the reason of low NP in wheats in barrel field experiment.At the same time,fumigation experiment showed that the water-soluble ¹⁴C content of microorganisms increased from 1.75% to 3.01%.It can be seen that microorganisms help to increase the content of NP-binding part and reduce the content of soluble part.?4?The degradation of 12 NP isomers in soil is related to their structure.The degradation of isomers in soil can be fitted by the first order kinetics equation.The half-life of isomers in soil has a good correlation with steric resistance index and mean information index for the magnitude of distance(I_dwbar).