| Erythromycin is one of the most commonly used macrolide antibiotics.A comprehensive understanding of the environmental behavior of erythromycin in soil is the basis for the scientific assessment of its ecological risk.In this experiment,14C tracer was used to systematically study the mineralization,extractable residues and bound residues of[N-methyl-14C]-erythromycin in three typical soils,and the effects of soil microorganisms and chicken manure on these processes.On this basis,the dynamic release and transformation of 14C-erythromycin bound residues in red soil,which is easy to form bound residues were studied,and the bioavailability in Brassica parachinensis were also discussed.The effects of adding exogenous organic manure(chicken manure and activated sludge)on this process were also investigated.This study is of great significance for the scientific assessment of the environmental risk of erythromycin contamination in soil The main results are as follows:(1)Soil types have an important influence on mineralization of erythromycin in soils.There are significant differences in mineralization rate and total mineralization amount of 14C-erythromycin in three different soils.Within 20 d,the average mineralization rates of FS,BS and RS were 4.04%,3.64%and 0.14%per day,respectively.The mineralization rates/total amount of FS and BS were about 26 and 29 times of RS,and the total mineralization amount of the three soils were 91.83%,87.33%and 25.75%respectively at 120 d.(2)Soil types play an important role in the formation of bound residues of erythromycin in soil.Bound residues were rapidly formed in three soils,and the total amount of 14C-BR reaches its peak at 10 d,accounting for 21.02%,48.31%and 64.68%in FS,BS and RS,respectively.The total amount of 14C-BR in three soils decreased gradually after 10 d and reached equilibrium at 40 d,and the total amount of 14C-BR in three soils is 10.18%,11.02%and 53.06%,respectively,at equilibrium,were 8.34,5.57 and 1.79 times of its extractable residues.Therefore,the traditional assessments of erythromycin residue are mainly based on extractable residues,which may underestimate the total amount of erythromycin residues in soils and need to be revised.(3)Microorganisms play a major role in the mineralization of erythromycin in soil and the formation of bound residues.At 120 d,the mineralization amount in sterilized soil was only 3.68%of the introduced amount,and was only 4.01%of the control;at 120 d,the amount of 14C-BR was 43.06%,which was about 4.23 times of the control.It suggested that microbial remediation might be an effective way to reduce erythromycin contamination in soil.(4)The addition of chicken manure can significantly inhibit the mineralization and degradation of extractable residues,and promote the formation of bound residues of erythromycin.When cultured for 20 d,the total amount of mineralization was only 0.32%,only accounting for 0.40%in the blank soil(80.74%);the total amount of mineralization was 45.33%at 120 d,about 49%of the blank soil;and the total amount of 14C-BR in soil was 38.11%at 120 d,about 3.74 times of the blank soil.The results showed that the addition of livestock manure could greatly inhibit the mineralization of erythromycin in soil and promote the formation of bound residues of erythromycin.(5)The root of plants can promote the transformation of bound residues and further absorb and transport them to edible parts of the Chinese Flowering Cabbage,indicating that bound residues of erythromycin are bioavailable.The application of organic fertilizers to plants,such as chicken manure and activated sludge,can promote the absorption of 14C-erythromycin in plants,and lead to the accumulation of bound residues in soil,which is a risk to the environment.(6)Humic acid fractioning results showed that erythromycin-bound residues were mainly concentrated in fulvic acid(87.92%-97.21%).It is necessary to clarify the formation mechanism of bound residues of erythromycin through further research in order to provide scientific measures for reducing erythromycin residue in soil. |
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