Molecular characteristics and biological effects of dissolved organic matter leached from microplastics during sludge hydrothermal treatment

Previous knowledge of dissolved organic matter leached from microplastics (MP-DOM) was mainly based on the aquatic environment. The molecular characteristics and biological effects of MP-DOM in other environments have rarely been examined. In this work, FT-ICR-MS was applied to identify MP-DOM leached from sludge hydrothermal treatment (HTT) at different temperatures, and the plant effects and acute toxicity were investi-gated. The results showed that the molecular richness and diversity of MP-DOM increased with rising temper-ature, accompanied by molecular transformation in the meantime. The oxidation was crucial whereas the amide reactions mainly occurred at 180-220 oC. MP-DOM promoted root development of Brassica rapa (field mustard) by affecting the expression of genes and the effect was enhanced with rising temperature. Specifically, the lignin -like compounds in MP-DOM down-regulated Phenylpropanoids biosynthesis, while CHNO compounds up -regulated the nitrogen metabolism. Correlation analysis presented that alcohols/esters leached at 120-160 oC were responsible for the promotion of root, while glucopyranoside leached at 180-220oC was vital for root development. However, MP-DOM produced at 220 oC showed the acute toxicity to luminous bacteria. Consid-ering the further-treatment of sludge, the optimum HTT temperature could be controlled at 180 oC. This work provides novel insight into the environmental fate and eco-environmental effects of MP-DOM in sewage sludge.

Automated summary

This study used FT-ICR-MS to investigate the molecular characteristics and biological effects of microplastics dissolved organic matter (MP-DOM) leached from sludge hydrothermal treatment (HTT) at different temperatures. The results showed that the molecular richness and diversity of MP-DOM increased with rising temperature, accompanied by molecular transformation. The MP-DOM influenced the root development of Brassica rapa by affecting gene expression, with lignin-like compounds inhibiting Phenylpropanoids biosynthesis and CHNO compounds promoting nitrogen metabolism. The optimal HTT temperature for the further treatment of sludge was found to be 180℃.