Oxidative Stress And DNA Damage Indued By Polyhydroxyalkanoate Microplastics On Earthworms In Soil

In order to solve the environmental pollution caused by non-degradable plastics,degradable plastics have been widely developed and used.According to the degradation process,degradable plastics can be divided into truly degradable plastics and partially degradable plastics.Truly degradable plastics refer to plastics that can be completely degraded into carbon dioxide,water,methane,and biomass by microorganisms,light and water in the environment.Currently,truly degradable plastics mainly include polylactic acid(PLA),polyhydroxyalkanoate(PHA),polycaprolactone(PCL),and poly(butylene succinate)(PBS).However,the complete degradation of truly degradable plastics also requires certain conditions and time.And,the specific conditions and time required to ensure complete degradation of truly degradable plastics can be challenging achieve.Several studies have reported that similar to non-degradable plastics,biodegradable plastics in natural environments can also generate microplastics.As a type of emerging pollutants,effects of microplastics on ecosystems have attracted worldwide attention,while the existing studies mainly focused on non-degradable microplastics,and studies on degradable microplastics is relatively scarce.PHA is a kind of intracellular polyester synthesized by a variety of bacteria.Except for the properties that are similar to synthetic plastics,it also has some excellent properties that synthetic plastics do not have,such as biodegradability,and biocompatibility.Thus,PHA has broad application prospects in degradable packaging materials,tissue engineering materials,electrical materials and medical materials.In this study,earthworms(Eisenia fetida)were exposed to 0%,0.25%,0.5% and 1%(w/w)PHA microplastics for 28 d to investigate the oxidative stress and DNA damage induced by PHA microplastics on earthworms.In addition,the integrated biomarker response index(IBR)was calculated to reveal the relationship between the toxicity of PHA microplastics and the exposure concentrations.This study will provide new insights into the ecological risk assessment of degradable microplastics in terrestrial ecosystems.The main results are summarized as follows:(1)Exposure to 0.25%,0.5% and 1% PHA microplastics can result in significant increase in the contents of reactive oxygen species(ROS),changes in the activities of antioxidant enzymes(superoxide dismutase(SOD)and catalase(CAT))and detoxification enzymes(glutathione S-transferase(GST)),and increase in the contents of DNA oxidative damage product 8-hydroxydeoxyguanosine(8-OHd G),which in turn induced oxidative stress in earthworms.(2)Exposure to 0.25%,0.5%,1% PHA microplastics can lead to DNA strand breaks in earthworm coelomocyte,this is,significant increase in the olive tail moment(OTM)values,and then caused DNA damage in earthworm coelomocyte.In addition,the degree of DNA damage in earthworm coelomocyte increased with the increase of PHA microplastics exposure concentrations.(3)The IBR values increased with the increase of PHA microplastics exposure concentrations,indicating that the toxicity of PHA microplastics to earthworms was concentration-dependent.