| As an emerging pollutant,microplastics(MPs)pollution in water has acquired extensive attention in recent years due to their small particle size and stable properties,which can act as a carrier for pollutants in the water environment and have toxic hazards to aquatic organisms.After enter into aquatic environment,MPs are readily to undergo varied types of weathering process(i.e.,hydrolysis,photo and heat oxidation,and mechanical abrasion),leading to shifted surface morphology and physicochemical properties and resulting in promoted ecological risks to aquatic organisms.Photo aging process of MPs in water environments is a free radical associated chain reaction process,which affects the molecular arrangement and mechanical properties of microplastics,inducing the further fragmentation of microplastics to form smaller size MPs even in nanoplastic particles.However,the aging process of MPs in natural waters are also readily to be affected by polymer types?plastic additives,halogen ions,and natural organic matters,leading to great difference between laboratory accelerated weathering and long-term aging process of MPs in natural waters.Therefore,studying the combined effects of plastic additives and water quality conditions on the aging process of microplastics will be helpful to evaluate the environmental behavior,toxicological effects,and ecological risks of aged MPs in natural waters.Based on the above considerations,we explored the impact of water components(i.e.,fresh water,ultrapure water,estuary water and seawater)and plastic additives on the photo aging of MPs.Finally,we investigated the sorption behavior of TCS onto aged PP MPs to access the impact of aged microplastics as the carrier on the fate organic pollutants in the water environment.For the impact of water conditions on the aging process of microplastics,the results showed that aging process of PP MPs in freshwater and seawater was significantly inhibited.Natural organic matter(NOM)and nitrate(NO3-)in fresh water are the main factors that inhibit the photoaging process of microplastics.The inhibitory mechanism of NOM to PP MPs aging process was assigned to the NOM could quench hydroxyl radical(HO·)and superoxide anions(O2·-)and prevented the free radical associated indirect photo oxidation of PP MPs in water under light irradiation.Besides,NOM was able to adhere onto the surface of MPs,and impended the effective adsorption of plastics to light irradiation and inhibit the direct photo oxidation of MPs.Differing from freshwater environment,Differing from freshwater system,Cl-was the primary factor for the inhibitory effect of PP MPs aging process in seawater.The aging degree of PP MPs decreased with the increase of Cl-concentration,which may be due to the fact that the formed dichloride radical(Cl2·-)in seawater can quench hydroperoxy radical(HO2·)and prevent the formation of superoxide anion(O2·-)produced in the aging process of PP MPs.Impact of plastic additives on the aging of MPs in water was conducted by comparing the aging process of pure PP MPs without additives and additive contained PP MPs commercial products(meal boxes and tea cups).The results revealed that photoaging rate of the additive-contained PP MPs is affected,highlighting the significant role of plastic additives on the photo aging of MPs in water.GC-MS analysis discovered that antioxidant Irgafos 168(3(2,4-di-tert-butylphenyl)phosphate ester)is the main additive controlling the photo aging process of additive contained PP MPs in water.The inhibitory mechanism may due to the presence of antioxidant Irgafos168 could react with hydroperoxides produced by PP MPs during aging process and impended the generation of hydroxyl radicals in the system,thus inhibiting the polymer chain reaction for PP MPs in water.Moreover,by comparing the sorption of TCS onto pristine and aged PP MPs,we discovered that the adsorption performance of microplastic particles on TCS increased with the increase of the aging degree of MPs.This may due to the fact that the aging process can reduce the MPs particle size and crystallinity,increase the specific surface area and roughness,and provide more effective sites for adsorbing pollutants.In addition,caition of Ca2+and Na+were also demonstrated as important factors for the adsorption of TCS onto MPs,and the mechanism can be explained as salting out effect.Salting out effect mainly promotes the precipitation of TCS from water by reducing the solubility of TCS,and increases the interaction probability with microplastics.The results of the paper emphasize the important role of water quality factors,especially halogen ions and natural organic matter in the photoaging process of microplastics in the water environment.It also showed that MPs may have different aging duration and mechanism in different water marices.In addition,plastic additives,especially antioxidants,also play an important role in the aging process of microplastics.The research results of the paper can also provide theoretical support for comprehensively and systematically assessing the environmental behavior,toxicological effects and ecological risks of aged MPs in natural water environment. |
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