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Effects of the Exposure of Aged Micro-Polyethylene Terephthalate on the Growth Status and Photosynthesis of Chlorella sp. UTEX1602
Summary
This study found that microplastics aged through UV exposure, strong acids, or strong alkalis were significantly more toxic to the freshwater microalga Chlorella than unaged microplastics, inhibiting growth and disrupting photosynthetic pigments. The results highlight that weathered microplastics in the environment — rather than pristine particles — pose the greater ecological risk to aquatic primary producers.
Abstract Microplastics (MPs) are ubiquitous in aquatic ecosystems worldwide, but their effects on plankton, especially the effect of aged MPs on freshwater microalgae, are not well-known. To investigate this issue, we studied the effects of untreated micro-polyethylene terephthalate (untreated-mPET) and strong alkali micro-polyethylene terephthalate (NaOH-mPET), strong acid micro-polyethylene terephthalate (HCl-mPET), high temperature micro-polyethylene terephthalate (HT-mPET) and ultraviolet micro-polyethylene terephthalate (UV-mPET) on the growth and photosynthetic pigment yield of Chlorella sp. UTEX1602 (8d). The results showed that aged mPET enhanced the toxicity of mPET to Chlorella sp. UTEX1602 compared to the toxicity of untreated-mPET. Moreover, 100 mg/L and 200 mg/L NaOH-mPET, and 20 mg/L UV-mPET and HT-mPET inhibited the growth of Chlorella sp. UTEX1602, as well as chlorophyll and carotenoids. The changes in the concentration of key active enzymes also confirmed the toxic effect of MPs on Chlorella sp. UTEX1602. Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS) and Zetasizer were used to determine the effect of aging on the surface characteristics of mPET. The reduction of hydroxyl and zeta potential affected the interaction between MPs and microalgae, thereby increasing the toxicity of aged MPs. By using a liquid chromatography-high-resolution quadrupole time-of-flight tandem mass spectrometer, we determined the effect of aging on the leachate of MPs. The increased content of dibutyl phthalate (DBP) and bis(2-ethylhexyl) phthalate (DEHP) indicated that the toxic effect of MPs on microalgae might be caused by MPs and the leachate of MPs. Aged-mPET stimulated an increase in the content of extracellular polysaccharides (EPS) produced by Chlorella sp. UTEX1602 and alduronic acid in EPS; thus, the biopolymer based on microalgae can be used as a bio-flocculant to remove MPs. The results help to better understand the impact of aging on MPs in the environment and presented here provide more evidence regarding the risks that MPs bring into freshwater ecosystems. Future studies on MPs aging should narrow the knowledge gap between laboratory simulations and actual conditions and increase environmental relevance.
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