In this study, the influences of polystyrene microplastics (PS MPs) on the volatilization, photodegradation and photoinduced toxicities of anthracene and pyrene were determined in freshwater and artificial seawater. The PS MPs reduced the volatilization of anthracene and pyrene, and the volatilization reduction was highly dependent on the PS MPs sizes and concentrations. The PS MPs increased the photodegradation kinetics ( k p ) of anthracene by promoting 1 O 2 generation and altered the photodegradation pathways through OH attack of the photodegradation byproducts. However, the k p of pyrene was decreased by PS MPs suppressing the transfer of electrons from excited pyrene to oxygen. The PS MPs modified the pathways of pyrene photodegradation via OH attack of the photodegradation byproducts. Due to light shielding by DOM and/or PS MPs aggregates in seawater, the modification of the photodegradation pathways of anthracene and pyrene by PS MPs was hardly happened in seawater compared with in freshwater. By changing the concentrations of anthracene or pyrene and their photodegradation byproducts, the PS MPs greatly affected the photoinduced toxicities of anthracene and pyrene to Selenastrum capricornutum and Phaeodactylum tricornutum . The influences of PS MPs on the volatilization, photodegradation and photoinduced toxicity of anthracene and pyrene are important and should be carefully considered during environmental risk assessments of anthracene and pyrene.
Silver nanoparticles (AgNPs) have little impact on organisms at environmentally relevant concentrations. However, AgNPs coexisting with photoactive minerals may show an elevated combined ecotoxicity due to the additional photoinduced cytotoxicity caused by the Ag loading, which increases the photocatalytic activity. Herein, key pathway perturbations in the algae Chlorella pyrenoidosa (C. pyrenoidosa) under exposure to AgNPs, hematite nanoparticles (HemNPs), and their mixtures (direct exposure (MX1) and exposure after interaction (MX2)) were explored under illumination using transcriptomic and metabolomic approaches. The results showed that the MX2 group exhibited the strongest C. pyrenoidosa growth inhibition. The AgNPs, HemNPs, MX1 and MX2 groups significantly triggered ROS production in algal cells, which increased by 11.05%, 5.54%, 4.79% and 13.58%, respectively. Notably, the cell membrane was obviously damaged only in the MX2 group. Transcriptomic and metabolomic analyses showed that metabolic pathways, such as starch and sucrose metabolism, pantothenate and CoA biosynthesis, and amino acid metabolism, were significantly altered. To examine the internal mechanisms behind these differences in genes and metabolites, ultraviolet–visible (UV–vis) diffuse reflectance spectroscopy, electrochemical impedance spectroscopy (EIS) and photocurrent response measurements were used to determine the photochemical properties of the four systems. AgNPs attachment enhanced the photoelectric properties of the AgNPs/HemNPs composite (MX2), improving the photoinduced electron–hole pair separation efficiency and charge separation efficiency. Electron paramagnetic resonance (EPR) results also showed that the MX2 system yielded the highest amount of free radicals. Free radicals caused photoinduced cytotoxicity in algae, leading to aggravated toxicity of AgNPs to C. pyrenoidosa in the presence of HemNPs.
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