Solar light photodegradation of nicotine in the presence of aged polystyrene microplastics

Limited information exists on the potential of aged microplastics to induce photodegradation of organic pollutants under sunlight irradiation. In this work, nicotine (NIC), a widespread emerging contaminant, was used as a model organic substrate to investigate this innovative degradation process. Polystyrene (PS) pellets were artificially aged and became rich in oxygenated moieties with their carbonyl index reaching 0.43 ± 0.04 after 4 d of aging. The degradation of NIC photosensitized by aged PS at different pH values was monitored for 6 h under simulated sunlight irradiation (650 W/m2). The maximum degradation rate was observed at pH = 11 (75 % NIC removal from a 10 mg L-1 solution containing 50 g L-1 aged PS pellets), suggesting that the unprotonated NIC is the most photoreactive form. Increasing the PS load from 50 to 200 g L-1 accelerated NIC degradation. The addition of 2.5 mg L-1 humic acids had a slight enhancement role (82 % NIC degradation), which confirms their effectiveness as photosensitizers. NIC photosensitization by aged PS was also studied in the presence of t-butanol (55 % NIC removal in solutions containing 100 mg L-1 t-butanol) and in anoxic conditions (NIC solution purged with N2; 95 % NIC removal), to gain insight into the respective roles of the potentially formed •OH and 1O2. The main photo-produced reactive species involved in NIC degradation likely were the triplet states of the PS beads (3PS*). Differently from most advanced oxidation processes, NIC's photodegradation by aged PS was not affected by increasing amount of chloride and we observed negligible differences between NIC degradation in ultra-pure water and seawater. The effectiveness of irradiated PS towards NIC photodegradation was also investigated in tap water and secondary wastewater. Overall, the possibility to decontaminate polluted water with waste-derived materials is interesting in the framework of circular economy.

Adverse effects of pristine and aged polystyrene microplastics in mice and their Nrf2-mediated defense mechanisms with tissue specificity

Health hazards associated with microplastics (MPs) remain largely unknown, and the effects of aged MPs, one of their persistent forms, are poorly characterized. Male ICR mice were intratracheally instilled with 0.01 and 1 mg/day pristine and ultraviolet (UV)-aged polystyrene microplastics (PS and APS) with an average diameter of 4 - 5 μm daily for 1 week. UV irradiation caused the PS to have a rough surface, become fragmented, and increase their carbonyl groups. Both PS and APS caused structural damage to the mouse gut, liver, spleen, and testis. Inflammatory infiltration in liver, swollen and congested gut, and loose spleen globules, as well as the loose interstitium of the seminiferous tubules in testis were found in 1 mg/day APS group. Increases in serum alanine aminotransferase and immunoglobulin A levels in 1 mg/day APS group (p < 0.05) demonstrated that APS exposure could induce greater liver and spleen functional damage than PS. Meanwhile, triglyceride and total cholesterol levels in liver were enhanced in 1 mg/day APS group (p < 0.05). Superoxide dismutase and glutathione contents in 0.01 and 1 mg/day APS groups significantly decreased (p < 0.05), which suggesting that PS and APS could interfere with the antioxidant capacity in mice. Nuclear factor erythroid 2-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1) levels in the PS and APS groups showed significant increases in the liver and testis (p < 0.05), and a significant decrease in the spleen (p < 0.05), which were analyzed to get a first survey for Nrf2/HO-1-mediated tissue-specific defense mechanisms. In conclusion, acute exposure to PS and APS induced potential metabolic disorders, and APS could produce more serious immune damage and reproductive toxicity. These findings provide new insights in health risk assessment of aged MPs.