Meilin He

Microplastics (MPs) have been shown to exert time-dependent toxic effects on microalgae, with toxicity either intensifying or alleviating over prolonged exposure. However, the underlying mechanisms driving this phenomenon remain unclear, particularly regarding the role of external nutrient depletion in the surrounding medium. Herein, we performed bioassays and computational modeling to evaluate the effects of polyvinyl chloride microplastics (mPVC, 10, 50, and 100 mg L⁻¹) on the growth and physiology of Desmodesmus sp. under varying initial medium nutrient levels (100%, 25%, 8%, and 4%) for 96 h. The results demonstrated that nutrient levels in the culture medium modulated the toxic impact of mPVC. Under a 25% nutrient concentration, exposure to 100 mg L⁻¹ mPVC significantly inhibited algal growth by 6.5%, whereas at a 4% nutrient level, the growth of Desmodesmus sp. was significantly enhanced by 7.0%. Consistently, mPVC exposure at 25% nutrient concentration led to a sharper decline in intracellular pigment content (13.1–15.5%), soluble sugars content (8.2–27.0%), and photosynthetic efficiency (4.3–20.5%). In contrast, exposure to mPVC at 4% nutrient level improved the light use efficiency (11.9–15.4%) and electron transport rate (9.2–13.9%) of the algal cells. Independent action modeling revealed that as medium nutrient levels decreased, the interaction effects of mPVC exposure shifted from a synergistic to an antagonistic relationship. Overall, our findings identify medium nutrient availability as a critical regulatory factor influencing the toxic effects of mPVC on microalgae, potentially providing different insights into understanding the time-dependent toxicity of MPs.

Biofertilizers derived from microalgae are increasingly used as promising materials for improving crop growth and development, producing fewer catastrophic environmental effects. Hence, the large-scale production of eco-friendly and broad-spectrum microalgae biofertilizers is mandatory. Therefore, this study was designed to examine the potential efficacy of isolated algae strains, such as Spirulina platensis, Spirulina maxima, and Chlorella vulgaris, to improve the growth and development of Pak Choi. A completely randomized design (CRD) was carried out, with five replications and six levels (0, 0.5, 1.0, 1.5, 2.0, and 2.5 g) of each microalga biofertilizer, using Pak Choi as the test plant. Treatment with microalgae biofertilizers was found to increase Pak Choi’s overall growth performance, biochemical development, and nutritional composition. The application of Spirulina platensis and Spirulina maxima microalgae at 2 g as a biofertilizer showed significant (p < 0.05) positive impacts on above- and below-ground biomass, photosynthetic parameters, biochemical composition, and the nutritional attributes of different parts of Pak Choi tissues. With the addition of biofertilizer, incorporating Chlorella vulgaris (2.5 g) showed remarkable (p < 0.05) impacts on the development of above- and below-ground biomass and biochemical and nutritional attributes. Thus, our results highlight that Chlorella vulgaris (2.5 g) outperforms other biofertilizer treatments and could be considered a sustainable approach for producing leafy vegetables.

Polyethylene terephthalate-based glitters (PET glitters) are a potential source of primary microplastics in the environment. However, the bioeffects of PET glitters and the associated leachates remain largely unknown. In this study, we investigated the individual and combined toxicity of five colors (silver, black, red, green, and blue) of PET glitters and their corresponding leachates on the cellular responses of Desmodesmus sp. The results indicated that the photosynthesis of Desmodesmus sp. could be partly affected by PET glitters through the shading effect, but not that of growth. Conversely, the leachates of red and green PET glitters significantly inhibited the growth of the microalga, suggesting a higher risk associated with additives leached from these colors of PET glitters. Furthermore, the adverse effects of the co-occurrence of PET glitters and leachates were closely related to oxidative stress responses in the microalgal cells, along with a color effect, which could be mainly attributed to variations in the composition and abundance of toxic additives in different colors of PET glitters. Overall, our findings provide insights into the ecological risks posed by glitters in aquatic environments and emphasize the importance of considering color factors in assessing microplastics toxicity.