Are Microplastics Always Toxic? --Certain Concentrations of Polystyrene Are Promoters of Marine Algae Growth and Heavy Metal Bioremediation

The influence of microplastics on the bioremediation capabilities of algae in aquatic environments is an area of growing concern, particularly when these tiny plastic particles interact with heavy metals like cadmium (Cd). Such interactions could alter the algae's natural ability to detoxify and purify water, posing significant challenges to maintaining the health and stability of aquatic ecosystems. This study investigated the effects of different types (including Polystyrene (PS), Polyvinyl Chloride (PVC), and Polyethylene Terephthalate (PET)) and concentrations (1-100 mg/L) of microplastics on the ability of algae to absorb Cd, focusing on whether the simultaneous presence of microplastics and heavy metals can affect both algal growth and heavy metal bio-uptake. The study results indicated that Cd or different types of microplastics individually inhibit algal growth. However, when algae are co-exposed to Cd and microplastics, a PS concentration of 1 mg/L combined with Cd significantly promotes algal growth, demonstrating an antagonistic effect, whereas the other two types of microplastics exhibit a synergistic effect with Cd. Additionally, regardless of exposure duration, when PS is present at 1 mg/L, it enhances the bio-uptake of Cd in algae compared to treatments with Cd alone. Among the various types and concentrations of microplastics studied, the combination of 1 mg/L PS and Cd was found to not only promote algal growth in aquatic environments but also enhance heavy metal bio-uptake, thereby mitigating heavy metal pollution. Consequently, the presence of microplastics at certain concentrations (such as 1 mg/L PS) may not necessarily be considered "pollutants" in aquatic environments. These findings provide a new perspective for re-evaluating the role of microplastics in aquatic ecosystems and suggest a strategy for leveraging microplastics to enhance algal bioremediation of heavy metals.