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Role of Residual Monomers in the Manifestation of (Cyto)toxicity by Polystyrene Microplastic Model Particles
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Researchers investigated whether the toxicity observed in laboratory studies using polystyrene microplastic particles might actually come from leftover styrene monomer trapped in the particles rather than the plastic itself. They found that standard commercial polystyrene particles containing residual monomers showed mild toxicity to mammalian cells, while thoroughly purified particles did not. The study suggests that some reported toxic effects of microplastics in lab settings may be partly attributed to chemical residues rather than the plastic particles alone.
Polystyrene (PS) is an important model polymer for the investigation of effects of microplastic (MP) and nanoplastic (NP) particles on living systems. Aqueous dispersions of PS MP or NP contain residual monomers of styrene. In consequence, it is not clear if the effects observed in standard (cyto)toxicity studies are evoked by the polymer (MP/NP) particle or by residual monomers. We addressed that question by comparing standard PS model particle dispersions with in-house synthesized PS particle dispersions. We proposed a rapid purification method of PS particle dispersions by dialysis against mixed solvents and developed a simple method of UV-vis spectrometry to detect residual styrene in the dispersions. We found that standard PS model particle dispersions, which contain residual monomers, exerted a low but significant cytotoxicity on mammalian cells, while the in-house synthesized PS, after rigorous purification to reduce the styrene content, did not. However, the PS particles per se but not the residual styrene in both PS particle dispersions resulted in immobilization of Daphnia. Only by using freshly monomer-depleted particles, will it be possible in the future to assess the (cyto)toxicities of PS particles, avoiding an otherwise not controllable bias effect of the monomer.
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