Comparative toxicity of exfoliating products containing microplastics and alternative particles from Nepal

Plastic pollution is a global problem, with numerous studies focusing on the effects of microplastics (1- 1000 μm). Cosmetic products like exfoliators have been identified as an important source of primary microplastics. After abundant reports on the hazards caused by microplastics, subsequent banning or voluntary removal from cosmetics is going on, causing them to be replaced by the non- plastic alternative particles. However, the replacement by so- called natural particles seems to be just a marketing strategy and lacks enough research verifying if they are actually safer than microplastics. The present study investigated the chemical and particle toxicity of eight exfoliators containing microplastics and alternative particles used in Nepal. This was addressed by means of two in vitro and one in vivo assay. The bioluminescent bacteria Photobacterium leiognathi was exposed to 2- 300 μg product and particles extracts and luminescence inhibition was measured. The recombinant yeast strain Saccharomyces cerevisiae containing a gene coding for human estrogen receptor alpha was exposed to 500 μg product and particle extract and estrogenicity was measured. Daphnia magna neonates (< 24 h old) were exposed to 2- 45 μm microplastic and alternative particles at 0.8 – 500 mg/L for 21-days and survival and reproduction was examined. The chemical toxicity from products was higher than the particle toxicity for bacteria with no significant differences among microplastic and alternative particles. Most of the ingredients in the products were unknown and thus the observed toxicity could not be attributed to any specific chemical. In the YES, only one sample that contained parabens was estrogenic in the product extract but not the particle extract. Both types of particles did not show any adsorbance. From in vivo assay, the alternative particles had stronger effects in the lethality of D. magna whereas microplastics caused higher reproductive effects. Based on the findings of this study, alternative particles cannot be considered safer than microplastics and with regards to products from Nepal, chemicals used in the cosmetics seem to be of more concern. Since this study analyzed only exfoliators, study on effects of other classes of cosmetics using environmentally relevant concentrations and other bioassays needs to be done in the future.