Vector effect of polystyrene film microplastic in enriching Sudan III from natural particles and its burst release into simulated digestive fluid containing fatty acid

Microplastics (MPs) have aroused tremendous attentions because of their ability in accumulating contaminants from adjacent environment. However, their capability of concentrating hydrophobic organic contaminants might be influenced by huge amounts of coexisting natural particles (NaPs). Yet, our knowledge about the relative concentrating capability of MPs versus NaPs is still rare. Herein, the distribution behavior of several hydrophobic pollutants was studied in simplified MPs/NaPs/pollutant/water quaternary systems. We found that 1-(4-(phenylzao)phenyl)azo-2-naphthol (Sudan III) had similar distribution behavior with many hydrophobic pollutants and thus was used as a model pollutant. Polyethylene (PE) film debris derived from disposable plastic wrap was the most efficient microplastic which concentrated tens of times Sudan III than coexisting NaPs including bentonite, kaolin, sawdust, and diatomite. An enrichment coefficient of over 1000 times was observed in the case of PE film debris versus quartz sand. The concentrating capability of PE film MPs was found approximately equal to biochar particles. MPs seem to have limited contribution on the long distance transportation of hydrophobic organic pollutants. However, notably, over 70% of the adsorbed Sudan III could be released back into water within 0.5 h in the presence of 0.5% sodium oleate, which is a common amphipathic matter forming micelles in digestive fluid. Microplastics might play an important vector-like role in increasing the biological accumulation of hydrophobic pollutants via intestine digestive absorption. Due to much bigger quantity of NaPs, the relative concentrating effect of MPs to hydrophobic organic pollutants over NaPs is possibly a more reasonable reference when considering their potential ecological risk.