Polycyclic aromatic hydrocarbon accumulation in aged and unaged polyurethane microplastics in contaminated soil

The interaction of microplastics (MPs) and common environmental organic pollutants has been a frequently discussed topic in recent years. Although the estimated contamination caused by MPs in terrestrial ecosystems is one order of magnitude higher than that in the oceans, experiments have been conducted solely in an aqueous matrix. Therefore, an experiment was carried out with two soils differing in their concentrations of polycyclic aromatic hydrocarbons (PAHs) and polyurethane foams used for scent fences along roads and crop fields. Two types of polyurethane foam (biodegradable and conventional in aged and unaged form) were exposed to soils containing PAHs that originated from historically contaminated localities. The exposure lasted 28 days, and a newly developed three-step procedure to separate MPs from soil was then applied. Biodegradable polyurethane MPs exhibited a strong tendency to accumulate PAHs after 7 days, and their concentrations significantly grew over time. In contrast, the sorption of PAHs on conventional polyurethane MPs was substantially lower (a maximum of 3.6 times higher concentration than that in the soil). Neither type of foam changed their sorption behaviors after the aging procedure. The results indicate that the flexibility of the polyurethane polymeric network could be the main driving factor for the sorption.