Biodegradation of renewable polyurethane foams in marine environments occurs through depolymerization by marine microorganisms

Abstract

Accumulation of plastics in the Earth's oceans is causing widespread disruption to marine ecosystems. To help mitigate the environmental burden caused by non-degradable plastics, we have previously developed a commercially relevant polyurethane (PU) foam derived from renewable biological materials that can be depolymerized into its constituent monomers and consumed by microorganisms in soil or compost. Here we demonstrate that these same PU foams can be biodegraded by marine microorganisms in the ocean and by isolated marine microorganisms in an ex situ seawater environment. Using Fourier-transform infrared (FTIR) spectroscopy, we tracked molecular changes imparted by microbial breakdown of the PU polymers; and utilized scanning electron microscopy (SEM) to demonstrate the loss of physical structure associated with colonization of microorganisms on the PU foams. We subsequently enriched, isolated, and identified individual microorganisms, from six marine sites around San Diego, CA, that are capable of depolymerizing, metabolizing, and accumulating biomass using these PU foams as a sole carbon source. Analysis using SEM, FTIR, and gas chromatography–mass spectrometry (GCMS) confirmed that these microorganisms depolymerized the PU into its constitutive diols, diacids, and other PU fragments. SEM and FTIR results from isolated organismal biodegradation experiments exactly matched those from ex situ and ocean biodegradation samples, suggesting that these PU foam would undergo biodegradation in a natural ocean environment by enzymatic depolymerization of the PU foams and eventual uptake of the degradation products into biomass by marine microorganisms, should these foams unintentionally end up in the marine environment, as many plastics do.