Photoaging enhances the leaching of di(2-ethylhexyl) phthalate and transformation products from polyvinyl chloride microplastics into aquatic environments

Increasing chemical pollution is a threat to sustainable water resources worldwide. Plastics and harmful additives released from plastics add to this burden and might pose a risk to aquatic organisms, and human health. Phthalates, which are common plasticizers and endocrine-disrupting chemicals, are released from polyvinyl chloride (PVC) microplastics and are a cause of concern. Therefore, the leaching kinetics of additives, including the influence of environmental weathering, are key to assessing exposure concentrations but remain largely unknown. We show that photoaging strongly enhances the leaching rates of di(2-ethylhexyl) phthalate (DEHP) by a factor of 1.5, and newly-formed harmful transformation products, such as mono(2-ethylhexyl) phthalate (MEHP), phthalic acid, and phthalic anhydride from PVC microplastics into the aquatic environment. Leaching half-lives of DEHP reduced from 449 years for pristine PVC to 121 years for photoaged PVC. Aqueous boundary layer diffusion (ABLD) is the limiting mass transfer process for the release of DEHP from pristine and photoaged PVC microplastics. The leaching of transformation products is limited by intraparticle diffusion (IPD). The calculated mass transfer rates can be used to predict exposure concentrations of harmful additives in the aquatic environment.