Interfacial-mediated fast formation of toxic derivatives of phthalate esters

Phthalate esters (PAEs) are of significant concern due to their ubiquitous persistence in homogeneous environments and severe health effects on respiratory, reproductive, and endocrine systems. However, their fates in heterogenous environments remains elusive. Here, using integrated microdroplet experiments, and ab initio molecular dynamics, we demonstrate that PAEs undergo spontaneous degradation with short half-lives (<10 min) on microdroplet surfaces, representing a 4 to 11 orders of magnitude enhancement compared with bulk aqueous or gaseous phases. This fast process is driven by a unique interfacial mechanism initiated by spontaneously generated hydroxyl radicals, leading to stepwise dealkylation and hydroxylation. Critically, this pathway produces hydroxylated and, predominantly, carboxylated transformation products (TPs). Computational toxicology models further predict that these TPs, especially the carboxylated ones, exhibit amplified human hepatotoxicity (up to 37.5-fold increase), enhanced skin sensitization (~1.5-fold increase), and comparable developmental toxicity with respect to the parent PAEs. The study fundamentally challenges our understanding of PAE environmental fate and highlights a previously unrecognized global risk vector due to rapid PAE transformation in ubiquitous microdroplet systems, necessitating urgent revision on environmental persistence models and risk assessment frameworks to incorporate interfacial chemistry.