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Mechanical aging of tire microplastics enhances the bioavailability of pre-adsorbed 17β-estradiol in goldfish
Original title: Mechanical aging of tire microplastics enhances the bioavailability of pre-adsorbed 17β‑estradiol in goldfish
Summary
Rain and road friction break down tire microplastics into smaller, looser particles that release absorbed chemicals—like the hormone estrogen—more easily, according to a new study in goldfish. This matters because tiny tire particles constantly wash into waterways, and as they break down further, they may become more effective at delivering hormone-disrupting pollutants into fish (and potentially other animals up the food chain), raising questions about long-term ecological and health impacts we're only beginning to understand.
Tire microplastics (TMPs) are emerging contaminants in aquatic environments, posing ecological risks from both their ingredients and adsorbed pollutants. However, the transformation of TMPs by mechanical forces on wet-road surfaces and its effects on the carrier behavior of TMPs remain poorly understood. Here, we employed wet ball-milling to simulate mechanical TMP aging after rainfall by repeated TMP-road surface friction. The mechanical aging significantly increased the proportion of fine particles (1-10 μm) from 6.4% to 73.1%, accompanied by a change from dense, compact structures into loosely aggregated particles. In vitro desorption experiments showed that the aging enhanced the release of C-labeled 17β-estradiol (E) pre-adsorbed onto the TMPs in simulated fish digestive fluids. This enhancement was likely due to shortened intraparticle diffusion pathways, leading to increased bioavailability. Goldfish exposure experiments revealed that the aged TMPs modulated the absorption, distribution, and clearance of E in vivo, promoting its intestinal release while delaying its hepatic accumulation, thereby altering the temporal response of the estrogen-responsive biomarker vitellogenin. Our findings indicate that mechanical aging under wet-road conditions not only refines TMP particles and alters their structure, but also increases their environmental risks as carriers of low-molecular-weight organic pollutants.