The release process of Cd on microplastics in a ruminant digestion in-vitro method

Abstract Microplastics (MPs), polymer particles capable of accumulating heavy metals from ambient medias, have been widely found in agriculture and pasture soils. Through the consumption of MPs in soils, heavy metals adsorbed on MPs can be transported into ruminant digestive guts. To explore the behavior of Cd loaded MPs in ruminant digestive system, we initially established a ruminant digestive in-vitro method (RDM) that simulates the rumination cycle between mouth and rumen to evaluate the release rates of Cd on 4 most commonly used undegradable MPs (PE, PP, PVC, and PS) and a biodegradable MP (PLA). After 120 h of adsorption, the Cd adsorption capabilities by 5 MPs ranged from 0.23 μg/g to 2.45 μg/g. Through RDM, all tested Cd loaded MPs released high proportions of Cd with release rates from 21.5% to 41.8%, where PLA showed the highest Cd release rate. Cadmium was mainly released in rumen and abomasum phases, and the rumination cycle between mouth and rumen can affect the Cd release from MPs. The present study provides a new view on the environmental hazard of heavy metal and MP pollution that their co-exposure to ruminants should be taken into account.