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In vitro characterization of cadmium transport across the gastro-intestinal membrane of the fathead minnow (Pimephales promelas) in the presence and absence of microplastics
Summary
An in vitro gut sac experiment using fathead minnows found that microplastics did not themselves cross the gut wall, and surprisingly, fish exposed to cadmium bound to microplastics actually absorbed less cadmium than those exposed to cadmium alone. This suggests that in some conditions microplastics may reduce — rather than increase — the uptake of certain heavy metal contaminants through the gut, complicating simple "Trojan horse" assumptions about microplastics as metal vectors.
There is concern that microplastics can act as a vector for cadmium through adsorption and desorption of free-ionic cadmium. Little is known about the uptake of cadmium following ingestion of cadmium-microplastic complexes. This study used an in vitro gut sac technique to investigate the translocation of cadmium across the gut barrier of fathead minnows following the simulated ingestion of cadmium, microplastics, or their complexed mixture. Microplastics did not cross the gut membrane, nor did microplastics alter the rate of cadmium translocation, which was estimated to be 1.2 ± 0.04 ng Cd / hour. Less cadmium translocated when cadmium-microplastic complexes were injected than the equivalent dose of only cadmium, indicating that the presence of microplastics was protective of dietary cadmium uptake. This work highlights the importance of considering dietary uptake and the role of microplastics acting as a vector for cadmium in aquatic environments and stresses the need to understand how environmental (digestive or ambient) characteristics govern cadmium-microplastic interactions.