Sunlight mediated cadmium release from colored microplastics containing cadmium pigment in aqueous phase

Abstract

The plastics industry is the biggest consumer of cadmium pigments. Little is known about the leaching of hazardous Cd2+ from colored microplastics containing cadmium pigment in aquatic systems. Here, we reported the release of Cd2+ from different sized microplastics containing cadmium pigment in aqueous phase under simulated sunlight. The release of Cd2+ was caused by the photo-dissolution of cadmium pigment. The release kinetics is highly size-dependent. It was relatively low for microplastics with size larger than 0.85 mm but increased significantly with decreasing size for microplastics smaller than 0.85 mm. The polymer matrix was oxidized during light exposure, leading to lower average molecular weight and the formation of oxygen-containing groups. Part of the polymer matrix was degraded into soluble organic carbon under simulated sunlight, resulting in continuous Cd2+ release from the pigment particles embedded in the polymer. The polymer degradation rate is also highly size-dependent. The degradation of the polymer matrix and the release of Cd2+ were intertwined. Cadmium leaching from microplastics from a commercial product containing cadmium pigment was confirmed in water under simulated sunlight. This work suggests that the photochemical processes of inorganic pigments will lead to the release of heavy metals from colored plastic debris.

TSC Opinion

Le cadmium est un des métaux lourds qui augmente le plus rapidement, année après année, dans les eaux côtières européennes. Un indicateur est en place qui mesure le cadmium dans les coquillages filtreurs de manière régulière. La première source incriminée était principalement les piles qui se retrouvaient souvent dans les déchets urbains non ou mal triés et enfouis. Les emballages plastiques constituent une autre source moins connue du grand public, mais pointée du doigt par l’INRS, en France, dans un rapport récent de 2019. On le trouve par exemple dans les fameux legos, pour lequel on peut sérieusement se poser la question comment un producteur peut mettre en conscience un produit toxique dans un objet qui sera utilisé par les enfants. L’économie circulaire commence là aussi, par le respect de ses clients !