Insight into the photodegradation and universal interactive products of 2,2′,4,4′–tetrabromodiphenyl ether on three microplastics

The transformation process of contaminants on microplastics (MPs) exposed to sunlight has attracted increasing attention. However, the interactions between them are typically disregarded; therefore, this work investigated the photodegradation of 2,2′,4,4′–tetrabromodiphenyl ether (BDE–47) on three MPs (polystyrene (PS), polypropylene (PP) and polyethylene (PE)) and the interactions between these two. The inhibition of aged PS on the elimination of BDE–47 was due to light shielding, while aged PP and PE increased the degradation rate. More hydroxyl radicals (HO•) was detected in the PS system, which resulted in the higher degradation rate of BDE–47 on PS. A total of 33 different products were identified and four reaction pathways were presented, and the reaction mechanisms mainly included debromination, hydroxylation, carbon–oxygen–bond breaking and interactive reactions. The Ecological Structure Activity Relationship (ECOSAR) and Toxicity Estimation Software Tool (TEST) programs were used to evaluate the toxicity of reaction products, and the results indicated that even though BDE–47 was the most toxic, the interaction products were still toxic or harmful to aquatic organisms. This study provides significant information on the photodegradation of contaminants on common microplastics and their interaction, which cannot be ignored.