Organophosphate (OP) diesters and a review of sources, chemical properties, environmental occurrence, adverse effects, and future directions

•At least 23 OP diesters have been reported as contaminants or as degradation products of OP triesters.•OP diesters containing halogen atoms and aryl groups could be more persistent in environmental matrices.•Multiple sources of OP diesters existed, i.e. industrial production and biotic or abiotic degradation from OP triesters.•Total annual output of OP diesters was estimated to be 17,050 metric tons (underestimated).•Various adverse effects following exposure to OP diesters in organisms have been reported.