Combined Pollution Characteristics and Ecological Risk Assessment of Organophosphate Esters and Phthalate Esters in Cropland

Aiming to investigate the combined pollution of organophosphate esters (OPEs) and phthalate esters (PAEs) in cropland, this study collected soil samples from a cropland near a cable production zone. The soil samples were taken at different distances (5-100 m) to the cable production zone and at each sampling site three soil columns (0-50 cm) were collected. The concentrations of 15 OPEs and 5 PAEs in the soil samples were determined. Through correlation analysis, the pollution sources of OPEs and PAEs were traced and the impacts of soil organic carbon were studied. Additionally, ecological risk assessment on OPEs and PAEs was conducted by using the risk quotient (RQ) method. This study found that the concentrations of ∑₁₅OPEs and ∑₅PAEs in soil were 77.6-349.4 and 691.3-2 405.3 ng·g^-1, respectively. The concentrations of ∑₁₅OPEs decreased to some extent along with the horizontal distance from the cable production zone, while the levels of ∑₅PAEs increased first and then decreased. It might be attributable to the different routes of OPEs and PAEs entering the cropland. In the vertical profile of soil, both the concentrations of ∑₁₅OPEs and ∑₅PAEs decreased first, then increased, and finally decreased with the soil depth. Moreover, there existed a spatial difference on the distribution of different kinds of OPEs and PAEs. Among the OPEs, halogenate OPEs (35.9-236.4 ng·g^-1) occupied the highest proportion, followed by alkyl OPEs (35.8-154.8 ng·g^-1). The levels of aryl OPEs (2.9-15.6 ng·g^-1) and oligomeric OPEs (1.2-30.7 ng·g^-1) were much lower than those of halogenate OPEs and alkyl OPEs. As for the PAEs, the ones with relatively high concentrations were dimethyl phthalate (DMP, 293.4-1 822.5 ng·g^-1), di-n-octyl phthalate (DNOP, 112.8-664.2 ng·g^-1), and diethyl phthalate (DEP, 45.3-461.5 ng·g^-1). Besides, it is interesting to find that certain OPEs and PAEs were significantly correlated, probably due to their similar sources from the cable factories. In addition, soil organic carbon affected the occurrence of some OPEs and PAEs. According to the results of ecological risk assessment, it indicates that most of the individual OPEs and PAEs (median, RQ=0.02, 0.09) had a low risk, but the combined risk of OPEs or PAEs (MRQ=0.58, 0.44) could reach a medium level and the ecological risk caused by the combined pollution of OPEs and PAEs (MRQ=1.04) was much higher. This study revealed that the combined pollution of OPEs and PAEs in cropland soil should be paid great attention, and further research are required to explore the health risk of OPEs and PAEs in cropland and also the related soil remediation technologies.