No abstract

Samples of water, sediment and suspended particulates were collected from 13 sites in the middle and lower reaches of the Yellow River in China. Phthalic acid esters (PAEs) concentrations in different phases of each sample were determined by Gas Chromatogram GC-FID. The results are shown as follows: (1) In the Xiao Langdi-Dongming Bridge section, PAEs concentrations in water phase from the main river ranged from 3.99 x 10(-3) to 45.45 x 10(-3) mg/L, which were similar to those from other rivers in the world. The PAEs levels in the tributaries of the Yellow River were much higher than those of the main river. (2) In the studied branches, the concentration of PAEs in sediment for Luoyang Petrochemical Channel (331.70 mg/Kg) was the highest. The concentrations of PAEs in sediment phase of the main river were 30.52 to 85.16 mg/Kg, which were much higher than those from other rivers in the world. In the main river, the concentration level of PAEs on suspended solid phases reached 94.22 mg/Kg, and it reached 691.23 mg/Kg in the Yiluo River - one tributary of the Yellow River. (3) Whether in the sediment or on the suspended solid phases, there was no significant correlation between the contents of PAEs and TOC or particle size of the solid phase; and the calculated Koc of Di (2-Ethylhexyl) Phthalate (DEHP) in the river were much less than the theoretical value, which inferred that PAEs were not on the equilibrium between water and suspended solid phases/sediment. (4) Among the measured PAEs compounds, the proportions of DEHP and di-n-butyl phthalate (DBP) were much higher than the others. The concentrations of DEHP exceeded the Quality Standard in all the main river and tributary stations except those in the Mengjin and Jiaogong Bridge of the main river. This indicates that more attention should be paid to pollution control and further assessment in understanding risks associated with human health.

The equilibrium partitioning (EqP) method has been applied to establish sediment quality criteria (SQC); however, it does not consider the nonlinear irreversible sorption of many organic contaminants. In this research, the sorption and desorption of two phthalate esters (PAEs), dimethyl phthalate (DMP) and di(2-ethylhexyl) phthalate (DEHP), in four natural sediments collected from the Yangtze River and the Yellow River were studied; the impact of irreversible sorption of DMP and DEHP on SQC has been evaluated. Based on the reversible and irreversible biphasic sorption model, the values of maximum irreversible sorption capacity (q(max)(irr)) were 125.19 μg g(-1)-337.37 μg g(-1) for DMP and 515.87 μg g(-1)-591.40 μg g(-1) for DEHP. The q(max)(irr) value was positively related to the organic carbon and black carbon contents, cation exchange capacity, and surface area of the sediments. The values of the irreversible sorption coefficient K(oc)(irr) for both DEHP and DMP in the four sediments approximated to a constant of 10(6.46 ± 0.38), which was 1-2 orders of magnitude higher than their reversible sorption coefficient K(oc)(irr). The values of SQC for PAEs based on the EqP method were modified by involving the irreversible sorption. The modified SQC of DEHP could be 2 to 20 times higher than the value predicted by the EqP method, and the assessment results for DEHP contamination in the sediments with the modified SQC were more reasonable than those with the non-modified SQC. It indicated that the current SQC based on the EqP method may be unnecessarily strict for specific organic compounds and the irreversible sorption should be taken into account.