Evaluation of the environment risk, fractions and mobilization of nickel (Ni) in sediments of the Jialing River by sediment quality guidelines, sequential extraction and Chelex-AgI gel DGT probe

The Jialing River is one of the largest tributaries of the Yangtze River and has the largest drainage area. Nickel (Ni) is a one of the most serious heavy metal contaminants in the downstream section of the Jialing River as a result of the prosperity of nearby chemical, electronic and mining industries. In the present work, sediment quality guidelines (SQGs), a Community Bureau of Reference (BCR) sequential extraction and the diffusive gradients in thin films (DGT) technique were applied to evaluate the environment risk, fractions and remobili- zation of Ni in the downstream Jialing River. The results indicated that the average total concentration of Ni (54.7 mg kg(-1) ) at all sites was higher than the background values of soil in China and Sichuan (26.9 and 35.8 mg kg(-1) , respectively). Environment risk assessment with four types of SQG values found that at three sites, the Ni concentration was over two high guideline values (probable effect concentration, PEC; effect range median, ERM), indicating that Ni may frequently pose a threat to the local aquatic ecosystem. The DGT results showed that C DGT -Ni had an inverse variation trend with C DGT -Fe and presented a significant increasing trend at the bottom of the DGT probes. Flux results revealed that sediments at S1, S2 and S3 were the source for Ni release across the sediment -water interface (SWI), and only S4 was a sink for Ni. Two further studies found that C DGT - Ni presented a significant negative correlation with C DGT -Fe. In addition, the hotspot of C DGT -Ni at the bottom correlated well with the ?dark area ? of C DGT -S. These results indicated that Fe and S were factors that mitigated the release of Ni in the sediments.