Geochemical Characteristics Of Heavy Metals Pollution In Sediments From Tuojiang Drainage

The author chooses sediments of Tuojiang drainage as the subject of research. The total concentration and speciation of elements (As,Cd,Cr,Ni,Cu,Pb,Zn), were determined in sediment cores collected from the Tuojiang drainage. Based on this, the spatial and temporal distributions, speciation, sources, transport and accumulation were investigated. Several ecological assessment methods, which based on two different assessment systems (total concentration and sequential extraction), were applied to assess the heavy metals pollution and potential biotoxicity in sediments from the Tuojiang drainage. The interrelationship and correspondence relationship of different evaluation methods were also discussed. The research resμlts are as follows.The result showed that the average content of some elements: Mianyuan River: As 10.04μg/g, Cd 0.79μg/g, Hg 0.09μg/g; Shiting River: As 6.72μg/g, Cd 0.99μg/g, Hg 0.85μg/g; Tμojiang River: As 11.84μg/g, Cd 1.48μg/g, Hg 0.67μg/g. In the spatial distribution, the results show that before two tributaries converged, the content of heavy metals increase from upper to downstream. After two tributaries converging, the contents of heavy metals increase obviously, which shows that additive effects of two rivers have greater impacts on the downstream of Tuojiang River. Compared with previous stμdies, the content of heavy metals increased.The speciation characteristics of heavy metals were determinated. Various heavy metals in residua, and changes of the content of recoverable fraction was slight. The proportion of acid soluble heavy metals, acid soluble in the proportion present in the geographical a certain degree of variation. Acid soluble in the upper reaches higher than downstream and migration of heavy metals is strong, while it is poor in the downstream. Different metals have different proportion of the acid in this research, Cd, Pb, As and Ni in migration is strong; while Cr, Cu, Zn migration is poor. Based on the potential ecological risk of heavy metals total concentration evaluation, Cd is the main pollution factor in the Tuojiang River Drainage sediments. The potential ecological risk of Cd is medium in Mianyuan River and Shiting River, and strong in Tuojiang River. The pollution degree of mianyuan is, Cd> As> Hg> Pb> Cu> Cr> Zn; Shiting River, Cd> Hg> Pb> Cu> As> Cr> Zn; Tμojiang, Cd> Hg> Pb> Cu> As> Cr> Zn. The contamination levels of sediments are from light to moderate; Tuojiang River is more serious than Shitingjiang River and Mianyuanhe River.Based on the potential ecological risk evaluation of heavy metals speciation the morphological evaluation of two different overall results are consistent, the entire river drainage. The potential ecological risk of Shiting River was the highest the pollution, followed by the Mianyμan River, Tuojiang River pollution in the slightest, which is different from total heavy metals of potential ecological risk assessment. The result of RSP: the extent of pollution of all elements are different, Cd is in the most serious pollution. For the various elements of sort, as follows: Cd> As> Cu> Ni> Pb> Zn > Cr. The resμlt of Phase Enrichment Factor (PEF): Cd is in the most serious pollution.