Accumulation and transformation of heavy metals in surface sediments from the Yangtze River estuary to the East China Sea shelf

The concentration and speciation of heavy metals (Cu, Co, Ni, Zn, Cr, Pb and Cd) were studied in surface sediment from the Yangtze River(YR)to the East China Sea (ECS) shelf. The results showed that high contents of metals were found in the YR estuary (YRE) and in the nearshore muddy area, while lower concentrations were found in the YR channel and the ECS shelf. However, after standardization, the total content of most heavy metals from the YR showed little change or slightly increased during the transport process from the river to the estuary but decreased significantly outside the estuary, especially in the sediments of the ECS shelf. The residual fraction is the dominant fraction for all the metals, while the oxidizable and reducible fractions are the most important forms of the nonlithogenic fractions. The total amount of heavy metals from the YR to the continental shelf is mainly affected by the filtration of the estuary and the barrier impacts of the coastal current in the ECS. The environmental physicochemical conditions that vary significantly in the turbidity zone greatly influence the associated forms of metals. The metals in the acid-soluble fraction are mostly affected by the pH change in the sediment and the discharge of human activities, while the reducible fraction is significantly affected by the bottom water DO. The oxidizable fraction was affected by oxidation-reduction potential (ORP), primary productivity, as well as OM content. Therefore, with changes in the physicochemical conditions of the environment, the metals have undergone significant changes in their speciation from the YR to the ECS shelf. Various complex effects in the estuary area have not only a large filtration effect on the total amount of metals but also a major impact on the geochemical forms of the metals. (C) 2018 Elsevier Ltd. All rights reserved.

对长江（YR）至东海（ECS）陆架表层沉积物中重金属（铜、钴、镍、锌、铬、铅和镉）的浓度及形态进行了研究。结果表明，在长江河口（YRE）和近岸泥质区发现金属含量较高，而在长江河道和东海陆架含量较低。然而，经标准化后，长江中大多数重金属的总含量在从河流到河口的输送过程中变化不大或略有增加，但在河口外显著降低，特别是在东海陆架的沉积物中。残余态是所有金属的主要形态，而可氧化态和可还原态是非岩石成因部分的最重要形态。从长江到大陆架的重金属总量主要受河口过滤和东海沿岸流的阻隔影响。浊度区显著变化的环境物理化学条件极大地影响了金属的结合形态。酸溶态金属主要受沉积物pH值变化和人类活动排放的影响，可还原态金属则显著受底层水溶解氧（DO）的影响。可氧化态受氧化还原电位（ORP）、初级生产力以及有机质（OM）含量的影响。因此，随着环境物理化学条件的变化，从长江到东海陆架金属的形态发生了显著变化。河口地区的各种复杂作用不仅对金属总量有较大的过滤作用，而且对金属的地球化学形态也有重大影响。（C）2018爱思唯尔有限公司。保留所有权利。