Geochemical controls on the distribution of mercury and methylmercury in sediments of the coastal East China Sea

• Published in: The Science of the total environment 2019-06, Vol.667, p.133-141
• Main Authors: Zhao, Lu, Wang, Rui, Zhang, Chi, Yin, Daqiang, Yang, Shouye, Huang, Xiangtong
• Format: Article
• Language: English
• Subjects: Methylation; Organic matter; Particle size; Sediment; Yangtze River
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2019.02.334

We examined the spatial and vertical distribution of total mercury (THg) in 119 surface sediment samples and 4 sediment cores from the coastal East China Sea. The THg concentrations (3.6–69.2 μg kg−1, average 34.7 μg kg−1) in surface sediments exhibited a decreasing trend from the inner shelf towards the outer shelf. The THg levels in sediment cores showed a significant increasing trend from the bottom to the top layer. Both the spatial and vertical distribution of THg indicates the impacts of anthropogenic inputs. The THg concentrations in the surface sediments of Yangtze River estuary were strongly correlated with sediment particle size and organic matter, governing by the Yangtze River inputs. The relatively higher THg levels in the surface sediments of southern inner shelf were attributed to the stronger binding affinity of the finer-grained sediments, the nature of organic matter, as well as local inputs. The spatial distribution of toxic methylmercury (MeHg) was distinct from THg, controlled by direct terrigenous MeHg inputs and in situ MeHg formation. The net Hg methylation potential (indicated by MeHg/THg ratio) in surface sediments were significantly influenced by both geochemical factors (DO, temperature and water depth) and the physicochemical properties of sediments (grain size, TOC, S, Fe2O3 and MnO), and exhibited the highest correlation with TOC, suggesting the key role of organic matter in governing net MeHg production. Moreover, sites with high MeHg/THg ratios mainly occurred within the summer hypoxia zones adjacent to the Yangtze River estuary, suggesting special attention on Hg ecological risks should be paid in this region. [Display omitted] •Sediments THg distribution in East China Sea (ECS) indicates anthropogenic inputs.•Organic matter and sediment grain size control the spatial distribution of THg.•Terrigenous inputs and in situ MeHg formation control the MeHg spatial distribution.•Organic matter plays key role in governing Hg methylation potential in the ECS.•Sites with high methylation potential mainly occurred in the summer hypoxia zones.