The Temporal and Spatial Distribution of Mercury and Arsenic in the Central Bohai Sea

Abstract:

To study the temporal and spatial distribution of Mercury (Hg) and Arsenic (As) in the central Bohai Sea, we collected water samples of the surface, middle, and bottom layers in four survey cruises in May (spring), July (summer), November (autumn) and December (winter) in 2013. The results showed that the content of Hg was in the range of 0.0029–0.3926 μg/L with an average of 0.0676 μg/L. The vertical distribution of Hg concentration followed the order: bottom layer > middle layer > surface layer; the seasonal distribution showed the pattern: spring > winter > autumn > summer. Except for the surface layer in summer, Hg concentration in all water samples failed to meet the national water quality standard (GB3097–1997). The concentration of As ranged from 0.65 to 10.83 μg/L with the mean value of 1.50 μg/L, which met the requirement for the national water quality standard (GB3097–1997). The vertical distribution of As followed the order: surface layer > middle layer > bottom layer, and the seasonal distribution displayed an even pattern. The limit of As concentration is 20 μg/L according to the national water quality standards, thus the As level met the first water quality standard. However, the Hg level was readily higher than the first (0.05 μg/L) or second water quality national water quality standard (0.20 μg/L). These data suggested that the overall water quality of the central Bohai Sea was unsatisfying, and there was obvious pollution probably caused by human activities. Therefore the environmental risks in the Bohai Sea should be carefully evaluated in the future economic activities.