Abstract
This study evaluated the sources of Zn pollution in Tokyo Bay, Japan, on the basis of δ66Zn in a sediment core. The Zn concentration in sediments in the 1980s-2000s was considerably higher than the background concentration, suggesting that there remain important sources of Zn in the bay. The δ66Zn (+0.51‰) of anthropogenic Zn estimated in the core was significantly higher than those (approximately –0.1‰ - +0.2‰) of treated water from sewage treatment plants and vehicle-related sources. A large number of electroplating plants are located in Tokyo areas. It is assumed that Zn in effluents from electroplating operations is isotopically heavier owing to a negative isotopic effect on Zn electroplating. This tends to support the hypothesis that river bottom sediments, which were contaminated with Zn in the untreated effluents from electroplating plants in the past, are the principal sources of anthropogenic Zn in Tokyo Bay in the 1980s-2000s.
Highlights
Aquatic regions, which are surrounded by populated and industrialized areas, accumulate toxic trace substances, including heavy metals, organochlorine compounds (e.g., PCBs and dioxins), and other compounds of anthropogenic origin
It is assumed that Zn in effluents from electroplating operations is isotopically heavier owing to a negative isotopic effect on Zn electroplating. This tends to support the hypothesis that river bottom sediments, which were contaminated with Zn in the untreated effluents from electroplating plants in the past, are the principal sources of anthropogenic Zn in Tokyo Bay in the 1980s-2000s
Zn in the untreated effluents from electroplating plants may explain the high δ66Zn of anthropogenic Zn in the sediments from Tokyo Bay. If this is the case, it is assumed that the untreated effluents from electroplating plants located in the Tokyo area were discharged directly into rivers before the 1970s when pollution control was not sufficiently established, and contributed significantly to Zn pollution in Tokyo Bay
Summary
Aquatic regions, which are surrounded by populated and industrialized areas, accumulate toxic trace substances, including heavy metals, organochlorine compounds (e.g., PCBs and dioxins), and other compounds of anthropogenic origin. The history of pollution by these metals has frequently been recorded in sediment cores from closed aquatic regions such as bays and lakes. A downward historical trend of their pollution has been generally observed in the cores owing to pollution control in industries and utilities (e.g., Hirao et al, 1986; Pearson et al, 1997; Fox et al, 1999; Hornberger et al, 1999; Yasuhara & Yamazaki, 2005; Heim et al, 2004; Mahler et al, 2006; Sakata et al, 2008; Hosono et al, 2010). Clarifying the sources in aquatic environments is essential for achieving the effective reduction of the environmental risks associated with Zn and the conservation of ecosystems (Tang et al, 2014)
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