Author(s): Shinichiro Yano, Takaaki Taninaka, Edistri Nur Fathya, Satoshi Matsumoto, Akito Matsuyama, Akihide Tada, Herawaty Riogilang
Linked Author(s): Shinichiro Yano
Keywords: Mercury, particle size distribution, suspended solids
Abstract: Minamata disease was officially confirmed in Japan, in 1956. Although 60 years have passed, it has been concerned about influence of mercury released into natural environments on human health around the world. To manage risks of mercury in marine environment, to understand mercury dynamics is necessary. In order to develop a numerical model to predict mercury fate, we have been carrying out monthly in-situ measurement of mercury concentration in seawater from 2006. We have carried out seawater sampling in five layers at three observation points in Minamata Bay around the maximum ebb tide to measure mercury concentration, and also in-situ measurement of suspended solids (SS) particle size distribution (PSD) by LISST-100X, which is the only instrument to observe PS spectrum of SS in in-situ seawater directly. Yano et al. (2013) found out the weak correlation between particulate total mercury (P-THg) concentration and SS-PSD by using the data from 2010 to 2011. However, there was a problem for reliability because of subjective method to divide data into groups. In this study, we used a cluster analysis to divide the data. Secondly, we judged the best grouping using the entropy method. This method can determine the optimal number of group, into which the shape of PSD is categorized. Thirdly, we confirmed statistical significance of relationship between each group and P-THg concentration with both of Bartlett test and Kruskal-Wallis test. Finally, we tried to determine relationship between P-THg concentration and SS-PS fraction. As a result, the followings were found: (1) The most optimal group number of SS-PSD was six; (2) Statistically significant correlation between P-THg and SS-PSD was seen; and, (3) It can be seen from the present relationship between P-THg and SS-PS fraction that P-THg depends on source of SS and mixing condition with SS from rivers and other possible sources
Year: 2017