Studies on Chemical Forms of the Mercury Compound in the Mud of Minamata Bay

Abstract

In the mud of Minamata Bay from where the Minamata disease was originated, a large amount of mercury compound(s) has been deposited, and the majority of it has been estimated to be chemically inactive mercury (II) sulfides.
In this study, a mercury compound(s) hitherto unknown and soluble in dimethyl sulfoxide (DMSO) was detected from dried samples of the mud collected at the three locations of MinaInata bay and its properties were investigated.
The total mercury in the mud w as 44∼152μg/g, dry weight, in which the DMSO-soluble mercury accounted for 1.0∼4.6% of the total. Its percentage appreciably differed among the sampling locations. The DMSO-soluble mercury changed in amount during the passage of time, which was confirmed by the measurement of content of the reducible mercury i. e., the mercury directly reduced with tin(II) chloride. When separated on a reversed-phase column, the reducible mercury was eluted in the fraction nearby the void volume; this mercury compound was assumed to be a salt of inorganic mercury compound(s).
Utilizing the property of mercury(II) halide to form a comple x with halide ions in excess, a method has been established to analyze the mercury compound by ion-pair chromatography in the presence of the counter ion. By this method, the reducible mercury is confirmed as a mercury(II) halide. Since th emethylation of inorganic mercury is considered to take place through a soluble mercury(II) compound(s), a possibility is suggested that the reducible mercury found in this study may account for one of themercury compounds contributable to the methylation.