2001 年 35 巻 4 号 p. 159-168
On the basis of the congener-specific analysis of dioxins in a dated sediment core, surface sediment, and soil samples, the sources and mass balance of dioxins in Tokyo Bay basin, Japan, were estimated. The dioxins in the sediment core showed that their deposition in the bay increased rapidly during the 1960s, peaked in the early 1970s and then decreased gradually. Principal component analysis of the congener-specific data showed that three major sources existed: combustion, pentachlorophenol (PCP), and chloronitrophen (CNP). PCP and CNP are paddy field herbicides used extensively in Japan in the past. The time trends of source contributions were estimated by multiple regression analysis using the source congener profiles. The results revealed that dioxin emission from PCP and CNP herbicides was high in the 1960s and the early 1970s, respectively. The total contribution in terms of TEQ from the two herbicides was at their maximum of 70% in the 1970s and decreased thereafter. Their contribution, however, was as high as 50% in recent sediment, indicating that dioxins sprayed as herbicide impurity were still remaining in terrestrial soil and river sediment of the basin and running off gradually.
