Dioxin Impurity in Agrochemicals

Abstract
While dioxins have been known to be formed as by-products in the synthesis process of chloroaromatics, incineration processes have received attention in Japan. Some Japanese agrochemical formulations, however, were found to have contained high concentrations of dioxins. These are pentachlorophenol (PCP) and chloronitrophen (CNP) which were used extensively as herbicides in the 1960s and 1970s. The amount of dioxins sprayed on agriculture fields in the 1960s and 1970s, was estimated to be nearly 20 kg TEQ/year. The dioxin emissions from other agrochemicals were estimated to be negligible compared to these two chemicals.
The dioxin concentration recorded in the sediment core of Tokyo Bay and Lake Shinji revealed a trend of dioxin pollution caused by the use of PCP and CNP. The pollution was at the highest around 1970 and decreased gradually thereafter. However, the pollution has not decreased enough in the surface sediment, probably due to the runoff from agricultural fields. Counter measures against the dioxin stock in the environment, burying agrochemicals in the soil as a disposal measure, and those kept unused in farmer's barns should be considered.

Key words: dioxin, agrochemical, impurity, pentachlorophenol, chloronitrophen