Estimation of Residual Amount and Outflow of Dioxins in Paddy Soil in Kanagawa

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  • 水田土壌中のダイオキシン類残留量及び流出量の推計
  • スイデン ドジョウ チュウ ノ ダイオキシンルイ ザンリュウリョウ オヨビ リュウシュツリョウ ノ スイケイ

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Abstract

Environmental risk management is important concept for taking better countermeasures, in particular the estimation of sources and mass abundances are requisite to reduce the risk from persistent organic pollutants (POPs) in the environment and make administrative services more efficient. POPs such as the Dioxins is toxic, resist degradation, bio-accumulate and “Stockholm convention on persistent organic pollutants” was adopted in 2001. The Convention prescribes that each party should implement, for example, measures to reduce or eliminate releases from unintentional production. Therefore the grasp of the present status by dioxins pollutions released from unintentional production in the past is important.<BR>In this study, we conducted a survey on the concentration and congener information of dioxins in samples of paddy soils by three layers, saved samples, rivers, its environmental investigation, and then presumed their sources and mass abundances in Kanagawa prefecture, Japan. The concentration of dioxins was 93 pg-TEQ/g in first layer (0∼15 cm) of paddy soils, 53 pg-TEQ/g in second layer (15∼30 cm), and 3.1 pg-TEQ/g in third layer (30∼45 cm). In order to identify the dioxin source in the first layer of paddy soil, the multiple regression analysis was applied. It was found major two sources: pentachlorophenol (PCP), and chloronitrophen (CNP) amounts to about 90 %. PCP and CNP contained dioxin as impurity and were used extensively as paddy field herbicides in Japan in 1960s ∼ 1970s. The outflow of dioxins from paddy soil was estimated to be 2.97μg-TEQ/10a. Compared with the amount remaining in paddy soils 0.0151 % of dioxins have been flowed out from paddy field at 1 year. The concentration of dioxins from preserved samples showed that its half-lives in paddy soils were calculated to 11∼45 years. Further, dioxins concentrationin Zenba river estimated to be 2.2 pg-TEQ/L in irrigation period, 0.54 pg-TEQ/L in non-irrigation period, and 0.99 pg-TEQ/L in annual average concentration that considered direct influence of paddy field by the irrigation.

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