水田土壌における残留性有機汚染物質（POPs）の長期的消長

- 秋田県米代川流域を例として-

抄録

The concentrations of persistent organic pollutants (POPs) in paddy soil samples collected in 1982 and 1984 (1980s) and in 2000 and 2002 (2000s) from the Yoneshiro River basin, Japan, were measured to elucidate the temporal trend and mass balance of POPs in paddy soils. Aldrin, dieldrin, endrin, chlordanes and heptachlors were rarely detected in almost all the samples collected in the 1980s and 2000s, whereas DDTs, HCHs, HCB and PCBs were detected in relatively many samples. The concentrations of these compounds were lower than the PCDD/DF concentrations reported in our previous study regardless of sampling year. The concentrations of p,p'-DDD, α-HCH, β-HCH,δ-HCH and lower-chlorinated PCBs (M₁CB, D₂CB, T₃CB and T₄CB) decreased significantly (paired t-test, p<0.05) from the 1980s to 2000s, whereas those of the other compounds such as higher-chlorinated PCBs did not decrease. The half-lives of the compounds were calculated as follows: p,p'-DDD, 5.2 years; α-HCH, 5.6 years; β-HCH, 5.0 years; δ-HCH, 4.0 years; M₁CB, 4.5 years; D₂CB, 5.8 years; T₃CB, 5.5 years; and T₄CB, 8.5 years. The half-lives of these compounds correlated with their water solubility. We estimated the total input and remaining amounts of DDTs and HCHs in the paddy fields to determine their long-term fate in the basin within the period of 1962∼2002. Result of the estimation, revealed that approximately 97 % of the DDTs and HCHs applied to the basin were disappeared from the paddy soil by the 1980s.