Persistent organic pollutants in rain at Niigata, Japan

Abstract Atmospheric monitoring of POPs ( α -HCH, HCB and p , p ′-DDT) was conducted at three different sites in Niigata area, Japan, the first characterized as remote (top of a mountain, 634 m height), the second suburb and third urban. Concurrent and continuous samplings through seven days of environmental air and rain were carried out in the term from May to November 2001. Weighted average concentrations in rain are 585–710 pg l −1 for α -HCH, 67–80 pg l −1 for HCB and 30–52 pg l −1 for p , p ′-DDT. No significant difference was observed in weight average concentrations of POPs in rain among the three sites, while the average atmospheric concentration of POPs at the remote site was lower than those at other sites. The concentrations of HCB and DDT in rain varied depending on the rainfall: the concentrations of DDT and HCB showed higher values in the less rainfall weeks. On the other hand, the concentration of α -HCH hardly depended on the rainfall. The H ′ value defined as the ratios of POPs concentrations in air to those in rain were calculated and compared to the Henry’s law constant, H . The H ′ value of α -HCH at high temperature is compatible with H value, which indicates that equilibrium is established between α -HCH in rain and that in ambient gaseous phase. However, the H ′ values were lower than the H values at lower temperature, and larger difference between H ′ and H was observed at the lower temperature. This could be interpreted by an increase of particulate α -HCH existing in solid phases such as suspended particles or dry depositions. For HCB and DDT, the H ′ values were smaller than the H values in all the temperature ranges, indicating that these substances tend to be adsorbed on particulate matter in ambient air, and tend to be deposited on the ground directly and/or by rain.