Daily variations and factors of atmospheric PCDD/Fs in post-harvest paddy fields: PCDD/F source estimation using a Bayesian semi-factor model

Abstract

We investigated the daily variations in the concentration of atmospheric dioxins (PCDD/Fs and DL-PCBs) in paddy fields after the autumn harvest. The geometric mean of the concentrations of dioxins during the research period was 0.042 pg-TEQ/m3, and the concentrations ranged from 0.0058 to 0.53 pg-TEQ/m3. When the weather was calm with no rain or snow and the atmosphere was stable, relatively high concentrations of dioxins were observed. The characteristics of congeners and homologues produced through the combustion of PCDD/Fs were classified into four groups using principal component analysis and cluster analysis. In addition, agricultural chemicals (pentachlorophenol, PCP and chlornitrofen, CNP) were identified as the source of PCDD/Fs using a Bayesian semifactor model. When the dioxin concentrations were high, the combustion of TeCDFs and PeCDFs produced large emissions, representing the impact of open burning of rice straw. When the dioxin concentrations were low, the contribution of CNP was strong, indicating the effects of the release of previously used agricultural chemicals from the soil.