SUBSTANTIAL MIGRATION OF DIOXINS IN AGROCHEMICAL FORMULATIONS

摘要

Contaminants with low water solubility and high carbon-water partitioning are generally considered to have low mobility in soils. However, the presence of co-contaminants can act as transport facilitators for otherwise low mobility organic compounds (LMOCs). Little is known about facilitated contaminant migration and this process is rarely considered in evaluations of off-site transport and groundwater contamination potential for LMOCs. This study investigated the vertical migration of dioxins in soil, released together with high volumes of pesticides and adjuvants following an accidental fire at a pesticide production facility. Two intact cores (to 6.7 m) were obtained below clay-lined ponds where contaminated run-off water was contained. PCDD/Fs were found throughout both cores, with maximum concentrations (130 and 94 ng/g) at 2-2.5 meters. A reversed mobility was observed throughout the core depths with the least mobile congener OCDD transported further than the relatively more mobile TCDD. Such a reversal is consistent with surfactant facilitated transport, which is suggested to be the primary pathway for the observed migration. These results highlight that the paradigm of LMOCs being non-mobile in soils should be considered carefully together with application-specific and environmental factors which may have the ability to considerably change the predicted environmental fate of these chemicals.