Effect of soil layer thickness on the environmental fate of organic chemicals by the sensitivity analysis using fugacity model
2006
Wei, Y.(National Inst. for Agro-Environmental Sciences, Tsukuba, Ibaraki (Japan)) | Kobara, Y. | Nishimori, M.
Soil depth is an important parameter used in multimedia models for estimating the environmental fate of bio-accumulative chemicals in such uncultivated land as forest and grassland. In this study, by using six hypothetical chemicals with different Log Kow values as the targets, the impacts of changes in the uncultivated soil depth upon the environmental persistence and the mass fraction partitions of these chemicals were evaluated under four different emission scenarios based on the well-used EQC model. The results showed that, for all emission scenarios, the environmental persistence and the mass fraction partitions varied in terms of the soil depths. The most remarkable variance was found for both scenarios that represented a complete emission to soil and an equal emission to air, water and soil, respectively. Besides, sensibility analysis results indicated that, for chemicals having Log Kow values above four, the impacts of changes in the soil depth became no longer notable; and a tendency of residence within the surface 5 cm layer of the soil medium was revealed. These coincided with those obtained based on the OECD guideline and other existing data, thus suggesting that a depth of 5-20 cm for uncultivated soils, which has been conventionally used in existing multimedia models, may overestimate the contribution of the soil medium. It is concluded that soil depth of 5 cm is sufficient; especially for multimedia models aimed for assessment of the environmental fate of highly bio-accumulative chemicals having Log Kow above four.
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