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The octanol-air partition coefficient ͑K OA ͒ is a key physicochemical parameter for describing the partition of organic pollutants between air and environmental organic phases. Experimental determination of K OA is costly and time consuming, and sometimes restricted by lack of sufficiently pure chemicals. There is a need to develop a simple but accurate method to estimate K OA. In the present study, a fragment constant model based on five fragment constants and one structural correction factor, was developed for predicting log K OA at temperatures ranging from 10 to 40°C. The model was validated as successful by statistical analysis and external experimental log K OA data. Compared to other quantitative structure-property relationship methods, the present model has the advantage that it is much easier to implement. As aromatic compounds that contain C, H, O, Cl, and Br atoms, were included in the training set used to develop the model, the current fragment model applies to a wide range of chlorinated and brominated aromatic pollutants, such as chlorobenzenes, polychlorinated naphthalenes, polychlorinated biphenyls, polychlorinated dibenzo-p-dioxins and dibenzofurans, polycyclic aromatic hydrocarbons, and polybrominated diphenyl ethers, all of which are typical persistent organic pollutants. Further study is necessary to expand the utility of the method to all halogenated aliphatic and aromatic compounds.

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This paper described a multi-layer column device constructed with six cylindrical polythene tubes with installation of Rhizon soil moisture samplers (Rhizon SMS). The feasibility of using the column device to collect soil solution and percolate and to monitor leachability of nitrate in two sludge-amended soils was evaluated under glasshouse conditions. The soil moisture sampler in the device was demonstrated to be a non-destructive, simultaneous, sequential, convenient and rapid sampling tool for multiple-site porewater extraction. The device provided an in situ monitoring technique for leachability of nitrate in a soil profile following application of the anaerobically digested sewage sludge. The monitored results showed that surface soil amendment of the sewage sludge increased markedly the concentration of nitrate in the soil solutions at depths of 10-30 cm in a neutral paddy soil and at 30-50 cm in an acid red paddy soil. This amendment also largely increased nitrate in the percolates of the acid red soil. The movement and distribution patterns of nitrate in the profile were related to soil types, profile depths and experimental periods. Land application of sewage sludge may pose a risk in groundwater contamination of nitrate.

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