The objectives of this study were to investigate the distribution of thallium in soils collected near suspected areas such as cement plants, active and closed mines, and smelters and to examine the extraction of thallium in the soils using 19 single chemical and sequential chemical extraction procedures. Thallium concentrations in soils near cement plants were distributed between 1.20 and 12.91 mg kg(-1). However, soils near mines and smelters contained relatively low thallium concentrations ranging from 0.18 to 1.09 mg kg(-1). Thallium extractability with 19 single chemical extractants from selected soils near cement plants ranged from 0.10% to 8.20% of the total thallium concentration. In particular, 1.0 M NH4Cl, 1.0 M (NH4)2SO4, and 1.0 M CH3COONH4 extracted more thallium than other extractants. Sequential fractionation results of thallium from different soils such as industrially and artificially contaminated soils varied with the soil properties, especially soil pH and the duration of thallium contamination.

Remediated soil can be one of valuable resources for sustainable agriculture after improving its quality and properties with proper treatments. Therefore, this study was conducted to estimate changes in soil properties and soil quality for improving remediated soil contaminated with petroleum as affected by the applications of various organic amendments as soil conditioners including biochar (BC), charcoal (CC), and livestock manure compost (LC). Two remediated soils, remediated soil A and B (RSA and RSB) that previously contaminated with different concentrations of total petroleum hydrocarbons, were alkaline soils with up to 8.5 of soil pH, very low soil organic matter (SOM) contents and available phosphate (available P 2 O 5 ) concentrations, and very high exchangeable Ca concentrations. Thus, these soils had very unfavorable conditions for crop growth. RSA and RSB were treated with BC, CC, and LC in levels of 0.0%, 1.0%, and 5.0% on dry weight bases. The remediated soils treated with organic soil conditioners were incubated for 2, 4, 8 and 16 weeks at room temperature (24 ± 2°C). SOM contents increased with all the treatments. In particular, SOM in RSB increased up to 19.5 g kg -1 with BC 5.0% treatment (BC5, 16-week), which was 2 times higher than that in both RSA and RSB soils without BC applications (Control soils). Also, available P 2 O 5 concentrations increased to 24.9 mg kg -1 (RSA, 16-week), and 17.0 mg kg -1 (RSB, 8-week) with BC5. However, available P 2 O 5 concentration in the remediated soils was very lower than that of the optimal value for cultivating crops suggested by National Institute of Agricultural Sciences in the Republic of Korea. Available P 2 O 5 was negatively correlated with soil pH (p < 0.01) and exchangeable Ca (p < 0.01). Soil quality index (SQI) and weight additive soil quality index (SQI W ) were positively correlated with SOM (p < 0.01). The mean value of soil quality indices were 39.3, 56.0, 40.0, and 54.5 for RSA Control, RSA BC5, RSB Control, and RSB BC5, respectively. The highest soil quality index was found in the remediated soil with BC treatment. The remediated soils require the immediate solution for the poor soil quality, and thus should need methodical and continuous management.