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Chloroform‐extractable green fraction (CEGF) was detected in the supernatant obtained by alkali precipitation from the HCI‐dimethylsulfoxide (DMSO) extract of Pg‐rich soil. In the alkaline solution, the color of CEGF was green and CEGF showed strong Pg‐like absorption bands. Ultraviolet and visible (UV‐VIS) spectral analysis and gel chromatography on Sephadex G‐50 were performed to compare several properties between CEGF and Pg. CEGF, which was purified by gel chromatography on Bio‐Beads SX‐1, displayed strong absorption bands at 609, 562, 445 and 280 inn in the alkaline solution. These absorption bands were almost similar to those of Pg. Furthermore, the UV‐VIS spectrum of CEGF in the organic solvents showed a similar characteristic pattern of 4,9‐dihydroxyperylene‐3,10‐quinone (DHPQ), which was considered to be a chromophore of Pg. Based on the results of gel chromatography on Sephadex G‐50, CEGF mainly consisted of two fractions, corresponding to the G2 and G3 fractions of Pg. These results indicated that the method for extracting CEGF from Pg‐rich soil in the present study was easy and selective and that CEGF was one of the components of, or a closely related substance to Pg. A colorimetric method for the estimation of the CEGF content in soils was developed. The calibration curve of CEGF was linear over a wide range of contents from 2.75 to 220 mg L−1. The CEGF content in twelve samples of various soils was examined. CEGF was detected in all the soil sampled (5 orders) including three samples (3 orders) where Pg was not detected, and the content ranged from 0.07 to 1.66 g kg−1 (dry soil). Therefore, the method for estimating the CEGF content in soils developed in the present study was found to be suitable for various soil orders and it was assumed that CEGF occurred in various soil orders.

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The aim of this research was to evaluate the feasibility of aqueous saponin for the removal and biodegradation of polycyclic aromatic hydrocarbons (PAHs) from contaminated soil. Dissolution test confirmed the ability of saponin to increase the apparent solubility of the tested 3-5 rings PAH above the critical micelle concentration (approximately 1000 mg/L). Microbial test with pure culture of Sphingomonas sp. showed that saponin significantly enhanced the degradation of pyrene. For example, the percent degradation was 2.1 times higher in the presence of 2500 mg/L saponin than that of control without saponin after 60 hours incubation at around 10(8) CFU/mL initial cell loading. These results suggest that the binding of pyrene with saponin does not pose a serious constraint to bacterial uptake. Contrary to pyrene, saponin was chemically stable against the PAHs degrader. It is also not toxic to the cell at least up to 2500 mg/L. Finally, using a spiked soil sample, extraction tests with 10,000 mg/L of saponin showed that around 52.7% and 0.3% of pyrene was removed from low and high organic spiked soils, respectively. The results from this study indicate that aqueous saponin is appropriate as a washing agent as well as biodegradation enhancer for the detoxification of PAHs-contaminated low organic carbon soil.