Extraction of organic pollutants from environmental solids with sub- and supercritical water

Low-polarity organic pollutants such as polycyclic aromatic hydrocarbons (PAHs) typically have very low solubilities (e.g., ppb) in water at ambient conditions because of water's high polarity (dielectric constant, [epsilon] = 80). However, the dielectric constant can be drastically lowered by raising the temperature of the water under moderate pressure with dramatic increases (e.g., to percent levels) in the solubility of low-polarity organics. For example, subcritical water at 250[degree]C and 50 bar has [epsilon] = 27, which allowed quantitative extractions of PAHs in 15 min from soil and urban air particulates. Decreasing the polarity of water by sequentially raising the extraction temperature from 50 to 250[degree]C (subcritical water) and finally to 400[degree]C (supercritical water if P > 221 bar) allowed class-selective extractions of polar organics (e.g., chlorinated phenols), low-polarity organics (e.g., PAHs), and nonpolar organics (alkanes) to be performed. Simple methods for using sub- and supercritical water for quantitative extraction of organics from environmental solids are presented. 30 refs., 6 figs., 5 tabs.

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