EXTRACTION OF ORGANIC POLLUTANTS FROM ENVIRONMENTAL SOLIDS WITH SUBCRITICAL 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 degrees 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 degrees C (subcritical water) and finally to 400 degrees 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.