Pressurised hot water/steam extraction of polychlorinated dibenzofurans and naphthalenes from industrial soil

Unique solvent properties of water, which can be changed by adjusting the temperature, were fully exploited to extract low polarity organic pollutants from soil samples. Solubility enhancement of the non-polar compounds due to the temperature increase of water together with enhanced thermal desorption and compounds' vapour pressures theoretically and in practice opens the way to extract this kind of compound with pure water. Pressurised hot water extraction (PHWE), here defined as both water and steam extraction, of spiked polychlorinated dibenzofurans (PCDFs) from sand was investigated under different conditions. Optimum extraction conditions for these hydrophobic compounds were found at temperatures between 300 degrees C and 350 degrees C. Most effective extraction took place in the gas phase at a pressure of 50 atm. With steam at 300 degrees C and 50 atm quantitative extraction (compared to Soxhlet extraction) of polychlorinated naphthalenes from real industrial soil was achieved. Additionally, compared to the values obtained by an international laboratory comparison study, the toxicity of the soil, caused by PCDFs, was reduced at least 90% using PHWE. In most cases the RSD was less than 20%, which showed good repeatability of the whole analytical method including the PHWE step.