Resistant desorption of hydrophobic organic contaminants in typical Chinese soils: implications for long-term fate and soil quality standards

Soil contamination is an enormous problem in China and severely threatens environmental quality and food safety. Establishing realistic soil quality standards is important to the management and remediation of contaminated sites and must be based on thorough understanding of contaminant desorption from soil. In the present study, we evaluated sorption and desorption behaviors of naphthalene, phenanthrene, atrazine, and lindane (four common soil contaminants in China) in two of the most common Chinese soils. The desorption of these compounds exhibited clear biphasic pattern-a fraction of contaminants in soil was much less available to desorption and persisted much longer than what was predicted with the conventional desorption models. The unique thermodynamic characteristics associated with the resistant-desorption fraction likely have important implications for the mechanism(s) controlling resistant desorption. Experimental observations in the present study are consistent with our previous work with chlorinated compounds and different adsorbents and could be well modeled with a biphasic desorption isotherm. We therefore suggest that more accurate biphasic desorption models should be used to replace the conventional linear sorption/desorption model that is still widely adopted worldwide in contaminant fate prediction and soil quality standard calculations.