The Distribution Coefficient of Atrazine with Illinois Soils: A Laboratory Exercise in Environmental Chemistry

The soil distribution coefficient (Kd) of the corn herbicide atrazine and the fraction of organic carbon (foc) were measured on Illinois soils of low and high organic-matter content collected by students. Reverse-phase high-performance liquid chromatography was used for the Kd determination, and the foc was measured through loss on ignition.Taking into account that uncertainty existed in both organic-matter fraction and distribution coefficient data, least squares analysis showed that the distribution coefficient varied linearly with the foc and followed the relationship Kd = 57.2 (± 4.9) x foc -0.06 (± 0.04). This confirms that soils with high levels of organic matter will retain organic molecules of low water solubility better than soils with low levels of organic matter.Students learned one way in which soil chemistry controls contaminant transport, and how meaningful relationships can be extracted even when the data are highly variable.