Sorption and Desorption of Tire Rubber and Roadway-Derived Organic Contaminants in Soils and a Representative Engineered Geomedium

We investigated the sorption and desorption of four representative roadway runoff-derived organic contaminants [1,3-diphenylguanidine (DPG), N,N -dicyclohexylmethylamine, 1-cyclohexyl-3-phenylurea, and hexa(methoxymethyl)melamine] with five soils. Isotherm data from batch studies were well fitted by the Freundlich model ( R 2 = 0.855–0.999). For ionic contaminants, log K oc values were affected by pH. These contaminants also exhibited sorption–desorption hysteresis that increased at higher concentrations. Additionally, to reflect common stormwater treatment practices, a 40% compost/60% sand engineered geomedium was evaluated as a representative model sorbent. For this geomedium, the sorption of the primary roadway-derived contaminants listed above was evaluated along with seven additional stormwater contaminants, including neutral and cationic compounds. Sorption affinities varied across different contaminants, with the positively charged DPG (log K oc = 3.12–4.11) and N,N -dicyclohexylmethylamine (log K oc = 2.65–4.51) exhibiting the highest sorption potential compared to those of neutral compounds in all soils except for 726 Toledo soil. Weak log D ow and log K oc correlations indicated that specific interactions such as hydrogen bonding and electrostatic attraction often affected sorption, although sorption to the organic matter rich engineered geomedium was dominated by hydrophobic interactions. As commonly observed, sorption affinities were influenced by aspects of contaminant structural diversity and chemical properties that induced differing interaction mechanisms.