Mineralization kinetics of chemicals in soils in relation to environmental conditions

The mineralization kinetics of the detergent n-dodecylbenzenesulfonate ([14C]LAS) and the plasticizer di(2-ethylhexyl)phthalate ([14C]DEHP) were studied in three fresh sampled soils of different type. Time series of 14CO2 evolution were fitted with various linear and nonlinear models. The kinetics could be represented best by a 3/2-order function with linear adaptation and three parameters: x1 describing the gradient of the exponential part of the curve, x2 the lag phase, and x3 the last, asymptotic part. These parameters as well as the maximal degraded amounts (A) were correlated with various environmental conditions. For LAS, A was similar in all three soils and was positively related to pH in two soils and to humidity in one soil (rendzina). The parameters x1-x3 were positively influenced by soil humidity in all three soils. The degraded amounts A, expressed as percentage of added dose, were independent of initial concentration. Both A and the parameters x1-x3 increased with increasing temperature. Degradation was negligible below 3 degrees C. For DEHP, the degradation was much slower than that of LAS and was most rapid and most complete in the rendzina soil. Relative degradation A was lower for higher initial application rates. Temperature influenced both A and the lag phase. Degradation was not significant below 10 degrees C.