MINERALIZATION KINETICS OF CHEMICALS IN SOILS IN RELATION TO ENVIRONMENTAL-CONDITIONS

The mineralization kinetics of the detergent n-dodecylbenzenesulfonate ([C-14]LAS) and the plasticizer di(2-ethylhexyl)phthalate ([C-14]DEHP ) were studied in three fresh sampled soils of different type. Time se ries of (CO2)-C-14 evolution were fitted with various linear and nonli near models. The kinetics could be represented best by a 3/2-order fun ction with linear adaptation and three parameters: x(1) describing the gradient of the exponential part of the curve, x(2) the lag phase, an d x(3) the last, asymptotic part. These parameters as well as the maxi mal degraded amounts (A) were correlated with various environmental co nditions. 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). Th e parameters x(1)-x(3) were positively influenced by soil humidity in all three soils. The degraded amounts A, expressed as percentage of ad ded dose, were independent of initial concentration. Both A and the pa rameters x(1)-x(3) increased with increasing temperature. Degradation was negligible below 3 degrees C. For DEHP, the degradation was much s lower than that of LAS and was most rapid and most complete in the ren dzina soil. Relative degradation A was lower for higher initial applic ation rates. Temperature influenced both A and the lag phase. Degradat ion was not significant below 10 degrees C. (C) 1996 Academic Press, I nc.