A Comparative Study of In-Field and Laboratory Mineralization Rates of 2,4-D and 17ß-Estradiol - Preliminary Results.

Understanding the rate of mineralization of pesticides and estrogens in soil is crucial to our comprehension of the persistence and transport of these chemicals in the landscape. Mineralization studies are usually performed in a laboratory using incubators to control temperature. However, very limited information exists to how representative these laboratory studies are in relation to in-field mineralization. The overall aim of this research is to quantify the mineralization of 2,4-D (a pesticide) and 17β-estradiol (an estrogen) in 10 Manitoba soil series under both laboratory-controlled and field conditions. The soils ranged in texture from sandy loam to heavy clay. Preliminary results from two field seasons and one laboratory study will be presented here. The field study component involved the design of an in-field microcosm technique for which the two chemicals (carbon-14 radiolabelled 2,4-D and 17β-estradiol) were added to soils in microcosms (5 replicates) and all microcosms were installed in the Ap horizon of a clay soil. Temperature sensors installed both in soil profiles in the field and in the field-installed microcosms were used to observe the effect of temperature on mineralization rates.  In the laboratory study component, the soils were incubated in environmental growth chambers at a constant temperature as well as at fluctuating temperatures similar to conditions observed in the field. Mineralization from each soil-chemical-temperature combination were measured on an approximately weekly basis for 48 days. Data were used to calculate first-order chemical mineralization rate constants and to obtain the total amount of the chemical mineralized. Soils were ranked from the highest to lowest rates of mineralization and the rankings of the soils under various research method designs were compared. The results of this research will be used to determine which research method is most effective to describe field conditions, while considering the practicality of each method.