Predicting 2,4-Dichlorophenoxyacetic Acid Ester Transformation Rates in Periphyton-Dominated Ecosystems

Using batch cultures, we determined transformation rate coefficients for microbial transformation of 2,4-dichlorophenoxyacetic acid butoxyethyl ester (2,4-DBE) in periphyton-dominated ecosystems. Rates of 2,4-DBE loss were measured over short periods of time (usually less than 10 h), and first-order transformation rate coefficients (k₁) were determined under the specific conditions of low 2,4-DBE concentrations and no growth. Values for k₁ were divided by total plate counts and by biomass measured as ash-free dry weight to give second-order rate coefficients (k_b and k_AFDW, respectively) for use in predictive models. Using periphyton attached to Teflon strips, we also determined second-order rate coefficients based on the ratio of colonized surface area to container volume (k_A). Mean second-order rate coefficients were used to predict 2,4-DBE transformation rates in microcosms having diverse chemical and biological environments. The observed transformation rates among the microcosms were most accurately predicted by using k_A.