Diffusion Limitation for Atrazine Biodegradation in Soil

Copyright © 2013 Teresa A. Johnson et al. This is an open access article distributed under the Creative Commons Attribution Li-cense, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Effects of sub-millimeter scale heterogeneity in chemical and microbial distributions on atrazine degradation were ex-amined using Pseudomonas sp. strain ADP introduced into soil at a population mimicking atrazine-adapted soils (~2000 cells/g), and employing a range of soil water pressures (−100, −300, −500 kPa). Heterogeneous cell distribution was employed in all treatments whereas uniformity of distribution was a variable for atrazine introduction. Two methods of initially distributing atrazine in soil were examined. Proximally-applied atrazine (PAA) was intended to yield elevated atrazine concentrations in the vicinity of the degraders. Dispersed atrazine (DA) was introduced to distribute the chemi-cal uniformly as compared to the distribution of degraders. Both rate and extent of degradation were greater than PAA, regardless of water content, presumably due to proximity of atrazine to degraders. Biodegradation decreased with de-creasing water content for both application methods, attributed to decreases in atrazine’s effective diffusion. Minerali-zation of nearly 100 % of DA in soils receiving a heterogeneous inoculum with a greater cell density (~107 cells/g) indi-cates that biodegradation was limited by the distance atrazine had to diffuse. Results support the hypothesis that en-hanced populations of atrazine degraders, as reported elsewhere for atrazine-adapted soils, though heterogeneously dis