Abstract
Effects of sub-millimeter scale heterogeneity in chemical and microbial distributions on atrazine degradation were examined 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 chemical 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 decreasing water content for both application methods, attributed to decreases in atrazine’s effective diffusion. Mineralization of nearly 100% of DA in soils receiving a heterogeneous inoculum with a greater cell density (~107 cells/g) indicates that biodegradation was limited by the distance atrazine had to diffuse. Results support the hypothesis that enhanced populations of atrazine degraders, as reported elsewhere for atrazine-adapted soils, though heterogeneously distributed, may overcome bioavailability limitations.
Highlights
The herbicide, atrazine (2-Chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine) has been used for more than fifty years [1], and remains among the most widely used herbicides globally, though recently banned in the European Union in 2004 [2]
Mineralization and bound residues were assumed the only degradation products. 14CO2 evolution data presented for the dispersed atrazine treatments in Figure 1 show a profound effect of initial P
Soils are often conceptualized as liquid cultures of bacteria, comprised of water contained in habitable pores that surround aggregates containing inaccessible micropores [17], and dissolved xenobiotic outside the micropores is considered bioavailable and homogeneously distributed [54]
Summary
The herbicide, atrazine (2-Chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine) has been used for more than fifty years [1], and remains among the most widely used herbicides globally, though recently banned in the European Union in 2004 [2]. The ecology of atrazine degraders has been examined to use a variety of approaches [7,8], including most recently, stable isotope probing [9]. Though theoretically feasible [10], applications of 15N-DNA-stable isotope probing to examine organisms causing enhanced degradation of atrazine at field rates provided equivocal results, owing to bioavailability limitations [6]. 50% to 80% of atrazine applied to soil becomes sorbed [19], detection of the herbicide in drainage water several years following its last application [20,21], suggests atrazine residues exhibit limited bioavailability despite modest sorption, possibly due to physical inaccessibility
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
