Abstract
AbstractThe bioavailability and desorption characteristics of nonextractable soil‐aged atrazine were investigated to examine the significance of this potentially large contaminant fraction in agricultural soils. Radiolabeled atrazine‐applied soil was aged for 3 months and then extracted by one of three methods—methanol‐water (4: 1) at 75°C, acetone, and artificial soil water—representing a range of extraction efficiencies. Viable microcosms were constructed with the dried, extracted soil to compare rates and extents of microbially facilitated release and mineralization with desorption rates in sterile microcosms. The most rigorously extracted soil exhibited slow desorption over a 90‐d period, but the other soil treatments showed continued slow sorption after reaching an initial maximum desorption concentration within 1 to 5 d. No microbially facilitated release of the nonextractable atrazine was detected for any of the treatments. Rates of ring‐and chain‐labeled atrazine mineralization declined with decreasing extractability of the soilassociated atrazine fraction. However, the extent of biodegradation (less than 2% of the total atrazine for all extracted soil treatments) was less than the extent of abiotic desorption. Mass‐balance calculations suggest that all biodegradation occurred in the dissolved phase.
Published Version
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