Biodegradation of atrazine as affected by high concentration, co-contaminant presence, and sorption-desorption processes

Brandon Clay Grigg, Purdue University

Abstract

Atrazine contamination of mix-load sites can be high, and is often present with other co-contaminants. This in conjunction with sorption-desorption to soil components, can affect the efficiency of bioaugmentation of these sites. Our goal was to determine the effects of these multiple factors on the bioaugmentation with an atrazine mineralizing culture. First, our culture was supplied with high concentrations of atrazine. At initial concentrations of 0.046 M and 0.23 M, the mixed culture degraded 78% and 21% of atrazine applied to soil and 90% and 56% of the atrazine applied in liquid culture, within 100 d and 80 d for soil and culture experiments, respectively. Decreased percentage of degradation at the 0.23 M concentration was possibly due to an unbalanced nutrient supply. The culture's ability to mineralize other s-triazines was also evaluated, and cyanazine and simazine were rapidly degraded in liquid culture. The presence of other s-triazine herbicides did not affect atrazine degradation. Cyanazine was degraded to persistent metabolites. The culture was unable to degrade metribuzin. Atrazine was also degraded in the presence of co-contaminants alachlor, metolachlor, trifluralin, or combinations of these co-contaminants. Atrazine degradation was not affected by single co-contaminant herbicides or NO$\sb3$-N, a common N contaminant. However, mixtures of co-contaminants increased half-life values of atrazine. Sorption-desorption experiments were conducted for atrazine, alone or mixed with alachlor, cyanazine, or NH$\sb4$Cl, and with and without bioaugmentation. Sorbents were either a Drummer surface soil (Typic Haplaquolls) or Ca-montmorillonite. Atrazine sorption was not significantly affected by co-contaminant presence, although atrazine mineralization by the culture increased with in the presence of co-contaminants. Our culture rapidly mineralized available atrazine in solution and increased atrazine desorption from sorbent surfaces through rapid reduction of solution concentration. Bioaugmentation results in bioremediation of atrazine contamination, both in mineralization of existing solution concentrations and desorbed atrazine. Increased desorption of atrazine due to bioaugmentation also occurs in the presence of co-contaminant herbicides and NH$\sb4.$ Results suggest that bioremediation utilizing this mixed culture could be successfully accomplished across a wide range of atrazine concentrations and in multiple contaminant environments.

Degree

Ph.D.

Advisors

Turco, Purdue University.

Subject Area

Agronomy|Microbiology|Environmental science|Agricultural chemicals|Soil sciences

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