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Microbial changes linked to the accelerated degradation of the herbicide atrazine in a range of temperate soils

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ABSTRACT

Accelerated degradation is the increased breakdown of a pesticide upon its repeated application, which has consequences for the environmental fate of pesticides. The herbicide atrazine was repeatedly applied to soils previously untreated with s-triazines for >5 years. A single application of atrazine, at an agriculturally relevant concentration, was sufficient to induce its rapid dissipation. Soils, with a range of physico-chemical properties and agricultural histories, showed similar degradation kinetics, with the half-life of atrazine decreasing from an average of 25 days after the first application to <2 days after the second. A mathematical model was developed to fit the atrazine-degrading kinetics, which incorporated the exponential growth of atrazine-degrading organisms. Despite the similar rates of degradation, the repertoire of atrazine-degrading genes varied between soils. Only a small portion of the bacterial community had the capacity for atrazine degradation. Overall, the microbial community was not significantly affected by atrazine treatment. One soil, characterised by low pH, did not exhibit accelerated degradation, and atrazine-degrading genes were not detected. Neutralisation of this soil restored accelerated degradation and the atrazine-degrading genes became detectable. This illustrates the potential for accelerated degradation to manifest when conditions become favourable. Additionally, the occurrence of accelerated degradation under agriculturally relevant concentrations supports the consideration of the phenomena in environmental risk assessments.

Electronic supplementary material: The online version of this article (doi:10.1007/s11356-017-8377-y) contains supplementary material, which is available to authorized users.

No MeSH data available.


Comparison of modelling approaches for the dissipation of atrazine in GRA over three applications. Using the regulatory single first-order (SFO) approach (a), with each application modelled separately and the ‘growth-linked model’ described in this study (b). The growth-linked model enabled all applications to be modelled simultaneously. In both modelling approaches, the model fit of % atrazine remaining is shown as a solid black line and individual soil sub-samples as diamonds (n = 4). For the growth-linked model (b), the grey dashed line represents the number of atrazine degraders
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Fig2: Comparison of modelling approaches for the dissipation of atrazine in GRA over three applications. Using the regulatory single first-order (SFO) approach (a), with each application modelled separately and the ‘growth-linked model’ described in this study (b). The growth-linked model enabled all applications to be modelled simultaneously. In both modelling approaches, the model fit of % atrazine remaining is shown as a solid black line and individual soil sub-samples as diamonds (n = 4). For the growth-linked model (b), the grey dashed line represents the number of atrazine degraders

Mentions: It is evident that the vast majority of these soils are exhibiting an accelerated rate of atrazine degradation within 60 days of applying atrazine. Using a sterile control, it was shown that sterile soil displayed a DT50 of 107.7 days compared to 20.4 days in a matched non-sterile soil (Online Resource 11). This confirmed in-line with previous studies that accelerated degradation of atrazine is microbially driven (Zablotowicz et al. 2007). However, the modelling approaches applied above do not take into account the kinetics of microbial growth or microbial adaptation over multiple applications. In fact, the SFO kinetics applied to the first application of atrazine fails to capture the rate of atrazine decay, which clearly begins to accelerate between 28 and 45 or 45 and 60 days for most soils. This is illustrated in the GRA soil in which time points at 28 and 60 days deviate significantly from the exponential fit (Fig. 2). Similar poor fits are also observed during the degradation of the first atrazine application in the other soils (Online Resources 12–18).Fig. 2


Microbial changes linked to the accelerated degradation of the herbicide atrazine in a range of temperate soils
Comparison of modelling approaches for the dissipation of atrazine in GRA over three applications. Using the regulatory single first-order (SFO) approach (a), with each application modelled separately and the ‘growth-linked model’ described in this study (b). The growth-linked model enabled all applications to be modelled simultaneously. In both modelling approaches, the model fit of % atrazine remaining is shown as a solid black line and individual soil sub-samples as diamonds (n = 4). For the growth-linked model (b), the grey dashed line represents the number of atrazine degraders
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

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Fig2: Comparison of modelling approaches for the dissipation of atrazine in GRA over three applications. Using the regulatory single first-order (SFO) approach (a), with each application modelled separately and the ‘growth-linked model’ described in this study (b). The growth-linked model enabled all applications to be modelled simultaneously. In both modelling approaches, the model fit of % atrazine remaining is shown as a solid black line and individual soil sub-samples as diamonds (n = 4). For the growth-linked model (b), the grey dashed line represents the number of atrazine degraders
Mentions: It is evident that the vast majority of these soils are exhibiting an accelerated rate of atrazine degradation within 60 days of applying atrazine. Using a sterile control, it was shown that sterile soil displayed a DT50 of 107.7 days compared to 20.4 days in a matched non-sterile soil (Online Resource 11). This confirmed in-line with previous studies that accelerated degradation of atrazine is microbially driven (Zablotowicz et al. 2007). However, the modelling approaches applied above do not take into account the kinetics of microbial growth or microbial adaptation over multiple applications. In fact, the SFO kinetics applied to the first application of atrazine fails to capture the rate of atrazine decay, which clearly begins to accelerate between 28 and 45 or 45 and 60 days for most soils. This is illustrated in the GRA soil in which time points at 28 and 60 days deviate significantly from the exponential fit (Fig. 2). Similar poor fits are also observed during the degradation of the first atrazine application in the other soils (Online Resources 12–18).Fig. 2

View Article: PubMed Central - PubMed

ABSTRACT

Accelerated degradation is the increased breakdown of a pesticide upon its repeated application, which has consequences for the environmental fate of pesticides. The herbicide atrazine was repeatedly applied to soils previously untreated with s-triazines for >5 years. A single application of atrazine, at an agriculturally relevant concentration, was sufficient to induce its rapid dissipation. Soils, with a range of physico-chemical properties and agricultural histories, showed similar degradation kinetics, with the half-life of atrazine decreasing from an average of 25 days after the first application to <2 days after the second. A mathematical model was developed to fit the atrazine-degrading kinetics, which incorporated the exponential growth of atrazine-degrading organisms. Despite the similar rates of degradation, the repertoire of atrazine-degrading genes varied between soils. Only a small portion of the bacterial community had the capacity for atrazine degradation. Overall, the microbial community was not significantly affected by atrazine treatment. One soil, characterised by low pH, did not exhibit accelerated degradation, and atrazine-degrading genes were not detected. Neutralisation of this soil restored accelerated degradation and the atrazine-degrading genes became detectable. This illustrates the potential for accelerated degradation to manifest when conditions become favourable. Additionally, the occurrence of accelerated degradation under agriculturally relevant concentrations supports the consideration of the phenomena in environmental risk assessments.

Electronic supplementary material: The online version of this article (doi:10.1007/s11356-017-8377-y) contains supplementary material, which is available to authorized users.

No MeSH data available.