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Application of animal manure amendments to agricultural soils is a common practice to improve soil fertility through the addition of essential plant nutrients. This practice may increase the potential for atrazine (2-chloro-4-ethylamino-6-isopropylamino-1, 3, 5-triazine) leaching due to competition for adsorption sites between the pesticide and dissolved organic carbon (DOC) added through manure. We evaluated the influence of liquid cow manure (LCM) application on soil properties, atrazine adsorption, and the physicochemical controlling mechanisms in an Andisol. The LCM was applied at rates equivalent to 0, 100,000, 200,000, and 300,000 L ha(-1), resulting in treatments S-0, S-100, S-200, and S-300, respectively. The LCM application increased DOC and pH of the soils immediately on addition, but pH returned to S-0 values 30 d after application. The LCM application did not modify atrazine adsorption with the two lowest application rates (S-100 and S-200), but atrazine adsorption was decreased in S-300 (K(f) = 0.96) compared with the control (S-0) (K(f) = 1.19), possibly due to the competitive adsorption of DOC with the pesticide. The Fourier-transformed infrared analysis showed that LCM increased aliphaticity and presence of N-containing groups and polysaccharide-like groups in amended soils; however, these properties did not modify the atrazine interaction in the studied amended soils. Interestingly the addition of DOC to soil at the high application rate (S-300) reduced atrazine adsorption in this rich OM Andisol despite the LCM not raising the concentration of stable organic matter. The application of high rates of liquid manure containing DOC incurs an increased risk of pesticide leaching.

The effects of repeated atrazine application (40 mg a.i.kg(-1)) on its degradation, microbial communities and enzyme activities were studied in a peat based biomixture composed by straw, soil and peat in the volumetric proportions of 2:1:1 that can be used in on-farm biopurification system. Atrazine removal efficiency was high (96%, 78% and 96%) after each atrazine application and did not show a lag phase. Microbial enzyme activities were reduced significantly with atrazine application but rapidly recovered. Microbial diversity obtained by BiologEcoplate was similar after the first and second atrazine application. However, an inhibitory effect was observed after the third application. After each atrazine application, culturable fungi were reduced, but rapidly recovered without significant changes in culturable bacteria and actinomycetes compared to the control. Denaturing gradient gel electrophoresis (DGGE) patterns demonstrated that microbial community structure remained relatively stable in time when compared to the controls. In conclusion, our results demonstrated that after successive ATZ applications, the peat based biomixture had a good degradation capacity. Moreover, microbiological assays demonstrated the robustness of the peat based biomixture from a microbiological point of view to support pesticide degradation.

Pesticides are normally used to control specific pests and to increase the productivity in crops; as a result, soils are contaminated with mixtures of pesticides. In this work, the ability of Streptomyces strains (either as pure or mixed cultures) to remove pentachlorophenol and chlorpyrifos was studied. The antagonism among the strains and their tolerance to the toxic mixture was evaluated. Results revealed that the strains did not have any antagonistic effects and showed tolerance against the pesticides mixture. In fact, the growth of mixed cultures was significantly higher than in pure cultures. Moreover, a pure culture (Streptomyces sp. A5) and a quadruple culture had the highest pentachlorophenol removal percentages (10.6% and 10.1%, resp.), while Streptomyces sp. M7 presented the best chlorpyrifos removal (99.2%). Mixed culture of all Streptomyces spp. when assayed either as free or immobilized cells showed chlorpyrifos removal percentages of 40.17% and 71.05%, respectively, and for pentachlorophenol 5.24% and 14.72%, respectively, suggesting better removal of both pesticides by using immobilized cells. These results reveal that environments contaminated with mixtures of xenobiotics could be successfully cleaned up by using either free or immobilized cultures of Streptomyces, through in situ or ex situ remediation techniques.