Atrazine, chlorpyrifos, and iprodione effect on the biodiversity of bacteria, actinomycetes, and fungi in a pilot biopurification system with a green cover

Biodegradation of pesticide-contaminated wastewaters from a formulation plant employing a pilot scale biobed

In this work, a pilot biobed was built up to treat pesticide-contaminated wastewaters discharged from a formulation plant. The pre-treated wastewater was spiked with additional pesticides in order to simulate a scenario of higher contamination: glyphosate, atrazine, imidacloprid, prometryn and carbendazim were added to reach a final Total Organic Carbon (TOC) concentration of 70 mg L^-1. An Intermediate Bulk Container (IBC) was filled with a biomixture of soil and foxtail millet stubble (50:50% v v^-1), and 200 l of the wastewater was added to the system recycling tank. The recirculation to the IBC was established for 12 h. After that (Day 0), the recirculation was turned on during the assay only to maintain the moisture for 180 days. Biomixture and wastewater samples were taken periodically to analyse pesticides and phytotoxicity in both matrices. In addition, hydrolytic and phenoloxidase activities, total bacteria and yeast and fungi communities were determined in the biomixture. The designed pilot scale biobed allowed to treat wastewaters with high concentration of pesticides reaching a complete removal of glyphosate, AMPA, atrazine, carbendazim and prometryn at 180 days. A good degradation percentage of the recalcitrant imidacloprid was achieved (60%) and the biomixture showed enough biological activity to continue treating additional wastewater. The root elongation index from the germination test showed low toxicity on day 180 both in biomixture and wastewater. The millet stubble resulted an appropriate lignocellulosic material to be used in biobeds to treat a wide variety of pesticides. The application of the seed germination test proved to be a low cost and simple tool to determine the end point of the process.

Microbial growth in biobeds for treatment of residual pesticide in banana plantations

Background

High doses of ethylenebisdithiocarbamate (EBDC) are used in banana production, and unused pesticide mixture (solution) is often disposed of improperly. This can result in soil and water contamination and present an undue risk to rural communities and the environment. An alternative to reduce the environmental impacts caused by pesticide residues is the biobeds treatment. It is necessary to establish if the composition of the proposed biomixtures supports microbial activity to degrade pesticides in biobeds. This research aimed to evaluate the EBDC effect on the distribution and abundance of microbial populations in polluted biomixtures .

Methods

For this purpose, a biomixture based on banana stem, mulch, and Fluvisol soil (50:25:25% v/v) was prepared and polluted with 1,000 mg L^-1 EBDC. The response variables kinetics were determined every 14 days for three months, such as pH, organic matter, moisture, cation exchange capacity, microbial colonies, and cell counts at three depths within the experimental units.

Results

EBDC reduced the number of microbial colonies by 72%. Bacterial cells rapidly decreased by 69% and fungi 89% on the surface, while the decrease was gradual and steady at the middle and bottom of the biobed. The microbial populations stabilized at day 42, and the bacteria showed a total recovery on day 84, but the fungi slightly less. At the end of the experiment, the concentration of EBDC in the biomixture was 1.3-4.1 mg L^-1. A correlation was found between fungal count (colonies and cells) with EBDC concentration. A replacement of the biomixture is suggested if the bacterial population becomes less than 40 × 10⁶ CFU mL^-1 and the fungal population less than 8 × 10⁴ CFU mL^-1 or if the direct cell count becomes lower than 50 × 10⁴ cells mL^-1 in bacteria and 8 × 10² cells mL^-1 in fungi.

Conclusion

The biomixture based on banana stem supports the microbial activity necessary for the degradation of the EBDC pesticide. It was found that fungi could be used as indicators of the pollutant degradation process in the biomixtures. Microbial counts were useful to establish the mobility and degradation time of the pesticide and the effectiveness of the biomixture. Based on the results, it is appropriate to include the quantification of microbial populations to assess the effectiveness of pesticide degradation and the maturity level of the biomixture.

Pesticide-tolerant bacteria isolated from a biopurification system to remove commonly used pesticides to protect water resources

In this study, we selected and characterized different pesticide-tolerant bacteria isolated from a biomixture of a biopurification system that had received continuous applications of a pesticides mixture. The amplicon analysis of biomixture reported that the phyla Proteobacteria, Firmicutes, Bacteroidetes and Actinobacteria were predominant. Six strains grew in the presence of chlorpyrifos and iprodione. Biochemical characterization showed that all isolates were positive for esterase, acid phosphatase, among others, and they were identified as Pseudomonas, Rhodococcus and Achromobacter based on molecular and proteomic analysis. Bacterial growth decreased as both pesticide concentrations increased from 10 to 100 mg L^-1 in liquid culture. The Achromobacter sp. strain C1 showed the best chlorpyrifos removal rate of 0.072–0.147 d^-1 a half-life of 4.7–9.7 d and a maximum metabolite concentration of 2.10 mg L^-1 at 120 h. On the other hand, Pseudomonas sp. strain C9 showed the highest iprodione removal rate of 0.100–0.193 d^-1 a half-life of 4–7 d and maximum metabolite concentration of 0.95 mg L^-1 at 48 h. The Achromobacter and Pseudomonas strains showed a good potential as chlorpyrifos and iprodione-degrading bacteria.