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Biobed systems are an important option to control point pollution in agricultural areas. Substrates used and microbial diversity present in a biomixture perform an essential function in pesticide dissipation. In this study, the effects of soil (50% of volume/volume [V/V] proportion for all biomixtures) and four soil-based biomixtures (miniaturized biobeds; addition of novel substrates from southeastern Mexico) on dissipation of high concentrations of 2,4-dichlorophenoxyacetic acid (2,4-D), atrazine, carbofuran, diazinon, and glyphosate and on microbial diversity in biomixtures were evaluated. Small residual amounts of all pesticides at 20 (<2%) and 41 (<1%) days were observed; however, the lowest efficiency rates were observed in soil. Glyphosate was the only pesticide that completely dissipated in soil and biomixtures. Archaea, bacteria, and fungi were identified in biobeds, with bacteria being the most diverse microorganisms according to the identified species. The presence of white-rot fungi (normally related to pesticide degradation in biomixtures) was observed. Effects of the pesticide type and of biomixtures on pesticide dissipation were significant ( P < 0.05); however, only the effect of biomixtures on microbial diversity was significant ( P < 0.05); microbial diversity and richness had a significant effect on the residual amount of pesticides ( P < 0.05). Microbial diversity in terms of phyla was directly related to physicochemical parameters such as organic matter, lignin, water-holding capacity, and pH of soil and biomixtures. [ABSTRACT FROM AUTHOR]

Pesticides are used worldwide in farming activities to guarantee crop yields. In southeastern Mexico, groundwater is the primary source of water for humankind. However, because of the soil characteristics and of intensive agricultural practices, the aquifer is vulnerable to pollution as shown by the regular detection of pesticide residues in groundwater. Within this context, the dissipation and adsorption of four of most used pesticides (2,4-D, atrazine, diazinon, and glyphosate) by farmers in southeastern Mexico were studied to determine their fate in agricultural soil and estimate their risk for the aquifer. Forty-one days after their application, the four pesticides were entirely dissipated from the soil. 2,4-D and glyphosate were the most persistent according to DT50. Diazinon was the most adsorbed to the soil at equilibrium time. All pesticides were volatilized in substantial amounts, reaching 10.1, 22.3, 22.4, and 43.4% of initial amount 72 h after application of glyphosate, atrazine, 2,4-D, and diazinon, respectively. Volatilization was dependent on time and pesticide type (P < 0.05). Following their KOC, diazinon and glyphosate were found to be the most prone to leach. Therefore, in the absence of mitigation measures, their use represents a significant threat for the groundwater in Southeastern Mexico. [ABSTRACT FROM AUTHOR]