The Interaction of Pesticides with Humin Fractions and Their Potential Impact on Non-Extractable Residue Formation

Abstract

The constant influx of pesticides into soils is a key environmental issue in terms of their potential retention in the soil, thus reducing their negative impact on the environment. Soil organic matter (SOM) is an important factor influencing the environmental fate of these substances. Therefore, the aim of this research was to assess the chemical behavior of pesticides (flufenacet, pendimethalin, α-cypermethrin, metazachlor, acetamiprid) toward stable soil humin fractions (HNs) as a main factor affecting the formation of non-extractable residues of agrochemicals in soil. This research was conducted as a batch experiment according to OECD Guideline 106. For this purpose, HNs were isolated from eight soils with different physicochemical properties (clay content = 16–47%, pHKCl = 5.6–7.7, TOC = 13.3–49.7 g·kg−1, TN = 1.06–2.90 g·kg−1, TOC/TN = 11.4–13.7) to reflect the various processes of their formation. The extraction was carried out through the sequential separation of humic acids with 0.1 M NaOH, and then the digestion of the remaining mineral fraction with 10% HF/HCl. The pesticide concentrations were detected using GC-MS/MS. The pesticides were characterized based on the different sorption rates to HNs, according to the overall trend: metazachlor (95% of absorbed compound) > acetamiprid (94% of absorbed compound) > cypermethrin (63% of partitioning compound) > flufenacet (39% of partitioning compound) > pendimethalin (28% of partitioning compound). Cypermethrin and metazachlor exhibited the highest saturation dynamic, while the other agrochemicals were much more slowly attracted by the HNs. The obtained sorption kinetic data were congruous to the pseudo-first-order and pseudo-second-order models related to the surface adsorption and interparticle diffusion isotherm. The conducted research showed that the processes of pesticide sorption, apart from physicochemical phenomena, are also affected by the properties of the pollutants themselves (polarity, KOC) and the soil properties (SOM content, clay content, and pHKCl).

The function of microbial enzymes in breaking down soil contaminated with pesticides: a review

“…In general, the properties of the compound, such as water solubility, persistency, leachability, mobility, and volatility (vapor pressure), as well as the characteristics of the soil, such as the type of soil, have a significant impact on the pesticide's environmental fate [ 5 , 8 , 12 , 19 ]. Table 2 demonstrates the distinct properties of pesticides that attributes to their varying spatial distributions in the environmental compartments.…”

“…Among the most accomplished bioremediation methods are bioaugmentation and bio-stimulation. Bioaugmentation is the introduction of microorganisms into a contaminated environment, while bio-stimulation is the addition of water, oxygen, and nutrients to increase microbial breakdown activity [ 19 ].

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“…Currently, microbial remediation is carried out mostly using natural, non-engineered microorganisms that have the potential to metabolize or bio-transform the target contaminant into less toxic compounds [ 5 , 21 ]. They are isolated from contaminated sources [ 18 , 19 ].…”

“…Despite the advancements in synthetic biology and microbial engineering that have led to the creation of microorganisms with new metabolic pathways or optimization for better fitness in harsh conditions, the use of genetically altered bacteria in the environment remains controversial. The reasons are twofold: first, potential adverse genotypes can be easily mobilized in the environment, which is perceived as a negative attribute of indigenous organisms; second, the unstable nature of inserted genetic material acknowledges that the efficiency of engineered microbes is relied on their tendency to carry the genetic material [ 19 , 21 , 22 , 27 , 32 ]. As a result, despite the benefits afforded by altered microorganisms, governments such as the United States and Europe restrict the use of genetically modified organisms in the exposing environment [ 21 ].…”

“…Concerned about the possible negative effects of genetically modified microorganisms, researchers are referring to cell-free synthetic biology technologies, which are distinct from engineered microbes [ 12 , 19 , 21 ]. Cell-free synthetic biology is derived, cell-free catalytic systems with non-replicative properties.…”