Soil Enzyme Activities as an Integral Part of the Environmental Risk Assessment of Nanopesticides

Microplastics alter microbial structure and assembly processes in different soil types: Driving effects of environmental factors

Microplastics (MPs) are emerging pollutants with potential impacts on soil ecosystems. However, it is unclear how MPs-induced changes in the soil environment drive microbial structure and assembly in different soils. Here we investigated the responses of microbial structure, enzyme activities and soil properties to biodegradable polylactic acid (PLA) and conventional polythene (PE) with different doses in different soil types. Results showed that PLA generally decreased soil NH4+-N and NO3--N levels but increased dissolved organic carbon (DOC) and pH, whereas PE exhibited contrasting effects depending on soil type. MPs significantly stimulated soil urease, sucrase, catalase and phosphatase activities, with dose-dependent responses observed under PLA treatments in fluvo-aquic soil. Additionally, MPs altered microbial composition and colonized specific bacterial taxa in different soils. In microbial assemblies dominated by stochastic processes, MPs, especially PE promoted the deterministic processes. Co-occurrence patterns showed lower microbial complexity under PLA treatments compared to PE. Notably, we revealed soil-type-specific response patterns: DOC emerged as the primary driver in red soil ecosystems, while pH exerted dominant control in fluvo-aquic soil systems. Furthermore, perturbation of microbial communities by MPs affected functions related to metabolism. These findings highlight that MPs-induced shifts in microbial communities and assembly processes are soil-type-specific and mediated by soil characteristics changes, providing critical insights for assessing the ecological risks of MPs in diverse agricultural soils.

Mining and rational design of psychrophilic catalases using metagenomics and deep learning models

A complete catalase-encoding gene, designated soiCat1, was obtained from soil samples via metagenomic sequencing, assembly, and gene prediction. soiCat1 showed 73% identity to a catalase-encoding gene of Mucilaginibacter rubeus strain P1, and the amino acid sequence of soiCAT1 showed 99% similarity to the catalase of a psychrophilic bacterium, Pedobacter cryoconitis. soiCAT1 was identified as a psychrophilic enzyme due to the low optimum temperature predicted by the deep learning model Preoptem, which was subsequently validated through analysis of enzymatic properties. Experimental results showed that soiCAT1 has a very narrow range of optimum temperature, with maximal specific activity occurring at the lowest test temperature (4 °C) and decreasing with increasing reaction temperature from 4 to 50 °C. To rationally design soiCAT1 with an improved temperature range, soiCAT1 was engineered through site-directed mutagenesis based on molecular evolution data analyzed through position-specific amino acid possibility calculation. Compared with the wild type, one mutant, soiCAT1S205K, exhibited an extended range of optimum temperature ranging from 4 to 20 °C. The strategies used in this study may shed light on the mining of genes of interest and rational design of desirable proteins. KEY POINTS: • Numerous putative catalases were mined from soil samples via metagenomics. • A complete sequence encoding a psychrophilic catalase was obtained. • A mutant psychrophilic catalase with an extended range of optimum temperature was engineered through site-directed mutagenesis.

Earthworms improve the rhizosphere micro-environment to mitigate the toxicity of microplastics to tomato (Solanum lycopersicum)

Microplastics (MPs) are widespread in agricultural soil, potentially threatening soil environmental quality and plant growth. However, toxicological research on MPs has mainly been limited to individual components (such as plants, microbes, and animals), without considering their interactions. Here, we examined earthworm-mediated effects on tomato growth and the rhizosphere micro-environment under MPs contamination. Earthworms (Eisenia fetida) mitigated the growth-inhibiting effect of MPs on tomato plant. Particularly, when exposed to environmentally relevant concentrations (ERC, 0.02% w/w) of MPs, the addition of earthworms significantly (p < 0.05) increased shoot and root dry weight by 12-13% and 13-14%, respectively. MPs significantly reduced (p < 0.05) soil ammonium (NH4+-N) (0.55-0.69 mg/kg), nitrate nitrogen (NO3--N) (7.02-8.65 mg/kg) contents, and N cycle related enzyme activities (33.47-42.39 μg/h/g) by 37.7-50.9%, 22.6-37.2%, and 34.2-48.0%, respectively, while earthworms significantly enhanced (p < 0.05) inorganic N mineralization and bioavailability. Furthermore, earthworms increased bacterial network complexity, thereby enhancing the robustness of the bacterial system to resist soil MPs stress. Meanwhile, partial least squares modelling showed that earthworms significantly influenced (p < 0.01) soil nutrients, which in turn significantly affected (p < 0.01) plant growth. Therefore, the comprehensive consideration of soil ecological composition is important for assessing MPs ecological risk.

Impacts of nano-acetamiprid pesticide on faba bean root metabolic response and soil health

The associated benefits and potential environmental risks of nanopesticides on plant and soil health, particularly in comparison with traditional pesticides, have not been systematically elucidated. Herein, we investigated the impacts of the as-synthesized nano-acetamiprid (Nano-Ace, 20 nm) at low (10 mg/L), medium (50 mg/L), high (100 mg/L) doses and the corresponding high commercial acetamiprid (Ace, 100 mg/L) on the physiological and metabolic response of faba bean (Vicia faba L.) plants, as well as on rhizosphere bacterial communities and functions over short-, medium- and long-term exposures. Overall, Nano-Ace exposure contributed to basic metabolic pathways (e.g., flavonoids, amino acids, TCA cycle intermediate, etc.) in faba bean roots across the whole exposure period. Moreover, Nano-Ace exposure enriched rhizosphere beneficial bacteria (e.g., Streptomyces (420.7%), Pseudomonas (33.8%), Flavobacterium (23.3%)) and suppressed pathogenic bacteria (e.g., Acidovorax (44.5%)). Additionally, Nano-Ace exposure showed a trend of low promotion and high inhibition of soil enzyme activities (e.g., invertase, urease, arylsulfatase, alkaline phosphatase) involved in soil C, N, S, and P cycling, while the inhibition was generally weaker than that of conventional Ace. Altogether, this study indicated that the redox-responsive nano-acetamiprid pesticide possessed high safety for host plants and soil health.

Copper-oxide nanoparticles exert persistent changes in the structural and functional microbial diversity: A 60-day mesocosm study of zinc-oxide and copper-oxide nanoparticles in the soil-microorganism-nanoparticle system

Recent advances in nanotechnology and development of nanoformulation methods, has enabled the emergence of precision farming - a novel farming method that involves nanopesticides and nanoferilizers. Zinc-oxide nanoparticles serve as a Zn source for plants, but they are also used as nanocarriers for other agents, whereas copper-oxide nanoparticles possess antifungal activity, but in some cases may also serve as a micronutrient providing Cu ions. Excessive application of metal-containing agents leads to their accumulation in soil, where they pose a threat to non-target soil organisms. In this study, soils obtained from the environment were amended with commercial zinc-oxide nanoparticles: Zn-O_xNPs_(10-30), and newly-synthesized copper-oxide nanoparticles: Cu-O_xNPs_(1-10). Nanoparticles (NPs) in 100 and 1000 mg kg^-1 concentrations were added in separate set-ups, representing a soil-microorganism-nanoparticle system in a 60-day laboratory mesocosm experiment. To track environmental footprint of NPs on soil microorganisms, a Phospholipd Fatty Acid biomarker analysis was employed to study microbial community structure, whereas Community-Level Physiological Profiles of bacterial and fungal fractions were measured with Biolog Eco and FF microplates, respectively. The results revealed a prominent and persistent effects exerted by copper-containing nanoparticles on non-target microbial communities. A severe loss of Gram-positive bacteria was observed in conjunction with disturbances in bacterial and fungal CLPPs. These effects persisted till the end of a 60-day experiment, demonstrating detrimental rearrangements in microbial community structure and functions. The effects imposed by zinc-oxide NPs were less pronounced. As persistent changes were observed for newly synthesized Cu-containing NPs, this work stresses the need for obligatory testing of nanoparticle interactions with non-target microbial communities in long-term experiments, especially during the approval procedures of novel nano-substances. It also underlines the role of in-depth physical and chemical studies of NP-containing agents, which may be tweaked to mitigate the unwanted behavior of such substances in the environment and preselect their beneficial characteristics.

Development of a Preemergent Nanoherbicide: From Efficiency Evaluation to the Assessment of Environmental Fate and Risks to Soil Microorganisms

Nanoparticles based on biodegradable polymers have been shown to be excellent herbicide carriers, improving weed control and protecting the active ingredient in the crop fields. Metribuzin is often found in natural waters, which raises environmental concerns. Nanoencapsulation of this herbicide could be an alternative to reduce its losses to the environment and improve gains in its efficiency. However, there is a paucity of information about the behavior of nanoformulations of herbicides in environmental matrices. In this study, the stability of nanoencapsulated metribuzin in polymeric nanoparticles (nanoMTZ) was verified over time, as well as its dissipation in different soils, followed by the effects on soil enzymatic activity. The physiological parameters and control effects of nanoMTZ on Ipomoea grandifolia plants were investigated. No differences were verified in the half-life of nanoencapsulated metribuzin compared to a commercial formulation of the herbicide. Moreover, no suppressive effects on soil enzymatic activities were observed. The retention of nanoMTZ in the tested soils was lower compared to its commercial analogue. However, the mobility of nanoencapsulated metribuzin was not greatly increased, reflecting a low risk of groundwater contamination. Weed control was effective even at the lowest dose of nanoMTZ (48 g a.i. ha-1), which was consistent with the higher efficiency of nanoMTZ compared to the conventional herbicide in inhibiting PSII activity and decreasing pigment levels. Overall, we verified that nanoMTZ presented a low environmental risk, with increased weed control.

Enantioselective degradation of prothioconazole in soil and the impacts on the enzymes and microbial community

In this work, the stereoselective degradation of prothioconazole in five soils was investigated and the metabolite prothioconazole-desthio was determined. The effects of prothioconazole on soil enzymes activities and microbial community were also studied. The dissipation of prothioconazole fitted with a first-order kinetic equation with half-lives ranging from 3.45 to 9.90 days. In addition, R-prothioconazole degraded preferentially than S-prothioconazole in all soils with EF values >0.5. Prothioconazole-desthio formed rapidly with preference in R-enantiomer, and the concentration kept at a considerable level even at the end of the incubation, indicating it was relatively persistent in soil. Prothioconazole and its metabolite inhibited the activity of dehydrogenase, catalase and urease in soils, and could affect the diversity of the soil microbiota as well. Redundancy analysis (RDA) and Spearman analysis showed the abundance of Proteobacteria, Fusobacteria, Firmicutes, Thaumarchaeota, Saccharibacteria, Chloroflexi, Chlorobi, Actinobacteria and Nitrospirae might be related to the enantioselective degradation. The work was helpful for understanding the environmental behavior of the fungicide prothioconazole and its primary metabolite on an enantiomeric level.

Multiple Roles of Mesoporous Silica in Safe Pesticide Application by Nanotechnology: A Review

Pollution related to pesticides has become a global problem due to their low utilization and non-targeting application, and nanotechnology has shown great potential in promoting sustainable agriculture. Nowadays, mesoporous silica-based nanomaterials have garnered immense attention for improving the efficacy and safety of pesticides due to their distinctive advantages of low toxicity, high thermal and chemical stability, and particularly size tunability and versatile functionality. Based on the introduction of the structure and synthesis of different types of mesoporous silica nanoparticles (MSNs), the multiple roles of mesoporous silica in safe pesticide application using nanotechnology are discussed in this Review: (i) as nanocarrier for sustained/controlled delivery of pesticides, (ii) as adsorbent for enrichment or removal of pesticides in aqueous media, (iii) as support of catalysts for degradation of pesticide contaminants, and (iv) as support of sensors for detection of pesticides. Several scientific issues, strategies, and mechanisms regarding the application of MSNs in the pesticide field are presented, with their future directions discussed in terms of their environmental risk assessment, in-depth mechanism exploration, and cost-benefit consideration for their continuous development. This Review will provide critical information to related researchers and may open up their minds to develop new advances in pesticide application.