Insights into the recent advances in nano-bioremediation of pesticides from the contaminated soil -

Insights into the recent advances in nano-bioremediation of pesticides from the contaminated soil

Introduction

The extensive use of pesticides in Indian agriculture during the green revolution, particularly between 1967 and 1972, contributed to increased crop production but raised significant environmental and health concerns. Pesticides, with only 1% effectively targeting pests, contaminate soil, water, and air, affecting the entire ecosystem. These chemicals not only enter the food chain but also disrupt soil health by impacting the soil microbiome and enzyme activity. Around 40% of applied pesticides transform into persistent products, posing long-term threats to soil and groundwater. Residues in the food chain harm human health, affecting organs, causing endocrine disruptions, neurological disorders, cytotoxic effects, and mutations.

Chlorpyrifos, an organophosphate pesticide, has been linked to reduced intelligence in children. Animals, both farm and wild, experience various health issues due to pesticide exposure, including cancer, immunosuppression, birth defects, and reproductive problems. Pesticides also have detrimental effects on biodiversity, leading to a decline in bird populations, insect species, and beneficial insects like bees. This environmental impact has economic consequences, with estimates suggesting losses up to 100 times greater than conservation spending. Soil health is also compromised by long-term pesticide use, affecting microflora, microfauna, and macrofauna.

In light of these challenges, there is a pressing need for remediation measures. Nanomaterials present promising applications in bioremediation processes for effectively addressing the contamination of the environment by pesticides and heavy metals. This review aims to underscore the significance, impact, and key applications of nanomaterials in the bioremediation of toxic pollutants, offering potential solutions for the mitigation of pesticide-related environmental issues.

Techniques of remediation

The soil has its capacity for degradation of compounds used in the pesticides up to a certain extent but a high concentration of these compounds is toxic for the soil microflora involved in the bioremediation and therefore needs necessary interventions in this area (Cheng et al., 2016a). Several techniques based on physical, chemical and physicochemical principles have been used for the bioremediation of the soil (Baldissarelli et al., 2019).

Physiochemical processes of bioremediation

Physicochemical processes, particularly advanced oxidative processes, have been employed as effective techniques for the remediation of soil contaminated with pesticides. One such method is the Fenton process, involving the oxidation of iron ions in the presence of hydrogen peroxide to produce hydroxyl radicals that oxidize organic pollutants. While Fenton’s reaction is environmentally friendly and can be used in situ or ex situ, it may reduce soil pH, impacting the soil microbiome. Heterogeneous photocatalysis, plasma oxidation, and ozonation are other advanced oxidative processes tested for soil bioremediation, each having its own merits and limitations. Additionally, techniques like soil washing, chemical extraction-solvent extraction, and electrokinetics have been applied to remove contaminants from soil, each with its specific efficacy and considerations. Advanced oxidation processes, particularly Fenton’s reaction, stand out as promising methods for a wide range of contaminants due to their versatility, environmental friendliness, and relatively low operation costs. However, alternative techniques such as biodegradation and the use of microorganisms also offer effective decontamination options for soil and water.

Nano-phytoremediation of contaminated soil

Nano-phytoremediation, a method for remediating pollutants and contaminants, involves the use of synthesized nanoparticles derived from plants. Plants, being natural detoxifiers, can absorb various compounds and detoxify them, a process known as phytoremediation. Nanotechnology has significantly improved the efficacy of soil and water remediation. Nano-sized zerovalent irons have been employed to degrade organic contaminants like atrazine, molinate, and chlorpyrifos. Encapsulating enzymes in nanoparticles has also proven to enhance bioremediation efficiency. Several factors, including the physical and chemical properties of compounds, molecular weight, solubility in water, soil environment characteristics (pH, temperature, organic matter percentage), and plant traits, influence the effectiveness of nano-bioremediation. The integration of nanoparticles and phytoremediation is crucial for the success of nano-phytoremediation. Studies show that the application of nanoparticles effectively detoxifies various organic, inorganic, and metal pollutants from the soil. Nano-zerovalent iron and magnetite nanoparticles have demonstrated rapid degradation of organic pollutants in the soil. Nano-phytoremediation has proven effective for a broad range of soil pollutants, enhancing pollutant uptake by plants and improving their stress tolerance capacity.

Important factors in the interaction of plants and nanoparticles

In the interaction between plants and nanoparticles, the size of nanoparticles is a critical factor influencing their uptake by plants. Nanoparticles can be transported into plants through apoplastic transport (via xylem vessels) or symplastic transport (between the cytoplasm and sieve plates). Additionally, soil temperature plays a significant role, affecting plant growth substances and root lengths. The properties of the plants themselves are also crucial for nano-bioremediation efficiency. Ideal plants for high efficiency should have fast growth, large biomass, a well-developed root system, high toxicity tolerance, high accumulation capacity, non-consumable traits for animals, and genetic manipulability. Nanoparticles used in this context should be non-toxic for plants and possess properties that enhance germination, root-shoot elongation, enzyme production, plant growth hormone stimulation, and the ability to bind with soil contaminants.

Nano-phytoremediation technology has been applied to both natural and genetically engineered plants. Nanoparticles have been shown to increase plant growth, stimulate the production of plant growth hormones, and enhance the uptake of soil pollutants. However, the efficacy and safety of nanoparticles depend on various factors such as chemical composition, size, shape, stability, concentration, surface coating, reactivity, and the specific plant involved. Physiological changes induced by nanoparticles contribute to increased phytoremediation efficacy. Nevertheless, challenges exist, including the need for extensive studies beyond microcosm levels, addressing nanoparticle aggregation through surface modifications, and evaluating the toxicity of nanoparticles to soil and the environment.

Microbial nano-bioremediation

Microbial nano-bioremediation is a two-phase process that combines nanoparticles with soil microbes to enhance biodegradation. In the first phase, nanoparticles enter the system, and the pollutants undergo various processes such as adsorption, absorption, dissolution, and photocatalysis. The second phase involves biotic processes like biostimulation and biotransformation, playing a crucial role in removing particles from the system. This process has been employed for a range of pollutants, both inorganic and organic. In the biotic phase, microorganisms uptake metal ions and reduce them, resulting in the conversion of metal ions into useful nanoparticles. Microbial enzymes, in collaboration with metals, contribute to the formation of nanoparticles, facilitating nano-bioremediation.

Microbial nano-bioremediation for heavy metals

Heavy metals, such as Pb, As, and Cd, pose significant threats to the environment and biotic components due to their toxic effects. In response to this environmental challenge, microbial nano-bioremediation emerges as a promising approach. Nanoparticles, including bio-organic nanoparticles synthesized using biological organisms, play a crucial role in the removal of heavy metals from soil. For instance, silver nanoparticles produced in Morganella psychrotolerans and iron oxide nanoparticles coated with polyvinyl pyrrolidone (PVP) in combination with Halomonas sp. have been utilized for the bioremediation of lead, cadmium, and other heavy metals. Magnetic nanoparticles of Fe3O4 coated with phthalic acid, treated with S. aureus, demonstrated high efficiency in removing Cu, Ni, and Pb.

In addition, heavy metal-resistant bacteria, such as B. cereus and L. macroides, in combination with zinc oxide nanoparticles, have been employed for the efficient remediation of metals like Cu, Cd, Cr, and Pb. B. cereus strain XMCr−6 showcased the reduction of Cr+6 to Cr+3, forming chromium oxide nanoparticles as a byproduct. Selenium nanoparticles, in conjunction with probiotic bacteria L. casei, demonstrated enhanced efficiency in the treatment of cadmium-contaminated land and water compared to L. casei alone.

The approach of bio-organic nanoparticle synthesis involves selective microbes for heavy metal removal, yielding value from waste. For example, Enterococcus faecelis was employed for the removal and recovery of lead, synthesizing lead nanoparticles with high catalytic efficiency. Tellurium nanoparticles were synthesized from anaerobic sludge using riboflavin supplementation in the presence of Rhodobacter capsulates, utilizing polluted tellurite Te4+ oxy anions in wastewater. These examples highlight the effectiveness of nano-bioremediation in addressing heavy metal toxicity in various environmental contexts.

Nano-bioremediation of organic pollutants

Nano-bioremediation proves to be a effective strategy for addressing the remediation of persistent organic pollutants (POPs), which can have detrimental impacts on human and environmental health. Various combinations of nanoparticles with microorganisms have been employed for the effective remediation of organic pollutants from soil.

– Magnetic nanoparticles, in conjunction with Rhodococcus engthropolis, demonstrated the desulfurization of dibenzothiophene (DBT), showcasing their efficacy in addressing specific organic pollutants.

– Bimetallic (Pd/nFe) nanoparticles, combined with Sphingomonas wittichii, were utilized for the bioremediation of NBR.2,3,7,8-tetrachlorodibenzo-p-dioxin hydrocarbons, highlighting their potential in dealing with specific hazardous organic compounds.

– Silica nanoparticles biofunctionalized with the lipid bilayer of Pseudomonas aeruginosa were employed to clean up polycyclic aromatic hydrocarbons (PAH), such as benzo[a]pyrene, with the membrane lipids of Pseudomonas playing a crucial role in enhancing PAH sequestration.

– Graphene oxide nanoparticles, in conjunction with the laccase enzyme of Trametes versicolor, were studied for the biodegradation of PAH, demonstrating their effectiveness in PAH remediation.

– Alcaligenes faecelis, combined with iron oxide nanoparticles, improved the degradation of hydrocarbon compounds in crude oil contamination, showcasing the potential for addressing broader hydrocarbon pollutants.

– Sphingomonas strain NM05, when treated with Pd/FeO bimetallic nanoparticles, exhibited approximately a two-fold enhancement in the degradation efficacy for hexachlorocyclohexane (HCH).

– Perovskite (LaFeO3) nanoparticles, in combination with proteobacteria, were employed for the degradation of organic contaminants in marine sediments, demonstrating their potential application in marine environments.

Moreover, nanoparticles have not only shown effectiveness in enhancing the remediation efficacy of microbes but have also been reported to improve soil health. For instance, silicon nanoparticles were found to enhance soil microflora and biomass, promoting the growth of rhizospheric microbes. This dual functionality emphasizes the potential of nano-bioremediation not only for pollutant removal but also for overall soil improvement.

Algae mediated nano-bioremediation

Phyto-nanotechnology, an eco-friendly strategy, involves algae-mediated nano-bioremediation for the efficient removal of toxic compounds from ecosystems. Algae, being the largest photoautotrophic group, serve as nano-machineries for synthesizing various metal nanoparticles like silver, gold, and palladium. Algal species from different groups, including Chlorophyceae, Cyanophyceae, Phaeophyceae, and Rhodophyceae, have been utilized for nanoparticle fabrication due to their high metal uptake potential, easy handling, low cost, and low toxicity. Algae, such as Chlorella vulgaris and Nannochloropsis oculata, demonstrate efficient removal of heavy metals like gold and copper, respectively, from acid mine drainage and wastewater. Immobilization of microalgae biomass and the use of microalgae consortia have shown promise in wastewater treatment for heavy metal remediation. While microalgae exhibit potential for heavy metal removal, further research is needed to optimize remediation efficiency and biomass utilization.

Fungi mediated nano-bioremediation

Fungi, including molds, yeasts, and mushrooms, are utilized as biocatalysts in nano-bioremediation due to their resilience in harsh conditions and elevated heavy metal concentrations. In green nanotechnology, fungi play a crucial role in synthesizing metal nanoparticles, offering advantages such as high metal uptake capacity, cost-effectiveness, metal tolerance, scalability, and stability. Various fungi, such as Fusarium, Verticillium, Penicillium, and Aspergillus, have been employed to synthesize nanoparticles like silver, gold, platinum, titanium, selenium, and silica.

The green synthesis of nanoparticles by different fungi has found applications in the remediation of hazardous organic pollutants through heavy metal adsorption. Factors such as the type of metal, environmental conditions, and fungal biomass influence biosorption capacity. Fungi, including arbuscular mycorrhizal fungi, Allescheriella sp., Botryosphaeria rhodina sp., and Stachybotrys sp., exhibit proficient metal-binding capabilities. Fungi like Fusarium solani, known for their tolerance to heavy metals, demonstrate efficient nanoparticle synthesis.

The combination of nanoparticles with white-rot fungi (WRF) shows immense potential in bioremediation. Studies report successful remediation of contaminants like antibiotics and heavy metals through the immobilization of WRF with magnetic nanoparticles. Fungi such as Phanerochaete chrysosporium, when combined with various nanoparticles, have shown enhanced remediation efficiency for pollutants like cadmium, 2,4-dichlorophenol, phenols, and zinc.

Conclusion

In conclusion, the escalating levels of pesticide contamination in soil pose significant threats to human, soil, and environmental health. It is imperative to promote rational pesticide use, particularly in underdeveloped and developing countries lacking efficient monitoring systems. Prioritizing pesticides with short half-lives and high biodegradability, when necessary, is crucial. Enhancing soil health can be achieved through effective implementation of crop rotation programs and increased use of organic manure.

While various techniques exist for remediating soil pesticide contamination, many have inherent limitations. Experiments integrating nanoparticles with bioremediation processes have displayed promising potential, yet further extensive research is needed in this domain. Although nanoparticles have demonstrated enhanced bioremediation efficacy, concerns persist regarding their safety in the environment and the food chain. Therefore, comprehensive research on the safety analysis of nanoparticles is essential.

Reference:

SINGH, Y. AND SAXENA, M.K., 2022. Insights into the recent advances in nano-bioremediation of pesticides from the contaminated soil. Frontiers in Microbiology, 13, p.982611.