Microbial Degradation of Aldrin and Dieldrin: Mechanisms and Biochemical Pathways

Synergistic insights into pesticide persistence and microbial dynamics for bioremediation

Rampant use of fertilizers and pesticides for boosting agricultural crop productivity has proven detrimental impact on land, water, and air quality globally. Although fertilizers and pesticides ensure greater food security, their unscientific management negatively impacts soil fertility, structure of soil microbiome and ultimately human health and hygiene. Pesticides exert varying impacts on soil properties and microbial community functions, contingent on factors such as their chemical structure, mode of action, toxicity, and dose-response characteristics. The diversity of bacterial responses to different pesticides presents a valuable opportunity for pesticide remediation. In this context, OMICS technologies are currently under development, and notable advancements in gene editing, including CRISPR technologies, have facilitated bacterial engineering, opening promising avenues for reducing toxicity and enhancing biological remediation. This paper provides a holistic overview of pesticide dynamics, with a specific focus on organophosphate, organochlorine, and pyrethroids. It covers their occurrence, activity, and potential mitigation strategies, with an emphasis on the microbial degradation route. Subsequently, the pesticide degradation pathways, associated genes and regulatory mechanisms, associated OMICS approaches in soil microbes with a special emphasis on CRISPR/Cas9 are also being discussed. Here, we analyze key environmental factors that significantly impact pesticide degradation mechanisms and underscore the urgency of developing alternative strategies to diminish our reliance on synthetic chemicals.

Repercussions of Prolonged Pesticide Use on Natural Soil Microbiome Dynamics Using Metagenomics Approach

The residual pesticides in soil can affect the natural microbiome composition and genetic profile that drive nutrient cycling and soil fertility. In the present study, metagenomic approach was leveraged to determine modulations in nutrient cycling and microbial composition along with connected nexus of pesticide, antibiotic, and heavy metal resistance in selected crop and fallow soils having history of consistent pesticide applications. GC-MS analysis estimated residuals of chlorpyrifos, hexachlorbenzene, and dieldrin showing persistent nature of pesticides that pose selective pressure for microbial adaptation. Taxonomic profiling showed increased abundance of pesticide degrading Streptomyces, Xanthomonas, Cupriavidus, and Pseudomonas across the selected soils. Genes encoding for pesticide degrading cytochrome p450, organophosphorus hydrolase, aldehyde dehydrogenase, and oxidase were predominant and positively correlated with Bacillus, Sphingobium, and Burkholderia. Nitrogen-fixing genes (nifH, narB, and nir) were relatively less abundant in crop soils, correlating to the decrease in nitrogen-fixing bacteria (Anabaena, Pantoea, and Azotobacter). Microbial enzymes involved in carbon (pfkA, gap, pgi, and tpiA) and phosphorus cycle (gmbh and phnJ) were significantly higher in crop soils indicating extensive utilization of pesticide residuals as a nutrient source by the indigenous soil microbiota. Additionally, presence of antibiotic and heavy metal resistance genes suggested potential cross-resistance under pressure from pesticide residues. The results implied selective increase in pesticide degrading microbes with decrease in beneficial bacteria that resulted in reduced soil health and fertility. The assessment of agricultural soil microbial profile will provide a framework to develop sustainable agriculture practices to conserve soil health and fertility.

Comprehensive investigation of the mutagenic potential of six pesticides classified by IARC as probably carcinogenic to humans

Pesticides are significant environmental pollutants, and many of them possess mutagenic potential, which is closely linked to carcinogenesis. Here we tested the mutagenicity of all six pesticides classified probably carcinogenic (Group 2A) by the International Agency of Research on Cancer: 4,4'-DDT, captafol, dieldrin, diazinon, glyphosate and malathion. Whole genome sequencing of TK6 human lymphoblastoid cell clones following 30-day exposure at subtoxic concentrations revealed a clear mutagenic effect of treatment with captafol or malathion when added at 200 nM or 100 μM initial concentrations, respectively. Each pesticide induced a specific base substitution mutational signature: captafol increased C to A mutations primarily, while malathion induced mostly C to T mutations. 4,4'-DDT, dieldrin, diazinon and glyphosate were not mutagenic. Whereas captafol induced chromosomal instability, H2A.X phosphorylation and cell cycle arrest in G2/M phase, all indicating DNA damage, malathion did not induce DNA damage markers or cell cycle alterations despite its mutagenic effect. Hypersensitivity of REV1 and XPA mutant DT40 chicken cell lines suggests that captafol induces DNA adducts that are bypassed by translesion DNA synthesis and are targets for nucleotide excision repair. The experimentally identified mutational signatures of captafol and malathion could shed light on the mechanism of action of these compounds. The signatures are potentially suitable for detecting past exposure in tumour samples, but the reanalysis of large cancer genome databases did not reveal any evidence of captafol or malathion exposure.

Bioenergetic Shifts in Humpback Whale Fibroblasts Upon Chemical Exposure

Southern Hemisphere humpback whales accumulate persistent and toxic chemicals, which are transported to Antarctica through distant sources and in situ usage. The extreme seasonal migration-associated fast of humpback whales results in the remobilization of persistent and lipophilic environmental contaminants from liberated fat stores. Mitochondria play a key role in lipid metabolism, and any disruption to mitochondrial function is expected to influence whole-organism bioenergetics. It is therefore of interest to advance understanding of the impact of known contaminants of the Antarctic sea-ice ecosystem upon humpback whale cellular bioenergetics. Using cell line-based in vitro testing, this study employed the Seahorse Extracellular Flux Analyzer to study cellular metabolic activity in live humpback whale fibroblast cells. The assay, based on oxygen consumption rate, provides insights into the cause of cellular bioenergetic disruption. Immortalized skin fibroblasts were exposed to four priority environmental chemicals found in the Antarctic sea-ice ecosystem. Our findings reveal chemical-dependent functional alterations and varying bioenergetic profile responses. Chlorpyrifos was observed to decrease mitochondrial basal oxygen consumption; dieldrin increased basal oxygen consumption; trifluralin's impact was dose-specific, and endosulfan displayed no effect. Our results provide unique insights into environmental chemical mechanisms of action on cellular bioenergetics, generating much-needed taxa-specific chemical effect data in support of evidence-based conservation policy and management.

Analysis of nationwide soil pesticide pollution: Insights from China

China is a typical agricultural country that heavily relies on pesticides. Some pesticides can remain in the soil after application and thus pose a significant threat to human health. In order to characterize the status and hazards of nationwide soil contamination, this study extracted concentration data from published literature and analyzed them by a scoring approach, standard comparison and health risk assessment. For the soil pollution score, northern regions got the highest values, such as Henan (0.63), Liaoning (0.55), Heilongjiang (0.54) and Jilin (0.53), which implies high soil pesticide residues in these provinces. In contrast, Qinghai (-0.77), Guizhou (-0.64) and Tibet (-0.63) had lower scores. China's soil pesticide standards cover only 16 pesticides, and these pesticide concentrations were all below the corresponding standards. Direct exposure to soil pesticides in this study generally posed a negligible risk to children. Furthermore, pesticide dissipation and usage intensity in each province were analyzed as they were possible influences on pollution. The result showed that soil in the northern regions could accumulate more pesticides than those in the southern regions, and this geographic pattern was basically consistent with the distribution of soil pollution. However, the relationship between agricultural activities and soil pollution was less well characterized. It is recommended to establish a long-term monitoring database for pesticides and include more pesticides in regulatory frameworks. Additionally, efforts to accelerate pesticide degradation and shift the planting structure to reduce pesticide usage can help alleviate the pressure on soil from pesticides. This study can serve as a critical reference for policymakers and stakeholders in the field of agriculture.

Dieldrin accumulation, distribution in plant parts and phytoextraction potential for several plant species and Cucurbita pepo varieties

Dieldrin, an organochlorine pesticide (OCP) widely used for crop protection in the second half of the 20th century till the 70's, is worldwide still present in arable soils. It can be transferred to crops, notably cucurbits, depending on plant species and cultivars. Finding strategies to decrease OCP bioavailability in soil is therefore a main concern. Phytomanagement strategies could provide (i) ready-to-use short term solution for maintaining the production of edible plant parts with dieldrin concentrations below the Maximum Residue Limits (MRL) and (ii) long-term solution for dieldrin phytoextraction reducing progressively its bioavailability in the soil. This field study aimed at determining dieldrin accumulation capacities and allocation pattern in 17 non-Cucurbitaceae species and 10 Cucurbita pepo varieties, and assessing the dieldrin phytoextraction potential of these plant species when grown to maturity in a historically dieldrin-contaminated soil. Out of the non-Cucurbitaceae species, vetiver was the only one able to accumulate significant amounts of dieldrin, which mainly remained in its roots. All C. pepo varieties were able to uptake and translocate high dieldrin amounts into the shoots, leading to the highest phytoextraction potential. Despite the intraspecific variability in dieldrin concentration in zucchini plant parts, mainly in the reproductive organs, the phytoextraction capacity for shoots and fruits was high for all tested varieties (147 to 275 μg dieldrin plant-1, corresponding to 5.6 % of the n-heptane extractable soil dieldrin), even for the one with low fruit dieldrin concentration. Both food safety and phytoextraction could be achieved by selecting productive zucchini varieties displaying low dieldrin concentration in fruits and high one in shoots.

First report on pollutant accumulation and associated microbial communities in the freshwater sponge Spongilla lacustris (Linnaeus, 1759) from the sub-Arctic Pasvik River (Norway)

This explorative study was aimed at first characterizing the sponge Spongilla lacustris (Linnaeus, 1759) from the sub-Arctic Pasvik River (Northern Fennoscandia), in terms of associated microbial communities and pollutant accumulation. Persistent organic pollutants were determined in sponge mesohyl tissues, along with the estimation of the microbial enzymatic activity rates, prokaryotic abundance and morphometric traits, and the analysis of the taxonomic bacterial diversity by next-generation sequencing techniques. The main bacterial groups associated with S. lacustris were Alphaproteobacteria and Gammaproteobacteria, followed by Chloroflexi and Acidobacteria. The structure of the S. lacustris-associated bacterial communities was in sharp contrast to those of the bacterioplankton, being statistically close to those found in sediments. Dieldrin was measured at higher concentrations in the sponge tissues (3.1 ± 0.4 ng/g) compared to sediment of the same site (0.04 ± 0.03 ng/g). Some taxonomic groups were possibly related to the occurrence of certain contaminants, as was the case of Patescibacteria and dieldrin. Obtained results substantially contribute to the still scarce knowledge of bacterial community diversity, activities, and ecology in freshwater sponges. PRACTITIONER POINTS: Microbial community associated with Spongilla lacustris is probably shaped by the occurrence of certain contaminants, mainly dieldrin and heavy metals. A higher accumulation of dieldrin in the sponge mesohyl tissues than in sediment was determined. S. lacustris is suggested as sponge species to be used as a sentinel of pesticide pollution in the Pasvik River. S. lacustris, living in tight contact with soft substrates, harbored communities more similar to sediment than water communities.

Application of biochar on soil bioelectrochemical remediation: behind roles, progress, and potential

Bioelectrochemical systems (BESs) that combine electrochemistry with biological methods have gained attention in the remediation of polluted environments, including wastewater, sludge, sediments, and soils. The most attractive advantage of BESs is that the solid electrode is used as an inexhaustible electron acceptor or donor, and biocurrent directly converted from organics can afford the reaction energy of contaminant breakdown, crossing the internal energy barrier of endothermic degradation, which achieves a continuous biodegradation process without the simultaneous use of exogenetic chemicals and bioelectricity recovery. However, soil BESs are hindered by expensive electrode materials, difficult pollutant and electron transfer, low microbial competitive activity, and biocompatibility in contamination remediation. Fortunately, introducing biochar into soil BESs could reveal a high potential in addressing these BES inadequacies. The characteristics of biochar, e.g., conductivity, transferability, high specific surface area, high porosity, large functional groups, and biocompatibility, can improve the performance of soil BESs. In fact, biochar not only carries electrons but also transfers nutrients, pollutants, and even bacteria by facilitating transmission in the bioelectric field of BESs. Consequently, the abilities of biochar make for better functionality of BESs. This review collates information on the roles, application, and progress of biochar in soil BESs, and future prospects are given. It is beneficial for environmental researchers and engineers to extend BES application in environmental remediation and to assist the progress of carbon sequestration and emission reduction based on the inertia of biochar and the blocking of electron flow to form methane.

Deciphering the kinetics and pathway of lindane biodegradation by novel soil ascomycete fungi for its implication in bioremediation

Lindane, an organochlorine pesticide, negatively affects living beings and the ecosystem. In this study, the potential of 9 Ascomycetes fungi, isolated from an hexachlorocyclohexane dumpsite soil, was tested for biodegradation of lindane. The strain Pleurostoma richardsiae (FN5) showed lindane biodegradation rate constant (K value) of 0.144 d-1 and a half-life of 4.8d. The formation of intermediate metabolites upon lindane degradation including γ-pentachlorocyclohexene, 2,4-dichlorophenol, phenol, benzene, 1,3- cyclohexadiene, and benzoic acid detected by GC-MS and the potential pathway adopted by the novel fungal strain FN5 for lindane biodegradation has been elucidated. The study of gene profiles with reference to linA and linB in strain FN5 confirmed the same protein family with the reported heterologs from other fungal strains in the NCBI database. This study for the first time provides a thorough understanding of lindane biodegradation by a novel soil-borne Ascomycota fungal strain for its possible application in field-scale bioremediation.

Exploring the role of microbes for the management of persistent organic pollutants

Persistent organic pollutants (POPs) are chemicals which have been persisting in the environment for many years due to their longer half-lives. POPs have gained attention over the last few decades due to the unsustainable management of chemicals which led to their widespread and massive contamination of biota from different strata and environments. Due to the widespread distribution, bio-accumulation and toxic behavior, POPs have become a risk for organisms and environment. Therefore, a focus is required to eliminate these chemicals from the environment or transform into non-toxic forms. Among the available techniques for the removal of POPs, most of them are inefficient or incur high operational costs. As an alternative to this, microbial bioremediation of POPs such as pesticides, polycyclic aromatic hydrocarbons, polychlorinated biphenyls, pharmaceuticals and personal care products is much more efficient and cost-effective. Additionally, bacteria play a vital role in the biotransformation and solubilization of POPs, which reduces their toxicity. This review specifies the Stockholm Convention that evaluates the risk profile for the management of existing as well as emerging POPs. The sources, types and persistence of POPs along with the comparison of conventional elimination and bioremediation methods of POPs are discussed comprehensively. This study demonstrates the existing bioremediation techniques of POPs and summaries the potential of microbes which serve as enhanced, cost-effective, and eco-friendly approach for POPs elimination.

Distribution, Sources, and Risk Assessment of Organochlorine Pesticides in Water from Beiluo River, Loess Plateau, China

The Loess Plateau has been a focus of public discussion and environmental concerns over the past three decades. In this study, in order to investigate the effect of OCP pollution in water of the Beiluo River, concentrations of 25 OCPs at 17 locations in the water were examined. The results showed that the concentration of ∑OCPs in the water ranged from 1.76 to 32.57 ng L^-1, with an average concentration of 7.23 ng L^-1. Compared with other basins in China and abroad, the OCP content in the Beiluo River was at a medium level. Hexachlorocyclohexane (HCH) pollution in the Beiluo River was mainly from the mixed input of lindane and technical HCHs. Dichlorodiphenyltrichloroethane (DDT) pollution was mainly from the mixed input of technical DDTs and dicofol. Most of the OCP pollution came from historical residues. The risk assessment results showed that hexachlorobenzene (HCB) and endosulfan had high ecological risks in the middle and lower reaches of the Beiluo River. Most residual OCPs were not sufficient to pose carcinogenic and non-carcinogenic health risks to humans. The results of this study can provide a reference for OCP prevention and control and watershed environmental management.

A review on simultaneous heavy metal removal and organo-contaminants degradation by potential microbes: Current findings and future outlook

Industrial processes result in the production of heavy metals, dyes, pesticides, polyaromatic hydrocarbons (PAHs), pharmaceuticals, micropollutants, and PFAS (per- and polyfluorinated substances). Heavy metals are currently a significant problem in drinking water and other natural water bodies, including soil, which has an adverse impact on the environment as a whole. The heavy metal is highly poisonous, carcinogenic, mutagenic, and teratogenic to humans as well as other animals. Multiple polluted sites, including terrestrial and aquatic ecosystems, have been observed to co-occur with heavy metals and organo-pollutants. Pesticides and heavy metals can be degraded and removed concurrently from various metals and pesticide-contaminated matrixes due to microbial processes that include a variety of bacteria, both aerobic and anaerobic, as well as fungi. Numerous studies have examined the removal of heavy metals and organic-pollutants from different types of systems, but none of them have addressed the removal of these co-occurring heavy metals and organic pollutants and the use of microbes to do so. Therefore, the main focus of this review is on the recent developments in the concurrent microbial degradation of organo-pollutants and heavy metal removal. The limitations related to the simultaneous removal and degradation of heavy metals and organo-pollutant pollutants have also been taken into account.

Organochlorine residues in muscle of European eels (Anguilla anguilla) from four Spanish Mediterranean wetlands and coastal lagoons

European eels (Anguilla anguilla) are an endangered species throughout their range, and chlorine organic compounds are some of the most important pollutants for marine species. Data on contaminants in eel stocks remain incomplete, so organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) in muscle of European eels from four Spanish Mediterranean ecosystems were analyzed. COPs are presents in eels from all areas, but some compounds are not detected: HCH α, β and γ (lindane), endosulfan sulfate, heptachlor, and PCBs 28, 52 and 180. The high percentage of DDT 2,4' in eels from S'Albufera des Grau Natural Park, an ecosystem with good ecological status according to the Water Framework Directive, and the presence of PCBs in S'Albufereta Natural Reserve indicate the need to carry out further studies in the future. The results obtained can improve the management of this species in the studied areas.

Metolachlor adsorption using walnut shell biochar modified by soil minerals

The removal of pesticide residues in soil is a research hotspot. The metolachlor (MET) adsorption by walnut shell biochar (BC) modified with montmorillonite (MBC), illite (IBC), and kaolinite (KBC), as well as the original BC (OBC) was investigated. The characteristics of samples were studied by scanning electron microscopy and mapping analysis, Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetry, and chemical stability analysis. The effects of the dosage, ionic strength, and pH, and determined the adsorption kinetics and isotherms for MET with the BCs were analyzed. In addition, response surface methodology regression model analysis was conducted and the adsorption mechanisms were investigated. The results showed that the thermal stability and chemical stability of MBC, IBC, and KBC were higher than those of OBC, and MBC had the greatest stability. The MET adsorption rates of OBC, MBC, IBC, and KBC were 62.15%, 92.47%, 87.97%, and 83.31%, respectively. The kinetic fitting results and adsorption mechanisms showed that the modification of BC with minerals enhanced the physical adsorption of MET. The maximum MET adsorption capacities by OBC, MBC, IBC, and KBC were 39.68 mg g^-1, 68.49 mg g^-1, 65.79 mg g^-1, and 65.36 mg g^-1, respectively. Hydrogen bonds, π-π bonds, coordination bonds, and hydrophobic interactions were the key adsorption mechanisms. Therefore, the mineral-modified BCs were characterized by high adsorption rates and stability. This approach can make BC more efficient, with higher performance as a low cost soil amendment.