Persistent Pesticides Research Articles

Structure-Energetics-Property Relationships Support Computational Design of Photodegradable Pesticides.

Development of high-performing pesticides with tunable degradation properties is vital to increasing the safety and effectiveness of tomorrow's analogs. Chromophoric dissolved organic matter in the excited triple state (3CDOM*) is known to play a key role in the removal of pesticides via indirect photodegradation. However, the potential of these transformations to guide the design of safer chemicals has not yet been fully realized. Here, we report a two-tier computational framework developed to probe and predict both kinetics and thermodynamics of 3CDOM*-pesticide interactions. In the first tier, robust in silico models were constructed by fitting free energies obtained from density functional theory (DFT) calculations to cell potentials and second-order rate constants for the 3CDOM*-pesticide electron transfer. In the second tier, Gibbs free energies and corresponding free energy barriers, determined in solution using the Marcus theory, were applied to develop a quick yet accurate screening approach based on the frontier molecular orbital (FMO) Theory. Being highly mechanistic and spanning ca. 1500 unique 3CDOM*-pesticide interactions, our approach is both robust and broadly applicable. To that end, the outcomes of our computational models were integrated into an easy-to-use decision framework that can guide structure-based design of less persistent pesticide analogs.

Eliminating pesticide quinalphos from surface waters using synthesized GO-ZnO nanoflowers: Characterization, degradation pathways and kinetic study

The presence of highly toxic and persistent pesticides in water bodies causes serious problems to human beings as well as aquatic life. Quinalphos is one such widely used organophosphorus pesticide in agricultural fields. Herein, for degradation and mineralization of quinalphos, ZnO nanoflowers and their hybrid nanocomposite with graphene oxide have been synthesized. FESEM analysis confirmed the formation of ZnO nanoflowers over nanosheets of graphene oxide having a thickness of 20 ± 10 nm. GO-ZnO composite exhibited remarkable photocatalytic activity in comparison to pure ZnO. 98 % degradation of quinalphos was achieved using GO-ZnO nano-catalyst at 6 pH within 45 min of irradiations, whereas it was 80 % for bare ZnO nanoflowers. Higher degradation with hybrid nanocomposite was attributed to improved surface area (36 m2 g−1), a substantial reduction in bandgap energy from 3.10 to 2.90 eV and enhanced charge separation (e−/h+ pairs) after the addition of GO. Reaction kinetics study followed pseudo-first-order behaviour. Further, mineralization to the extent of 90 % in 90 min was confirmed by TOC analysis. Based on identified intermediates, using LCMS analysis, degradation pathways were proposed. The plausible pathways confirmed the presence of smaller and safer reaction intermediates supported by excitation of e− from nanocomposite followed by oxidation of quinalphos with huge free radicals. Overall, this study is significant in terms of using photocatalysis as a tertiary treatment of quinalphos pesticide wastewater at pH 6 in a short duration.

Assessment of toxicity and potential health risk from persistent pesticides and heavy metals along the Delhi stretch of river Yamuna

The present study aims at the assessment of environmental quality of the most polluted stretch of river Yamuna along the megacity of Delhi. The study was conducted in order to examine toxicity and health hazards associated with persistent pollutants present in the fluvial ecosystem. Eighty four sediment and 56 vegetable samples from same locations were collected from the Delhi segment of river Yamuna flood plain in order to examine 20 organochlorine pesticides (OCPs) and 9 heavy metals (Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn). Both the organic and inorganic groups of persistent toxic substances were monitored and analysed for the extent of eco-toxicological as well as dietary health risks posed to the local population. Eco-toxicological assessment was done based on sediment quality guidelines, enrichment factor, geo-accumulation index, degree of contamination and Pollution Load Index. The dietary-risk was assessed with the help of translocation factors (TF) of these pollutants in vegetables. Carcinogenic and non-carcinogenic health risks from consumption of vegetables were also investigated.The level of concern for heavy metals was greater than that of OCPs as per the sediment quality guidelines. DDT, Cd, Pb and Zn had maximum concentrations corresponding to level 3 of concern, while Cr and Ni reached up to the highest i.e., 4th level of concern. Sediment samples were found to be enriched and contaminated significantly with Cd and moderately with Pb, as represented respectively by enrichment factors and contamination factors (CF). CF for metals lied in order Zn > Cd > CrNi > PbCu. Pollution load index was highest at the location lying on the exit point of Yamuna in Delhi. TF values greater than 1 were observed in majority of samples analysed for Ni, Cr, Cu and Zn. Spinach topped among vegetables in terms of metal contamination. Cd, Ni and Pb accumulated more in the roots, as against Mn, Zn, Cu and Cr which had higher accumulation in the shoots. Translocation factors were substantially high in vegetables for most of the OCPs, clearly indicating bioaccumulation and potential health risk to the consumers. Health risk to humans was assessed for non-carcinogenic and carcinogenic potentials from ingestion of vegetables. Hazard Quotient (HQ) > 1 due to radish (roots and leaves) and cauliflower consumption in children indicated non-carcinogenic risk. Hazard Index (HI) beyond 1 for all the vegetables (except onion leaves) confirmed substantial cumulative risk. Lifetime cancer risk (LCR) revealed moderate (spinach, radish, beet root and cauliflower) to low (all the others) levels of carcinogenic risk to humans. Cancer risks from γ-HCH, β- HCH, Hept, Hept Ep, Ald, p,p’-DDT, and Cr exposure through the food chain could be well established.

Conceptual approaches to rehabilitation of pesticide-polluted soils of Ukraine

The Concept of Rehabilitation of Contaminated Soils has been developed, which substantiates the ways to restore areas contaminated with persistent organic pesticides. The practical implementation of the Concept will contribute to the transfer of existing land use systems to the principles of sustainable agricultural development, as well as the preservation, reproduction and expansion of biodiversity, as well as improving the environmental safety of agro-ecosystems for sustainable development of the Agrosphere. The Concept combines ways of practical implementation of environmentally friendly methods of cleaning pesticide-contaminated areas and further use of rehabilitated land in the process of agricultural activity in Ukraine. The problem of pesticide pollution of agroecosystems is proposed to be solved by using scientifically sound ecologically safe methods of soil remediation with multicomponent pesticide pollution developed at the Institute of Agroecology and Environmental Management of NAAS, in particular using bioremediation methods. The following are proposed for use: methods of agroecological monitoring of areas contaminated with persistent organic pollutants, methods of phytotesting and phytoremediation of soils contaminated with resistant pesticides. For phytoremediation of contaminated soils, it is proposed to use annual cultivated (barley, wheat, beans, soybeans, zucchini, pumpkin) and wild (dandelion, bitter wormwood, common wormwood, wheatgrass) species of plant-mediators, which are suitable for phytostabilation and in the conditions of multicomponent soil pollution. The main stages of the Concept implementation are: complex agroecological monitoring of soils contaminated with residues of persistent organic pollutants (POPs); comprehensive ecotoxicological assessment of soil condition; determining the degree of chemical degradation of soils; adaptation of remediation technologies to the specifics of the area in need of cleaning; introduction of ecologically safe remediation methods into practical use; realization of prospects of further use of rehabilitated soils in various branches of agriculture; taking into account the ecological and economic efficiency of the use of remediation methods. Possibility and ways of using restored areas in the process of agricultural activity, taking into account the main stages of implementation of the Concept are set out in the developed in the Institute of Agroecology and Environmental Management of NAAS «Scientific and methodological recommendations for restoration of soil contaminated with organochlorine pesticides depending on their toxicity» and «Scientific and methodological recommendations for the use of restored areas in the process of agricultural activity».

Persistence and diffusion behaviour of chlorpyrifos in five different species of vegetables: A comparative analysis

Understanding of pesticide persistence and diffusion on the fresh vegetables are extremely important in food safety and decontamination process. In this study, we examine the persistence and diffusion behaviour of chlorpyrifos pesticide in five different species of vegetables. The chlorpyrifos pesticide was spiked on the vegetable surfaces and the extracted samples from peel and tissues were subjected to Gas Chromatography equipped with a Flame Photometric Detector (GC-FPD). Further, the chlorpyrifos diffusion behaviour was compared with the osmotic potential, shear strength, cuticular chemical profile and microstructure of peel surface of vegetables. The persistence analysis results revealed that chlorpyrifos level was decreased in peel surface and diffusion rate was increased in inner tissue with respect to durations. Within 72 h exposure, chlorpyrifos reached 0.7 cm depth into the inner tissue of vegetables. Significant level of chlorpyrifos diffusion with P ≤ 0.05 was observed in beetroot (2.47%), khon khol (1.46%) and brinjal (0.92%) compared to cucumber and potato. Remarkably, there was no direct linkage between the chlorpyrifos diffusion rate, osmotic potential and toughness of vegetables. In addition, the Gas Chromatography Mass Spectroscopy (GC-MS) and Scanning Electron Microscopy (SEM) analyses revealed that epicuticular surface microstructure and chemical profiles were not correlated with the chlorpyrifos diffusion in all the tested vegetables. The study results concludes that chlorpyrifos diffusion is vegetable species specific and it is highly variable between the species.

Mobilization and transport of pesticides with runoff and suspended sediment during flooding events in an agricultural catchment of Southern Brazil

Brazil is one of the largest consumers of pesticides in the world, and these chemicals present a high contamination risk for the country's water bodies. The mechanisms of mobilization and transport of pesticides from cropland to river systems are controlled by runoff and erosion processes occurring at the catchment scale. In addition to the excessive use of pesticides, the transport processes of these substances are also accelerated by inadequate soil management and the absence of soil conservation measures at the catchment scale. The current research relied on hydrological monitoring to investigate the transport and persistence of pesticides in response to hydrological dynamics. The study was conducted in the Conceição River watershed where runoff and suspended sediment fluxes are continuously monitored at the outlet. This study area is representative of the grain production system in southern Brazil including the application of large amounts of pesticides combined with extensive runoff and erosion problems. Sample collection in the river for pesticide analysis included the analysis of both water and suspended sediment. The sediment deposit analysis was performed in a single location at 4 depths. Results demonstrate the occurrence of pesticides including simazine, 2,4-D, carbendazim, imidacloprid, tebuconazole, propiconazole, tetraconazole, and trifloxystrobin in water, while glyphosate and AMPA were detected in suspended sediments, and AMPA and carbendazim were found in sediment deposits. The study demonstrated the strong dependence of the mechanisms of pesticide mobilization and transport in the catchment with the intra- and interevent variability of hydro-sedimentary processes. Pesticide detections can be related to several factors, including the magnitude of the rainfall event, the period of pesticide application, or the transport of suspended sediment. All these factors are correlated, and the mechanisms of transportation play an important role in the connections between sink and sources. The results suggest that pesticide monitoring should take into account the runoff and erosion pathways in each particular catchment, and it should especially include the monitoring of major rainfall events for identifying and quantifying the occurrence of pesticides in the environment. The transport of pesticides indicates to be potentiated by intensive pesticide use, the magnitude of rainfall-runoff events, and the absence of runoff control measures (e.g., terracing). These results demonstrate that water and soil conservation techniques should be planned and coordinated at the watershed scale to reduce the connectivity of water and sediment flows from agricultural areas to river systems with the implementation of effective runoff control practices. This will control the mobilization agents (runoff), as well as limit the connection between the sources and the water bodies.

Persistent pesticides: effects of endosulfan at the molecular level on the aquatic invertebrate Chironomus riparius.

Although banned in multiple areas, due to its persistence in the environment, endosulfan constitutes a significant environmental concern. In this work, fourth instar Chironomus riparius larvae were exposed at environmentally relevant endosulfan concentrations of 0.1, 1, and 10 μg/L for 24 h to analyze the possible effects of this acaricide on gene expression and enzymatic activity. Transcriptional changes were studied through the implementation of a real-time polymerase chain reaction array with 42 genes related to several metabolic pathways (endocrine system, detoxification response, stress response, DNA reparation, and immune system). Moreover, glutathione-S-transferase (GST), phenoloxidase (PO), and acetylcholinesterase (AChE) activities were assessed. The five pathways were differentially altered by endosulfan exposure with significant changes in the E93, Dis, MAPR, Met, InR, GSTd3, GSTt3, MRP1, hsp70, hsp40, hsp24, ATM, PARP, Proph, and Def genes. Besides, all of the measured enzymatic activities were modified, with increased activity of GST, followed by PO and AChE. In summary, the results reflected the effects provoked in C. riparius at molecularlevel despite the absence of lethality. These data raise concerns about the strong alteration on different metabolic routes despite the low concentrations used. Therefore, new risk assessment strategies should consider include the effects at the sub-organismal level as endpoints in addition to the classical ecologically relevant parameters (such as survival). This endeavor will facilitate a comprehensive evaluation of toxicants in the environment.

Evidence of Chlordecone Resurrection by Glyphosate in French West Indies.

The widespread use of pesticides in agriculture during the last several decades has contaminated soils and different Critical Zone (CZ) compartments, defined as the area extended from the top of the vegetation canopy to the groundwater table, and it integrates interactions of the atmosphere, lithosphere, biosphere, and hydrosphere. However, the long-term fate, storage, and transfer dynamics of persistent pesticides in CZ in a changing world remain poorly understood. In the French West Indies, chlordecone (CLD), a toxic organochlorine insecticide, was extensively applied to banana fields to control banana weevil from 1972 to 1993 after which it was banned. Here, to understand CZ trajectories we apply a retrospective observation based on marine sediment core analyses to monitor long-term CLD transfer, fate, and consequences in Guadeloupe and Martinique islands. Both CLD profiles show synchronous chronologies. We hypothesized that the use of glyphosate, a postemergence herbicide, from the late 1990s onward induced CZ modification with an increase in soil erosion and led to the release of the stable CLD stored in the soils of polluted fields. CLD fluxes drastically increased when glyphosate use began, leading to widespread ecosystem contamination. As glyphosate is used globally, ecotoxicological risk management strategies should consider how its application affects persistent pesticide storage in soils, transfer dynamics, and widespread contamination.

Isolation and Characterization of a Bacterial Strain Enterobacter cloacae (Accession No. KX438060.1) Capable of Degrading DDTs Under Aerobic Conditions and Its Use in Bioremediation of Contaminated Soil

DDT is one of the most persistent pesticides among all the different types of organo-chlorine pesticides used. Among all the degradation methods, bacterial degradation of DDT is most effective. The present study was conducted to isolate different bacteria present in waste samples which have the ability to degrade DDT present in the soil in the minimum possible period of time and to observe the effect of different physical and chemical properties of the soil samples. Many pesticide degrading bacteria were isolated and identified through cultural, biochemical tests and further identified by 16S RNA sequencing method. The most potent strain DDT 1 growth in mineral salt medium supplemented with DDT as the only source of carbon (5-100 PPM) and was monitored at an optical density of 600 nm. The growth parameters at different physio-chemical conditions were further optimized. The result showed that Enterobacter cloacae had maximum growth in 15 days. FTIR analysis of the residual DDT after 15 days incubation showed that Enterobacter cloacae was able to degrade pesticide into its further metabolites of DDD, DDE, DDNU and other components can be used for biodegradation of DDT present in contaminated soil and water ecosystems.

Persistence of carbaryl pesticide in environment using system dynamics model

Carbaryl, one of the carbamate insecticides are used extensively for pest control in agriculture. The chemical is highly valued for its rapid action and relatively short environmental persistence. Because of its widespread and intensive use, residues of carbaryl have the potential to contaminate the environment. This study aims to formulate a system dynamics model to simulate a degradation process of carbaryl. Since carbaryl was not readily volatilizing, this study only estimates the concentration and degradation of carbaryl in soil and water. The result revealed that carbaryl degraded rapidly, with a half-life of 7 days in soil and two days in water. The model was validated with a laboratory experiment using solid phase extraction reversed-phase high-performance liquid chromatography to determine carbaryl concentration. 12.82 % percentage error compared to the experimental value indicated that the developed model’s prediction was acceptable. The model can be used to estimate the presence of carbaryl pesticide in soil and water. Findings from this study can be used to assess the fate and the impact of carbaryl pesticide in the environment.

Pesticide occurrence and persistence entering recreational lakes in watersheds of varying land uses.

Currently little is known of newer pesticide classes and their occurrence and persistence in recreational lakes. Therefore, the objectives of this study were to (1) assess average pesticide concentrations and loadings entering recreational lakes in three mixed land use watersheds throughout the growing season, (2) evaluate pesticide persistence longitudinally within the lakes, and (3) perform an ecotoxicity assessment. Six sampling campaigns were conducted at three lakes from April through October 2018 to measure the occurrence and persistence during pre, middle, and post growing season. Polar organic chemical integrative samplers (POCIS) were placed in streams near lake inlets and monthly samples were collected for analysis of twelve pesticides. Additional monthly grab water samples were taken at each POCIS location and at the midpoint and outlet of each lake. All pesticide samples were analyzed using liquid chromatography/tandem mass spectrometry (LC/MS/MS) and individual pesticide loading rates were determined. Occurrence and persistence of specific pesticides were significantly different between lakes in varying watershed land uses. Specifically, the recreational lake receiving predominately urban runoff had the highest load of pesticides, likely in the form of biocides, entering the waterbody. Concentrations of imidacloprid exceeded acute and chronic invertebrate levels for 11% and 61% of the sampling periods, respectively, with the recreational lake receiving predominately urban runoff having the most occurrences. Findings from this study are critical for preventing and mitigating potential effects of pesticides, specifically applied as biocides in urban landscapes, from entering and persisting in recreational lakes.

The impact of dosing sequence on the removal of the persistent pesticide metaldehyde using powdered activated carbon with coagulation and clarification

Removal of pesticides from drinking water remains a challenge for water treatment suppliers throughout the world. A combined treatment of dissolved air flotation (DAF) and powdered activated carbon (PAC) was investigated as a treatment process for removal of the recalcitrant pesticide metaldehyde. The PAC dosing position relative to the coagulant was studied regarding its impact on the removal of NOM and pesticide, floc formation and the clarification efficiency. Four different water sources were spiked with the pesticide and treated using PAC. A PAC dose of 100 mg/L using a contact time of 20 min was required in order to effectively remove pesticide to the compliance concentrations for all of the water sources. The pesticide adsorption rate (kmet) decreased as the source water DOC increased, moving from 79.5–21.0 mg/μg/min with an increase in DOC from 2.6 to 6.5 mg/L. When combined with coagulation, the sequence of addition of PAC followed by coagulant was most effective due to increased incorporation of PAC into the floc, large floc size (median floc size 800 μm) and a high level of pesticide removal, reducing the metaldehyde concentration to 0.18 μg/L. Limited incorporation of PAC into flocs was observed when the adsorbent was added after the coagulant. The results provide a rational basis for selection of process conditions for pesticide removal using PAC and clarification.

Persistent Organic Pollutants and Kidney Function over a 6-year follow-up: Findings from the Hispanic Community Health Study/Study of Latinos (HCHS/SOL)

Background: Few studies have evaluated associations between persistent organic pollutants (POPs) and kidney function. We aimed to determine if levels of POPs measured at baseline were associated with estimated glomerular filtration rate (eGFR) and urine albumin-creatinine ratio (ACR) after 6 years of follow up. Methods: We measured serum levels of multiple polybrominated diphenyl ethers (PBDEs), polychlorinated biphenyls (PCBs) and persistent pesticides, and markers of kidney function among participants in the Hispanic Community Health Study/Study of Latinos (HCHS/SOL) Persistent Organic Pollutants, Endogenous Hormones and Diabetes in Latinos Ancillary Study. The ancillary study selected males and females aged 45 to 74 years with normal glucose or prediabetes at baseline. Individual weighted linear regression models were used to examine if natural log (ln) transformed summary measures of POP concentrations were associated with eGFR and ln transformed ACR at study visit 2, adjusting for baseline kidney function, time between visits, and relevant covariates. Results: The study included 1,072 participants (mean age 54 years, 80% born outside the United States, baseline geometric mean ACR 6.3 mg/g, and mean eGFR 93 ml/min/1.73 m2). Total PBDEs were inversely associated with eGFR at visit 2 (β=-1.5 (95% CI -2.8, -0.26) ml/min/1.73 m2 for an increase of 1 lnPBDE, p=0.02). An increase of 1 ln∑PCB concentration was associated with an increase of β=0.14 (95% CI -0.01, 0.29) mg/g in lnACR (p=0.06). We observed similar positive associations between total estrogenic PCBs (p=0.01) and Warner CYP2B PCBs (p=0.04) with ACR. An increase of 1 lnDDE concentration was associated with a decrease in lnACR (β=-0.08 (95% CI -0.15, -0.01) mg/g, p=0.02). Conclusions: The estimated changes observed suggest that POPs may play a role in kidney disease. Possible mechanisms awaiting further exploration include interference with cytochrome p450 activity by PCBs and inhibition of activity of endogenous androgens harmful to kidney function by DDT/DDE.

Correlates of persistent endocrine disrupting chemical mixtures among reproductive-aged Black women

Background: Polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), and persistent pesticides are endocrine-disrupting chemicals (EDCs). Demographic and dietary variables have been associated with EDC exposure, but few studies have examined correlates of EDC mixtures.Methods: We used cross-sectional data from a Detroit-based prospective cohort of Black women aged 23-35 years. At baseline, we measured PCBs, PBDEs, and pesticides in non-fasting plasma samples of 765 women. Socioeconomic, demographic, and dietary data were collected through self-administered questionnaires, interviews, and clinic visits. We conducted a principal component analysis (PCA) to characterize profiles of exposure to mixtures of log-transformed lipid-adjusted chemicals. Three principal components (PCs) explained >75% of the variance. We used multivariable linear regression to estimate mean differences (β) in PC scores for each correlate, controlling for confounders determined a priori.Results: PC-1 accounted for 50.9%, PC-2 for 15.0% and PC-3 for 9.2% of the variance of chemical concentrations. PC-1 explained the most variance for organochlorine pesticides and PCB Wolff Groups 2B and 3 (PCB 99, 138/158, 146, 153, 156, 170, 180, 183, 187, 194, 196/203, 199, hexachlorobenzene, oxychlordane, trans-nonachlor, and 2,2-bis(4-chlorophenyl)-1,1-dichloroethene); PC-2 for brominated flame retardants (PBDE 28, 47, 99, 153 and 209); and PC 3 for Wolff Group 2A plus PCB 28 (PCB 28, 66, 74, 105, and 118). Having been breastfed in infancy was positively associated with PC-1 (β=0.33, 95% CI=-0.14,0.53) and negatively associated with PC-2 (β=-0.13, 95% CI=-0.26,-0.13) and PC-3 (β=-0.12, 95% CI=-0.21,-0.02). Age, smoking, fish and alcohol consumption were positively associated with PC-1, suggesting these factors are related to higher concentrations of PC-1 biomarkers. Other findings included a positive association of BMI with PC-2, and an inverse association of lactation with PC-1 and PC-3.Conclusions: We characterized distinct profiles of EDC mixtures among Black women in our study, which may help to describe exposure pathways and target interventions.

In-situ fabrication of ternary (3D/2D/2D) prism‒like structures with dramatically enhancement on degradation of profenofos: A systemic study

In the present work, a novel (3D/2D/2D) prism-like ZGO‒MOF hybrid nanocomposite was successfully prepared via two-pot hydro-thermal process and employed as a catalyst for the degradation of organic persistent pesticide such as profenofos (PF). Due to more toxicity, the removal of such organic compounds are necessary in environmental aspects. The prepared nanocomposites were characterized and well explained using FT‒IR, XRD, UV‒DRS, SEM‒EDX, TEM, TGA‒DTA, PL and BET surface area measurements. The OH and O2− radicals was benign effective oxidative species involved in the ZGO‒MOF system for the mineralization of organic pollutants. Besides, ZGO‒MOF showed excellent photo-stability over five repetitive runs for the removal of organic pesticides with minimal drop on catalytic activity. Eventually, the intended photocatalytic mechanisms and degradation pathways of PF are readily determined in detail based on experimental results. The catalyst achieves excellent efficiency of about 94 %. Possible PQ oxidative pathways and their reaction intermediates were observed by LC–MS. Therefore, the pollutant which primarily oxidize into ring-ruptured components into innocuous products like H2O, CO2 and a few in-organic salts. With the concern of its environmental friendly, low‒cost, and benign simple synthesis, ZGO‒MOF was expected to be a promising choice for applications in wastewater management.

Biodegradation of Pesticides at the Limit: Kinetics and Microbial Substrate Use at Low Concentrations.

The objective of our study was to test whether limited microbial degradation at low pesticide concentrations could explain the discrepancy between overall degradability demonstrated in laboratory tests and their actual persistence in the environment. Studies on pesticide degradation are often performed using unrealistically high application rates seldom found in natural environments. Nevertheless, biodegradation rates determined for higher pesticide doses cannot necessarily be extrapolated to lower concentrations. In this context, we wanted to (i) compare the kinetics of pesticide degradation at different concentrations in arable land and (ii) clarify whether there is a concentration threshold below which the expression of the functional genes involved in the degradation pathway is inhibited without further pesticide degradation taking place. We set up an incubation experiment for four weeks using 14C-ring labeled 2-methyl-4-chlorophenoxyacetic acid (MCPA) as a model compound in concentrations from 30 to 20,000 μg kg–1 soil. To quantify the abundance of putative microorganisms involved in MCPA degradation and their degradation activity, tfdA gene copy numbers (DNA) and transcripts (mRNA) were determined by quantitative real-time PCR. Mineralization dynamics of MCPA derived-C were analyzed by monitoring 14CO2 production and 14C assimilation by soil microorganisms. We identified two different concentration thresholds for growth and activity with respect to MCPA degradation using tfdA gene and mRNA transcript abundance as growth and activity indices, respectively. The tfdA gene expression started to increase between 1,000 and 5,000 μg MCPA kg–1 dry soil, but an actual increase in tfdA sequences could only be determined at a concentration of 20,000 μg. Accordingly, we observed a clear shift from catabolic to anabolic utilization of MCPA-derived C in the concentration range of 1,000 to 5,000 μg kg–1. Concentrations ≥1,000 μg kg–1 were mainly associated with delayed mineralization, while concentrations ≤1,000 μg kg–1 showed rapid absolute dissipation. The persistence of pesticides at low concentrations cannot, therefore, be explained by the absence of functional gene expression. Nevertheless, significant differences in the degradation kinetics of MCPA between low and high pesticide concentrations illustrate the need for studies investigating pesticide degradation at environmentally relevant concentrations.

Enhanced degradation of diuron by two Bacillus species isolated from diuron contaminated sugarcane and pineapple-cultivated soils in Kenya

It has been shown from diverse geographical locations that soils with repeated applications of pesticides display enhanced degradation of the pesticides which usually remain recalcitrant for a long time. In Kenya, agricultural activities have been using many different persistent pesticides for pest control. A study was undertaken to determine if the soils with repeated application history could show enhanced degradation of diuron. Laboratory degradation studies using non sterile sugarcane and pineapple-cultivated soils with over 5 years' application history showed enhanced degradation amounting to 80.2% and 86.2% of 5 mg/g initially applied diuron while sugarcane and pineapple-cultivated soils without application history degraded 34.4% and 48.4% of initially applied diuron after 146 days of incubation, respectively. Through liquid culture experiments with sugarcane and pineapple-cultivated soils and diuron as the carbon source, two bacterial strains capable of degrading diuron were isolated. By use of 16S rRNA comparative gene sequence technique, the strains were shown to be closely related to Bacillus muralis/Bacillus simplex and Bacillus pseudomycoides, respectively. These pure isolates were able to degrade diuron up to 51.0% and 54% of 50 mg/L after 46 days of incubation, respectively. The metabolites N-(3,4-dichlorophenyl)-N-methylurea and 3,4-dichloroaniline were reported as major by-products of diuron degradation in the two study sites with adapted microbes. The biodegradation capability of the strains isolated in this study indicates their microbial bioremediation potential for diuron mineralization in the contaminated soils.

The quality of soil organic matter, accessed by 13C solid state nuclear magnetic resonance, is just as important as its content concerning pesticide sorption

The global increase of food production has been achieved mainly through the intensive use of inputs such as pesticides. Once released to the soil, sorption (which could be represented by Freundlich solid-water distribution coefficients – KF) and degradation are two governing processes that determine the distribution and persistence of pesticides in the environment. In spite of the huge dataset, the only apparent generalisation is the high correlation between KF and soil organic matter (SOM) content. However, in this work no correlation was observed between KF and organic C content (OC) and so the obtained KOC (KF normalised by OC) spread out in a wide range: 1100 to 11,400 mL g−1 for abamectin; and 30–150 mL g−1 for atrazine, both ranges corroborate with data from literature. These high variabilities indicate that other soil components or SOM quality strongly interfere in the pesticide sorption in addition to SOM content. Seeking to estimate the influence of SOM quality in the abamectin and atrazine KOC values, the humic acids, a fraction of the SOM, was analysed by 13C nuclear magnetic resonance spectroscopy (13C NMR) and Principal Component (PC) Regression. The first PC of 13C NMR spectra presented negative loadings for aliphatic compounds and positive loadings for aryl C, typical of partially oxidised pyrogenic C. Their scores showed strong correlation with the abamectin KOC values (R2 = 0.91, p < 5 10−8) and weaker with atrazine KOC (R2 = 0.63, p < 0.0001), in addition to a smaller standardised slope: 1.01 for abamectin and 0.76 for atrazine. These results could be explained by the higher hydrophobicity of abamectin, being thus more prone to interact with the polycondensed aryl groups from the pyrogenic C. It is also important to highlight that humic acids are useful proxies for understanding the paramount interaction of SOM with pesticides.

Plasmid-Mediated Biodegradation of Chlorpyrifos and Analysis of Its Metabolic By-Products.

Organophosphate pesticide persistence is an emerging menace to the environment and despite this fact, its use has been enhanced due to its high efficiency. Bioremediation using microorganisms would be the only means by which these hazardous compounds could be wiped out without disturbing the environmental harmony. The current work studied the molecular mechanism of degradation of Chlorpyrifos (CP) by a bacterial consortium C5 comprising of three soil isolates Staphylococcus warneri (CPI 2), Pseudomonas putida (CPI 9) and Stenotrophomonas maltophilia (CPI 15), which unveiled that the property is plasmid borne. All the isolates were found to possess a 4kb plasmid which could be cured only by using sodium azide. The Escherichia coli JM109 cells when transformed individually with the plasmid of the isolates showed CP degradation in mineral salts medium (MSM) that contained CP as the sole carbon source. The degradative enzyme organophosphorus hydrolase (~ 60 KDa) of the isolates was extracted and purified to 31.85, 26 and 37.74 fold, respectively. The possible metabolic by-products of CPdegradation by the consortium C5, were also analysed. The LC-Q-Tof MS analysis revealed the presence of the major metabolite 3, 5, 6 -trichloropyridine (TCP) with the formation of chlorpyrifos oxon as the intermediate. The isolates also showed trichloropyridine degradation (> 80%) individually in MSM-TCP medium proving its efficiency to remediate both CP and TCP.

Local-scale dynamics of plant-pesticide interactions in a northern Brittany agricultural landscape

Soil pollution by anthropogenic chemicals is a major concern for sustainability of crop production and of ecosystem functions mediated by natural plant biodiversity. Understanding the complex effects of soil pollution requires multi-level and multi-scale approaches. Non-target and agri-environmental plant communities of field margins and vegetative filter strips are confronted with agricultural xenobiotics through soil contamination, drift, run-off and leaching events that result from chemical applications. Plant-pesticide dynamics in vegetative filter strips was studied at field scale in the agricultural landscape of a long-term ecological research network in northern Brittany (France). Vegetative filter strips effected significant pesticide abatement between the field and riparian compartments. However, comparison of pesticide usage modalities and soil chemical analysis revealed the extent and complexity of pesticide persistence in fields and vegetative filter strips, and suggested the contribution of multiple sources (yearly carry-over, interannual persistence, landscape-scale contamination). In order to determine the impact of such persistence, plant dynamics was followed in experimentally-designed vegetative filter strips of identical initial composition (Agrostis stolonifera, Anthemis tinctoria/Cota tinctoria, Centaurea cyanus, Fagopyrum esculentum, Festuca rubra, Lolium perenne, Lotus corniculatus, Phleum pratense, Trifolium pratense). After homogeneous vegetation establishment, experimental vegetative filter strips underwent rapid changes within the following two years, with Agrostis stolonifera, Festuca rubra, Lolium perenne and Phleum pratense becoming dominant and with the establishment of spontaneous vegetation. Co-inertia analysis showed that plant dynamics and soil residual pesticides could be significantly correlated, with the triazole fungicide epoxiconazole, the imidazole fungicide prochloraz and the neonicotinoid insecticide thiamethoxam as strong drivers of the correlation. However, the correlation was vegetative-filter-strip-specific, thus showing that correlation between plant dynamics and soil pesticides likely involved additional factors, such as threshold levels of residual pesticides. This situation of complex interactions between plants and soil contamination is further discussed in terms of agronomical, environmental and health issues.