Atrazine Degradation In Soil Research Articles

Tracking atrazine degradation in soil combining 14C-mineralisation assays and compound-specific isotope analysis

The quantification of pesticide dissipation in agricultural soil is challenging. In this study, we investigated atrazine biodegradation in both liquid and soil experiments bioaugmented with distinct atrazine-degrading bacterial isolates. This was achieved by combining 14C-mineralisation assays and compound-specific isotope analysis of atrazine. In liquid experiments, the three bacterial isolates mineralised over 40% of atrazine, demonstrating their potential for extensive degradation. However, the kinetics of mineralisation and degradation varied among the isolates. Carbon stable isotope fractionation was similar for Pseudomonas isolates ADPT34 and ADP2T0, but slightly higher for Chelatobacter SR27. In soil experiments, atrazine primarily degraded into atrazine-desethyl, while atrazine-hydroxy was mainly observed in experiments with SR27. Atrazine mineralisation in soil by ADPT34 and SR27 exceeded 40%, whereas ADP2T0 exhibited a mineralisation rate of 10%. In experiments with ADPT34 and SR27, atrazine 14C-residues were predominantly found in the non-extractable fraction, whereas they accumulated in the extractable fraction in the experiment with ADP2T0. Compound-specific isotope analysis (CSIA) relies on changes of stable isotope ratios and holds potential to evaluate herbicide transformation in soil. CSIA of atrazine indicated atrazine biodegradation in water and solvent extractable soil fractions and varied between 29% and 52%, depending on the bacterial isolate. Despite atrazine degradation in both soil fractions, a significant portion of atrazine residues persisted, depending on the bacterial degrader, initial cell concentration, and mineralisation and degradation rates. Overall, our approach can aid in quantifying atrazine persistence and degradation in soil, and in optimizing bioaugmentation strategies for remediating soils contaminated with persistent herbicides.

Prediction of atrazine degradation in soil based on XGBoost model.

We established the optimal model by using the automatic machine learning method to predict the degradation efficiency of herbicide atrazine in soil, which could be used to assess the residual risk of atrazine in soil. We collected 494 pairs of data from 49 published articles, and selected seven factors as input features, including soil pH, organic matter content, saturated hydraulic conductivity, soil moisture, initial concentration of atrazine, incubation time, and inoculation dose. Using the first-order reaction rate constant of atrazine in soil as the output feature, we established six models to predict the degradation efficiency of atrazine in soil, and conducted comprehensive analysis of model performance through linear regression and related evaluation indicators. The results showed that the XGBoost model had the best performance in predicting the first-order reaction rate constant (k). Based on the prediction model, the feature importance ranking of each factor was in an order of soil moisture > incubation time > pH > organic matter > initial concentration of atrazine > saturated hydraulic conductivity > inoculation dose. We used SHAP to explain the potential relationship between each feature and the degradation ability of atrazine in soil, as well as the relative contribution of each feature. Results of SHAP showed that time had a negative contribution and saturated hydraulic conductivity had a positive contribution. High values of soil moisture, initial concentration of atrazine, pH, inoculation dose and organic matter content were generally distributed on both sides of SHAP=0, indicating their complex contributions to the degradation of atrazine in soil. The XGBoost model method combined with the SHAP method had high accuracy in predicting the performance and interpretability of the k model. By using machine learning method to fully explore the value of historical experimental data and predict the degradation efficiency of atrazine using environmental parameters, it is of great significance to set the threshold for atrazine application, reduce the residual and diffusion risks of atrazine in soil, and ensure the safety of soil environment.

Core bacteria carrying the genes associated with the degradation of atrazine in different soils

Atrazine residues can pose serious threats to soil ecology and human health. Currently, the underlying relationship between soil microbial communities and the degradation genes associated with atrazine degradation remains unclear. In this study, the degradation characteristics of atrazine was investigated in ten different soil types. Further, diversity and abundance of degradation genes and succession of the bacterial community were also studied. The degradation of 10 mg/kg atrazine in different soil types exhibited an initial rapid trend followed by a gradual slowdown, adhering to the first-order kinetic equation. Atrazine significantly increased the absolute abundance of atz degradation genes. The increase in the absolute abundance of atzC gene was the largest, whereas that of atzA gene was the smallest, and the trzD gene was only detected in the Binzhou loam soil. Co-occurrence network analysis showed that the number of potential bacterial hosts of atzC was the highest compared with the other atz genes. Atrazine also altered the structural composition of the soil microbial community. The relative abundances of Ochrobactrum, Nocardiopsis, Lactobacillus, and Brevibacterium was increased in the atrazine-treated soils, while those of Conexibate, Solirubacter, and Micromonospora was decreased significantly compared with the control. Additionally, four atrazine-degrading bacterial strains Rhizobium AT1, Stenotrophomonas AT2, Brevibacterium AT3, and Bacillus AT4 were isolated from the atrazine-treated soils. After 14 d for inoculation, their degradation rate for 10 mg/L atrazine ranged from 17.56 % to 30.55 %. Moreover, the relative abundances of the bacterial genera, including these four isolates, in the atrazine-treated soil were significantly higher than those in the control, indicating that they were involved in the synergistic degradation of atrazine in the soil. This study revealed the degradation characteristics of atrazine, distribution of degradation genes, and succession of microbial communities, and explored the internal relationship between microbial community structure and atrazine degradation mechanisms in different soil types.

Experimental degradation of atrazine in soil by dielectric barrier discharge and optimization

In this study, a self-made rotating double-media barrier reactor was used for remediation of atrazine contaminated soil, aiming to provide a reference for industrial application of low-temperature plasma treatment of organic contaminated soil. The effects of applied voltage and reactor state on the reactor discharge performance were investigated. When the applied voltage was increased, the energy efficiency of low-temperature plasma increased; the effect of reactor state was not significant. The effects of input voltage, reactor rotational speed and soil water content on the degradation efficiency of atrazine were investigated, and the results showed that the degradation rate of atrazine increased when the input voltage was 35 kV and the treatment time was 25 min, and the degradation rate of atrazine was 71.12%; when the reactor rotational speed and soil water content were 18.7 r/min and 0.8%, the degradation rates were 73.25% and 65.41%. The response surface method was applied to optimize the selection. The results showed that the significance degree of each factor was input voltage > soil water content > rotating motor speed, and the optimal conditions were 0.6% soil water content, 37 kV input voltage, 18 r/min reactor speed, and 51.93% atrazine degradation rate.

Effects of atrazine on microbial metabolic limitations in black soils: Evidence from enzyme stoichiometry

Long-term input of agricultural chemicals such as pesticides into the soil can increase soil pollution, thereby affecting the productivity and quality of black soil. Triazine herbicide atrazine has been shown to have long-lasting residual effects in black soil. The atrazine residues affected soil biochemical properties, further leading to microbial metabolism restriction. It is necessary to explore the strategies to mitigate the limitations on microbial metabolism in atrazine-contaminated soils. Here, we evaluated the effect of the atrazine on microbial nutrient acquisition strategies as indicated by extracellular enzyme stoichiometry (EES) in four black soils. Atrazine degradation in soil followed the first-order kinetics model across various concentrations ranging from 10 to 100 mg kg−1. We found that the atrazine was negatively correlated with the EES for C-, N-, and P-acquisition. Vector lengths and angles decreased and increased significantly with an increase of atrazine concentration in tested black soils except for Lishu soils. Moreover, the vector angles were >45° for tested four black soils, indicating that atrazine residue had the greatest P-limitation on soil microorganisms. Interestingly, microbial C- and P-limitations with different atrazine concentrations showed a strong linear relationship, especially in Qiqihar and Nongan soils. Atrazine treatment significantly negatively affected microbial metabolic limitation. Soil properties and EES interaction explained up to 88.2% for microbial C-/P-limitation. In conclusion, this study confirms the EES as a useful method in evaluating the effects of pesticides on microbial metabolic limitations.

Remediation of atrazine contaminated soil by microwave activated persulfate system: Performance, mechanism and DFT calculation

Effective remediation of pesticide-contaminated sites is challenging due to high concentrations of pollutants with complete habitat destruction. Herein, microwave (MW)-activated persulfate (PS) system was proposed for remediation of organochlorine pesticide contaminated soil with atrazine (ATZ) as representation. The results revealed that the MW/PS system could achieve 97.9% of ATZ (50 mg/kg) degradation after treatment of 60 min, superior to that by conventional heat-activated PS. And more excellent degradation performance was identified in relatively higher microwave temperature (80 °C) with appropriate PS concentration (24 mmol/L), MW power (400 W) and water-soil ratio (1:1). Moreover, the MW/PS system possessed high tolerance to co-existing substances including Cl−, HCO3− and H2PO4−, and appropriate organic substance content favored ATZ degradation in soil. Reactive oxygen species consisting of SO4•−, OH•, O2•− and 1O2 contributed to ATZ decomposition, among which O2∙− played a principal role. The ATZ degradation pathway was then elucidated by combination of HPLC/MS spectra and DFT calculations, and ATZ overall toxicity was effectively alleviated in MW/PS system in term of toxicity assessment. Additionally, the MW/PS system presented high-performance degradation on such organochlorine pesticides as trichloro ethylene, tetrachloride, hexachlorobenzene and chlordane, suggesting great potentials of this system for remediation of organochlorine pesticides contaminated sites.

Enhanced phytoremediation of atrazine-contaminated soil by vetiver (Chrysopogon zizanioides L.) and associated bacteria.

The intensive and long-term use of atrazine (ATZ) has led to the contamination of agricultural soils and non-target organisms, posing a series of threats to human health through the transmission of the food chain. In this study, a 60-day greenhouse pot experiment was carried out to explore the phytoremediation by Chrysopogon zizanioides L. (vetiver). The uptake, accumulation, distribution, and removal of ATZ were investigated, and the degradation mechanisms were elucidated. The results showed that the growth of vetiver was inhibited in the first 10 days of the incubation; subsequently, the plant recovered rapidly with time going. Vetiver grass was capable of taking up ATZ from the soil, with root concentration factor ranging from 2.36 to 15.55, and translocating to the shoots, with shoot concentration factor ranging from 7.51 to 17.52. The dissipation of ATZ in the rhizosphere soil (97.51%) was significantly higher than that in the vetiver-unplanted soil (85.14%) at day 60. Metabolites were identified as hydroxyatrazine (HA), deethylatrazine (DEA), deisopropylatrazine (DIA), and didealkylatrazine (DDA) in the samples of the shoots and roots of vetiver as well as the soils treated with ATZ. HA, DEA, DIA, and DDA were reported first time as metabolites of ATZ in shoots and roots of vetiver grown in soil. The presence of vetiver changed the formation and distribution of the dealkylated products in the rhizosphere soil, which remarkably enhanced the occurrence of DEA, DIA, and DDA. Arthrobacter, Bradyrhizobium, Nocardioides, and Rhodococcus were the major atrazine-degrading bacterial genera, which might be responsible for ATZ degradation in the rhizosphere soil. Our findings suggested that vetiver grass can significantly promote ATZ degradation in the soil, and it could be a strategy for remediation of the atrazine-contaminated agricultural soil.

Effect of H3PO4-modified biochar on the fate of atrazine and remediation of bacterial community in atrazine-contaminated soil

The application of chemically modified biochar is a promising strategy for the remediation of contaminated (e.g., pesticides) soil. In this study, H3PO4 was used to modify peanut shell to improve the remediation performance of biochar. Surface area (980.19 m2/g), pore volume (0.12 cm3/g), and the functional groups (OH, CO, and phosphorus-containing groups) on the biochar were increased by H3PO4 treatment. The sorption experimental data were well fitted by Freundlich model, while the sorption affinity (Kf) of H3PO4 modified biochar (PBC) for atrazine was 128 times greater than that of the untreated biochar (BC) in the aquatic systems. The Kf values of PBC-amended soil to atrazine were increased by 13.57 times than that of single soil. The strong sorption of PBC on atrazine delayed the degradation of atrazine in soil, and the residual percentage of atrazine in soil and soil-PBC mixture were 4.90% and 71.44% at the end of 60-day incubation, with the degradation half-life increased from 13.3 to 121.6 d. The analysis of high-throughput sequencing results showed that atrazine reduced the diversity of soil microbial community, but the abundance of microorganisms with degradation function increased and became dominant species. The addition of PBC in soil accelerated the microbial remediation of atrazine stress, which may promote the soil nitrogen cycle. Therefore, amendment of atrazine contaminated soil with PBC can reduce the environmental risk of atrazine and benefit the soil microbial ecology.

Modeling Bioavailability Limitations of Atrazine Degradation in Soils

Pesticide persistence in soils is a widespread environmental concern in agro-ecosystems. One particularly persistent pesticide is atrazine, which continues to be found in soils and groundwater in the EU despite having been banned since 2004. A range of physical and biological barriers, such as sorption and mass-transfer into bacterial cells, might limit atrazine degradation in soils. These effects have been observed in experiments and models working with simplified systems. We build on that work by developing a biogeochemical model of the degradation process. We extended existing engineered system models by including refined representations of mass-transfer processes across the cell membrane as well as thermodynamic growth constraints. We estimated model parameters by calibration with data on atrazine degradation, metabolite (hydroxyatrazine) formation, biomass, and isotope fractionation from a set of controlled retentostat/chemostat experiments. We then produced site-specific model predictions for arable topsoil and compared them with field observations of residual atrazine concentrations. We found that the model overestimated long-term atrazine biodegradation in soils, indicating that this process is likely not limited by bioavailability or energetic constraints of microbial growth. However, sorption-limited bioavailability, could explain the long-term fate and persistence of the main degradation metabolite hydroxyatrazine. Future studies should seek alternative controls that drive the observed atrazine persistence in soil. This work helps to bridge the gap between engineered and natural systems, allowing us to use laboratory setups to gain insight into real environmental systems.

Comparative evaluation of industrial hemp varieties: Field experiments and phytoremediation in Hawaii

Industrial hemp (Cannabis sativa L.) is a fast-growing and high biomass producing plant species with wide usage of its materials such as fiber, food, and fuel. There are many varieties containing low concentration of tetrahydrocannabinol (THC). In the present study, it assessed the agricultural feasibility of three industrial hemp varieties with different water management and nitrogen fertilizer treatments, and determined the best ones to cultivate in Hawaii, then evaluated the effects of plant density on the yield and the potential phytoremediation for the herbicide atrazine. The field experiments indicated that it was difficult to grow the variety F75 in Hawaii with a final weight of 13 g and did not live for the full growth season. However, the subtropical fiber hemp variety CHG grew to height of about 190 cm and its weight varied from 150 g to 280 g between two planting densities (100 plants m−2 and 28 plants m−2, respectively). The subtropical seed hemp variety CHY was intermediate at a mean height and weight of about 130 cm and 130 g, respectively. Estimated crop yields were 19 tons acre-1 year-1 (dry weight) for CHG stalks that could be used for building construction and 16 tons acre-1 year-1 (dry weight) for leaves could be used as animal forage. Approximately, 1.7 tons of seeds could be harvested per acre per year from variety CHY. Little water consumption (10 mm week-1) was needed, which corresponds with drought resistance of CHG variety. Use of nitrogen fertilizer at a rate of 100 kg ha-1 did not improve growth of CHG variety more than the existing nitrogen levels in the soil. Phytoremediation potential of industrial hemp was also assessed by field pot studies, in which field soils were fortified with 0, 0.25 and 0.50 mg kg-1 of atrazine. The half-life (t1/2) of atrazine in hemp watered pots was 15 days, whereas t1/2 was approximately 50 and 28 days in the no plant non-watered pots and the no plant watered pots, respectively, suggesting the degradation of atrazine in soils showed a higher efficiency planted with hemp under water irrigation condition. The CHG plants accumulated atrazine from soils, and the enrichment factor in CHG was increased over the course of 28 days (from 0.22 %–0.31 % to 0.63 %–0.89 %), then decreased after 49 days (0.28 %–0.30 %). Overall, these findings revealed that industrial hemp plants were useful for phytoremediation of soils contaminated with atrazine.

Coexisting antibiotic changes the persistence and metabolic profile of atrazine in the environment

Pesticides are widely used in agriculture to control weeds, pests and plant diseases. Antibiotics may be introduced to the agricultural environment by manure fertilizer or wastewater irrigation. Co-existence of antibiotics in field may lead to profound impacts on pesticide residue. In this study, the impacts of oxytetracycline on the environmental fate and metabolic profile of atrazine was investigated, and the disturbance of oxytetracycline on functional genes related to atrazine degradation in soils was also studied. Oxytetracycline could inhibit the degradation of atrazine significantly and prolong the half-life to 1.27 and 1.59 times longer at 5 mg/kg and 50 mg/kg. Also, oxytetracycline altered the composition of atrazine metabolites, including three chloro-s-triazine metabolites (DEA, DIA, DDA) and three hydroxyl metabolites (OH-ATZ, OH-DEA, OH-DIA). Oxytetracycline decreased the ratio of hydroxyl metabolites, while increased the chloro-s-triazine metabolites which had higher toxicity and were easily leached in soil. Atrazine hydrolase genes atzA and trzN were down-regulated by oxytetracycline, which might decrease the hydroxyl metabolite formation and detoxification of atrazine. Oxytetracycline changed the degradation of atrazine and the composition of the metabolites probably by altering the soil microorganisms. The increased persistence and the percentage of the chloro-s-triazine metabolites induced by oxytetracycline might result in increased environmental problems.

Degradation of atrazine in soil by dielectric barrier discharge plasma – Potential singlet oxygen mediation

Dielectric barrier discharge (DBD) was used for the first time to remediate atrazine-polluted soil in a plane-to-grid plasma reactor operating with air at atmospheric pressure. It was established that atrazine degradation efficiency is an increasing function of applied voltage and discharge frequency. The degradation efficiency of atrazine in dry soil reached as high as 86.9% and 98.1% after 60 min of plasma treatment, starting from initial pollutant concentrations of 100 and 10 mg/kg, respectively. Low soil moisture content (5–10%) was found to enhance atrazine degradation in the DBD reactor in comparison to dry soil conditions. Atrazine mineralization after 60 min of treatment was 65.5% as confirmed by total organic carbon (TOC) analysis. The degradation profile of atrazine under DBD treatment was assessed using Fourier transform infrared spectroscopy (FTIR) and ultra-performance liquid chromatography-mass spectrometry (UPLC-MS). Several degradation pathways of atrazine were identified in addition to those previously reported with OH, H2O2, or O3 as the main oxidizing agents. The detected degradants included des-ethyl atrazine, hydroxy atrazine and de-ethylated oligomers of atrazine with the isopropyl group being largely preserved. An atrazine degradation mechanism under DBD conditions is proposed that is consistent with the intermediates identified and supports the dominant involvement of singlet oxygen in initiating the degradation under DBD conditions.

Colonization of plant roots and enhanced atrazine degradation by a strain of Arthrobacter ureafaciens

Our previous research found that culturable atrazine degraders associated with maize roots were dominated by genetically similar strains of Arthrobacter ureafaciens, suggesting their rhizosphere competence. The present study aimed to assess the root-colonizing capacity of strain A. ureafaciens DnL1-1 and to evaluate consequent root-associated degradation of atrazine. A soil-sand assay and pot experiments provided evidence that A. ureafaciens DnL1-1 competitively colonized roots of maize, wheat, and alfalfa following seed inoculation. Atrazine was not absolutely required but promoted colonization of plant roots by the bacterium. In association with plants, A. ureafaciens DnL1-1 enhanced the degradation of atrazine and strongly reduced accumulation of its dealkylated metabolites. Our results show that after low-level inoculation of seeds, the bacterium A. ureafaciens DnL1-1 can establish root populations sufficient for the rapid degradation of atrazine in soil that makes it a promising bioremediation agent which can be easily applied to large areas of polluted soil. Application of the root-colonizing, atrazine-degrading Arthrobacter bacteria as seed inoculants may be a reliable remediation strategy for soils contaminated with chlorinated s-triazines and their degradation products.

Enhanced atrazine degradation is widespread across the United States.

Atrazine (ATZ) has been a key herbicide for annual weed control in corn, with both a soil and post-emergence vegetation application period. Although enhanced ATZ degradation in soil with a history of ATZ use has been reported, the extent and rate of degradation in the US Corn Belt is uncertain. We show that enhanced ATZ degradation exists across much of the country. Soils from 15 of 16 surveyed states had enhanced ATZ degradation. The average ATZ half-life was only 2.3 days in ATZ history soils, compared with an average 14.5 days in soils with no previous ATZ use, meaning that ATZ degrades an average 6 times faster in soils with previous ATZ use. When ATZ is used for several years, enhanced degradation will undoubtedly change the way ATZ is used in agronomic crops and also its ultimate environmental fate. © 2017 Society of Chemical Industry.

Alginate immobilized enrichment culture for atrazine degradation in soil and water system

ABSTRACTAn atrazine degrading enrichment culture, a consortium of bacteria of genus Bacillus along with Pseudomonas and Burkholderia, was immobilized in sodium alginate and was used to study atrazine degradation in mineral salts medium (MSM), soil and wastewater effluent. Sodium alginate immobilized consortium, when stored at room temperature (24 ± 5°C), was effective in degrading atrazine in MSM up to 90 days of storage. The survival of bacteria in alginate beads, based on colony formation unit (CFU) counts, suggested survival up to 90 days and population counts decreased to 1/5th on 120 days. Comparison of atrazine degrading ability of the freely suspended enrichment culture and immobilized culture suggested that the immobilized culture took longer time for complete degradation of atrazine as a lag phase of 2 days was observed in the MSM inoculated with alginate immobilized culture. The free cells resulted in complete degradation of atrazine within 6 days, while immobilized cells took 10 days for 100% atrazine degradation. Further, immobilized cultures were able to degrade atrazine in soil and wastewater effluent. Alginate beads were stable and effective in degrading atrazine till 3rd transfer and disintegrated thereafter. The study suggested that immobilized enrichment culture, due to its better storage and application, can be used to degrade atrazine in soil water system.

Impacts of nitrogen and phosphorus on atrazine-contaminated soil remediation and detoxification by Arthrobacter sp. strain HB-5

The relationship of atrazine-degrading bacteria Arthrobacter sp. HB-5 and nitrogen and phosphorus fertilizer to atrazine degradation and detoxification in soil was investigated in a microcosm pot experiment. Treatments of soil containing atrazine (AW) with atrazine plus strain HB-5 alone (A), together with atrazine and strain HB-5 plus nitrogen alone (AN), phosphate alone (AP), and nitrogen and phosphate together (ANP) were used to investigate atrazine degradation and ecotoxicity. Atrazine residues in the soils were determined by high performance liquid chromatography, while soil ecotoxicity was tested by micronucleus (MN) assay of Vicia faba root tip cells. The results showed that degradation of atrazine in soil could be facilitated by the treatment of strain HB-5 as well as strain HB-5 application with the addition of nitrogenous and/or phosphorus fertilizers. The degradation rates varied as the following: ANP > AP > AN > A > AW in different treatments. At 10 days post treatment, degradation efficiency of over 90 % was achieved in all strain HB-5 treatments except AW, but with no statistically significant differences found between treatments. Soil ecotoxicity was significantly reduced along with the degradation of atrazine by strain HB-5, and the ecotoxicity of soils with applied fertilizer was below that of treatments without fertilizer. On the seventh day and later, the MN frequencies of all treatments were decreased in the control levels except for AW. Thus, adjusting soil nutrient contents not only promoted strain HB-5 to remove atrazine in soil but also mitigated soil ecotoxicity effects caused by atrazine. These results are important keystones for future remediation of atrazine-contaminated soils.

Atrazine degradation in soil: effects of adjuvants and a comparison of three mathematical models

There are few reports on the effects of spray adjuvants on pesticide persistence. The role of three adjuvants used with atrazine on the herbicide's degradation in soil was examined. Three mathematical models were used to describe pesticide disappearance from soil: pseudo-first-order kinetics, the non-linear Gustafson-Holden model and the biexponential function. A mixture of atrazine with Atpolan 80 EC significantly inhibited herbicide soil degradation (DT50 = 78 days), while Adpros 85 SL and Break-Thru S 240 (DT50 = 25 and 24 days respectively) had little effect (DT50 = 22 days, atrazine alone). These results suggest that adjuvant can be a factor in field persistence. DT50 values obtained using the Gustafson-Holden and biexponential models were similar. Only the biexponential model requires an iterative method. A significant effect of one adjuvant on atrazine persistence in soil was observed. The biexponential model best described the disappearance of atrazine in the soil, as indicated by the values of R(2) and RMS and the relative concentration of the herbicide in the soil.

Immobilization of Pseudomonas sp. strain ADP: A stable inoculant for the bioremediation of atrazine

Storage and delivery of beneficial microorganisms are fundamental issues determining their value and effectiveness for a wide range of industrial and environmental purposes. One such application is the use of bacteria for the remediation of soil pollutants such as polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and persistent pesticides. Liquid cultures of a candidate for atrazine degradation in soil and water, Pseudomonas sp. strain ADP (3.67×109 colony-forming units, cfu/mL), when stored at 4 and 25°C, showed a 1 log reduction in cfu/mL occurs after approximately 4 and 2weeks, respectively. When immobilized onto natural zeolite from two sources (a New Zealand and an Australian quarry) and stored in open containers exposed to the atmosphere, survival at 25°C was poor. However, when the cells were immobilized onto the Australian zeolite with xanthan gum and stored in closed containers, survival at 25°C was superior to control cells stored at 4°C. The initial growth medium, zeolite substratum and immobilization matrix excipients all appear to play an important role in the stabilization of Pseudomonas sp. strain ADP. The bacteria immobilized onto Australian zeolite with xanthan remained viable within 1 log unit of initial cfu/g loading and retained their ability to degrade atrazine (as measured by zone clearance on atrazine containing plates) for at least 10weeks at 25°C.

Field Persistence of Repeated Use of Atrazine in Sandy Clay Loam Soil under Maize

Field experiments were conducted with maize as a test crop during 2006-2009 to study the effect of atrazine on its persistence and residue in soil and crop produce as influenced by the quantity of application and seasons. The treatments imposed were control, 0.5 and 1.0 kg ai of atrazine ha-1 and were replicated thrice in randomized block design. For residue analysis, the soil samples were collected at periodical intervals from 0 day to harvest and the crop produce were also sampled at post harvest. The atrazine was determined using GC equipped with FID detector. Persistence of atrazine in soil showed a gradual degradation with advancement in crop growth. The application of atrazine at recommended dose left no residue in the soil whereas the application of atrazine at double the recommended dose recorded 0.056 ppm of atrazine residue in the post harvest soil. Pooled data showed that the dissipation of atrazine was biphasic in nature and the degradation was faster at higher dose of application than at the lower dose. Degradation of atrazine in soil followed first order kinetics and the mean half life of atrazine was 21.54 days. Persistence of atrazine was also influenced by the season and years of application.

The capacity of switchgrass (Panicum virgatum) to degrade atrazine in a phytoremediation setting

Atrazine is a widely used herbicide in agriculture. Non-point source contamination of groundwater and drinking water may pose a significant threat to humans, wildlife, and the environment. Phytoremediation may provide a cost-effective strategy for reducing non-point source contamination of atrazine from agricultural runoff. Previous studies have shown that the rhizosphere of the native prairie grass, switchgrass (Panicum virgatum) is capable of enhancing the degradation of atrazine in soils. Biodegradation also may occur within the plant biomass; however, the extent to which this occurs has not been studied. We hypothesize that switchgrass has the capacity to degrade atrazine in vivo, in addition to the microbial biotransformation that occurs in its rhizosphere. The goals of this study were to characterize the ability of switchgrass to take up atrazine from soils, quantify the amount of biodegradation occurring in the plant, and quantify the amount of degradation occurring in the rhizosphere. Switchgrass seedlings were transplanted into autoclaved and non-autoclaved sand containing 10 µg/g atrazine in sand. Treatments were sacrificed on days 0, 3, and 7. Sand and plant tissue extracts were analyzed by gas chromatography to determine the concentration of atrazine and metabolites in sand and plant tissues. Results demonstrated that leaf biomass is capable of detoxifying atrazine, because metabolites were present in leaf material and not in the sand or root.