Study of the bioremediation of atrazine under variable carbon and nitrogen sources by mixed bacterial consortium isolated from corn field soil in Fars province of Iran

Immediate effects of atrazine application on soil organic carbon and selected macronutrients and amelioration by sawdust biochar pretreatment

Increasing use of herbicides has contributed immensely to current soil and water degradation in the tropics. Published works on effects of herbicides on soil organic carbon (SOC) – a major indicator for soil health and macronutrients and their enhancement by biochar are scarce for soils in Africa despite heavy herbicide applications every cropping season. This incubation trial evaluated immediate effects of atrazine application on SOC and selected soil macronutrients. The potential of sawdust (SD) biochar to mitigate associated SOC and macronutrients depletion was also assessed. A total of 950 g soil was placed in each leaching column (20 cm length and 7 cm diameter). The experiment was a factorial combination of four SD biochar types: SD + poultry manure (PM) pyrolyzed at 350 °C, SD-PM at 350 °C, SD + PM at 450 °C and SD-PM at 450 °C applied at two rates of 5 and 10 t/ha equivalent to 2.38 and 4.76 g/950 g soil, respectively. Atrazine alone and absolute control (AC) that received neither biochar nor atrazine were included for comparison. The treatments were replicated thrice in completely randomized design. Appropriate biochar was applied within 5 cm soil depth, moistened to field capacity, and left to equilibrate for 2 weeks. Thereafter, 20 mL atrazine solution was applied at 2.5 kg a.i/ha (achieved through 6.75 g atrazine powder/l of distilled water). Basal NPK 15:15:15 fertilizer mixed with urea at 0.1 and 0.03 g/900 g soil, respectively, was applied to mimic farmers’ practice on atrazine treated fields. Maize seeds were thereafter sown in the treated soils and nurtured for 2 weeks. Data taken on soil pH, SOC, exchangeable bases, available phosphorus, and dry biomass weight (DBW) of maize seedlings at the expiration of the trial were subjected to two-way analysis of variance using Genstat Statistical Package with means separated using LSD at 5% probability level. There were significant reductions in soil pH (5.8%), SOC (31%), and Ex. Ca (27%) in atrazine alone soil compared to AC. Contrarily, similar atrazine treated soil pretreated with SD biochar had increased soil pH, SOC, exchangeable Ca, available P, and DBW by 5.6 (in SD + PM@450 °C), 73.6 (SD-PM@450 °C), 84 (SD + PM@450 °C), 2,338.4 (SD + PM@450 °C), and 154.8% (SD + PM@350 °C), respectively, dominantly at 10 t/ha compared to AC. Sole atrazine treated soil was, however, higher in soil available P (23.8 mg/kg) and TDBW (0.56 g) against 5.42 mg/kg and 0.42 g from AC, respectively. Biochar pH and organic carbon were the most influential biochar properties contributing significantly to SOC sequestration and macronutrient enrichment in the atrazine treated soil. Pretreatment of soils with sawdust biochar prior to atrazine application is, therefore, recommended for mitigating associated organic carbon and macronutrient depletion in the soils for enhanced maize production.

Use of wood and cork in biofilters for the simultaneous removal of nitrates and pesticides from groundwater

About 13% and 7% of monitored groundwater stations in Europe exceed the permitted levels of nitrates (50 mg NO₃^- L^-1) or pesticides (0.1 μg L^-1), respectively. Although slow sand filtration can remove nitrates via denitrification when oxygen is limited, it requires an organic carbon source. The present study evaluates the performance of the use of wood pellets and granulated cork as carbon sources in bench-scale biofilters operated under water-saturated and water-unsaturated conditions for more than 400 days. The biofilters were monitored for nitrate (200 mg L^-1) and pesticide (mecoprop, diuron, atrazine, and bromacil, each at a concentration of 5 μg L^-1) attenuation, as well as for the formation of nitrite and pesticide transformation products. Microbiological characterization of each biofilter was also performed. The water-saturated wood biofilter achieved the best nitrate removal (>99%), while the cork biofilters lost all denitrification power over time (from 38% to no removal). The unsaturated biofilter columns were not effective for removing nitrates (20-30% removal). As for pesticides, all the biofilters achieved high removal rates of mecoprop and diuron (>99% and >75%, respectively). Atrazine removal was better in the wood-pellet biofilters than the cork ones (68-96% vs. 31-38%). Bromacil was only removed in the water-unsaturated cork biofilter (67%). However, a bromacil transformation product was formed there. The water-saturated wood biofilter contained the highest number of denitrifying microorganisms, with Methyloversatilis as the characteristic genus. Microbial composition could explain the high removal of pesticides and nitrates achieved in the wood-pellet biofilter. Overall, the results indicate that wood-pellet biofilters operated under water-saturated conditions are a good solution for treating groundwater contaminated with nitrates and pesticides.

Managing the efficiencies of three different bacterial isolates for removing atrazine from wastewater

Three individual bacterial isolates previously isolated from two types of soil with a different history of atrazine applications were chosen, purified, and subjected to subsequent work. Identification of the individual bacterial isolates was conducted using molecular methods 16S rRNA and then tested for their atrazine degradation potentials. Effects of different parameters like mixing, starvation, UV exposure, and sodium citrate for enhancing the atrazine bioremediation process by identified bacteria were also studied. The molecular method identified individual bacterial isolates as Stenotrophomonas sp. strain SD2 (strain SD2), Bacillus cereus strain BC3 (strain BC3), and Paenarthrobacter ureafaciens strain AD3 (strain AD3). The bacterial isolate strain AD3 was able to degrade 47.95% of atrazine after 28 days. Mixing strain AD3 with strain BC3 showed almost doubled of atrazine degradation percentage (61.39%) of using strain BC3 as an individual isolate (36.59%). The atrazine degradation efficacy for Stenotrophomonas sp. strain SD2, Bacillus cereus strain BC3, and Paenarthrobacter ureafaciens strain AD3 was increased between 1.28 and 4.32 folds after the starvation process. The UV exposure enhanced the efficiencies of the tested isolates either individual or mixtures (from 1.08 to 4.63-fold). Adding sodium citrate as a stimulator to the media of growing the tested isolates enhanced their potential for atrazine degradation.

PWC-based evaluation of groundwater pesticide pollution in the Júcar River Basin

Predicting pesticides' behavior in the environment is necessary to anticipate and minimize their adverse effects. Despite the use of pesticides in Spain is increasing, the implementation and use of predictive mathematical models is seldomly done in practice due to the lack of available data. In this original work, the Pesticide Root Zone Model version 5 (PRZM 5) mathematical model under the Pesticide in Water Concentration 1.52 (PWC) interface has been applied to model pesticide behavior in nine groundwater bodies located inside the Júcar River Basin (JRB) in Spain. Mathematical modeling allowed calculating the maximum concentration of pesticides after completing the calibration process. Bromacil, terbuthylazine, atrazine, desethyl-terbuthylazine, and terbumeton concentrations in groundwater were simulated between 2006 and 2019. Results show that the maximum pesticide concentration value on every well exceeds the current Spanish Maximum Concentration Limit (0.1 μg/L). PRZM 5 was able to reproduce pesticide concentration observations over time despite the limited amount of available data. This study contributes to assessing environmental risks caused by the use of pesticides inside the JRB and can potentially be applied in other areas of interest.

Correlating biodegradation kinetics of 2,3,7,8-tetrachlorodibenzo-p-dioxin to the dynamics of microbial communities originating from soil in Vietnam contaminated with herbicides and dioxins

We studied the succession of bacterial communities during the biodegradation of 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD). The communities originated from a mesocosm with soil from Bien Hoa airbase in Vietnam heavily contaminated with herbicides and dioxins. They were grown in defined media with different carbon and Gibbs energy sources and 2,3,7,8-TCDD. Cultures with dimethyl sulfoxide (DMSO) as the sole carbon and energy source degraded about 95% of 2,3,7,8-TCDD within 60 days of cultivation. Those with an additional 1 mM of vanillin did that in roughly 90 days. Further 16S rRNA gene amplicon sequencing showed that the increase in relative abundance of members belonging to the genera Bordetella, Sphingomonas, Proteiniphilum, and Rhizobium correlated to increased biodegradation of 2,3,7,8-TCDD in these cultures. A higher concentration of vanillin slowed down the biodegradation rate. Addition of alternative carbon and Gibbs energy sources, such as amino acids, sodium lactate and sodium acetate, even stopped the degradation of 2,3,7,8-TCDD completely. Bacteria from the genera Bordetella, Achromobacter, Sphingomonas and Pseudomonas dominated most of the cultures, but the microbial profiles also significantly differed between cultures as judged by non-metric multidimensional scaling (NMDS) analyses. Our study indicates that 2,3,7,8-TCDD degradation may be stimulated by bacterial communities preadapted to a certain degree of starvation with respect to the carbon and energy source. It also reveals the succession and abundance of defined bacterial genera in the degradation process.

Optimizing the metribuzin degrading potential of a novel bacterial consortium based on Taguchi design of experiment

Metribuzin (MB) is used for control of weeds in crops like potato, maize and sugarcane. Its extensive and unjudicial use has resulted in various environmental issues; hence it is very critical to remediate this herbicide at the respective point source. Plant associated, MB degrading bacterial strains, Rhodococcus rhodochrous sp. AQ1, Bacillus tequilensis sp. AQ2, Bacillus aryabhattai sp. AQ3 and Bacillus safensis sp. AQ4 were isolated, and a consortium MB3R was developed. For degradation of MB by the consortium MB3R, various parameters i.e., pH, temperature, inoculum density and pesticide concentration were optimized by using Taguchi design of experiment (DOE). MB degradation was dependent upon all the four factors. The contribution of each factor on MB degradation was according to the order: temperature > inoculum density > pH > pesticide concentration. Fitness of Taguchi DOE in forecasting the optimum response, was confirmed experimentally by using optimized levels of the four factors i.e., pH 7.0, temperature 30 °C, pesticide concentration 45 mg l^-1 and an inoculum density of 5.0 × 10 ⁵ CFU ml^-1 whereby 98.63% MB degradation was observed. Appearance and subsequent degradation of three MB metabolites, desamino-metribuzin (DA), diketo-metribuzin (DK) and desamino-diketo-metribuzin (DADK) during biodegradation by the consortium was observed.

Novel hydrolytic de-methylthiolation of the s-triazine herbicide prometryn by Leucobacter sp. JW-1

s-Triazine herbicides have been widely used in recent decades and caused serious concern over contamination of groundwater, surface water and soil. A novel bacterial strain JW-1 was isolated from activated sludge and identified as Leucobacter sp. based on comparative morphology, physiological characteristics and comparison of the 16S rDNA gene sequence. JW-1 was capable of using methylthio-s-triazine prometryn as a sole source of carbon and energy in pure culture. Favorable conditions for prometryn degradation were found at pH7.0-9.0 and temperature of 37-42°C. The degradation half-life of prometryn at 50mgL^-1 was remarkably as short as 1.1h, and increased to 6.0h when the initial concentration increased to 400mgL^-1. The strain JW-1 could degrade 100% of ametryn, 99% of simetryn, 41% of propazine, 43% of atrazine, 28% of simazine, 12% of terbutylhylazine, 10% of prometon and 13% of atraton at 50mgL^-1 of each herbicide in 2days. Prometryn was converted to 2-hydroxypropazine and methanthiol via a novel hydrolysis pathway. 2-Hydroxypropazine was then transformed to N-isopropylammelide and the final product cyanuric acid via two sequential deamination reactions. In addition to biodegradation by Leucobacter sp. JW-1, the hydrolytic de-methylthiolation would be valuable in biocatalysis.

Photocatalytic degradation of atrazine herbicide with Illuminated Fe+3-TiO2 Nanoparticles

BACKGROUND

Atrazine is a herbicide that is widely used to control broadleaf and grassy weeds for growing many crops especially in maize production. It is a frequently detected herbicide in many groundwater resources. This study aimed to assess the feasibility of using ultraviolet radiation UV and fortified nanoparticles of titanium dioxide (TiO₂) doped with trivalent iron to remove atrazine from aqueous phase and determin the removal efficiency under the optimal conditions.

RESULTS

The results of this study demonstrated that the maximum atrazine removal rate was at pH = 11 in the presence of Fe^{+ 3}-TiO₂ catalyst =25 mg/L and the initial concentration of atrazine equal to 10 mg/L. As the reaction time increased, the removal rate of herbicide increased as well. Atrazine removal rate was enhanced by the effect of UV radiation on catalyst activation in Fe⁺³-TiO₂/UV process. It was also revealed that pH has no significant effect on atrazine removal efficiency (p > 0.05).

CONCLUSION

Based on the data obtained in this study, atrazine removal efficiency was increased by increasing pH, initial atrazine concentration, catalyst, and contact time. The results also showed Fe⁺³-TiO₂/UV process was an appropriate method to reduce atrazine in contaminated water resources. In conclusion, Fe⁺³-TiO₂/UV process may enhance the rate of atrazine reduction in highly polluted water resources (more than 99%).

Biodegradation of 2,4-dichlorophenoxyacetic acid by bacteria with highly antibiotic-resistant pattern isolated from wheat field soils in Kurdistan, Iran

Recently, there has been increasing interest to clean up the soils contaminated with herbicide. Our aim was to determine the bioremediation of 2,4-dichlorophenoxyacetic acid (2,4-D) from wheat fields which have a long history of herbicide in Sanandaj. Based on our literature survey, this study is the first report to isolate and identify antimicrobial resistant bacteria from polluted wheat field soils in Sanandaj which has the capacity to degrade 2,4-D. From 150 2,4-D-exposed soil samples, five different bacteria were isolated and identified based on biochemical tests and 16S ribosomal RNA (rRNA). Pseudomonas has been the most frequently isolated genus. By sequencing the 16S rRNA gene of the isolated bacteria, the strains were detected and identified as a member of the genus Pseudomonas sp, Entrobacter sp, Bacillus sp, Seratia sp, and Staphylococcus sp. The sequence of Sanandaj 1 isolate displayed 87% similarity with the 16S rRNA gene of a Pseudomonas sp (HE995788). Similarly, all the isolates were compared to standard strains based on 16S rRNA. Small amounts of 2,4-D could be transmitted to a depth of 10-20 cm; however, in the depth of 20-40 cm, we could not detect the 2,4-D. The isolates were resistant to various antibiotics particularly, penicillin, ampicillin, and amoxicillin.

The nonylphenol biodegradation study by estuary sediment-derived fungus Penicillium simplicissimum

Nonylphenols (NPs) are persistent organic pollutants (POPs) with estrogenic properties that can perform endocrine-disrupting activities. By using high-concentration NP as environmental selection pressure, one NP biodegradation strain named NPF-4 was isolated and purified from estuary sediment of the Moshui River. It was identified as Penicillium simplicissimum (PS1) by appearance and 18S rDNA analysis. In different culture situations, the strain mass growth and biodegradation ability were evaluated. Within 4-n-nonylphenol (4-n-NP) initial concentration of 20 mg L(-1), it could be degraded 53.76, 90.08, and 100.00 % at 3, 7, and 14 days, respectively. In feeding experiments, it showed that NPF-4 could use 4-n-NP as a sole carbon source. Based on seven products/intermediates detected with GC and LC-MS, a novel biopathway for 4-n-NP biodegradation was proposed, in which sequential hydroxylation, oxidation, and decarboxylation at terminal β-C atom may occur for 4-n-NP detoxification, even complete mineralization in the end.

Atrazine and its metabolites degradation in mineral salts medium and soil using an enrichment culture

An atrazine-degrading enrichment culture was used to study degradation of atrazine metabolites viz. hydroxyatrazine, deethylatrazine, and deisopropylatrazine in mineral salts medium. Results suggested that the enrichment culture was able to degrade only hydroxyatrazine, and it was used as the sole source of carbon and nitrogen. Hydroxyatrazine degradation slowed down when sucrose and/or ammonium hydrogen phosphate were supplemented as the additional sources of carbon and nitrogen, respectively. The enrichment culture could degrade high concentrations of atrazine (up to 110 μg/mL) in mineral salts medium, and neutral pH was optimum for atrazine degradation. Further, except in an acidic soil, enrichment culture was able to degrade atrazine in three soil types having different physico-chemical properties. Raising the pH of acidic soil to neutral or alkaline enabled the enrichment culture to degrade atrazine suggesting that acidic pH inhibited atrazine-degrading ability. The study suggested that the enrichment culture can be successfully utilized to achieve complete degradation of atrazine and its persistent metabolite hydroxyatrazine in the contaminated soil and water.

Optimizing photo-Fenton like process for the removal of diesel fuel from the aqueous phase

BACKGROUND

In recent years, pollution of soil and groundwater caused by fuel leakage from old underground storage tanks, oil extraction process, refineries, fuel distribution terminals, improper disposal and also spills during transferring has been reported. Diesel fuel has created many problems for water resources. The main objectives of this research were focused on assessing the feasibility of using photo-Fenton like method using nano zero-valent iron (nZVI/UV/H2O2) in removing total petroleum hydrocarbons (TPH) and determining the optimal conditions using Taguchi method.

RESULTS

The influence of different parameters including the initial concentration of TPH (0.1-1 mg/L), H2O2 concentration (5-20 mmole/L), nZVI concentration (10-100 mg/L), pH (3-9), and reaction time (15-120 min) on TPH reduction rate in diesel fuel were investigated. The variance analysis suggests that the optimal conditions for TPH reduction rate from diesel fuel in the aqueous phase are as follows: the initial TPH concentration equals to 0.7 mg/L, nZVI concentration 20 mg/L, H2O2 concentration equals to 5 mmol/L, pH 3, and the reaction time of 60 min and degree of significance for the study parameters are 7.643, 9.33, 13.318, 15.185 and 6.588%, respectively. The predicted removal rate in the optimal conditions was 95.8% and confirmed by data obtained in this study which was between 95-100%.

CONCLUSION

In conclusion, photo-Fenton like process using nZVI process may enhance the rate of diesel degradation in polluted water and could be used as a pretreatment step for the biological removal of TPH from diesel fuel in the aqueous phase.

Removal of 2,4-Dichlorophenolyxacetic acid (2,4-D) herbicide in the aqueous phase using modified granular activated carbon

BACKGROUND

Low cost 2,4-Dichlorophenolyxacetic acid (2,4-D) widely used in controlling broad-leafed weeds is frequently detected in water resources. The main objectives of this research were focused on evaluating the feasibility of using granular activated carbon modified with acid to remove 2,4-D from aqueous phase, determining its removal efficiency and assessing the adsorption kinetics.

RESULTS

The present study was conducted at bench-scale method. The influence of different pH (3-9), the effect of contact time (3-90 min), the amount of adsorbent (0.1-0.4 g), and herbicide initial concentration (0.5-3 ppm) on 2,4-D removal efficiency by the granular activated carbon were investigated. Based on the data obtained in the present study, pH of 3 and contact time of 60 min is optimal for 2,4-D removal. 2,4-D reduction rate increased rapidly by the addition of the adsorbent and decreased by herbicide initial concentration (63%). The percent of 2,4-D reduction were significantly enhanced by decreasing pH and increasing the contact time. The adsorption of 2,4-D onto the granular activated carbon conformed to Langmuir and Freundlich models, but was best fitted to type II Langmuir model (R2 = 0.999). The second order kinetics was the best for the adsorption of 2,4-D by modified granular activated carbon with R2 > 0.99. Regression analysis showed that all of the variables in the process have been statistically significant effect (p < 0.001).

CONCLUSIONS

In conclusion, granular activated carbon modified with acid is an appropriate method for reducing the herbicide in the polluted water resources.