Removal of triazines, triazoles and organophophates in biomixtures and application of a biopurification system for the treatment of laboratory wastewaters

Earthworm injury test for in-situ biomonitoring of pesticides in biobeds

Biobeds are presented as an alternative for good pesticide wastewater management on farms. This work proposes a new test for in-situ biomonitoring of pesticide detoxification in biobeds. It is based on the assessment of visually appreciable injuries to Eisenia fetida. The severity of the injury to each exposed individual is assessed from the morphological changes observed in comparison with the patterns established in seven categories and, an injury index is calculated. A linear relationship between the proposed injury index and the pesticide concentration was determined for each pesticide sprayed individually in the biomixture. The five pesticides used were atrazine, prometryn, clethodim, haloxyfop-P-methyl and dicamba. In addition, a multiple linear regression model (i.e., a multivariate response surface) was fitted, which showed a good generalization capacity. The sensitivity range of the injury test was tested from 0.01 to 630 mg kg-1 as the total pesticide concentration. This index is then used to monitor the detoxification of these pesticides in a biomixture (composed of wheat stubble, river waste, and soil, 50:25:25% by volume) over 210 days. The results are compared with standardized tests (Eisenia fetida avoidance test and Lactuca sativa seed germination test) carried out on the same biomixture. The results are also compared with data on the removal of pesticides. The injury test showed a better correlation with the removal of pesticides than the avoidance test and seed germination test. This simple and inexpensive test has proved to be useful for decontamination in-situ monitoring in biobeds.

Biological treatment of pesticide-containing wastewater from coffee crops: selection and optimization of a biomixture and biobed design

The biopurification systems (BPS) or biobeds are employed for the treatment of pesticide-containing wastewater of agricultural origin. The use of these devices for pesticide removal requires the proper optimization of the composition of biomixtures (BPS active matrix) according to the target pesticides applied on a specific crop and the available materials used in their elaboration. This work aims to design a biomixture for the simultaneous treatment of several pesticides applied in coffee crops, according to local practices in Costa Rica. Three biomixtures containing either coffee husk, coconut fiber or rice husk (as the lignocellulosic substrate) were applied for the removal of 12 pesticides. The profiles of pesticide elimination and the mineralization of radiolabeled chlorpyrifos (14C-chlorpyrifos) revealed that the best performance was achieved with the coconut fiber biomixture, even though similar detoxification patterns were determined in every biomixture (according to immobilization in Daphnia magna and germination tests in Lactuca sativa). The optimization of this biomixture's composition by means of a central composite design permitted the definition of two optimal compositions (compost:soil:coconut fiber, % v/v) that maximized pesticide removal: i. 29:7.3:63.7 and ii. 11:7.3:81.7. The validation of these optimized compositions also included the use of an alternative soil from another coffee farm and resulted in overall DT50 values of 7.8-9.0 d for the pesticide mixture. Considering the removal kinetics in the optimized biomixture, a 1 m3 BPS prototype was dimensioned to be eventually used in local coffee farms. This work provides relevant information for the design and implementation of BPS at on-farm conditions for the treatment of pesticide-containing wastewater of a major crop.

Fabrication of β-cyclodextrin-polyacrylamide/covalent organic framework hydrogel at room temperature for the efficient removal of triazole fungicides from environmental water

Triazole is frequently-used fungicide, which can leach into surface water through farmland and cause serious environmental pollution. Continuous exposure to triazole fungicides may cause harm to human health. Herein, β-cyclodextrin-polyacrylamide/covalent organic framework (β-CD-PAAM/TFPB-BD) hydrogel was fabricated at room temperature and used for the efficient removal of triazole fungicides. It displayed a short adsorption equilibrium time (50 min) and a total qe of 79.92 mg g-1. The adsorption process for triazole fungicides on β-CD-PAAM/TFPB-BD hydrogel conforms to the pseudo-second-order kinetic model and Freundlich model. The prepared hydrogel was recyclable and resistant to salt, high temperature, acid, and alkali. The reusability of fabricated sorbent can be achieved (i.e., five extraction cycles) for removal of target fungicides. Moreover, the β-CD-PAAM/TFPB-BD hydrogel was successfully applied to remove triazole fungicides in environmental water with removal efficiency ranging from 79.4% to 99.0%.

Combining Culture-Dependent and Independent Approaches for the Optimization of Epoxiconazole and Fludioxonil-Degrading Bacterial Consortia

Epoxiconazole (EPO) and fludioxonil (FLU) are two widely used fluorinated pesticides known to be highly persistent and with high ecotoxicological potential, turning them into pollutants of concern. This work aimed to optimize two degrading bacterial consortia, previously obtained from an agricultural soil through enrichment with EPO and FLU, by characterizing the contribution of their corresponding bacterial isolates to the biodegradation of these pesticides using both culture-dependent and independent methodologies. Results showed that a co-culture of the strains Hydrogenophaga eletricum 5AE and Methylobacillus sp. 8AE was the most efficient in biodegrading EPO, being able to defluorinate ca. 80% of this pesticide in 28 days. This catabolic performance is likely the result of a commensalistic cooperation, in which H. eletricum may be the defluorinating strain and Methylobacillus sp. may assume an accessory, yet pivotal, catabolic role. Furthermore, 16S rRNA metabarcoding analysis revealed that these strains represent a minority in their original consortium, showing that the biodegradation of EPO can be driven by less abundant phylotypes in the community. On the other hand, none of the tested combinations of bacterial strains showed potential to biodegrade FLU, indicating that the key degrading strains were not successfully isolated from the original enrichment culture. Overall, this work shows, for the first time, the direct involvement of two bacterial species, namely H. eletricum and Methylobacillus sp., in the biodegradation of EPO, while also offering insight on how they might cooperate to accomplish this process. Moreover, the importance of adequate culture-dependent approaches in the engineering of microbial consortia for bioremediation purposes is also emphasized.

Degradation pathway of triazole fungicides and synchronous removal of transformation products via photo-electrocatalytic oxidation tandem MoS2 adsorption

A simple and effective tandem process of photo-electrocatalytic oxidation (PECO)-MoS₂ adsorption was developed for the synchronous removal of triazole fungicides (TFs) and toxicological transformation products (TPs). In order to accurately identify trace TPs and evaluate degradation pathway during water treatment, a sensitive analytical method was developed on the basis of the stir bar sorptive extraction (SBSE) pretreatment tandem LC-MS/MS technique. Firstly, the typical TFs (PRO, TET, and DIN, C₀ = 1.0 mg/L) in actual water samples were treated under the optimal process (bias voltage 1.8 V, pH 4, irradiation intensity 50 mW/cm², 0.05 g MoS₂/100 mL, 350 rpm, adsorption of 5 min). The result indicated that the residues of PRO, TET, and DIN in secondary effluent were 0.0973, 0.0617, and 0.0012 mg/L, respectively, with the removal rates of 90.3%, 93.8%, and 99.9%, respectively, undergoing 30-min photo-electrocatalysis and 5-min adsorption. The alkaline medium was favorable for the adsorption of MoS₂ to TFs. The assessment results of potential cancer risk indicated that the residues of TFs in secondary effluent were safe for drinking water consumption. Besides, the major TPs were identified via the SBSE-HRLC-MS/MS technique, and one possible transformation pathway of TFs was proposed. TFs mainly underwent dehydrochlorination, cyclization, hydroxylation, etc. to produce a series of nitrogenous heterocyclic compounds that possess higher polarity than parents, hinting that TPs might pose potential aquatic toxicity. However, TPs can be removed synchronously by this tandem technique. The current study can provide a theoretical basis for the harmless treatment of TFs in the water environment.

Application of immobilized mycelium-based pellets for the removal of organochlorine compounds: a review

Organochlorines have diverse structures and applications and are included in the list of persistent organic pollutants (POPs) due to their toxicity and environmental persistence. The reduced capacity of conventional wastewater treatment plants to remove these compounds encourages the development of cost-effective and efficient remediation approaches. Fungal biotechnology can contribute to the development of these technologies through their enzymatic machinery but faces several drawbacks related to the use of dispersed mycelium. In this sense, investigations concerning the degradation of organochlorines using immobilized fungi demonstrated an increase in contaminant removal efficiency compared with degradation by free cells. Despite this interest, the mechanisms of immobilized fungi have not been comprehensively reviewed. In this paper, recent advances of laboratory and field studies in organochlorine compounds removal by fungi are reviewed, focusing on the role of immobilization techniques. Firstly, the mechanisms of organochlorines bioconversion by fungi and the factors affecting enzyme activity are elucidated and discussed in detail. Then, the main targeted compounds, fungi, technics, and materials used for immobilization are discussed, as well as their advantages and limitations. Furthermore, critical points for future studies of fungi immobilization for organochlorine removal are proposed.

Occurrence and risk evaluation of organophosphorus pesticides in typical water bodies of Beijing, China

AbstractHuman activities, particularly in large cities, can lead to pollution caused by micropollutants such as pesticides in water bodies, which have been recognized as serious threats to the environment and human health. The pollution level of six organophosphorus pesticides, three herbicides, and one bactericide in groundwater and the Wenyu River, and their fates in three sewage treatment plants (STPs) and a hospital were investigated in this study. The concentrations of the ten detected pesticides ranged from not detected (ND) to 323.44 ng L^-1 in different water samples from Beijing; metalaxyl was detected to have the highest concentration (89.58 ng L^-1), and the detection frequencies of atrazine and metalaxyl were 100%. The maximum concentrations of pesticides in the Wenyu River, STPs, and the hospital were 1-2 orders of magnitude higher than those in the groundwater. Good removal efficiencies by the treatment processes were observed for ametryn (100%), while the removal efficiencies for atrazine and omethoate were the lowest in the three STPs (- 9.6% and 12.67%, respectively). Finally, risk quotient (RQ) values of each contaminant were estimated from the maximum values determined for typical urban to assess the ecology and health effects. In the case of environmental toxicity, the highest RQ values (> 1) were obtained for dichlorvos and omethoate. In the case of health toxicity, the RQ values show that the pesticides found in groundwater pose no potential health risks to humans at current concentrations.

Microbial degradation of two highly persistent fluorinated fungicides - epoxiconazole and fludioxonil

Biodegradation of two highly persistent fluorinated fungicides, epoxiconazole (EPO) and fludioxonil (FLU), by microbial consortia enriched from estuarine sediment and agricultural soil is reported. After an enrichment period of 6 months, four microbial consortia were able to completely remove and defluorinate the fungicides in co-metabolic conditions. Defluorination was biologically mediated and results suggest it is not a primary catabolic step, as fungicide removal was always faster than its defluorination. Three of the four enriched consortia had similar biodegradation performances in the absence of a co-substrate. Biodegradation kinetics revealed that microbial degradation followed a first-order kinetics, with cultures being capable of biodegrading concentrations up to 10 mg L^-1 of EPO or FLU, in a maximum of 21 days. Estimated half-life values for these compounds were significantly lower than those reported in literature, highlighting the unique metabolic performance of the obtained consortia. Analysis of their microbial composition revealed that they integrate several bacterial species belonging to the Proteobacteria phylum, with the most common genera being Pseudomonas, Ochrobactrum and Comamonas. This is the first study providing clear evidence on the biodegradation of EPO and FLU, opening doors for the design of bioremediation technologies for the recovery of ecosystems polluted with such recalcitrant compounds.

Destination of pesticide residues on biobeds: State of the art and future perspectives in Latin America

Land-use intensification with a high demand for pesticides is a consequence of human population increase. Feasible alternatives for correct concentrated residues discharge are necessary to avoid soil and water resources contamination. Biobeds are in situ bioreactors for treating pesticide residues, used by several European and American countries due to its low cost and simple construction, whose efficiency has been scientifically proved for over 20 years. This review presents the state of the art of biobeds in Latin America (LA), identifying advances and future research needs. Factors affecting the efficiency of biobeds are discussed, like ideal temperature, moisture, and microbial communities, followed by methods for evaluating the bioreactor's efficiency. It was necessary to adapt this technology to the climatic and economic conditions of Latin-American countries, due to its European origins. Guatemala is the LA country that uses biobeds as official technology. Brazil, Argentina, Costa Rica and Chile are examples of countries that are actively investigating new substrates and pursuing legal aspects for the establishment of the biobeds. Robust scientific evidences may enable farmers start using this technology, which is an environmentally safe system to protect water resources.

Ecotoxicological test based on inhibition of fungal laccase activity: Application to agrochemicals and the monitoring of pesticide degradation processes

Ecotoxicological evaluations require the use of assays with several bioindicators from different trophic levels. Only a few ecotoxicological tests using fungi have been developed, reason why, detection of adverse effects from compounds that exert fungicide action may be overlooked. This work developed a toxicity test based on the inhibition of laccase enzymatic activity in the fungus Trametes versicolor. The test was applied to several fungicides and succeeded to determine inhibition values (half maximum effective concentration, EC₅₀) for most of them (flusilazole, imazalil, pyrimethanil, tetraconazole), though a clear dose-response was not evident for others (thiabendazole, metalaxyl). The application on atrazine (herbicide), imidacloprid (insecticide) and oxytetracycline (antibiotic), proved the proposed test is suitable towards other agrochemicals. The test was also used to estimate the detoxification resulting from two different approaches employed in the removal of agrochemicals. (a) First, in the liquid-phase elimination by fungal biomass simultaneously removing atrazine, imazalil, tebuconazole and triadimenol, the test showed a significant decrease in toxicity by biodegradation (adsorption contribution to detoxification was negligible). (b) Second, a solid-phase biomixture (used for pesticide degradation from agricultural wastewater) partially removed atrazine, imazalil, metalaxyl and pyrimethanil after 33 d; nonetheless, this system could not reduce the toxicity of the matrix, and higher laccase inhibition was detected after the treatment. The design test increases the battery of available bioassays to determine the toxicity of agrochemicals, and provides an interesting tool to monitor biodegradation processes.

Simultaneous removal of neonicotinoid insecticides by a microbial degrading consortium: Detoxification at reactor scale

Neonicotinoid insecticides show high persistence in the environment, and standard biological approaches such as biopurification systems have shown mostly inefficient removal of such compounds. In this work, soil pre-exposed to imidacloprid was used to obtain presumptive imidacloprid-degrading consortia. Cometabolic enrichment yielded a microbial consortium composed of eight bacterial and one yeast strains, capable of degrading not only this compound, but also thiamethoxam and acetamiprid, as demonstrated in cross-degradation assays. The biological removal process was scaled-up to batch stirred tank bioreactors (STBR); this configuration was able to simultaneously remove mixtures of imidacloprid + thiamethoxam or imidacloprid + thiamethoxam + acetamiprid, reaching elimination of 95.8% and 94.4% of total neonicotinoids, respectively. Removal rates in the bioreactors followed the pattern imidacloprid > acetamiprid > thiamethoxam, including >99% elimination of imidacloprid in 6 d and 17 d (binary and ternary mixtures, respectively). A comprehensive evaluation of the detoxification in the STBR was performed using different biomarkers: seed germination (Lactuca sativa), bioluminescence inhibition (Vibrio fischeri), and acute oral tests in honeybees. Overall, ecotoxicological tests revealed partial detoxification of the matrix, with clearer detoxification patterns in the binary mixture. This biological approach represents a promising option for the removal of neonicotinoids from agricultural wastewater; however, optimization of the process should be performed before application in farms.