Dissipation of propanil and 3,4 dichloroaniline in three different rice management systems

Microbiome resistance mediates stimulation of reduced graphene oxide to simultaneous abatement of 2,2',4,4',5-pentabromodiphenyl ether and 3,4-dichloroaniline in paddy soils

Paddy soils near electrical and electronic waste recycling sites generally suffer from co-pollution of polybrominated diphenyl ethers and 3,4-dichloroaniline (3,4-DCA). This study tested the feasibility of reduced graphene oxide (rGO) to stimulate the simultaneous abatement of 2,2',4,4',5-pentabromodiphenyl ether (BDE99) and 3,4-DCA in percogenic paddy soil (PPS) and hydromorphic paddy soil (HPS). rGO improved the debromination extent of BDE99 and the transformation rate of 3,4-DCA in PPS, but did not affect their abatement in HPS. The inhibition of specific fermenters, acetogens, and methanogens after rGO addition contributed to BDE99 debromination by obligate organohalide-respiring bacteria (OHRB) in PPS, but relevant soil microbiomes (e.g., fermenters, acetogens, methanogens, and obligate OHRB) responded little to rGO in HPS. For 3,4-DCA, the enhanced activities of nitrogen-metabolic chloroaniline degraders by rGO increased its transformation rate in PPS, but was compensated by the decreased biotransformation from 3,4-DCA to 3,4-dichloroacetanilide after the addition of rGO to HPS. The discrepant stimulation of rGO between PPS and HPS was mediated by soil microbiome resistance. rGO has the application potential to stimulate the simultaneous abatement of polybrominated diphenyl ethers and chloroanilines in paddy soils with relatively low microbiome resistance.

Development, Validation and Application of an Ultra-High-Performance Liquid Chromatography-Tandem Mass Spectrometry (UHPLC-MS/MS) Method after QuEChERS Cleanup for Selected Dichloroanilines and Phthalates in Rice Samples

Dichloroanilines and phthalic acid esters (phthalates) are food contaminants, stable in solution even at high temperatures, which exhibit considerable toxic effects, while acting as endocrine disruptors. In the present study, a quick and easy UHPLC-MS/MS method for simultaneously analyzing two dichloroanilines (3,4-DCA and 3,5-DCA) and six phthalates (DMP, DnBP, BBP, DnOP, DEHP, and mBP) in commercial rice samples was developed, validated, and applied. For the cleanup process, the methodology of quick, easy, cheap, effective, rugged, and safe (QuEChERS) was applied, whereas different dispersants (GCB, C18, and PSA) were tested. What was developed and presented had limits of detection ranging from 0.017 up to 0.12 mg/kg, recoveries (trueness) below 120%, and relative standard deviations (RSD; precision) <15% for all target analytes, whilst no significant matrix effects occurred for all analytes. It was determined that the rice samples analyzed using this developed technique did not contain any of the two dichloroaniline compounds (3,4-DCA and 3,5-DCA) nor two of the six phthalate (DMP and mBP) compounds analyzed, while the levels of other phthalates (DEHP, BBP, DnBP and DnOP) were within the legal limits. The current method ensures a fast and easy approach for the high-throughput quantification of the selected food contaminants in rice.

Evaluation of an outdoor pilot-scale tubular photobioreactor for removal of selected pesticides from water

This work assesses the capacity of a microalgae-based system to remove three highly to medium polar pesticides typically found in freshwater: acetamiprid, bentazone, and propanil. Degradation of the pesticides was firstly studied individually at batch lab-scale reactors and abiotic and heated-killed controls were employed to clarify their removal pathways. At lab-scale, propanil and acetamiprid were completely removed after 7 days whereas bentazone was not removed. Four and two transformation products (TPs) were generated in the biodegradation process for acetamiprid and propanil, respectively. Then, the simultaneous removal of the pesticides was assessed in an outdoor pilot photobioreactor, operated with a hydraulic residence time of 8 days. During the steady-state, high removal efficiencies were observed for propanil (99%) and acetamiprid (71%). The results from batch experiments suggest that removal is mainly caused by algal-mediated biodegradation. Acetamiprid TPs raised throughout the operational time in the photobioreactor, while no propanil TP was detected at the pilot-scale. This suggests complete mineralization of propanil or residual formation of its TPs at concentrations below the analytical method detection limit. Aiming at biomass valorization, diverse microalgae harvesting methods were investigated for biomass concentration, and the effect of residual pesticides on the biogas yield was determined by biochemical methane potential tests. Anaerobic digestion was not inhibited by the pesticides as verified by the digestion performance. The results highlight the potential of microalgae-based systems to couple nutrient removal, biomass production, micropollutant biodegradation, and biofuel production.

Anaerobic Degradation of Propanil in Soil and Sediment Using Mixed Bacterial Culture

The widespread use of the herbicide, propanil, causes severe environmental problems. In this study, the effects of propanil on the bacterial community in a sediment slurry were determined. Moreover, the degradation of the herbicide by pure and mixed cultures was first conducted under anaerobic conditions. The results showed that propanil caused significant changes in the bacterial community under anaerobic conditions. Four bacterial strains, i.e., Geobacter sp. Pr-1, Paracoccus denitrificans Pr-2, Pseudomonas sp. Pr-3, and Rhodococcus sp. Pr-4, isolated from the an enrichment sediment slurry were the first pure cultures that degraded propanil and 3,4-dichloroaniline (3,4-DCA) under anaerobic conditions. Some individual isolates showed the slow degradation of propanil and 3,4-DCA, but the mixture of the four strains increased the degradation rates of both compounds. The mixed culture of these isolates transformed more than 90% of propanil within 10 days in liquid media with the amendment of dextrose, glucose, or acetate. The determination of degradation pathway showed that propanil was transformed to 3,4-DCA and some other products before degrading completely. This study provides valuable information on the effects of propanil on the bacterial community and the synergistic degradation of propanil under anaerobic conditions.

Cytogenotoxic effect of propanil using the Lens culinaris Med and Allium cepa L test

Propanil can produce methemoglobinemia, hemolytic anemia, hepatotoxicity, metabolic disorder and nephrotoxicity. It also has a genotoxic effect, although it is not listed as a carcinogen and it continues to be applied excessively throughout the world. Consequently, in this study the cytogenotoxic effect of propanil was evaluated, using apical root cells of Allium cepa and Lens culinaris. In which, L. culinaris seeds and A. cepa bulbs were subjected to 6 treatments with propanil (2, 4, 6, 8, 10 and 12 mg L^-1) and to distilled water as control treatment. Subsequently, the root growth was measured every 24 h for 3 days. Next, the mitotic index and cellular anomalies were determined. Whereby, decreased root development was observed in all treatments. Likewise, greater inhibition of mitosis was evidenced in L. culinaris compared to A. cepa. In addition, chromosomal abnormalities, such as nucleus absence, sticky chromosomes in metaphase and binucleated cells, were present in most of the treatments. Thus, the presence of micronuclei and the results of L. culinaris, indicate the high cytogenotoxicity of propanil and the feasibility of this species as bioindicator.

The role of direct photolysis in the photodegradation of the herbicide bentazone in natural surface waters

The photochemical fate of the herbicide bentazone was assessed by lab experiments and modeling tools. Experimental and modeling results showed that bentazone is mainly photodegraded by direct photolysis in natural water samples, even in the presence of dissolved organic matter (DOM) that can act as light-screening agent, photosensitizer and scavenger of reactive species. Even when it was dissolved in natural water samples containing different DOM amounts, the phototransformation kinetics of bentazone was unchanged compared to irradiation runs in ultrapure water. This finding suggests that the DOM and the other components of our samples did not affect the direct photolysis of bentazone by light-absorption competition, at least at the experimental optical path lengths, and did not induce significant indirect photodegradation by producing reactive transient species. Photochemical modeling in a lake-water photoreactivity scenario corroborated the observed experimental results, showing the predominant role of direct photolysis in the overall (direct + indirect) photodegradation of bentazone at different water depths and DOM contents. However, the model predicted a minor but non-negligible contribution of indirect photochemistry (i.e., reactions triggered by HO^•, CO₃^•- and ³CDOM*) to the herbicide degradation. This contribution (especially by ³CDOM*) could become crucial in deep and DOM-rich water bodies. Finally, several photoproducts formed by direct photolysis and HO^•-induced photodegradation were identified, which should not be particularly toxic for aquatic organisms and Vibrio fischeri bacteria.

Characterization of dissolved organic carbon in shallow groundwater of chronic kidney disease affected regions in Sri Lanka

Number of Chronic Kidney Disease patients with no identifiable cause (Chronic Kidney Disease Unknown Aetiology, CKDu) are escalating in the North Central Province (NCP) of Sri Lanka. This study examined distribution of dissolved organic carbon (DOC) in shallow groundwater of three CKDu risk zones (high risk, HR; low risk, LR and no risk, NR) and a control zone (CR) from wet to dry seasons. The interactions of DOC with calcium and magnesium ions and metabolites of selected pesticides were also examined. The lowest COD_MnDOC values of 0.60 ± 0.19, 0.58 ± 0.17 were reported in the DOC of the HR water in the wet and dry seasons, respectively, and this DOC fraction encompasses organic compounds with the lowest labile C with the highest aromaticity. Four distinct fluorescence DOC fractions in the HR water were identified with fulvic acid component associated as dominant non-labile C fraction. The essential building blocks of non-labile C were concentrated into molecular weight (MW) fraction II (900-1800 Da). The DOC source in all groundwater was identified as autochthonous (fluorescence index > 1.8). In the HR water, pentachlorophenol (PCP) was also detected in appreciable quantities. The factor loadings based on principal component analysis (PCA) showed a positive correlation between DOC and sulfate, calcium, total iron, PCP in the HR groundwater. Accordingly, it can be inferred that divalent cations (Ca²⁺, Mg²⁺) abundant in the HR groundwater interact with phenolate and carboxylate functional groups in DOC at alkaline pH.

Evidence of an Important Role of Photochemistry in the Attenuation of the Secondary Contaminant 3,4-Dichloroaniline in Paddy Water

The secondary pollutant 3,4-dichloroaniline (DCA) is produced by the biological degradation of several herbicides, including propanil in paddy fields. The enzymatic hydrolysis of propanil yields DCA with almost quantitative yield. DCA undergoes rather fast photodegradation in paddy water, mostly by direct photolysis. An exception might be represented by the cases (rather rare in paddies) of quite high nitrate concentration (around 50 mg of NO₃^- L^-1), when DCA degradation by CO₃^•- would play a comparable role to that by direct photolysis. The experimentally measured photoreactivity parameters were used as input data for a photochemical model, which predicted a DCA lifetime of 0.5-1 days in sunlit paddy fields in late May, when propanil is usually applied. The model predictions compare remarkably well with the DCA attenuation data reported in field studies, carried out in paddies in temperate regions. Moreover, a consecutive reaction model based on typical biological (propanil) and photochemical (DCA) lifetimes reproduced quite well the time trends of both compounds in paddies, as reported in the literature. These successful comparisons suggest that photodegradation in general, and direct photolysis in particular, may play a key role in DCA attenuation in paddy water.

Phototransformation of the Herbicide Propanil in Paddy Field Water

When irradiated in paddy-field water, propanil (PRP) undergoes photodegradation by direct photolysis, by reactions with ^•OH and CO₃^•-, and possibly also with the triplet states of chromophoric dissolved organic matter. Irradiation also inhibits the nonphotochemical (probably biological) degradation of PRP. The dark- and light-induced pathways can be easily distinguished because 3,4-dichloroaniline (34DCA, a transformation intermediate of considerable environmental concern) is produced with almost 100% yield in the dark but not at all through photochemical pathways. This issue allows an easy assessment of the dark process(es) under irradiation. In the natural environment, we expect PRP photodegradation to be important only in the presence of elevated nitrate and/or nitrite levels, e.g., [NO₃^-] approaching 1 mmol L^-1 (corresponding to approximately 60 mg L^-1). Under these circumstances, ^•OH and CO₃^•- would play a major role in PRP phototransformation. Because flooded paddy fields are efficient denitrification bioreactors that can achieve decontamination of nitrate-rich water used for irrigation, irrigation with such water would both enhance PRP photodegradation and divert PRP dissipation processes away from the production of 34DCA, at least in the daylight hours.

3,4-Dichloroaniline revisited: A study on the fate of the priority pollutant in a sediment-water system derived from a rice growing region in Italy

As ultimate sink for xenobiotics released into the environment, sediments play an important role concerning the evaluation of the fate of foreign compounds. 3,4-Dichloroaniline (3,4-DCA) is a degradation product of herbicide propanil and some urea herbicides. Propanil was extensively used worldwide in rice cultivation. The aim of the study was to examine the fate of ¹⁴C-labeled 3,4-DCA in a sediment-water system; the sediment was derived from a rice field in Northern Italy. After application of ¹⁴C-3,4-DCA, a time-course study was performed using incubation periods from 4h to 56days. Fractions obtained from assays were water phase, sediment phase including methanol and Soxhlet extract as well as non-extractable residues (NER), and mineralized portion (¹⁴CO₂). Soluble fractions were examined by TLC, HPLC and GC-MS. NER found in sediment phases were further fractionated in non-humics, humic acids, fulvic acids and humin. Stability of systems was checked by microbial activity, dissolved oxygen and pH. After 56days of incubation, 23.1% of applied ¹⁴C was mineralized, only 1.30% remained in the water phase, whereas 60.8% was found in the sediment phase, 53.3% of which were NER. Minor metabolites identified were 3,4-dichloroacetanilide (3,4-DCAA) and 3,3',4,4'-tetrachloroazobenzene (TCAB; 2.63% after 56days). According to pH, dissolved oxygen and microbial activity, systems appeared to be stable and not influenced by applied 3,4-DCA. Most striking result was the high mineralization rate as compared to previously published data. This finding suggested an adaptation of the microbial community in the sediment possibly due to decade-long treatment of rice fields with propanil.