Persistence of fipronil and its metabolites in soil under field conditions

Death zone minimizes the impact of fipronil-treated soils on subterranean termite colonies by negating transfer effects

The use of nonrepellent liquid termiticides against subterranean termites has long relied on the assumption that foraging termites in soils could transfer toxicants to nestmates to achieve population control. However, their dose-dependent lethal time can lead to rapid termite mortality in proximity of the treatment, triggering secondary repellency. The current study characterizes the dynamic nature of the "death zone," i.e., the area adjacent to soil termiticides that termites would avoid owing the accumulation of cadavers. Using whole subterranean termite laboratory colonies of Coptotermes gestroi (Wasmann) with 3 × 15 m foraging distances, fipronil was implemented at 1.5 m, 7.5 m, or 12.5 m away from colony central nests, emulating a corrective action against an termite structural infestation. For treatments at 7.5 m and 12.5 m, the death zone stabilized at an average of ~2.56 m away from the treatment after 40 d post-treatment, and colonies suffered as little as 1.5% mortality by 200 d post-treatment. Colonies located 1.5 m away from the treatment minimized the death zone to ~1.1 m and suffered as little as 23.5% mortality. Mortality only occurred within the first few days of treatment from initial exposure, as the rapid emergence of the death zone negated further transfer effects among nestmates over time. In some cases, foraging termites were trapped within the infested structure. While technically nonrepellent, fipronil becomes functionally repellent from the rapid mortality onset near the treatment. Even if diligently implemented to successfully protect structures, surrounding termite colonies are minimally impacted by fipronil soil treatments.

Investigation of dissipation kinetics and half-lives of fipronil and thiamethoxam in soil under various conditions using experimental modeling design by Minitab software

To determine the extent of pesticide buildup and their environmental contamination, the environmental half-lives of pesticides are examined. The influence of the factors affecting the half-lives of fipronil and thiamethoxam including soil type, sterilization, temperature, and time and their interactions was studied using experimental modeling design by Minitab software. Based on the dissipation kinetics data, fipronil concentrations reduced gradually over 60 days while thiamethoxam concentrations decreased strongly. Also, fipronil and thiamethoxam dissipated more rapidly in calcareous soil than in alluvial soil. Thiamethoxam, however, disappeared more rapidly than fipronil in all treatments. Incubation at 50 °C leads to rapid the pesticide degradation. For prediction of the dissipation rate, model 5 was found to be the best fit, Residue of insecticide (%) = 15.466 - 11.793 Pesticide - 1.579 Soil type + 0.566 Sterilization - 3.120 Temperature, R2 = 0.94 and s = 3.80. Also, the predicted DT50 values were calculated by a model, DT50 (day) = 20.20 - 0.30 Pesticide - 7.97 Soil Type + 0.07 Sterilization - 2.04 Temperature. The shortest experimental and predicted DT50 values were obtained from treatment of thiamethoxam at 50 °C in calcareous soil either sterilized (7.36 and 9.96 days) or non-sterilized (5.92 and 9.82 days), respectively. The experimental DT50 values of fipronil and thiamethoxam ranged from 5.92 to 59.95 days while, the modeled values ranged from 9.82 to 30.58 days. According to the contour plot and response surface plot, temperature and sterilization were the main factors affecting the half-lives of fipronil and thiamethoxam. The DT50 values of fipronil and thiamethoxam increased in alluvial soil and soil with low temperature. In general, there is a high agreement between the experimental results and the modeled results.

Allium cepa test vs. insecticides: a scientometric and meta-analytical review

Insecticides stand out as the most dangerous pesticides, and many of them can cause cytotoxic and genotoxic effects in organisms. For this reason, a systematic review was performed focusing on the effect of insecticides on Allium cepa system by two ways: (1) a scientometric study to identify trends and gaps in the literature on the evaluation of insecticides to guide future research efforts and (2) a meta-analytical approach compiling the information to obtain an overall result about insecticide effect on A. cepa. It was found that there is an increasing production of articles in this research area. The H-index of our data set was 11, with an average of 13.72 citations per item. The leader country in this research area was India, followed by Turkey and Brazil. The best cited research area was "Environmental Sciences" and "Environmental Sciences and Ecology," followed by "Cell Biology." The most used keywords were genotoxicity, pesticides, and insecticide. The meta-analytical test showed that the number of micronuclei found in onion cells treated with insecticides is higher than that in untreated ones, and the use of pesticides reduced the mitotic index. In conclusion, it is evident the need for more studies about biotechnology, nanotechnology, and biopesticides to develop safer pesticides.

Determination of fipronil and its metabolites in environmental water samples by meltblown nonwoven fabric based solid-phase extraction combined with gas chromatography-electron capture detection

In this study, a new method for determination of fipronil and its three metabolites in environmental water samples was developed based on meltblown nonwoven fabric solid-phase extraction combining with gas chromatography-electron capture detection. As the core material of medical mask, meltblown nonwoven fabric is made of polypropylene superfine fibers which are randomly distributed and bonded together with a relatively large specific surface area and good permeability. Polypropylene as a high molecular hydrocarbon-based polymer, has the characteristics of good hydrophobicity and lipophilicity, which can be applied for separation and enrichment of hydrophobic substances in food, environment and biology samples. The meltblown nonwoven fabric is soft and can fill the solid-phase extraction cartridge tightly. This aspect also makes it suitable to be used as an ideal solid-phase extraction sorbent. A series of parameters influencing the extraction efficiency were investigated, and under the optimized conditions, fipronil and its three metabolites had good linear relationship in the range of 0.2-100 μg/L with correlation coefficient R² more than 0.999. The recoveries at three spiked concentrations were in the range of 99.2-107.3% with the relative standard deviations less than 9.8% (intra-day) and 8.1% (inter-day). The limit of detection for the four target analytes were in the range of 0.02-0.06 μg/L. Finally, this method was successfully applied in the analysis of fipronil and its three metabolites in various types of environmental water samples. This article is protected by copyright. All rights reserved.

Biodegradation of fipronil: current state of mechanisms of biodegradation and future perspectives

Fipronil is a broad-spectrum phenyl-pyrazole insecticide that is widely used in agriculture. However, in the environment, its residues are toxic to aquatic animals, crustaceans, bees, termites, rabbits, lizards, and humans, and it has been classified as a C carcinogen. Due to its residual environmental hazards, various effective approaches, such as adsorption, ozone oxidation, catalyst coupling, inorganic plasma degradation, and microbial degradation, have been developed. Biodegradation is deemed to be the most effective and environmentally friendly method, and several pure cultures of bacteria and fungi capable of degrading fipronil have been isolated and identified, including Streptomyces rochei, Paracoccus sp., Bacillus firmus, Bacillus thuringiensis, Bacillus spp., Stenotrophomonas acidaminiphila, and Aspergillus glaucus. The metabolic reactions of fipronil degradation appear to be the same in different bacteria and are mainly oxidation, reduction, photolysis, and hydrolysis. However, the enzymes and genes responsible for the degradation are somewhat different. The ligninolytic enzyme MnP, the cytochrome P450 enzyme, and esterase play key roles in different strains of bacteria and fungal. Many unanswered questions exist regarding the environmental fate and degradation mechanisms of this pesticide. The genes and enzymes responsible for biodegradation remain largely unexplained, and biomolecular techniques need to be applied in order to gain a comprehensive understanding of these issues. In this review, we summarize the literature on the degradation of fipronil, focusing on biodegradation pathways and identifying the main knowledge gaps that currently exist in order to inform future research. KEY POINTS: • Biodegradation is a powerful tool for the removal of fipronil. • Oxidation, reduction, photolysis, and hydrolysis play key roles in the degradation of fipronil. • Possible biochemical pathways of fipronil in the environment are described.

Dissipation behaviour and risk assessment of fipronil and its metabolites in paddy ecosystem using GC-ECD and confirmation by GC-MS/MS

Fipronil -a broad spectrum phenylpyrazole insecticide has high level of toxicity towards environment. Therefore, an easy and reliable analytical method was developed for residue estimation of fipronil to ensure food and environmental safety. A modified QuEChERS technique was followed for estimation of fipronil (5% SC) in paddy ecosystem using GC-ECD and confirmation by GC-MS/MS. The initial residues (0.168-0.794 μg g^-1) of total fipronil i.e., sum of fipronil and its metabolites (viz., desulfinyl and sulfone) in leaf and soil were dissipated following first order kinetics. About 92-96% of fipronil residues were degraded after 15 days with half-life of 3.4-4.1 days and pre-harvest interval of 19.4-25.7 days in plant. Residues were below level of quantification (<0.005 μg g^-1) in plant and soil at harvest. The fipronil residues in rice grain present low dietary risk (RQ_d < 1) to human health. However, high risk (RQ_d > 1) was predicted for cattle health due to fipronil residues in paddy leaf up to 10 days. The residual level in soil was also at highrisk (RQ_s > 1) for soil ecological health.

Inclusion of Pesticide Transformation Products Is Key to Estimating Pesticide Exposures and Effects in Small U.S. Streams

Improved analytical methods can quantify hundreds of pesticide transformation products (TPs), but understanding of TP occurrence and potential toxicity in aquatic ecosystems remains limited. We quantified 108 parent pesticides and 116 TPs in more than 3 700 samples from 442 small streams in mostly urban basins across five major regions of the United States. TPs were detected nearly as frequently as parents (90 and 95% of streams, respectively); 102 TPs were detected at least once and 28 were detected in >20% samples in at least one region-TPs of 9 herbicides, 2 fungicides (chlorothalonil and thiophanate-methyl), and 1 insecticide (fipronil) were the most frequently detected. TPs occurred commonly during baseflow conditions, indicating chronic environmental TP exposures to aquatic organisms and the likely importance of groundwater as a TP source. Hazard quotients based on acute aquatic-life benchmarks for invertebrates and nonvascular plants and vertebrate-centric molecular endpoints (sublethal effects) quantify the range of the potential contribution of TPs to environmental risk and highlight several TP exposure-response data gaps. A precautionary approach using equimolar substitution of parent benchmarks or endpoints for missing TP benchmarks indicates that potential aquatic effects of pesticide TPs could be underestimated by an order of magnitude or more.

A full evaluation of chiral phenylpyrazole pesticide flufiprole and the metabolites to non-target organism in paddy field

Pesticides applied to paddy fields may pose considerable danger to non-target aquatic organisms and further threaten human health. Flufiprole is a pesticide used in rice fields; considering the widespread existence of rice-fish-farming ecosystems, the acute toxicities of flufiprole enantiomers and its six metabolites (fipronil, flufiprole sulfide, flufiprole sulfone, detrifluoromethylsulfinyl flufiprole, desulfinyl flufiprole, and flufiprole amide) to four common aquatic organisms in rice fields including Misgurnus anguillicaudatus (pond loach), Carassius gibelio (Prussian carp), Pelophylax nigromaculatus (black-spotted frog), and Daphnia magna (water flea) were investigated. Genotoxicity, pathological changes and the effects on the antioxidant system of M. anguillicaudatus were also evaluated after exposure. The LC₅₀ (EC₅₀) values showed that fipronil and desulfinyl flufiprole were the most toxic compounds and were approximately about six times as toxic as flufiprole. No enantioselective toxicity was observed between the two enantiomers. The activity of antioxidant defense enzymes and the content of malondialdehyde (MDA) in the liver and gills of M. anguillicaudatus were significantly increased by the chemicals in most cases. In addition, fipronil and desulfinyl flufiprole were found to induce an increase in the micronucleus rate in M. anguillicaudatus. Histopathological analysis showed that the liver of M. anguillicaudatus was not significantly affected by flufiprole. Our study demonstrated a potential negative effect on flufiprole-treated aquatic organisms. As an alternative to fipronil, the environmental risk of flufiprole and its metabolites to non-target organisms in rice fields cannot be ignored.

Biodegradation of Chiral Flufiprole in Chlorella pyrenoidosa: Kinetics, Transformation Products, and Toxicity Evaluation

Pesticide pollution of surface water represents a considerable risk for algae and thus affects the structure and stability of aquatic ecosystems. To investigate the risk of flufiprole to phytoplankton, the digestion and uptake of flufiprole as well as the toxic effects of flufiprole enantiomers and the six metabolites to Chlorella pyrenoidosa were investigated. Flufiprole enantiomers were mainly metabolized to flufiprole amide and detrifluoromethylsulfinyl flufiprole in culture medium, while various metabolites were formed in algae, notably the amide derivative and fipronil. Chlorella pyrenoidosa showed a strong absorption capacity for the flufiprole series. The EC₅₀ values (96 h) indicated that fipronil was the most toxic compound, approximately 5 times as toxic as rac-flufiprole. R-flufiprole was more toxic than S-flufiprole. The contents of chlorophylls, malondialdehyde (MDA), reactive oxygen species (ROS), and total antioxidant capacity (T-AOC) were significantly altered by the chemicals in most cases, especially fipronil. Our results supported the potential detrimental effect of the metabolites of flufiprole on algae.

Tissue Distribution, Accumulation, and Metabolism of Chiral Flufiprole in Loach (Misgurnus anguillicaudatus)

Flufiprole is an insecticide used in the rice field and may pose a potential threat to aquatic organisms including loach. To investigate the transformation products of flufiprole in loach, the accumulation, elimination, and tissue distribution in vivo as well as the metabolism in vitro at the enantiomeric level were studied. Flufiprole enantiomers rapidly accumulated and were metabolized to flufiprole sulfone, fipronil, and flufiprole amide in the tissues. Enantiomeric fractions showed the preferential accumulation and degradation of S-flufiprole. The residue of the chiral metabolite flufiprole amide was also enantioselective. The individual enantiomer treatment indicated that S-flufiprole was preferentially metabolized to flufiprole sulfone and R-flufiprole to fipronil. The metabolites were more persistent than flufiprole with longer half-lives. The metabolism in liver microsomes also reached consistent conclusions. The dietary risk assessment indicated that flufiprole would not cause unacceptable threats to human health. However, the metabolites of flufiprole should be considered in the risk evaluation.

Determination and dissipation of fipronil and its metabolites in peanut and soil

In this study, a modified quick, easy, cheap, effective, rugged, and safe (QuEChERS) method was established for the extraction and cleanup of fipronil and its three metabolites (fipronil solfone, sulfide, and desulfinyl) in peanut kernel, shell, straw, seedling, and soil samples, and liquid chromatography-tandem mass spectrometry (LC-MS/MS) was used for analysis. The average recoveries were 66-116% at the level of 0.001-0.1 mg/kg with the RSD <19%, and the limit of detection was 0.3 ng/g for all matrices. The dissipation experiment results demonstrated that fipronil dissipated more rapidly in peanut seedling than in soil, with half-lives of <1 day in peanut seedling and 32-57 days in soil depending on the soil pH. The final residues at harvest of peanut kernels were all below 0.02 mg/kg, whereas in peanut shell and straw, the total highest residues were 0.99 and 0.30 mg/kg, respectively. Fipronil-desulfinyl and fipronil-sulfone were the highest residue metabolites in peanut plant (seedling and straw) and soil samples, respectively.

Photochemical and Ga2O3-photoassisted decomposition of the insecticide Fipronil in aqueous media upon UVC radiation

Fipronil is degraded photolytically and photocatalytically (β-Ga₂O₃ and TiO₂) in aqueous media under UVC illumination and under reductive and oxidative conditions.