Fipronil, a phenyl-pyrazole insecticide, has a wide range of uses, from agriculture to veterinary medicine. Due to its large-scale applications, the risk of environmental and occupational exposure and bioaccumulation raises concerns. Moreover, relatively little is known about the intracellular mechanisms of fipronil in trophoblasts and the endometrium involved in implantation. Here, we demonstrated that fipronil reduced the viability of porcine trophectoderm and luminal epithelial cells. Fipronil induced cell cycle arrest at the sub-G1 phase and apoptotic cell death through DNA fragmentation and inhibition of DNA replication. These reactions were accompanied by homeostatic changes, including mitochondrial depolarization and cytosolic calcium depletion. In addition, we found that exposure to fipronil compromised the migration and implantation ability of pTr and pLE cells. Moreover, alterations in PI3K-AKT and MAPK-ERK1/2 signal transduction were observed in fipronil-treated pTr and pLE cells. Finally, the antiproliferative and apoptotic effects of fipronil were also demonstrated in 3D cell culture conditions. In summary, our results suggest that fipronil impairs implantation potentials in fetal trophectoderm and maternal endometrial cells during early pregnancy.

The occurrence, spatiotemporal variations, influence factors and environmental risks of eight common neonicotinoids (NEOs), fipronil, and three fipronil metabolites (fipronil and its metabolites are collectively referred to as FIPs) in different seasons from the estuary to the inner area of Jiaozhou Bay, China were comprehensively investigated. First- and second-generation NEOs were found to be the predominant pesticides in this area. The average contents of ∑NEOs and ∑FIPs from the estuary to the inner bay decreased from 12.99 ng/L to 0.82 ng/L and from 1.10 ng/L to 0.17 ng/L, respectively. NEO and FIP concentrations were higher in summer and autumn. High ∑NEO content is distributed in main inflow rivers, such as Dagu River and Licun River, which are influenced by pesticide application. NEO concentrations in all rivers were high upstream and low downstream because of the influence of heavy rainfall and seawater dilution in summer. NEO concentrations were high along the coast and low at the mouth and center of Jiaozhou Bay in summer and autumn and evenly distributed in winter and spring. Temperature has a great influence on most NEOs and FIPs owing to its effect on their degradation. Nitrogen-containing nutrients have an important influence on the distribution of fipronil and acetamiprid, which may be due to the activity of nitrogen-containing functional groups in their structure. Only Licun River, Dagu River and Haibo river sewage treatment plant in summer posed a certain risk of chronic toxicity for NEOs using the new threshold established by the species sensitive distribution (SSD) method for Chinese native aquatic lives. These findings should arouse people's attention.

The occurrence and spatial distribution of selected pesticides were investigated along a 200-km reach of the St. Lawrence River (SLR) and tributaries in Quebec, Canada. Surface water samples (n = 68) were collected in the summer 2017 and analyzed for glyphosate, atrazine (ATZ), 8 systemic insecticides (acetamiprid, clothianidin, dinotefuran, fipronil, imidacloprid, nitenpyram, thiacloprid, and thiamethoxam) and some metabolites. Overall, 99% of the surface water samples were positive to at least one of the targeted pesticides. The most recurrent compounds were glyphosate (detection frequency: 84%), ATZ (82%), thiamethoxam (59%), desethylatrazine (DEA: 47%), and clothianidin (46%). Glyphosate displayed variable levels (4–3,000 ng L−1), with higher concentrations in south tributaries (e.g., Nicolet and Yamaska). In positive samples, the sum of ATZ and DEA varied between 5 and 860 ng L−1, and the sum of 6 priority neonicotinoids between 1.5 and 115 ng L−1. From Repentigny to the Sorel Islands, the spatial distribution of pesticides within the St. Lawrence River was governed by the different upstream sources (i.e., Great Lakes vs. Ottawa River) due to the limited mixing of the different water masses. Cross-sectional patterns revealed higher concentrations of glyphosate and neonicotinoids in the north portions of transects, while the middle and south portions showed higher levels of atrazine. In Lake St. Pierre and further downstream, cross-sections revealed higher levels of the targeted pesticides near the southern portions of the SLR. This may be due to the higher contributions from south shore tributaries impacted by major agricultural areas, compared to north shore tributaries with forest land and less cropland use. Surface water samples were compliant with guidelines for the protection of aquatic life (chronic effects) for glyphosate and atrazine. However, 31% of the samples were found to surpass the guideline value of 8.3 ng L−1 for the sum of six priority neonicotinoids.

A general consensus that an increased logKₒw led to an increase in xenobiotic uptake and bioaccumulation is accepted. In this study we compared the toxicokinetics of two chemically different xenobiotics, i.e. benzo[a]pyrene and fipronil in female green frogs. Surprisingly, the uptake rates and the bioconcentration factors (BCF) of the two contaminants were not predicted by their logKₒw. The uptake rates obtained were of the same order of magnitude for the two contaminants and the BCFs measured for fipronil were about 3-fold higher than those obtained for benzo[a]pyrene. Fipronil appeared to be more recalcitrant than benzo[a]pyrene to detoxification processes leading to the accumulation of sulfone-fipronil especially in the ovaries. This phenomenon may explain reproductive influence of this contaminant described in other studies. Detoxification processes, including metabolism and the excretion of pollutants, are of importance when considering their persistence in aquatic organisms and trying to quantify their risks.

Laboratory tests of fipronil and its degradation products have revealed acute lethal toxicity at very low concentrations (LC50) of <0.5 μg/L to selected aquatic macroinvertebrates. In streams draining basins with intensive rice cultivation in southwestern Louisiana, USA, concentrations of fipronil compounds were an order of magnitude larger than the LC50. The abundance (ρ = -0.64; p = 0.015) and taxa richness (r2 = 0.515, p < 0.005) of macroinvertebrate communities declined significantly with increases in concentrations of fipronil compounds and rice-cultivation land-use intensity. Macroinvertebrate community tolerance scores increased linearly (r2 = 0.442, p < 0.005) with increases in the percentage of rice cultivation in the basins, indicating increasingly degraded stream conditions. Similarly, macroinvertebrate community-tolerance scores increased rapidly as fipronil concentrations approached about 1 μg/L. Pesticide toxicity index determinations indicated that aquatic macroinvertebrates respond to a gradient of fipronil compounds in water although stream size and habitat cannot be ruled out as contributing influences. Aquatic macroinvertebrate commmunities in southwestern Louisiana streams respond to a gradient of fipronil compounds in water.

Aquatic organisms are exposed to complex mixtures of pesticides in the environment, but traditional risk assessment approaches typically only consider individual compounds. In conjunction with exposure to pesticide mixtures, global climate change is anticipated to alter thermal regimes of waterways, leading to potential co-exposure of biota to elevated temperatures and contaminants. Furthermore, most studies utilize aqueous exposures, whereas the dietary route of exposure may be more important for fish owing to the hydrophobicity of many pesticides. Consequently, the current study aimed to determine the effects of elevated temperatures and dietary pesticide mixtures on swimming performance and lipid metabolism of juvenile Chinook salmon, Oncorhynchus tshawytscha. Fish were fed pesticide-dosed pellets at three concentrations and three temperatures (11, 14 and 17 °C) for 14 days and swimming performance (Uₘₐₓ) and expression of genes involved in lipid metabolism and energetics were assessed (ATP citrate lyase, fatty acid synthase, farnesoid x receptor and liver x receptor). The low-pesticide pellet treatment contained five pesticides, p,p’-DDE, bifenthrin, esfenvalerate, chlorpyrifos and fipronil at concentrations based on prey items collected from the Sacramento River (CA, USA) watershed, with the high-pesticide pellet treatment containing a six times higher dose. Temperature exacerbated effects of pesticide exposure on swimming performance, with significant reductions in Uₘₐₓ of 31 and 23% in the low and high-pesticide pellet groups relative to controls at 17 °C, but no significant differences in Uₘₐₓ among pesticide concentrations at 11 or 14 °C. At 14 °C there was a significant positive relationship between juvenile Chinook salmon pesticide body residues and expression of ATP citrate lyase and fatty acid synthase, but an inverse relationship and significant downregulation at 17 °C. These findings suggest that temperature may modulate effects of environmentally relevant pesticide exposure on salmon, and that pesticide-induced impairment of swimming performance may be exacerbated under future climate scenarios.

The house fly, Musca domestica L., is a cosmopolitan insect pest of public and animal health importance that serves as a mechanical vector of pathogens. Aimed at prospective resistance management to reduce environmental pollution, we characterized the inheritance pattern, realized heritability, fitness cost, cross resistance, stability and mechanism of clothianidin resistance in M. domestica that were collected from the poultry farm. By continuous selection with clothianidin for 11 generations, the clothianidin selected M. domestica strain (Clotha-SEL) developed a 3827-fold resistance compared to a susceptible strain. However, resistance to clothianidin was proved to be unstable when selection with clothianidin was removed for five generations (G₇ to G₁₂). Inheritance pattern analysis at G₈ of Clotha-SEL (RR = 897) revealed that resistance to clothianidin was polygenic, autosomal and incompletely dominant. Realized heritability (h²) for resistance value was 0.38 (at G₁₁) in the tested strain. Synergist bioassays showed that microsomal oxidases and esterases might not contribute significantly in resistance evolution. Fitness costs of clothianidin resistance were present, for example, reduction in growth potential of the Clotha-SEL strain in comparison to the untreated counterpart strain (UNSEL) was observed. No cross resistance to bifenthrin and fipronil and a very low cross-resistance to spinosad were observed. These insecticides could be alternated with clothianidin as an insecticide resistance management tool to sustain its efficacy for a longer time period. These results shall be utilized to devise a proactive resistance management strategy for use of clothianidin against M. domestica that will be helpful to alleviate the allied threats to environmental and human health.

Water treatment and reuse initiatives are essential to combat declining water supplies in a changing climate, especially in arid and semi-arid regions. Pollution of water resources intensifies the search for strategies to provide water for potable and non-potable reuse that mitigates detrimental ecological and human health effects. Fipronil and synthetic pyrethroids are common urban-use insecticides that exert aquatic toxicity at trace levels and have been often found in urban surface streams. In this study, samples were collected from the 182 ha Prado Wetlands in Southern California for seven months to assess the occurrence of fipronil and its degradation products as well as pyrethroids (bifenthrin and cyfluthrin) in water, sediment, and plants in a 4.45 ha vegetated surface flow constructed wetland (CW). Concentration-based removal values and changes in mass flux were calculated to determine the efficacy of CW treatment. Observed water concentrations were further used to calculate toxic units for the invertebrates Hyalella azteca and Chironomus dilutus. Pesticide concentrations in water, sediment, and plant samples consistently decreased during passage through the CW at all time points. Removal values for fipronil desulfinyl, fipronil sulfide, fipronil, fipronil sulfone, bifenthrin, and cyfluthrin were 100%, 99.7–100%, 57.8–88.1%, 75.6–100%, 74.7–100%, and 36.6–82.2%, respectively, and there was a general net deposition of pesticides into CW compartments. Toxic unit values decreased in every instance for both aquatic invertebrates. Settling of contaminated particles, adsorption to sediment, plant uptake or adsorption, and subsequent degradation contributed to the effective removal of these urban-use insecticides, which highlights the potential of CWs for protecting urban water quality.

Biodegradable plastics have been introduced and widely used as a promising alternative to traditional nondegradable plastics. However, the differences in sorption behavior of pesticides on nondegradable and biodegradable microplastics has been insufficiently studied. Here, four types of nondegradable [polyethylene (PE), polystyrene (PS), polyvinyl chloride (PVC), polypropylene (PP)] and two types of biodegradable [polylactic acid (PLA), polybutylene succinate (PBS)] microplastics were selected to investigate the sorption mechanism of fipronil based on their sorption kinetics and isotherms. The results indicated that the sorption rates of PLA and PBS were much higher than those of PE, PP, PVC and PS and that the sorption capacities of fipronil on microplastics followed the order of PBS > PLA > PP > PE > PS > PVC. The sorption kinetics followed a pseudo-second-order kinetics model (R² = 0.953–0.998) for all tested microplastics. External mass transport and intraparticle diffusion were the main rate controlling steps of the sorption of fipronil on microplastics. Furthermore, isotherm results indicated that a Langmuir model provided the best fit for fipronil sorption on PE, PS, PVC and PP (R² = 0.997–0.999), while a Freundlich model was the most appropriate model for PLA and PBS (R² = 0.998–0.999). The presence of surface O-containing functional groups and the spatial arrangement of rubbery domains are likely to affect the sorption process. The results from this work suggest that microplastics, especially biodegradable ones, may play an important role in the fate and transport of pesticides, and their effects on soil organisms (e.g., earthworms) require further investigation.

Urban-use pesticides present a unique risk to non-target organisms in surface aquatic systems because impervious pavement facilitates runoff that may lead to serious contamination and ensuing aquatic toxicity. Fipronil is an insecticide used at high rates in urban environments, especially in regions such as California. This compound and its biologically active degradation products have been detected in urban runoff drainage and downstream surface water bodies at concentrations exceeding toxicity thresholds for sensitive aquatic invertebrates, necessitating a better understanding of the runoff sources and causes of this contamination at sites of application. In this study, we evaluated sorption of fipronil, fipronil desulfinyl, fipronil sulfide, and fipronil sulfone in urban dust, soil, and concrete, matrices commonly associated with the perimeter of a residential home. Samples were also collected from five single family homes treated with fipronil in Riverside, California, for five months to determine the occurrence of fipronil and its degradates in runoff water, urban dust, soil, and on concrete surfaces. Statistical analysis was performed to determine which urban matrices contributed more significantly to the contaminant levels in runoff water. Freundlich sorption coefficients for fipronil and its degradation products in dust were 3- to 9-fold greater than their values in soil. Fipronil and its degradates were detected in 100% of runoff samples and their presence was observed in dust, soil, and concrete wipe samples for 153 d after the treatment. Linear regression analysis showed that concrete surfaces were a primary source of all four compounds to runoff, and loose dust on concrete pavement also served as an important contributor. This study represents the first comprehensive investigation of the sources and causes for surface runoff contamination by fipronil and its degradation products. Findings highlight the importance to reduce fipronil residues on concrete surfaces through improved application methods and other mitigation practices.