Microbial degradation mechanism and pathway of the insecticide thiamethoxam by isolated Bacillus Cereus from activated sludge.

The high water solubility and ecotoxicity of thiamethoxam (TMX) is a potential hazard to ecosystems and human health. Here, a strain of Bacillus cereus with high TMX degradation activity was isolated from the sediment of the A2O process in the wastewater treatment plant and was able to utilize TMX as its sole carbon source. Under different environmental conditions, the degradation efficiency of TMX by Bacillus cereus-S1 (strain S1) ranged from 41.0% to 68.9% after 216 h. The optimum degradation conditions were DO = 3.5 mg/L and pH 9.0. The addition of an appropriate carbon-to-nitrogen ratio could accelerate the degradation of TMX. A plausible biodegradation pathway has been proposed based on the identified metabolites and their corresponding degradation pathways. TMX can be directly converted into Clothianidin (CLO), TMX-dm-hydroxyl and TMX-Urea by a series of reactions such as demethylation, oxadiazine ring cleavage and C=N substitution by hydroxy group. The main products were TMX-dm-hydroxyl and TMX-Urea, the amount of CLO production is relatively small. This study aims to provide a new approach for efficient degradation of TMX; furthermore, strain S1 is a promising biological source for in situ remediation of TMX contamination.

Toxicokinetics and bioavailability of indoxacarb enantiomers and their new metabolites in rats.

Indoxacarb is a chiral insecticide that consists of two enantiomers, S-(+)-indoxacarb and R-(-)-indoxacarb, of which only S-(+)-indoxacarb has insecticidal activity. Previous enantioselective toxicology studies of indoxacarb focused mostly on simple environmental model organisms. The lack of a toxicology evaluation of indoxacarb conducted in a mammalian system could mean that the extent of the potential health risk posed by the insecticide to humans is not adequately known. In this study, we reported on a new pair of enantiomers, S-IN-RM294 and R-IN-RM294, derived from the metabolic breakdown of S-(+)-indoxacarb and R-(-)-indoxacarb, respectively, in rats. The toxicokinetics of S-(+)-indoxacarb, R-(-)-indoxacarb, S-IN-RM294, and R-IN-RM294 in rats were evaluated to provide a more comprehensive risk assessment of these molecules. The bioavailability and excretion rates of both S-(+)-indoxacarb and R-(-)-indoxacarb were relatively low, which may be due to their faster metabolism and accumulation in the tissues. In addition, there were significant differences in the metabolism and distribution between the two indoxacarb enantiomers and their metabolites in vivo. S-(+)-Indoxacarb was found to be more easily metabolized in the blood compared with R-(-)-indoxacarb, as shown by the differences in pharmacokinetic parameters between oral and intravenous administration. Analysis of their tissue distribution showed that S-(+)-indoxacarb was less likely to accumulate in most tissues. The results obtained for the two metabolites were consistent with those of the two parent compounds. S-IN-RM294 was more readily cleared from the blood and less likely to accumulate in the tissues compared with R-IN-RM294. Therefore, whether from the perspective of insecticidal activity or from the perspective of mammalian and environmental friendliness, the application of optically pure S-(+)-indoxacarb in agriculture may be a more efficient and safer strategy.

Sublethal effect and detoxifying metabolism of metaflumizone and indoxacarb on the fall armyworm, Spodoptera frugiperda.

The fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith) (Lepidoptera, Noctuidae), is a highly polyphagous invasive pest that damages various crops. Pesticide control is the most common and effective strategy to control FAW. In this study, we evaluated the toxicity of metaflumizone and indoxacarb against third-instar FAW larvae using the insecticide-incorporated artificial diet method under laboratory conditions. Both metaflumizone and indoxacarb exhibited substantial toxicity against FAW, with LC50 values of 2.43 and 14.66 mg/L at 72 h, respectively. The sublethal effects of metaflumizone and indoxacarb on parental and F1 generation FAW were investigated by exposing third-instar larvae to LC10 and LC30 concentrations of these insecticides. Sublethal exposure to these two insecticides significantly shortened adult longevity, extended pupal developmental times and led to reduced pupal weight, pupation rates, and adult fecundity in the treated parental generation and F1 generation at LC10 or LC30 concentrations, in comparison to the control group. The larval developmental times were shortened in the parental generation but prolonged in the F1 generation, after being treated with sublethal concentrations of metaflumizone. Furthermore, larvae exposed to LC10 or LC30 concentrations of indoxacarb exhibited elevated activity levels of cytochrome P450 monooxygenase and glutathione S-transferase, which coincides with the observed synergistic effect of piperonyl butoxide and diethyl maleate. In conclusion, the high toxicity and negative impact of metaflumizone and indoxacarb on FAW provided significant implications for the rational utilization of insecticides against this pest.

Toxic effects of commercial grade indoxacarb and endosulfan on Gammarus kischineffensis (Schellenberg, 1937) (Crustacea: Amphipoda).

This study was designed to investigate the toxic effects of two frequently used commercial insecticides containing endosulfan and indoxacarb on a freshwater amphipod Gammarus kischineffensis. In this context, the 24, 48, 72 and 96 h LC50 values of these pesticides were determined for G. kischineffensis. Then the histopathological effects of these pesticides on the gill tissues of this species were evaluated. At the end of the study, the 96 h LC50 values of commercial-grade endosulfan and indoxacarb for G. kischineffensis were determined as 1.861 µg L-1 and 20.212 mg L-1, respectively. Histopathologically, the most common histopathological alterations in individuals exposed to sublethal concentrations of commercial-grade endosulfan and indoxacarb were pillar cell hypertrophy resulting in atrophy of the hemocoelic space and hemocytic infiltration. Considering these results, it can be said that commercial-grade endosulfan is extremely and indoxacarb is slightly toxic to G. kischineffensis.

Does commercial indoxacarb pose ecotoxicological consequences? Employing a multi-marker approach in the model species Theba pisana.

Indoxacarb is one of the most extensively used oxadiazine insecticides worldwide, but it may exert detrimental effects on ecosystems, population dynamics, and health. Due to the lack of knowledge on the ecotoxicity of indoxacarb, it is still challenging to assess whether this insecticide poses an ecotoxicological impact on terrestrial environments. Therefore, our study aims to provide novel data on the toxic effects of 28-day dietary exposure to commercial grade indoxacarb at two environmentally relevant concentrations, 0.02 µg/mL and tenfold (0.2 µg/mL) on the model species, Theba pisana. Their effects were studied using a multiple biomarker approach by evaluating physiological, biochemical, and histopathological responses. After 28 days of treatment, indoxacarb at both concentrations significantly reduced the food intake and growth of the treated snails. Also, it caused decreases in lipid peroxidation (LPO)  levels after 7 and 14 days of exposure, whereas an opposite effect occurred after 21 and 28 days. All treated snails were found to exhibit a lower content of glutathione (GSH) after all times of exposure. Moreover, catalase (CAT), glutathione-S-transferase (GST), and glutathione peroxidase (GPx) activities, as well as protein content (PC), were elevated in the treated snails after all time intervals. Post exposure to both realistic indoxacarb concentrations, changes in acetylcholinesterase (AChE) activity between a decrease and an increase were observed. Furthermore, indoxacarb caused histo-architectural changes in the hepatopancreas of T. pisana. Our results demonstrate that, at environmentally relevant concentrations, indoxacarb poses negative consequences for T. pisana, indicating its ecotoxicological impacts.

Exposure to neonicotinoid pesticides induces physiological disorders and affects color performance and foraging behavior in goldfish.

We investigated the effects of neonicotinoid pesticides (NEOs) on the spontaneous swimming and foraging behavior, as well as the morphological and physiological changes of goldfish. Most fish reared in thiamethoxam (THM)-sprayed rice fields showed the scales easily peeled off, and increased ascites. Some individuals showed decreased bio-defense activity and low plasma Ca2+. Similar changes were found in the exposure test to THM (1.0 and 20.0 µg/L) and dinotefuran (1.2 and 23.5 µg/L). Next, the effects of a low concentration of THM (1.0 µg/L) on the spontaneous swimming and foraging behavior of fish were examined. Fish exposed to THM for 1 week became restless and had increased the swimming performance, especially under natural light, white LED lighting and blue LED lighting. Goldfish exposed to THM had also increased intake of shiny white beads under green LED illumination. These results indicate that the exposure to NEO, even for a short period and at low levels, not only suppressed bio-defense activities and metabolic abnormalities, but also stress response, the swimming and foraging behavior of the fish are likely to be significantly suffered.

A simple method to measure cell viability in proliferation and cytotoxicity assays

Resazurin dye has been broadly used as indicator of cell viability in several types of assays for evaluation of the biocompatibility of medical and dental materials. Mitochondrial enzymes, as carriers of diaphorase activities, are probably responsible for the transference of electrons from NADPH + H+ to resazurin, which is reduced to resorufin. The level of reduction can be quantified by spectrophotometers since resazurin exhibits an absorption peak at 600 çm and resorufin at 570 çm wavelengths. However, the requirement of a spectrophotometer and specific filters for the quantification could be a barrier to many laboratories. Digital cameras containing red, green and blue filters, which allow the capture of red (600 to 700 çm) and green (500 to 600 çm) light wavelengths in ranges bordering on resazurin and resorufin absorption bands, could be used as an alternative method for the assessment of resazurin and resorufin concentrations. Thus, our aim was to develop a simple, cheap and precise method based on a digital CCD camera to measure the reduction of resazurin. We compared the capability of the CCD-based method to distinguish different concentrations of L929 and normal Human buccal fibroblast cell lines with that of a conventional microplate reader. The correlation was analyzed through the Pearson coefficient. The results showed a strong association between the measurements of the method developed here and those made with the microplate reader (r² = 0.996; p < 0.01) and with the cellular concentrations (r² = 0.965; p < 0.01). We concluded that the developed Colorimetric Quantification System based on CCD Images allowed rapid assessment of the cultured cell concentrations with simple equipment at a reduced cost.