Did the prolonged residual efficacy of clothianidin products lead to a greater reduction in vector populations and subsequent malaria transmission compared to the shorter residual efficacy of pirimiphos-methyl?

BACKGROUND

The residual activity of a clothianidin + deltamethrin mixture and clothianidin alone in IRS covered more than the period of malaria transmission in northern Benin. The aim of this study was to show whether the prolonged residual efficacy of clothianidin-based products resulted in a greater reduction in vector populations and subsequent malaria transmission compared with the shorter residual efficacy of pirimiphos-methyl.

METHODS

Human bait mosquito collections by local volunteers and pyrethrum spray collections were used in 6 communes under IRS monitoring and evaluation from 2019 to 2021. ELISA/CSP and species PCR tests were performed on Anopheles gambiae sensu lato (s.l.) to determine the infectivity rate and subspecies by commune and year. The decrease in biting rate, entomological inoculation rate, incidence, inhibition of blood feeding, resting density of An. gambiae s.l. were studied and compared between insecticides per commune.

RESULTS

The An. gambiae complex was the major vector throughout the study area, acounting for 98.71% (19,660/19,917) of all Anopheles mosquitoes collected. Anopheles gambiae s.l. collected was lower inside treated houses (45.19%: 4,630/10,245) than outside (54.73%: 5,607/10,245) after IRS (p < 0.001). A significant decrease (p < 0.001) in the biting rate was observed after IRS in all departments except Donga in 2021 after IRS with clothianidin 50 WG. The impact of insecticides on EIR reduction was most noticeable with pirimiphos-methyl 300 CS, followed by the clothianidin + deltamethrin mixture and finally clothianidin 50 WG. A reduction in new cases of malaria was observed in 2020, the year of mass distribution of LLINs and IRS, as well as individual and collective protection measures linked to COVID-19. Anopheles gambiae s.l. blood-feeding rates and parous were high and similar for all insecticides in treated houses.

CONCLUSION

To achieve the goal of zero malaria, the optimal choice of vector control tools plays an important role. Compared with pirimiphos-methyl, clothianidin-based insecticides induced a lower reductions in entomological indicators of malaria transmission.

Investigation of the miRNA levels changes to acceptable daily intake dose pesticide mixture exposure on rat mesentery and pancreas

Consumers are constantly exposed to a variety of chemical mixtures as part of their everyday activities and lifestyle. Food, water and commercial products are only some examples of the possible ways people get exposed to these mixtures. However, following federal and local guidelines for risk assessment related to chemical exposure, risk analysis focuses on a single substance exposure scenario and not on a mixture, as in real life. Realizing the pronounced gap of this methodology, the real-life risk simulation scenario approach tries to address this problem by investigating the possible effect of long-term exposure to chemical mixtures closely resembling the actual circumstances of modern life. As part of this effort, this study aimed to identify the cumulative effects of pesticides belonging to different classes and commonly used commercial products on long-term exposure with realistic doses. Sprague Dawley rats were given a pesticide mix of active ingredients and formulation chemicals in a daily acceptable dose (ADI) and 10xADI for 90 days. Following thorough everyday documentation of possible side-effects, after 90 days all animals were sacrificed and their organs were examined. Exposure to pesticides particularly affects the miRNA levels at that point will provide us with more information about whether they can be potential biomarkers.

Incremental cost and cost-effectiveness of the addition of indoor residual spraying with pirimiphos-methyl in sub-Saharan Africa versus standard malaria control: results of data collection and analysis in the Next Generation Indoor Residual Sprays (NgenIRS) project, an economic-evaluation

Background

Malaria is a major cause of morbidity and mortality globally, especially in sub-Saharan Africa. Widespread resistance to pyrethroids threatens the gains achieved by vector control. To counter resistance to pyrethroids, third-generation indoor residual spraying (3GIRS) products have been developed. This study details the results of a multi-country cost and cost-effectiveness analysis of indoor residual spraying (IRS) programmes using Actellic^®300CS, a 3GIRS product with pirimiphos-methyl, in sub-Saharan Africa in 2017 added to standard malaria control interventions including insecticide-treated bed nets versus standard malaria control interventions alone.

Methods

An economic evaluation of 3GIRS using Actellic^®300CS in a broad range of sub-Saharan African settings was conducted using a variety of primary data collection and evidence synthesis methods. Four IRS programmes in Ghana, Mali, Uganda, and Zambia were included in the effectiveness analysis. Cost data come from six IRS programmes: one in each of the four countries where effect was measured plus Mozambique and a separate programme conducted by AngloGold Ashanti Malaria Control in Ghana. Financial and economic costs were quantified and valued. The main indicator for the cost was cost per person targeted. Country-specific case incidence rate ratios (IRRs), estimated by comparing IRS study districts to adjacent non-IRS study districts or facilities, were used to calculate cases averted in each study area. A deterministic analysis and sensitivity analysis were conducted in each of the four countries for which effectiveness evaluations were available. Probabilistic sensitivity analysis was used to generate plausibility bounds around the incremental cost-effectiveness ratio estimates for adding IRS to other standard interventions in each study setting as well as jointly utilizing data on effect and cost across all settings.

Results

Overall, IRRs from each country indicated that adding IRS with Actellic^®300CS to the local standard intervention package was protective compared to the standard intervention package alone (IRR 0.67, [95% CI 0.50–0.91]). Results indicate that Actellic^®300CS is expected to be a cost-effective (> 60% probability of being cost-effective in all settings) or highly cost-effective intervention across a range of transmission settings in sub-Saharan Africa.

Discussion

Variations in the incremental costs and cost-effectiveness likely result from several sources including: variation in the sprayed wall surfaces and house size relative to household population, the underlying malaria burden in the communities sprayed, the effectiveness of 3GIRS in different settings, and insecticide price. Programmes should be aware that current recommendations to rotate can mean variation and uncertainty in budgets; programmes should consider this in their insecticide-resistance management strategies.

Conclusions

The optimal combination of 3GIRS delivery with other malaria control interventions will be highly context specific. 3GIRS using Actellic^®300CS is expected to deliver acceptable value for money in a broad range of sub-Saharan African malaria transmission settings.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12936-022-04160-3.

Variable residual activity of K-Othrine® PolyZone and Actellic® 300 CS in semi-field and natural conditions in the Democratic Republic of the Congo

Background

Indoor Residual Spray (IRS) against vector mosquitoes is a primary means for combating malaria transmission. To combat increased patterns of resistance to chemicals against mosquito vectors, alternative candidate insecticide formulations should be screened. With mortality as the primary endpoint, the persistence of residual efficacy of a polymer-enhanced pyrethroid suspension concentrate containing deltamethrin (K-Othrine® PolyZone—KOPZ) applied at 25 mg active ingredient (ai)/m² was compared with a microencapsulated organophosphate suspension formulation of pirimiphos-methyl (Actellic® 300CS—ACS) applied at 1 g ai/m².

Methods

Following standard spray application, periodic contact bioassays were conducted for at least 38 weeks on four types of wall surfaces (unbaked clay, baked clay, cement, and painted cement) sprayed with either KOPZ or ACS in simulated semi-field conditions. Similarly, two types of existing walls in occupied houses (painted cement and baked clay) were sprayed and examined. A colonized strain of female Anopheles arabiensis mosquitoes were exposed to treated or untreated surfaces (controls) for 30 min. For each wall surface test period, 40 treatment mosquitoes (4 cones × 10) in semi-field and 90 (9 cones × 10) in ‘natural’ house conditions were used per wall. 30 mosquitoes (3 cones × 10) on a matching unsprayed surface served as the control. Insecticide, wall material, and sprayed location on wall (in houses) were compared by final mortality at 24 h.

Results

Insecticide, wall material, and sprayed location on wall surface produced significant difference for mean final mortality over time. In semi-field conditions, KOPZ produced a 72% mean mortality over a 38-week period, while ACS gave 65% (p < 0.001). Painted cement wall performed better than other wall surfaces throughout the study period (73% mean mortality). In the two occupied houses, KOPZ provided a mean mortality of 88%, significantly higher than ACS (p < 0.001). KOPZ provided an effective residual life (≥ 80% mortality) between 7.3 and 14 weeks on experimental walls and between 18.3 and 47.2 weeks in houses, while ACS persisted between 3 and 7.6 weeks under semi-field conditions and between 7.1 and 17.3 weeks in houses. Household painted cement walls provided a longer effective residual activity compared to baked clay for both formulations. Greater mortality was recorded at the top and middle sections of sprayed wall compared to the bottom portion near the floor.

Conclusion

KOPZ provided longer residual activity on all surfaces compared to ACS. Painted cement walls provided better residual longevity for both insecticides compared to other surfaces. Insecticides also performed better in an occupied house environment compared to semi-field constructed walls. This study illustrates the importance of collecting field-based observations to determine appropriate product active ingredient formulations and timing for recurring IRS cycles.

Insecticidal effect of diatomaceous earth and pirimiphos-methyl against phosphine-susceptible and phosphine-resistant populations of two stored product beetle species

In the present study, we evaluated the insecticidal efficacy of diatomaceous earth (DE) and pirimiphos-methyl for the control of phosphine-susceptible and phosphine-resistant populations of Tribolium castaneum (Herbst) and Sitophilus oryzae (L.). Insecticides were applied on wheat or rice at two doses: DE was applied at 1000 and 2000 ppm and pirimiphos-methyl at 1 and 5 ppm. Adult mortality was measured after 7, 14, and 21 days of exposure, and progeny production capacity on the treated substrates was evaluated 65 days later. For T. castaneum, we found that DE, at 2000 ppm, was able to provide 100% control of two of the three populations tested, while for the third population mortality reached only 84%. Similarly, there were differences in mortality levels after exposure to DE-treated grains between the two S. oryzae populations tested. At 1 ppm, pirimiphos-methyl was not effective for any of the T. castaneum populations tested, but complete mortality was recorded for all populations at 5 ppm. In general, populations of S. oryzae were more susceptible than those of T. castaneum, for both commodities. Our data indicate that both insecticides can be used with success in phosphine resistance management programs, but there are populations of a given species that may be less susceptible, which constitutes a preliminary screening essential.

Exposure of Tribolium castaneum (Herbst) females to pirimiphos-methyl alters the fitness of their progeny

Insecticidal treatment is a common practice for the control of stored-product insect pests. Most studies are focused on the direct effects of insecticides on target insects, while there are no data on the indirect effects on adults in terms of progeny fitness. This study deals with the effect of pirimiphos-methyl on adults of Tribolium castaneum (Coleoptera: Tenebrionidae), investigating their exposure time cost to progeny fitness. For this purpose, females of T. castaneum were exposed for 1, 3, 8, 16, 24, and 72 h to pirimiphos-methyl and progeny birth or death rates were calculated. The fecundity, as well as the survival of progeny, was affected by the parental exposure to the insecticide. When females were exposed for 1 and 3 h to pirimiphos-methyl, the net reproductive rate of the progeny was 4.1 and 4.3 females/female, respectively, which did not statistically differ with the progeny in control treatment (6.3 females/female). Further exposure time to pirimiphos-methyl affected significantly the progeny net reproductive rate, where the lowest value was observed at the 72-h exposure time (0.97 females/female). The intrinsic rate of increase, as well as the finite rate of increase, did not differ between the progeny of the control treatment (0.029 females/female/day and 1.029, respectively) and the progeny of exposed females at 1 h (0.021 females/female/day and 1.021, respectively) or 3 h (0.023 females/female/day and 1.023, respectively). By increasing the time of exposure to pirimiphos-methyl, a detrimental effect to progeny fitness was revealed based on the values of the intrinsic and finite rate of increase. The lowest values of these parameters were observed at the 72-h exposure time (0.001 females/female/day and 1.000, respectively). The same trend was observed in the values of the doubling time. In contrast, the mean generation time did not statistically differ between control and all insecticide treatments. The fact that the exposure of parental females of T. castaneum to pirimiphos-methyl negatively affects the demographic parameters of their offspring production should be seriously taken into account when management strategies are applied against this notorious stored-product insect species since it could reduce the repeatedly insecticidal applications in storage facilities.

Malaria vector species composition and entomological indices following indoor residual spraying in regions bordering Lake Victoria, Tanzania

Background

Vector control through long-lasting insecticidal nets (LLINs) and focal indoor residual spraying (IRS) is a major component of the Tanzania national malaria control strategy. In mainland Tanzania, IRS has been conducted annually around Lake Victoria basin since 2007. Due to pyrethroid resistance in malaria vectors, use of pyrethroids for IRS was phased out and from 2014 to 2017 pirimiphos-methyl (Actellic® 300CS) was sprayed in regions of Kagera, Geita, Mwanza, and Mara. Entomological surveillance was conducted in 10 sprayed and 4 unsprayed sites to determine the impact of IRS on entomological indices related to malaria transmission risk.

Methods

WHO cone bioassays were conducted monthly on interior house walls to determine residual efficacy of pirimiphos-methyl CS. Indoor CDC light traps with or without bottle rotator were hung next to protected sleepers indoors and also set outdoors (unbaited) as a proxy measure for indoor and outdoor biting rate and time of biting. Prokopack aspirators were used indoors to capture resting malaria vectors. A sub-sample of Anopheles was tested by PCR to determine species identity and ELISA for sporozoite rate.

Results

Annual IRS with Actellic® 300CS from 2015 to 2017 was effective on sprayed walls for a mean of 7 months in cone bioassay. PCR of 2016 and 2017 samples showed vector populations were predominantly Anopheles arabiensis (58.1%, n = 4,403 IRS sites, 58%, n = 2,441 unsprayed sites). There was a greater proportion of Anopheles funestus sensu stricto in unsprayed sites (20.4%, n = 858) than in sprayed sites (7.9%, n = 595) and fewer Anopheles parensis (2%, n = 85 unsprayed, 7.8%, n = 591 sprayed). Biting peaks of Anopheles gambiae sensu lato (s.l.) followed periods of rainfall occurring between October and April, but were generally lower in sprayed sites than unsprayed. In most sprayed sites, An. gambiae s.l. indoor densities increased between January and February, i.e., 10–12 months after IRS. The predominant species An. arabiensis had a sporozoite rate in 2017 of 2.0% (95% CI 1.4–2.9) in unsprayed sites compared to 0.8% (95% CI 0.5–1.3) in sprayed sites (p = 0.003). Sporozoite rates were also lower for An. funestus collected in sprayed sites.

Conclusion

This study contributes to the understanding of malaria vector species composition, behaviour and transmission risk following IRS around Lake Victoria and can be used to guide malaria vector control strategies in Tanzania.

Does the exposure of parental female adults of the invasive Trogoderma granarium Everts to pirimiphos-methyl on concrete affect the morphology of their adult progeny? A geometric morphometric approach

Insecticidal applications may result to morphological deformations upon exposed insects or their offspring production. In the present study, we tested whether pirimiphos-methyl can induce deformities to wings of progeny production of the invasive khapra beetle, Trogoderma granarium (Coleoptera: Dermestidae) when its parental female adults have been treated with this organophosphorus active ingredient. For that purpose, we analysed both elytra and hindwings of both sexes of T. granarium progeny production by using the geometric morphometrics method. Our results showed that the wings of progeny of the pirimiphos-methyl-treated T. granarium parental female adult individuals suffered certain changes in their usual shape depending on size. Deformations occurred on both pairs of wings, but changes were more noticeable on the hindwings. A longer than 5-h exposure of parental female adults to pirimiphos-methyl, resulted in progeny with more deformed wings than in those individuals emerged after the exposure of their parental female adults in shorter periods on the toxicant. Generally, wings of both sexes were sensitive to pirimiphos-methyl, distinguishing the control group from the insecticidal treatments. The existence of deformed adults could be a useful indicator of earlier insecticidal applications as surface treatments and/or grain protectants in the storage facilities.

LC-MS/MS method for the determination of organophosphorus pesticides and their metabolites in salmon and zebrafish fed with plant-based feed ingredients

The composition of Atlantic salmon feed has changed considerably over the last two decades from being marine-based (fishmeal and fish oil) to mainly containing plant ingredients. Consequently, concern related to traditional persistent contaminants typically associated with fish-based feed has been replaced by other potential contaminants not previously associated with salmon farming. This is the case for many pesticides, which are used worldwide to increase food production, and may be present in plant ingredients. Earlier studies have identified two organophosphorus pesticides, chlorpyrifos-methyl and pirimiphos-methyl, in plant ingredients used for aquafeed production. In the present study, we developed a reliable and sensitive analytical method, based on liquid chromatography coupled to tandem mass spectrometry, for the determination of these pesticides and their main metabolites in warm water (zebrafish) and cold water (Atlantic salmon) species, where possible differences in metabolites could be expected. The method was tested in whole zebrafish and in different salmon tissues, such as muscle, bile, kidney, fat, and liver. The final objective of this work was to assess kinetics of chlorpyrifos-methyl and pirimiphos-methyl and their main metabolites in fish tissue, in order to fill the knowledge gaps on these metabolites in fish tissues when fed over prolonged time.

Entomological impact of indoor residual spraying with pirimiphos-methyl: a pilot study in an area of low malaria transmission in Senegal

Background

Scaling-up of effective anti-malarial control strategies in Central-West region of Senegal has resulted in the sharp decline in malaria prevalence in this area. However, despite these strategies, residual malaria transmission has been observed in some villages (hot spots). The objective of this study was to assess the impact of indoor residual spraying (IRS) with pirimiphos-methyl on malaria transmission in hot spot areas.

Methods

The malaria vector population dynamics were monitored in each of the six selected villages (4 of which used IRS, 2 were unsprayed control areas) using overnight human landing catches (HLC) and pyrethrum spray catches (PSC). The host source of blood meals from freshly fed females collected using PSC was identified using the direct ELISA method. Females caught through HLC were tested by ELISA for the detection of Plasmodium falciparum circumsporozoite protein and Anopheles gambiae complex was identified using PCR.

Results

Preliminary data shown that the densities of Anopheles populations were significantly lower in the sprayed areas (179/702) compared to the control. Overall, malaria transmission risk was 14 times lower in the intervention zone (0.94) compared to the control zone (12.7). In the control areas, three Anopheles species belonging to the Gambiae complex (Anopheles arabiensis, Anopheles coluzzii and Anopheles melas) maintained the transmission, while only An. coluzzii was infective in the sprayed areas.

Conclusion

The preliminary data from this pilot study showed that IRS with the CS formulation of pirimiphos-methyl is likely very effective in reducing malaria transmission risk. However, additional studies including further longitudinal entomological surveys as well as ecological and ethological and genetical characterization of vectors species and their populations are needed to better characterize the entomological impact of indoor residual spraying with pirimiphos-methyl in the residual transmission areas of Senegal.

Determination of the residual efficacy of carbamate and organophosphate insecticides used for indoor residual spraying for malaria control in Ethiopia

Background

Indoor residual spraying is one of the key vector control interventions for malaria control in Ethiopia. As malaria transmission is seasonal in most parts of Ethiopia, a single round of spraying can usually provide effective protection against malaria, provided the insecticide remains effective over the entire malaria transmission season. This experiment was designed to evaluate the residual efficacy of bendiocarb, pirimiphos-methyl, and two doses of propoxur on four different wall surfaces (rough mud, smooth mud, dung, and paint). Filter papers affixed to wall surfaces prior to spraying were analyzed to determine the actual concentration applied. Cone bioassays using a susceptible Anopheles arabiensis strain were done monthly to determine the time for which insecticides were effective in killing mosquitoes.

Results

The mean insecticide dosage of bendiocarb applied to walls was 486 mg/m² (target 400/mg). This treatment lasted 1 month or less on rough mud, smooth mud, and dung, but 4 months on painted surfaces. Pirimiphos-methyl was applied at 1854 mg/m² (target 1000 mg/m²), and lasted between 4 and 6 months on all wall surfaces. Propoxur with a target dose of 1000 mg/m² was applied at 320 mg/m², and lasted 2 months or less on all surfaces, except painted surfaces (4 months). Propoxur with a target dose of 2000 mg/m², was applied at 638 mg/m², and lasted 3 months on rough mud, but considerably longer (5–7 months) on the other substrates.

Conclusions

It would appear that the higher dose of propoxur and pirimiphos-methyl correspond best to the Ethiopian transmission season, although interactions between insecticide and the substrate should be taken into account as well. However, the insecticide quantification revealed that the dosages actually applied differed considerably from the target dosages, even though care was taken in the mixing of insecticide formulations and spraying of the walls. It is unclear whether this variability is due to initial concentrations of insecticides, poor application, or other factors. Further work is needed to ensure that target doses are correctly applied, both operationally and in insecticide evaluations.

Electronic supplementary material

The online version of this article (10.1186/s12936-017-2122-3) contains supplementary material, which is available to authorized users.

Multiple insecticide resistance in Anopheles gambiae from Tanzania: a major concern for malaria vector control

BACKGROUND

Malaria vector control in Tanzania is based on use of long-lasting insecticide treated nets (LLINs) and indoor residual spraying (IRS), which both rely on the use of chemical insecticides. The effectiveness of these control tools is endangered by the development of insecticide resistance in the major malaria vectors. This study was carried out to monitor the susceptibility status of major malaria vectors to insecticides used for IRS and LLINs in mainland Tanzania.

METHODS

Mosquito larvae were collected in 20 sites of Tanzania mainland in 2015. Phenotypic resistance was determined using standard WHO susceptibility tests. Molecular assay were used to determine distribution of Anopheles gambiae sub-species. A microplate assay approach was used for identifying enzyme levels on single mosquitoes from each sites compared with a susceptible reference strain, An. gambiae sensu stricto (s.s.) Kisumu strain.

RESULTS

Anopheles arabiensis was the dominant malaria specie in the country, accounting for 52% of the sibling species identified, while An. gambiae s.s. represented 48%. In Arumeru site, the dominant species was An. arabiensis, which was resistant to both pyrethroids (permethrin and deltamethrin), and pirimiphos-methyl, and had significant elevated levels of GSTs, non-specific esterases, and oxidase enzymes. An. arabiensis was also a dominant species in Kilombero and Kondoa sites, both were resistant to permethrin and deltamethrin with significant activity levels of oxidase enzymes. Resistance to bendiocarb was recorded in Ngara site where specie composition is evenly distributed between An. gambiae s.s. and An.arabiensis. Also bendiocarb resistance was recorded in Mbozi site, where An. gambiae s.s. is the dominant species.

CONCLUSIONS

Overall, this study confirmed resistance to all four insecticide classes in An. gambiae sensu lato in selected locations in Tanzania. Results are discussed in relation to resistance mechanisms and the optimization of resistance management strategies.

Atmospheric degradation of the organothiophosphate insecticide - Pirimiphos-methyl

The gas phase atmospheric degradation of pirimiphos-methyl (a widely used organophosphate insecticide and acaricide in many European regions) has been investigated at the large outdoor European Photoreactor (EUPHORE) in Valencia, Spain. Its photolysis has been studied under sunlight conditions and its reaction rate constant with OH radicals was measured by the relative rate method. The reaction with ozone was also investigated. The tropospheric degradation of pirimiphos-methyl is controlled mainly by the OH radical reaction. The rate coefficient of the OH reaction with pirimiphos-methyl, k, was measured by a conventional relative rate technique, where aniline was taken as a reference. The resulting value of the OH reaction rate constant with pirimiphos-methyl was k=(1.14±0.2)×10^-10cm³molecule^-1s^-1. The tropospheric lifetime of pirimiphos-methyl with respect to the reaction with OH radicals was estimated to be around 1.6h (283±10) K and atmospheric pressure. Significant aerosol formation was observed in the OH reaction with yields that ranged from 25 to 37%, and with particle diameters below 550nm. This therefore reveals a high human risk due to PM<1, without taking into account the chemical composition of the degradation products. SO₂, glyoxal and other oxygenated and nitrogenated compounds were the main degradation products detected.

Degradation of bifenthrin and pirimiphos-methyl residues in stored wheat grains (Triticum aestivum L.) by ozonation

Pesticide insecticides are used on wheat grains in storage units but their efficiency is hindered by persistent residues in the grains. Therefore, this study aims to evaluate the effectiveness of ozone (O3) gas treatment on the degradation of residual bifenthrin and pirimiphos-methyl insecticides commonly used in storage wheat grains, as well as to evaluate degradation of their by-products. The residues of bifenthrin decreased after 180 min of exposure in a concentration of 60 μmol/mol (a 37.5 ± 7.4% reduction) with 20% moisture content and 0.9 water activity. On the other hand, under the same experimental conditions, the pirimiphos-methyl residues significantly decreased in the wheat grains (71.1 ± 8.6%) after 30 min of exposure. After O3 gas treatment, three by-products of pirimiphos-methyl (m/z=306.1) containing different molecular mass to charge ratios (m/z=278.1, 301.1 and 319.2) were identified by LC-MS. O3 is a strong oxidizer that has shown the potential to reduce pesticide residues in stored grain in order to ensure food quality and safety.

Theoretical study on the atmospheric transformation mechanism of pirimiphos-methyl initiated by O3

Pirimiphos-methyl (PMM) is a widely used organophosphorus pesticide that can be released into the atmosphere in gas and condensed phases. It possesses a PS bond and an N,N-dialkyl group adjacent to pyrimidine, which are common functional groups for pesticides. Currently, the reaction mechanisms of O3 with these functional groups are poorly understood. In this study, the mechanisms and possible degradation products for O3-initiated atmospheric oxidation of PMM were investigated using the Density Functional Theory (DFT) method. The results show that H abstraction from the alpha carbon of the N,N-diethyl group and its subsequent reactions (hydroxylation, N-dealkylation, and carbonylation reactions), as well as the transformation of the PS bond to the PO oxone form, are the most favorable reaction pathways for PMM and O3. The Gibbs free energy (ΔG) indicates that the subsequent reactions tend to take place more spontaneously once the initial reaction occurs. In addition, theoretical calculations indicate that water can serve as an effective catalyst in the N-dealkylation reaction process. Water-assisted reactions lead to the activation energy decreasing by 20.2 kcal mol(-1) compared with direct reactions, and thus may represent a dominant reaction pathway for the N-dealkylation process in the atmosphere. These theoretical results provide new insights into O3-initiated degradation of PMM and its analogues.

Application of microcosmic system for assessment of insecticide effects on biomarker responses in ecologically different earthworm species

Earthworms from different ecological categories--epigeic Eisenia andrei and Lumbricus rubellus, endogeic Octolasion lacteum and anecic Lumbricus terrestris--were exposed in a microcosmic system to three commonly used insecticides. The effects of the insecticides were evaluated by measuring the following molecular biomarkers-the activities of AChE, CES, CAT, GST and the concentration of GSH. The results showed that environmentally relevant doses of organophosphates dimethoate and pirimiphos-methyl significantly affected the measured biomarkers, whereas pyrethroid deltamethrin did not affect the earthworms at the recommended agricultural dose. Considering the ecological category of earthworms, the results were inhomogeneous and species-specific differences in the biomarker responses were recorded. Since the biomarker responses of the investigated earthworm species were different after exposure to organophosphates in a microcosm compared to the exposure via standardized toxicity tests, two types of species sensitivity should be distinguished-physiological and environmental sensitivity. In addition, the hormetic effect of organophosphates on AChE and CES activities was recorded. The detection of hormesis in a microcosm is of great importance for future environmental research and soil biomonitoring, since in a realistic environment pollutants usually occur at low concentrations that could cause a hormetic effect. The results demonstrate the importance of the application of microcosmic systems in the assessment of the effects of environmental pollutants and the necessity of taking into account the possible differences between physiological and environmental species sensitivity.