Effects Of Pesticide Mixtures Research Articles

Interactive effects of pesticide mixtures, predators, and environmental regimes on the toxicity of two pesticides to red‐eyed tree frog larvae

Global amphibian declines have many corroborative causes, and the use of pesticides in agriculture is a likely contributor. In places with high pesticide usage, such as Costa Rica, agrochemical pesticides may interact with other factors to contribute to rapid species losses. Classical ecotoxicological studies rarely address the effects of a pesticide in combination with other stressors. The present study investigated the synergistic roles of 2 pesticides (chlorothalonil and endosulfan), predator stress, and environmental regimes (controlled laboratory environments versus ambient conditions) on the survival of red-eyed tree frog larvae (Agalychnis callidryas). No synergistic effects of pesticide mixtures or predator stress were found on the toxicity of either chlorothalonil or endosulfan. Both pesticides, however, were considerably more toxic under realistic ambient temperature regimes than in a climate-controlled laboratory. Overall, endosulfan displayed the highest toxicity to tadpoles, although chlorothalonil was also highly toxic. The median lethal concentration estimated to kill 50% of a tested population (LC50) for endosulfan treatments under ambient temperatures was less than one-half of that for laboratory treatments (3.26 µg/L and 8.39 µg/L, respectively). Studies commonly performed in stable temperature-controlled laboratories may significantly underestimate toxicity compared with more realistic environmental regimes. Furthermore, global climatic changes are leading to warmer and more variable climates and may increase impacts of pesticides on amphibians.

Estimating the Toxicity of Pesticide Mixtures to Aquatic Organisms: A Review

ABSTRACT A major difficulty in addressing chemical mixtures through legislation or regulations revolves around our limited understanding of their potential impacts. This review provides an overview of recent research on pesticide mixture toxicity to aquatic biota and the methods employed to predict toxic effects. The most common approaches are to assume concentration-addition or independent action of chemicals in a mixture. There are a number of cases in the literature of interactions between pesticides. However, models accounting for possible interactions between mixture components are used infrequently. Although results are limited, studies investigating the effects of pesticide mixtures have not demonstrated significant synergism at environmentally relevant concentrations. Based on the results of our review, we conclude that the concentration-addition model is a generally conservative and practical first-tier model for the ecological assessment of pesticide mixtures in aquatic systems.

The PERICLES research program: An integrated approach to characterize the combined effects of mixtures of pesticide residues to which the French population is exposed

Due to the broad spectrum of pesticide usages, consumers are exposed to mixtures of residues, which may have combined effects on human health. The PERICLES research program aims to test the potential combined effects of pesticide mixtures, which are likely to occur through dietary exposure.The co-exposure of the French general population to 79 pesticide residues present in the diet was first assessed. A Bayesian nonparametric model was then applied to define the main mixtures to which the French general population is simultaneously and most heavily exposed. Seven mixtures made of two to six pesticides were identified from the exposure assessment.An in vitro approach was used for investigating the toxicological effects of these mixtures and their corresponding individual compounds, using a panel of cellular models, i.e. primary rat and human hepatocytes, liver, intestine, kidney, colon and brain human cell lines. A set of cell functions and corresponding end-points were monitored such as cytotoxicity, real-time cell impedance, genotoxicity, oxidative stress, apoptosis and PXR nuclear receptor transactivation. The mixtures were tested in equimolar concentrations. Among the seven mixtures, two appeared highly cytotoxic, five activated PXR and depending on the assay one or two were genotoxic. In some experiments, the mixture effect was quantitatively different from the effect expected from the addition concept.The PERICLES program shows that, for the most pesticides mixtures to which the French general population is exposed, the toxic effects observed on human cells cannot be easily predicted based on the toxic potential of each compound. Consequently, additional studies should be carried on in order to more accurately define the mixtures of chemicals to which the consumers are exposed, as well as to improve the investigation, prediction and monitoring of their potential human health effects.

Dietary exposure to a low dose of pesticides alone or as a mixture: The biological metabolic fingerprint and impact on hematopoiesis

Consumers are exposed to a mixture of pesticides through their food intake. These compounds are considered risk factors for human health, and the impact of dietary exposure to low doses of pesticide mixtures remains poorly understood. For this study we developed a mouse model to mimic consumer exposure in order to compare the effect of pesticides both alone or combined at doses corresponding to their Acceptable Daily Intake value. Female mice were exposed to pesticides throughout gestation and lactation. After weaning pups were fed the same pesticide-enriched diet their mothers had received for an additional 11 weeks. A metabonomic approach using 1H NMR-based analysis of plasma showed that exposure to each pesticide produced a specific metabolic fingerprint in adult offspring. Discriminant metabolites between groups were glucose or lactate, choline, glycerophosphocholine and phosphocholine. Interestingly, metabolite differences were observed as early as weaned animals that had not yet been directly exposed themselves. Studies of the hematopoietic system revealed that dietary exposure to one particular pesticide, endosulfan, produced a significant decrease in red blood cell and hemoglobin levels, consistent with hemolytic anemia. Moreover, cell signaling profiles of bone marrow progenitors were also clearly affected. Expression of cell signaling proteins such as P35, CDC27, FAK, P38 MAP kinase, calcineurin and caspase as well as proteins involved in the stability or structure of the cytoskeleton (vinculin, MAP2) was changed upon dietary exposure to pesticides. Finally, we found that dietary exposure to a mixture of pesticides had effects that differed and were often lesser or equal to that of the most efficient pesticide (endosulfan), suggesting that the effect of pesticide mixtures cannot always be predicted from the combined effects of their constituent compounds.

Repeated and multiple stress (exposure to pesticides) on aquatic organisms

A systematic literature search identified publications relevant to repeated (94 papers) and mixture exposure (152 papers) of aquatic organisms. Limited data are available on pulsed exposure of pesticides and reports on repeated pulse or fluctuating exposures are even rarer. Although there has been recognition of the need for more realistic testing scenarios these lack a systematic approach. Among the reports on pesticide mixtures most of the plant studies evaluated interactions between mixtures of herbicides or fungicides / algicides. A small number of reports evaluated the effects on invertebrates of mixtures of pesticides with the same mode of action and these showed additive toxicity. More studies in invertebrates assessed interactions between pesticides with different modes of action including herbicide/ insecticide combinations some of which showed toxicity greater than additive. The majority of studies in fish have investigated the toxicity of insecticide mixtures. The toxicity of most combinations was at most additive, with a small number antagonistic. A small number of papers reported mixture effects of pesticides in amphibians; more than additive effects were observed with atrazine combinations. Simple models can be used to determine the additive toxicity of pesticide mixtures based on concentration addition or independent action. More complex models to determine the scale of synergy are speciesand dose-dependent and rely on an understanding of the interactions involved. Further work is required to develop a greater understanding of the species, dose and time dependence of exposure to pesticide mixtures in which more complex interactions occur. In the interim, in the majority of cases the increase in toxicity is no greater than 3 fold when compared to additive, the deviation from additivity decreases with the increasing number of components in the mixture, and where no known interactions have been reported this may be an appropriate factor to include in risk assessments.

Assessing, mapping and validating site-specific ecotoxicological risk for pesticide mixtures: A case study for small scale hot spots in aquatic and terrestrial environments

Mixture toxicity is a real world problem and as such requires risk assessment solutions that can be applied within different geographic regions, across different spatial scales and in situations where the quantity of data available for the assessment varies. Moreover, the need for site specific procedures for assessing ecotoxicological risk for non-target species in non-target ecosystems also has to be recognised. The work presented in the paper addresses the real world effects of pesticide mixtures on natural communities. Initially, the location of risk hotspots is theoretically estimated through exposure modelling and the use of available toxicity data to predict potential community effects. The concept of Concentration Addition (CA) is applied to describe responses resulting from exposure of multiple pesticides The developed and refined exposure models are georeferenced (GIS-based) and include environmental and physico-chemical parameters, and site specific information on pesticide usage and land use. As a test of the risk assessment framework, the procedures have been applied on a suitable study areas, notably the River Meolo basin (Northern Italy), a catchment characterised by intensive agriculture, as well as comparative area for some assessments. Within the studied areas, the risks for individual chemicals and complex mixtures have been assessed on aquatic and terrestrial aboveground and belowground communities. Results from ecological surveys have been used to validate these risk assessment model predictions. Value and limitation of the approaches are described and the possibilities for larger scale applications in risk assessment are also discussed.

In vitro combined cytotoxic effects of pesticide mixtures simultaneously found in the French diet

In vitro combined cytotoxic effects of pesticide mixtures simultaneously found in the French diet

The effects of pesticide mixtures on degradation of pendimethalin in soils

Most agronomic situations involve a sequence of herbicide, fungicide, and insecticide application. On the other hand, use of pesticidal combinations has become a standard practice in the production of many agricultural crops. One of the most important processes influencing the behavior of a pesticide in the environment is its degradation in soil. It is known that due to several pesticide applications in one vegetation season, the pesticide may be present in mixtures with other pesticides or xenobiotics in soil. This study examines the role which a mixture of chemicals plays in pesticide degradation. The influence of other pesticides on the rate of pendimethalin (PDM) degradation in soil was measured in controlled conditions. Mixtures of PDM with mancozeb or mancozeb and thiamethoxam significantly influenced the degradation of pendimethalin under controlled conditions. The second type of mixtures, with metribuzin or thiamethoxam, did not affect the behavior of pendimethalin in soil. Also, we determined the influence of water content on the rate of pendimethalin degradation alone in two soils and compared it to the rate in three pesticide mixtures. We compared two equations to evaluate the predictors of the rate of herbicide dissipation in soil: the first-order kinetic and the non-linear empirical models. We used the non-linear empirical model assuming that the degradation rate of a herbicide in soil is proportional to the difference of the observed concentration of herbicide in soil at time and concentration of herbicide in the last day of measurement.

Combining polar organic chemical integrative samplers (POCIS) with toxicity testing to evaluate pesticide mixture effects on natural phototrophic biofilms

Polar organic chemical integrative samplers (POCIS) are valuable tools in passive sampling methods for monitoring polar organic pesticides in freshwaters. Pesticides extracted from the environment using such methods can be used to toxicity tests. This study evaluated the acute effects of POCIS extracts on natural phototrophic biofilm communities. Our results demonstrate an effect of POCIS pesticide mixtures on chlorophyll a fluorescence, photosynthetic efficiency and community structure. Nevertheless, the range of biofilm responses differs according to origin of the biofilms tested, revealing spatial variations in the sensitivity of natural communities in the studied stream. Combining passive sampler extracts with community-level toxicity tests offers promising perspectives for ecological risk assessment.

Dimethoate, fenvalerate and their mixture affects Hylyphantes graminicola (Araneae: Linyphiidae) adults and their unexposed offspring

1 Mixtures of organophosphorus and pyrethroid insecticides are widely used to combat resistance in agricultural pests, although few studies have been conducted on the effects of pesticide mixtures on beneficial nontarget organisms. 2 In the present study, we exposed adult females (F0) of Hylyphantes graminicola (Araneae: Linyphiidae) to fenvalerate, dimethoate and their commercially available 1 : 1 mixture (by mass). We investigated the acute toxicity of these pesticides to the exposed adults, as well as sublethal effects on reproduction and acetylcholinesterase and carboxylesterase activity. We also studied the effects of parental exposure on the size, development and enzyme activity of unexposed offspring. 3 All three formulations were acutely toxic to H. graminicola, with synergism between dimethoate and fenvalerate leading to greater toxicity in the 1 : 1 mixture than for the two insecticides alone. The sublethal effects of direct pesticide exposure were a reduction in acetylcholinesterase and carboxylesterase activity and a reduction in the number of egg sacs produced by exposed spiders relative to the control spiders. The unexposed offspring of the fenvalerate and mixture exposed spiders were smaller and took longer to mature than the control spiders. Offspring of all exposed spiders also had significantly reduced carboxylesterase activity relative to control spiders. 4 We concluded that the effects of parental exposure on the offspring were likely to increase their susceptibility to future pesticide exposures, and reduce the capacity of this spider to serve as a pest control agent.

Assessment of toxic effects of pesticide extracts on different green algal species by using chlorophyll a fluorescence

In this study, the toxicity of pesticides extracted from the Yamaska River watershed surface waters were tested on three species of green algae (Chlorella vulgaris, Scenedesmus obliquus and Pseudokirchneriella subcapitata) by using slow and fast fluorescence kinetics (Maxi-Imaging-Pulse-Amplitude-Modulated and Plant Efficiency Analysis). Two types of extractions for a variety of herbicides and insecticides (organosphosphorous-type (OP) and phenoxyacid-type (PA)) were conducted on the water samples of three sites having different pesticide concentrations (‘Deborah Stairs’, ‘Rivière Noire’ and ‘Rivière à la Barbue’). Our results showed that of the three species of green algae studied, S. obliquus was the most sensitive to both pesticide extracts. Moreover, PA pesticide extracts from ‘Rivière à la Barbue’ were the most toxic since the algae exposed to those extracts had the lowest photosynthetic activity when evaluated by the PSII quantum yields (ΦM and ), the photochemical quenching (qP(REL)) and the electron transport rate per reaction center (ET0/RC). The fast fluorescence kinetic data also indicate that the site of action of the different extracts was at the level of the primary photochemical events, probably electron flow blockage at the Q B binding site. This study demonstrated the advantages of using chlorophyll fluorometry in assessing toxic effect of pesticide mixtures.

Effects of an Atrazine, Metolachlor and Fipronil Mixture on Hyalella azteca (Saussure) in a Modified Backwater Wetland

We examined the toxicity mitigation efficiency of a hydrologically modified backwater wetland amended with a pesticide mixture of atrazine, metolachlor, and fipronil, using 96 h survival bioassays with Hyalella azteca. Significant H. azteca 96 h mortality occurred within the first 2 h of amendment at the upstream amendment site but not at any time at the downstream site. H. azteca survival varied spatially and temporally in conjunction with measured pesticide mixture concentrations. Hyalella azteca 96 h survival pesticide mixture effects concentrations ranges were 10.214–11.997, 5.822–6.658, 0.650–0.817, and 0.030–0.048 μg L−1 for atrazine, metolachlor, fipronil, and fipronil-sulfone, respectively.

Sublethal effects of pesticide mixtures on selected biomarkers of Carassius auratus

In the present study, the in vivo effects of commercial propoxur alone and in combination with isoprocarb and chlorpyrifos on acetylcholinesterase and glutathione S-transferases activities in goldfish ( Carassius auratus) were investigated. Brain and muscle AChE activity was significantly inhibited (88% and 85% at most, respectively) by propoxur after 5 d of exposure at concentrations between 141 and 2263 μg/L, bell-shaped concentration–response curves were obtained. In most cases, time dependence was apparent. Under insecticide mixture exposure (binary mixture propoxur/isoprocarb and ternary mixture propoxur/isoprocarb/chlorpyrifos), the inhibition of AChE activity was significant in all cases and linear concentration–response relationships were observed. Propoxur (alone and in combination) significantly inhibited gill GST activity, and both mixtures also induced significant inhibition of liver GST activity. However, concentration and time dependence were not apparent. AChE is likely to be more informative than GST and seems to be a good biomarker to diagnose exposure to anticholinesterase pesticides in wild populations of this species.

Organophosphorous insecticides as herbicide synergists on the green algae Pseudokirchneriella subcapitata and the aquatic plant Lemna minor

Models proposed for risk assessment of chemical mixtures assume no interactions between the chemicals. There are, however, studies indicating that some organophosporous insecticides can inhibit the detoxification of other chemicals in plants thereby enhancing their effect. The present study investigates whether interactions between selected organophosporous insecticides and herbicides can take place in the aquatic algae Pseudokirchneriella subcapitata and the aquatic macrophyte Lemna minor. For both species binary mixtures of the organophosphate insecticides: malathion, endosulfan and chlorpyrifos were tested together with the herbicides metsulfuron-methyl, terbutylazine and bentazone. For mixtures with malathion on algae, dose-response surfaces were made and the results tested against the model of concentration addition (CA) and independent action (IA). The Lemna minor tests showed no indication of synergy for any of the combinations, on the contrary, significant antagonism was found for several of the mixtures. The response surface analysis showed antagonism in relation to both concentration addition and independent action for mixtures between malathion and metsulfuron-methyl and terbuthylazine, while the mixtures with bentazone could be explained with CA. The study shows no indications of synergistic interactions between the tested pesticides, confirming the applicability of CA as a reference model predicting mixture effects of pesticides for aquatic plants and algae.

Effect of Pesticide Mixtures in Controlling Western Flower Thrips (Thysanoptera: Thripidae)

Greenhouse managers mix together pesticides to broaden the spectrum of pest control and to reduce pesticide and labor costs. However, the efficacy of pesticide mixtures has not been well-documented. This study assesses how mixtures of commercially available insecticides and miticides in two, three, and four-way combinations affected the control of western flower thrips, Frankliniella occidentalis Pergande, in greenhouse experiments and in a laboratory bioassay. The pesticides screened in the greenhouse experiments and laboratory bioassay were spinosad, abamectin, bifenazate, azadirachtin and imidacloprid. Each pesticide was applied at the maximum label-recommended rate. In the greenhouse experiments, transvaal daisy (Gerbera jamesonii H. Bolus ex Hook. f) and lisianthus (Eustoma grandiflorum G. Don ex Sweet) flowers were infested with 25 adult western flower thrips (mixture of females and males). Flowers were then sprayed with the designated treatments. After 72 h, flowers were dissected to assess the numbers of live and dead western flower thrips. In the laboratory bioassay, chrysanthemum (Dendranthema grandiflora Tzvelev) leaf sections, treated with solutions of each pesticide and all possible combinations, were exposed to 15 adult western flower thrips. The numbers of live and dead western flower thrips were assessed after 48 h. For all three experiments, we were not able to identify any antagonistic pesticide combinations. All treatments with spinosad, including the individual application and pesticide mixtures, resulted in high mortality of western flower thrips. Our data suggest that combinations of spinosad with the other pesticides tested do not affect the efficacy of spinosad in controlling western flower thrips. This information is important to greenhouse managers who wish to mix pesticides and still control western flower thrips in addition to the other plant-feeding arthropods found in greenhouses.

Behavioral and sex ratio modification of Japanese medaka (Oryzias latipes) in response to environmentally relevant mixtures of three pesticides

We exposed Japanese medaka (Oryzias latipes) to environmentally relevant concentrations of azinphos-methyl, chlorothalonil, endosulfan, and mixtures of all three to determine if combinations of these pesticides result in additive, less-than-additive, or more-than-additive effects. Medaka were exposed from fertilization until 7 days posthatching, and end points included survival, time to hatch, size at 7 days posthatching, activity level (as measured by distance swam) and foraging ability at 3 weeks posthatching, and adult size, liver size, and sex ratio at 5 months posthatching. Although exposure to individual pesticides or pesticide mixtures did not affect survival, hatching time, or foraging ability, fry exposed to azinphos-methyl were significantly smaller at 1 week of age, and those exposed to chlorothalonil and a combination of the chemicals showed reduced activity. Adult sex ratios were biased toward females in all groups exposed to pesticides, with those exposed to azinphos-methyl, chlorothalonil, and the pesticide mixture departing significantly from an even sex ratio. There was no evidence of additive or synergistic effects of pesticide mixtures.

705 Is it possible to establish a causal relationship between CFS (chronic fatigue syndrome) and chemical exposures? paracelsus paradigm implications

The effects of pesticide mixtures on cholinesterase activity in aggregate cultures of neural cells were investigated; we also determined whether exogenous rat-liver microsomal fraction (S-9) might be used in conjunction with the cultures to mimic the in vivo activation of pesticides such as malathion. Studies of the effects of pesticide mixtures on the cholinesterase activity of cultures demonstrated that a hepatic microsomal fraction (S-9) played a major role in the nature of the interaction between combinations of malathion and fenitrothion or carbofuran. In the absence of S-9, malathion potentiated the anti-cholinesterase effect of fenitrothion, while neither synergistic nor antagonistic interactions occurred with mixtures of carbofuran and malathion. When S-9 was added to cultures with the pesticide mixtures, malathion's interaction with fenitrothion was antagonistic, and a synergistic response was observed for the mixtures of malathion and carbofuran. The antagonistic interaction of mixtures of fenitrothion and carbofuran was demonstrated to be independent of exogenously added S-9. Neither antagonistic nor synergistic interactions were observed for mixtures of triallate and fenitrothion or carbofuran. The data indicate that the addition of exogenous S-9 may be used to mimic certain aspects of the in vivo biotransformation of pesticides in aggregate cultures of neural cells from rat brain. Furthermore, the effects on cholinesterase activity of several of the pesticide mixtures tested were dependent upon the presence of exogenous S-9.

Toxicity of pesticides to aquatic microorganisms: a review.

Microorganisms contribute significantly to primary production, nutrient cycling, and decomposition in estuarine eco-systems; therefore, detrimental effects of pesticides on microbial species may have subsequent impacts on higher trophic levels. Pesticides may affect estuarine microorganisms via spills, runoff, and drift. Both the structure and the function of microbial communities may be impaired by pesticide toxicity. Pesticides may also be metabolized or bioaccumulated by microorganisms. Mechanisms of toxicity vary, depending on the type of pesticide and the microbial species exposed. Herbicides are generally most toxic to phototrophic microorganisms, exhibiting toxicity by disrupting photosynthesis. Atrazine is the most widely used and most extensively studied herbicide. Toxic effects of organophosphate and organochlorine insecticides on microbial species have also been demonstrated, although their mechanisms of toxicity in such nontarget species remain unclear. There is a great deal of variability in the toxicity of even a single pesticide among microbial species. When attempting to predict the toxicity of pesticides in estuarine ecosystems, effects of pesticide mixtures and interactions with nutrients should be considered. The toxicity of pesticides to aquatic microorganisms, especially bacteria and protozoa, is an area of research requiring further study.

Toxicity of pesticides to aquatic microorganisms: A review

AbstractMicroorganisms contribute significantly to primary production, nutrient cycling, and decomposition in estuarine ecosystems; therefore, detrimental effects of pesticides on microbial species may have subsequent impacts on higher trophic levels. Pesticides may affect estuarine microorganisms via spills, runoff, and drift. Both the structure and the function of microbial communities may be impaired by pesticide toxicity. Pesticides may also be metabolized or bioaccumulated by microorganisms. Mechanisms of toxicity vary, depending on the type of pesticide and the microbial species exposed. Herbicides are generally most toxic to phototrophic microorganisms, exhibiting toxicity by disrupting photosynthesis. Atrazine is the most widely used and most extensively studied herbicide. Toxic effects of organophosphate and organochlorine insecticides on microbial species have also been demonstrated, although their mechanisms of toxicity in such nontarget species remain unclear. There is a great deal of variability in the toxicity of even a single pesticide among microbial species. When attempting to predict the toxicity of pesticides in estuarine ecosystems, effects of pesticide mixtures and interactions with nutrients should be considered. The toxicity of pesticides to aquatic microorganisms, especially bacteria and protozoa, is an area of research requiring further study.

Degradation of atrazine, metolachlor, and pendimethalin in pesticide‐contaminated soils: Effects of aged residues on soil respiration and plant survival

This study was conducted to determine the effects of pesticide mixtures on degradation patterns of parent compounds as well as effects on soil microbial respiration. Bioavailability of residues to sensitive plant species was also determined. Soil for this study was obtained from a pesticide‐contaminated area within an agrochemical dealer site. Degradation patterns were not affected by the presence or absence of other herbicides in this study. Atrazine concentrations were significantly lower at 21 through 160 days aging time compared to day 0 concentrations. Metolachlor and pendimethalin concentrations were not significantly different over time and remained high throughout the study. Microbial respiration was suppressed in treated soils from day 21 to day 160. Soybean and canola were the most successful plant species in the germination and survival tests. Generally, with increased aging of pesticides in soil, germination time decreased. Survival time of plants increased over time for some treatments indicating possible decreased bioavailability of pesticide residues. In some cases, survival time decreased at the longer 160‐day aging period, possibly indicating a change in bioavailability, perhaps as the result of formation of more bioavailable and phytotoxic metabolites. No interactive effects were noted for mixtures of pesticides compared to individually applied pesticides in terms of degradation of the parent compound or on seed germination, plant survival, or microbial respiration.