Synergism of mixtures of dicamba and 2,4-dichlorophenoxyacetic acid herbicide formulations on the neotropical fish Cnesterodon decemmaculatus (Pisces, Poeciliidae)

Can the Herbicide Dicamba Produce Oxidative Stress in the Native South American fish Jenynsia lineata at Environmentally Relevant Concentrations?

Dicamba (DIC) is one of the most applied auxin herbicides worldwide. Sublethal effects in the South American native fish Jenynsia lineata exposed to DIC concentrations close to environmental concentrations (0.03-30 µg/L) during 48 h were analysed thorough the evaluation of catalase (CAT), glutathione S-transferase (GST), superoxide dismutase (SOD) activities and malondialdehyde (MDA) and H2O2 levels for detecting potential oxidative stress. In gills MDA increased showing oxidative damage probably because of an inefficient antioxidant defense. This response evidenced the important role of gills as an organ of direct contact with waterborne contaminants. In addition, other changes in the biomarkers of oxidative stress were observed such as the inhibition of SOD activities in brain and the inhibition of GST in liver. These results show that short- term exposures to environmentally relevant concentrations of DIC could induce sublethal effects in native fish.

Do environmentally relevant concentrations of the neonicotinoid insecticide imidacloprid induce DNA damage and oxidative stress on Cnesterodon decemmaculatus (Jenyns, 1842)?

Lethal and sublethal effects of imidacloprid (IMI) were assessed on Cnesterodon decemmaculatus (Pisces: Poeciliidae) by acute exposure to environmentally relevant concentrations of the commercial formulation Punto 35® (Gleba S.A.) under laboratory conditions. Specimens were exposed for 96 h to 1, 10, 20, 25, 35, 75, 100, 125, 150 and 175 mg IMI L^-1 from which an LC₅₀ 96 h value of 35.59 mg IMI L^-1 was calculated. Moreover, sublethal concentrations 0.175, 0.35 and 1 mg IMI L^-1 for 96 h were employed for the evaluation of the comet assay and the variation of activities of catalase (CAT) and glutathione content (GSH). Result demonstrated an increased genetic damage index and activity of CAT was observed. Conversely, no significant variation was observed in GSH activity. Total protein content decreased in treated organisms. These results represent the first report of acute effects induced by IMI on C. decemmaculatus exposed under laboratory conditions.

2,4-Dichlorophenoxyacetic acid (2,4-D) affects DNA integrity and retina structure in zebrafish larvae

Monitoring the potential risk of herbicides in non-target organisms is a crucial issue for environmental safety. 2,4-D is an herbicide of high environmental relevance that has been shown to exert toxic effects to soil and aquatic biota. In the present study, we investigated the possible genotoxic and retinal development effects of 2,4-dichlorophenoxyacetic acid (2,4-D) herbicide in early life stages zebrafish (Danio rerio). Genotoxicity was evaluated by measuring DNA damage using the comet assay and also by the mRNA expression of genes implicated in apoptosis and/or DNA repair. Retinal development toxicity was evaluated with histological approach. The results obtained revealed that 2,4-D alters DNA integrity of zebrafish larvae. Moreover, transcriptomic data showed a significant induction of p-53 and casp-3 genes and a significant decrease of lig-4 in larvae exposed to the highest tested concentration of 2,4-D (0.8 mg/L). This suggested that p-53 gene regulates the process of DNA repair and apoptosis with increased levels of 2,4-D. The histopathological analysis revealed that early exposure to 2,4-D damaged the structure of larvae retina. Overall, this study is the first to report the DNA damage, casp-3, lig-4 and p-53 regulation, as well as the ocular developmental toxicity in zebrafish larvae at environmentally relevant concentrations of 2,4-D herbicide.

Sorption and degradation of prothioconazole and its metabolites in soils and water sediments, and its combinative toxicity to Gobiocypris rarus

To reduce detrimental effects to the environment, the application of prothioconazole and its metabolites requires comprehensive evaluation, which has been dine for the first time in this study. The behavior of prothioconazole, including degradation and sorption under aerobic and anaerobic conditions, was evaluated in three common soil types and two types of water-sediment systems under different environmental conditions. Individual and joint toxicities of prothioconazole and its metabolites, M01 and M04, on aquatic organisms, including the Gobiocypris rarus, are also investigated in the present study. Under aerobic and anaerobic conditions, the half-life of prothioconazole in the three types of soils ranged from 0.0565 to 2.27 days and 0.138-1.73 days, respectively. Under aerobic conditions, the half-life of prothioconazole in the Hunan paddy area and Beijing Qidu reservoir water-sediment samples were 2.18 and 1.58 days, respectively. In soil and water-sediment samples, prothioconazole degraded to M01 and M04, and the formation rate of M04 was higher than M01 under aerobic condition. M04 and M01 gradually increased to a peak value in soil and water-sediment systems, then decreased over time, while prothioconazole gradually decreased. The half-life of prothioconazole in soils was lower than its metabolites, with the DT₅₀ of metabolites ranging from 16.6 to 99.6 days, 15.8 and 50.7 days for M01 and M04 under aerobic condition, respectively. While the adsorption capacities (K_f values) of M04 and M01 ranged from 2.09 to 88.92 and 8.98 to 243.30 (μg/g)/(mg/L), respectively, in the three soils. Regarding toxicity to aquatic organisms, the metabolites did not show higher toxicity than prothioconazole, except M01 on Gobiocypris rarus. Joint toxicity assays showed that mixtures of prothioconazole with its metabolites exhibited higher toxicity than any compound individually and indicated synergistic interactions could occur at equitoxic ratios and equivalent concentrations. This study provides a comprehensive investigation on the fate and environmental risk posed by prothioconazole.

Genetic Structure of a Native Neotropical Fish Species: New Insights about a South American Bioindicator

The biodiversity of Neotropical region is affected by anthropogenic disturbance. Throughout Brazil, Argentina and Uruguay, the native fish, Cnesterodon decemmaculatus, is well distributed and widely used as an excellent bioindicator of environmental quality. We investigated the diversity and genetic structure of its populations along a water pollution gradient to answer the following questions: 1- Does the genetic diversity decrease under the stressful conditions of a severe water quality gradient? and 2- Is there any relationship between the haplotypes registered along the studied basin and those recorded in other distant basins? Two mitochondrial DNA markers, Cytochrome b and D-loop, were analyzed and four haplotypes were registered for both markers along the basin. H1 was present throughout all the river sections in high frequencies leading to a low genetic diversity. We suggest that only a few haplotypes tolerate the stressful conditions of mountain rivers. On the other hand, the presence of H4 at the site located downstream suggests a history of recent colonization from the southeast to the northwest of the biome. These results, together with the abundance decrease along the pollution gradient, and the non-migratory characteristic of C. decemmaculatus suggest that its populations may be at risk of local extinction.

New insights into crosstalk between apoptosis and necroptosis co-induced by chlorothalonil and imidacloprid in Ctenopharyngodon idellus kidney cells

Overuse and co-exposure of pesticides have become a public health problem and threat seriously water health and environmental organisms and even humans. Chlorothalonil (CT) and imidacloprid (IMI) are high-selling pesticides worldwide, which can persist in the environment, and present a series of severely toxic effects on non-target animals. However, the effect of co-application on aquatic organisms is unknown. Based on the concept of the toxic unit (TU), toxic interaction of CT and IMI was evaluated and showed the additive and synergistic toxicity on Ctenopharyngodon idellus (grass carp) kidney cell line (CIK cells). Cell death analysis found an obvious increase of the apoptosis and necrosis rates exposed to CT and IMI, and aggravation when applied together. Moreover, CT and IMI co-exposure accelerated the inhibition of CYP450s/ROS/HIF-1α signal, the decline of energy metabolism, mitochondrial dynamics disorder, activation of Bcl2/Bax/Cyt C/Casp3/Casp9 pathway and RIP1/RIP3/MLKL pathway. Bioinformatics analysis showed autophagy, cell response, NOD-like receptor signaling pathway might be affected by co-exposure. In summary, the above results indicate that co-exposure to CT and IMI has synergistic toxicity and aggravates cell death via inhibition of the CYP450s/ROS/HIF-1α signal. These data provide new insights for evaluating the stacking interaction and revealing the toxicological effects of pesticide mixture.

Integrated ecotoxicological assessment of the complex interactions between chlorpyrifos and glyphosate on a non-target species Cnesterodon decemmaculatus (Jenyns, 1842)

Pesticide mixtures are frequent in freshwaters systems around the world, threatening the biota exposed to these conditions. The aim of this study was to determine the single and joint effect of two widely used pesticides in southern South America on a widely distributed fish species. In a 96-h assay, individuals of Cnesterodon decemmaculatus were exposed to 0.84 nL/L and 8.4 nL/L of Clorfox and 0.2 mg/L and 2 mg/L of Roundup Max, commercial formulations of chlorpyrifos and glyphosate, respectively. Also, there were four mixture treatments with all the possible combinations of both pesticides. A multi-level approach was carried out to assess their effects covering the following relevant biomarkers: behavior (immobile time, line crossings and average speed), somatic conditions (Fulton condition factor and hepatosomatic index), serum parameters (cortisol levels, lactate dehydrogenase (LDH), and creatine phosphokinase activity (CPK)), brain and muscle acetylcholinesterase and cytological characteristics (micronuclei frequency and nuclear abnormalities in erythrocytes). Our results showed that Clorfox exposures affect behavioral parameters, serum cortisol, and nuclear characteristics of erythrocytes. Roundup Max affects only the cortisol levels whereas mixture treatments have an effect on behavioral parameters, cortisol levels, LDH and CPK activities, and nuclear characteristics of erythrocytes. Potentiation was the main interaction at the lowest concentrations of both pesticides whereas antagonism occurred at the highest concentrations of both pesticides. These results are highly significant since they arise from an integrated ecotoxicological assessment at several levels of biological organization but even more important is that the potentiated effects of the mixtures we registered are environmentally relevant concentrations.

Joint toxic impacts of cadmium and three pesticides on embryonic development of rare minnow (Gobiocypris rarus)

Although rare minnow (Gobiocypris rarus) has been employed in many toxicological investigations, most of them have only assessed the impacts of single chemical. In our current work, we investigated the single and joint toxic impacts of heavy metal cadmium (Cd) and three pesticides (thiamethoxam, bifenthrin, and tebuconazole) on G. rarus embryos. Results from the 96-h semi-static toxicity assay exhibited that bifenthrin possessed the highest intrinsic toxic effect on rare minnows with an LC₅₀ value of 1.86 mg L^-1, followed by tebuconazole with LC₅₀ values of 4.07 mg L^-1. Contrarily, thiamethoxam elicited the least toxic effect with an LC₅₀ value of 351.9 mg L^-1. Seven chemical mixtures (four binary mixtures of Cd-bifenthrin, thiamethoxam-bifenthrin, thiamethoxam-tebuconazole, and bifenthrin-tebuconazole, two ternary mixtures of Cd-thiamethoxam-tebuconazole and thiamethoxam-bifenthrin-tebuconazole, and one quaternary mixture of Cd-thiamethoxam-bifenthrin-tebuconazole) displayed synergistic impacts with equivalent concentration and equitoxic ratio on G. rarus. Our results offered valuable insights into ecological risk assessment of these chemical combinations to aquatic vertebrates. The simultaneous existence of a few chemicals in the aquatic ecosystem might result in elevated toxicity, leading to severe harm to the non-target organisms compared with single compound. The observed synergistic interactions underlined the necessity to revise water quality standards, in which the detrimental joint effects of these chemicals are likely to be underestimated.

Toxicity to Rhinella arenarum tadpoles (Anura, Bufonidae) of herbicide mixtures commonly used to treat fallow containing resistant weeds: glyphosate-dicamba and glyphosate-flurochloridone

Glyphosate (GLY)-dicamba (DIC) and GLY-flurochloridone (FLC) are herbicide mixtures which are widely used for treating fallow containing glyphosate resistant weeds. The aim of this study was to evaluate the acute toxic effects and the prevailing interactions on stage 36 tadpoles of the anuran species Rhinella arenarum when exposed to equitoxic and non-equitoxic combinations of these herbicide combinations. Experiments were realized using the following combinations of commercial formulations: 48% GLY-based Credit® + 57.71% DIC-based Banvel® and 48% GLY-based Credit® + 25% FLC-based Twin Pack Gold®. GLY-DIC and GLY-FLC equitoxic mixtures were assayed mixing each constituent with an equivalent individual toxicity able to induce the same lethality effect. After 96 h of exposure, GLY-DIC and GLY-FLC equitoxic mixtures presented toxic unit 50 values (TU50 96h) of 1.74 (confidence interval: 1.58-1.92) and 1.54 (confidence interval: 1.46-1.62) respectively, indicating the presence of a weak antagonistic interaction as TU values were greater than 1. For their part, most non-equitoxic combinations of GLY-DIC and GLY-FLC tested did not significantly differ from additivity, the only exception being when DIC and FLC were fixed at 0.33 TUs, where a weak antagonism was observed. Overall, results indicate that the toxicity of both GLY-DIC and GLY-FLC mixtures to R. arenarum tadpoles vary from additive to slightly antagonistic, depending on the proportion of constituting herbicide formulations present in the mixture.

Genotoxicity of mixtures of glyphosate with 2,4-dichlorophenoxyacetic acid chemical forms towards Cnesterodon decemmaculatus (Pisces, Poeciliidae)

Acute genotoxicity of commercial glyphosate (GLY) (Credit®)-, 2,4-D-acid (2,4-D) (Dedalo Elite)-, 2,4-D-amine (2,4-D DMA) (Weedar Full®)- and 2,4-D-ester (2,4-D BE) (Herbifen Super®)-based herbicide formulations alone and their combinations were analysed in Cnesterodon decemmaculatus. Mortality was evaluated as a lethal end-point and the single cell gel electrophoresis (SCGE) bioassay was used as a sublethal end-point. LC5096h values for Dedalo Elite was 0.46 mg/L and Herbifen Super® was 2.67 mg/L based on 2,4-D and 2,4-D BE, respectively. Results reveal a higher toxicity exerted on C. decemmaculatus after exposure to 2,4-D- rather than 2,4-D BE-based herbicide formulations. Overall, results demonstrated an enhancement in the genetic damage index committed to an enhancement of damaged erythrocytes of C. decemmaculatus when exposed to Credit®, Dedalo Elite, Weedar Full® and Herbifen Super® at 5% and 10% of LC5096h values alone as well as in their combinations. Overall, the combination of GLY plus 2,4-D or GLY plus 2,4-D DMA showed a synergistic pattern whereas the combination of GLY plus 2,4-D BE was antagonic. Furthermore, this research is pioneer in the assessment of lethality and genotoxicity induced by 2,4-D-, 2,4-D DMA- and 2,4-D BE-based formulations when combined with GLY-based formulated herbicides in fish after they are acutely exposed.

Single and joint effects of chronic exposure to chlorpyrifos and glyphosate based pesticides on structural biomarkers in Cnesterodon decemmaculatus

Worldwide freshwater bodies that cross agricultural or urban areas are exposed to mixtures of xenobiotics. In particular, pesticides are usually part of these mixtures and could come into direct or indirect contact with biota and therefore, organisms have to cope with this altered scenario and the detrimental effects of these substances. Commercial formulations of chlorpyrifos and glyphosate, and their mixtures were evaluated using a set of biomarkers in the native fish C. decemmaculatus exposed to relevant environmentally pesticides concentrations. The biomarkers measured were: histopathological indices and tissue ultrastructure in liver and nuclear abnormalities and micronuclei in erythrocytes. During 42 days adult females were exposed to the following concentrations of Clorfox and Roundup Max (chlorpyrifos and glyphosate, respectively): 0.84 nl/l and 8.4 nl/l of Clorfox (CF), 0.2 and 2 mg/l of Roundup Max (RM) and all the combinations of these concentrations. Being the low concentrations of both pesticides environmentally relevant. Nuclear abnormalities of erythrocytes were registered under CF, RM and only one mixture. Histological inflammatory alterations increased in individuals exposed to CF and two mixtures. Finally, some pesticide combinations increased the circulatory alterations in liver. Ultrastructural changes in hepatocytes were registered at all the pesticide treatments. The different biomarker responses showed in the mixtures treatments reflected complex interactions, showing the mixture of the low concentrations of both pesticides (the environmentally relevant), potentiated effects. According to our results the presence of these substances in freshwaters could impose important risks for natural populations by causing deleterious effects on the native fish species C. decemmaculatus.

Genotoxicity induced by widely used pesticide binary mixtures on Caiman latirostris (broad-snouted caiman)

In this study, we investigated the effects of three binary mixtures of pesticide formulations commonly used in soybean crop: Cypermethrin Atanor® (25% -CYP), Chlorpyrifos Lorsban 48E® (48% -CPF) and Glyphosate Roundup® Full II (66.2% -GLY) on broad-snouted caiman (Caiman latirostris) hatchlings exposed by voluntary immersion under controlled condition. Genotoxicity was evaluated in peripheral blood erythrocytes through the micronucleus (MN) test and other nuclear abnormalities (NAs) and besides, growth of caiman was analyzed in each experimental group. The results showed that pesticide formulations tested, at concentrations similar to those recommended for application in the field, induced an increase in the frequency of micronucleus (FMN; p = 0.001) and Notched nuclei (NN; p = 0.010) in the mixture CYP + CPF, while an increase in the frequency of buds and NN was observed in the mixture of GLY + CYP (pbuds = 0.016 and pNN = 0.021), compared to the vehicle control (VC). On the contrary, a possible antagonistic action was observed between the components in the mixture GLY + CPF. Growth was not affected in any exposed groups (p > 0.05). There was a clutch effect in the frequency of binucleated erythrocytes (BiN; p = 0.011), total length (TL; p = 0.001) and snout-vent length (SVL; p = 0.031). Biomarkers used in this study are considered important predictive tools for the evaluation of xenobiotics. In this study, we demonstrated genotoxicity of pesticide mixtures under conditions that simulate the real situation of exposure suffered by caiman and other wild species in Argentina.

2,4-Dichlorophenoxyacetic acid containing herbicide impairs essential visually guided behaviors of larval fish

Aquatic herbicides are used worldwide to eradicate nuisance and invasive plants despite limited knowledge of their toxicity to non-target organisms. 2,4-Dichlorophenoxyacetic acid (2,4-D) is a common active ingredient in commercial herbicide formulations, which triggers plant cell death by mimicking the plant-specific hormone auxin. Application practices of 2,4-D commercial herbicides typically coincide with yearly freshwater fish spawning periods. This practice exposes fish to xenobiotics at their vulnerable larval stages. The full impacts of 2,4-D on larval fish remains poorly understood, and hence, whether it may alter larval survival, larval behavior, fish populations, and ecosystem dynamics. In the present study, we exposed embryonic and larval zebrafish (Danio rerio) to the active ingredient 2,4-D (pure 2,4-D) or a 2,4-D containing commercial herbicide DMA4^®IVM (DMA4) and evaluated morphology, survival, behavior, and nervous system function. At 2,4-D concentrations producing no overt morphological defects during embryonic or early larval stages, we observed reduced survival throughout a 21-day larval assay (4-8 ppm DMA4 and 0.75-4 ppm pure 2,4-D). Notably, prey capture, a behavior essential to survival, was reduced in 2,4-D-exposed larval zebrafish (4-8 ppm DMA4 and 0.75-4 ppm pure 2,4-D) and yellow perch (Perca flavescens) (4-20 ppm DMA4). In zebrafish, 8 ppm DMA4 exposure reduced prey capture when exposure was restricted to the period of visual system development. Consistent with these results, larval zebrafish exposed to 8 ppm DMA4 showed reduced neural activity within the optic tectum following prey exposure. Together, our results suggest that 2,4-D alters the development and function of neural circuits underlying vision of larval fish, and thereby reduces visually guided behaviors required for survival.

DNA damage exerted by mixtures of commercial formulations of glyphosate and imazethapyr herbicides in Rhinella arenarum (Anura, Bufonidae) tadpoles

Glyphosate (GLY) and imazethapyr (IMZT) are two herbicides commonly used worldwide, either alone or in mixtures. They represent key pesticides in modern agricultural management. The toxicity that results when employed as mixtures has not been characterized so far. Acute toxicity of the 48% GLY-based herbicide (GBH) Credit® and the 10.59% IMZT-based herbicide (IBH) Pivot® H alone and their binary combinations was analyzed in Rhinella arenarum tadpoles exposed in a semi-static renewal test. Lethal effects were determined using mortality as the end-point, whereas sublethal effects were determined employing the single-cell gel electrophoresis (SCGE) bioassay. Based on mortality experiments, results revealed LC5096 h values of 78.18 mg/L GBH and 0.99 mg/L IBH for Credit® and Pivot® H, respectively. An increase in the genetic damage index (GDI) was found after exposure to Credit® or Pivot® H at 5 and 10% of LC5096 h values. The combinations of 5% Credit®-5% Pivot® H LC5096 h and 10% Credit®-10% Pivot® H LC5096 h concentrations significantly enhanced the GDI in comparison with tadpoles exposed only to Credit® or Pivot® H. Thus, the effect of interaction between GBH and IBH inducing DNA damage in R. arenarum blood cells can be considered to be synergistic.