Ecological consequences when organisms avoid a contaminated environment: A study evaluating the toxicity of fipronil.

The ability of aquatic organisms to sense the surrounding environment chemically and interpret these signals correctly is crucial to their survival and ecological niche. This study applied the Heterogenous Multi-Habitat Assay System - HeMHAS to evaluate the avoidance potential of Daphnia magna to detect fipronil-contaminated habitats in a connected landscape after a short (48 h), previous, forced exposure to an environmentally relevant concentration of the same insecticide. The swimming of daphnids was also analyzed by recording the total distance covered. D. magna preferred areas with less contamination, although the effect of fipronil on their swimming ability (a decrease) was observed for all the concentrations tested. The application of non-forced multi-compartment exposure methodologies is a recent trend and is ecologically relevant as it is based on how contamination can really produce changes in an organism's habitat selection. Finally, we consider the importance of more non-forced exposure approaches where Stress Ecology can be aggregated to improve systemic understanding of the risk that contaminants pose to aquatic ecosystems from a broader landscape perspective.

Exposure to fipronil, 2,4-D and vinasse influences macroinvertebrate assemblage structure: An experimental mesocosm approach.

Sugarcane is one of the main monocultures in Brazil and widely uses herbicide 2,4-D and fipronil insecticide. In addition, vinasse can be mentioned as it is widely used in this plantation. These compounds occurring simultaneously in the aquatic environment can potentiate the deleterious effects on organisms. Thus, this study aimed to evaluate the composition, abundance and ecological indices of the benthic macroinvertebrate community, as well as its ability to reestablish itself considering environmental contamination by the pesticides Regent® 800WG (active ingredient - a.i. fipronil) (F) and DMA® 806BR (a.i. 2,4-D) (D) and vinasse (V), alone and in mixtures: pesticides - M and the three contaminants - MV. The study was conducted using open-air mesocosms. The macroinvertebrate community was monitored by colonization structures, the physical-chemical parameters, metals and pesticides were determined and the effects of contaminants were evaluated over the exposure time in 1, 7, 14, 28, 75 to 150 days. A multiple regression was performed between the water parameters and significant relationships were found between parameters associated with vinasse contamination (pH, total nitrogen, turbidity, and dissolved oxygen) and concentration of fipronil and the ecological variables studied. Over time, changes were observed in the composition of the community. The dominance and richness increased in treatments V and MV. The family Chironomidae and subclass Oligochaeta were more sensitive to the treatment V and MV, while individuals from the families Phoridae, Ephydridae and Sciomyzidae were occasionally found (depending on the experimental time) in these treatments. The insects were sensitive to treatments F and M, disappearing in these mesocosms after contamination, reappearing only after 75 days. The results reveal that sugarcane management practices associated with the use of pesticides and vinasse as fertilizer pose risks to the macroinvertebrate community with consequences for the trophic chains, given its importance in freshwater ecosystems and adjacent terrestrial environments.

Toxicity of fipronil and 2,4-D pesticides in Daphnia similis: a multiple endpoint approach.

In Brazil, among the pesticides widely applied simultaneously in sugarcane monocultures are the Regent® 800 WG insecticide (active ingredient (a.i.) fipronil) and the DMA® 806 BR herbicide (a.i. 2,4-D). Thus, this study aimed to investigate, through different endpoints, the effects of the fipronil and 2,4-D pesticides, isolated and as mixtures, on the cladoceran Daphnia similis. To do this, acute toxicity tests were carried out with the compounds acting in isolation and in mixture, where the survival of the organisms was evaluated, and chronic toxicity tests with the isolated compounds, where reproduction and maternal and neonatal body length were evaluated. In this study, the physiological endpoints of D. similis were also analyzed, through the analysis of feeding rates (filtration and ingestion) in exposure and post-exposure scenarios, in order to verify the cladoceran food recovery capacity. In addition, D. similis data were compared with other species when exposed to the studied pesticides, using species sensitivity distribution curves. Acute toxicity tests of the fipronil and 2,4-D showed an average EC50-48 h of 66.68 µg a.i./L and 327.07 mg a.i./L, respectively. In both cases, D. similis showed lower sensitivity compared to other species. For the mixture test, the evaluation by the IA model (independent action) and deviation DR (dose ratio dependent) indicated the occurrence of mostly antagonistic effects. The chronic test with fipronil showed a decrease in the fecundity of the organism at a concentration of 16 µg a.i./L, a concentration already found in aquatic environments. For 2,4-D, no significant differences were observed for reproduction at the concentrations tested. Regarding the maternal body length, there were no significant changes when D. similis were exposed to both fipronil and 2,4-D, but these differences were observed in the body length of the neonates only for 2,4-D. There were no significant changes in the feeding rates of the organisms when exposed to both pesticides.

Short and long-term exposure to the pesticides fipronil and 2,4-D: Effects on behavior and life history of Daphnia magna.

The high levels of contamination in aquatic ecosystems caused by pesticides and the organisms' consequent continuous exposure to it has made them vulnerable to damage. However, mobile organisms can avoid this continued exposure to contaminants by moving to less disturbed habitats. Therefore, through the use of the Heterogenous Multi-Habitat Assay System (HeMHAS), our objective was to evaluate the ability of Daphnia magna to detect and avoid habitats contaminated by fipronil and 2,4-D, in a spatially connected landscape. Further, the role of contamination by these pesticides, isolated and in mixtures, concerning the colonization of habitats by daphnids was also evaluated. Given that not all organisms successfully escape contamination, the chronic toxicity of the same pesticides using different parameters for D. magna (maternal survival, fecundity and maternal body length) was also evaluated. When evaluating the avoidance response by D. magna exposed to pesticides, there was no preference for the less contaminated areas for both compounds. However, organisms did not move to contaminated zones in the colonization experiments, with no immigration of daphnids to the zones with intermediate and the highest levels of fipronil, nor to the highest concentration of 2,4-D. Finally, the colonization by daphnids was significantly prevented when exposed to a mixture of the pesticides, in which the areas with the highest combinations of pesticide concentrations were not colonized by D. magna. Regarding the long-term chronic effects, negative consequences were observed, particularly for maternal body length, fecundity and maternal survival, due to the exposure to fipronil. Considering that pesticides can limit the areas colonized by organisms by making them unattractive, the risk of local population extinction may be underestimated if only standard endpoints involving forced exposure are studied.

Toxic tests show the sensitivity of the Daphnia similis (Crustacea, Cladocera) and Pseudokirchneriella subcapitata (Chlorophyceae) to commercial pesticides.

Pesticides have reached aquatic ecosystems and have caused numerous impacts on organisms. The present study aimed to assess the sensitivity of Daphnia similis Straus 1820 and Pseudokirchneriella subcapitata (Korshikov) F.Hindák to three commercial pesticides with different active ingredients: Siptran 500SC® (atrazine), Dimilin® (diflubenzuron), and Aproach Prima® (picoxystrobin + cyproconazole). For this purpose, we performed acute toxicity tests on these organisms. The compound most toxic to D. similis was the insecticide Dimilin® (toxic up to 5 µg/L of the active ingredient), followed by the fungicide Aproach Prima® (48h-EC50: 47.33 µg of the active ingredients/L) and the herbicide Siptran 500SC® (48h-EC50: 534.69 mg of the active ingredient/L). In contrast, Siptran 500SC® was the most toxic compound (96h-IC50: 52.61 µg/L) to P. subcapitata, followed by Aproach Prima® (96h-IC50: 164.73 µg/L) and Dimilin® (non-toxic up to 1 g/L). The toxicity of the fungicide to algae and microcrustaceans demonstrates that compounds developed for certain organisms are able to affect others, indicating the relevance of conducting ecotoxicological tests on different organisms.

Avoidance responses by Danio rerio reveal interactive effects of warming, pesticides and their mixtures.

Temperature variations and thermal extremes events caused by climate change can have profound implications for the toxicity of pesticides in aquatic organisms. Using an innovative system (Heterogeneous Multi-Habitat Test System - HeMHAS) that allows the simulation of different scenarios within a spatially heterogeneous landscape, the effects on the habitat selection of Danio rerio fish caused by the pesticides fipronil and 2,4-D were studied as single compounds and in mixture and integrated with air temperature variation (20, 24 and 28 °C). As a result, D. rerio detected and avoided both pesticides at air temperatures of 20 and 24 °C; however, at 28 °C no significant difference was observed in habitat choice by fish. Additionally, when pesticides were mixed in a heterogeneously contaminated landscape, it was observed that D. rerio detected contamination and preferred the clean zone at 20 and 24 °C; however, at 28 °C the potential to escape from the most contaminated areas was impaired. Thus, contamination by both pesticides made the habitat selection behavior of fish at 20 and 24 °C more noticeable. In addition, the association between pesticides and temperature showed negative effects on the response of fish to detect and escape from contaminated environments, suggesting the influence of temperature in altering the ability of the organism to provide an efficient response to stress.

Influence of temperature on the toxicity of the elutriate from a pesticide contaminated soil to two cladoceran species.

Brazil has become one of the largest consumers of pesticides in the world. However, there are still few studies evaluating pesticide toxicity integrating local aquatic and terrestrial environments. In addition, there is growing concern about the influence of temperature conditions related with climate change on contaminants toxicity. The aim of the present study was to evaluate the elutriate toxicity of the insecticide Kraft® 36 EC (a.i. abamectin), the fungicide Score® 250 EC (a.i. difenoconazole) and their mixture to the cladocerans Ceriodaphnia silvestrii and Daphnia similis, using model ecosystems (mesocosms). To this end, mesocosms were filled with natural soil and subjected to the following treatments: Control (Milli-Q water), Kraft (10.8 g abamectin ha-1), Score (20 g difenoconazole ha-1), and Kraft + Score (10.8 g abamectin ha-1 + 20 g difenoconazole ha-1). The experiment lasted 18 days, and the applications were made on days 1, 8, and 15; the occurrence of rainfall was simulated on days 1, 8, and 15 after applications and only rainfall simulation on days 4, 11, and 18. The experiment was conducted under two different temperatures: 23 °C and 33 °C. At 23 °C, single Kraft treatment and in combination with Score showed high toxicity to both cladocerans. At 33 °C, elutriate of the Kraft® and mixture treatments were highly toxic to D. similis but not to C. silvestrii. The results indicate that while Kraft had higher toxicity than Score to both cladocerans, this toxicity was counteracted at 33 °C only for the exotic species, D. similis. The results portray the complexity of pesticide toxicity when considering realistic experimental settings including different organisms and temperature treatments.

Lethal and sublethal toxicity of pesticides and vinasse used in sugarcane cultivation to Ceriodaphnia silvestrii (Crustacea: Cladocera).

With the growing use of agrochemicals in Brazil, there is also a growing need for more realistic toxicity assessments that aid in understanding the potential risks of environmental-realistic agrochemical (mixture) exposures in the natural ecosystems. The aim of the present study was therefore to evaluate the lethal and sublethal effects of environmental realistic (single and mixture) concentrations of the pesticides DMA® 806 BR (active ingredient - a.i. 2,4-D) and Regent® 800 WG (a.i. fipronil) and sugarcane vinasse to the Neotropical cladoceran Ceriodaphnia silvestrii. This evaluation was carried out through lethal (survival), sublethal (reproduction and intrinsic rates of population increase - r) and post-exposure (feeding rate and also reproduction) tests conducted in situ and with water from mesocosms contaminated with the recommended doses of these compounds. The results showed high acute toxicity for treatments containing fipronil and vinasse when acting in isolation, with survival rates only returning to control values on the last sampling day (75 days post application). Reproduction of surviving cladocerans was reduced in all treatments until the end of the experiment and were potentiated effect in the mixture of the three test compounds. The intrinsic rates of population increase were reduced in all treatments except the single 2,4-D treatment. Post-exposure feeding rate and reproduction, however, were not impaired under the conditions analyzed. The results show the high toxicity of recommended doses of fipronil and vinasse (and especially their mixture) and the importance of evaluating the risks of agrochemical mixtures at environmental-realistic concentrations.

Bioaccumulation and chronic toxicity of arsenic and zinc in the aquatic oligochaetes Branchiura sowerbyi and Tubifex tubifex (Annelida, Clitellata).

Oligochaetes feed on bulk sediment and penetrate the sediment through the construction of burrows, making them especially vulnerable to sediment metal contamination. However, the few oligochaete species that have been tested to date are almost exclusively temperate test species. Although the warmwater adapted species Branchiura sowerbyi has been indicated as a promising candidate for tropical sediment toxicity testing, few (especially chronic) studies have been conducted so far to confirm this. Therefore, the aim of the present study was to evaluate the bioaccumulation and chronic 28d lethal and sublethal toxicity of arsenic (As) and zinc (Zn) to both the warmwater-adapted B. sowerbyi and the coldwater-adapted oligochaete Tubifex tubifex for comparison. Arsenic was more toxic to both oligochaete species than Zn. Inter- and intra-species variability in toxicity values of the two test species and other benthic invertebrates was within an order of magnitude. However, B. sowerbyi was the most sensitive species to As even for sediment concentration (EC50: 36.6 ± 2.1 µg/g and 147.1 ± 21.7 µg/g, for B. sowerbyi and T. tubifex, respectively) and for tissue concentration (ER50: 9.2 ± 0.9 µg/g and 887.0 ± 35.0 µg/g, for B. sowerbyi and T. tubifex, respectively). Finally, the Tissue Residue-effects Approach (TRA) using Effective Tissue Residues appears to be a promising way forward in advancing in this since it considers internal body concentrations.

Acute toxicity of the insecticide abamectin and the fungicide difenoconazole (individually and in mixture) to the tropical stingless bee Melipona scutellaris.

Stingless bees have been recognized as essential plant pollinators and producers of various natural products in neotropical areas. Research into the potential risks of pesticides they may be exposed to in agricultural fields, however, remains meagre. Especially the toxicity of pesticide mixtures likely to occur under real-world conditions and that are likely to exert synergetic effects has been poorly studied. The aim of the present study was therefore to evaluate the single and mixture acute contact and oral toxicity of commercial products containing the insecticide abamectin and the fungicide difenoconazole in laboratory bioassays with the Brazilian native stingless bee Melipona scutellaris. In addition, a comparison of the insecticide sensitivity of stingless bees relative to the honeybee Apis mellifera was made based on previously published toxicity data. Except for oral exposure to abamectin, M. scutellaris appeared to be more sensitive that A. mellifera in the single compound toxicity tests. A difenoconazole concentration at the NOEC (no observed effect concentration) level indicated a synergetic toxic interaction with abamectin. A sensitivity comparison based on published toxicity data for A. mellifera and stingless bees indicated several insecticidal modes of action having a high relative sensitivity to stingless bees that need especial consideration in future studies. The research findings highlight the need for testing native bee species and environmentally relevant pesticide mixtures in risk assessments to avoid underestimation of potential risks to bee populations and the subsequent loss of pollination ecosystem services.

Changes in soil mesofauna structure due to different land use systems in south Minas Gerais, Brazil.

Essential to the provision of important ecosystems services, i.e., food production, soil is suffering great pressure. The degradation of natural areas in order to turn them into croplands has been causing severe effects to the soil quality, including the maintenance of their biodiversity. Soil physical disruption reduce the soil biodiversity and, consequently, may cause negative effects to the supporting services, i.e., organic matter degradation and nutrient cycling, which will directly or indirectly impact agroecosystems. In this study, the influence of three different types of land uses (native forest (NF), conventional agriculture (CA), and organic agriculture (OA)) to the soil mesofauna (emphasizing collembolan and mites) were assessed under real scenarios in the southeast part of Brazil. Both conventional and organic fields were of strawberries, and the greatest difference in their processes was the use of synthetic fertilizers and pesticides, performed at CA. Soil fauna organisms were collected and identified to main groups, except the collembolan species which were further separated into four main groups/family. Results showed that not only the physical changes due to soil tillage caused negative effects to soil fauna. In the field where the use of agricultural products was allowed, organisms were much more severely affected. Hence, the conversion of natural forested areas to agricultural lands may harm soil fauna communities through biodiversity loss. This study not only adds significant information to the knowledge regarding the relation between biodiversity loss and agricultural practices worldwide, but it also helps to improve Brazilian knowledge of the edaphic fauna in agroecosystems.

Combination of P-limitation and cadmium in photosynthetic responses of the freshwater microalga Ankistrodesmus densus (Chlorophyceae).

In the environment, microalgae are exposed to a multitude of stressors simultaneously, inducing physiological adjustments. It is well documented that both phosphorus (P) limitation and trace metals exposure affect microalgal physiology. However, investigations regarding the combination of both P limitation and excess trace metals still deserve attention. In the present study, we evaluated the changes in photosynthetic parameters in the green microalga Ankistrodesmus densus acclimated to different P concentrations prior to exposure to Cd. Our results indicate that different concentrations of P in the medium were responsible for significant changes in some parameters, especially those related to photoprotection mechanisms. Cadmium also altered some of these variables in all P scenarios, and greater damage (i.e., synergism) was observed in the combination P-limited and high Cd, with all the evaluated parameters affected under the adverse scenario. Among the parameters analyzed, rapid light curves were the most sensitive to exposure of one or the combination of both stressors (Cd and P limitation). Based on our data, we suggest that P-limited algae activated photoprotective mechanisms as a response to nutrient limitation, especially at the most limited condition. The addition of Cd did not change linearly the parameters related to photoprotection mechanisms under P-limitation, i.e., synergism was observed in the intermediate P-limitation combined with Cd, while in the most P-limited, P seems to be the driving force affecting these mechanisms. Based on our results, we suggest the use of rapid light curves as a tool to complement the assessment of the impacts of stressors, such as metals, in ecotoxicological studies.

Integrated ecosystem models (soil-water) to analyze pesticide toxicity to aquatic organisms at two different temperature conditions.

In order to increase the knowledge about pesticides considering the soil-water interaction, ecosystem models (mesoscosms) were used to analyze the of leachate on the immobility and feeding rate of the cladocerans, Ceriodaphnia silvestrii and D. similis and algae Raphidocelis subcapitata, at two different temperatures. Mesocosm were filled with natural soil (latosolo) that were contaminated with insecticide/acaricide Kraft 36 EC® and fungicide Score 250 EC®, using the recommended concentration for strawberry crops (10.8 g abamectin/ha and 20 g difenoconazole/ha). Pesticides were applied once (hand sprayers) and the precipitation was simulated twice a week (Days 1, 4, 8, 11, 15 and 18). The mesocosm were kept in a room with a controlled temperature (23 and 33 °C) and photoperiod (12h light/12h dark). The Kraft 36 EC® insecticide showed toxicity for both species of cladocerans tested, with effects on immobility and feeding rate, both at 23 and 33 °C. Score 250 EC® showed to be toxic only for the experiments that analyzed the immobility of C. silvestrii at 23 °C and the feeding of D. smilis at 33 °C, demonstrating that the effects are species-specific and related to the temperature at which they are tested. While for species R. subcapitata there was an effect only for mixture treatments of the pesticides analyzed at both temperatures. Thereby, zooplanktonic organisms may be at risk when exposed to this compound even after percolating in a soil column, which could lead to effects on the entire aquatic trophic chain and that temperature can influence the organism response to the contaminant.

Not Only Toxic but Repellent: What Can Organisms' Responses Tell Us about Contamination and What Are the Ecological Consequences When They Flee from an Environment?

The ability of aquatic organisms to sense the surrounding environment chemically and interpret such signals correctly is crucial for their ecological niche and survival. Although it is an oversimplification of the ecological interactions, we could consider that a significant part of the decisions taken by organisms are, to some extent, chemically driven. Accordingly, chemical contamination might interfere in the way organisms behave and interact with the environment. Just as any environmental factor, contamination can make a habitat less attractive or even unsuitable to accommodate life, conditioning to some degree the decision of organisms to stay in, or move from, an ecosystem. If we consider that contamination is not always spatially homogeneous and that many organisms can avoid it, the ability of contaminants to repel organisms should also be of concern. Thus, in this critical review, we have discussed the dual role of contamination: toxicity (disruption of the physiological and behavioral homeostasis) vs. repellency (contamination-driven changes in spatial distribution/habitat selection). The discussion is centered on methodologies (forced exposure against non-forced multi-compartmented exposure systems) and conceptual improvements (individual stress due to the toxic effects caused by a continuous exposure against contamination-driven spatial distribution). Finally, we propose an approach in which Stress and Landscape Ecology could be integrated with each other to improve our understanding of the threat contaminants represent to aquatic ecosystems.

Effect of phosphorus on the toxicity of zinc to the microalga Raphidocelis subcapitata.

The aim of this study was to evaluate the effect of phosphorus (P) on the toxicity of zinc (Zn) for the alga Raphidocelis subcapitata. P was provided in three concentrations: 2.3 x 10-4 mol L-1, 2.3 x 10-6 mol L-1 and 1.0 x 10-6 mol L-1. Algal cells were acclimated to the specific P concentrations before the start of the experiment. The chemical equilibrium software MINEQL+ 4.61 was employed to calculate the Zn2+ concentration. After acclimated, the algal cells were inoculated into media containing different Zn concentrations (0.09 x 10-6 mol L-1 to 9.08 x 10-6 mol L-1). The study showed that besides the reduction in algal growth rates, phosphorus had an important influence on the toxicity of zinc for microalga. The inhibitory Zn2+ concentration values for R. subcapitata were 2.74 x 10-6 mol L-1, 0.58 x 10-6 mol L-1 and 0.24 x 10-6 mol L-1 for the microalgae acclimated at P concentrations of 2.3 x 10-4 mol L-1, 2.3 x 10-6 mol L-1 and 1.0 x 10-6 mol L-1, respectively. Ecotoxicological studies should consider the interaction between metal concentrations and varying P values to provide realistic data of what occurs in phytoplankton communities in environments.

Acute and chronic toxicity of 2,4-D and fipronil formulations (individually and in mixture) to the Neotropical cladoceran Ceriodaphnia silvestrii.

Brazil is the largest producer of sugarcane and the world's top pesticide market. Therefore, environmental consequences are of concern. The aim of the present study was to evaluate the acute and chronic toxicity of pesticide formulations largely used in sugarcane crops: the herbicide DMA® 806 BR (a.i. 2,4-D) and the insecticide Regent® 800 WG (a.i. fipronil), isolated and in mixture, to the Neotropical cladoceran Ceriodaphnia silvestrii. Toxicity tests with the individual formulated products indicated 48h-EC50 values of 169 ± 18 mg a.i./L for 2,4-D and 3.9 ± 0.50 µg a.i./L for fipronil. In the chronic tests, the 8d-EC50 values for reproduction were 55 mg a.i./L (NOEC/LOEC: 50/60 mg a.i./L) and 1.6 µg a.i./L (NOEC/LOEC: 0.40/0.80 µg a.i./L) for 2,4-D and fipronil, respectively. A significant decrease in reproduction of C. silvestrii in all concentrations tested of fipronil, except at the lowest, was observed. Regarding 2,4-D, the organisms had total inhibition of reproduction in the two highest concentrations. Probably your energy reallocation was focused (trade-off) only on its survival. The acute pesticide mixture toxicity (immobility) revealed a dose level dependent deviation with antagonism at low and synergism at high concentrations. For chronic mixture (reproduction) toxicity, antagonism occurred as a result of the interaction of the pesticides. Based on our results and concentrations measured in Brazilian water bodies, fipronil represents ecological risks for causing direct toxic effects on C. silvestrii. These results are worrisome given that agricultural production is likely to increase in the coming years.

Herbicides employed in sugarcane plantations have lethal and sublethal effects to larval Boana pardalis (Amphibia, Hylidae).

The increasing demand for biofuels favored the expansion of sugarcane and, as a consequence, in the consumption of pesticides in Brazil. Amphibians are subject to pesticide exposure for occurring in or around sugarcane fields, and for breeding at the onset of the rainy season when pesticide consumption is common. We tested the hypothesis that herbicides used in sugarcane crops, although employed for weed control and manipulated at doses recommended by the manufacturers, can cause lethal and sublethal effects on amphibian larvae. Boana pardalis was exposed to glyphosate, ametryn, 2,4-D, metribuzin and acetochlor which account to up to 2/3 of the volume of herbicides employed in sugarcane production. High mortality was observed following prolonged exposure to ametryn (76%), acetochlor (68%) and glyphosate (15%); ametryn in addition significantly reduced activity rates and slowed developmental and growth rates. AChE activity was surprisingly stimulated by glyphosate, ametryn and 2,4-D, and GST activity by ametryn and acetochlor. Some of these sublethal effects, including the decrease in activity, growth and developmental rates, may have important consequences for individual performance for extending the larval period, and hence the risk of dessication, in the temporary and semi-permanent ponds where the species develops. Future studies should seek additional realism towards a risk analysis of the environmental contamination by herbicides through experiments manipulating not only active ingredients but also commercial formulations, as well as interactions among contaminants and other environmental stressors across the entire life cycle of native amphibian species.

Impact of temperature on the toxicity of Kraft 36 EC® (a.s. abamectin) and Score 250 EC® (a.s. difenoconazole) to soil organisms under realistic environmental exposure scenarios.

Pesticides can affect all receiving compartments, especially soils, and their fate and effects may be enhanced by temperature, increasing their risk to ecological functions of soils. In Brazil, the most widely used pesticides are the insecticide Kraft 36 EC® (a.s. abamectin) and the fungicide Score 250 EC® (a.s. difenoconazole), which are commonly used in strawberry, often simultaneously as a mixture. The aim of this study was to evaluate the toxicity of realistic environmental applications, single and in mixtures, for both pesticides to the springtail Folsomia candida and the plant species Allium cepa (onion) and Lycopersicum esculentum (tomato). Mesocosms filled with Brazilian natural soil (lattosolo) were dosed with water (control), Kraft (10.8 g a.s/ha), Score (20 g.a.s/ha) and Kraft + Score (10.8 + 20 g a.s./ha). The applications were repeated every 7 days, during 18 days of experiment, and simulating rainfall twice a week. Collembola reproduction tests were conducted with soils from the first (day 1) and last day (day 18) of experiment for each treatment. Plant toxicity tests were carried out in the experimental units. The experiments were run at 23 °C and 33 °C. Kraft, alone and in the binary mixture, showed high toxicity to the springtails in soils from both days 1 and 18, especially at 23 °C where it caused 100% mortality. Score however, was not toxic to the springtails. Plant growth was reduced by Score, but responses varied depending on temperature. This study indicates a high environmental risk of the insecticide Kraft, particularly at lower temperatures (23 °C), and an influence of temperature on pesticide fate and effects.

Lethal toxicity of the herbicides acetochlor, ametryn, glyphosate and metribuzin to tropical frog larvae.

Despite the high amphibian biodiversity and increasing pesticide use in tropical countries, knowledge on the sensitivity of tropical amphibians to pesticides remains limited. The aim of this study was to evaluate the acute toxicity of the active ingredients of four of the main herbicides used in Brazilian sugarcane production to tadpoles of two tropical frog species: Physalaemus cuvieri and Hypsiboas pardalis. The calculated 96 h-LC50 (median lethal concentration; in mg a.s./L) values for P. cuvieri and H. pardalis were 4.4 and 7.8 (acetochlor); 15 and <10 (ametryn); 115 and 106 (glyphosate); and 85 and 68 (metribuzin), respectively. These toxicity values demonstrated little interspecies variation and the toxicity of the herbicides appeared to be at least partly related with the respective octanol-water coefficient. Published acute toxicity data of fish and amphibians for herbicides were also compiled from the US-EPA ECOTOX database. These data indicated little difference in herbicide sensitivity between tropical amphibians and both non-tropical amphibians and fish. These findings indicate that temperate (fish and amphibian) herbicide toxicity data are also protective for tropical amphibians. Constraints in such extrapolations and indications for future research are discussed.

The direct effects of a tropical natural humic substance to three aquatic species and its influence on their sensitivity to copper.

Few studies have been conducted so far into the effects of humic substances (HS) on aquatic organisms and their influence on the toxicity of chemical pollutants in the tropics. The aim of the present study was therefore to evaluate the direct effects of locally-derived tropical natural HS on the cladoceran Daphnia similis, the midge Chironomus xanthus and the fish Danio rerio. The influence of a HS concentration series on the acute toxicity of copper to these organisms was also assessed through laboratory toxicity testing. The HS did not exert direct acute effects on the test organisms, but long-term exposure to higher HS concentrations provoked a stress response (increase in feces production) to D. rerio and exerted effects on chironomid adult emergence and sex ratio. The biotic ligand model proved to be a useful tool in converting total copper concentrations to the appropriate bio-available fraction to which tropical aquatic organisms are exposed.