Effects of acute toxicity of the pesticide Chlorpyrifos and the metal Cadmium, both individually and in mixtures, on two species of native neotropical cladocerans.

The excessive use of pesticides in agriculture and the widespread use of metals in industrial activities and or technological applications has significantly increased the concentrations of these pollutants in both aquatic and terrestrial ecosystems worldwide, making aquatic biota increasingly vulnerable and putting many species at risk of extinction. Most aquatic habitats receive pollutants from various anthropogenic actions, leading to interactions between compounds that make them even more toxic. The aim of this study was to assess the effects of the compounds Chlorpyrifos (insecticide) and Cadmium (metal), both individually and in mixtures, on the cladocerans Ceriodaphnia rigaudi and Ceriodaphnia silvestrii. Acute toxicity tests were conducted for the compounds individually and in mixture, and an ecological risk assessment (ERA) was performed for both compounds. Acute toxicity tests with Cadmium resulted in EC50-48 h of 0.020 mg L-1 for C. rigaudi and 0.026 mg L-1 for C. silvestrii, while tests with Chlorpyrifos resulted in EC50-48 h of 0.047 µg L-1 and 0.062 µg L-1, respectively. The mixture test for C. rigaudi showed the occurrence of additive effects, while for C. silvestrii, antagonistic effects occurred depending on the dose level. The species sensitivity distribution curve for crustaceans, rotifers, amphibians, and fishes resulted in an HC5 of 3.13 and an HC50 of 124.7 mg L-1 for Cadmium; an HC5 of 9.96 and an HC50 of 5.71 µg L-1 for Chlorpyrifos. Regarding the ERA values, Cadmium represented a high risk, while Chlorpyrifos represented an insignificant to a high risk.

Ecological Implications on Aquatic Food Webs Due to Effects of Pesticides on Invertebrate Predators in a Neotropical Region.

Predation presents specific behavioral characteristics for each species, and the interaction between prey and predator influences the structuring of the food web. Concerning insects, predation can be affected in different ways, such as exposure to chemical stressors, e.g., pesticides. Therefore, analyses were carried out of the effects of exposure to insecticide fipronil and the herbicide 2,4-D on predation, parameters of food selectivity, and the swimming behavior of two neotropical predatory aquatic insects of the families Belostomatidae (giant water bugs) and larvae of Libellulidae (dragonfly). These predatory insects were exposed for 24 h to a commercial formulation of the chlorophenoxy herbicide, 2,4-D at nominal concentrations of 200, 300, 700, and 1400 µg L-1, and to a commercial formulation of the phenylpyrazole insecticide, fipronil at nominal concentrations of 10, 70, 140, and 250 µg L-1. In a control treatment, the insects were placed in clean, unspiked water. At the end of the exposure, the maximum swimming speed of the predators was evaluated. Afterward, the predators were placed in clean water in a shared environment for 24 h with several prey species, including the cladoceran Ceriodaphnia silvestrii, larvae of the insect Chironomus sancticaroli, the amphipod Hyalella meinerti, the ostracod Strandesia trispinosa, and the oligochaete Allonais inaequalis for 24 h. After this period, the consumed prey was counted. The results reveal that predators from both families changed prey consumption compared with organisms from the control treatment, marked by a decrease after exposure to fipronil and an increase in consumption caused by 2,4-D. In addition, there were changes in the food preferences of both predators, especially when exposed to the insecticide. Exposure to fipronil decreased the swimming speed of Belostomatidae individuals, possibly due to its neurotoxic effect. Exposure to the insecticide and the herbicide altered prey intake by predators, which could negatively influence the complex prey-predator relationship and the functioning of aquatic ecosystems in contaminated areas.

Fate and toxicity of 2,4-D and fipronil in mesocosm systems.

2,4-D and fipronil are among Brazil's most used pesticides. The presence of these substances in surface waters is a concern for the aquatic ecosystem health. Thus, understanding the behavior of these substances under environmentally relevant conditions is essential for an effective risk assessment. This study aimed to determine the degradation profiles of 2,4-D and fipronil after controlled application in aquatic mesocosm systems under influencing factors such as environmental aspects and vinasse application, evaluate pesticide dissipation at the water-sediment interface, and perform an environmental risk assessment in water and sediment compartments. Mesocosm systems were divided into six different treatments, namely: control (C), vinasse application (V), 2,4-D application (D), fipronil application (F), mixture of 2,4-D and fipronil application (M), and mixture of 2,4-D and fipronil with vinasse application (MV). Pesticide application was performed according to typical Brazilian sugarcane management procedures, and the experimental systems were monitored for 150 days. Pesticide dissipation kinetics was modeled using first-order reaction models. The estimated half-life times of 2,4-D were 18.2 days for individual application, 50.2 days for combined application, and 9.6 days for combined application with vinasse. For fipronil, the respective half-life times were 11.7, 13.8, and 24.5 days. The dynamics of pesticides in surface waters resulted in the deposition of these compounds in the sediment. Also, fipronil transformation products fipronil-sulfide and fipronil-sulfone were quantified in water 21 days after pesticide application. Finally, performed risk assessments showed significant potential risk to environmental health, with RQ values for 2,4-D up to 1359 in freshwater and 98 in sediment, and RQ values for fipronil up to 22,078 in freshwater and 2582 in sediment.

Ethylparaben Toxicity on Cladocerans Daphnia Similis and Ceriodaphnia Silvestrii and Species Sensitivity Analysis.

Parabens, a group of preservatives with a wide industrial range, threaten human and aquatic biota health due to their toxicity and endocrine disruption potential. As conventional wastewater treatment may not be enough to keep natural environments safe, toxicity studies are useful tools for supporting ecological risk assessments. Here, we focused on assessing ethylparaben's, one of the most common kinds of paraben, toxicity in the cladocerans Daphnia similis and Ceriodaphnia silvestrii. The EC50 sensitivity for D. similis and C. silvestrii was 24 (21-28) mg L- 1 and 25 (19-33) mg L- 1, respectively. Inhibition of reproduction and late development of females were observed in C. silvestrii exposed to 8 mg L- 1. Furthermore, species sensitivity distribution was used to assess ecological risk, and ethylparaben demonstrated low potential risk for aquatic biota.

Ecological risk assessment for metals in sediment and waters from the Brazilian Amazon region.

Pollution by metals is a matter of concern around the world. In recent decades, the high population growth in urban centers has significantly magnified the entry of these pollutants into aquatic ecosystems. The Amazon region, intense migratory flow, gold mining, and industrialization have been considered the main driving forces for increasing metal pollution. Thus, the main aim of this study is to conduct, for the first time, an Ecological Risk Assessment (ERA) based on metal concentrations measured in the sediment and water of several aquatic environments from the Amazon basin, based on the risk quotient values (RQ = measured environmental concentration - MEC/predicted no effect concentration - PNEC). In addition, the metal contamination factor (CF) was estimated. Although metal concentrations in water were generally low, these values were far above the limits established by current national legislation in many areas, showing higher concentrations for the metals Co, Pb, Cr, Cu, and Ni. Concentrations of Mn, Cu, Ba, Pb, Co, Ni, Cr, Zn, Cd, and As were especially high in the sediment for several evaluated environments. The ERA for the water compartment revealed that 56% of the studied areas presented high risk (RQ > 1) for aquatic biota. In the sediment, 66% of the sites presented a high risk and 40% medium risk (RQ = 0.1-1). The CF indicated that 49% of the sampling points had high contamination and only 24%, had low contamination. These results reveal that monitoring studies in the Amazon region, provides important information so that public policies for the preservation of water resources can be strengthened in the Amazon.

Environmental Risk Assessment of Drugs in Tropical Freshwaters Using Ceriodaphnia silvestrii as Test Organism.

In this study we evaluated the acute (immobility/mortality) and chronic (survival and reproduction) effects of the drugs caffeine, diclofenac sodium salt, ketoprofen, paracetamol and salicylic acid on the cladoceran Ceriodaphnia silvestrii. The environmental risks of these substances for tropical freshwaters were estimated from the risk quotient MEC/PNEC. Sensitivity in acute exposures varied up on the drug as follows: salicylic acid (EC50 = 69.15 mg L- 1) < caffeine (EC50 = 45.94 mg L- 1) < paracetamol (EC50 = 34.49 mg L- 1) < ketoprofen (EC50 = 24.84 mg L- 1) < diclofenac sodium salt (EC50 = 14.59 mg L- 1). Chronic toxicity data showed negative effects of the drugs on reproduction. Paracetamol and salicylic acid caused reduction in fecundity in concentrations starting from 10 mg L- 1 and 35 mg L- 1, respectively. Ketoprofen caused total inhibition at 5 mg L- 1. MEC/PNEC values were relatively low for all drugs. The risk was estimated as low or insignificant, except for caffeine, whose MEC/PNEC value was greater than 1 (moderate risk).

Toxicity of Binary Metal Mixtures to the Tropical Ostracod Strandesia Trispinosa.

The ecotoxicity of metals is generally assessed individually, in part because current knowledge does not allow for the accurate prediction of the toxicity of metal mixtures to aquatic organisms. The objective of this study was to investigate the toxic effects of binary combinations of metal salts (copper sulphate-CuSO4, cadmium chloride-CdCl2, mercury chloride-HgCl2 and manganese sulphate-MnSO4) on the tropical ostracod Strandesia trispinosa through acute toxicity tests. To this end, ostracods were exposed to each individual metal salt as well as to their combinations by applying a full factorial design. The model that best explained the effects of the mixtures CuSO4 x CdCl2, CuSO4 x HgCl2 and CuSO4 x MnSO4 on the survival of S. trispinosa was Concentration Addition, whereas this was Independent Action for the CdCl2 x HgCl2 mixture. The observed synergistic interactions are likely to result in unacceptable risks to aquatic ecosystems under real field conditions. This is especially the case if CuSO4 predominates the metal mixture, as observed for its combination with mercury and manganese.

Irrigation with Water Contaminated by Sugarcane Pesticides and Vinasse Can Inhibit Seed Germination and Crops Initial Growth.

Sugarcane crops are dependent on chemicals for maintaining plantations. Therefore, environmental consequences concern adjacent areas that can be affected by contaminants in common use, including pesticides and vinasse (i.e., a by-product from the ethanol industry). This study aimed to evaluate phytotoxicity through two plant bioassays with water from mesocosms contaminated with the herbicide 2,4-D (447.0 µg L-1), the insecticide fipronil (63.5 µg L-1), and sugarcane vinasse (1.3%). First, the germination test (4 d) with Eruca sativa L. assessed water samples collected three times after the contamination (2 h, 14 d, and 30 d), considering germination, shoot, and root growth. The results from this bioassay indicated higher phytotoxicity for 2,4-D as it fully inhibited the shoot and root growth even in low concentrations (0.2 µg L-1). However, no significant effect was reported for fipronil and vinasse. Also, the 2,4-D effects drastically decreased due to an expressive concentration reduction (99.4% after 30 d in mixture with vinasse). Second, the irrigation test with Phaseolus vulgaris L. and Zea mays L. considered shoot and root growth and biomass under 21 days after plants emergence. The herbicide 2,4-D inhibited the initial growth of tested species, especially the roots (up to 45% inhibition). Furthermore, sugarcane vinasse caused harmful effects on plant growth (up to 31% inhibition). Therefore, our data showed that these contaminants could inhibit plant germination and initial growth under our tested conditions. These evaluations can endorse risk assessments and water management in sugarcane crops surrounding areas.

Toxicity and Risk Assessment of Zinc and Aluminum Mixtures to Ceriodaphnia silvestrii (Crustacea: Cladocera).

Despite the co-occurrence of metals in aquatic environments, their joint effects are generally not considered during risk assessments. Data on the combined effects of zinc (Zn) and aluminum (Al) on aquatic animals are extremely scarce in the literature, although these metals are commonly used in domestic and industrial activities. In the present study, we investigated the effects of mixtures of Zn and Al on the cladoceran Ceriodaphnia silvestrii. We evaluated immobility (at 48 h) and ingestion rates (at 24 h). We also performed chronic toxicity tests for single metals. The environmental risks of these substances for tropical freshwaters were estimated from the risk quotient (measured environmental concentration/predicted no-effect concentration). In immobility tests, our results showed a 48-h median effect concentration (EC50) of 0.22 mg Zn L-1 and 0.52 mg Al L-1 , and we observed synergistic effects of Zn and Al, following the independent action model. The ingestion rates of C. silvestrii were inhibited at 0.1, 0.4, and 0.5 mg Al L-1 , and they were increased at 0.08 mg Zn L-1 ; we observed antagonistic effects in all treatments combined with 0.5 mg Al L-1 . In terms of chronic toxicity, a 7-d EC50 occurred at 0.11 mg Zn L-1 and 0.37 mg Al L-1 . The risk assessment suggests a potential risk of these metals at environmentally relevant concentrations, especially when in a mixture. Therefore, we recommend mixture toxicity tests during risk assessments to ensure that zooplankton are protected. Environ Toxicol Chem 2021;40:2912-2922. © 2021 SETAC.

Acartia tonsa Dana 1849 as a Model Organism: Considerations on Acclimation in Ecotoxicological Assays.

The copepod Acartia tonsa was standardized as model organism in acute toxicity bioassays due to its key position in coastal food chains and high sensitivity. Once bioassays are performed according to a protocol their results may become tools for the protection of aquatic ecosystems. However, there are divergences in bioassays methods using A. tonsa. This study aimed to investigate: (i) the need for acclimation of A. tonsa collected from the environment for use in acute toxicological bioassays; and (ii) differences in sensitivity between copepods collected from the environment and laboratory-grown copepods. Laboratory-grown copepods are more sensitive to SDS than A. tonsa from the environment. The acclimation time of 30 h helped organisms to recover from stress of collection/handling and changing environment/conditions. Therefore, laboratory-grown copepods showed to be more sensitive than organisms from environment; and for ecotoxicological bioassays acclimating A. tonsa collected from the environment for 30 h can be adopted.

Toxicity of fipronil and 2,4-D formulations (alone and in a mixture) to the tropical amphipod Hyalella meinerti.

Conventional farming uses a large volume of pesticides that may reach aquatic ecosystems. This is also the case for the insecticide fipronil and the herbicide 2,4-D, which are widely used in many crops. This study aimed at evaluating the individual and mixture toxicity of these pesticides to the tropical amphipod Hyalella meinerti. To this end, acute toxicity tests (96 h) were conducted. Chronic bioassays (10 days) were also carried out, in which the body length and dry biomass were evaluated as endpoints. In addition, a complete factorial mixture chronic toxicity test was carried out. H. meinerti was sensitive to fipronil in the acute toxicity tests, with a LC50-96-h of 0.86 µg L-1 (95% CI 0.26-0.46), and no acute effects were observed after 2,4-D exposure even at the highest test concentration of 100 mg L-1. In the chronic toxicity tests, all tested concentrations of both pesticides decreased the growth of H. meinerti, in which losses on biomass reached 45% and 65% for 2,4-D and fipronil, respectively. The pesticide mixture indicated antagonism although it still significantly decreased the body growth. The results obtained indicate a high sensitivity of H. meinerti exposed to environmentally realistic concentrations, demonstrating that there are risks for the species in real field conditions.

Impact of 2,4-D and fipronil on the tropical midge Chironomus sancticaroli (Diptera: Chironomidae).

Increased use of pesticides in conventional agriculture implies potential risks to the environment. In aquatic ecosystems, benthic organisms may be exposed to pesticides via contaminated water and sediment, leading to several potential cascading effects on the food web. The aim of this study was to assess the functional implications of environmental realistic concentrations of the herbicide 2,4-D and the insecticide fipronil (alone and in combination) to the native tropical chironomid Chironomus sancticaroli. These two pesticides are widely applied to different crops and have frequently been detected (together) in surface water bodies in Brazil and elsewhere. Commercial products containing fipronil (Regent® 800WG) and 2,4-D (DMA® 806BR) were evaluated in 8-day toxicity tests for their effects on larval survival, growth (body length and biomass), head capsule width, development, and mentum deformities. Fipronil decreased the larval survival at the highest test concentration and the effective concentrations (EC) after eight days of exposure were: EC10 = 0.48 µg L-1 (0.395-0.565), EC20 = 1.06 µg L-1 (0.607-1.513), and EC50 = 3.70 µg L-1 (1.664-5.736). All sublethal test concentrations of fipronil decreased the larval growth, causing reductions in biomass up to 72%. The two highest test concentrations of fipronil decreased the head capsule width and after exposure to 3.7 µg fipronil L-1, only half of the larvae reached the fourth instar. The incidence of deformities was increased by fipronil in a concentration dependent manner with an increase ranging from 23% to 75%. The highest test concentration of 2.4-D (426 µg L-1) decreased the head capsule width, but larval development was unaffected at all concentrations evaluated. In the mixture tests, antagonism was observed at lower fipronil concentrations and synergism at higher fipronil concentrations for growth. The incidence of deformities rose with increasing fipronil concentrations. The results showed that environmental realistic concentrations of fipronil may have serious ecological implications for C. sancticaroli populations and that a mixture with the herbicide 2,4-D can have synergistic effects, potentiating the risks to the aquatic ecosystem.

Functional responses of Hyalella meinerti after exposure to environmentally realistic concentrations of 2,4-D, fipronil, and vinasse (individually and in mixture).

Sugarcane crops management in Brazil includes the use of pesticides, as well as alternative organic fertilizers such as vinasse obtained from waste of the ethanol industry. In order to assess the effects of the environmental contamination generated by such sugarcane practices, this study was aimed to investigate the effects of the pesticides 2,4-Dichlorophenoxyacetic acid (2,4-D) and fipronil, as well as vinasse, on the survival, behavior, and reproduction of the native epibenthic macroinvertebrate Hyalella meinerti through in situ and laboratory experiments. In situ assays were conducted in mesocosms with six treatments, i.e. untreated control, 2,4-D, fipronil, and vinasse, the mixture of the two pesticides, and both pesticides mixed with vinasse. Survival, swimming behavior, and reproduction were evaluated over time post contamination, from 0-96 h (T1) and 7-14 days (T2) through in situ experiments and 30-44 days (T3) and 75-89 days (T4) post contamination by laboratory bioassays with mesocosm water. In the T1 period, survival of H. meinerti was registered only in controls and mesocosms treated with 2,4-D. In the T2 period, treatments containing fipronil and vinasse (isolated or in both mixture treatments) still caused 100 % of mortality. Survival was recorded only in 2,4-D and control treatments, whereas reproduction only occurred in the control. In the T3 period, no survival occurred to fipronil and both mixture treatments. Vinasse and 2,4-D decreased total reproduction in comparison to control. In the T4 period, amphipods survival was detected when exposed to fipronil and its mixture with 2,4-D. However, these same treatments decreased the amplexus rates and total reproduction, with synergism denoted for the pesticide mixture. The swimming activity of males, females, and couples was decreased in surviving organisms exposed to 2,4-D, fipronil, vinasse, and the mixture of pesticides along all experimental periods. Our study showed that the application of fipronil, 2,4-D, and vinasse isolated or mixed at realistic concentrations of actual sugarcane management practices may negatively impact functional responses of indigenous amphipods in natural aquatic systems.

Fipronil and 2,4-D effects on tropical fish: Could avoidance response be explained by changes in swimming behavior and neurotransmission impairments?

Brazil is the largest producer of sugarcane, a crop largely dependent on chemical control for its maintenance. The insecticide fipronil and herbicide 2,4-D stand out among the most commonly used pesticides and, therefore, environmental consequences are a matter of concern. The present study aimed to investigate the toxicity mechanisms of Regent® 800 WG (a.i. fipronil) and DMA® 806 BR (a.i. 2,4-D) pesticides using forced and non-forced exposures through an integrative approach: firstly, to assess whether contamination by fipronil and 2,4-D can trigger the avoidance behavior of the fish Danio rerio (zebrafish) and Hyphessobrycon eques (serpae tetra or mato-grosso). Additionally, the effects on fish were analyzed considering the swimming behavior together with a biomarker of neurotoxicity, the activity of acetylcholinesterase (AChE). In avoidance tests with pesticide gradients, D. rerio avoided the highest concentrations of the two compounds and H. eques avoided only the highest concentration of 2,4-D. The swimming behavior (distance moved) was reduced and AChE was inhibited when D. rerio was exposed to fipronil. The 2,4-D affected the swimming (maximum speed) of H. eques, but AChE was not altered. Avoidance response seemed not to have been affected by possible effects of contaminants on swimming behavior and Ache activity. This study showed the importance of knowing the avoidance capacity, swimming behavior and neurotoxic effects of pesticides on fish in an integrated and realistic context of exposure in environments contaminated with pesticides and can be useful as ecologically relevant tools for ecological risk assessment.

Exposure to environmental concentrations of fipronil and 2,4-D mixtures causes physiological, morphological and biochemical changes in Raphidocelis subcapitata.

The occurrence of pesticides and their mixtures in the environment can alter the ecological relationships between aquatic food chains. Since fipronil and 2,4-dichlorophenoxyacetic acid (2,4-D) are commonly found together in Brazilian water bodies, the present study aimed to investigate through an integrative approach the toxicity mechanisms of environmentally relevant concentrations of pesticides Regent® 800 WG (active ingredient - a.i. fipronil), DMA® 806 BR (a.i. 2,4-D) isolated and in mixtures on the green alga Raphidocelis subcapitata using multiple parameters: physiological (growth rate and chlorophyll a fluorescence), morphological (cell complexity and size), biochemical (composition of lipid classes) and related to the photosynthetic activity (variable fluorescence, the maximum quantum yield of the photosystem II - PSII - and the efficiency of the oxygen evolving complex - OEC - of PSII). The results indicated that fipronil significantly inhibited algal population growth, increased the chlorophyll a content (observed by fluorescence), cell size and lipid class content of triacylglycerol (TAG), free fatty acid (FFA) and acetone mobile polar lipid (AMPL) and, on the other hand, decreased variable fluorescence of algae. The tested concentrations of 2,4-D increased the chlorophyll a fluorescence, the cell size and the lipid classes TAG and FFA. The pesticide mixtures have had more effects on algae than isolated compounds, causing alterations in all parameters analyzed, including photosynthetic activity (maximum quantum yield and efficiency of the oxygen evolving complex of the PSII), in which no alterations were observed for the toxicity of the single pesticides. The results suggest that these analyses are important to evaluate pesticide toxicity mechanisms in ecological risk assessments of tropical regions. Thus, here we demonstrate the importance of using multiple parameters in ecotoxicological studies to obtain a better understanding of the toxicity of these compounds for phytoplankton.

Life-History Traits Response to Effects of Fish Predation (Kairomones), Fipronil and 2,4-D on Neotropical Cladoceran Ceriodaphnia silvestrii.

Aquatic environments are constantly exposed to a cocktail of contaminants mainly due to human activities. As polluted ecosystems may simultaneously present other multiple natural stressors, the objective of the present study was to evaluate joint effect of stressors (natural and anthropogenic) on life history traits of the Neotropical cladoceran, Ceriodaphnia silvestrii. For this purpose, the effects of water conditioned with predator kairomones (fish) and environmental concentrations (sublethal) of two pesticides widely used in sugarcane monoculture in Brazil, the insecticide Regent® 800 WG (active ingredient-a.i. fipronil) and the herbicide DMA® 806 BR (a.i. 2,4-D) were evaluated using chronic toxicity testing, isolated and in mixture, for this cladoceran species. The environmental risks of pesticides for tropical freshwater biota were also estimated from the risk quotient MEC/PNEC. Among the characteristics of the life history of C. silvestrii evaluated after 8 days of exposure, compared with the mean value of control, the age of primiparous females was not affected by any evaluated treatment. However, species average survival decreased in the treatment of kairomones mixed with fipronil (FK) and in the treatment with a mixture of fipronil, 2,4-D, and kairomones (MFKD). The body length of maternal females was shorter than in the control after exposure in treatments with only kairomones (K) and FK. Fecundity of this cladoceran was reduced when exposed to FK and MFKD treatments, and the intrinsic rate of population increase significantly decreased for organisms exposed to treatment with fipronil (F) and to mixtures of fipronil and 2,4-D (MFD), MFDK, and FK. The results indicated that the combination of anthropogenic and natural stressors causes changes in C. silvestrii life history traits, which can contribute to the decline in populations, and our preliminary risk assessment results are a matter of concern regarding biota conservation.

Effects of abamectin-based and difenoconazole-based formulations and their mixtures in Daphnia magna: a multiple endpoint approach.

This study evaluated the toxicity of pesticide formulations Kraft® 36 EC (active ingredient-a.i. abamectin) and Score® 250 EC (a.i. difenoconazole), and their mixtures in Daphnia magna at different biological levels of organization. Survival, reproduction and biochemical markers (cholinesterase (ChE), catalase (CAT) and lipid peroxidation (LPO)) were some of the endpoints evaluated. Total proteins and lipids were also studied together with energy consumption (Ec). D. magna neonates were exposed for 96 h to Kraft (2, 4, and 6 ng a.i./L) and Score (12.5, 25, and 50 µg a.i./L) for the biochemical experiments, and for 15 days to abamectin (1-5 ng a.i./L) and to difenoconazole (3.12-50 µg a.i./L) to assess possible changes in reproduction. Exposures of organisms to both single compounds did not cause effects to antioxidant and detoxifying enzymes, except for LPO occurring at the highest concentration of difenoconazole tested. For ChE and CAT there was enzymatic induction in mixture treatments organisms, occurring at minor pesticides concentrations for CAT and at the two highest concentrations for ChE. There were no significant differences for total protein in D. magna but lipids showed an increase at the highest concentrations of pesticide mixture combinations. There was a significant increase of Ec in individuals of all treatments tested. In the chronic test, increased fecundity occurred for D. magna under difenoconazole exposures and mixtures. This study demonstrated that mixtures of these pesticides caused greater toxicity to D. magna than when tested individually, except for Ec. Therefore, effects of mixtures are very hard to predict only based on information from single compounds, which most possibly is the result of biological complexity and redundancy in response pathways, which need further experimentation to become better known.

Dynamics of (total and methyl) mercury in sediment, fish, and crocodiles in an Amazonian Lake and risk assessment of fish consumption to the local population.

Increasing concerns have been raised about the toxicity of mercury (Hg) to humans, especially for those that consume a great amount of fish. High Hg concentrations have previously been measured in Amazonian waterbodies, both resulting from natural and anthropogenic sources. However, few studies have been conducted so far in Amazonian lakes that are fished by local populations. In addition, few of those studies included methylmercury (MeHg), the most toxic and bioaccumulative Hg form, and evaluated the influence of physico-chemical conditions and season on Hg dynamics. In the present study, total Hg (THg) and MeHg concentrations were measured in bottom sediment as well as in two fish and two crocodile species of the Amazonian Cuniã Lake. Bottom sediment MeHg concentrations were higher in the dry season than in the wet season, which is related to differences in physico-chemical (pH and electrical conductivity) conditions. Diet appeared to be related with animal tissue MeHg concentrations, with the herbivorous fish having lower MeHg levels than the predatory fish and crocodiles. Based on the measured tissue concentrations and published data on local person weight and fish consumption, MeHg risk to Cuniã Lake populations was estimated. Although the MeHg fish tissue concentrations did not exceed national and international standards, a significant risk to the local population is anticipated due to their high fish consumption rates. Graphical abstract.

Sensitivity of tropical cladocerans to chlorpyrifos and other insecticides as compared to their temperate counterparts.

The use of temperate toxicity data in tropical risk assessments has often been disputed. Previous sensitivity comparisons between temperate and tropical species, however, have not shown a consistent sensitivity difference between climatically-distinct species. Such comparisons were often limited by a small tropical toxicity dataset. In addition, differences in the taxonomic compositions of the temperate and tropical species assemblages used to construct species sensitivity distributions curves also hampered direct comparisons (e.g. type and ration of crustaceans and insects). The aim of the present study was to compare the sensitivity of temperate and tropical cladocerans to insecticides. Acute laboratory toxicity tests were conducted with five Neotropical cladocerans exposed to a concentration series of the insecticide chlorpyrifos. Subsequently, their EC50 values were compared with those reported in the literature for non-tropical cladocerans. An additional literature toxicity data search for insecticides other than chlorpyrifos was also conducted for both temperate and tropical cladocerans to enable a comparison for a wider range of insecticides and taxa. The order of sensitivity of the native cladocerans to chlorpyrifos was Ceriodaphnia silvestrii (0.039 µg L-1) > Diaphanosoma birgei (0.211 µg L-1) = Daphnia laevis (0.216 µg L-1) > Moina micrura (0.463 µg L-1) = Macrothrix flabelligera (0.619 µg L-1). A regulatory acceptable concentration based on temperate cladoceran toxicity data of both chlorpyrifos and other insecticides also appeared to be sufficiently protective for tropical cladoceran species. Implications for the use of temperate toxicity data in tropical risk assessments and indications for tropical cladoceran test species selection are discussed.

Freshwater neotropical oligochaetes as native test species for the toxicity evaluation of cadmium, mercury and their mixtures.

The toxicity of metals, whether isolated or in mixtures, involves changes in biochemical processes as well as in cell membranes, which may lead to deleterious short- and long-term effects on the affected organisms. Among metals, cadmium and mercury stand out due to their abundance in nature, frequent use for industrial activities and biological accumulation, with high levels of residence in trophic chains. Benthic communities are particularly prone to metal pollution since metals usually accumulate in sediments. The aim of this study was to evaluate the acute toxicity of mercury and cadmium, single and in mixture, to two native species of epibenthic oligochaetes: Allonais inaequalis and Dero furcatus. In order to assess the potential of these species as bioindicators, we compared their sensitivity with those of other internationally used species by applying the species sensitivity distribution approach. The 96h-LC50 of cadmium chloride was 627 and 364 µg L-1 for A. inaequalis and D. furcatus, respectively, evidencing that the latter species is almost twice as sensitive to this metal than A. inaequalis. For mercury chloride, the 96h-LC50 was 129 µg L-1 for A. inaequalis and 92 µg L-1 for D. furcatus. The sensitivities of these oligochaetes were superior or similar to that of other frequently used oligochaete test species such as Tubifex tubifex and Lumbriculus variegatus. The metal mixtures had synergism in general (D. furcatus) or at high doses only (A. inaequalis), implying a potentiation of their toxic effects when both metals co-occur in the environment. By comparing the derived toxicity values with concentrations of cadmium and mercury measured in the field, it can be concluded that aquatic organisms are likely to be at risk when exposed to the environmental relevant concentrations of cadmium and mercury here tested, especially when they are both present.