Acute toxicity tests with the tropical cladoceran Pseudosida ramosa: The importance of using native species as test organisms

Toxicant Responses and Culturing Characteristics of Long-Term Laboratory-Reared and Field Populations of Ceriodaphnia dubia

Ceriodaphnia dubia is a standardized test organism for regulatory toxicity testing of surface waters and commercial chemicals because of its simplicity to culture and responsiveness to toxicants. For testing convenience, C. dubia is often cultured for extended periods in the laboratory with little knowledge of the impact on subsequent generations. Extended laboratory rearing could impact how they respond to stressors and decrease the accuracy of test results. The present study investigated if C. dubia cultured for an extended period were representative of three recently collected field populations by comparing their culturing characteristics and sensitivities to toxicants. For culturing characteristics, the field cultures were more challenging because they had shorter body lengths, fewer neonates, and higher mortality rates than the laboratory culture. Comparative chronic toxicity tests with sodium chloride and the neonicotinoid insecticide thiamethoxam indicated that the laboratory and field organisms did not differ much in their toxicological responses but did differ in the variability of responses (percentage of coefficient of variation). The differences between the laboratory and field cultures found in the present study highlight the challenges of addressing discrepancies between laboratory and field applications in existing standardized methodologies. Environ Toxicol Chem 2024;43:159-169. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Proposing Effective Ecotoxicity Test Species for Chemical Safety Assessment in East Asia: A Review

East Asia leads the global chemical industry, but environmental chemical risk in these countries is an emerging concern. Despite this, only a few native species that are representative of East Asian environments are listed as test species in international guidelines compared with those native to Europe and America. This review suggests that Zacco platypus, Misgurnus anguillicaudatus, Hydrilla verticillata, Neocaridina denticulata spp., and Scenedesmus obliquus, all resident to East Asia, are promising test species for ecotoxicity tests. The utility of these five species in environmental risk assessment (ERA) varies depending on their individual traits and the state of ecotoxicity research, indicating a need for different applications of each species according to ERA objectives. Furthermore, the traits of these five species can complement each other when assessing chemical effects under diverse exposure scenarios, suggesting they can form a versatile battery for ERA. This review also analyzes recent trends in ecotoxicity studies and proposes emerging research issues, such as the application of alternative test methods, comparative studies using model species, the identification of specific markers for test species, and performance of toxicity tests under environmentally relevant conditions. The information provided on the utility of the five species and alternative issues in toxicity tests could assist in selecting test species suited to study objectives for more effective ERA.

Toxicity of benzyl paraben on aquatic as well as terrestrial life

Parabens are derivatives of alkyl esters of p-hydroxybenzoic acid and come in different classes. These compounds are primarily used as antimicrobial preservative agents in many commercial products, including cosmetics and pharmaceuticals. Accordingly, Benzyl paraben (BeP) is known to be a potential endocrine disruptor. The aim of this study was to determine the toxicity of benzyl paraben (BeP) on aquatic and terrestrial organisms, specifically Scenedesmus sp., Moina macrocopa, and Eisenia fetida. All the organisms were treated with different concentrations of BeP (0.025 mg/L and 1000 mg/L), and LC25, LC50, and LC90 values were used to measure the toxicity levels. Results showed the LC values of BeP for M. macrocopa (3.3 mg/L, 4.7 mg/L, 7.3 mg/L) and E. fetida (173.2 mg/L, 479.8 mg/L, 1062 mg/L), respectively. Toxicity tests on green algae (Scenedesmus sp.) were conducted, the green algae were subjected to various BeP concentration. At 50 mg/L of BeP, cell viability was reduced to 56.2% and the MTT (3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide) assay indicated 35.4% viable cells. The chlorophyll value and the biochemical parameters of the algal cells were corroborative with the cell viability test. Lethal indices (LC50) for M. macrocopa and E. fetida were evaluated for their toxicity on biochemical properties and were found to be catalase (0.111 mg/L, 0.5 mg/L), lipid peroxidation (0.072 mg/L, 0.056 mg/L), and total protein (0.309 mg/L, 0.314 mg/L), respectively. Overall, this study demonstrated the toxic impact of BeP on non-target aquatic as well as terrestrial species.

Multixenobiotic defence mechanism in native and exotic freshwater snails as a biomarker for land uses-changes

Human activities such as agriculture and urbanization generate a large number of substances like personal care products, pharmaceutical compounds, and pesticides, which often reach aquatic environments and represent a threat to biodiversity. Many organisms have developed different evolutionary strategies to remove pervasive substances from their bodies, allowing them to persist even in polluted environments, and one of these is the multixenobiotic resistance (MXR) mechanism associated with the expression of membrane proteins like P-glycoprotein (P-gp). Numerous chemical compounds with diverse functions and structures can modulate this mechanism, which can be employed as a pollution biomarker. We examined the MXR activity in two species of snails that inhabit Patagonian freshwaters. Functional assay measurements of MXR were conducted on the native Chilina dombeiana and the exotic Physella acuta in stream reaches affected by anthropogenic impacts. Results indicated that at agricultural sites, C. dombeiana snails had a more active MXR system than organisms sampled at reference and moderately disturbed urban sites, whereas P. acuta snails from agricultural and highly disturbed urban sites showed better detoxifying activity than organisms from reference sites. Only in exotic snails, part of this activity was due to the action of P-gp. The most important environmental variables explaining MXR activity were ammonium, nitrate and nitrite, phosphates, and electrical conductivity. These results show the promise of measuring MXR activity in native and exotic snails, as a biomarker in the environmental monitoring of Patagonian freshwaters.

Are standard aquatic test species and methods adequate surrogates for use in environmental risk assessment of pesticides in tropical environments?

In regulatory risk assessment, surrogate species of fish, aquatic invertebrates, and primary producers are tested to assess toxicity and subsequently the risk of pesticides to freshwater biota. This study evaluates whether the standard, surrogate test species (mostly temperate in latitudinal distribution) used in many parts of the world are suitable surrogates for first-tier risk assessments involving tropical freshwater biota. Data for the toxicity of pesticides to tropical fish, invertebrates, and primary producer species were extracted from the USEPA ECOTOX database and peer-reviewed literature. For each pesticide, the most sensitive regulatory endpoint extracted from the US Environmental Protection Agency (USEPA) and European Food Safety Authority (EFSA) dossiers for freshwater fish, invertebrates, and primary producers was selected. The ratios of the endpoint for tropical species and for the most sensitive regulatory endpoint for the appropriate taxonomic group were determined. A value >1 indicates that the tropical species is less sensitive than the respective standard regulatory species. Tropical fish species were less sensitive than standard fish species in 84% of the comparisons, and in 93.5% of the comparisons, tropical fish were less or similarly sensitive (within a factor of 5). For aquatic invertebrates, 78.1% of the evaluated tropical species were less sensitive than standard species and 93.3% of tropical invertebrates species were less or similarly sensitive. For primary producers, 96% of tropical species were less sensitive than standard test species. Overall, standard species used globally were more sensitive or similarly sensitive compared to tropical species in more than 93% of the cases. In conclusion, the data show that freshwater toxicity data for pesticides from tests using standard test species, tested according to international accepted guidelines, are appropriate for use in first-tier risk assessments for tropical environments. Integr Environ Assess Manag 2023;19:202-212. © 2022 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Identification of Microcrustaceans as Potential Bioindicators of Arsenic in Tropical Water Bodies

We investigated microcrustaceans inhabiting arsenic contaminated and non-contaminated freshwater to identify potential bioindicators of arsenic contamination in the tropical freshwater of Matehuala in northern Mexico. We collected water, sediment, and zooplankton, at five sampling points during three sampling campaigns. We determined water temperature, pH, electrical conductivity, dissolved oxygen, alkalinity, salinity, and total arsenic concentration in water. Additionally, we determined total arsenic and arsenic speciation in sediment samples. We identified microcrustaceans and determined abundance, richness, and Shannon Index. We also investigated relationships and correlations between physiochemical and ecological variables. Results showed that arsenic concentrations in freshwater ranged from 0.001 to 53.23 mg/L, while total arsenic in sediments ranged from 10.37 to 2472.84 mg/kg as As + 5. Six microcrustacean species were found in highly and moderately contaminated water (Latonopsis australis, Eucyclops chihuahuensis, Acanthocyclops americanus, Pleuroxus (Picripleuroxus) quasidenticulatus, Macrocyclops albidus, and Paracyclops chiltoni), while five species were found in arsenic-free water (Simocephalus punctatus, Alona glabra, Eucyclops leptacanthus, M. albidus, and P. quasidenticulatus). An inverse relationship was observed between microcrustacean richness and arsenic. However, the scope of the data did not allow for a strong and significant correlation. Nevertheless, among the species inhabiting As-free water, S. punctatus showed potential to be further tested as a bioindicator of As contamination in Matehuala. Identification of potential bioindicators could help monitor water quality and increase understanding of the incorporation and toxicity of As in freshwater-sensitive and freshwater-metallotolerant microcrustaceans, which, in turn, might help us to understand As incorporation in the food web.

High sensitivity of invertebrate detritivores from tropical streams to different pesticides

Freshwater organisms are often sensitive to pesticides, but their sensitivity varies across different taxa and with pesticide type and action mode, as shown by multiple acute toxicity tests. Such variability hampers predictions about how freshwater ecosystems may be altered by pesticide toxicity, which is especially critical for understudied areas of the world such as the tropics. Furthermore, there is little information about the sensitivity of some organisms that are key components of stream food webs; this is the case of litter-feeding detritivorous invertebrates, which contribute to the fundamental process of litter decomposition. Here, we examined the sensitivity of three common detritivores [Anchytarsus sp. (Coleoptera: Ptilodactylidae), Hyalella sp. (Amphipoda: Hyalellidae) and Lepidostoma sp. (Trichoptera: Lepidostomatidae)] to three pesticides commonly used (the insecticides bifenthrin and chlorpyrifos and the fungicide chlorothalonil) using acute (48 or 96 h) toxicity tests. Our study demonstrates that common-use pesticides provoke the mortality of half their populations at concentrations of 0.04-2.7 μg L-1. We found that all species were sensitive to the three pesticides, with the highest sensitivity found for chlorpyrifos. Additionally, we used the approach of species sensitivity distributions (SSD) to compare our study species with Daphnia magna and other temperate and tropical invertebrates. We found that the study species were among the most sensitive species to chlorpyrifos and chlorothalonil. Our results suggest that tropical detritivores merit special attention in ecological risk assessment of pesticides and highlight the need for accurate ecotoxicological information from ecologically relevant species in the tropics.

Rearing methods and life cycle characteristics of Chironomus sp. Florida (Chironomidae: Diptera): A rapid-developing species for laboratory studies

The species Chironomus sp. “Florida” has several qualities that make it a potential aquatic laboratory model to be used in Puerto Rico. Its use as such, however, requires a rearing protocol and life cycle description not previously reported. The present study addresses this lack of information by first describing a rearing method obtained through three years of observations. Next we describe and discuss the life cycle and the effects of temperature and feeding on development. The species has a short life cycle (typically 11 days) and larval stages easily identified using body measurements. Temperature affects the duration of the life cycle, with warm temperatures producing faster development than cold temperatures. The effects of different food concentrations vary: in large water volumes, concentrations of 2 mg/larva/day produce faster developmental times, but at low water volumes, small food concentrations of 0.5 mg/larva/day produce faster developmental times. The rearing protocol and life cycle parameters presented in this study are intended to promote the use of this species as a laboratory model. The fast development of Chironomus sp. “Florida” makes it ideal for toxicological studies.

Biotransformation in the fish Prochilodus lineatus: An organ-specific approach to cyp1a gene expression and biochemical activity

The biotransformation ability of the organism is the result of organ-specific responses. This paper presents a molecular and biochemical approach to elucidate the biotransformation mechanisms in different organs of Prochilodus lineatus induced at 6, 24, and 96 h after a benzo[a]pyrene (B[a]P) injection. The induction in cyp1a transcription showed an organ-specific intensity at every tested time time. The EROD (ethoxyresorufin-O-deethylase) activity increased rapidly (6 h) in the liver and the kidney; the gills and the brain showed an increase at 24 h; and the gills demonstrated the highest activity among all the organs tested. There was no increase in glutathione S-transferase (GST) activity or lipoperoxidation. The decreased hepatic glutathione content (GSH) may be due to its role as an antioxidant. B[a]P was detected in the bile, confirming the xenobiotic efflux from the metabolizing organs. The gills, liver, brain, and kidney of P. lineatus presented an integrated mechanism to deal with the xenobiotic biotransformation.

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.

Update on the use of Pristina longiseta Ehrenberg, 1828 (Oligochaeta: Naididae) as a toxicity test organism

Ecotoxicological bioassays have been widely applied to evaluate the toxicity of substances in standardized test organisms. Nevertheless, the main challenge for researchers is the use of native species to express the effects of pollutants on aquatic biota. Thirty years ago, Smith and collaborators evaluate the possible use of Pristina longiseta (as Pristina leidyi) in acute toxicity test, developing some experiments using cadmium and vanadium as toxicants. The present work aimed to update the use of P. longiseta, in acute bioassays, presenting the occurrence and general characteristics of the species; adaptation of cultivation to tropical conditions; sensitivity tests using potassium chloride (KCl) and copper sulfate (CuSO₄) as reference substances standardized by OECD, USEPA, and ABNT; and acute exposure to zinc chloride (ZnCl₂). The results showed a successful use of this species as tropical test organism, which presented easy laboratory rearing and responded to the classical ecotoxicological index. The present study can increase the utilization of P. longiseta in bioassays for tropical regions and improve the evaluation of environmental impacts using a native species in ecotoxicological studies.

Acclimation alters glyphosate temperature-dependent toxicity: Implications for risk assessment under climate change

The evaluation of temperature-dependent chemical toxicity (TDCT) is imperative for future risk assessments of pesticides under global climate change scenarios. Few TDCT studies have so far considered the ability of organisms to acclimate to altered temperatures prior to pesticide exposure, although this may change their thermal tolerance range and hence their susceptibility to pesticide stress. The objective of this study was to evaluate the effect of temperature acclimation on the sensitivity of the cladoceran Ceriodaphnia silvestrii to Glyphosate. We used the shift in sensitivity of the organisms to Glyphosate when exposed to short term temperature changes as a proxy for the effect of the developmental acclimation on sensitivity. We observed that acclimation to higher temperatures reduces the sensitivity to Glyphosate when organisms are exposed to this pesticide in lower temperatures. Therefore, acclimation to high temperatures offers some protective effect against Glyphosate toxicity. We argue that pesticide risk assessments based on tests conducted at one standard temperature should be considered with care. Realistic risk assessments considering climate change scenarios should assess the mode of which organisms are exposed to temperature, therefore taking into consideration the potential effect of temperature acclimation on the sensitivity of a species to a toxicant.

Ecotoxicological assessment of synthetic and biogenic surfactants using freshwater cladoceran species

Surfactants have been continuously detected within aquatic environments as a consequence of their use on a global scale. Lipopeptides are biosurfactants naturally produced by Bacillus subtilis that have been explored as green alternatives. The assessment of ecotoxicological parameters of synthetic and biogenic surfactants are required for evaluating toxicity values and to verify the eco-friendly behaviour of the biological compounds. This study aimed to conduct toxicity testing for different surfactants - sodium dodecyl sulphate and Triton X-100 - and biosurfactants - surfactin, iturin and fengycin - at different concentrations using Daphnia magna as model organism and Dendrocephalus brasiliensis as alternative test species for monitoring of pollutants in tropical freshwaters. According results, both species showed high sensitivity for the anionic compound SDS concerning the recommended dosage use, exhibiting EC_50-48h values of 24.1 and 15.4 mg/L for D. magna and D. brasiliensis, respectively. Although the biological source, surfactin showed the lower safety behaviour among the biogenic surfactants, while iturin and fengycin revealed very low toxicity effects on both organisms. Besides, data exhibited a higher responsiveness of D. brasiliensis for all tested compounds in comparison to D. magna, highlighting the importance of this species for monitoring of pollutants in tropical and subtropical environments.

The toxicity of coated silver nanoparticles to Daphnia carinata and trophic transfer from alga Raphidocelis subcapitata

Nanoparticles (NPs) are causing threats to the environment. Silver NPs (AgNPs) are increasingly used in commercial products and may end up in freshwater ecosystems. The freshwater organisms are vulnerable due to water-borne and dietary exposure to AgNPs. Surface properties play an important role in the fate and behavior of AgNPs in the aquatic environment and their effects on organisms. However, effects of surface properties of AgNPs on organisms are poorly understood. In this study, we explored the effects of AgNPs coated with three different ligands; Tyrosine (T-AgNP), Epigallocatechin gallate (E-AgNP) and Curcumin (C-AgNP) in relation to the toxicity to a key aquatic organism; Daphnia carinata. The study focused on how coatings determine fate of NPs in the medium, mortality, feeding behaviour, bioaccumulation and trophic transfer from the freshwater alga, Raphidocelis subcapitata to daphnids. NP stability tests indicated that T-AgNPs were least stable in the ASTM daphnia medium while C-AgNPs were most stable. 48 h EC50 values of AgNPs to D. carinata were in the order of E-AgNP (19.37 μg L-1) > C-AgNP (21.37 μg L-1) > T-AgNP (49.74 μg L-1) while the 48 h EC50 value of Ag+ ions was 1.21 μg L-1. AgNP contaminated algae significantly decreased the feeding rates of daphnids. However, no significant differences were observed in feeding rates between algae contaminated with differently coated AgNPs. Trophic transfer studies showed that AgNPs were transferred from algae to daphnids. The bioacumulation of AgNPs in algae and the diet-borne bioaccumulation of AgNPs in daphnids varied for differently coated AgNPs. Bioaccumulation of C-AgNPs in algae was 1.5 time higher than T-AgNPs. However, the accumulation of T-AgNPs in daphnids via trophic transfer was 2.6 times higher than T-AgNPs. The knowledge generated from this study enhances the understanding of surface property dependent toxicity, bioaccumulation and trophic transfer of AgNPs in aquatic environments.

Effects of florfenicol and oxytetracycline on the tropical cladoceran Ceriodaphnia silvestrii: A mixture toxicity approach to predict the potential risks of antimicrobials for zooplankton

Antimicrobials are commonly used in aquaculture to treat infectious diseases in fish. The overuse of these chemicals, however, has made them a contamination source for the aquatic environments. In this study, single and combined effects of florfenicol (FLO) and oxytetracycline (OTC), two antimicrobials widely used in the fish farming, were evaluated in acute and chronic toxicity tests using the tropical cladoceran Ceriodaphnia silvestrii as a model species. Also, a preliminary risk characterization of FLO and OTC for zooplankton was carried out, taking into account different exposure scenarios. The results obtained revealed that FLO and OTC have adverse effects on the mobility, reproduction and population growth rate of C. silvestrii in single exposures. In addition, mixture effects on the C. silvestrii were more severe than predicted effects based on the Concentration Addition model, showing a synergistic deviation for the mobility and a dose-level dependent deviation for the reproduction (synergism at higher levels than EC₆₀). In relation to the risk characterization, risk quotients (RQs) exceeded 1 for chronic toxicity data obtained in both OTC and mixture exposures, indicating that the concentrations of these chemicals in Brazilian freshwater bodies could potentially present risks for the reproduction of zooplankton species in tropical regions. The RQs obtained for the mixtures were higher than those obtained for each chemical separately. Therefore, it is highly recommended that RQs are derived from single and mixture exposure data in order to obtain a more accurate risk characterization.

Acute ecotoxicity bioassay using Dendrocephalus brasiliensis: alternative test species for monitoring of contaminants in tropical and subtropical freshwaters

In International guidelines for standard ecotoxicological bioassays, Daphnia magna is the most applied microcrustacea for assessing toxicity of different pollutants. However, in research realized in tropical and subtropical areas, autochthonous species must be prioritized because they are adapted to the specificities of ecosystems. In this sense, the present study aimed to assess and compare (with D. magna) the sensitivity of the tropical species Dendrocephalus brasiliensis as alternative test species for monitoring of contaminants in tropical and subtropical freshwaters, by carrying out acute toxicity tests with different pollutants. According results, D. brasiliensis presented EC50-48 h values lower than D. magna for all substances tested, indicating higher sensitivity of the tropical organism in relation to the temperate organism. Furthermore, comparing the results obtained with data from other studies, D. brasiliensis is more sensitive to the chemicals tested than D. magna and has similar sensitivity to Pseudosida ramosa and Ceriodaphnia dubia, common species in tropical areas. In view of this, we suggest that D. brasiliensis can be used as alternative test species for monitoring of contaminants in tropical and subtropical freshwaters.

Acute and chronic toxicity of diuron and carbofuran to the neotropical cladoceran Ceriodaphnia silvestrii

In order to contribute to the increase of the body of knowledge on the sensitivity of tropical indigenous species to pesticides, acute and chronic toxicity tests were conducted with the neotropical cladoceran Ceriodaphnia silvestrii. Tests were carried out with the active ingredients diuron and carbofuran and one of their commercial formulations, the Diuron Nortox® 500 SC and the Furadan® 350 SC, respectively. For carbofuran, the active ingredient was more toxic than the commercial product, whereas for diuron, the commercial product appeared more toxic. In addition, hormetic effects on fertility were recorded for intermediate diuron concentrations. Acute and chronic toxicity data indicated that C. silvestrii was among the most sensitive invertebrate species for both test compounds. Based on concentrations measured in Brazilian water bodies, these compounds represent ecological risks for causing direct and indirect toxic effects on C. silvestrii and other aquatic organisms. Our results support previous claims on the advantages of using native species to better tune ecological risk assessment of chemicals in tropical ecosystems.

Toxic effect of commercial detergents on organisms from different trophic levels

The toxic effects of four powder detergents: two laundry detergents (A and B), one household detergent (C), one dishwashing detergent (D), and the surfactant alkylbenzene sulfonate (LAS) were analyzed in this study on organisms from different trophic levels (microalgae, cladocerans, ostracods, amphipods, macrophytes, and fish). LC₅₀ and EC₅₀ values obtained in the toxicity bioassays varied between 0.019 and 116.9 mg L^-1. The sensitivity of the organisms to the detergents was (from most sensitive to least sensitive) Ostracods > microalgae > amphipods > cladocerans > fishes > macrophytes. The toxicity of the commercial products (from most toxic to least toxic) was LAS > D (dishwashing detergent) > A (laundry detergent) > B (laundry detergent) > C (household detergent). When comparing the sensitivity of organisms that inhabit temperate zones (T = 18 °C) to those that are found in tropical zones (T > 25 °C), it was clear that the species that inhabit the tropics are more sensitive to detergents.

Toxicity of abamectin and difenoconazole mixtures to a Neotropical cladoceran after simulated run-off and spray drift exposure

Aquatic risk assessments of pesticides in tropical countries have often been disputed for being largely based on risk evaluations conducted in temperate regions. Although pesticide sensitivity comparisons between temperate and tropical freshwater organisms have indeed not revealed consistent differences, risk assessments are currently still based on a relatively small tropical toxicity dataset. In addition, greater levels of runoff and spray drift may be expected in tropical than in temperate agroecosystems, indicating that aquatic life in edge-of-field water bodies is likely to be subjected to higher concentrations of pesticides and their mixtures. The aim of the present study was to evaluate the toxicity of Kraft^® 36 EC (a.i. abamectin), Score^® 250 EC (a.i. difenoconazole) and their mixture to the Neotropical cladoceran Macrothrix flabelligera. Laboratory toxicity tests with the individual formulated products indicated EC50-48h values of 3.1 and 659μg a.i./L given as nominal test concentrations, respectively. Mixtures of the two pesticides revealed a concentration-dependent deviation of the independent action model, with antagonism at low and synergism at high pesticide mixture concentrations. Laboratory toxicity tests were also conducted with microcosm water that was treated with the individual or mixtures through runoff or direct overspray. Microcosm tanks receiving runoff water from experimental soil plots applied with recommended doses of the individual pesticides did not show toxicity to the test organism. Microcosms that received runoff water containing the pesticide mixture, however, did cause a short-term effect on immobility. The microcosms that were treated by direct overspray of both pesticide formulations showed the most pronounced toxic effects. Study findings suggest a potential risk of these pesticides at environmentally relevant concentrations, especially when they are both present.

Use of cholinesterase activity as an ecotoxicological marker to assess anatoxin-a(s) exposure: Responses of two cladoceran species belonging to contrasting geographical regions

The specificity of cholinesterase (ChE) activity to detect the presence of anatoxin-a(s) and sublethal effects of a 7-day exposure to Anabaena spiroides extract containing anatoxin-a(s) were assessed in two freshwater cladoceran species. Activities of ChE of both Pseudosida ramosa and Daphnia magna can be used to indicate the presence of the neurotoxin anatoxin-a(s), but not for the hepatotoxic microcystin. Activity of ChE of P. ramosa, however, performed better as a biomarker of exposure to A. spiroides than that of D. magna. Furthermore, sublethal exposure to A. spiroides extract significantly inhibited the ChE activity in P. ramosa and negatively affected both individual and population endpoints. For D. magna, the inhibition of ChE activity was not related to effects at higher levels of biological organization, since no direct effect was recorded on the individual and population endpoints. The activity of ChE in P. ramosa also proved to be a good predictor of chronic effects of the A. spiroides extract at higher levels of biological organization, since 48-h ChE inhibition was linked to the sublethal effects on the individual and population. These relationships could not be established for D. magna. Since relationships between the effects of A. spiroides extract at different levels of biological organization were species-specific, it can be concluded that the choice of test organism interferes with the accuracy of the environment risk assessment of this neurotoxin and, hence, the use of native species is recommended for its assessment.

Toxicity of Vertimec® 18 EC (active ingredient abamectin) to the neotropical cladoceran Ceriodaphnia silvestrii

The aim of the present study was to evaluate the toxicity of abamectin to the neotropical cladoceran Ceriodaphnia silvestrii. To this end, acute and chronic bioassays were conducted with the commercial formulation Vertimec® 18 EC. In addition, the toxicity of water samples taken from a microcosm experiment evaluating the effects of a single application (144μga.i./L) and two applications (2×36μga.i./L) of Vertimec® 18 EC, in the presence or absence of a tadpole species (Lithobates catesbeianus), was also assessed. The acute LC50-48h for immobilization was 1.47μga.i./L and chronic NOEC-8d for survival and fertility (number of neonates per female) were 169 and 84nga.i./L, respectively. Irrespective of the presence of tadpoles, water samples from the microcosms applied with the single concentration of 144μga.i./L remained toxic until the end of the experiment, even when samples were diluted 32 times with culture medium. Water in the repeated pesticide treatment showed a similar toxic response after both applications. Toxicity of water samples from the microcosms was lower than that expected based on the generated LC50 values, which is explained by a potential reduced bioavailability of the test compound resulting from absorbance to organic material. Potential side-effects on C. silvestrii related with the use of Vertimec® 18 EC in Brazil and the suitability of this species for tropical toxicity testing are discussed.

The toxicity of carbofuran to the freshwater rotifer, Philodina roseola

In this study, the effects of exposing the rotifer Philodina roseola to the pesticide carbofuran were investigated. Its range of sensitivity to potassium dichromate, the acute toxicity of active ingredient carbofuran and of carbofuran dosed as its commercial form, Furadan(®) 350 SC were determined. Chronic toxicity of carbofuran dosed as Furadan(®) 350 SC on P. roseola survival and fecundity were also studied. The sensitivity of P. roseola to K2Cr2O7 ranged from 29.52 to 64.67 mg L(-1), averaging 47.10 mg L(-1). The 48-h EC50 were 13.36 ± 2.63 mg L(-1) for carbofuran and 89.32 ± 6.52 mg L(-1) for commercial form. Chronic toxicity tests showed that the survival of this rotifer was not affected by the carbofuran dosed as Furadan(®) 350 SC at the concentrations tested and that at 1.56 and 3.12 mg L(-1) their fecundity was higher than in the absence of this commercial product, characterizing the hormesis phenomenon. The sensitivity profile of several species to carbofuran indicated that P. roseola is more susceptible to this pesticide than the fish Clarias batrachus, the bacterium Vibrio fischeri, the protozoan Paramecium caudatum and the rotifer Brachionus calyciflorus, although the acute toxicity of carbofuran dosed as Furadan(®) 350 SC to P. roseola is much lower than that of active ingredient carbofuran. The results also imply that the exacerbated use of pesticides and the constant, accelerated expansion of agricultural activity will make aquatic non-target species even more vulnerable. Furthermore, the relevant role of benthic organisms in aquatic environments justifies the inclusion of P. roseola and other benthic species in toxicity screening for risk assessment, regarding this environmental compartment.

Measurements of cholinesterase activity in the tropical freshwater cladoceran Pseudosida ramosa and its standardization as a biomarker

The activity of cholinesterases (ChE) has been recognized as a useful tool for assessing the toxicity in the environmental assessment programs. Nevertheless, the prior optimization of the experimental conditions for the appropriate measuring of the ChE activity enables us to get reliable results. Thus, the main objective of this study was to adapt and optimize a microplate assay for measuring the activity of ChE in the tropical cladoceran Pseudosida ramosa. The best readings for the reaction rates were obtained with buffers of pH 8.0 and molarity of 0.02M. The measurements of the reaction rates for the different substrate concentrations showed that the maximum reaction rate (32mODmin(-1)) was achieved by the final concentration of 2mM of substrate. In relation to the enzyme concentration, reaction rates were directly proportional to the protein concentration, which confirmed the linear kinetics for a maximum reaction rate. On the basis of the results of the assays for the effect of the number of individuals and homogenate dilution on the reaction rate of substrate hydrolysis and ChE activity, we recommend using of 30 individuals (3 days-old) in 250μL of buffer, 20 individuals (7 days-old) in 250μL of buffer and 15 individuals (both 14 and 21 days-old) in 300μL of buffer. The limits of quantitation obtained were 1.419mODmin(-1) (≤72h-old), 1.670mODmin(-1) (7 days-old), 0.943mODmin(-1) (14 days-old) and 0.797mODmin(-1) (21 days-old). In conclusion, it was possible to measure the ChE activity in P. ramosa with the methodology adapted, thus contributing to the implementation of a biochemical biomarker in freshwater toxicity assessments in tropical regions.

Acute and chronic toxicity of chromium and cadmium to the tropical cladoceran pseudosida ramosa and the implications for ecotoxicological studies

In this study, the acute and chronic toxicity of the metals chromium and cadmium were tested against the tropical freshwater cladoceran Pseudosida ramosa. Acute tests showed that the 48-h LC50 of chromium was 29 μg L(-1) , while that of cadmium was 12 μg L(-1) . P. ramosa had a similar sensitivity to those of other cladoceran species cultured in the same conditions as in this study, or a higher sensitivity when water hardness was raised. Long-term chronic exposure of P. ramosa to chromium decreased maternal survival, fecundity, and fertility at a concentration of 10 μg L(-1) . For cadmium, reductions in the same endpoints were observed at a concentration of 3 μg L(-1) . Moreover, the degree of toxicity of the chromium and cadmium to P. ramosa after release of the first brood was similar to the result obtained after 21 days, using reproduction as the endpoint. Brazilian water bodies located near industrial areas already show concentrations of chromium and cadmium higher than levels causing acute and chronic toxicity to P. ramosa in our study. Many water quality criteria in tropical regions are based on ecotoxicological tests with non-native species and, consequently, this may lead to errors of interpretation when the permitted maximum levels of for each toxic substance are established. Therefore, we reinforce the idea of using native species to establish the maximum concentrations of toxic substances in water quality criteria, especially for metals, since their effects are related to water hardness, pH, and temperature specific to each region.

Acute effects of Anabaena spiroides extract and paraoxon-methyl on freshwater cladocerans from tropical and temperate regions: links between the ChE activity and survival and its implications for tropical ecotoxicological studies

Cholinesterase (ChE) activity was measured in Pseudosida ramosa and Daphnia magna, which had previously been exposed to Anabaena spiroides extract or to paraoxon-methyl for 48 h. These activities were then related to survival at 48 h. For A. spiroides extract, the observed 48-h LC50 was 2.27 and 2.70 × 10(6)cells mL(-1), while for paraoxon-methyl it was 0.60 and 2.17 μg L(-1), respectively, for P. ramosa and D. magna. Dose-response relationships were obtained for both P. ramosa and D. magna, when exposed to A. spiroides extract or paraoxon-methyl. Thus, when the tested concentrations of the toxicants increased, ChE activity and survival decreased. The ratio between 48-h IC50 for ChE and 48-h LC50 ranged from 75% to 81% for P. ramosa and from 77% to 81% for D. magna. This indicated that the concentrations of both A. spiroides extract and paraoxon-methyl that cause 50% mortality also inhibit ChE activity by 50%. Also, it was found that, for P. ramosa, a 50% inhibition of ChE activity was associated with a survival of 59.5% and 60.9%, respectively, for A. spiroides extract and paraoxon-methyl. However, for D. magna, at high levels of inhibition of ChE activity, almost no mortality was detected. In this specific case, 50% inhibition of the ChE activity was associated with 90.4 and 95.4% survival for A. spiroides extract and paraoxon-methyl, respectively. In contrast, enzyme inhibition slightly above 60% had a strong detrimental effect on survival in D. magna. These different patterns found in the relationship between ChE inhibition and survival may be due to species-specific differences in the affinities of both acetylcholinesterase and pseudocholinesterases, since the cladoceran ChE assays were performed with whole-body homogenates. In conclusion, when using ChE as a biochemical biomarker in risk assessment of cyanobacterial neurotoxic blooms in tropical regions, it is strongly recommended that native species are used, since our results revealed that P. ramosa was more sensitive than D. magna for both assay endpoints and both toxicants. Furthermore, the relationship between ChE activity and survival had a species-specific response. Therefore, the use of the model species D. magna in acute toxicity tests and ChE assays in tropical regions may lead to errors in the estimation of risks to the local species.

Acute and chronic effects of atrazine and sodium dodecyl sulfate on the tropical freshwater cladoceran Pseudosida ramosa

Toxicities of atrazine and sodium dodecyl sulfate (SDS) to the tropical freshwater cladoceran Pseudosida ramosa were studied in the laboratory. Acute tests showed that the 48-h LC₅₀ of atrazine was 20.9 mg l⁻¹, while that of SDS was 11.1 mg l⁻¹. P. ramosa showed to be slightly more sensitive than the other species of temperate cladocerans, in the assay conditions specified for each one. Long-term exposure of P. ramosa individuals to atrazine decreased the 21-day fecundity, the 21-day fertility and r(m), at concentrations ranging from 0.8 to 3.2 mg l⁻¹. Furthermore, fecundity and fertility at each brood decreased from the first to the fifth, at concentrations ranging from 0.8 to 3.2 mg l⁻¹ and for the first three broods at the concentration of 0.4 mg l⁻¹. Long-term exposure of female P. ramosa to SDS decreased the 21-day fecundity, the 21-day fertility and r(m), at concentrations of 2 and 4 mg l⁻¹. Fecundity and fertility of each brood were reduced from the first to the fifth, at concentrations of 2-4 mg l⁻¹, and for the first three at concentrations of 0.5 and 1 mg l⁻¹. The survival and moulting of the adult females were not affected by either chemical at the concentrations tested. Many water quality criteria in tropical regions are based on ecotoxicological tests with non-native species and this may lead to errors in setting the maximum permissible levels of chemicals in water bodies. Therefore, we reiterate here the idea of using native species in ecotoxicological assessments.

Effects of dietary copper on life-history traits of a tropical freshwater cladoceran

Life-history parameters of Ceriodaphnia cornuta (Cladocera: Daphniidae) fed on Pseudokirchneriella subcapitata (Chlorophyceae) exposed to different copper concentrations were investigated. C. cornuta individuals were reared in four treatments: (a) reconstituted water and non-contaminated algae (RW); (b) reconstituted water and copper-contaminated algae with either 1.28 × 10(-13) (10(-7)Cu) or (c) 1.93 × 10(-13) g Cu cell(-1) (10(-6)Cu); and (d) natural water from a local reservoir and non-contaminated algae (NW). Copper content in C. cornuta individuals increased as diet-borne exposure increased (RW < 10(-7)Cu < NW < 10(-6)Cu), except for NW individuals, which exhibited higher copper body burden than RW and 10(-7)Cu individuals, suggesting that some copper was available in the natural water. The results suggest that subacute levels of dietary copper stimulated C. cornuta's growth and reproduction, whereas organisms reared on reconstituted water showed nutritional deficiency. Depending on copper exposure concentration, either growth (lower Cu concentration) or reproduction (higher Cu concentration) was further stimulated, suggesting that an alteration of resource allocation is involved in diet-borne copper exposure. Because differences among treatments were only significantly different after day 12 of the experiment, our results reinforce that full life-cycle tests are more appropriate than the standard 7 day or three-brood chronic bioassays used to evaluate dietary copper effects at low, chronic copper inputs and that the use of standard test-organisms may not address site-specific situations for tropical environments.

Checklist de Cladocera de água doce do Estado de São Paulo

Neste trabalho é apresentada uma lista atualizada das espécies de Cladocera do Estado de São Paulo com base em levantamentos anteriores e em revisão da literatura recente, a qual inclui em grande parte os estudos oriundos do Programa Biota FAPESP. Levantamentos realizados há uma década apontaram a ocorrência de 112 espécies de Cladocera no Brasil e 84 para o Estado de São Paulo. A presente revisão evidencia a ocorrência de 96 espécies deste grupo no Estado de São Paulo, o que representa um acréscimo de 15% na riqueza de espécies. Dentre os 300 corpos de água amostrados em 23 unidades de gerenciamento dos recursos hídricos do Estado de São Paulo, no âmbito do Programa BIOTA/FAPESP, as unidades Mogi-Guaçu e Aguapeí são aquelas com maior riqueza de espécies, tendo sido registradas 27 espécies de Cladocera em cada. Dentre os avanços obtidos pelo Programa BIOTA/FAPESPdestacaram-se a ampla cobertura geográfica e o registro das novas ocorrências de espécies, das quais 12 são espécies nativas e 2 são espécies exóticas. Este estudo evidenciou que ainda existem importantes lacunas no conhecimento, especialmente em relação à taxonomia, pois muitas espécies que foram consideradas cosmopolitas são provavelmente um complexo de espécies, sendo necessárias revisões taxonômicas detalhadas acopladas a estudos ecológicos das espécies. Acredita-se que com a continuidade destes estudos a riqueza de espécies de Cladocera poderá aumentar consideravelmente.

Comparison of the effects of two herbicides and an insecticide on tropical freshwater plankton in microcosms

Natural plankton communities from a tropical freshwater reservoir (Combani Reservoir, Mayotte Island, Mozambique Channel) were exposed, in 20-l nutrient-enriched microcosms, to two nominal concentrations of three pesticides: the herbicides diuron (2.2 and 11 μg/l) and paraquat (10 and 40.5 μg/l) and the insecticide fenitrothion (10 and 100 μg/l), commonly used in the tropics for agriculture and disease vector control. Bacterioplankton, phytoplankton, and zooplankton communities were monitored for 5 days after exposure, and the concentrations of toxicant and major nutrients were measured. Bacterioplankton growth was noticeable in all systems and was slightly affected by pesticide at any concentration. A transitory increase in thymidine-based bacterial production was observed in diuron- and fenitrothion-treated microcosms, followed by a marked decrease in all microcosms after 5 days. The functional diversity of bacterioplankton, evaluated using BIOLOG ECO(®) microplates, was reduced by exposure to the highest pesticide concentrations. Phytoplankton was affected by pesticides in different ways. Chlorophyll biomass and biovolumes were increased by diuron addition and decreased by paraquat, whereas fenitrothion-treated microcosms remained unaffected relative to controls. Phytoplankton taxonomic diversity was decreased by paraquat and high doses of fenitrothion but was unaffected by addition of diuron. The decrease in diversity was due to a reduction in the number of species, whereas the density of small cells increased, especially after addition of paraquat. Heterotrophic flagellates were sensitive to paraquat and to the highest diuron concentration; a reduction in biomass of up to 90% was observed for 40.5 μg/l paraquat. Zooplankton, dominated by Thermocyclops decipiens and Diaphanosoma excisum, was slightly sensitive to diuron, and very sensitive to paraquat. High concentrations of the insecticide fenitrothion were effective only on young stages. The potential direct and indirect effects of pesticide contamination on such a simplified plankton food web, typical of newly constructed reservoirs, appear to differ significantly depending on the biological compartment considered. The overall sensitivity of tropical plankton is comparable to the sensitivity for temperate systems, and direct and indirect effects appeared rapidly, within 5 days of exposure.

Sensitivity of two Mesocyclops (Crustacea, Copepoda, Cyclopidae), from tropical and temperate origins, to the herbicides, diuron and paraquat, and the insecticides, temephos and fenitrothion

Ecotoxicological assessment in the tropics is based mainly on knowledge gained from temperate organisms, although many studies have shown the need for models that are more appropriate to tropical regions. The toxicity of two herbicides and two insecticides to nauplii of two freshwater zooplankton species, Mesocyclops aspericornis (von Daday in Inseln Zool Jb Syst 24:175-206, 1906) from a tropical reservoir and a Mesocyclops sp. from a temperate pond, were compared. Both strains were sensitive to paraquat, temephos and fenitrothion, tropical M. aspericornis being generally more tolerant (EC50s of 207, 1,450 and 1,840 μg L(-1) for paraquat, temephos and fenitrothion, respectively) than the temperate Mesocyclops sp. (EC50s of 152, 45 and 1,017 μg L(-1) for paraquat, temephos and fenitrothion, respectively) whereas diuron was only slightly toxic (LOEC = 446 μg L(-1) for both strains). The nauplii mortality increased with the exposure time for both species during each experiment. Further isolation of model organisms from tropical ecosystems is needed, to meet the requirements for a tropical risk assessment scheme.