Evaldo Luiz Gaeta Espíndola

A toxicidade em ambientes aquáticos: discussão e métodos de avaliação

Aquatic toxicity tests are assays performed with different aquatic organisms of different ecological organization levels. Such tests are a source of information on the toxicity of a given substance or wastewater under controlled conditions, and they complement the physico-chemical analyses. Moreover, they allow one to evaluate the risks resulting from the presence of toxic substances in the environment. Algae, crustaceans, fishes and bacteria are frequently used in toxicity tests. In this work, we will present the main aspects related to the aquatic toxicity tests and a discussion of their applicability will also be presented.

Lethal effects of abamectin on the aquatic organisms Daphnia similis, Chironomus xanthus and Danio rerio

Abamectin is used as an acaricide and insecticide for fruits, vegetables and ornamental plants, as well as a parasiticide for animals. One of the major problems of applying pesticides to crops is the likelihood of contaminating aquatic ecosystems by drift or runoff. Therefore, toxicity tests in the laboratory are important tools to predict the effects of chemical substances in aquatic ecosystems. The aim of this study was to assess the potential hazards of abamectin to the freshwater biota and consequently the possible losses of ecological services in contaminated water bodies. For this purpose, we identified the toxicity of abamectin on daphnids, insects and fish. Abamectin was highly toxic, with an EC(50) 48 h for Daphnia similis of 5.1 ng L(-1), LC(50) 96 h for Chironomus xanthus of 2.67 μg L(-1) and LC(50) 48 h for Danio rerio of 33 μg L(-1).

Biomarker responses as indication of contaminant effects in Oreochromis niloticus.

The current study investigated oxidative stress parameters (enzymes activities, metallothionein content and lipid peroxidation) in freshwater fish, Oreochromis niloticus, tilapia exposure to Monjolinho River (in 4 months of year: January, April, July and November). One critical site in Monjolinho River (site B) was assessed in comparison to a reference site (site A). Water pH and oxygen concentration was lower than that recommended by CONAMA (Brazilian National Environmental Committee), resolution 357/2005 for protection of aquatic communities, and ammonium and the metals Cu, Zn, Mn and Fe (on all months) concentrations were higher than the maximum concentration recommended. Glutathione peroxidase (GPx) and superoxide dismutase (SOD) activities were significantly decreased in liver and muscle in tilapia from Monjolinho River, throughout the year, in relation to reference except in gills that SOD activity increased. Glutathione S-transferase (GST) activity was significantly increased in liver of the tilapia from Monjolinho River in all sites, in relation to reference except in gills that GST activity increased in July and decreased in November, suggesting that GST activity could be induced to neutralize the pollutants toxicity. On the other hand, GST activity was significantly decreased in white muscle indicating a toxic effect of pollutants, resulting in a decreased ability of tilapia to perform defense reactions associated to GSTs. The decrease of catalase (CAT) activity in gills of the O. niloticus together with the increase of SOD activity, could explain the increased lipid peroxidation (LPO) level in this organ. Metallothionein levels in liver and gills were significantly high in all sites. Results indicate that the exposure to metals caused severe damage to tissues; despite the consensually assumed antioxidant induction as a sign of exposure to contaminants the effects seem in part to be mediated by suppression of antioxidant system with SOD, CAT and GPx as potential candidates for tissues toxicity biomarkers of pollutants.

Limnological and ecotoxicological studies in the cascade of reservoirs in the Tietê river (São Paulo, Brazil)

An evaluation was made of the quality of samples of water and sediment collected from a series of reservoirs in the Tietê River (SP), based on limnological and ecotoxicological analyses. The samples were collected during two periods (Feb and Jul 2000) from 15 sampling stations. Acute toxicity bioassays were performed using the test organism Daphnia similis, while chronic bioassays were carried out with Ceriodaphnia dubia and Danio rerio larvae. The water samples were analyzed for total nutrients, total suspended matter and total cadmium, chromium, copper and zinc concentrations, while the sediment samples were examined for organic matter, granulometry and potentially bioavailable metals (cadmium, chromium, copper and zinc). The results obtained for the limnological variable, revealed differences in the water quality, with high contribution of nutrients and metals for Tietê and Piracicaba rivers, besides the incorporation and sedimentation, consequently causing a reduction of materials in Barra Bonita reservoir, thus promoting the improvement of the water quality in the other reservoirs. The toxicity bioassays revealed acute toxicity for Daphnia similis only in the reservoirs located below Barra Bonita dam. On the other hand, chronic toxicity for Ceriodaphnia dubia and acute for Danio rerio showed a different pattern, decreasing in magnitude from Barra Bonita to Três Irmãos, demonstrating an environmental degradation gradient in the reservoirs.

Genotoxicity and mutagenicity of water samples from the Monjolinho River (Brazil) after receiving untreated effluents

Cytotoxicity, genotoxicity and mutagenicity assays, using the Allium cepa test-system, were carried out in order to evaluate the effects of domestic and industrial effluents in the Monjolinho River in different seasons of the year. In the summer and intermediate seasons, chromosome aberration, micronuclei, cell death and inhibition of the mitotic index were observed in water samples collected at different sites. In the winter, either chromosome or cellular alterations were not observed. Through chemical analysis, we infer that the excessive metals such as Pb, Ni and Cu were mainly responsible for the effects observed in A. cepa cells. Limnologic analysis like electrical conductivity, dissolved oxygen and the presence of nitrogen and phosphated compounds showed that the rivers contamination is due to organic matter discharge along its course. Moreover we note that this river had a higher self-depurative capacity at the end of its course, before its confluence with the Jacaré-Guaçu River.

Alterations on growth and gill morphology of Danio rerio (Pisces, Ciprinidae) exposed to the toxic sediments

The objective of this work was to assess the toxicity of sediment samples from six cascade reservoirs in Tiete river system, in Sao Paulo State, Brazil, through chronic-partial toxicity bioassays with Danio rerio larvae as test-organisms. Histology of gills and biometric measurements were used to determine the existence of toxicity problems. The alterations on gill morphology here detected were considered of first stage (hyperplasia, lamellar junction and excess of mucous cells) in the first reservoirs and very slight in the last ones. The biometric analysis pointed to inadequate conditions for the growth of the test-organisms when exposed to the sediment of the rivers and upstream reservoirs and also indicated an improvement of environmental conditions along the system.

Integrated ecological risk assessment of pesticides in tropical ecosystems: A case study with carbofuran in Brazil

The aim of the present study is to contribute an ecologically relevant assessment of the ecotoxicological effects of pesticide applications in agricultural areas in the tropics, using an integrated approach with information gathered from soil and aquatic compartments. Carbofuran, an insecticide/nematicide used widely on sugarcane crops, was selected as a model substance. To evaluate the toxic effects of pesticide spraying for soil biota, as well as the potential indirect effects on aquatic biota resulting from surface runoff and/or leaching, field and laboratory (using a cost-effective simulator of pesticide applications) trials were performed. Standard ecotoxicological tests were performed with soil (Eisenia andrei, Folsomia candida, and Enchytraeus crypticus) and aquatic (Ceriodaphnia silvestrii) organisms, using serial dilutions of soil, eluate, leachate, and runoff samples. Among soil organisms, sensitivity was found to be E. crypticus < E. andrei < F. candida. Among the aqueous extracts, mortality of C. silvestrii was extreme in runoff samples, whereas eluates were by far the least toxic samples. A generally higher toxicity was found in the bioassays performed with samples from the field trial, indicating the need for improvements in the laboratory simulator. However, the tool developed proved to be valuable in evaluating the toxic effects of pesticide spraying in soils and the potential risks for aquatic compartments.

Laboratory measurements of biomarkers and individual performances in Chironomus xanthus to evaluate pesticide contamination of sediments in a river of southeastern Brazil.

This study aimed at evaluating biomarkers, individual and population responses in the native Chironomus xanthus to assess the toxicity of pesticide-contaminated sediments from the Monjolinho River (Southeast Brazil). We measured cholinesterase (ChE) and glutathione S-transferase activities (GST), as biomarkers and survival, individual growth and adult emergence, as individual performances. There was no response of the ChE activity and a tendency to decreased GST activity in contaminated sites, but this was generally not statistically significant. Therefore, there was no association of the biomarker responses with exposure to sediment containing pesticides. In contrast, ash free dry mass was significantly increased and male emergence was decreased in C. xanthus exposed to the same sediments. In conclusion, the selected biomarkers were not sensitive and specific enough to detect and anticipate effects of pesticide contamination at the levels measured in the study area. Nevertheless, individual performances alterations pointed to potential pollution problems and possible ecological consequences.

Copper-driven avoidance and mortality in temperate and tropical tadpoles

Amphibians have experienced an accentuated population decline in the whole world due to many factors, one of them being anthropogenic contamination. The present study aimed to assess the potential effect of copper, as a worldwide and reference contaminant, on the immediate decline of exposed population due to avoidance and mortality responses in tadpoles of three species of amphibians across climatic zones: a South American species, Leptodactylus latrans, a North American species, Lithobates catesbeianus, and a European species, Pelophylax perezi. A non-forced exposure system with a copper gradient along seven compartments through which organisms could freely move was used to assess the ability of tadpoles to detect and avoid copper contamination. All species were able to avoid copper at a concentration as low as 100 μg L(-1). At the lowest (sublethal) concentrations (up to 200 μg L(-1)) avoidance played an exclusive role for the population decline, whereas at the highest concentrations (> 450 μg L(-1)) mortality was the response determining population decline. The median concentrations causing exposed population immediate decline were 93, 106 and 180 μg L(-1) for Le. latrans, Li. catesbeianus and P. perezi, respectively. Contaminants might, therefore, act as environmental disruptors both by generating low-quality habitats and by triggering avoidance of tadpoles, which could be an important response contributing to dispersion patterns, susceptibility to future stressors and decline of amphibian populations (together with mortality).

Avoidance response of Danio rerio to a fungicide in a linear contamination gradient

The present study examines the ability of juvenile Danio rerio to avoid pyrimethanil-contaminated water. An avoidance assay system was used with a contamination gradient formed by seven compartments, through which the fish could move and choose the preferred compartment(s). Additionally, the influence of fish movements in promoting the mixing between compartments and thus disruption of the gradient over time was also examined by testing sodium chloride (NaCl) at sublethal concentrations. Samples with pyrimethanil were obtained from the commercial formulation Mythos®, which was applied to mesocosm systems. Samples of the pyrimethanil-contaminated mesocosms water were collected and a series of seven concentrations (0.2 to 1.4mgL(-1) plus a control) diluted with reference (uncontaminated) mesocosm water were added to the system to form the gradient. After 4h exposure, fish avoidance in the three highest pyrimethanil concentrations ranged from 29 to 66%. The 4h-AC50 (concentration at which 50% of the fish avoided pyrimethanil after 4h exposure) was 1.10 (confidence interval: 1.07 to 1.12)mgL(-1). However, the avoidance pattern after 12h was strongly reduced and it was not possible to calculate the AC50. This is explained by the results of the NaCl experiment, which showed that the movement of fish in the system accelerates the mixing of the solutions between compartments. As pyrimethanil can trigger avoidance response in D. rerio, this fungicide, even at non-lethal concentrations, could be considered an environmental disturber.