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.Keywords: reservoirs ecology, limnology, ecotoxicology, Tietê River. RESUMO Estudos limnológicos e ecotoxicológicos na cascata de reservatórios do rio Tietê (São Paulo, Brasil)O presente trabalho visou avaliar a qualidade de amostras de água e sedimento dos reservatórios em cascata do rio Tietê (SP) através de análises limnológicas e ecotoxicológicas. Foram realizadas coletas de água e sedimento em dois períodos (fevereiro e julho de 2000) e em 15 estações de amostragem. Foram realizados bioensaios de toxicidade aguda para Daphnia similis, de toxicidade crônica para Ceriodaphnia dubia e para larvas pós-eclodidas de Danio rerio. Análises de nutrientes totais, material em suspensão total e cádmio, cromo, cobre e zinco foram realizadas para as amostras de água e análises de matéria orgânica, granulometria e metais biodisponíveis (cádmio, cromo, cobre e zinco) para o sedimento. Os resultados obtidos para as variáveis limnológicas, revelaram diferenças na qualidade da água, com elevado aporte 698 RODGHER, S. et al.
The objective of this work was to assess the toxicity of sediment samples from six cascade reservoirs in Tietê river system, in São Paulo State, Brazil, through chronic-partial toxicity bioassays with Danio rerio larvae as testorganisms. 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.
“In situ” bioassays (96 h), using Chironomus xanthus, were conducted in October/03 and January/04, in 4 sampling stations at Monjolinho river. Laboratory bioassays were conducted using 60g of sediment and 240 ml of ASTM medium, for 96 h. Six organisms were added to each test-chamber and the toxicity evaluation was given by the mean survival. The “in situ” bioassay test chambers (PVC) were covered by a 300 μm mesh. The sediment of each sampling station was added to the chambers together with 10 organisms at IV instars. The laboratory bioassays showed survivals ranging between 0% (Federal, Oct/03) and 100% (Federal, Jan/04). The results “in situ” bioassays showed high mortality (between 84% and 97% in Oct/03 and between 60% and 70% in Jan/04). However, the results did not show, necessarily, that the sediments were toxic or not, because of the high mortality that occurred in the river ́s spring (over 60%), which may be associated to other factors, like screen saturation with suspended matter and different sediment textures. The presence of indigenous organisms may have influenced the results, due the competition and predation in the chamber. Thus, we can infer that the protocol for “in situ” bioassays using C. xanthus must be improved in order to minimize the influence of confounding factors on the tests results.
With the objective of evaluating the effects of organochlorine pesticides (aldrin and heptachlor) on the survival, growth and gill morphology of juvenile zebrafish (Danio rerio), four partial chronic toxicity bioassays were conducted (seven days' duration) with both compounds in a semi-static system with renewal every 24 h. The results did not show any effects on the fish's survival, but did on their growth and gill morphology. Aldrin was more toxic than heptachlor, since the chronic value (CV) for growth was nearly 8.7 times less, a result confirmed by analyzing the histology of the gills, in which the changes detected were considered more severe for the former substance. In general, they were found branchial lesions of first stage, in other words, cell proliferation between the secondary lamellae, hyperplasia, lifting of respiratory epithelial cells; fusion of several secondary lamellae and dilation of blood vessels. Aneurysms (alterations of second stage) they were verified in the exposed organisms to the aldrin, which also presented about 10% of reduction in the standard length and 30% of reduction in the total weight in relation to the exposed organisms to the control. For heptachlor these values were of 8% and 25%, respectively. The intensity of the gill lesions and growth of the fish did not depend on the pesticide concentration, suggesting different modes of action of the products.
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