The Pirapó river watershed (Paraná State, Brazil) compounds a relatively industrialized and urbanized region, undergoing great pressure from the discharge of industrial, agricultural and domestic wastes. We evaluated the environmental quality of ten streams belonging to this watershed in April and June 2008 by performing acute and chronic toxicity tests with Daphnia similis and Ceriodaphnia silvestrii from water and sediment samples. We tested the hypothesis that the streams located in urban areas are more exposed to the influence of pollutants, than those outside the city limits. In addition, we obtained the measures of physical and chemical parameters, and identified the main polluted sources. Contrary to what was expected, the rural streams were more toxic than those located in urban area. These results demonstrate that the water bodies located in rural areas are being affected by the pollution of aquatic ecosystems as far as those found in urban areas, requiring the same attention of environmental managers in relation to its monitoring. IntroductionThe increasing contamination of aquatic, terrestrial and atmospheric environments with substances from human activities has attracted attention from political organizations and environmental managers, as well as from society as a whole. Many researchers have searched for solutions through effluent treatment, solid waste recycling and clean energy production. In spite of their efforts, many counties still do not possess sewage collection networks that include all inhabitants or suitable local systems for garbage disposal. Hence, some domestic discharges and industrial effluents reach watercourses untreated, causing environmental damage.Due to the complexity and variability of organic and inorganic compounds that enter water bodies and because little information about the interactions between these substances is known, it is not possible to establish allowable discharged concentrations using only the physical and chemical analyses commonly performed by environmental managers. The char- acterization of aquatic systems needs to go beyond routine analyses to evaluate the overall effects of pollutants on the environments and organisms. The evaluation of effects on the biological components through biomonitoring and toxicity tests is a more effective tool for predicting or detecting several types of impacts (COSTA and ESPÍNDOLA, 2000).Toxicity tests are widely used, but a great majority is restricted to aquatic compartment, even though the importance of sediment to aquatic ecosystems is now recognized (COSTA and ESPÍNDOLA, 2000). Although tests with surface water, groundwater, industrial and domestic wastewater, are responsible for the detection of toxic substances and control the level of pollutants entering the aquatic ecosystems, monitoring should also include sediment, because it has a high ability to accumulate compounds that may eventually be released to the water column due to changes (physical, chemical and biological -bioturbation) in environmental condit...

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