Abstract
Water hardness is a property depending on the presence of alkaline earth metals, mainly calcium and magnesium. Among the strategies for water quality monitoring, ecotoxicological assays are performed to minimize impacts and classify water bodies. For these laboratory evaluations parameters are previously defined in the guidelines, including water hardness for both cultivation and testing medium. The present work was performed to evaluate the effects of different levels of water hardness on the survival and reproduction of the freshwater snail Biomphalaria glabrata and discuss the influence of natural water hardness on the results of ecotoxicological tests with these environmental samples. Comparing the groups it was possible to observe that those maintained in waters with least hardness had lower reproductive success, while the groups maintained in highest hardness showed better reproduction. These data show that waters with low hardness make the reproduction of the snail B. glabrata unfeasible, and this reveal a problem for ecotoxicity assays using natural water samples.
Highlights
Water is one of the natural resources essential to sustaining life
As CONAMA Resolution No357/05 (Brasil, 2005) recommends ecotoxicological testing as an additional parameter for assessing water quality, and as there is sometimes a gap between the water hardness standards for laboratorial cultivation of species and those found in field samples, the objective of this study was to evaluate the effects of changing conditions of water hardness on survival and reproduction of Biomphalaria glabrata snails, in order to emphasize the degree of accuracy that this parameter can generate in the results of ecotoxicological assays with environmental samples and in water quality standards
The first was a natural water (NW) obtained from a spring in the area of Embrapa Cerrados, in Planaltina, Federal District, Brazil (15°35’41.5”S and 47°44’45.3”W), with hardness about 2±1 mg/L CaCO3, and the other three were reconstituted waters prepared according to the guidelines described by ABNT (2004) and with the following standards of hardness in CaCO3: 10±2 mg/L, soft water (SW1); 40±5 mg/L, soft water (SW2) and 120±2 mg/L, moderately hard (MH1) all using distilled water with added salts according to this standard protocol
Summary
Water is one of the natural resources essential to sustaining life. To diagnose problems related to pollution of aquatic environments, it has become necessary to adopt control methods and strategies for monitoring their quality. For this aspect, in Brazil, CONAMA Resolution No357/05, published on March 17, 2005 (Brasil, 2005), establishes maximum allowable values for various physical, chemical and biological parameters as limiting for water quality, and its innovation lies in the determination of acute and chronic ecotoxicological effects as a quality criterion related to the maintenance of aquatic life. Regarding laboratory observation of chronic effects on aquatic species, the seven-day Ceriodaphnia dubia survival and reproduction test is one of the most adopted.
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