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Universidad de la Republica / Uruguay Seccion Oceanografia y Ecologia Marina / Facultad de Ciencias - UDeLaR (Igua 4225, Montevideo 11400, Uruguay) *Corresponding author: pmmaciel@fcien.edu.uy Turbidity is a measurement of the clarity of water that has been used as an indicator of the environmental health of water bodies (GIPPEL, 1989). This physical property of water is caused mainly by the presence of suspended solids, such as silt, clay, organic matter, plankton, microorganisms and colored substances that cause the incident light to be scattered and absorbed instead of transmitted through the water sample (SADAR, 1996; UNITED STATES, 1999). It has been used as a surrogate measure of suspended solids in water analyses, in monitoring programs of water quality (LEWIS, 1996; SADAR, 1996; ORWIN; SMART, 2005). A detailed description of the principles of turbidity measurement and instrument designs can be found in SADAR (1996). As an ecological factor, its role is fundamental, affecting many aspects of the trophic webs at different levels: it affects the availability of light and the capability of primary producers being suspended in the water column, the encounter rates between prey and predators, modifies the behavioral responses of prey to control the risk of predation and induces changes in the diet of some piscivorous fishes (DAVIES-COLLEY; SMITH, 2001; ABRAHAMS; KATTENFELD, 2007; CARTER et al., 2010). Bioturbation (activity of benthic organisms modifying the sediment structure) measured as turbidity generation has been postulated as a sensitive endpoint in studies of sub-lethal responses to assess the toxicity of aquatic sediments ( BARTSCH et al., 1999; BRIGGS et al., 2003). Tests that measure sub-lethal responses allow the detection of effects on biota at low concentrations of contaminants (RAND et al., 1995). These effects, without being lethal in the short term can lead to ecological changes that affect an organism's long-term ability to survive. They are useful in the analysis of areas with moderate to severe pollution (BRIGGS et al., 2003; ALLEN et al., 2006). When relatively uncontaminated sediments are spiked with a gradient of concentrations of cadmium, copper or PAHs, the turbidity generated by the activity of the organisms exposed to these spiked sediments responded in a concentration-dependent manner (BARTSCH et al., 1999; BRIGGS et al., 2003). Thus organisms affected by the concentrations of contaminants added to the sediments respond by modifying their activity pattern. In applying this type of test, Briggs et al. (2003) using turbidity measuring equipment of simple, inexpensive construction, with amphipods Corophium volutator (Pallas), quickly detected those sediments which would require further analysis to determine the cause of their potential toxicity. Nevertheless, the use of turbidity as an end point in toxicity testing presents some difficulties, as represented, for example, by grain size which can be a confounding factor in its applicability (BRIGGS et al., 2003). Sand particles sink faster than smaller ones such as silt or clay, and this physical property of a sediment can affect the generation of turbidity by the organisms and therefore the objective of the test, that is to detect sub-lethal toxicity in the target sediment. The undertaking of this test also requires that the number of organisms present per experimental unit should be determined, since different organism

brazilian journal of oceanography

A simple Home-Made Turbidimeter (HMT) for turbidity measurements using Hyalella curvispina Shoemaker 1942 (Crustacea: Amphipoda) for the assessment of environmental quality of coastal waters