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Sediment Quality Assessment and Management: Insight and Progress Edited by M. Munawar© 2003 Ecovision World Monograph Series Aquatic Ecosystem Health & Management Society Assessing metal impacts in sediments: key questions and how to answer them U. Borgmann National Water Research Institute, Environment Canada, Burlington, Ontario L7R 4A6, Canada. Keywords: toxicity, bioavailability, cause Introduction There are four key questions that need to be answered when environmental impact assessments of contaminants are made. These are: 1. Are contaminants getting in the system? 2. Are contaminants bioavailable? 3. Is there a measurable response? 4. Are the contaminants causing this response? These questions were articulated in the Aquatic Effects Technology Evaluation (AETE) program, a Canadian government-industry program which reviewed appropriate technologies for assessing the impacts of mine effluents on the aquatic environment (AETE, 1997; ESG, 1999). Although AETE focused on mine effluents, the four questions which provided the focus for evaluating assessment tools are equally valid for other forms of metal contamination (e.g. atmospheric transport) and for other contaminants. An environmental assessment tool must be able to address one or more of the above questions, and no assessment of environmental contamination is complete unless all four questions can be answered. The concept behind the four key questions is not new. For example, Chapman and Long (1983) listed three central questions vital to any marine pollution assessment. The first two of these (“Are contaminant levels high?” and “Are 24 these contaminants bioavailable?”) are equivalent to the first two AETE questions. Their third question (“Do these contaminants have the potential to cause significant adverse effects to the biota?”) is a combination of AETE questions 3 and 4. Splitting the latter into two questions, as done inAETE, is advantageous, however, because this forces a separate evaluation of whether there are effects and whether the effects are due to contaminants. Many contaminated locations, such as harbours, suffer from multiple stresses, including, for example, habitat alterations, eutrophication, and alien species invasions. There may be clearly defined biological impacts which correlate with, but are not caused by, toxic chemical contamination. The four AETE key questions, therefore, provide a useful focus for environmental assessments, including assessment of metal impacts in sediments. Methods which can be used to answer these questions are discussed below. Impacts of metals in sediments of lakes in the Sudbury area. An example of how an environmental impact assessment can address the four critical questions is demonstrated in a recent (1996-1998) study on the effect of atmospherically transported metals in the Sudbury area conducted by the National Water Research Institute, Environment Canada (Borgmann et al., 2001b). This study examined metal contamination and biological effects in sediments from twelve lakes, four near (6-12 km) the smelter at Copper Cliff, four at an intermediate distance (32-52 km), and four reference lakes between 94 and 154 km from Sudbury. Although the area has been severely impacted by smelter emissions in the past (Gunn, 1995), some lakes are reasonably well buffered and have never become acidified. These were chosen to study the impacts of metals. In addition, sediments from Hamilton Harbour and Lake Erie served as controls for toxicity tests. Selected data from this study will be used to demonstrate how the four key AETE questions can be answered in a sediment assessment. Are contaminants getting in the system? The first question can be addressed by measuring metal concentrations in water and sediments. Metal concentrations in sediment core profiles can be useful in quantifying temporal trends in contamination and in demonstrating that metal contamination is due to industrial activity and is not natural in a given area. Spatial surveys can evaluate the extent of contamination in the field, but the method of sediment collection is important. The sediment sampling device should collect sediments down to a specific and constant depth. Grab samplers, such as the miniponar grab, do not sample from a defined depth and metal concentrations in sediments collected by them can be quite variable if metal concentrations in the field vary through the sediment core. Effluent chemistry and toxicity can also provide a measure of the release of 25 toxic substances into the environment. Acute toxicity testing (using rainbow trout and Daphnia magna) was recommended as one of the tools for addressing the first question with respect to mine effluents (ESG, 1999).Toxicity testing of effluents is a means of determining if contaminants are being released even if the identity of the contaminants is unknown. Acute toxicity testing has been used...


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