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	In the<a href="http://participatoryscience.org/mercury-watersheds/introduction-mercury-environment"> Introductory Unit </a>we introduced students to mercury. They learned that it is toxic and they should, also, have at least a rough idea of the kinds of quantities that we might expect to find in human hair and in fish. They should also have a general familiarity with the way that mercury, in its different forms, moves through the environment; more specifically they should think about how it moves through their study site and organisms.