Grade 9 Environmental Chemistry Practice Test

Contaminants that persist in the environment and resist breakdown tend to build up inside organisms and become more concentrated at higher levels of the food chain. In water, mercury can be released in inorganic form and is transformed by microbes into methylmercury, a form that readily accumulates in aquatic organisms and increases in concentration in predators higher up the food web. This pattern—bioaccumulation and biomagnification—explains why fish tissue often shows high mercury levels, especially in top predators. Sodium, calcium, and chloride are common ions that nourish or balance physiology and do not persist in tissues in a way that leads to harmful accumulation through the food chain; their levels in fish reflect the water’s chemistry rather than accumulation of a toxic contaminant. Therefore, mercury is the contaminant most commonly associated with bioaccumulation in fish tissue from polluted water.