Bioaccumulation, as defined by Cunningham et al. (2003), is the selective absorption and concentration of molecules by cells. This mechanism is both beneficial and harmful to an organism's cells, allowing the accumulation of important nutrients and minerals. At the same time, dilute toxins may be absorbed and harmful amounts may build up inside the cells. As a result biomagnification occurs, which is the concentration of toxins increasing as each trophic level is reached (Cunningham et al., 2003). Mercury levels are a major concern in water bodies because aquatic vegetation and organisms absorb it and through bioaccumulation and biomagnification fish and wildlife obtain high mercury levels (Environment Canada, 2003). Mercury is a major environmental concern because it causes permanent neurological, renal, and immune damage that can ultimately lead to death in fish, wildlife and humans (Environment Canada 2004). .
Mercury is a unique element because it remains liquid at room temperature (Environment Canada 2002). Its high surface tension allows it to form spherical beads when released. When bonding with other elements it can form organic and inorganic molecules (Environment Canada 2003). Under natural circumstances mercury is found in large deposits under ground and is released slowly through erosion. Human activities have roughly double or tripled the amount of mercury in the atmosphere since pre-industrial times by burning coal and fossil fuels, metal smelting and cement manufacturing (Environment Canada 2002). Mercury most frequently occurs as cinnabar, which is the chief ore mineral of mercury (Environment Canada 2003). .
Mercury is very lethal and is considered a type of neurotoxin (Koren 1991). A neurotoxin is a poison that attacks nerve cells (Cunningham et al., 2003). Continual exposure to high amounts of mercury can cause extensive permanent damage to both the brain and kidneys, and ultimately ending in death (Koren 1991).