Fish and shellfish have a natural tendency to concentrate inorganic and organic toxins and pollutants in their bodies, including methylmercury, a highly toxic organic compound of mercury, polychlorinated biphenyls (PCBs), and microplastics. Species of fish that are high on the food chain, such as shark, swordfish, king mackerel, albacore tuna, and tilefish contain higher concentrations of these bioaccumulants. This is because bioaccumulants are stored in the muscle tissues of fish, and when a predatory fish eats another fish, it assumes the entire body burden of bioaccumulants in the consumed fish. Thus species that are high on the food chain amass body burdens of bioaccumulants that can be ten times higher than the species they consume. This process is called biomagnification.