Krill oil comes from a marine animal that is similar to shrimp known as krill. It does not occurring naturally in any other food source; however, it is concentrated and sold as a dietary supplement for its health benefits. It might be dangerous in high doses due to an accumulation of toxins such as methylmercury. Additionally, a high concentration of pesticides has been discovered in krill harvested in Antarctica. Krill oil is also dangerous for individuals with a shellfish allergy.
Krill have been harvested as food for human consumption for hundreds of years but they have only recently been harvested for their oil. Krill oil is used in much the same way as omega-3 fatty acids from fish. Because krill are lower on the food chain than the fish that are harvested for omega-3 fatty acids, they contain a smaller accumulation of harmful toxins. There is some ethical controversy about harvesting krill for krill oil because they are a food source for many marine animals such as whales, seals and penguins. To avoid consuming a potentially harmful dose of the contaminants that can be found in krill oil supplements, consumers should not take more than the recommended dose as listed on the supplement container.