Wildlife—and humans—are exposed to toxins via air, water, land, and food. People are responsible for introducing many types of toxins into the environment through industrial emissions, pesticides, medications, fertilizers, oil spills, sewage, garbage, and even lead bullets. The effects of toxins on wildlife can be difficult to ascertain and, usually, harder to remedy. Once toxins enter the environment, they accumulate in the food chain, affecting all levels of the ecosystem. Understanding the intricacies of these systems and the effects of these contaminants often requires extensive scientific research, and many years and conservation dollars to reverse.