Toxic wastes often contain carcinogens, and exposure to these by some route, such as leakage or evaporation from the storage, causes cancer to appear at increased frequency in exposed individuals. For example, a cluster of the rare blood cancer polycythemia vera was found around a toxic waste dump site in northeast Pennsylvania in 2008.The Human & Ecological Risk Assessment Journal conducted a study which focused on the health of individuals living near municipal landfills to see if it would be as harmful as living near hazardous landfills. They conducted a 7-year study that specifically tested for 18 types of cancers to see if the participants had higher rates than those that don’t live around landfills. They conducted this study in western Massachusetts within a 1-mile radius of the North Hampton Regional Landfill.People encounter these toxins buried in the ground, in stream runoff, in groundwater that supplies drinking water, or in floodwaters, as happened after Hurricane Katrina. Some toxins, such as mercury, persist in the environment and accumulate. As a result of the bioaccumulation of mercury in both freshwater and marine ecosystems, predatory fish are a significant source of mercury in human and animal diets.