1,3-butadiene is a gas made from petroleum and is used to manufacture materials like synthetic rubber and plastics. Because it is a gas, 1,3-butadiene can easily leak out of production, storage, or disposal containers and enter the air. People who work in or live near facilities using 1,3-butadiene are most at risk of inhaling it, but even people in heavily polluted cities breathe air with 1,3-butadiene in it. Exposure to 1,3-butadiene can cause cardiovascular, neurological, lung, and blood defects. It is also suspected to cause birth defects and decreased birth weight. The Environmental Protection Agency, Department of Health and Human Services, and International Agency for Research on Cancer have all determined that 1,3-butadiene causes cancer. Studies of people who worked in facilities using 1,3-butadiene found that they had increased incidence of blood and immune system cancers compared to the general population.