A byproduct from incomplete burning of an carbon-based material, such as in industrial processes, vehicle emissions, wood fires, and also cigarette smoke. It can contaminate drinking water due to the leaching from linings of water storage tanks and distribution lines, and to harmful emissions in the air. If ingested in high doses, it can cause harmful changes to the nervous system, reproductive organs and kidneys. It has been suggested that low level, long-term exposure increases the risk for developing cancer.