Legacy pollution

Legacy pollution or legacy pollutants are persistent materials in the environment that were created through a polluting industry or process that have polluting effects after the process has finished. Frequently these include persistent organic pollutants, heavy metals or other chemicals residual in the environment long after the industrial or extraction processes that produced them. Often these are chemicals produced by industry and polluted before there was widespread awareness of the toxic effects of the pollutants, and subsequently regulated or banned. Notable legacy pollutants include mercury, PCBs, Dioxins and other chemicals that are widespread health and environmental effects. Sites for legacy pollutants include mining sites, industrial parks, waterways contaminated by industry, and other dump sites.

These chemicals often have outsized impact in countries jurisdictions with little or no environmental monitoring or regulation—because the chemical were often produced in new jurisdictions after they were banned in more heavily regulated jurisdictions. Often in these countries, there is a lack of capacity in environmental regulatory, health and civic infrastructure to address the impact of the pollutants.

The impact of legacy pollutants can be visible many years after the initial polluting process, and require environmental remediation. Grassroots communities and environmental defenders frequently advocate for responsibility of industry and states through environmental justice action and advocacy for recognition of human rights, such as the right to a healthy environment.

Brownfield is previously developed land that has been abandoned or underused, and which may carry pollution, or a risk of pollution, from industrial use. The specific definition of brownfield land varies and is decided by policy makers and land developers within different countries. The main difference in definitions of whether a piece of land is considered a brownfield or not depends on the presence or absence of pollution. Overall, brownfield land is a site previously developed for industrial or commercial purposes and thus requires further development before reuse.

In mining, tailings or tails are the materials left over after the process of separating the valuable fraction from the uneconomic fraction (gangue) of an ore. Tailings are different from overburden, which is the waste rock or other material that overlies an ore or mineral body and is displaced during mining without being processed. Waste valorization is the evaluation of waste and residues from an economic process in order to determine their value in reuse or recycling, as what was gangue at the time of separation may increase with time or more sophisticated recovery processes.

An abandoned mine refers to a former mining or quarrying operation that is no longer in use and has no responsible entity to finance the cost of remediation and/or restoration of the mine feature or site. Such mines are typically left unattended and may pose safety hazards or cause environmental damage without proper maintenance. The term incorporates all types of old mines, including underground shaft mines and drift mines, and surface mines, including quarries and placer mining. Typically, the cost of addressing the mine's hazards is borne by the public/taxpayers/the government.

An abandoned mine may be a hazard to health, safety or environment.

Orphan, orphaned, or abandoned wells are oil or gas wells that have been abandoned by fossil fuel extraction industries. These wells may have been deactivated due to becoming uneconomic, failure to transfer ownerships (especially at bankruptcy of companies), or neglect, and thus no longer have legal owners responsible for their care. Decommissioning wells effectively can be expensive, costing several thousands of dollars for a shallow land well to millions of dollars for an offshore one. Thus the burden may fall on government agencies or surface landowners when a business entity can no longer be held responsible.