The present guidelines provide guidance for the environmentally sound management (ESM) of wastes consisting of elemental mercury and wastes containing or contaminated with mercury. Mercury emissions and releases can be human-caused (anthropogenic) and may also come from natural sources. Once mercury is released into the environment, it persists in the atmosphere (mercury vapour), soil (ionic mercury) and aquatic phase (methylmercury (MeHg, or CH3Hg+)). Some mercury in the environment ends up in the food chain because of bioaccumulation and biomagnification and is eventually ingested by humans.