The organisation gave the warning in a statement signed by the WHO Nigeria Officer-in-Charge, Dr Clement Peter.
WHO issued the statement following a one-day health sensitisation programme held in Minna to flag-off field assessments of ASGM activities in Nigeria.
Peter said that although ASGM was a key source of income generation for many in the affected states, it was also the main source of the largest release of mercury emissions around the world.
He listed the states to include Niger, Osun, Zamfara, Kebbi, Katsina, Kaduna, Kwara, Borno, Kaduna, Jigawa and Yobe as well as the Federal Capital Territory (FCT).
“In March 2019, the Federal Ministry of Health (FMoH) and WHO identified some communities in the 12 states mentioned earlier as having the highest risk of poisoning from mercury as a result of ASGM.
“In Niger state for instance, many women have complained that the waters in the community are contaminated with strange substances.
“Hajiya Khadija Balama, a Community Leader from Galadima, Shiroro Local Government Area of Niger state, said they have noticed that the water has some strange particles and have since reported to the authorities.
Balama said “the taste of our water has drastically changed, the colour seems darker and the texture is thicker than usual.
“We are scared that this water can cause diseases and affect our livestock if care is not taken.
“Unknown to Hajiya Balama and the women in her community, the particles they describe are residues of mercury, popularly used in mining activities in Shiroro LGA, a very popular ASGM town in the state.
“WHO is currently supporting FMoH to conduct the assessment in two states, namely, Niger and Osun in collaboration with the ministries of Environment, and Mines and Steel Development, Global Environment Facility (GEF), United Nations Industrial Development Organisation (UNIDO) and the Swiss Tropical Institute,” Peter said.
He said that in addition to the assessment in the two states, the organisation was also supporting the FMoH to build capacities of health workers on management of mercury poisoning and environmental health activities.
The WHO official said that these needed to be periodically carried out in order to monitor and reduce health risks of ASGM in the country.
Peter said that exposure to mercury posed very dangerous and toxic health effects on the nervous, digestive and immune systems, including sensitive organs such as the lungs, kidney, skin and eyes.
He said that it could also pose serious health threats to unborn babies and children under the age of five.
The WHO officer-in-charge assured that the organisation would continue to play its role of providing technical guidance to Nigeria on safe management of chemicals of public health importance.
He also assured that WHO would strengthen the capacity of the FMoH in the implementation of the provisions of the Minimata Conventions on Mercury.