Mercury concentrations in sampled water from Ghana's Pra and Ankobra rivers were more than 55 times the average recorded in streams in the United States, according to a baseline study by the US Geological Survey (USGS) presented at a US Embassy symposium in Accra, The Ghanaian Chronicle reported on 12 November 2026.
River sediments contained between two and 25 times the US stream average, and communities closer to active small-scale mining sites recorded higher concentrations, Dr Grace Armstrong of the USGS Mercury, Metals and Microplastic Research Laboratory told the Ambassador's Water Experts Programme symposium. She named Bamianko as one of the communities with the highest mercury levels in its sediments.
What was sampled
According to the USGS, samples were collected in October 2024 at eight communities downstream of gold mining on the Ankobra and Pra in the Western Region, in partnership with the Ghanaian NGO Hen Mpoano. The field team took surface water, community drinking water, sediment, fish, cassava and cocoa.
The samples were analysed at the USGS mercury laboratory in Madison, Wisconsin, and the underlying dataset has been published. The work was funded by the US Department of State and the USGS under the Embassy Science Fellows programme.
Drinking water below limits
Every drinking-water sample from pipes, boreholes and wells was below both the US Environmental Protection Agency limit of 2 parts per billion and the World Health Organization limit of 1 part per billion, Dr Armstrong said. Fish samples from some communities were also below the EPA fish-consumption criterion, but fish were scarce during sampling and most came from two communities, so they may not represent the wider area.
Mercury was detected in cassava and cocoa, but too few samples were taken to draw conclusions.
Much of the mercury in river water was attached to suspended particles: filtered samples showed concentrations more than 10 times lower than the matching unfiltered samples. Dr Armstrong said this mattered for how mercury travels downstream and into the sea, where it can be converted into toxic methylmercury that builds up in fish.
A snapshot, not a national measure
Dr Armstrong said artisanal and small-scale gold mining accounts for more than 35% of global atmospheric mercury emissions. She stressed that the assessment was a small-scale baseline and should not be used to draw broad conclusions about mercury across Ghana or as the sole basis for policy.
The USGS itself describes the samples as a "snapshot" (a one-time measurement at a few sites) intended to give the government baseline data for future monitoring.
The 55-times and two-to-25-times comparisons are as presented at the symposium and reported by The Ghanaian Chronicle; StatsGH has not yet seen a USGS report with the summary figures.
Sources: Dr Grace Armstrong, USGS, at the US Embassy Ambassador's Water Experts Programme symposium in Accra, as reported by The Ghanaian Chronicle; USGS, "Exploring how gold mining impacts mercury releases in Western Ghana"; USGS dataset, "Mercury Concentrations in Waters, Fish, Plants, and Sediments from Ghana, 2024".