Mercury in water sampled from the Pra and Ankobra rivers was more than 55 times the average level recorded in streams in the United States, a US Geological Survey (USGS) scientist told a symposium in Accra, The Ghanaian Chronicle reported on Thursday.
Dr Grace Armstrong presented the findings of a USGS baseline study at the Ambassador's Water Experts Programme symposium, organised by the US Embassy. Diplomatic Times also reported on the symposium, where US Chargé d'Affaires Rolf Olson pledged support for mercury monitoring in Ghana.
What the data show
The samples are not new. They were collected from October 8 to 10, 2024, at eight communities downstream of gold mining: Sanwoma, Bamianko-Dominase, Akango-Doale and Kukuavile on the Ankobra, and Shama, Atwereboanda, Daboase and Beposo on the Pra. The USGS published the data in April 2025, with Grace Armstrong and Sarah Janssen as authors, working with the Ghanaian NGO Hen Mpoano.
In the USGS data, total mercury in unfiltered river water ranged from about 432 to 665 nanograms per litre across the eight sites. The highest river-water and sediment readings were both at Bamianko-Dominase. The published data release does not state the US average used in the 55-times comparison.
Dr Armstrong said most of the mercury in the rivers was attached to suspended particles, the Chronicle reported. In the USGS data, filtered samples were roughly six to 13 times lower than unfiltered ones.
The Chronicle reported that sediment levels were between two and 25 times the US stream average.
Drinking water and food
All drinking water samples from pipes, boreholes and wells were below the US Environmental Protection Agency limit of two parts per billion, Dr Armstrong said. The highest, a piped sample at Akango-Doale, was about 0.67 parts per billion in the USGS data, slightly higher than that community's river-water sample but still below the limit.
Fish from some communities were below the EPA's fish consumption criterion, she said, but few fish were available and most came from two communities. The highest fish reading in the data was in a smoked tilapia from Kukuavile.
Mercury was also detected in cassava and cocoa samples, but there were too few to draw firm conclusions, according to the Chronicle.
Why it matters
The USGS says mercury is used in small-scale gold mining to separate gold and is then heated off, releasing it into the air, from where it can settle in rivers, soil and crops. In water it can build up in fish.
Dr Armstrong stressed that the work was a small baseline study that should not be used to draw broad conclusions about mercury across Ghana or as the sole basis for policy, the Chronicle reported. The USGS itself describes the sampling as a one-time snapshot.
She called for further research into atmospheric mercury, the movement of contaminated particles and mercury build-up in fish.