pH affects mercury distribution, not methylation

Changing values of the pH in natural sediment-water systems did not affect the total amount of methylmercury generated in the sediments. However, partition of methylmercury between water and sediment did change, the amount of methylmercury in the water column doubling for a decrease in pH of 1.0 (sand) to 2.0 (organic sediment) units. This change is enough to explain, quantitatively, the observed elevations in mercury levels in fish taken from lakes of low pH.