AbstractEquilibrium sorption of tributyltin chloride (TBT) was measured on selected estuarine and freshwater sediments. Isotherms from 24‐h equilibrations were linear, with sorption coefficients between 1.1 × 102 and 8.2 × 103 L/kg. The similarity of sorption and desorption coefficients for these sorbates showed that TBT sorption is reversible. Sorption coefficients decreased with increasing salinity and varied by a factor of 2 over the salinity range 0 to 34%. Desorption kinetics indicated an initial fast rate followed by a slower rate of desorption, similar to published data for metal ions and hydrophobic organic molecules on sediments. Water and sediment concentrations of TBT at locations in the Chesapeake Bay system were used to calculate apparent sorption coefficients, which generally agreed with laboratory‐measured sorption coefficients. Exceptionally high apparent sorption coefficients were found near areas of high vessel activity and may be due to TBT paint chips in the sediment.