Sediment and soil incubations. Preparations. Prior to transferring the 13 C-PEG solutions (t0 to t3) into the incubation bottles, residual H2O2 from the solutions was removed by adding 0.05 mL of catalase from bovine liver (Sigma Aldrich, aqueous suspension, 1 • 10 4 to 4 • 10 4 units mg -1 protein, 0.44 mg protein mL -1 ) to the 7 mL PEG solution, followed by gentle stirring for 10 minutes. The same amount of catalase in 7 mL of H2O2 solution without C-PEG, was added to the background incubations, to account for any effects on the background mineralization.