The titration curve results for the three rates of AGN 205327 addition essayed are presented in Fig. 1a, where the pH of the water–soil mixture and the percentage of Pb dissolved are plotted against the moles of acid added. The lowest rate is 35 (mmol of acid) (kgsoil)–1 h–1, increasing to 2.5- and 10-fold that value in the other two experiments. The total amount of nitric or acetic added by the end of the experiment is 5 (mol of acid) (kgsoil)–1 so the experiment with a slower rate takes about 6 days while the faster one takes 14 h. These flow rates are denominated as acid flow ratios (AFRs) referenced to the lowest rate. The reproducibility of the experiments was assessed by triplicate assays for the highest value of the acid addition rate (AFR = 10); the error bars presented in Fig. 1a represent two standard deviations of these triplicates. For the pH, we have chosen the representation of the maximum and minimum values of the triplicates. The mass balance for lead was in all cases between 88% and 109%.