As seen in Table and Figure , the poly(S-r-limonene) sorbent is fastest at neutral or nearneutral pH, with reduced rates of mercury uptake below or above pH 7. For example, within 5 minutes, 500 mg sorbent captured 95, 96, 94 and 90% of mercury from solutions at pH 3, 5, 9 and 11, respectively. In contrast, the sorbent removed 99% of the mercury in the same 5 minute period in the neutral sample under otherwise identical conditions. The pH might alter the mercury speciation, which could account for these differences in rates of mercury uptake. Note that for neutral and low pH the single reaction model fits the experimental data well, suggesting that the availability of sorption sites is not significantly affected by these pH values. This is also shown by Figure where there is no apparent flattening of the curves for cases A, B and C. This contrasts with the high pH cases where a two-reaction model with a competing reaction was required. For high pH, hydroxide might potentially break S-S bonds in the polysulfide which could hinder both the measured rate of mercury sorption in addition to the capacity of the sorbent, which is reflected in the flattening of the model curve in Figures and. Indeed prolonged exposure to high pH resulted in degradation of the polymer coating (see desorption experiments for additional discussion of this observation).