Binding Strength of Methylmercury to Aquatic NOM

作者：Khwaja Abdul R; Bloom Paul R; Brezonik Patrick L^*

来源：Environmental Science & Technology, 2010, 44(16): 6151-6156.

DOI：10.1021/es101088k

A competitive-ligand, equilibrium-dialysis technique using bromide measured methylmercury (MeHg(+)) binding to Suwannee River fulvic acid (SRFA) and NOM from a lake and a bog in Minnesota Distribution coefficients (K(OC)) and stability constants (K') varied only slightly over a range of [Br(-)] and ratios of MeHg(+) to reduced sulfur, S(re), the putative NOM binding site For SRFA at pH 3 0, K(OC) ranged from 10(7 7) to 10(8 2) and K' ranged from 10(15 5) to 10(16) (0) over MeHg(+) S(re) ratios from 1.1220 to 1:12 200 (well below S(re) saturation). The importance of pH depends on the calculation model for binding constants Over pH 2 98-7 62, K(OC) had little pH dependence (slope = 0 2, r(2) = 0 4; range 10(7) (7)-10(9 1)), but K' calculated using thiol ligands with pK(a) = 9.96 had an inverse relationship (slope = -0.8, r(2) = 0 9, range 10(15 6)-10(12 3)) A pH-independent model was obtained only with thiol pK(a) <= similar to 4. The mean K'(4) for SRFA (K' with thiol pK(a) = 4 2) was 10(9 8) (range 10(9 11)-10(10 27)) and small slope (0.02) Similar values were found for Spring Lake NOM, bog S2 NOM had values one-tenth as large. These constants are generally similar to published values; differences reflect variations in methods, pH, types of NOM, and calculation models.

• 出版日期2010-8-15