Importance of dissolved neutral mercury sulfides for methyl mercury production in contaminated sediments

被引:172
作者
Drott, Andreas
Lambertsson, Lars
Bjorn, Erik
Skyllberg, Ulf [1 ]
机构
[1] Swedish Univ Agr Sci, Dept Forest Ecol, S-90183 Umea, Sweden
[2] Umea Univ, Dept Chem, S-90187 Umea, Sweden
关键词
D O I
10.1021/es061724z
中图分类号
X [环境科学、安全科学];
学科分类号
08 ; 0830 ;
摘要
Biotic transformation of inorganic mercury, Hg(II), to mono methyl mercury (MeHg) is proposed to be largely controlled by passive uptake of neutral Hg complexes by sulfate reducing bacteria (SRB). In this study, the chemical speciation of Hg(II) in seven locally contaminated sediments covering environments such as (i) brackish water, (ii) low-productivity freshwater, and, (iii) high-productivity freshwater was related to potential Hg methylation rates, determined by incubation at 23 degrees C for 48 h under N-2(g), and to total MeHg concentrations in sediments. Pore water speciation was modeled considering Hg complexes with halides, organic thiols [Hg(SR)(2)(aq), associated to dissolved organic matter], monosulfides, and bisulfides. The sum of neutral mercury sulfides [Hg(SH)(2)(0)(aq)] and [HgS0(aq)] was significantly, positively (p < 0.001, n = 20) correlated to the specific methylation rate constant (K-m, day(-1)) at depths of 5-100 cm in two brackish water sediments. Total Hg, total mercury sulfides or Hg(SR)(2)(aq) in pore water gave no significant relationships with K-m. In two sub-sets of freshwater sediments, neutral mercury sulfides were positively correlated to total Hg in pore water, and therefore, total Hg also gave significant relationships with K-m. The sum of [Hg(SH)(2)(0)(aq)] and [HgS0(aq)] was significantly, positively correlated to total sediment MeHg (mu g kg(-1)) in brackish waters (p < 0.001, n = 23), in southern, high-productivity freshwaters (p < 0.001, n = 20), as well as in northern, low-productivity freshwater (p = 0.048, n = 6). The slopes (b, b') of the relationships K-m (day(-1)) = a + b([Hg(SH)(2)(0)(aq)] + [HgS0(aq)]) and MeHg (mu g kg(-1)) = a' + b'([Hg(SH)(2)(0)(aq)] + [HgS0(aq)]) showed an inverse relationship with the C/N ratio, supposedly reflecting differences in primary production and energy-rich organic matter availability among sites. We conclude that concentrations of neutral inorganic mercury sulfide species, together with the availability of energy-rich organic matter, largely control Hg methylation rates in contaminated sediments. Furthermore, Hg(SH)(2)(0)(aq) is suggested to be the dominant species taken up by MeHg producing bacteria in organic-rich sediments without formation of HgS(s).
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页码:2270 / 2276
页数:7
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