Dissolved Organic Carbon Thresholds Affect Mercury Bioaccumulation in Arctic Lakes

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• 作者：Todd D. French ; Adam J. Houben ; Jean-Pierre W. Desforges ; Linda E. Kimpe ; Steven V. Kokelj ; Alexandre J. Poulain ; John P. Smol ; Xiaowa Wang ; Jules M. Blais
• 刊名：Environmental Science & Technology
• 出版年：2014
• 出版时间：March 18, 2014
• 年：2014
• 卷：48
• 期：6
• 页码：3162-3168
• 全文大小：440K
• 年卷期：v.48,no.6(March 18, 2014)
• ISSN：1520-5851

文摘

Dissolved organic carbon (DOC) is known to affect the Hg cycle in aquatic environments due to its overriding influence on complexation, photochemical, and microbial processes, but its role as a mediating factor in the bioaccumulation of Hg in aquatic biota has remained enigmatic. Here, we examined 26 tundra lakes in Canada鈥檚 western Arctic that span a large gradient of DOC concentrations to show that total Hg (Hg_T) and methyl mercury (MeHg) accumulation by aquatic invertebrates is defined by a threshold response to Hg-DOC binding. Our results showed that DOC promotes Hg_T and MeHg bioaccumulation in tundra lakes having low DOC (<8.6 鈥?8.8 mg C L^鈥?; DOC threshold concentration, T_C) whereas DOC inhibits Hg_T and MeHg bioaccumulation in lakes having high DOC (>DOC T_C), consistent with bioaccumulation results in a companion paper (this issue) using a microbial bioreporter. Chemical equilibrium modeling showed that Hg bioaccumulation factors were elevated when Hg was associated mainly to fulvic acids, but became dramatically reduced when DOC was >8.5 mg C L^鈥?, at which point Hg was associated primarily with strong binding sites on larger, less bioaccessible humic acids. This study demonstrates that the biological uptake of Hg in lakes is determined by binding thresholds on DOC, a water quality variable predicted to change markedly with future environmental change.