Photochemical reactions between mercury (Hg) and dissolved organic matter decrease Hg bioavailability and methylation.
Atmospheric deposition of mercury (Hg) to surface water is one of the dominant sources of Hg in aquatic environments and ultimately drives methylmercury (MeHg) toxin accumulation in fish. It is known that freshly deposited Hg is more readily methylated by microorganisms than aged or preexisting Hg; however the underlying mechanism of this process is unclear. We report that Hg bioavailability is decreased by photochemical reactions between Hg and dissolved organic matter (DOM) in water. Photo-irradiation of Hg-DOM complexes results in loss of Sn(II)-reducible (i.e. reactive) Hg and up to an 80% decrease in MeHg production by the methylating bacterium Geobacter sulfurreducens PCA. Loss of reactive Hg proceeded at a faster rate with a decrease in the Hg to DOM ratio and is attributed to the possible formation of mercury sulfide (HgS). These results suggest a new pathway of abiotic photochemical formation of HgS in surface water and provide a mechanism whereby freshly deposited Hg is readily methylated but, over time, progressively becomes less available for microbial uptake and methylation.
Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA; Department of Chemistry, University of Science and Technology of China, Hefei, 230026, China.
Hong-Wei
HW
Luo
Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
Xiangping
X
Yin
Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
Aaron M
AM
Jubb
Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
Hongmei
H
Chen
Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
Xia
X
Lu
Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA; School of Environmental Science and Engineering, Sun Yat-Sen University, Guangzhou, 510006, China.
Weihua
W
Zhang
Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
Hui
H
Lin
Department of Chemistry, University of Science and Technology of China, Hefei, 230026, China.
Han-Qing
HQ
Yu
Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA; Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA, 99352, USA.
Liyuan
L
Liang
Department of Chemistry, University of Science and Technology of China, Hefei, 230026, China.
Guo-Ping
GP
Sheng
Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA. Electronic address: gub1@ornl.gov.
Baohua
B
Gu
D001419:Bacteria / Q000378:metabolism*; D001682:Biological Availability; D008628:Mercury / Q000032:analysis* / Q000737:chemistry / Q000378:metabolism; D008745:Methylation; D008767:Methylmercury Compounds / Q000032:analysis* / Q000737:chemistry / Q000378:metabolism; D055668:Photochemical Processes; D014867:Water / Q000737:chemistry; D014871:Water Microbiology; D014874:Water Pollutants, Chemical / Q000032:analysis* / Q000737:chemistry / Q000378:metabolism
D008767:Methylmercury Compounds; D014874:Water Pollutants, Chemical; D014867:Water; D008628:Mercury
Biogeochemical transformation; Dissolved organic matter; Hg-DOM photolysis; HgS precipitation; Methylmercury