Quantification of Mercury Bioavailability for Methylation Using

Overview

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Key numbers

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• sometimes correlated with the 0.2 μm filter passing Hg fraction and the GSH-extractable Hg fraction. These results suggest for
• bioavailability in microcosms while controlling for the isotopic compositions of all Hg stocks are shown in Table S1.
• by three approaches: (1) cumulative uptake of Hg into the pyruvate as a means to stimulate the methylating microbial
• GSH-extractable fraction of Hg in the slurry at each time dark for 4 days. An additional replicate slurry with a resazurin
• point.17 Microbial community abundance and diversity, indicator (0.001%) changed from dark pink to colorless over
• the range of 50−200 ng g−1 d.w. (the amount of each isotope Hg mass from each isotope spike (and normalized to total Hg
• end once per day. Replicate jars (n = 3 or 4) were sacrificed isotopic composition of individual Hg endmembers as input
• frozen for later analysis of MeHg, total Hg contents, the GSH- Greengenes 13_8 reference database at 97% sequence
• centrifugation (<1150 RCF for 5 min) and passed through a slurry (Figure 1), where the %MeHg values were calculated
• 0.22 μm polyethersulfone filter. The GSH-extractable Hg for from MeHg and total Hg values measured in the slurries
• in replicate slurries with no GSH added. The GSH-extractable endmembers (204Hg2+, 196Hg-humic) and lower for the initially
• In both mesohaline and freshwater slurries, the percentage of Hg-humic isotope spikes (0.05 to 0.2%) than the particulate
• the native Hg as MeHg was lower than the Hg isotope spikes, Hg-FeS and 200HgS isotope endmembers (0.01 to 0.04%)
• MeHg during the 4 day preincubation step prior to Hg isotope GSH-extractable Hg content was similar for each isotope
• the GSH-extractable fraction, as determined by selective extraction with 1 mM glutathione (GSH). Each time point represents the average of 4 and
• dissolved Hg endmembers (2−4%) than the particulate Hg Rather, uptake into the sampler depends on the reactivity of
• endmembers (1−2%). Hg in the slurry (including Hg bound to solid phases) for
• Hence for deposition of 200Hg from nano-200HgS to occur in slurries, correlations between the %MeHg and %Hg accumu-
• to solid phases immediately after addition to the slurry. R2 values were <0.1 in plots of %MeHg versus filtered Hg in
• The relationships between %MeHg and the GSH-extractable isotopes were added and decreased to approximately 350 mg
• previous study17 proposing the GSH-extractable Hg fraction as mesohaline experiment and increasing in concentration (from
• previous report by Ticknor et al.17) is that the %MeHg values and 5.3 (±0.2) in mesohaline and freshwater slurries,
• of the experiment (Figure S6). The dominant microbial classes filtered porewater Hg and GSH-extractable Hg were observed
• ∼20%; freshwater (F) ∼10%), Alpha- (M 5%; F ∼10%) and rates were approximately 10 times faster for the freshwater
• Gammaproteobacteria (M ∼10%; F ∼25%), unclassified (M than for the mesohaline experiment even though Hg
• ∼20%; F <10%), and environmental (M <5%; F ∼15%) bioavailability (as indicated by DGTs) was similar in both
• bacteria, and Actinobacteria (M/F ∼10%). For the major slurries. This difference in methylation rates was not explained
• groups of Hg-methylators, Clostridia spp. constituted ∼1% in by the genomic sequencing and hgcA gene abundance data.
• both environments, while the Methanomicrobia (M ∼2%; F Further work in assessing the activity of the methylating
• ∼0.1%) and Deltaproteobacteria (M ∼0.1%; F ∼1%) showed community is needed.
• stituted at most ∼2.5−4.5% (mesohaline) and 1−2% (fresh- methylation than the other measures of bioavailability (i.e.,
• methylators in the samples, the mesohaline had more potential tration over 5 days (Δ(SO42−) ∼ −150 mg/L or −1.6 mM).
• (38) Hintelmann, H.; Ogrinc, N. Determination of Stable Mercury

Methods (brief)

• Diffusive Gradient in Thin-Film Samplers
• passive samplers to a thiol-based selective extraction method with
• methylating community. Regardless, these methods are ex Each DGT sampler entailed a 25 mm circular plastic housing
• situ applications that are susceptible to changes in sample (DGT Research Ltd., Lancaster, UK) layered with a 0.45 μm
• and storage, a potential problem for samples originating from binding layer of thiolated silica beads supported on a
• Passive samplers such as diffusive gradients in thin films Sediment and surface water samples from two different
• agarose) layered over a chelating resin.32 The high affinity of collected on 30th September 2015, were stored at 4 °C, and
• diffusion gel that drives the time dependent mass uptake of made from these samples were designated the “mesohaline”
• bioavailability of Hg(II) and MeHg to aquatic macro- collected by hand from the edge of this pond and were used for
• invertebrates.28,29 These samplers might also provide informa- the “freshwater” slurry microcosms within 2 days of collection
• DGT sampler; (2) quantification of the 0.2 μm filter passing community in these slurries. The slurries were sealed with
• sampler was added to each jar, and the jars were stored under Hg endmember was calculated via matrix deconvolution on a
• the anaerobic chamber. Porewater was collected by filtering 15 Illumina Miseq 2 × 300 bp system (Illumina, San Diego, CA)
• sulfone) filter (VWR). This filtered sample was apportioned GCCGCGGTAA) and Lee926R (CCGYCAATTYMTTTRA-
• into samples designated for total Hg analysis, major cations GTTT).40,41 Sequences were joined, depleted of barcodes, and
• aliquots of the unfiltered slurry were immediately collected and method45 in QIIME. Sequences were queried against the
• contents were quantified by cold vapor inductively coupled by TA cloning (Thermo Fisher Scientific) and sequencing
• plasma mass spectrometry (ICP-MS). Other cations were (Eurofins Genomics, Louisville, KY) with the degenerate

Implications

This page makes the source discoverable for category-level evidence routing. Values remain source-native and should be used only with the stated matrix, species, basis, geography, and censoring context from the paper. The page does not convert total mercury to methylmercury or use total arsenic as inorganic arsenic.

Wiki pages this source may touch

• Fish — marine, non-predatory (sardines, anchovies, salmon, cod)
• Shellfish (shrimp, crab, lobster, clams, oysters, mussels)
• Mercury
• Mercury

Verification notes

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Update history

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