ELECTRONIC SUPPLEMENTARY INFORMATION
IN SITU EXPERIMENTS FOR ELEMENT SPECIES-SPECIFIC ENVIRONMENTAL REACTIVITY OF TIN AND MERCURY COMPOUNDS USING ISOTOPIC TRACERS AND MULTIPLE LINEAR REGRESSION
Pablo Rodriguez-Gonzalez, Sylvain Bouchet, Mathilde Monperrus, Emmanuel Tessier and David Amouroux.
Sampling Sites
Site description of the Adour Estuary (coastal plume).
The Adour Estuary is located in the south-west of France and flows into the Gulf of Biscay (Atlantic Ocean). The estuarine waters are under anthropogenic pressure of the industrialized and urbanized downstream area (1, 2). The whole mixing zone of this estuary (0-25 km) presents a narrow channel exhibiting a width about 500 m to only 200 m at the mouth (2). This results in a very low residence time for both waters and particles entering the estuary, and therefore, a dominant transfer to the ocean during medium to high flow conditions (1). The water flow entering the estuary during the campaign was comprised between 400 m3 s-1 and 900 m3 s-1. Water samples were collected in the estuary of the river Adour (South France) during spring between 7th and 13th April 2007 during the campaign METADOUR2 aboard the French research vessel “Côte de la Manche” (CNRS/INSU). The surface waters were sampled in the Adour plume, in the deeper part of the shelf. Depth profiles of hydrological parameters for all samples were determined using a CTD probe, (Seabird SBE-25). The water column was stratified and influenced by the estuarine plume at low tide and by the ocean at high tide. The pH of the water samples employed for the incubation experiments was 8.36 ± 0.02 and the temperature was 13.5 ºC. The surface water employed for the incubation was saturated with oxygen and the salinity was 30.4 PSU. The concentration of suspended particulate matter was 4.6 mg/L and the particulate organic carbon was 9%.
FIGURE S.1. Map of the Adour Estuary indicating the Station in which the water samples were taken to perform the field incubations.
Site description of the Arcachon Bay (mesotidal lagoon)
The Arcachon Bay is a 156 km² mesotidal lagoon, subject to eutrophication, located on the French Atlantic coast (44°40′ N, 1°10′ W) (3, 4). The tide is semi-diurnal and the tidal amplitude varies from 1.1 m to 4.9 m. Surface water temperature fluctuates annually between 1 and 25°C, and surface water salinity between 22 and 32 PSU. The landward part of the bay is affected by river inputs and underground freshwater discharges. At low tide, large tidal flats (114 km², 70 Km2 covered by Zostera noltii meadows) are exposed to the atmosphere for several hours (15 h). The sampling station for sediment samples is located in the inner part of the lagoon, on a tidal mudflat free of macrophytes located off shore from the Port de Cassy (3, 4). Water and sediment samples were collected between September 2007 and January 2008, respectively, at high tide with a rubber boat and at low tide using in both case clean polypropylene containers (4). The sampling station for water samples is located in the subtidal part of the channel that receives the drainage waters of the tidal flats. The sampled areas are covered by cohesive silty-mudd material (15-50 µm, porosity ~ 0.8) and characterized by a high organic carbon (3.4 to 4.4 % dw) and sulphur content (1.5 to 2.0 % dw) (4). The water column is well mixed and largely influenced by exchanges with the intertidal sediments during tidal cycle and also by the terrestrial fresh water inputs. When sampled in October 2007, the water characteristics were: temperature 17.6 – 19.3 ºC, pH 7.8 ± 0.1, oxygenation 98 ± 4 %, salinity 31.3 – 32.1 PSU, suspended particles 11 ± 4 mg L-1.
FIGURE S.2. Map of the Arcachon Bay indicating the Stations in which the water and sediments samples were taken to perform the field incubations
Experimental Incubation procedure
FIGURE S.3. General scheme of the field incubation experiments.
Analytical procedure
All sample preparation procedures have been previously validated in our laboratory and details of the specific sample preparation protocols can be found in the literature for water (3, 5, 6) and sediment samples (7-9). Volatile mercury species were analyzed by cryotrapping GC-ICP-MS (10). Briefly, species-specific isotopically enriched tracers in combination with GC-ICP-MS were employed for quantification purposes by IDMS (Isotope dilution Mass Spectrometry). Typically, the instrumental precision obtained in a determination by species-specific IDMS of Sn and Hg species is ≤ 1% RSD (three GC-ICP-MS injections of the same sample) whereas the reproducibility of the methodology is normally ≤ 2-3% (three independent aliquots of the same sample). Details on the analytical characteristics of the methodologies employed in this work can be found elsewhere (3, 5-9). It is worth stressing that all samples analysed in this work have been injected in triplicate in the GC-ICP-MS system. Also for every different environmental condition studied in this work, a triplicate of incubation experiments was performed. The instrumental uncertainty was in all cases lower than the uncertainty of the whole incubation procedure.
Description of the incubation system
Mercury
Figure S.4 shows the different reaction pathways of the mercury compounds in the environment. In this work, we have not considered the transformation of Hg(0) to either MMHG (oxidative methylation) or Hg(II) (oxidation). As no isotopically enriched Hg(0) has been employed in this work to perform the field incubation experiments, it is not possible to calculate the transformation yield of each specific reactions involving Hg(0) transformation. Whenever possible a net reduction yield of the ionic mercury species was calculated after the measurements of the dissolved gaseous mercury produced or lost during the water incubation.
Figure S4. Reactivity model of the mercury species.
Equations S.1. and S.2 show the linear system of equations expressed in matrix notation followed in this work to quantify the molar fraction of the species after the incubation procedure. Due to the absence of additional isotopically enriched standards, the samples were first analyzed to calculate the isotope composition of the species and then, another aliquot of the sample was spiked with natural abundance standards to quantify the concentration of the species in the sample.
[S.1]
[S.2]
Tin
Figure S.5 shows the scheme of the butyltin compounds reactivity under real environmental conditions. As expected, all buthylation reactions were shown to be negligible under the conditions studied in this work, thus, they are shown as dotted arrows in the scheme of Figure S.5.
Figure S5. Reactivity model of the butyltin compounds.
Equation S.3., S.4 and S.5 and S.6 shows the linear systems of equations expressed in matrix notation to quantify the molar fractions of the butyltin compounds after the incubation procedure. In this case a spike solution containing a mixture of Sn(IV), mono-, di, and tributyltin enriched in the isotope 119Sn is used to quantify the concentration of the endogenous and exogenous butyltin compounds. In this way, a single analysis of the samples provides the direct calculation of the molar fractions.
[S.3]
[S.4]
[S.5]
[S.6]
Figure S6. Cryotrapping-GC-ICPMS chromatogram of a water sample collected in the sampling station of the Adour estuary. Dimethyl mercury was not observed in any of the collected samples (dimethyl mercury retention time was 130s).
Figure S7. Cryotrapping-GC-ICPMS chromatogram of a water sample collected in the sampling station of the Arcachon Bay. Dimethyl mercury was not observed in any of the collected samples (dimethyl mercury retention time was 130s).
1
Full data set of the field incubation experiments
Table S1 and Table S2 shows the full data set of the incubation experiments carried out to study the effect of the medium in which the isotopically enriched tracers are diluted and the concentration level for Hg and Sn, respectively. In addition, Tables S3, S4, S5 and S6 show the concentration of the exogenous and isotopically enriched added tracers of the incubation experiments of Figure 1 and Figure 2.
Table S1. Concentrations of endogenous and exogenous species, methylation and demethylation yields and half lives of Hg and MeHg in sediments under different spiking conditions. The uncertainty values correspond to 1s standard deviation of three independent incubation experiments.
Tracer in HCl (1%) / Tracer diluted in interstitial water / 10 fold concentrated Tracer in HCl (1%)t=0 / t=1 day / t=7 days / t=0 / t=1 day / t=7 days / t=0 / t=1 day / t=7 days
Endogenous Concentrations
MeHg (ng g-1) / 1.2 ± 0.2 / 1.0 ± 0.5 / 0.5 ± 0.1 / 1.3 ± 0.1 / 1.0 ± 0.3 / 1.0 ± 0.4 / 1.4 ± 0.3 / 2.0 ± 1.0 / 3.1 ± 0.8
Hg (II) (ng g-1) / 202.5 ± 10.4 / 194.7 ± 17.0 / 201.8 ± 11.6 / 232.6 ± 16.5 / 203.9 ± 7.3 / 241.4 ± 19.3 / 196.3 ± 18.6 / 194.1 ± 5.5 / 195.3 ± 5.6
Tracer Concentrations
A 201-MeHg (ng g-1) / 0.5 ± 0.2 / 0.1 ± 0.0 / 0.0 ± 0.0 / 0.6 ± 0.1 / 0.1 ± 0.0 / 0.0 ± 0.0 / 5.4 ± 0.9 / 2.4 ± 1.0 / 0.9 ± 0.4
B 201-Hg (II) (ng g-1) / 1.4 ± 0.6 / 1.7 ± 0.6 / 1.9 ± 0.4 / 0.1 ± 0.0 / 1.2 ± 0.1 / 2.0 ± 0.3 / 5.4 ± 2.7 / 6.8 ± 0.0 / 8.6 ± 0.4
C 199-MeHg (ng g-1) / 0.1 ± 0.0 / 0.7 ± 0.3 / 0.5 ± 0.1 / 0.1 ± 0.0 / 1.3 ± 0.3 / 0.8 ± 0.2 / 0.9 ± 0.4 / 12.0 ± 5.7 / 21.8 ± 6.4
D 199-Hg (II) (ng g-1) / 97.2 ± 19.2 / 90.5 ± 28.5 / 96.1 ± 19.6 / 105.6 ± 6.1 / 94.0 ± 10.4 / 108.6 ± 15.8 / 969.4 ± 227.9 / 844.2 ± 34.1 / 802.9 ± 10.0
Net Methylation Yield [C/(C+D)]*100 (%) / 0.1 ± 0.0 / 0.9 ± 0.5 / 0.5 ± 0.1 / 0.1 ± 0.0 / 1.4 ± 0.4 / 0.9 ± 0.2 / 0.1 ± 0.0 / 1.4 ± 0.6 / 2.8 ± 0.6
Net Demethylation Yield
100-[At/At=0]*100 (%) / ---- / 81.4 ± 6.5 / 97.3 ± 0.7 / ---- / 85.0 ± 4.3 / 96.4 ± 0.1 / ---- / 55.1 ± 19.1 / 83.8 ± 7.3
Oxidative Demethylation
[B/(A+B)]*100 (%) / 71.6 ± 15.2 / 93.8 ± 1.1 / 99.3 ± 0.3 / 12.2 ± 3.1 / 92.5 ± 2.3 / 98.9 ± 0.1 / 48.8 ± 14.3 / 74.3 ± 7.7 / 90.7 ± 4.1
Half Lives (d)
Hg (II) t=Ln2/k / ---- / 99 ± 62 / 1058 ± 183 / ---- / 55 ± 18 / 682 ± 231 / ---- / 57 ± 25 / 194 ± 53
MeHg t=Ln2/k / ---- / 0.4 ± 0.1 / 1.3 ± 0.1 / ---- / 0.4 ± 0.1 / 1.5 ± 0.0 / ---- / 1.0 ± 0.6 / 2.7 ± 0.7
Table S2. Concentrations of endogenous and exogenous species, debutylation yields and species-specific half lives of Sn in sediments under different spiking conditions. The uncertainty values correspond to 1s standard deviation of three independent incubation experiments.
Acid spike / Spike diluted in interstitial water / Acid spike (10 fold concentrated)t=0 / t=1 day / t=7 days / t=0 / t=1 day / t=7 days / t=0 / t=1 day / t=7 days
Endogenous Concentrations
TBT (ng g-1) / 1.44±0.09 / 1.60±0.23 / 1.68±0.07 / 1.76±0.11 / 1.56±0.08 / 2.11±0.86 / 0.00±0.00 / 0.01±0.01 / 0.46±0.79
DBT (ng g-1) / 1.57±0.12 / 1.69±0.32 / 1.55±0.06 / 1.94±0.30 / 1.61±0.14 / 2.02±0.20 / 0.00±0.00 / 0.00±0.00 / 0.00±0.00
MBT (ng g-1) / 5.75±0.42 / 5.89±0.14 / 5.55±0.28 / 5.26±0.48 / 4.92±0.31 / 5.06±0.44 / 17.03±3.18 / 13.03±0.37 / 11.10±2.85
Sn(IV) (ng g-1) / ± / ± / ± / ± / ± / ± / 559.71±65.68 / 570.17±98.46 / 706.75±94.63
Tracer Concentrations
A 117-TBT(ng g-1) / 11.72 ± 2.46 / 11.66±0.09 / 11.15±0.61 / 8.24±0.26 / 8.54±0.70 / 8.19±2.32 / 108.03±6.57 / 105.50±18.71 / 110.48±4.67
B 118-TBT (ng g-1) / 0.00±0.04 / 0.05±0.05 / -0.02±0.02 / -0.02±0.03 / -0.01±0.04 / 0.00±0.05 / 0.18±0.10 / 0.23±0.08 / 0.23±0.12
C 116-TBT (ng g-1) / ± / ± / ± / ± / ± / -0.01±0.07 / 0.17±0.12 / 0.39±0.28
D 117-DBT (ng g-1) / 0.12±0.02 / 0.09±0.04 / 0.30±0.06 / 0.08±0.02 / 0.09±0.05 / 0.41±0.19 / 1.15±0.15 / 0.62±0.13 / 3.67±0.09
E 118-DBT(ng g-1) / 11.85±2.39 / 11.86±0.10 / 11.36±0.57 / 10.31±0.18 / 10.46±0.74 / 10.30±2.66 / 119.3±5.5 / 105.06±17.45 / 111.40±0.73
F 116-DBT(ng g-1) / -0.01±0.07 / 0.01±0.09 / 0.02±0.05
G 117-MBT (ng g-1) / 0.01±0.08 / 0.11±0.01 / 0.07±0.04 / 0.10±0.01 / 0.08±0.03 / 0.15±0.12 / 1.18±0.49 / 0.94±0.47 / 1.32±0.72
H 118-MBT(ng g-1) / 0.23±0.16 / 0.20±0.02 / 0.48±0.05 / 0.64±0.18 / 0.69±0.06 / 0.90±0.20 / 7.67±1.46 / 6.05±0.88 / 8.24±0.62
I 116-MBT(ng g-1) / 0.05±0.07 / 0.04±0.06 / 0.07±0.03
J 117-Sn(IV) (ng g-1) / 3.24±2.99 / 3.45±1.12 / 2.27±1.37
K 118-Sn(IV) (ng g-1) / 2.74±2.91 / 0.29±0.50 / 1.73±4.88
L 116-Sn(IV) (ng g-1) / 103.35±9.64 / 102.93±7.45 / 104.43±7.73
Debutylation Yields
TBT to DBT [D/(A+D+G+J)]*100 / 1.02±0.31 / 0.72±0.34 / 2.58±0.55 / 0.91±0.24 / 1.01±0.56 / 4.70±1.85 / 1.02±0.16 / 0.57±0.12 / 3.13±0.07
TBT to MBT [G/(A+D+G+J)]*100 / 0.04±0.75 / 0.96±0.07 / 0.66±0.40 / 1.20±0.13 / 0.97±0.33 / 1.53±1.21 / 1.05±0.45 / 0.81±0.31 / 1.14±0.65
TBT to Sn (IV) [J/(A+D+G+J)]*100 / 2.89±2.66 / 3.07±0.54 / 1.67±1.55
DBT to MBT [H/(B+E+H+K)]*100 / 1.80±1.03 / 1.67±0.17 / 4.03±0.40 / 5.85±0.60 / 6.17±0.12 / 8.10±0.28 / 6.44±1.28 / 5.47±0.77 / 6.78±0.49
DBT to Sn (IV) [K/(B+E+H+K)]*100 / 2.29±2.36 / 0.23±0.40 / 1.32±3.91
Half Lives (d)
TBT to DBT t1/2=Ln2/K / 111±47 / 195±46 / 87±53 / 113±40 / 126±29 / 155±3
TBT to MBT t1/2= Ln2/K / 73±5 / 912±423 / 78±29 / 251±105 / 97±46 / 576±409
TBT to Sn (IV) t1/2= Ln2/K / 23±4 / 203±63
DBT to MBT t1/2= Ln2/K / 42±4 / 121±11 / 11±0 / 60±2 / 13±2 / 72±5
DBT to Sn (IV) t1/2= Ln2/K / 99 / 85
Table S3. Concentration of the mercury species in the sediment samples of Figure 1. The uncertainty values correspond to 1s standard deviation of three independent replicates.
September 2007 / October 2007 / January 2008Diurnal Cycle / 24 Hours dark / Diurnal Cycle / 24 Hours dark / Diurnal Cycle / 24 Hours dark
Endogenous Concentrations
MeHg (ng g-1) / 0.87±0.07 / 1.04±0.53 / 2.1±0.3 / 1.2±0.2 / 1.3±0.2 / 1.1±0.2
Hg (II) (ng g-1) / 241± 9 / 195±17 / 196±11 / 204±24 / 199±6 / 197±8
Tracer Concentrations
201-MeHg (ng g-1) / 0.19±0.04 / 0.10±0.03 / 1.23±0.19 / 0.86±0.11 / 1.4±0.4 / 1.1±0.2
201-Hg (II) (ng g-1) / 1.7±0.6 / 1.7±0.4 / 1.88±0.32 / 1.68±0.58 / 0.2±0.2 / 0.4±0.2
199-MeHg (ng g-1) / 0.23±0.06 / 0.73± 0.25 / 2.73±0.32 / 1.82±0.38 / 0.7±0.2 / 0.6±0.2
199-Hg (II) (ng g-1) / 91±2 / 91±28 / 245±5 / 242±19 / 223±5 / 221±8
Table S4. Concentration and transformation yield of the mercury species in the water samples of Figure 2. The uncertainty values correspond to 1s standard deviation of three independent incubation experiments.