Olivier Clarisse

Measurements of dissolved methylmercury in natural waters using diffusive gradients in thin film (DGT)

A diffusive gradient in thin films (DGT) technique for measuring methylmercury (MeHg) concentrations in natural waters was developed using 3-mercaptopropyl-functionalized silica gel to preconcentrate the methylmercury. The new resin was characterized and calibrated. Methylmercury is efficiently accumulated at a pH range of 3-9. Basic performance tests of the new DGT device confirmed the applicability of Ficks first law for such DGT measurements. The diffusion coefficient of methylmercury in polyacrylamide gel was 5 x 10(-6) cm(2) s(-1). Methylmercury concentrations determined by DGT deployed for different time periods in the field are statistically not different from results obtained through direct measurements. The DGT technique represents therefore an alternative in situ sampling method for methylmercury. The detection limit of the overall method is 1 pg of MeHg, which correspond to approximately 30 pg L(-1) of MeHg in a water sample, when deploying a typical DGT device for 24 hours. Lower MeHg concentrations are measurable using longer deployment times or thinner diffusive gel layers.

Deposition of Mercury Species in the Ny-Ålesund Area (79°N) and Their Transfer during Snowmelt

Arctic snowpacks are often considered as temporary reservoirs for atmospheric mercury (Hg) deposited during springtime deposition events (AMDEs). The fate of deposited species is of utmost importance because melt leads to the transfer of contaminants to snowmelt-fed ecosystems. Here, we examined the deposition, fate, and transfer of mercury species (total Hg (THg) and methylmercury (MeHg)) in an arctic environment from the beginning of mass deposition of Hg during AMDEs to the full melt of the snow. Following these events, important amounts of THg were deposited onto the snow surface with concentrations reaching 373 ng.L(-1) and estimated deposition fluxes of 200-2160 ng.m(-2). Most of the deposited Hg was re-emitted to the atmosphere via photochemical reactions. However, a fraction remained stored in the snow and we estimated that the spring melt contributed to an input of 1.5-3.6 kg.year(-1) of THg to the fjord (i.e., 8-21% of the fjords THg content). A monitoring of MeHg in snow using a new technique (DGT sensors) is also presented.

Methylmercury speciation in the dissolved phase of a stratified lake using the diffusive gradient in thin film technique.

The diffusive gradient in thin film (DGT) technique was successfully used to monitor methylmercury (MeHg) speciation in the dissolved phase of a stratified boreal lake, Lake 658 of the Experimental Lakes Area (ELA) in Ontario, Canada. Water samples were conventionally analysed for MeHg, sulfides, and dissolved organic matter (DOM). MeHg accumulated by DGT devices was compared to MeHg concentration measured conventionally in water samples to establish MeHg speciation. In the epilimnion, MeHg was almost entirely bound to DOM. In the top of the hypolimnion an additional labile fraction was identified, and at the bottom of the lake a significant fraction of MeHg was potentially associated to colloidal material. As part of the METAALICUS project, isotope enriched inorganic mercury was applied to Lake 658 and its watershed for several years to establish the relationship between atmospheric Hg deposition and Hg in fish. Little or no difference in MeHg speciation in the dissolved phase was detected between ambient and spike MeHg.

Biomonitoring and assessment of monomethylmercury exposure in aqueous systems using the DGT technique

A series of laboratory experiments was conducted under realistic environmental conditions to test the ability of the Diffusive Gradient in Thin film (DGT) technique to mimic monomethylmercury (MMHg) bioaccumulation by a clam (Macoma balthica, Baltic clam). Using isotope enriched MMHg as tracers, bioavailability was determined by comparing the rate of MMHg uptake by novel DGT devices and sentinel organism over time. Experiments were conducted under varying conditions of salinity and MMHg speciation. Depending on MMHg level and speciation in the dissolved phase, MMHg uptake rates by the sentinel organism varied greatly from 0.4 to 2.4Lg(-1)d(-1). Reproducibilities of MMHg uptakes by DGT and clams were estimated at 7 and 38%, respectively. A significant linear relationship (log basis) between MMHg accumulation by DGT and clams was observed (r(2)=0.89). The study demonstrates that DGT results reasonably predict MMHg uptake by clams from the aqueous phase and provide the basis for application of the DGT device as a surrogate for sentinel organism for monitoring bioavailable MMHg.

Predicting Net Mercury Methylation in Sediments Using Diffusive Gradient in Thin Films Measurements

Diffusive gradient in thin film (DGT) sediment probes for methylmercury (MMHg) were successfully deployed for up to 30 h in three mudflat sediments in San Francisco Bay for measuring labile fractions of dissolved MMHg in pore water. Our calculations show that the local DGT-induced depletion of MMHg in sediment pore waters should be fully compensated by the natural in situ MMHg production and its subsequent remobilization from the solid phase. DGT results were interpreted in terms of labile pore water concentration and provide MMHg concentration depth profiles with a centimeter resolution. Average concentrations of DGT-labile MMHg were 2.10 ± 0.29 and 1.64 ± 0.30 ng L(-1) at China Camp and Hamilton Army Airfield sediment pore waters, respectively, while the riverine location at Petaluma showed a distinct peak of 7.1 ng L(-1) near the sediment surface. Using isotope-enriched mercury species, high resolution depth profiles of MMHg net production rates ranging from 0.2 to 9.8 ng g(-1) d(-1) were obtained in parallel sediment cores sampled closely to DGT deployment sites. A positive, linear relationship between MMHg net production rates and labile MMHg concentrations acquired through DGT measurements was found and explained 79% of the variability in the data set. The latter illustrates that mercury methylation, a biogeochemical process, strongly affected the quantity of MMHg accumulated by the DGT device in the sediment and suggests that DGT measurements have the potential to predict net methylation rates.

Quantification of 226Ra at environmental relevant levels in natural waters by ICP-MS: Optimization, validation and limitations of an extraction and preconcentration approach

Radium (Ra) at environmental relevant levels in natural waters was determined by ICP-MS after an off-line pre-concentration procedure. The latter consisted of Ra selective elution from potential interfering elements (i.e. other alkaline earth cations: Ba2+, Sr2+, Ca2+, Mg2+) on a series of two different ion exchange resins (AG50W-X8 and Sr-resin). The overall analytical method was optimized according to the instrumental performance, the volume of water sample loaded on resins, and the sample salinity. Longer acquisition time (up to 150 s) was required to ensure stable measurement of Ra by ICP-MS at ultra trace level (1.0pgL-1). For a synthetic groundwater spiked with Ra at 10.0pgL-1, the analytical procedure demonstrated efficient separation of the analyte from its potential interfering elements and a complete recovery, independent of the sample volume tested from 10 up to 100mL. For synthetic seawater spiked at a level of 10.0pgL-1 of Ra, the total load of salts on the two resins should not exceed 0.35g in order to ensure a complete separation and recovery of Ra. The method was validated on natural waters (i.e. groundwater, freshwater and seawater samples) spiked with Ra at different levels (0.0, 0.5, 1.0 and 5.0pgL-1). Absolute Ra detection limits were determined at 0.020pgL-1 (0.73mBqL-1) and 0.12pgL-1 (4.4mBqL-1) respectively for 60.0mL of freshwater sample and for 10.0mL of seawater.

Assessment of saliva, hair and toenails as biomarkers of low level exposure to manganese from drinking water in children

HighlightsMeasured Mn in drinking water, childrens saliva, hair and toenails.Mn concentrations in drinking water are very low.Mn in hair and toenail reflect reasonably well Mn exposure from drinking water.Mn in saliva correlates less strongly to Mn in drinking water. ABSTRACT We evaluated hair, toenails, and saliva (whole and supernatant) as biomarkers of exposure to manganese (Mn) in 274 school age children (6–13 years) consuming well water in southeastern New Brunswick, Canada. Mn concentrations in tap water ranged from <0.03 to 1046 &mgr;g L−1 (geometric mean 5.96 &mgr;g L−1). The geometric mean of Mn intake resulting from the consumption of water was 0.25 (0–34.95) &mgr;g kg−1 day−1. Both Mn concentration in water and Mn intake were significantly correlated with Mn in hair (r = 0.60 and r = 0.53, respectively), Mn in toenail (r = 0.29 and r = 0.37 respectively) and to a lesser extent with Mn in saliva supernatant (r = 0.14 and r = 0.18, respectively). Mn in whole saliva did not correlate with Mn in water or Mn intake. Both Mn in hair and Mn in toenail allowed to discriminate the most exposed group from the least exposed group, based on Mn in water and Mn intake from water. In this group of children with low level Mn exposure, Mn concentrations in hair, and toenails reflected reasonably well Mn exposure from drinking water, whereas Mn content in saliva correlated less strongly.

Radium geochemical monitoring in well waters at regional and local scales: an environmental impact indicator-based approach

To assess radium (226Ra) as a potential indicator of impact in well waters, we investigated its behavior under natural conditions using a case study approach. 226Ra geochemistry was investigated in 67 private wells of southeastern New Brunswick, Canada, a region targeted for potential shale gas exploitation. Objectives were to i) establish 226Ra baseline in groundwater; ii) characterize 226Ra spatial distribution and temporal variability; iii) characterize 226Ra partitioning between dissolved phase and particulate forms in well waters; and iv) understand the mechanisms controlling 226Ra mobility under natural environmental settings. 226Ra levels were generally low (median = 0.061 pg L-1, or 2.2 mBq L-1), stable over time, and randomly distributed. A principal component analysis revealed that concentrations of 226Ra were controlled by key water geochemistry factors: the highest levels were observed in waters with high hardness, and/or high concentrations of individual alkaline earth elements (i.e. Mg, Ca, Sr, Ba), high concentrations of Mn and Fe, and low pH. As for partitioning, 226Ra was essentially observed in the dissolved phase (106 ± 19%) suggesting that the geochemical conditions of groundwater in the studied regions are prone to limit 226Ra sorption, enhancing its mobility. Overall, this study provided comprehensive knowledge on 226Ra background distribution at local and regional scales. Moreover, it provided a framework to establish 226Ra baselines and determine which geochemical conditions to monitor in well waters in order to use this radionuclide as an indicator of environmental impact caused by anthropogenic activities (e.g. unconventional shale gas exploitation, uranium mining, or nuclear generating power plants).