Canario, João

This work presents a new online method using gas chromatography coupled to the multicollector-inductively coupled plasma-mass spectrometer for methylmercury (MMHg) isotope ratio measurement. An extraction method using distillation was developed that effectively extracted MMHg from up to 5 grams of sediment, imparting no isotope fractionation on MMHg during extraction. Isotope ratios from transient signals were calculated using three different data treatment approaches, facilitated by a data processing application, IsoCor. Peak Area Integration using 80% of the peak gave the most accurate and precise results. Using the proposed methodology, an external precision (2 SD) of ± 0.59‰ for NIST 3177 was measured. This method can be applied to samples with MMHg concentration as low as 0.1 ng/g and was successfully applied to real sediment samples however, additional research to improve the precision of the method is required for the detection of small differences between samples.

Author Keywords: compound specific isotopic ratios, isotope ratio measurement, MC-ICP-MS, methylmercury

Thawing permafrost due to increasingly warm temperatures in northern subarctic regions is releasing mercury. The consequent formation of thaw ponds in the peatland palsa valley of the Sasapimakwananisikw (SAS) river in Whapmagoostui-Kuujjuarapik, Québec may provide a pool for MMHg formation and a potential risk to aquatic and human life, if these ponds facilitate MMHg export through hydrological connections to nearby waterways. Hg methylation and MMHg demethylation activities were examined in thaw pond sediments using a Hg tracer isotope incubation experiment. Analysis by coupling gas chromatography cold-vapor atomic fluorescence spectrophotometry (GC-CVAFS) with inductively coupled mass spectrometry (ICP-MS) techniques showed that MMHg was produced at a higher rate and within the first 2 h of incubation for both summer and winter seasons. For thaw ponds SAS1A, SAS1B and SAS2A, MMHg was formed at 0.0048 % h-1, 0.0012 % h-1, and 0.0008 % h-1, respectively during winter and at 0.0001 % h-1, 0.0016 % h-1, and 0.0010 % h-1, respectively during summer. Detection of MMHg losses were not as expected likely due to limitations of the combined tracer spike and overestimation of the in situ ambient mercury levels. Physical and chemical properties vary within ponds, among ponds and between winter and summer. SAS1B's location nearby an organic carbon rich palsa may be ideal to study DOC – Hg interactions. Variability in pond characteristics including depth, surface area, age, pH, temperature, colour, oxygen concentration, total dissolved and suspended solids, conductivity, carbon, mercury, ammonium, calcium, magnesium, sulfate, total phosphorous, potassium, and sodium between seasons indicate the challenge of predicting future environmental impacts of climate change related thaw pond creation in the north.

Author Keywords: demethylation, mercury, methylation, methylmercury, SAS, thaw ponds