Methylmercury (MeHg) is the most toxic species of mercury (Hg), and is an important ecosystem contaminant. In wetlands on the Canadian Shield, in NW Ontario, MeHg concentrations in peat and peat porewater ranged from 0.3 to 53 ng $ rm g sp{-1}$ and $<$0.1 to $ rm 7.3 ng l sp{-1},$ respectively. The greatest concentrations of MeHg occurred just below the water table, emphasizing the importance of redox reactions in Hg methylation. Methylmercury partition coefficients between peat and peat porewater ranged from $1.6 times 10 sp3$ to $8.6 times 10 sp5.$ No significant correlations between MeHg and concentrations of $ rm H sp+, NH sb4 sp+, NO sb3 sp-, NO sb2 sp-,$ total dissolved nitrogen (TDN), total dissolved phosphorus (TDP), $ rm SO sb4 sp{2-},$ and dissolved organic carbon (DOC) in the porewater of the wetlands were found. / Following shallow impoundment of a wetland, MeHg concentrations in the upper metre of peat porewater increased from $ rm 0.2 pm 0.2 ng l sp{-1}$ to $ rm 0.8 pm 0.8 ng l sp{-1}.$ Total mercury (T-Hg) and MeHg concentrations were determined in decomposing sedge, spruce needles, and Sphagnum moss, placed in a headwater wetland and the impounded wetland. The amount of T-Hg decreased in all tissues regardless of location. the amount of MeHg increased by as much as an order of magnitude in the tissues placed in the impounded wetland and wet areas (hollows and lawns) of the headwater wetland, but decreased in tissue placed in the dry areas (hummocks) of the headwater wetland. Therefore, it is during anaerobic decomposition of plant material that MeHg is produced in wetlands. / Incubations of peat were performed with addition of Hg, molybdate, $ rm SO sb4 sp{2-}, S sp{2-}, NH sb4NO sb3,$ pyruvate, and upland DOC. Methylmercury production was increased only after addition of $ rm SO sb4 sp{2-}$ and retarded only by $ rm NH sb4NO sb3.$ Although $ rm SO sb4 sp{2-}$ may not be required to methylate Hg, the increased availability of $ rm SO sb4 sp{2-}$ may influence the size and composition of the population of sulfate reducing bacteria in peat, thereby increasing the potential for Hg methylation.

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Decomposition and MeHg concentration were measured for Sphagnum fuscum, Sphagnum angustifolium and Chamaedaphne calyculata in a poor fen in the low boreal forest zone of the Canadian Shield. Litter bags were transplanted reciprocally into hummocks, hollows and lawns and retrieved after 1, 2, 3,11 and 15 months. / Mass losses follow the trend: Chamaedaphne calyculata >> S. angustifolium > S. fuscum. Between species differences were far more significant than differences between locations or depths, indicating that litter quality is the major control on decomposition. / McHg concentrations generally increased during decomposition, particularly near the water table: for C. calyculata up to 13000%, for the two Sphagnum mosses up to 500%, suggesting that decomposition stimulates mercury methylation or McHg scavenging. / The discovery of a high McHg substance on C. calyculata leaf surfaces (25 ng g-1) suggests that much plant MeHg data may by skewed by the presence of a biologically active 'film'.

The threat of environmental mercury (Hg), particularly methylmercury (MeHg), exposure to the health of humans has been well documented. Thus, it is important to monitor exposure and body burden for public health protection. The first objective of this thesis was to characterize the risk of Hg exposure in two Canadian coastal communities: Grand Marian (n = 91) and St. Andrews/St. Stephen (n = 52), New Brunswick, Canada, using dietary questionnaires and hair analysis. Average Hg intakes and body burden were below the most conservative guidelines. We attributed these results to the low Hg concentrations found in the species commonly consumed: haddock, canned tuna, lobster and pollock (all below 0.2 mg/kg). The analytical method employed to determine Hg in hair, cold vapor atomic absorption (CV-AAS), required a bundle of 100-150 hair strands and involved lengthy chemical digestion procedures which reduce throughput. Direct solid introduction techniques minimize these weaknesses. Our second and third objectives were to evaluate two such methods: (1) combustion, gold amalgamation, atomic absorption spectrometry (C-GA-AAS) and (2) laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) for measuring total Hg in single hair strands. Hair samples with a wide range of Hg exposure were obtained from communities. A 1:1 relationship was observed between C-GA-AAS and the established CV-AAS for analysis of 1-cm hair segments. Additionally, the average relative standard deviation (RSD) of Hg between hair strands within an individual was 6.5 +/- 2.8%, thus justifying the use of a single hair strand for biomonitoring. With a limit of quantification of 0.10 ng of total Hg, a single hair strand with average weight of 0.5 mg and Hg concentrations of 0.2 mg/kg can be measured routinely. Using LA-ICP-MS, we showed that a single laser shot can sample hair material within 50 mum along a single hair strand which is equivalent to less than one day of

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Indiana University-Purdue University Indianapolis (IUPUI) / Numerous studies have investigated the fate of pollutants in riparian buffers, but few studies have focused on the control of multiple contaminants simultaneously in riparian zones. To better understand what drives the biogeochemical cycles of multiple contaminants in riparian zones, a 19-month study was conducted in riparian buffers across a range of hydrogeomorphic (HGM) settings in the White River watershed in Indiana. Three research sites [Leary Webber Ditch (LWD), Scott Starling (SS) and White River (WR)] with contrasting hydro-geomorphology were selected. We monitored groundwater table depth, oxidation reduction potential (ORP), dissolved oxygen (DO), dissolved organic carbon (DOC), NO3-, NH4+, soluble reactive phosphorus (SRP), SO42- , total Hg and methylmercury (MeHg). Our results revealed that differences in HGM conditions translated into distinctive site hydrology, but significant differences in site hydrology did not lead to different biogeochemical conditions. Nitrate reduction and sulfate re-oxidation were likely associated with major hydrological events, while sulfate reduction, ammonia and methylmercury production were likely associated with seasonal changes in biogeochemical conditions. Results also suggest that the LWD site was a small sink for nitrate but a source for sulfate and MeHg, the SS site was a small sink for MeHg but had little effect on NO3-, SO42- and SRP, and the WR was an intermediate to a large sink for nitrate, an intermediate sink for SRP, and a small source for MeHg. Land use and point source appears to have played an important role in regulating solute concentrations (NO3-, SRP and THg). Thermodynamic theories probably oversimplify the complex patterns of solute dynamics which, at the sites monitored in the present study, were more strongly impacted by HGM settings, land use, and proximity to a point source.