Jeffrey J. Ridal

Sediment mercury dynamics and historical trends of mercury deposition in the St. Lawrence River area of concern near Cornwall, Ontario, Canada

The St. Lawrence River near Cornwall, Ontario was designated an Area of Concern by the International Joint Commission in 1985. Sediments from this area have historically been contaminated with mercury (Hg), and although concentrations have decreased since the 1970s, they still remain high. Nine sediment cores were collected from three sites within the Area of Concern in 2004/05 to determine the variability in historical profiles of Hg deposition to the river. Sediment and pore water phases were analyzed for total mercury (THg) and methyl mercury (MeHg) and cores were analyzed for 210Pb to determine chronologies of sedimentation at these sites. Mercury diffusion rates in pore waters within the sediment column were determined to be very low (between 0 and 2.15 ng cm(-2) year(-1), n = 3) compared to the recent Hg sedimentation rates at these sites (183+/- 30 ng cm(-2) year(-1) SE, n = 9) determined by multiplying surface Hg concentrations with 210Pb-derived sedimentation rates. These results indicate that Hg profiles in these cores accurately depict historical releases of Hg to the river bed. The influence of federal regulations in the early 1970s to restrict Hg emissions to the river was apparent in these dated sediment cores, as were the closures of several local industries in the mid 1990s. Mercury accumulation rates prior to 1970 were 60 times higher than those occurring after 1995. Methyl mercury showed surface enrichment in most of these sediment cores providing evidence that mercury methylation occurred most rapidly near the sediment surface.

Mercury transport between sediments and the overlying water of the St. Lawrence River area of concern near Cornwall, Ontario.

Contaminated sediments in the St. Lawrence River remain a difficult problem despite decreases in emissions. Here, sediment and pore water phases were analyzed for total mercury (THg) and methyl mercury (MeHg) and diffusion from the sediment to the overlying water was 17.5 + or - 10.6 SE ng cm(-2) yr(-1) for THg and 3.8 + or - 1.7 SE ng cm(-2) yr(-1) for MeHg. These fluxes were very small when compared to the particle-bound mercury flux accumulating in the sediment (183 + or - 30 SE ng cm(-2) yr(-1)). Studies have reported that fish from the westernmost site have higher Hg concentrations than fish collected from the other two sites of the Cornwall Area of Concern, which could not be explained by differences in the Hg flux or THg concentrations in sediments, but the highest concentrations of sediment MeHg, and the greatest proportions of MeHg to THg in both sediment and pore water were observed where fish had highest MeHg concentrations.

Occurrence of the Odor Compounds, 2-Methylisoborneol and Geosmin in Eastern Lake Ontario and the Upper St. Lawrence River

Abstract Unpleasant tastes and odors in drinking water from the upper St. Lawrence River were investigated in the fall of 1996 and 1997 as the result of increasing taste and odor events in recent years. Taste and odor events resulted in widespread public reaction to the earthy/musty tasting water produced and a need for accurate information to assist water treatment efforts. The presence of geosmin, (trans, trans-1,10-dimethyl-9-decalol) and 2-methylisoborneol (MIB2, 1,2,7,7-tetramethyl-exobicyclo[2.2.1]heptan-2-ol), the most common causes worldwide of earthy and musty odors in water, were investigated in eastern Lake Ontario and the upper St. Lawrence River. Gas chromatography-mass spectrometry was used for quantitation and confirmation of the presence of these compounds in water samples. Both geosmin and MIB2 were detected in river water samples at concentrations ranging from 5 to 20 ng/L and 2 to 25 ng/L, respectively. The compounds were also detected in southern coastal lake water which serves as a source to the St. Lawrence River, but not in mid-lake samples. Similar levels of geosmin and MIB2 were detected in untreated Lake St. Lawrence water, in samples taken following pre-chlorination for zebra mussel control, and in samples taken following conventional treatment at a water filtration plant.

Ebullition rates and mercury concentrations in St. Lawrence river sediments and a benthic invertebrate

Ebullition, the release of gas from anaerobic decomposition in sediments, was recorded in a mercury-contaminated depositional zone (Zone 1) of the St. Lawrence River Area of Concern in Cornwall, Ontario, Canada. The aim of the present study was to test if this disturbance affected the bioavailability of total mercury (THg) and methylmercury (MeHg) in surficial sediments to a benthic invertebrate (Echinogammarus ischnus). Ebullition rates ranged from <1 to 2,800 ml/m(2) daily, with methane gas comprising 29 to 84% of the total. No direct effects of ebullition were found on either abiotic (sediment or pore water THg or MeHg concentrations) or biotic (amphipod THg or MeHg concentrations) variables measured. Instead, amphipod MeHg concentrations were best predicted by pore water THg and MeHg concentrations, organic matter of surficial sediments, and water depth and location. Trend surface analyses demonstrated that a shallow, southwestern part of Zone 1 was most contaminated with pore water mercury, which decreased in a gradient toward the northeast. Further study is needed to determine if the amount of sediment resuspended by ebullition affects the spatial distribution of mercury.

Is Lake Ontario the Source of Taste and Odor Compounds to the Upper St. Lawrence River

Abstract The south and east coastal currents of Lake Ontario were investigated to determine if they serve as the major source of the common odour compounds, 2-methylisoborneol (MIB) and geosmin (GM), to the St. Lawrence River (SLR). MIB and GM at low parts per trillion levels produce earthy-musty off-tastes in drinking waters. Previous investigations in 1996 and 1997 identified the presence of GM and MIB in SLR and in the southern coastal jet of Lake Ontario, which contributes the bulk of the summertime flow to the St. Lawrence River. Water samples were collected in July and September 1998 during cruises of Lake Ontario and the SLR, extracted shipboard and analyzed for MIB and GM. In July, both compounds were detected only in the SLR, but were found in both Lake Ontario and SLR stations in September. However, MIB and GM were found at higher levels in the St. Lawrence River (17 to 60 ng/L and 2 to 18 ng/L, respectively) than in samples from the Lake Ontario coastal current (0.5 to 10 ng/L and

Dynamic mass balance model for mercury in the St. Lawrence River near Cornwall, Ontario, Canada

A dynamic mass balance model was developed for the St. Lawrence River near Cornwall, Ontario that predicts and hindcasts mercury concentrations and fluxes in three forms, elemental Hg (Hg(0)), divalent mercury (Hg(2+)), and methyl mercury (MeHg), in a six compartment environment (air, water, porewater, sediment, periphyton, and benthic invertebrates). Our objective was to construct a dynamic mass balance model for mercury in the St. Lawrence River near Cornwall, Ontario based on the framework and results of a steady-state mass balance model developed previously for this site. The second objective was to estimate industrial mercury emissions based on mercury residues deposited in sediments prior to 1970, the year when regulations were implemented to reduce mercury pollution in the environment. We compiled mercury concentrations, fluxes, and transformation rates from previous studies completed in this section of the river (area of approximately 100km(2)) to develop the model. Estimated mercury concentrations in all media were similar to measured data (R(2)=0.99), with only minor exceptions, providing a satisfactory overall description of the mercury loadings and transformation rates of the different mercury species. The estimated historical emissions prior to 1970 from local industries along the Cornwall waterfront were approximately 400kgyear(-1). A storm sewer discharge of 5000m(3)/day resulted in a significant increase in mercury concentrations, particularly in sediment (617ngg(-1) to 624ngg(-1); p=0.004). Model results suggest that discharges of mercury from sources such as local industries and storm sewers have an impact on mercury in media such as sediment and water. This model should provide a basis for predicting and hindcasting mercury concentrations in other river environments as well, because it considers three distinct forms of mercury, and contains environmental media common to all rivers, including some (e.g. periphyton) not typically included in previous mercury models.

Assessing the fish consumption beneficial use impairment in the Bay of Quinte

The state of contamination in Bay of Quinte fish was assessed to determine whether delisting criteria have been met, and to recommend further studies/actions to be undertaken. We examined fish contaminant data collected by the Ontario Ministry of the Environment between 1975 and 2008 for seven sites in Lake Ontario including the Bay of Quinte. Where sufficient data was available, we tested for differences in recent years by examining the post-1998 data for Walleye, Smallmouth Bass, Yellow Perch and Brown Bullhead. Our analysis specifically focused on known contaminants of concern within the Bay of Quinte: polychlorinated biphenyls (PCBs), mercury (Hg), as well as Mirex which is known to originate from Lake Ontario. Insufficient data was available for the examination of total TEQs (dioxins, furans and dioxin-like PCBs). When appropriate, we used the general linear model (GLM) to compare contaminant concentrations among sites as a function of fish length. When no significant relationship between contaminant concentration and fish length was found, mean values among sites were compared using analysis of variance. While there were no significant differences for the majority of contaminants among sites, some species and contaminant combinations at one or more of the Bay of Quinte sites had elevated fish concentrations compared to some reference sites. For instance, mercury concentrations in Yellow Perch and Brown Bullhead at Quinte sites exceeded those from some reference sites. Current consumption restrictions for Brown Bullhead and Yellow Perch are more severe in the Upper Bay of Quinte compared to the other sites, indicating impacts of local sources. As a result, the fish consumption beneficial use impairment continues to be classified as impaired for the Bay of Quinte. As many sport fish such as Walleye and Smallmouth Bass are large, long-lived and potentially wide-ranging species, it is difficult to link contaminant concentrations to local sources. To investigate the impact of sources within the Upper Bay of Quinte, comparison of contaminants in sentinel fish collected on the same scale as the source of the contamination is recommended.