The purpose of this study was to determine the potential for off-flavour tainting of water and/or fish in the Athabasca River by compounds discharged by bleached kraft and chemi-thermomechanical pulp mills. The opportunity to determine in-stream occurrence of common tainting compounds prior to the startup of the Alberta-Pacific mill was exploited. This study combined three different analytical methods commonly used in monitoring for the presence of odorous compounds in water supplies. Two trained flavour profile panels were used to characterize the odour of the samples, two trained analysts evaluated the samples using olfactory GC and all samples were quantitatively analyzed for the presence of target odour compounds using GC/MS. These three techniques all provide quite different information and all have certain limitations.
The flavour profile panel work, involving two independent panels, clearly indicated an impact of Hinton combined effluent on the odour of the Athabasca River for substantial distances downstream. The odour contributions to the Athabasca River from tributaries were minor. The odour contributions from other effluent sources (sewage treatment plants and chemi-thermomechanical pulp mills) were less distinctive than the Hinton combined effluent and their role in affecting downstream odour is not as clear. Notwithstanding these observations, the observed impacts on raw water odour could not be detected in the treated drinking water at Ft. McMurray, possibly because of removal of odorous compounds in treatment and / or masking of the raw water odour with chlorinous odours. The raw water supply at Ft. Chipeweyan was not particularly odorous and the finished water exhibited a very strong chlorine odour that would have masked any subtle odours present.
The CLSA-GC/MS for target compounds also suggests that there was limited contribution of odour compounds from the tributaries. None of the effluent samples, including the Hinton combined effluent, contributed substantial concentrations of the target odour compounds to the Athabasca River, with the possible exception of geosmin. Notwithstanding these findings, there was a very distinctive rise in 3,4,5-trichloroveratrole and a measurable, but less distinctive rise in 2,4,6-trichloroanisole in the Athabasca River downstream of Hinton. Because neither of these compounds were present in substantial concentration in the Hinton combined effluent, and their concentrations increased downstream of Hinton, there is not a simple explanation for a possible role of this effluent source in the observed Athabasca River system concentrations for these compounds. In any case, none of the target odour compounds, by themselves would explain the odour character that was perceived by the flavour panel in the Hinton combined effluent and affected downstream samples. The OGC should have provided a separate approach to account for non-target odorous compounds that might explain the odours perceived by the flavour panel. However, there were very few extra odour peaks detected by OGC with perhaps only a sulfiiry / septic odour and a sulfury/mercaptan/crude oil odour that were likely to have contributed in any substantial way to the pulp mill odour character. Identifying these compounds would likely assist the odour characterization process, but there are likely other contributing compounds that have not yet been detected by the methods employed in this survey. This possibility suggests the need for a better characterization of the compounds that are primarily responsible for creating the odour of pulp mill effluents.