Proceedings - Teaching and Learning Centre - Simon Fraser ...

Fraser River Action Plan
The Use of Silver Measurements in Sediments
as a Tracer of Sewage Inputs to Coastal Waters
K. Gordon’, T.F. Pedersen’ and R.W. MacDonald 2
‘Department of Oceanography
University of British Columbia
Institute of Ocean Sciences
3rd Research Workshop
Elevated silver concentrations in surface sediments from the Strait of Georgia reflect the submarine discharge
and northerly flow of primary-treated sewage from the Iona Island Wastewater Treatment Plant immediately
south of Vancouver. Silver can be used to trace sewage because silver concentrations in sewage particles and,
therefore, sewage-contaminated sediments, are higher than in uncontaminated sediments. Silver tends to be
more enriched in sewage wastes than other metals mainly because the metal is introduced to municipal
wastewater primarily from the photographic industry.
Silver concentrations near the Iona outfall were up to six times greater, around 600 ppb, than concentrations in
the middle of the Strait of Georgia, at about 100 ppb, indicating that sewage particles accumulate near the
outfall. The plume appeared to move northward from the outfall since higher silver concentrations extend to
the north. This observation was consistent with the northerly flow of deep water at this location.
dlT(LCL UJ
Georgia _
Silver (ppb)
‘Outfall