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Evaluation of factors affecting the ion-selective electrode (ISE) electrochemical measurement of total free sulfide in marine sediments

National Peer Review – National Capital Region

May 10-12, 2022
Virtual meeting

Chairpersons: Jay Parsons and Brittany Beauchamp


Under s.36 of the Fisheries Act  and associated Aquaculture Activities Regulations, Fisheries and Oceans Canada (DFO) regulates the conditions under which an aquaculture operator may deposit deleterious substances. DFO recognizes that there are interactions between aquaculture operations and the natural environment. The risks associated with these interactions are considered and addressed through a suite of regulatory tools, at both the federal and provincial levels. Examples of such tools include requiring that aquaculture operators monitor the oxic state of the seafloor beneath farms, and having defined thresholds and associated management actions that are required should the regulatory thresholds be exceeded.

Under both the Aquaculture Activities Regulations and provincial regulations, the aquaculture industry is required to conduct seafloor monitoring of finfish aquaculture sites. The measurement of sulfide from sediment samples is an accepted standard practice for soft-bottom seabeds. The protocols for conducting sampling, and for the measurement of sulfide from sediment samples, are outlined in the monitoring standard associated with the Aquaculture Activities Regulations.

The currently applied DFO monitoring protocols used at marine finfish sites were adopted by DFO during the development of the Aquaculture Activities Regulations, and incorporate some regional differences in Provincial program design. Specifically, these protocols may result in differences in the time between sample collection and the measurement of sulfide in the samples, as well as differences in the temperature at which samples are held prior to processing. DFO Aquaculture Management have asked for information on the effects of several factors on the measurement of sulfides in sediment samples, and have requested Science advice to support the development of a nationally harmonized approach to the collection and testing of sediment sulfide, which is used as a proxy for oxic state and biodiversity, which is linked to management protection goals.


The objectives of this meeting are to determine: 

  1. What are the effects of sediment sample storage time and conditions (e.g. temperature, vacuum-sealed) on the measurement of total free sulfide as compared to total free sulfide measured immediately upon sample collection?
  2. Are these relationships consistent across sediment types and/or total free sulfide concentrations?
  3. Is there a combination of storage conditions and storage time post collection that would result in expected total free sulfide measurements within +/- 5%, 10% and 15% of the value obtained from measuring total free sulfide immediately following sediment sample collection?
  4. Are there steps in the ion-selective electrode (ISE) total free sulfide measurement protocol that are open to interpretation by the analyst and to which differences will result in different measured concentrations of total free sulfides?
  5. Review ISE total free sulfide measurement methodologies and develop standard procedures for sample storage time, storage conditions, and analyses.
  6. In the consideration of the above questions, characterize the method variability in the context of natural, in situ, spatial variability of sediment sulfide levels.

Expected Publications

Expected Participation


Participation to CSAS peer review meetings is by invitation only.

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