Abstract:

Canadian Pulp and Paper Effluent Regulations and Metal and Diamond Mining Effluent Regulations require sublethal toxicity testing using a marine algae species for effluent discharged into marine and estuarine environments. Historically, the marine macroalgae Champia parvula was used in sublethal toxicity testing; however, this test species is no longer used at Canadian testing laboratories due to data quality concerns. As a result, Environment and Climate Change Canada recently drafted an add-on procedure to the ISO 10710:2010 method for the marine macroalgae Ceramium tenuicorne to facilitate its use in Canadian sublethal toxicity testing. The add-on procedure for C. tenuicorne testing was refined by conducting two series of exposures. First, simultaneous toxicity testing was conducted using two distinct size classes of C. tenuicorne (the current add-on requirement of 0.6-1.2 mm and a slightly larger size of 1.2-1.8 mm) to determine if plant size at test initiation influenced test sensitivity. Results show that C. tenuicorne test sensitivity was largely unaffected by plant size at test initiation when initial plant size ranged from 0.6-1.8 mm. The required plant size range for test initiation can therefore be widened to 0.6-1.8 mm to facilitate test initiation at commercial laboratories without compromising test sensitivity. The second series of exposures tested effluent samples voluntarily submitted by Canadian pulp and paper and mining facilities to characterize the sensitivity of the C. tenuicorne growth inhibition test. Overall, the growth rate of C. tenuicorne is a sensitive endpoint that produced typical dose-response curves and varies in response to diverse effluent types and quality. Collectively, results demonstrate that C. tenuicorne can be successfully used as a test species for sublethal toxicity testing of effluent samples from Canadian pulp and paper and mining facilities.