Microcystins detected in a drinking water source in subarctic Northwest Territories, Canada

Cyanotoxins have been a well-documented challenge for drinking water supplies across several Canadian provinces, but not in the northern territories (Yukon, Northwest Territories, and Nunavut). In this paper, we report on the first detection of microcystins in a municipal drinking source water (untreated) in the Northwest Territories based on Enzyme-Linked ImmunoSorbent Assay (ELISA) screening. In July 2024, a cyanobacteria bloom was observed in the seasonal fill reservoir of the drinking water treatment plant at Sambaa K'e, prompting the draining and re-filling of the reservoir and household water tanks. ELISA screening assays performed by an accredited commercial lab on surface water samples from the reservoir identified the presence of total microcystins above detection limits (0.2 µg/L) over four days of sampling, at concentrations ranging from 1.14 to 1.72 µg/L. Microscope analysis revealed that the bloom was numerically dominated by Dolichospermum (29.9%), Aphanocapsa (15.0%), and Microcystis (12.6%), all of which are capable of microcystin (and other cyanotoxin) production. The detection of microcystins in the drinking water reservoir at Sambaa K'e highlights the need to better understand potential public health risks from cyanotoxin exposure in small northern communities, and to develop policies and programs for monitoring and responding to cyanobacterial blooms in northern drinking source waters.