Burden of recreational water illness due to exposure to cyanobacteria and their toxins in freshwater beaches in Canada: protocol of a prospective cohort study.

INTRODUCTION: Cyanobacterial blooms are increasingly common in freshwater sources used for swimming and other recreational water contact activities in Canada. Many species of cyanobacteria can produce toxins that affect human and animal health, but there are limited data on the risk of illness associated with water contact at impacted beaches. METHODS AND ANALYSIS: This study will investigate the incidence of recreational water illness due to exposure to cyanobacterial blooms and their toxins in four targeted and popular freshwater beaches in Ontario, Manitoba and Nova Scotia, Canada. A prospective cohort design and One Health approach will be used. On-site recruitment of recreational water users will be conducted at two beaches per year during the summers of 2024 and 2025. The population of interest includes recreational water users of any age and their pet dogs. After enrolment, an in-person survey will determine beach exposures and confounding factors, and a 3-day follow-up survey will ascertain any acute illness outcomes experienced by participants or their dogs. The target sample size is 2500 recreational water users. Water samples will be taken each recruitment day and analysed for cyanobacterial indicators (pigments), cell counts and toxin levels. Bayesian regression analysis will be conducted to estimate the association with water contact, cyanobacterial levels and risks of different acute illness outcomes. ETHICS AND DISSEMINATION: This study has been approved by the Toronto Metropolitan University Research Ethics Board (REB 2023-461). Study results will be published in a peer-reviewed journal and as infographics on a project website.

An efficient and affordable laboratory method to produce and sustain high concentrations of microcystins by Microcystis aeruginosa.

Microcystis aeruginosa is a cosmopolitan cyanobacteria that continues to jeopardize freshwater ecosystem services by releasing the hepatotoxin microcystin, which can, in some cases, cause death to aquatic fauna and even humans. Currently, our abilities to understand the mechanisms of microcystin toxicology are limited by the lack of a method for producing high concentrations, which are central to large-scale and long-term research in natural systems. Here we present an efficient and affordable laboratory method to produce high concentrations of microcystins by a toxigenic strain of M. aeruginosa. Through batch culture studies, we yielded microcystins at concentrations that are environmentally relevant to freshwaters around the world (1-300 µg L-1), maintained these concentrations without resupplying fresh medium (further reducing costs), and utilized rate equations to model the relationship between the environmental conditions in the cultures and changes occurring within the M. aeruginosa cells. Our assessment suggests that steady production of microcystins depends on the availability of carbon throughout the experiment. Hence, we recommend the use of tissue culture treated flasks with a vented cap to ensure the production of microcystins is uninterrupted. This method demonstrates that microcystins can be produced in the laboratory at concentrations relevant to freshwater ecosystems. •The method demonstrates M. aeruginosa CPCC 300 is a reliable strain of freshwater cyanobacteria that can yield microcystins at environmentally relevant concentrations.•Validation showed M. aeruginosa CPCC 300 is resilient in carbon-limited situations and may respond to stress by shifting the ratio of microcystin congeners.•Cell culture flasks with vented caps -filled no more than 50 % of the flask volume to allow for sufficient air exchange- are an excellent and cost-effective approach to maintaining cell growth and producing microcystins at a range between 300 to 1200 µg L-1.