Aquatic environments have long served as sinks or depositories for municipal and industrial waste, as well as agricultural runoff. While water treatment plants can remove harmful chemicals and pollutants, they don’t treat all our waterbodies. This leaves many aquatic environments vulnerable, which may result in damage to, or the end of, valuable ecosystems and reduced biodiversity. 

There are several distinct ecosystems in aquatic environments, such as freshwater (rivers, lakes and ponds) and marine systems (coastal and deep ocean). Each ecosystem has unique physical and chemical properties that can greatly affect the toxicity of a toxicant. 

A toxicant is any pollutant that can seriously damage a biological system’s structure or function or produce death. There is ongoing research on selenium toxicity in fish, causing deformities during developmental stages. Natural and synthetic hormones exposed to fish can also have sex-altering effects.

The toxicity of a toxicant is the potential to cause harmful effects, based on concentration and length of exposure. A highly potent toxicant can cause adverse effects in small quantities for short periods of time.

It’s important for the health of our ecosystems that industry and municipalities monitor and measure the impact their activities have on aquatic environments, which is why there are regulatory limits in place. Extensive research in the field of aquatic toxicology has helped pave the way for standardized testing to ensure industry and municipalities are operating safely and responsibly. 

What is aquatic toxicology?
Aquatic toxicology is the study of the adverse effects of human-made materials (e.g., chemicals) on aquatic organisms. It’s a relatively new scientific field, but researchers are making progress on how it can be applied to environmental protection (e.g., setting regulatory limits).

At the Saskatchewan Research Council (SRC) Environmental Analytical Laboratories’ Aquatic Toxicology Laboratory, experts conduct aquatic toxicity tests to evaluate the effect of mine effluents, municipal wastewater discharges and chemical products on aquatic organisms. Water samples from various aquatic sources are sent to the lab for testing and analysis. Some samples are collected at the end of the pipe for periodic monitoring of a constant discharge. In comparison, some wastewater treatment lagoons need to pass the regulatory toxicity test before the lagoon can be emptied. In this case, 24 to 48 composite samples are taken for analysis. These tests provide industry and municipalities with quantitative and qualitative data that can be used for reporting requirements and to make operational decisions.

Short-term vs. Long-term toxicity tests
Acute toxicity tests evaluate the adverse effects (e.g. mortality) of toxicants on aquatic organisms over the short term. Aquatic organisms are used in these tests as the results provide the most direct and relevant prediction of the samples’ environmental impact. The exposure period is usually days, which gives clients a short turnaround time and allows them to respond immediately (if necessary). Many regulatory criteria require the mortality rate of the organisms in the whole sample to be less than 50 per cent. 

On the contrary, chronic toxicity tests examine adverse effects under long-term exposure at sub-lethal concentrations. These tests usually last an organism’s entire reproduction cycle. The exposure period can range from one week up to months. 

The most common adverse effect of a toxicant is mortality. If an aquatic organism can’t survive either the concentration of toxicant or the length of time exposed to it, then it’s a harmful toxicant to the environment. Changes in growth, reproduction and behaviour are also examined.

Regulatory framework for testing
Aquatic toxicity tests are widely used for Environmental Effects Monitoring studies, which identify the potential effects of effluents on fish, fish habitat and use of fish by humans. These studies help the Canadian government evaluate how well regulations are protecting aquatic habitats. 

Regulations set standards for testing frequency. Under the Metal and Diamond Mining Effluent Regulations, mine operators are initially required to collect samples once a month for acute lethality tests using Oncorhynchus mykiss (rainbow trout) and Daphnia magna (water flea) for freshwater ecosystems. Testing frequency is either increased or decreased depending on how adverse the effects of the toxicant are. 

Accredited laboratories, like SRC’s Aquatic Toxicology Laboratory and Environmental Analytical Laboratories, are continuously developing new standardized tests to support industry and municipalities. This work will create positive impacts for the environment and help to build a sustainable future for our ecosystems and the activities that affect them. 

Read the full article on SRC’s blog (Photo credit: SRC)



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