Beneath the surface: aquatic toxicology tests help identify pollutants in waterbodies

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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. 

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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 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, 24-48 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.

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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.

Can the effects of pollutants in waterbodies be reversed? Usually hormonal effects (e.g., from municipal waste) are reversible. For an ecosystem like an abandoned mine site (e.g., similar to sites SRC is remediating for Project CLEANS) organisms, such as animals and plants, may need to be re-introduced to the ecosystem. Our toxicity tests can provide an extra monitoring parameter to assess remediation success.

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A closer look at chemicals

Toxicity tests of a single chemical can determine the lowest concentration where adverse effects can be observed. These values help regulatory agencies to establish environmental guidelines. Traditional analytical methods that SRC Environmental Analytical Laboratories provides are often requested by industry and municipalities to monitor and control their processes and adhere to regulations.

Environmental monitoring and risk assessment become more complicated when evaluating chemical mixtures because there are many factors, such as pre-existing environmental conditions or location, that impact the aquatic environment. Identifying the cause of growth changes or mortality varies. In comparison to a single chemical, a chemical mixture can contain hundreds of unique contaminants at varying concentrations.

For instance, mine effluents (i.e., treated waste) may contain a unique set of contaminants depending on where the site is located, it’s geological characteristics and the extraction methods used. Municipal sewage treatment waste and lagoon discharge also contain many emerging contaminants related to pharmaceutical and personal care products (PPCP). 

When PPCPs are constantly released into the aquatic environment, this can impact the ecosystem by increasing microorganisms’ resistance to antibiotics, and impact fish development and reproduction. Furthermore, the effects of many PPCPs still remain unknown and it is extremely difficult to assess them when presented in a complex mixture.

A common misconception is that the total toxicity of a chemical mixture is the simple addition of the individual toxicity of all its toxic components. 

However, research studies show that chemical mixtures can have additive, antagonizing (less than additive), or synergizing (greater than additive) toxicity. A simple way to explain this concept is that 1+1 in a chemical mixture is not always equal to a toxicity of 2.

Although chemical analyses can provide a quick comparison of the chemical composition of a sample to the regulated limits, they might not paint the whole picture of the potential environmental impact. Toxicity tests with whole effluents or with sample extracts can complement chemical analyses by providing a clearer understanding of the chemical mixture and its affects on biological systems. This approach is known as Toxicity Identification Evaluation (TIE), in which we isolate toxicants based on their physical and chemical properties to identify the causing agent(s).

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 impact them.