What is Aquatic Toxicology?

Instructor: Sarah Friedl

Sarah has two Master's, one in Zoology and one in GIS, a Bachelor's in Biology, and has taught college level Physical Science and Biology.

Water is essential to life, but clean water is even more essential. Studying things in the water and how they affect aquatic life is a big task, but one that is taken on boldly by the field of aquatic toxicology.

Down the Drain

When you wash dirt from your hands, dishes, and clothes, or even flush your toilet, where do you think that stuff goes? If you live in a developed country, such as the United States, the dirty water sometimes gets treated at a water treatment facility and cleaned for re-use.

But other things, such as pollution in the air, fertilizers on the ground, and even many things that do go down the drain end up in lakes, rivers, streams, and the oceans. Aquatic toxicology is the field that studies the effect of these pollutants, compounds, and nutrients on the plants and animals that live in the water. The effects may be small scale and affect individuals, or they may be ecosystem-wide.

Agricultural runoff puts many substances in the water that affect aquatic life
agricultural runoff

Broad Implications

The field of aquatic toxicology is a broad one. It includes studying toxins in sediments and the water, both short- and long-term effects of toxins in plants and animals, and the sensitivity of organisms to contaminants. It also involves standardizing toxicity test methods and comparing how laboratory studies relate to issues int he actual environment.

One important thing that aquatic toxicology looks at is relationships. It is a field that exposes the 'big picture' of what might initially seem like a small problem. Take for example, the widely-used pesticide atrazine, which acts as an endocrine disrupter in frogs. As the name implies, these are things that interfere with or disrupt the endocrine system. What atrazine does is turn 1 in 10 male frogs into females. This may not sound like a lot, but despite the fact that this isn't a natural process, and that the new 'female' frogs can successfully mate with natural male frogs, all of their offspring will be male, which will skew the population so far that it will eventually be wiped out.

Accumulating and Magnifying Contaminants

Two other types of relationships that aquatic toxicology looks at are bioaccumulation, which is when an organism takes up (accumulates) a substance in its tissues faster than it can expel it, and biomagnification, which is when a substance increases in concentration as it moves up the food chain.

We can see bioaccumulation in fish and shellfish because they take up mercury in their tissues. When accumulated in the organism's tissue it is often passed on to whatever eats that organism. This is why women who are pregnant or planning to become pregnant are advised not to eat fish.

Toxins in the water can work their way up the food chain, increasing in concentration as they go
biomagnification of mercury

Biomagnification often comes with bioaccumulation, and a very famous example of this relationship between toxins and organisms involves the pesticide DDT. Once a widely used chemical for mosquito control, DDT accumulated in the tissue of each animal up the food chain, starting with the insects at the bottom and ending with birds of prey at the top. What caused alarm was that eagle populations were declining because the DDT made their eggs shells too soft, and when the birds sat on them in their nests they would break. DDT also got into the water and was taken up by animals like fish and shellfish, working its way up that food chain as well.

An Early Warning

The field of aquatic toxicology doesn't just look at problems after they happen. It also deals with risk assessment as well as using aquatic organisms to model the possible effects of contaminants on humans. In fact, aquatic toxicology is often the 'canary in the coalmine', as contaminant and chemical issues in the water have served as early warning signs. By monitoring water quality and contaminant levels, we can see when problems are arising before they become a large-scale public health crisis.

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