Bioaccumulation is the slow buildup of substances, such as pesticides or chemicals, inside a living thing. This happens when an organism takes in a substance faster than it can break it down or remove it from the body. If a harmful substance stays in the body for a long time, it increases the chance of long-term health problems, even if the amount of the substance in the environment is low.
Ecotoxicology is the study of how these harmful effects happen.
Bioaccumulation in fish, for example, can be studied using models. Some ideas about using the size of molecules to predict how likely a substance is to build up in organisms are not supported by evidence. The body can change how chemicals are processed, which can greatly affect how much of a chemical builds up.
Toxic effects from metals are linked to bioaccumulation and biomagnification. When a metal enters a body faster than it can be broken down or removed, it builds up over time. Understanding how chemicals and harmful substances behave in the environment helps scientists manage and control their use.
Organisms can take in chemicals by breathing, absorbing them through their skin, or swallowing them. When a chemical’s concentration inside an organism is higher than in the surrounding air or water, this is called bioconcentration. Biomagnification is another process connected to bioaccumulation. It happens when the concentration of a chemical or metal increases as it moves up the food chain from one level to the next. While bioaccumulation is a natural process that helps organisms grow and develop, harmful substances can also build up in their bodies.
Examples
Some plants, called hyperaccumulators, can collect large amounts of certain elements or ions. These plants can gather up to 1,000 times more of these substances than nearby plants that are not hyperaccumulators. Scientists have studied these plants as a way to remove heavy metals from polluted areas, like old mine sites. Using hyperaccumulators to collect valuable metals from soil, a process called phytomining, has also been explored. One major problem with hyperaccumulators is that some plants collect small amounts of selenium, which can harm animals that eat them.
Coastal fish, such as the smooth toadfish, and seabirds, such as the Atlantic puffin, are often tested for heavy metals that build up in their bodies. Methylmercury enters freshwater systems through factory pollution and rain. As this chemical moves up the food chain, it can reach dangerous levels for fish and the people who eat them.
Fish are usually tested for harmful chemical buildup when they are in water that contains these chemicals. Common fish tested include the common carp, rainbow trout, and bluegill sunfish. Fish often absorb chemicals through their body fat from water, or they may ingest harmful substances by eating other organisms in the water.
Toxins that occur naturally can also build up in animals. For example, coral reef fish can carry a toxin called ciguatoxin from the phytoplankton they eat, leading to a type of poisoning called ciguatera in humans. In some areas with high amounts of algae and bacteria, the concentration of pollutants may decrease as the food chain progresses, a process called biodilution.
When wetlands become more acidic, the amounts of chemicals or metals in the water can increase, making them more likely to be absorbed by marine plants and freshwater life. Both rooted and submerged plants in these areas can be affected by the availability of these metals.
Studies of turtles as model species
Bioaccumulation in turtles happens when man-made chemicals (like PFAS), heavy metals, or high levels of trace elements enter their bodies. This can harm their health. Although scientists are still studying how bioaccumulation affects turtles, factors such as pollution, climate change, and changes in the environment can influence the amount of toxins in ecosystems.
The most common elements studied in turtles are mercury, cadmium, lead, and selenium. Heavy metals are released into rivers, lakes, and oceans. Plants in these environments absorb the metals. Because aquatic ecosystems often have high levels of trace elements, turtles naturally consume these elements by eating plants and sediments. Once these substances enter a turtle’s bloodstream and muscle tissue, their concentration increases and can become harmful, potentially causing problems with metabolism, the endocrine system, and reproduction.
Some marine turtles are used in studies about bioaccumulation because they live near shorelines, making it easier to collect blood samples and other data. Turtles are a diverse group of animals that play an important role in biodiversity, so scientists often study many different species. Freshwater turtles are also used as models for studying bioaccumulation. Because they have limited home ranges, they are often linked to specific areas and the chemical makeup of those regions.
High levels of toxins in turtle eggs can harm the development of baby turtles. For example, in the Australian freshwater short-neck turtle (Emydura macquarii macquarii), PFAS from the environment were absorbed by the mother and passed to her eggs. This affected the metabolic processes and fat storage of the developing turtles. Evidence also shows that PFAS can change the gut bacteria in turtles that are exposed to these chemicals.
In terms of heavy metals, high levels have been linked to lower egg-hatching rates in the Amazon River turtle (Podocnemis expansa). In these eggs, heavy metals reduce the fat content and alter how water is filtered through the embryo. This can lower the survival rate of the eggs.