What is Bioaccumulation?

• Bioaccumulation is the slow accumulation of substances within an organism, such as pesticides or other toxins.
• Bioaccumulation happens when an organism absorbs a material at a quicker pace than it is removed or lost through catabolism and excretion.
• Thus, the longer the biological half-life of a toxin, the higher the danger of chronic poisoning, even if environmental concentrations of the toxin are not very high.
• Models can be used to forecast bioaccumulation, for example in fish.
• The data do not support the hypothesis for molecular size cutoff criteria used as bioaccumulation potential indicators.
• A biotransformation can significantly alter the bioaccumulation of substances within an organism.
• Metal-induced toxicity is linked to bioaccumulation and biomagnification.
• The accumulation of a metal is caused by its storage or absorption at a pace that exceeds the organism’s metabolic and excretory rates.
• With the right understanding of bioaccumulation, the presence of numerous chemicals and dangerous compounds in the environment may be examined and assessed, hence aiding in chemical management and application.
• Chemicals can be absorbed by an organism through breathing, skin absorption, or ingesting.
• When the concentration of a chemical is greater within an organism than in its environment (air or water), this is known as bioconcentration.
• Biomagnification is a bioaccumulation-related phenomenon in which the concentration of a chemical or metal increases as it goes up the trophic levels.
• Bioaccumulation is essential for an organism’s growth and development, but it can also lead to the accumulation of toxic compounds.

Definitions of Bioaccumulation

Bioaccumulation (increase in chemical concentration) is the process of chemical accumulation in an organism over time. Bioaccumulation, as defined by the International Union of Pure and Applied Chemistry, is the accumulation of a chemical in an organism due to direct uptake from the environmental matrix (bioconcentration) and uptake from food (biomagnification).

Bioaccumulation is only possible when absorption exceeds elimination.

Bioaccumulation = Rate of uptake  – Rate of elimination

• The aforementioned distinction is contingent upon an organism’s chemical (physicochemical) qualities.
• Several physical, chemical, and biological factors influence the bioaccumulation and bioavailability of substances.
• Bioaccumulation of chemicals in target tissues. The chemical content of accumulation sites can be measured to determine the extent of bioaccumulation.
• Defense mechanisms of an organism (such as the creation of metallothionein) can also be used to quantify the level of bioaccumulation and are referred to as biomarkers of exposure, which are used to describe the bioaccumulation of chemicals in tissues.
• Biomarkers can be used to describe the harmful consequences (mortality, reduction in growth and reproduction, mutagenicity, carcinogenicity, and sensitization) of a material present in an organism (e.g., damage of DNA).
• Although biomarkers and bioindicators can provide information on the accumulated dose of chemicals, they do not provide direct information on health or bad effects.
• Consequently, tissue concentrations should be correlated with biological effects based on the dose–response relationship.
• Significant is the link between chemical field concentrations and harmful consequences (if other toxins are absent).
• The chemical routes are determined by the hydrophilicity (readily removed) and hydrophobicity of the substance (persistent organic compounds, difficult to metabolize, accumulate in fat).
• It was discovered that bioaccumulation and lipophilicity are correlated.

Bioaccumulation Steps

1. Uptake

• Bioaccumulation, internal and external fate, and consequences cannot occur in the absence of exposure, which is dependent on behaviour, bioavailability, and bioaccessibility.
• These are affected by a variety of variables, including size, nutrition, heredity, hormones, gender, etc.
• The absorption can occur either directly (from the ambient medium) or indirectly (from another source) from the environment (air, water, soil) (from the food chain).
• Bioaccumulation is a risk posed by the eating of foods with elevated chemical levels.
• Root (soil, water, and occasionally air) and leaf (air, water) are the most common routes of absorption in plants. In animals, the respiratory, ingestive, and cutaneous routes are utilised.

2. Elimination

• The final body burden is determined by equilibrium processes of intake, distribution (tissue binding), metabolism, and elimination.

3. Distribution

• Blood transports a substance throughout an organism, where it accumulates heterogeneously based on tissue, species, and chemicals.

4. Metabolism

• The definition of metabolism is the transformation of ingested chemicals into various metabolites and their removal from an organism.
• A chemical can be metabolised, a process known as biodegradation and involving organic components.
• A chemical’s metabolism may involve splitting into smaller molecules or mineralization to CO2, water, and nutrients.

5. Storage

• A chemical can be kept in several locations within an animal’s body, such as adipose tissue and bones.

6. Excretion

• In general, plants excrete via the leaf surface, whereas animals excrete by urine, faeces, saliva, breast milk, perspiration, and breathing.

Bioaccumulation – Mechanisms

• The process of bioaccumulation follows complex food webs.
• The tissues of species at the top of the food chain have a greater concentration of substances. It relies on the species’ feeding habits, habitat, and metabolic activity.
• Bioaccumulated substances are converted to derivatives that may be more dangerous than the parent chemicals; for instance, less toxic inorganic mercury is converted to highly toxic methylmercury.
• Bioaccumulation is contingent on the stability of chemical binding within cellular compartments and the metabolic half-life.
• Elimination, which typically follows first-order kinetics, is necessary for bioaccumulation.
• There are three main pools: quick (a chemical dissipates within weeks/days/hours/minutes), slow (during months), and unabsorbed from the gastrointestinal tract (in animals; days).

How Do We Protect Ourselves From Bioaccumulation?

• To avoid exposure to harmful quantities of pollutants, we must consume foods from lower on the food chain. Plants are significantly less contaminated than animals.
• Avoid bottom feeders such as shrimp, crab, scallops, and lobster while consuming seafood. Heavy metals are so named because they are five times heavier than water and so sink to the bottom. Bottom-dwelling creatures will acquire these metals.
• Consume little fish. For instance, sardines, a little fish, contain significantly less mercury than tuna, a huge fish. You may get an up-to-date database of all safe fish at www.seachoice.org.
• Select organic products whenever possible. By definition, organic foods have fewer chemicals. I am frequently asked, “I can’t afford to buy everything organic; what do you propose as the most essential organic food?” My response begins with an explanation of bioaccumulation, followed by the response “all animal foods.”
• Spring and fall are the finest seasons of year to do a detoxification programme. There are numerous diets, vitamins, herbs, and superfoods that aid in the elimination of accumulated toxins.

Before humans began polluting the environment, individuals did not have to worry about bioaccumulation. Now, if we wish to maintain the body’s health and optimal function, we must comprehend this concept and make food choices accordingly.

Practical Applications of Bioaccumulation

The phenomena of bioaccumulation has practical applications:

• Toxicological and ecotoxicological testing — looking for quantitative relationships between dose and symptoms, determining the threshold value – the highest dose that does not cause any symptoms.
• In bioremediation of contaminated elements of the environment and wastewater treatment, hyperaccumulating organisms are utilised. Selection for organisms that can tolerate large levels of environmental contaminants and accumulate them in their biomass. These are species that have evolved protective systems against hazardous substances. An example is the creation of metallothioneins, which, due to their high thiol content, bind harmful metal ions and prevent them from the fundamental metabolic pathways, so protecting the organism from their toxic consequences.
• It has been shown that the bioaccumulation capacity increases as the size and organisation of an organism decrease. Microorganisms appear to be the most useful organisms when bioaccumulation is used as a wastewater treatment approach.

Examples of Bioaccumulation

Terrestrial Bioaccumulation examples

• An example of poisoning in the workplace is the expression “mad as a hatter” (18th and 19th century England).
• Mercury was employed to stiffen the felt used to make hats more than a century ago. Mercury forms organic compounds such as lipid-soluble methylmercury, which tends to collect in the brain, leading in mercury poisoning.
• Other fat-soluble toxins include tetraethyllead compounds (the lead found in leaded gasoline) and DDT.
• When the fatty tissues are utilised for energy, these chemicals are produced and cause acute poisoning.
• Strontium-90, a component of atomic bomb fallout, is chemically close enough to calcium to be used in osteogenesis, where its radiation can inflict long-lasting damage.
• Some animal species use bioaccumulation as a kind of protection; by consuming hazardous plants or animal prey, a species might store the toxin, which then serves as a deterrent to a future predator.
• One example is the tobacco hornworm, which consumes tobacco plants and accumulates a dangerous quantity of nicotine in its body. Poisoning of tiny consumers can be transmitted up the food chain to later consumers.
• Other substances that are not often considered poisonous can accumulate in organisms to toxic quantities. The classic example is vitamin A, which becomes concentrated in the livers of carnivores such as polar bears, which, as pure carnivores that prey on other carnivores (seals), collect exceptionally high levels of vitamin A.
• The aboriginal peoples of the Arctic knew that carnivore livers should not be consumed, yet Arctic explorers who consumed bear livers developed hypervitaminosis A. (and there has been at least one example of similar poisoning of Antarctic explorers eating husky dog livers).
• On Sir Douglas Mawson’s expedition, one of the explorers died after consuming the liver of one of the dogs.

Aquatic examples

• Coastal fish (like the smooth toadfish) and seabirds (like the Atlantic puffin) are frequently examined for bioaccumulation of heavy metals. Methylmercury enters freshwater systems by means of industrial pollutants and precipitation. As its concentration rises through the food chain, it can reach deadly levels for both fish and humans who eat fish.
• Toxins produced naturally can also bioaccumulate. The marine algal blooms known as “red tides” can cause local filter-feeding creatures such as mussels and oysters to become poisonous; coral reef fish can cause ciguatera when they acquire ciguatoxin from reef algae.
• In certain eutrophic aquatic environments, biodilution is possible. This trend is a drop in a contaminant with an increase in trophic level due to increasing populations of algae and bacteria that “dilute” the pollutant concentration.
• Wetland acidification can enhance chemical or metal concentrations, resulting in greater bioavailability in marine plants and freshwater organisms.
• The bioavailability of metals can have an effect on the local vegetation, including both rooted and submerged plants.

References

• Dehghani, Amir & Roohi Aminjan, Atabak & Dehghani, Allahverdi. (2022). Trophic transfer, bioaccumulation, and health risk assessment of heavy metals in Aras River: case study-Amphipoda-zander -human. Environmental Science and Pollution Research. 3. 10.1007/s11356-021-18036-7.
• Chojnacka, K., & Mikulewicz, M. (2014). Bioaccumulation. Encyclopedia of Toxicology, 456–460. doi:10.1016/b978-0-12-386454-3.01039-3 
• https://www.joshgitalis.com/bioaccumulation-what-you-must-know/
• https://energyeducation.ca/encyclopedia/Biomagnification
• https://sharkallies.org/learn-about-shark-products/shark-meat-what-is-bioaccumulation
• https://www.sciencelearn.org.nz/image_maps/119-bioaccumulation-in-the-sea
• https://en.wikipedia.org/wiki/Bioaccumulation