Bioaccumulation

Bioaccumulation definition and basics

Chemicals can enter organisms through various pathways such as ingestion, skin contact, or respiration. Over time, these substances can accumulate in body tissues, particularly in fat, due to their inability to be easily metabolised or excreted. This accumulation can have significant health impacts on the organisms.

How bioaccumulation affects ecosystems

Bioaccumulation has far-reaching implications for ecosystems, affecting individual organisms, populations, and entire communities. It influences the health and survival of species, leading to altered food webs and ecosystem dynamics.

• Health Impacts on Wildlife: Animals at the top of the food chain, such as birds of prey, marine mammals, and large fish, are particularly vulnerable to bioaccumulation. They ingest smaller organisms that have absorbed toxic substances, leading to a higher concentration of these toxins in their own bodies.
• Ecosystem Imbalance: High levels of toxic substances can lead to decreased populations of some species, while others may thrive, causing imbalances in the food web. This can result in loss of biodiversity and ecosystem functionality.
• Human Health Risks: Humans are also affected by bioaccumulation, especially those relying on fish and wildlife for their diet. Toxic substances transferred through the food chain can pose significant health risks to people.

Examples of Bioaccumulation in Nature

When discussing environmental science, bioaccumulation provides a significant insight into how pollutants move through and affect natural ecosystems. Here, you will explore some concrete examples of bioaccumulation in nature, highlighting its implications for both marine and terrestrial environments.

Bioaccumulation examples in marine life

Marine ecosystems are particularly vulnerable to bioaccumulation due to the vast and interconnected food webs present in oceans and seas. The presence of certain chemicals, often originating from human activities, can become concentrated in the tissues of marine organisms.

• Mercury in Fish: As previously mentioned, fish accumulate mercury, posing risks to predators, including humans.
• PCBs in Marine Mammals: Polychlorinated biphenyls (PCBs), used in various industrial applications, have been found in significant concentrations in whales and dolphins. These substances can lead to health issues such as immune system suppression and reproductive failures.
• Plasticisers in Seabirds: The ingestion of plastics by seabirds often leads to the accumulation of plastic-derived chemicals in their bodies, impacting their health and reproductive success.

Terrestrial examples of bioaccumulation

On land, bioaccumulation manifests through various vectors, impacting insects, birds, mammals, and even plants. The sources of contaminants are diverse, ranging from agricultural chemicals to industrial waste.

• Pesticides in Bees: Certain pesticides, such as neonicotinoids, accumulate in bees, leading to colony collapse disorder by affecting their navigation and foraging behavior.
• Heavy Metals in Birds: Birds of prey accumulate heavy metals like lead and cadmium through their diet, which can result in decreased fertility and eggshell thinning.
• Organic Pollutants in Carnivores: Top terrestrial predators, including eagles and other birds of prey, show high levels of organochlorine compounds, which are carried up through the food chain.

Bioaccumulation vs Biomagnification

Understanding the distinction between bioaccumulation and biomagnification is pivotal in grasping how pollutants affect environments and organisms. In environmental science, these processes play a critical role in the transfer and concentration of chemicals within ecosystems.

Understanding the difference

Both processes are interconnected, but they highlight different aspects of how pollutants can concentrate and exert effects within ecosystems. Bioaccumulation occurs within an individual organism, primarily due to exposure from its immediate environment, whereas biomagnification demonstrates how these concentrations magnify across food webs, affecting entire populations and ecosystems.

Biological magnification and bioaccumulation in food chains

In food chains, both bioaccumulation and biomagnification contribute to the increased concentration of pollutants in top predators, showcasing the cumulative effects of these processes.

• The base of the food chain usually comprises organisms that directly absorb pollutants from their environment, such as plankton in water bodies.
• These substances then bioaccumulate in the bodies of primary consumers who eat the plankton, setting the stage for biomagnification.
• As one moves higher up the food chain, through secondary and tertiary consumers, the concentration of pollutants increases significantly due to biomagnification.

Causes of Bioaccumulation

Understanding the causes of bioaccumulation is fundamental to assessing its environmental impact. Factors contributing to this phenomenon span both natural occurrences and human activities, each playing a distinct role in the accumulation of chemicals within organisms.

Natural causes of bioaccumulation

Natural processes can lead to the bioaccumulation of substances in organisms, affecting ecosystems without human intervention. These causes are inherent to the environment and are crucial for maintaining its balance.

• Geological Deposits: Natural deposits of minerals and metals can leach into water bodies, leading to the absorption of these substances by aquatic life.
• Biological Concentration: Certain plants and microorganisms have the ability to concentrate substances from their surroundings as part of their biological processes.
• Biochemical Processes: The transformation of substances by living organisms can lead to the creation of bioaccumulative compounds, such as the conversion of mercury to methylmercury by aquatic microorganisms.

Human-induced factors leading to bioaccumulation

Human activities significantly contribute to the levels and spread of bioaccumulative substances in the environment. Industrialisation, agriculture, and waste management practices are among the key drivers of chemical dispersion, leading to increased instances of bioaccumulation.

• Industrial Discharges: Factories and industrial plants often release heavy metals and organic pollutants into water bodies, air, and soil, increasing the availability of these substances to be absorbed by organisms.
• Agricultural Runoff: Pesticides and fertilisers used in farming can wash into rivers and lakes, concentrating in aquatic ecosystems and the organisms that inhabit them.
• Improper Waste Disposal: Pharmaceuticals and chemicals disposed of in landfills can leach into the surrounding environment, entering food chains through soil and water contamination.