Food chains do not only carry energy. They carry whatever the organisms happen to contain — including pollutants that will not break down. Add in the ways we alter the physical environment, and human activity ends up rewriting both the energy flows and the matter flows of an ecosystem.
These two words look similar and get muddled constantly, so pin the difference down now.
| Term | Where it happens | What builds up |
|---|---|---|
| Bioaccumulation | Inside a single organism, over its lifetime | The pollutant collects because the body cannot break it down or excrete it |
| Biomagnification | Along a food chain, from one trophic level to the next | Concentration rises at each level, because predators eat many contaminated prey |
The reason biomagnification works is the topic you have just been studying. Energy is lost between trophic levels, so a predator has to eat many prey items to survive. The pollutant in all of those prey ends up in one predator, while most of the biomass is respired away.
A widely used insecticide in the mid-twentieth century. Sprayed on crops, it leached into waterways and entered freshwater and marine ecosystems. It passed into plankton, then into fish, then into the birds that ate those fish. Because DDT is persistent and does not break down easily, it kept accumulating in birds of prey such as eagles and falcons, causing thinning of eggshells and reduced breeding success.
Released by activities such as coal-fired power generation and gold mining. In the environment it is converted into the highly toxic form methylmercury, which accumulates in fish. As larger fish eat smaller fish the concentration rises, so people who eat large predatory species such as tuna or swordfish are exposed.
In 1956 a chemical factory released methylmercury into wastewater entering Minamata Bay in Japan. Mercury built up in fish and shellfish, and local people who ate them suffered severe mercury poisoning, including paralysis, deaths and birth defects in newborns.
Microplastics are plastic particles usually smaller than 5 mm, coming from bottles, packaging and synthetic clothing. In the environment they behave a bit like sponges, absorbing non-biodegradable pollutants such as PCBs, pesticides and heavy metals including lead and mercury.
That makes them a delivery system. Marine animals ingest microplastics as they feed, the toxins accumulate in their bodies, and larger predators then eat those contaminated organisms — increasing the level of biomagnification.
Studies on oysters exposed to microplastics carrying pollutants found lower feeding rates, altered growth patterns and reduced reproductive success, harming both individual fitness and the population as a whole.
| Activity | Effect on energy and matter flow |
|---|---|
| Burning fossil fuels | Releases carbon dioxide, driving warming. Extra carbon dioxide can raise photosynthesis, but temperature rise and changed rainfall usually outweigh that, lowering primary productivity. Coal also releases sulfur dioxide, contributing to acid rain, which affects soil pH, plant health and nutrient availability |
| Deforestation | Causes habitat loss and disrupts food webs, and reduces the carbon sink capacity of forests, contributing to climate change |
| Urbanisation | Replaces natural habitat with impervious surfaces, increasing runoff and reducing infiltration; urban heat islands raise local temperatures |
| Agriculture | Intensive fertiliser, pesticide and monoculture use leads to soil degradation, water pollution and biodiversity loss |
Explain why top predators are most affected by biomagnification, using ideas about energy transfer.
A pesticide measures 0.5 ppm in zooplankton and 21 ppm in a fish that feeds on them. Calculate the magnification factor and suggest why it is so high.
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