Microplastics and pollutants at Higher Level: The same ideas as SL, with different examples: Arctic sea ice, fish in the English Channel, and coral reefs in the Asia-Pacific. At HL, expect a trend graph to read and a food chain to explain.
Practise this as you read
- Link each harm of plastic to an organism in the food chain.
- Read a trend: more plastic, longer exposure, more toxin.
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Plastic that never goes away: Plastic does not rot. It breaks into smaller and smaller pieces until it becomes microplastics, which now reach every sea on Earth.
The points to remember
- Microplastics are pieces of plastic smaller than 5 mm.
- Some are made small: microbeads in cosmetics, fibres shed when synthetic clothes are washed, factory pellets.
- Most are broken off bigger plastic by UV light, waves and currents.
- Plastic is non-biodegradable: it breaks into smaller pieces but does not rot away.
- Plastic reaches the sea from rivers, landfills near the coast, ships and lost fishing gear.
- Microplastics now travel far in ocean currents and are found in water, air, soil and living things everywhere.
Remember it as: Plastic does not rot, it just gets smaller.
Real example: scientists who melted cores of Arctic sea ice in 2018 found up to 12,000 microplastic particles in each litre, carried there by ocean currents from thousands of kilometres away.
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Microplastics are a problem even when an animal passes them out again, because they do not travel alone. Persistent pollutants in the water stick to them, in the same way that oil sticks to a plastic tub.
The points to remember
- Persistent pollutants such as PCBs and DDT dissolve poorly in water but well in oily substances.
- Plastic is oily, so these pollutants are absorbed into its surface.
- On a plastic pellet they can be up to a million times more concentrated than in the water around it.
- The longer a piece floats, the more pollutant it soaks up.
- So microplastics act as carriers (vectors) for toxins.
Remember it as: Oily plastic soaks up oily poisons.
Real example: beach pellets collected around the world by the International Pellet Watch project carry PCBs and DDT; the highest levels are on beaches near big industrial cities.
Say what the plastic carries: 'Microplastics are eaten' alone is only half the story. Say that toxins are absorbed onto the microplastics, so eating the plastic passes the toxins on.
Now the plastic enters the food chain, and the pollutants it carries go with it. From here, bioaccumulation and biomagnification take over (the ideas of the previous page).
The points to remember
- Small animals at low trophic levels (zooplankton, filter feeders such as mussels, small fish) mistake microplastics for food.
- In the gut, the toxins pass into the animal's tissues.
- The toxins bioaccumulate in the prey and biomagnify up the food chain.
- So microplastics increase the transmission of pollutants along the food chain.
- Top predators, including people who eat seafood, get the highest dose.
- More microplastic, and a longer time in the sea, means more toxin in the fish.
Remember it as: Mistaken for food, toxins in, up the chain.
Real example: in the English Channel, 36.5% of 504 fish from ten species had plastic in their guts, mostly fibres. In Belgium, a person who often eats mussels may swallow thousands of microplastic particles a year.
Reading a trend graph: If a graph shows microplastics rising over time, fish caught later hold more toxins for two reasons: more microplastic to eat, and a longer time for the toxins to build up.
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Bigger pieces of plastic harm sea life directly, before they ever break down. Learn these too: a question about plastic and a food chain credits them alongside the toxins.
The points to remember
- Large items look like food: a floating bag looks like a jellyfish to a turtle.
- Swallowed plastic fills the stomach, so the animal feels full and starves.
- Animals get entangled in lost fishing nets and six-pack rings, and drown or are injured.
- Plastic floating over the water blocks sunlight, so there is less photosynthesis; it can smother corals.
- Hard plastic scrapes corals, and the wounds become infected.
Remember it as: Mistaken for food, tangled, starved, smothered, scratched.
Real example: a survey of 159 coral reefs in the Asia-Pacific found that corals touching plastic were about 20 times more likely to be diseased (89% compared with 4%). About half of all sea turtles are thought to have swallowed plastic.
How this comes up: Paper 2, Section A: a food chain with the sources of plastic. Explain how plastic pollution could harm the organisms shown [3].
Figure 1 shows how PCBs from seawater reach harbour porpoises in the English Channel.
Explain how plastic pollution could have adverse effects on the organisms shown in Figure 1.
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