Year 9 Science · Unit 2 · Lesson 18
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Learning Goals
Real-world context
In 2023, the NSW Environment Protection Authority sampled stormwater drains in six Sydney suburbs after a heavy rain event. They found elevated microplastic concentrations in 100% of sites tested, with rubber tyre particles the dominant type, followed by polyethylene and polypropylene fragments. Concentrations were 10–15 times higher in the 24 hours after rain than during dry weather. The stormwater discharged directly to Sydney beaches and the Harbour with no filtration.
(a) Using your knowledge of microplastic sources, explain why tyre wear particles dominated the samples. Include in your answer: where tyre wear particles come from, how they enter stormwater, and why heavy rain increased concentrations.
(b) Predict what would happen to microplastic concentration in Sydney Harbour fish over the following decade if this stormwater problem is not addressed. Use the term "bioaccumulation" in your answer.
Read the diagram
Study the food chain below showing microplastic concentrations at each trophic level in an Australian coastal ecosystem. Then answer the questions.
Data: illustrative model based on published biomagnification factors; p/g = particles per gram of tissue.
(a) By what factor does microplastic concentration increase between zooplankton (0.04 p/g) and the great white shark (270 p/g)? Show your working.
(b) Explain, using the terms "bioaccumulation" and "biomagnification", why the great white shark has by far the highest concentration of microplastics despite not ingesting microplastics directly from the water.
(c) Suggest why humans who regularly eat tuna (a high trophic-level fish) may be exposed to more microplastics than people who eat only small fish such as sardines. Use the diagram as evidence.
1. The Great Pacific Garbage Patch covers an estimated 1.6–3.4 million km². A news headline reads: "Giant Island of Plastic in Pacific Now Twice the Size of NSW." Using what you know from the lesson, explain what is accurate and what is misleading about this headline.
2. CSIRO found 414 million pieces of plastic on the beaches of Cocos (Keeling) Islands, a remote Australian territory 2,750 km from the nearest coast. Explain how plastic items produced in other countries ended up on these beaches, and what this tells us about plastic pollution as a global problem.
Wrap Up
In one sentence, what was the main idea of this lesson?