Biology

Bio-accumulation: Plastic not-so-fantastic

Plastic is central to our way of life, but what happens when we’ve finished with it? A lot ends up in the oceans and it’s only now becoming clear how much of a problem that poses for marine food chains.

In this lesson you will investigate the following:

• How does persistent chemical pollution affect food chains?

• Why is plastic such a serious pollution problem?

• Why are flesh-footed shearwaters at risk?

• Are there sustainable alternatives to plastic?

So plastic fantastic? Let’s see.

This is a print version of an interactive online lesson. To sign up for the real thing or for curriculum details about the lesson go to www.cosmosforschools.com

Introduction: Bio-accumulation

How would you feel if 10% of your body weight was made up by pieces of plastic lodged permanently in your stomach?That’s the situation now faced by many seabirds – victims of plastic pollution.

Despite efforts to recycle and reuse more of the plastics we consume, a vast amount still makes its way into the world’s oceans.Once there, it can circulate in currents for centuries or wash up on beaches anywhere – from Canada to Antarctica.

Seabirds such as flesh-footed shearwaters often mistake floating pieces of coloured plastic for prey and snap them up. Over timetheir bellies grow heavy with the stuff.

It gets worse. Australian researchers recently found that the plastics consumed by seabirds might also expose them to thepoisonous effects of heavy metals. These substances are added to plastics in small amounts during production and includemercury, lead and arsenic.

Heavy metals also tend to stick to pieces of plastic as they float in seawater. This increases the potential harm to anything thatmistakenly eats them. And “green” biodegradable plastics might actually make this problem worse because they break into smallerpieces. The greater surface area of small fragments increases their ability to collect heavy metals.

Seabirds also suffer because of their position at the top of the marine ecosystem. Contamination levels skyrocket towards the topof a food chain as predators absorb the poisons contained within their prey.

A better understanding of the complex connections between animals at all levels of the marine ecosystem will hopefully help usreduce the impact of our appetite for plastics. 

Read the full Cosmos Magazine article here.

Plastics have many uses, some very high-tech, but a lot ends up in the ocean.

Question 1

Speculate: Some examples of marine debris are shown in the sketchpad. Firstly, order them according to how quickly you thinkthey break down in the ocean, starting at 1 for the quickest. Then guess how long it takes each type of material to break down.

When you've finished, your teacher will give you the answers. How close were you?

Gather: Bio-accumulation

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Question 1

Select: A marsh has been sprayed with the pesticide DDT at six-monthly intervals for the last three years.

Where would you expect to find the lowest concentration ofDDT?

In fish that eat other fish.

In birds that eat fish.

In the water.

In plankton.

In small, plankton-eating fish.

Question 2

Select: Where would you expect to find the highest

concentration of DDT?

In the water.

In fish that eat other fish.

In plankton.

In birds that eat fish.

In small, plankton-eating fish.

than they are taken in. Some of their chemical components canbuild up in tissues such as kidneys, muscles and feathers.

The gradual build up of pollutants through the lifetime of anindividual organism is known as bio-accumulation. Many of thesepollutants are poisonous, or toxic, and cause weakness, illness,sterility or – at high enough doses – death.

Question 3

Recall: Persistent substances do not easily break down.

True

False

Question 4

Recall: Toxic substances only ever accumulate in muscle.

True

False

Question 5

Describe: In your own words, describe the process of bio-accumulation.

Every organism stays alive by taking in matter from itsenvironment. Some of this matter is used for energy ornutrients that are built into the organism’s tissues while the restis got rid of as waste.

Some of the matter that organisms take in may be polluted.Pollutants that do not break down easily are called persistent.They may collect in the stomach or be removed more slowly

Bio-accumulation

Pollution levels can also increase up through food chains.

On land, the bottom of the food chain is made up of plants, which convert the Sun's energy into chemical energy byphotosynthesis. In the oceans, this role is played by phytoplankton – thousands of species of bacteria and algae that float near thesurface where they can absorb sunlight.

As they collect the nutrients they need from the water around them, phytoplankton can bio-accumulate persistent pollutants. When they are eaten by larger organisms – from microscopic zooplankton and small crustaceans right up to whales – the pollutantsare ingested too. And because large predators eat many smaller prey during their lifetimes they ingest greater quantities ofpollutants than smaller organisms.

This process is known as bio-magnification. Because it's repeated at each level of a food chain, the concentrations of pollutants atthe top levels can be hugely magnified.

Bio-magnification

Question 6

Multiply: Imagine a young flesh-footed shearwater has consumed 800 fish in its life. Each fish on average had fed on 600 smallcrustaceans, and each crustacean on 900 phytoplankton. Each phytoplankton had 1 picogram (pg) of a persistent toxin in it (1 pg =1 trillionth of a gram). Assuming that none of the toxin is lost from the food chain, how many picograms will the shearwater ingest?Multiply from the bottom of the food chain below to answer.

Note: the numbers in this exercise are examples only – in many cases real numbers are likely to be much greater. And in some cases there

will be additional steps in the food chain, for example, shrimp also eat zooplankton that feed on phytoplankton.

Question 7

Paraphrase: In your own words, explain why the concentration of persistent pollutants typically increases at each level up a foodchain.

Did you know?

The pesticide DDT (dichlorodiphenyltrichloroethane) was usedextensively in the 1940’s and 1950’s, liberally sprayed overswamps, streets, and sometimes even people's hair and bodies.It was a spectacular success controlling – and in some areas,eradicating – typhus, malaria and dengue fever, all carried byinsects. In 1948 Paul Müller, who discovered DDT’s pesticidaleffects, was awarded the Nobel Prize.

By the late 50's the cumulative effects of this usage werebecoming increasingly difficult to ignore, with populations ofbirds of prey, especially, showing drastic declines. In 1962Rachel Carson's book, Silent Spring, made the case against DDT.The book is generally held to have launched the modernenvironmental movement. In 1972 most uses of DDT in the USwere banned, and other countries followed.  

Process: Bio-accumulation

Plastics play an important part in our way of life. Not only are they used in many cheap common products, such as drink containersand plastic bags, they are also vital components in cutting-edge technologies such as prosthetic limbs and other medical devices,bulletproof vests, and spacecraft.

But on the downside, it is believed that virtually every piece of plastic ever manufactured still exists in some shape or form – plasticsare very persistent. And with world production at around 300 million tonnes a year, it looks like plastic is just going to keep onbuilding up.

Plastic

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Question 1

Recall: Which of the factors below cause plastic to break downin the ocean?

Salt

Plankton

Sun

Waves

Tides

Question 2

Consider:  Plastic litter reaching the sea is slowly "brokendown", but "breaking down" a substance can mean differentthings. From the information given above, is the breakdown ofplastics in the ocean mostly chemical or physical change?

Hint: chemical change always means a new type of substance is

formed.

Physical change

Chemical change

Question 3

Explain: If a plastic bottle top breaks into hundreds or even thousands of pieces, how does the surface area of the plastic change?Explain.

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Question 4

Assess: The videos describe how pollutants like DDT and mercury bind to the surfaces of pieces of plastic floating in the ocean.

Considering bio-magnification, what poses the greater risk to marine organisms – a single plastic bottle top or thousands ofmicroplastic particles?

Explain your answer. 

Question 5

Match: Listed below are the concentrations of mercury in the tissues of a range of organisms from different levels of a marine foodchain. Use your knowledge of the food chain to match the mercury concentrations to the organisms listed in the sketchpad, andcreate a bar graph to display the data.

0.05 ppm   |   0.2 ppm   |   0.9 ppm   |   1.8 ppm   |   6 ppm   |   121 ppm

Question 6

Deduce: Concentrations can be measured in different ways. In the video Jennifer Lavers uses parts per million (ppm), but analternative unit is milligrams per kilogram (mg/kg).

What is 1 mg/kg in ppm?

Hint: how many milligrams are there in a kilogram?

Question 7

Calculate: Using the data above, if a shearwater consumes 25 kg of small mercury-contaminated fish each month, how muchmercury will it ingest in 1 year?

Question 8

Evaluate: a) If the shearwater, weighing 500 g, had no mercury contamination to start with and absorbed all the mercury itingested into its tissues, what concentration of mercury would it have at the end of the year, in mg/kg? 

b) Shearwaters commonly live to 20, and sometimes into their 30's, but the mercury concentrations found in the bodies ofadults are not as great as this exercise suggests. Can you think why not?

For the final question in this section, you can choose to answer either Question 9 or Question 10.

Question 9

Explicate: Shearwaters live on small fish but also eat pieces of floating plastic, no doubt expecting that these might be nutritiousmorsels. Bring together all that you have learnt about bio-accumulation, bio-magnification and plastic in the ocean to explain whyshearwaters have such very high concentrations of mercury in their tissues.

Question 10

Present: Everyone in our society uses plastic in some way or other. Write a short newspaper article describing:

the current problems caused by plastic pollution,

the probable consequences if we continue our current practices for the production, use and disposal of plastic,

ways to improve the situation, and

challenges we might face making these changes.

Apply: Bio-accumulation

Product life-cycle analysis

Question 1

Evaluate: You are the chief researcher for an eco-solutions company that provides recommendations to consumers abouteveryday products. You have been tasked with evaluating the environmental impact of one everyday plastic product compared toan alternative made from a different material. 

Examples include:

drink bottle – plastic vs aluminium

bag – plastic vs paper

bag – plastic vs cloth

phone cover – plastic vs leather

Your teacher will organize you into teams to research your chosen products. Your team must research the environmental impactsat each stage of your product's life cycle:

1. sourcing raw materials

2. manufacture

3. distribution to end users

4. product use, reuse and maintenance

5. recycling, if any

6. disposal

Think of as many factors as you can for each stage, for example: energy usage, the resources required, toxicity of materials, wasteproducts, and impacts on flora, fauna and human societies. 

When you have completed your research, assess which material is better for the environment for each life-cycle stage. Then decidewhich is the better material, environmentally speaking, for this type of product overall.

Present your main findings in a table in the project space below. Include any supporting material in the project space as well. 

Conclusion

Question 2

Summarize: Which material, plastic or other, do you think is better for the environment for the product you chose. What are themain reasons you reached this conclusion?

Career: Bio-accumulation

Jennifer Lavers is a marine biologist, and feels as though she got there almost completely by accident. Growing up in theprairies in the middle of Alberta, Canada, Jennifer loved volunteering at veterinary clinics and for wildlife projects, but she wasalways far from the ocean. Nevertheless, when she was offered a PhD project working on seabirds she thought, on a whim, “Okay,let’s do this.”

Jennifer fell in love with her project right away. Her researchfocused on ocean plastic pollution and she still studies this nowat the University of Hobart, Tasmania.

Seabirds, Jennifer says, can be regarded as "sentinels" or"indicator species", acting as our eyes and ears for the health ofthe ocean. By studying the health and behaviour of seabirds andmonitoring their populations, Jennifer helps identify changesand problems in the marine environment.

In addition to her research, Jennifer works as the chief scientistfor Natural History Australia TV, a film company thatproduces educational stories about human interactions withnature. She works both behind the scenes as a researcher andin front of the camera as a presenter and interviewer. It’s a lot ofwork but she finds it incredibly rewarding – she especially lovesthe blooper reels that come out of filming.

When she isn’t surveying her seabirds or starring on film,Jennifer works on restoring her 130-year-old home, which sherecently bought with her partner. She hopes to turn the largegarden into a native wildlife sanctuary – one which the localbirds can enjoy.

Question 1

Imagine: Imagine that you are the chief scientist for a film company like Jennifer's. Think about the environmental issues in yourlocal area. What issue would you want to focus on for your next story, and why?

Cosmos Lessons team

Lesson author: Hayley BridgwoodIntroduction author: Campbell EdgarProfile author: Megan ToomeyEditor: Jim RountreeArt director: Wendy JohnsEducation director: Daniel Pikler

Image credits: iStock, Shutterstock, State Library QLD, ChrisJordan’s Photographs of Bird Carcasses, Brent Stephenson/Eco-VistaVideo credits: Biology/Medicine Animations HD, Alice Dunseath,ABCTVCatalyst, YouTube, Vimeo