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Reading passage Grade 6 Science

The Fibers in the Ossley River: Counting Microplastics

A grade 6 science reading passage on how a fictional volunteer team samples and counts microplastics, with a data table and seven comprehension questions.

Objectives

  1. Students will identify how a volunteer team samples and counts microplastics in a river.
  2. Students will infer the source of a pollutant from a pattern in sampling data.
  3. Students will explain how population growth would change the amount of fiber in a river.

Vocabulary

Key words: microplastic, fiber, fragment, synthetic, outfall, sample

Teacher overview

This passage follows a fictional volunteer team that samples a river for microplastics and works out where the pieces come from. It suits a unit on water pollution, on wastewater treatment, or on how scientists tell one source from another when several sources feed the same river. The misconception worth naming afterward is that a treatment plant either removes a pollutant or does not. Plants remove a large share of the plastic that reaches them, mostly by letting it settle with the sludge, yet a plant that catches almost everything still passes some material along, and a small share of a very large number can still be a large amount. The data table lets students see that idea rather than be told it.

The Fibers in the Ossley River: Counting Microplastics — Grade 6 Science
Name: ____________________________ Date: ______________

Passage

Maya Okonjo pulls the net out of the water and shakes it over a jar. The net is fine mesh, and the boat has been towing it slowly for twenty minutes. In the jar the sample looks like river water with a little grit in it, yet the county lab will find more than grit.

Maya volunteers with the Ossley River Watch, a fictional group in the town of Wellmont. Twice a month the volunteers take samples above and below the town's wastewater treatment plant. They are counting microplastics, which are plastic pieces smaller than five millimeters across. Some are too small to see without a microscope.

At the lab, a technician pours each sample through a stack of sieves. The material that stays behind is dried and spread on a dish. Then it goes under a microscope. The technician sorts what she finds into two shapes. Fibers are thin threads, often blue or clear, and they usually come from cloth. Fragments are broken bits with rough edges, and they usually come from harder plastic like bottle caps, paint, or tires.

Here is what the volunteers found last spring. Each number is the count in a thousand liters of river water. All of these readings were written for this passage.

Where and when the sample was taken Fibers Fragments
Above the plant, dry week 9 4
Below the plant, dry week 23 5
Below the plant, Monday morning 31 6
Below the plant, day after a storm 26 38

The pattern took the volunteers two seasons to trust. Fiber counts stayed higher below the plant than above it, week after week. Fibers also rose on Mondays. Fragments behaved differently. They barely moved from day to day, then jumped after every storm.

Rosa Delgado, who runs the treatment plant, was not surprised by the fibers. Washing machines send their water to her plant. A fleece jacket or an athletic shirt is made of synthetic cloth, which means the threads are made from plastic rather than grown from cotton or wool. Every wash shakes thousands of tiny threads loose. Those threads travel down the drain with the wash water.

The plant catches most of them. Water sits in large tanks where heavy material settles to the bottom, and fibers stick to that settling sludge. Rosa says her plant was built to remove waste that bacteria can eat, not to filter out threads, and it still takes out most of the plastic that arrives. Then she adds the part the volunteers repeat at every meeting. Removing most is not the same as removing all. The plant treats millions of liters a day, so even a small share that slips through adds up in the river below the outfall.

The fragments tell a different story. They do not arrive through the plant at all. Storms wash grit off streets and parking lots straight into the river through storm drains. That grit carries worn bits of tire, paint, and cracked plastic. On a dry week the streets hold their dust and the fragment counts stay flat.

Wellmont is now deciding what to do. The volunteers have proposed sampling the same two spots every month and again within a day of every storm over an inch, so the town can tell whether anything changes. The town council is looking at two steps. One is a filter that fits on a washing machine drain and catches fibers before they leave the house. The other is sweeping the main streets before forecast storms instead of after them.

Maya labels the jar and writes the time on the lid. The river looks no different than it did an hour ago, and only the count will show what it carries.

Questions

  1. According to the passage, what are the two shapes of microplastic the lab counts?
  2. How do the volunteers collect a sample from the river?
  3. Fragment counts jumped the day after a storm, but fiber counts did not. What does that difference suggest about where the fragments come from?
  4. Fiber counts were higher below the plant than above it. Use evidence from the passage to explain why.
  5. Rosa Delgado says that removing most is not the same as removing all. Explain what she means, using details from the passage.
  6. Suppose Wellmont grows and many more homes run washing machines each week. Use evidence from the passage to explain what would likely happen to the fiber counts, and why.
  7. The passage says a fleece jacket is made of synthetic cloth. Using the passage, explain what synthetic means and why it matters for the river.

From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.

Answer Key
  1. Answer: Fibers and fragments.
    The passage says the technician sorts what she finds into two shapes, thin threads called fibers and rough broken bits called fragments.
  2. Answer: With a fine mesh net towed behind a boat.
    The opening describes Maya pulling in a fine mesh net after the boat has towed it slowly for twenty minutes, then shaking it over a jar.
  3. Answer: The fragments come from streets and parking lots, not from the plant.
    Storms wash grit off paved surfaces into storm drains that run straight to the river. Because that path only carries water during storms, fragment counts jump after a storm and stay flat in dry weather. Accept any answer naming roads, storm drains, or runoff.
  4. Answer: Because the plant releases its treated water below that point.
    Washing machine water reaches the plant, the plant removes most of the fibers but not all of them, and the treated water leaves through the outfall into the river. The samples above the plant never receive that water.
  5. Answer: A small share of a very large amount of water is still a large number of fibers.
    The passage says the plant treats millions of liters a day. Even if the tanks catch most of the plastic, what slips through adds up in the river below the outfall.
  6. Answer: Fiber counts would likely rise.
    The passage links fibers to laundry, since every wash shakes threads loose from synthetic cloth and sends them to the plant. More homes washing more loads sends more fibers to a plant that already lets some pass, so more would reach the river.
  7. Answer: Synthetic means the threads are made from plastic rather than grown.
    The passage contrasts synthetic cloth with cotton or wool. It matters because plastic threads do not break down the way natural fibers do, so the threads that escape the plant stay in the river as microplastic.

Differentiation

Support

Read the passage aloud once while students follow along, then have partners reread the two paragraphs about the plant. Provide the data table on its own half sheet with the storm row highlighted. Offer answer stems for questions 3 and 4, such as "The fragments come from ___ because ___." Accept one-sentence answers for questions 5 through 7.

Extension

Ask students to write the two sentences the volunteers would put at the top of a report to the council, stating what the data show and what they do not show. A second option is to design the table the town would need in order to tell, three years from now, whether the washing machine filters made a difference, and to explain what would count as proof.

ELL supports

Pre-teach "microplastic," "fiber," "fragment," "synthetic," and "outfall" with real objects where possible, such as a piece of fleece beside a piece of cotton, and a simple drawing of a plant, a pipe, and a river. Provide the passage with these five key terms glossed in the margin. Allow students to answer questions 1 and 2 by pointing to the sentence in the text before writing.

Extensions

Students can run a small version of the fiber test by washing a scrap of fleece in a jar of clean water, shaking it for two minutes, then straining the water through a coffee filter and examining the filter with a hand lens next to a filter used on plain water. They can also look up whether their own community has a wastewater treatment plant, find where its outfall is on a map, and write a paragraph on which parts of the river are upstream and downstream of it.