2023 VT Nanoscience Professional Development Workshop for High School Teachers

Hands-On Activity: Microplastics & Nanoplastics

Introduction: Microplastics and nanoplastics are of significant importance due to their potential environmental and human health impacts. Here are some key reasons for their importance:

Environmental Contamination: Plastics are pervasive pollutants in various ecosystems, including oceans, rivers, lakes, and even terrestrial environments. Their small size and persistence make them difficult to remove and can lead to long-term contamination. They can accumulate in sediments, enter the food chain, and have detrimental effects on marine organisms, wildlife, and ecosystems as a whole.
Human Exposure: Plastics have been detected in drinking water, food, and even in the air we breathe. There is growing concern about human exposure to these particles and their potential health effects. While the full extent of their impact on human health is still being investigated, there are concerns about possible ingestion, inhalation, and absorption of these particles and associated chemicals. They could potentially cause inflammation, disrupt cellular functions, and have other adverse health effects.
Ecological consequences: Plastics can impact the functioning of ecosystems. They can alter nutrient cycles, affect the behavior and reproduction of organisms, and potentially disrupt entire food webs. The introduction of these particles into natural environments can have far-reaching consequences for biodiversity and ecological balance.

Activities:

Nanoplastics Experiment: Single-Use Beverage Cups!

Goal: To demonstrate how microplastics and nanoplastics can form during use of everyday products like disposable cups. The activity can be used to facilitate discussions about micro- vs. nanoplastics, primary vs. secondary particles, particle size and surface area, surface charge, and hydrophobicity and hydrophilicity, as well as nanoscale characterization techniques including dynamic light scattering and scanning electron microscopy. An overview of the procedure is given below along with key concepts for achieving learning objectives.

This activity is supported by pre-recorded lectures and slides on Emerging Contaminants and Nano-Enabled Solutions and Microplastics and Nanoplastics and the Environment.

Setting up the Activity

Challenge Scenario for Students: Develop an approach for capturing and characterizing microplastics and nanoplastics from the environment or from a contaminated wastewater stream.

After introducing nano-related concepts and challenges related to conventional filtration approaches and distinguishing synthetic plastics from natural organic matter, students can collaborate to devise treatment methods using samples of microplastics and nanoplastics that they make in the classroom.

Step 1: Prepare a Solution with Micro/Nanoplastics

We are using single-use hot beverage cups coated with low density polyethylene (LDPE) purchased from a retail grocery store or online. Recent research shows how trillions (yes trillions) of nanoplastics (<100 nm) are formed when the cup is filled with boiling water.

Boil water using a hot plate or electric tea pot. Add the hot water to the cup and shake for ~20 minutes using an orbital shaker, if available, or gently shake by hand for several minutes. CAUTION: Boiling water can cause severe burns!

Step 2: Visual Examination of Solutions

Inspect an aliquot of the solution collected from the cup after ~20 minutes with deionized water. Use borosilicate scintillation vials or other clear glass containers that are easy to see through. You will likely not detect an obvious difference between the two solutions.

Key Concept: The human eye can detect objects as small as ~30 micrometers (or 30,000 nanometers), which is similar to the width of a human hair. However, just because we cannot see particles in a solution does not mean they do not contain microplastics, which have sizes exceeding 1 micrometer (1,000 nanometers). Nanoscience research requires using characterization tools that can observe sizes much less than 1 micrometer, and even down to the angstrom size, similar to the size of atoms and bonds between atoms.

Step 3: Examine with a Laser Pointer

A standard green laser pointer (wavelength = 532 nanometers) is a useful qualitative tool to evaluate for the presence of particles <30 micrometers in a solution. Solutions containing a sufficient concentration of particles large enough to scatter visible light will show a "beam" similar to a flashlight or headlights shining through the fog. However, there is a size limit to this effect and it is only sensitive to particles that are approximately 1 micrometer in size. As such, particles <1 micrometer in size will not be obvious by eye.

We are developing a new method to aggregate microplastics and nanoplastics in aqueous solutions using a "magic" additive. The second image shows the "beam" created by the particles in solution that aggregated to the sizes of 10's of micrometers in size.

Nanoscale Characterization

Dynamic Light Scattering (DLS) is a technique used to measure the size distribution of particles or molecules in a liquid or solution. In DLS, a laser beam is directed onto the sample, and the scattered light is detected at various angles. The Brownian motion of particles in the sample causes fluctuations in the scattered light intensity, which are analyzed to obtain information about the size and movement of the particles.The underlying principle of DLS is based on the fact that the rate of Brownian motion is related to the size of the particles. Smaller particles undergo faster and more random motion compared to larger particles. By measuring the intensity fluctuations of the scattered light over time, DLS can determine the diffusion coefficient, which is related to the particle size through the Stokes-Einstein equation.

Scanning Electron Microscopy (SEM) is a powerful imaging technique used to observe the surface morphology and topography of samples at high resolution. It provides detailed information about the shape, size, and composition of the sample. In SEM, a focused beam of electrons is scanned across the surface of the sample. When the electron beam interacts with the sample, various signals are generated, including secondary electrons, backscattered electrons, and characteristic X-rays. These signals are collected and used to create an image of the sample's surface. SEM can produce detailed images with magnifications ranging from a few times to several hundred thousand times.

DLS and SEM are specialized instruments that are only available in research laboratories. NanoEarth can provide access for in-person demonstrations and mail-in samples for analysis.

Results: Dynamic Light Scattering (DLS)

Dynamic Light Scattering (DLS) shows the distribution of particle sizes formed in from the reaction of boiling water with the single-use beverage cup. A series of measurements under different conditions (see image) show that the solutions contain various different populations of particles with sizes ranging from <10 nm to several 100 nm, as well as particles that are >1 micrometer.

Results: Scanning Electron Microscopy (SEM)

These scanning electron microscope (SEM) images were collected during the workshop by our participants with help from Steve McCartney (NCFL). The sample was prepared by drying a droplet of water from single-use beverage cup experiment on a piece of carbon tape mounted on a SEM stub made of aluminum.

The lowest magnification image has a 1 micrometer (um) scale bar in the lower right corner and shows evidence of plastic particles. The particles form an irregular layer and have different sizes and shapes.

The additional images below were taken at higher magnification. Students can use the images with the scale bars to estimate sizes of the particles. There are additional images showing measurements of selected particles.

Link to news story of a study by researchers at the National Institute of Standards and Technology (NIST) describing the formation of nanoplastics from single-use beverage cup and high-resolution images.

Nanoplastic 30Kx.jpg

Microplastics Experiment with Dryer Lint!

Dryer lint can also be used to create a simulated wastewater for students to experiment with. For instance, magnetic iron oxide powder can be added to dryer lint mixed with water to demonstrate a method that combines adsorption and magnetic attraction for removing microplastics. The experiment provides

Supply List:

Large glass or plastic beaker or container (transparent)
Dryer lint (self supplied)
Magnetic iron oxide particles (link) or iron particles (link)
Magnet (link)