Silver Social Issues
This companion to the antimicrobial silver lab activity explores some of the implications of new technologies as it investigates the effects on the silver nanoparticles on health, the environment, and on economics.
If you have any questions about this activity, please contact Joe Muskin at (217) 265-6481 or by email at email@example.com.
The unit opens with an introduction to products currently available that incorporate silver nanoparticles as an antimicrobial agent. Students are asked to research another product and present it to the class. Next, students conduct an experiment testing the effects of silver nanoparticles on bacteria. This first-hand experience allows students to make connections between manufacturer's claims and their own experimental data. The concluding activity of the unit focuses on societal implications of this technology. Through a role-playing debate, students examine this technology from multiple perspectives.
Silver has been used for years as an antimicrobial agent. It may have had something to do with the phrase "born with a silver spoon." In that babies that used silver spoons tended to be healthier because their eating utensils had natural antimicrobial properties that helped prevent infections.
Silver is an expensive element. Even silver plating uses enough silver that the cost can be prohibitive. However, recent technologies have been developed to create nanoparticles of silver. These particles are very small, using very little silver. However, because they are so small, they have a high surface area to volume ratio. This gives them much more usable surface then their mass might suggest. These nanoparticles offer a real possibility to be used on objects as an antimicrobial agent. A small amount of silver can be used to generate a reasonably large surface area, and actually work as an effective antimicrobial agent.
Many products have recently begun to incorporate these silver nanoparticles in their structure with the idea that for a small increase in cost, the product can be infused with antimicrobial properties.
One common use of the antimicrobial agents is as an odor eliminator. Odors often are a result of bacterial activity and are not intrinsic to the object. For example, the smell of sweaty or stinky feet is not from the sweat, the foot, or even the sock that might be covering that foot. Rather, it is bacteria that exist on our feet being stimulated to produce chemicals that we smell. If the bacteria can be suppressed, then the odor will not occur.
In some of these products, the silver can become unbound and loose. Some products, such as the Samsung SilverCare™ washing machine, even plan on the particles being unbound. This washing machine lauders the clothes with water containing loose silver nanoparticles. Some of the nanoparticles will land on the cloth and come to rest there. They will remain on the cloth while the clothes are worn, preventing bacterial growth and stopping odor.
However, when the clothes are washed again, the silver will be washed off. Of course, the clothes are likely rewashed in the same SilverCare™ washing machine replacing with new nanoparticles. But the waste water will contain many of the silver nanoparticles.
These nanoparticles travel to the water treatment plant where they affect the bacteria present at the treatment plant. The bacteria at a water treatment plant are needed to break down and clean the water. This beneficial bacteria is often killed and the water treatment becomes less effective.
These nanoparticles next travel into the environment where their potential to do harm is even greater. Much controversy exists over how harmful these silver nanoparticles are to both the environment and to human health.
Activity 1: Investigating nanoproducts
- Students describe products containing silver nanopartilces.
- Students evaluate scientific explanations about products containing silver nanoparticles.
In this activity, students will investigate products containing silver nanoparticles. Through their research, students will begin to see that silver nanoparticles are used for their antimicrobial effects. Students will need to develop an oral presentation to be given in class that critiques the product that they researched.
The purpose of doing this activity is two fold—students are introduced to the wide range of products that use silver nanoparticles and begin to develop an understanding of what a valid scientific explanation is. In this initial activity, students are scaffold in developing a scientific explanation.
Introduce this activity by sharing an example of a critical evaluation of the Samsung SilverCare™ washing machine (See Teacher Resource: Samsung's SilverCare™ Washing Machine Evaluation). This particular product is significant in Activity 3 because it will be used to provide the context for the debate in the societal implications activity.
At this time, allow students to use the internet to identify and research their product. For additional information, see the student handout "Investigating Nanoproducts."
- Share with the class the Samsung SilverCare™ washing machine, an example of a product using silver nanoparticles
- Students research their own example of a product made incorporating silver nanoparticles
- Students prepare a 1-2 minute presentation of their chosen product – including a description of product, the manufacturer's claim of the product, their supporting evidence, the justification, and their critique of the manufacturer's claim.
- Students present their product to the class
As an optional activity, handout the Teacher Resource Samsung'SilverCare™ Washing Machine Evaluation and have students identify the three components of a scientific explanation (claim, evidence and reasoning) using the included rubric. Additional aspects of the rubric can be identified as well during this activity.
Activity 2: Determining the effectiveness of silver nanoparticles
- Students carry out an investigation examining the antimicrobial effects of silver nanoparticles.
- In a formal lab report, students develop a scientific explanation using evidence from their data
Activity 2 is adapted from the materials that can be found at either of the following two resources:
- Nano-CEMMS website at the University of Illinois
- The April/May 2008 issue of The Science Teacher: Muskin, J., Wattnem, J., Ragusa, M., & Hug, B. (April/May 2008). Real Science or Marketing Hype?. Science Teacher, 74(4): 57-61.
Activity 2 is a laboratory activity looking at the antimicrobial effects of silver nanoparticles. The Nano-CEMMS website contains a variety of resources that can be used to carry out this activity. On the website, you will find introductory materials, the laboratory procedure, student handouts, and scanning electron microscope images of the bacteria cultured with and without the silver nanoparticles.
See the student handout "Determining the Effectiveness of Silver Nanoparticles" for modifications made for this activity. In this handout, you will find a rubric for the lab report that students develop.
- Students will be introduced to microbiology techniques and vocabulary
- Students will prepare the silver nanoparticles for the next day's activity
- Students will perform the lab activity using E.coli
- Students will complete and turn in a formal lab write-up
- Students will finish activity
- When introducing microbiology on day 3, pass around an agar plate so students can feel the firmness of the agar. This will help them understand how much pressure can be applied when spreading bacteria.
- When making silver nanoparticles, the hot water bath should be almost boiling. The hotter the water is, the faster the reaction. However, if the water is boiling, the test tubes may bounce and crack.
- Remind students to be careful around the hot plate and when removing test tubes from the hot water bath.
- Students might be interested in testing the antimicrobial effects of other materials. You may want to get things such as soap, alcohol, and hydrogen peroxide. If a student tests one of these items, the student may find it creates a larger zone of inhibition than the silver nanoparticles. However, this does not necessarily mean that these other solutions are more effective than the silver nanoparticles. The larger zone of inhibition is due to the smaller size of these other antimicrobial molecules. The silver nanoparticles are on the order of 50 nanometers across, while for example alcohol and hydrogen peroxide molecules are smaller than 1 nanometer and therefore diffuse much faster.
- E. coli has a bad name in the popular press. There are strains of this bacteria that are harmful to humans. Most strains E. coli are harmless, including all strains you can order from any of the biological supply companies. However all bacteria must be disposed of properly by autoclaving or applying at least a 10% bleach solution to the bacteria.
- After the filter paper squares have been placed on the agar plate, let the plates sit for 5 minutes to give the squares time to adhere to the agar surface.
- Place the agar plates in the incubator upside down. Agar plates are incubated and stored upside down to prevent anything from falling onto the agar surface.
Activity 3: Societal implications of a new technology
- Using research, students determine a position based on relevant issues of their assigned roles.
- Students reach consensus taking into account the varying positions within a group.
- Students synthesis possible impacts of science and technology on society by proposing a group recommendation.
- Students explain their groups' recommendation using evidence from their research
In this activity, students will make a recommendation to a hospital board about the use of SilverCare™ washing machines as an alternative to a more traditional laundering process. Students need to consider a range of positions from different roles in the community.
To do this, students will research a particular role to identify the relevant issues that a person in this role would advocate. Students work with others assigned to the same role to develop talking points to use in a later discussion. A talking point consists of a claim, evidence that supports the claim, and explicit reasoning linking the two.
New groups are formed by assigning one participant from each role to this new group. This group will act as a hospital advisory board to make a recommendation about using the SilverCare™ laundering process. In order to do this, each member of the group will explain their position. The group will then use this information to form a reasoned recommendation that takes into account the societal impacts. These societal impacts should include both the impacts on individuals as well as society as a whole. This recommendation should be justified through scientific explanations (again, the claim, evidence, and reasoning linking the two). Groups will present their recommendation to the rest of the class.
As a concluding activity, students will write a one page reflection connecting their experiences in the unit and their views on science and society.
- Teacher will introduce the societal implication scenario and split the class into assigned roles.
- Students will research their roles with other members of their group.
- Students will work within their role groups to synthesize their positions.
- Students are reassigned to a hospital panel group consisting of one member from each role.
- Each hospital panel group will discuss their positions and reach a recommendation.
Day 9 or Homework (See Student Handout E: Reflection Paper)
- Students write a one page reflection
This activity uses the Jigsaw Strategy where students become experts in a particular role by first working with others in that same role. Students are then redivided into a mixed group where each role is represented by one student.
In this activity, students should consider both the individual and societal impacts of using silver nanoparticles. By considering both individual and societal impacts, students develop an understanding of the complex relationship of the individual within the society. The trade-offs between the benefits and the costs of decisions become apparent as they formulate their recommendation. Some of the issues students might want to consider are the impacts to the individual hospital patient, the health of the wider community in which the hospital is a part of, and the environment.
There is considerable debate in the scientific community about the possibility of bacteria developing resistance to silver. Some argue that since silver has been around for so long and bacteria have not developed a resistance to it that it is highly unlikely that bacteria will ever be able to develop a resistance to silver. However, others suggest that historically bacteria have not been exposed to the current level of silver. The earlier exposure level of silver to bacteria was not sufficient to put selective pressure on the bacteria to develop resistance to silver. These different possibilities could lead to a discussion of natural selection.
Clean – at what cost? (Entire Activity)
Instructor's guide containing all relevant information to conduct the activity.
Student Handout A: Investigating Nanoproducts
Student handout for Activity 1
Teacher Resource: Samsung SilverCare
Model product for teacher to demonstrate Activity 1
Student Handout B: Investigating Nanoparticles
Student handout for Activity 2
Student Handout C: Societal Implications of a New Technology
Student handout for Activity 3
Student Handout D: Student Role Sheets
Role sheets for students to use to start Activity 3
Student Handout E: Reflection Paper
Student handout for reflection paper
Goggles, gloves and aprons should be worn as in all chemistry laboratory activities. The hot water baths should be handled with care to avoid burns. Any liquids spilled on skin can be washed off with water.
This lab uses Escherichia coli, E. coli, a gram-negative rod-shaped bacterium that is part of the normal intestinal fauna in mammals. Some strains, particularly O157:H7, are pathogenic to humans; most strains, however, are benign. Because of the ease of culturing E. coli, it has become the "workhorse" of microbiology. Strains for use in laboratories and classrooms are derived from E. coli that grows very well on Petri dishes but very poorly in intestines. The E.coli used in this lab is non-pathogenic and likely wouldn't live in a human intestine, even if ingested in large amounts.
Thanks to Matt Ragusa for all his assistance and advice.
Thanks to Bill Metcalf for help with the lab.
Barbara Hug, Joe Muskin and Janet Wattnem