Research Project: Assessment of Silver Nanoparticles on Freshwater
Ecosystems.
Purpose
You will design a study to assess the impact of silver nanoparticles on aquatics
ecosystems. Ideally, your study will examine the impact of the silver nanoparticles
on both a representative aquatic plant and invertebrate. (You cannot conduct your
study on fish or other vertebrates).
Recommended aquatic plant: Elodea
Recommended aquatic invertebrate:
Daphnia
Elodea, as seen under a light microscope Daphina is a crustacean. The heart can
(400X). The small circular bodies within been seen through low power
the cell are chloroplasts.
magnification and changes in heart rate
can be monitored.
If you follow a problem-based learning approach consider beginning by listing the
following. Plan on doing at least 4-h of research before designing the investigation.
Things I know
Things I need to know
(What I must research)
eg Daphnia is a crustacean
eg. What place in the food
chain does daphnia
occuoy?
Things I need to do
(Experiments I need to do
or data I need to collect)
Problem
Silver nanoparticles have been placed in clothing, such as sweat socks, to reduce the
growth of bacteria that can cause the socks to smell. In addition, silver nanoparticles,
between 1 – 100 nm is size have been used in optics, electronics, and to catalyze
chemical reactions. Samsung has created and marketed a material called Silver
Nano™, that includes silver nanoparticles on the surfaces of household appliances.
What happens when silver nanoparticles enter the food chain in aquatics
ecosystems? Although silver is less toxic to humans than some heavy metals, such as
lead and mercury, it may still affect other organisms within an ecosystem
Background Information
Health Canada and the US Food and Drug Administration have approved the use of a
range of different silver-impregnated wound dressings to kill microbes. Silver
nanoparticles have also placed in clothing to help destroy microbes that cause
unpleasant odors. Long-term studies have shown that silver can accumulate in the
liver of humans and one study even shows low toxicity in brain tissue.
Determining the toxicity of silver or silver ions on aquatics invertebrates
In animals, toxicity can be measured as a lethal dose 50 or LD50, which means the
concentration of a toxic chemical, radiation or pathogen required to kill 50% of a
population within a specified time. Not surprisingly, the greater the duration of time
for exposure – the lower is the dosage of toxin required to kill 50% of the population.
It is important to compare any LD 50 study with a control that does not have any
silver nanoparticles added.
It should be noted that a determined toxicity in one invertebrate does not mean
translate into the same toxicity for all animals. Some organisms are able to detoxify
harmful chemicals. For example, humans can detoxify many potentially harmful
chemicals in the liver, thereby reducing toxicity. Environmental conductions, such
as water temperature and pH, can affect the absorption of toxins by animals, and
thereby, affect the LD 50.
Determining the toxicity of silver or silver ions on plants
In plants, harmful chemicals might interfere with a plants general health, which
could be measured as plant growth rate or leaf coloration, the ability to of the plant
carryout biochemical reactions, such as photosynthesis, or a plant’s ability to
reproduce.
Like animal testing, toxicity in plants must be defined according to amount of toxic
chemical added and the duration of exposure.
Two ways of measuring photosynthesis of Elodea
Chlorophyll monitors production of
Measuring plant growth
chlorophyll by elodea
1. In measuring photosynthesis for Elodea, use a scalpel to remove a small
portion of the stalk of Elodea. Any open tissue will quickly seal, reducing the
number of gas bubbles collected.
2. Place the elodea sprig upside down in the test tube or graduated cylinder so
that the gas travels from the sprig upwards.
3. Place the sprig in a 0.25% solution of sodium bicarbonate.
Source of Silver Nanoparticles
Silver Colloid
AgNO3 (aq)
Hypothesis
State a hypothesis for your investigation.
Copper wire in 1.0 mol/l
AgNO3 (aq)
Prediction
Make a prediction about how silver nanoparticles will affect Elodea and
Daphnia, before beginning the project. Begin your research. What do
scientists already know? What do you need to know?
1.
Present a bibliography of the articles that you have read prior to
beginning the project.
Design
Some classes may assign groups to do either the impact of silver nanoparticles on
aquatic plant or aquatic animal communities.

2.
3.
4.
5.
Note Silver nitrate solution can leave a black stain on your skin. Safety
goggles and lab coats must be worn.
Identify your manipulated and responding variables.
Identify controls for your experiments.
Identify the concentrations of solutions used. Why did you choose these
concentrations?
Identify the duration of exposure for both plants and animals. Why did
you choose the duration of exposure?
Present your study for approval prior to beginning any experimental work.
Materials
Whenever possible use small amounts of test solutions. Hint: small test tubes can be
used. Present your material list to your teacher prior to beginning the
investigation.
Evidence
Present your data using a table format. Some groups may use spreadsheets for data
tables. Make sure you list the concentration of the silver solution and the duration of
exposure for the test plant or animal.
Analysis
6.
7.
8.
Why must a control be used in the experiment?
Why is Daphnia an excellent animal to model toxicity. (Give 3 reasons)
Identify two possible sources of error in measuring the growth of a sprig
of elodea.
Evaluation
9.
10.
If a student finds the LD 50 for a 1.0 mol/L silver nitrate after 48-h for
Daphnia in the laboratory, can you conclude that silver nanoparticles are
harmful for Daphnia? Explain why or why not.
On the basis of your project, would you want to ban the use of silver
nanoparticles in clothing? Explain why or why not.
Synthesis
11.
12.
What additional studies would you want to perform to draw any
conclusion?
What things would you change if you were to repeat your study?