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Can microorganisms such as yeast be used to filter heavy metals?

Can microorganisms such as yeast be used to filter heavy metals?

Introduction: (Initial Observation)

Lead, mercury, iron, copper, manganese, cadmium, arsenic, nickel, aluminum, silver and beryllium are considered heavy metals. These metals have a variety of uses and in small quantity are harmless. In some cases, some of these metals are necessary for our bodies to function properly. When that quantity increases however, many problems arise. These heavy metals are very toxic if they are ingested in abnormal quantities.

This amount does not have to be very great. Lead poisoning is probably the most common of the heavy metals because of its use in home products. Historically lead pipes were used to transport water into the house. Lead was also used in paint and gasoline. There are still old homes with lead based paint on their walls. Mercury is a liquid metal that is very toxic and is still used in thermometers. All of these metals are used in various industries today and a big question that remains is whether the metals make it into the water system and pollute our drinking water. This is very possible and in some cases a proven fact. If these metals are ingested, they could create several serious illnesses. As a result, it is to no surprise that there is extensive research done to find the metals, and more importantly to detoxify our water.


If you have any questions, click on the help button at the top of this page to send me your questions. I may respond by email, but often I update this page with the information that you need.

Project Advisor

Project plan:

The following is a sample project plan based on material and equipment that are easily available to most students.

1. Use yeast culture to grow yeast. This ensures that fresh, active and metabolizing yeast is being used for the experiment.

2. Use a solution of copper sulfate, nickel sulfate or any other colorful inorganic metal salt as a source of heavy metal. In this way, any change in the quantity of metal may be observed by the loss of color in the solution.

3. Add yeast to the solution, wait for some time to pass, filter the solution and compare the color of the solution with its color before treatment. In this experiment quantity of yeast and the exposure time may be studied as possible independent (manipulated) variables.

Alternatively, if we cannot use color change as an indication of reduction of heavy metals, we may use a heavy metal test kit to determine any changes caused by yeast. In this case we must use very small amounts of heavy metal compound in our water sample.


Testing strong solutions of copper sulfate with yeast showed that the absorption of copper by yeast is not enough to cause a noticeable and measurable color change in a strong solution of copper sulfate.

Information Gathering:

Find out about Yeast and heavy metals. Read books, magazines or ask professionals who might know in order to learn about the effect of heavy metals on live organisms. Keep track of where you got your information from.

Following are samples of information that you may find:


The term heavy metal refers to any metallic chemical element that has a relatively high density and is toxic or poisonous at low concentrations. Examples of heavy metals include mercury (Hg), cadmium (Cd), arsenic (As), chromium (Cr), thallium (Tl), and lead (Pb).

Heavy metals are natural components of the Earth’s crust. They cannot be degraded or destroyed. To a small extent they enter our bodies via food, drinking water and air. As trace elements, some heavy metals (e.g. copper, selenium, zinc) are essential to maintain the metabolism of the human body. However, at higher concentrations they can lead to poisoning. Heavy metal poisoning could result, for instance, from drinking-water contamination (e.g. lead pipes), high ambient air concentrations near emission sources, or intake via the food chain.

Heavy metals are dangerous because they tend to bioaccumulate. Bioaccumulation means an increase in the concentration of a chemical in a biological organism over time, compared to the chemical’s concentration in the environment. Compounds accumulate in living things any time they are taken up and stored faster than they are broken down (metabolized) or excreted.

Heavy metals can enter a water supply by industrial and consumer waste, or even from acidic rain breaking down soils and releasing heavy metals into streams, lakes, rivers, and groundwater.

Environmental and health risks.

Now we are going to describe the effects of the heavy metals in the environment. The three most pollutants heavy metals are Lead, Cadmium, and Mercury.

Source: http://www.lenntech.com/heavy-metals.htm

The presence of heavy metals in aquatic environments is known to cause severe damage to aquatic life, beside the fact that these metals kill microorganisms during biological treatment of wastewater with a consequent delay of the process of water purification. Most of the heavy metal salts are soluble in water and form aqueous solutions and consequently cannot be separated by ordinary physical means of separation.

Physico-chemical methods, such as chemical precipitation, chemical oxidation or reduction, electrochemical treatment, evaporative recovery, filtration, ion exchange, and membrane technologies have been widely used to remove heavy metal ions from industrial wastewater.

Source: http://www.ejbiotechnology.info/content/vol7/issue1/full/2/

Notes on Yeast and Yeast Cultures:

  • Yeast requires warm place to grow
  • Yeast goes dormant at 63º F (14º C)
  • It grows best between 80º F – 95º F (24º C – 35º C)
  • Yeast growth slows down above this until it dies at about 109º F (46º C) Yeast cultures are fragile and are easily contaminated and killed by bacteria
  • Keep all wooden or plastic spoons, and everything that is added to the pot as sterile as possible
  • Do not use metal as your yeast culture pot (this includes the stirring utensil) – use a ceramic or plastic container
  • Place a loose fitting lid on top to allow the carbon dioxide to escape
  • Yeast changes sugar and simple starches into carbon dioxide and Ethel alcohol
  • It is possible for the yeast to kill itself by the alcohol it produces. For bakers yeast this happens at about 12 percent alcohol content. To prevent this from happening you must keep an eye on it. When it stops frothing it is either out of food or is nearing it’s toxicity level. Add more water and carbohydrates and if your crock is already full, dump some of it out.

An Excerpt from http://waltonfeed.com/old/yeast.html by Al Durtschi

What is yeast extract?

Yeast extract is a soluble concentrate extracted from yeast such as Saccharomyces species (Brewer’s yeast, Baker’s yeast) and Torula yeast and contains nutritional components such as amino acids, nucleotides, vitamins, and minerals. Yeast extracts have been mainly used in the food industry as flavor enhancers but also as a component of media for cell growth in the fermentation industry, pet foods, cosmetics materials, plant nutrition, etc.. Yeast extracts are generally manufactured by either autolysis or enzymatic treatment.

Dithizone, Reagent


C13H12N4S F.W. 256.32 CAS 60-10-6

The organic reagent best known under its common name dithizone was introduced into analytical practice by Hellmuth Fischer just over 50 years ago. By virtue of its thiol group, it can form formally unchanged chelate complexes

with a small group of metals (notably, Co, Ni, Zn, Pd, Ag, Cd, In, Sn, Pt, Au, Hg, Tl, Pb, and Bi) and since, like the reagent itself, these are intensely colored and very sparingly soluble in water though soluble in chloroform, carbon tetrachloride, and other water-immiscible organic solvents, dithizone lends itself to liquid-liquid extraction procedures and the spectrophotometric determination of trace metals at around the microgram level.

With the increasing popularity of atomic abosption spectrophotometry, this technique has tended to supplant spectrophotometry as the preferred finish in quantitative trace-metal determinations, but many other physical procedures are in current use.

The ability to preconcentrate certain metals by liquid-liquid extraction of their dithizonates plays an increasing role in environmental analysis, and chromatographic techniques now extend from thin layer chromatography to the use of columns for specific separations. The present review summarizes the basic analytical applications of dithizone that have become well established in the past half-century but highlights the more recent developments through a detailed review of papers published during the last 10 years. Particular attention is paid to the applications of dithizone in preconcentration and separation techniques, in electroanalytical procedures, in substoichiometry and in the design of liquid-membrane ion-selective electrodes.

Question/ Purpose:

What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.

The purpose of this project is to determine if microorganisms such as yeast may be used to filter small amounts of heavy metals from water.

Identify Variables:

When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.

Independent variable (also known as manipulated variable) is the amount of live yeast cells used per liter of water. This value can be described as cell count or by grams.

Dependent variable (also known as responding variable) is the rate of filtration. The rate of filtration will depend on the amount of yeast we put in the solution. Heavy metal contents may be tested and measured by a laboratory, determined by the instructions provided in a heavy metal test kit or described as Presence or absence of heavy metal using some simpler reagents.

Controlled variables are temperature and light.

Constants are the source and the type of water, yeast, heavy metal contaminant as well as the experiment method.

We will alter the amount of yeast and see how the solution is affected. It is extremely important to only change on variable at a time to see what variable is causing the change.


Based on your gathered information, make an educated guess about the results of your experiment or the answer to your original question. Identifying variables is necessary before you can make a hypothesis.

(A hypothesis is an assumption you make about the result of the experiment.)

Following is a sample hypothesis:

Adding more yeast into the solution of copper sulfate mixed with water will increase the presence of copper in the water.

Another sample hypothesis is:

Yeast will absorb the copper sulfate.

Your future observations will support or oppose this statement. It is ok to be wrong here, the hypothesis does not have to be correct.

Experiment Design:

Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”

In this experiment we will take water samples and dissolve one specific metal in the water. We will then take a natural organism (yeast) and test to see if the organism absorbs the harmful, toxic metals. Before we begin it is important to understand how this process works. There are two ways to do this. One is to research this on your own. The second one is to use the information in this project guide in conjunction with your own research to become more knowledgeable in the subject matter. It is important to learn and understand how the metals interact with the human body. When the metals enter the body via the drinking water, the metals in that water interact with the cells. The metal compounds binds itself to the cell, infecting it and eventually killing them. It leads us to believe that a metal will bind itself to any living cell thus any living organism. One good substance to use for this experiment is yeast. Yeast is nothing but a group of certain microscopic fungi. It is often used in cakes to make them grow. In this experiment we will see how yeast filtrates the solution we prepare with copper, one of the heavy metals.

In order to run this experiment you will need access to a lab that can test the water samples for you. This process is very involved and can be handled in several ways. One way is to use a Dithizone Reagent and check for heavy metals in water. Dithizone Reagent reacts with the specific metals and makes the water turn a different color depending on what metal and the amount. Off course in a lab, the lab technician can analyze the solution and discover everything in that exists in the water. Another possible way is the use of a heavy metal test kit that is able to show the presence / absence or the concentration of heavy metals.

What we will do for this experiment is take copper sulfate and dissolve it in the water. You should make a large amount of this solution because it will be divided into several beakers for use in different trials. We use copper sulfate because we need a metal compound that is soluble in water. To start we should use 50 grams of copper sulfate for every gallon. You should prepare several beakers or cups and pour equal amounts of the solution into each of the six beakers. Once we have our water solution with the copper sulfate dissolved inside, we are certain that this water has a heavy metal compound in it. Next we will take some yeast and drop it in the first beaker. For our control we do not add any yeast. A summary table like the one below is good to summarize your results and aid you in the creation of a graph.

Trial Amount of Yeast (Grams) Rate of Filtration
Control 0 grams
1 5 grams
2 10 grams
3 15 grams
4 20 grams
5 25 grams

The lab will measure the rate of filtration. The amount of yeast is just a suggestion. You can vary it the way you’d like. The greater the change the greater will be the change in the rate of filtration. Once you add the different amounts of yeast into the water solution, you should let is stand for at least six hours to allow the water solution to interact with the yeast. This experiment can be taken a step further. If you feel motivated and want to test another project, you can vary the amount of time instead of the amount of yeast in this experiment. The result may not be as easy to observe.

Materials and Equipment:

List of material may vary depending what is available to you. Following is a sample list of material and equipment.

  1. Distilled water or de-ionized water or fresh water that does not contain any heavy metals (one gallon).
  2. Copper Sulfate crystals (50 grams)
  3. Yeast (100 grams)
  4. 600 ml Beakers (6)
  5. Gram Scale (1)
  6. Water test laboratory or heavy metals test kit

Results of Experiment (Observation):

Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.


You may need to calculate the rate of filtration. To do this divide reduction in the amount of metal ion by the initial amount of metal ion.

Summary of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.


Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.

You have the results summarized in the table and now it is obvious what has happened. Summarize your results and explain what happened. Now that you have these several trials you can even create a mathematical equation to forecast further changes without running more trials. You should also create a graph, which can be easily done on the computer using the table or on paper. The graph will be helpful to create the equation. Is the graph what you expected? Are there any results that do not belong with the rest? In any experiment, it is very easy to make a mistake or get a result that does not fit. If there is a point that does not belong or deviates far from the trend, you should find possible solutions for this problem. Revisit your hypothesis and check to see if your observation support it or oppose it.


Now that you are done with you experiment and observations, it is time to write the abstract. The important thing to remember is that the abstract is the first part of your lab report but should be written last. An abstract is a short statement that summarizes the purpose, methods, and findings of your research project. It should be a single paragraph that grabs the reader’s attention.

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.

Grow yeast:

You may want to use a small amount of yeast culture to grow more yeast for your experiment. There are many recipes for growing yeast available on the Internet and books that you may use. In all cases you will need water, nutrients and a warm place. Among different nutrients suggested for yeast growth is a mixture of warm potato water and sugar. Potato water may be made by juicing potato and then filtering it. 200 grams of sugar in about 600 ml potato water and 200 ml water. Drop about 5 grams yeast in the mixture, cover it with a clean cloth and keep it warm. Solution will get saturated with yeast in about 4 days.

Note that certain contaminations may kill all the yeast and mold may grow on the solution if necessary precautions are not made.