Heavy Metal Plants Are Hard-Core Cleaners!

Some people think playing soft, peaceful music to their plants will get them to grow taller and healthier. But don’t play that stuff around plants with names like Al-

pine Pennycress or Golden Tufted Madwort. They like heavy metal. In fact, they eat it up (real metal, that is, like zinc, cadmium, and nickel—not “hard rock” music).

Long ago, European prospectors used these shrubs as a sign that metals lay hidden beneath the soil. Today, scientists want to use plants like pennycress to clean up soils contami-nated with heavy metals. Landfills and old mines are two examples of such sites.

Hyperaccumulator plants don’t actually eat the metals, though. Instead, they use their roots to draw in large amounts of the metals, which are then carried to the stems and leaves for storage. Pennycress may look small and dainty with its pretty white flowers. But its leaves can store toxic amounts of

Plants—The Hard-Core Cleaning Machines!Answer: A and C are both correct!

zinc and nickel that would kill or sicken nearly all other plants.But why “hunger” for heavy metals?Rufus Chaney, an Agricultural Research Service (ARS)

agronomist in Beltsville, Maryland, studies these metal-hun-gry plants, called “hyperaccumulators” (say, Hyper Ak-Yoom You Laters). He says, “The metal in the leaves kills chewing insects and also prevents certain plant diseases.”

At polluted sites, a crop of pennycress could be grown, harvested, and then burnt to remove and recycle its stored metals. This type of plant-powered clean up is called “phy-toextraction.” The cost is $250 to $1,000 per acre per year. That’s a lot cheaper than $1 million—the per-acre cost of current methods. These involve scooping up polluted soil and replacing it with clean soil.

So rock on little plants!

—Adapted from the ARS Science for Kids website by Jan Suszkiw, USDA, Agricultural Research Service, Information Staff

For further reading

Durham, Sharon. “Dainty Plant Outpowers Cadmium-Contaminated Soils,” Agricultural Research magazine, USDA-ARS Information Staff, Beltsville, Maryland, September 2004, p. 22. www.ars.usda.gov/is/AR/archive/sep04/plant0904.pdf.

Becker, Hank. “Phytoremediation: Using Plants To Clean Up Soils,” Agricultural Research magazine, USDA-ARS Information Staff, Beltsville, Maryland, June 2000, pp. 4−9. www.ars.usda.gov/is/AR/archive/jun00/soil0600.pdf.

Comis, Donald. “Metal-Scavenging Plants to Cleanse the Soil,” Agricultural Research magazine, USDA-ARS Information Staff, Beltsville, Maryland, November 1995, pp. 4−9. www.ars.usda.gov/is/AR/archive/nov95/cleanse1195.pdf.

QUIZWhy do these plants store heavy metals?

(Pick all that apply.)

A) Scientists believe it makes the plants less tasty to hungry insects.

B) It makes them more valuable.

C) It may help them fight off diseases.

D) It prolongs their blooming season.

Veggies with Vigor!

Introduction In this activity, you will see how plants can go from be-ing weak without water to becoming stronger when they gain water.

Materials• Celery stalk

• Disposable plastic cup

• Water

• Food coloring

• Scissors

Procedure1. On a sunny day, lay the celery stalk in the sun until it

is very wilted.2. Place a little water in the bottom of the cup. Add

10–15 drops of food coloring and mix well.3. With the assistance of an adult, carefully cut off

the base of the stalk. Place the stalk in the colored water.

4. Check the celery stalk every 30 minutes for the next few hours. What happened?

Where’s the chemistry? Celery, like all plants, is made up of cells. When its cells lose water through evaporation, celery wilts. But, when wilted celery is placed in water, the water moved up in a long series of tube-like cells inside of the stalk. Then the water moved to the rest of the cells. Once these cells are filled with water, the celery will stand straight.

Milli’s Safety Tips Safety First!ALWAYS:• Read and follow all directions for the activity.• Read all warning labels on all materials being used.• Use all materials carefully, following the directions given.• An adult must perform the portion of the activity that requires the use of scissors.• Follow safety warning or precautions, such as wearing gloves or tying back long hair.• Be sure to clean up and dispose of materials properly when you are finished with an activity.• Wash your hands well after every activity.

Never eat or drink while conducting an experiment, and be careful to keep all of the materials away from your mouth, nose, and eyes!

Phytoremediation

What is phytoremediation? Phytoremediation is

using plants and trees to

clean up soils or water.

Plants help remove heavy

metals such as lead or

neutralize contaminants found

in the soil or water. This concept is centuries old,

but humans began to apply it more widely in the late

20th century. One of the oldest forms of

phytoremediation has been

used by farmers. This form

of phytoremediation is crop

rotation. By rotating their crops,

farmers are preventing the

buildup of potentially hazardous

substances in the soil and enriching

the soil with plants like beans, which fix

nitrogen in the soil to make it available to

other plants. This practice has opened up

the door for other forms of phytoremediation

we now use today, such as using plants to pull pollut-

ants out of the ground and water.

How does phytoremediation work?

There are a number of forms of phytoremediation. Many

plants are able to uptake pollutants and store them. People

can plant these plants, and once they have grown and pulled

the pollutants out of the soil, harvest them and dispose of

them safely. This process can be used over again to reduce

the level of contamination to acceptable levels. Plants can

also be used to control the spread of pollution. Other plants

can grow microbes, which can then metabolize pollutants.

Ludy Avila is a Professor of Chemistry for the Department of Physical Sciences and Engineering at South Texas College in McAllen, Texas and a member of the ACS Committee on Community Activities.

By Ludy AvilaWhat are the most

common plants used for phytoremediation? Alfalfa, poplar, junipers, sun-

flowers, cabbage, and mustard

plants, to name a few, have been used

successfully in phytoremediation projects.

Some of these plants have been used to clean

up soils contaminated with pesticides and heavy metals. Many

researchers are in the process of finding more plants that can

be used for cleaning up other contaminants in both

soils and water.

What are some of the advantages and disadvantages of

using phytoremediation? Some of the advantages of phytoremediation are

that it is cost effective, environmentally friendly,

and low maintenance; that it does not involve

expensive equipment; that it can be used on large

areas of soil; and that remediation sites look nicer. Some

of the disadvantages are that it is slower than conventional

methods, especially if the site has high concentrations of con-

taminants, and that some plants only grow in certain climates.

Materials• 3 cups of grass clippings

• 2 plastic Ziplock bags

• 1 cup of potting soil

• Pencil (sharpened)

• Teaspoon

• Water

Introduction What do you think happens to grass clippings after they are cut and fall onto the ground? Do this activity and you will find out what happens.

From Grass to Soil—Let Microbes Toil!

Use Milli’s Safety Tips when doing this activity.

SAFETY!

Procedure1. Place one handful of grass clippings in each of the two

plastic bags.2. In one bag, add a cup of fresh potting soil and mix it to-

gether well. In the other bag, leave the clippings as they are. Seal both bags.

3. With a pencil, carefully poke 5−10 air holes in each side of the plastic bags. Be careful not to poke yourself.

4. Place the bags in a dark place. Once each week, open the bags and add a teaspoon of water. After one week open the bags and look inside. Look closely at the grass. Aside from being dirty in the soil bag, does the grass in either bag look like it changed from when you put it in?

5. After another week, look closely again at the grass in the two bags. What has happened to the grass that was in the soil? What happened to the grass without soil? Continue observing for the next few weeks.

Ask yourself…What happens out in the woods?

What happens to all of the leaves that fall year after year?

Do the leaves that fall on the ground just keep getting deeper and deeper?

Where’s the chemistry?Have you ever heard of a compost pile? In this activity, that is what you have made—compost! In a compost pile, dead plant material and soil are combined and kept moist. Tiny organisms (microorgan-isms) in the soil begin to eat the plant material, causing it to break down, or decom-pose. The decomposed plant material and the wastes in the microorganisms add nutrients to the soil. In fact, gardeners often use compost as a natu-ral fertilizer for growing plants.

By Margareta Séquin

Plants are very good at defending themselves. They need to be, as they have to be able to stay alive in hot or cold weather and sometimes have to survive

months without rain. But above all, they need to defend themselves against small and large animals that want to eat them. A plant is pretty much stuck in place with its roots and cannot move to another place if its life is in danger. So, why are plants still alive and not all eaten up? Plants have excel-lent ways to defend themselves. Some plants have sharp thorns and tough skins. And many plants have developed lots of powerful chemical compounds in their roots, leaves, and other plant parts. Some examples include morphine from the opium poppy, nicotine from the tobacco plant, or bitter quinine from the bark of the tropi-cal cinchona tree. Animals do not like to eat such plants. If they try, they become very ill or may even die.

People have known about many of these potent plant defenses since ancient times. While some plant materials are harmful to animals and humans, people have found ways to use small quantities of these sub-stances as medicines to help us fight against our own diseases. A large number of medicines that we buy today in a pharmacy or a drug store have their origins in defensive plant substances.

A famous story about a medicine that originally came from a plant is about aspirin, the common pain killer. Aspirin is re-lated to the chemical compound salicylic acid, which is found in the bark of willow plants. Salicylic acid is quite acidic and leads to an upset stomach when eaten. This makes it a good defense against animals that want to chew on willow branch-es. Long ago native people found out that chewing willow bark lowered their fever when they were sick. But they did not like the stomachaches they were getting. In later times, chemists figured out ways to change the structure of salicylic acid mol-ecules somewhat. These methods transformed salicylic acid into aspirin, which is better tolerated by our stomachs.

Morphine is a very strong plant chemical. If used in tiny amounts, it is still the most powerful painkiller that we know. Bitter quinine from the bark of a tropical tree has helped peo-ple to fight the disease malaria. Atropine from the belladonna plant can be used in very small amounts in eye medicine. And scientists keep finding new plant medicines. One of the latest ones is taxol, from the bark of the Pacific yew

Defensive Plants Make Medicines

tree. While the compound taxol protects yew trees from being eaten or from getting sick, taxol has recently been found to be a medicine that cures some types of cancer in human beings.

Plants also have gentle defenses to protect them against being eaten by animals. You may have heard of the succu-lent plant aloe vera. When a leaf blade of aloe is cut open, a yellow sap oozes out. An animal that tries to bite into such a leaf would hate this sap. On the other hand, people have used the aloe for hundreds of years to treat burns and many other

ailments. Strong odors in leaves are another form of plant defense. Think of herbs like mint, sage, or rosemary. While

we might like a few leaves in our food, would you like to eat an entire salad of mint, sage, or bay leaves? I think not! An animal does not like to munch on a sage or mint plant either.

Herbs and spices have been used since ancient times. Nowadays, we use them mainly for their taste and smell. But many herbs have originally been used as medicines. Herbs like thyme, basil, or oregano contain many antioxidants, sub-stances that can trap harmful substances in our body. Another example is the spice cloves, which we may like in hot cider or with certain meats. But an extract of cloves is also a mild pain-killer and is still used by dentists as a nice-smelling lotion to make our gums numb. In former times, some herbs and spices with strong tastes and smells were actually used to cover up the unpleasant smell and bad taste of spoiled food!

Plants are amazing machines. By making complex chemi-cal compounds that help them to defend themselves and to stay alive, they supply us with many medicines that help

people in the fight against diseases. Let us protect plants and learn much more about them, so that we can collect

even more knowledge on plant medicines.

Margareta Séquin is a Professor of Chemistry for the Department of Chemistry and Biochemistry at San

Francisco State University.

ActivitiesGrow your own herb garden.Pick up a package of seeds of oregano, thyme, or basil, and grow your own “antioxidants”!

Visit a botanical garden and find out if they have a section on medicinal plants. They probably do!

An interesting book:Judith Sumner, The Natural History of Medicinal Plants, Timber Press 2000.