Southwest Hydrology: The Resource of Semi-Arid Hydrology Volume 4 Number 2

• Description: Southwest Hydrology: The Resource of Semi-Arid Hydrology Volume 4 Number 2
• State: CO
• Date: 3/1/2005
• Title: Southwest Hydrology: The Resource of Semi-Arid Hydrology Volume 4 Number 2
• Water Supply Pro - Doc Type: Publication

EDUCATION
Parts per Million or Billion: A
Science Activity for Grades 4 -10
Judy Maben — Water Education Foundation
Have you ever been asked to lead a
water science activity for your child's
classroom? Were you stumped about what
to do? Here is a quick and easy activity
about water quality that you can do with
your child's classmates.
How Do We Define `Bad "?
Substances dissolved in water are usually
measured in parts per million (ppm) or
parts per billion (ppb). But is the solution
to pollution dilution? Different naturally
occurring elements, toxins or poisons, and
nutrients all may be considered hazardous
at different concentrations. Not all man-
made chemicals are toxic and not all
naturally occurring chemicals are non-
toxic. Almost any substance, synthetic or
natural, can be considered toxic if ingested
in a high enough dose. Salt is a good
example. Sodium chloride is a naturally
occurring chemical. A few grains sprinkled
on your dinner are okay, but if you were
to eat a couple of pounds per hour, you
would significantly damage your body.
Water Standards and Measurement
The U.S. Environmental Protection
Agency establishes standards for
contaminants that are sometimes found
in groundwater and in surface water.
These standards usually provide a
number that indicates the concentration
of contaminants in ppm or ppb. These
standards are enforced by individual states.
Some standards relate to human safety
for drinking water sources (like arsenic
or mercury), and some are for aquatic
ecosystems (like nitrates, which can cause
too much plant growth, or dissolved
oxygen, which is necessary for aquatic
animals). But what do those numbers
mean? And how much is too much?
Objective:
Students will:
1. perform a serial dilution using powers
of 10.
2. identify the importance of standards in
evaluating water quality.
Materials (per group):
• 9 clear containers or white plastic spoons
• 2 droppers
• white paper
• toothpicks
• liquid food coloring
Procedure:
1. Protect the surface (table or floor) you
are going to use with sheets of white
paper or toweling. Line up nine clear
containers or white plastic spoons.
Label them with numbers 1 through 9.
2. Put 10 drops of food coloring in #1.
Assume the food coloring is already at
a dilution of 1:10.
3. Put 9 drops of clear water in each of
the spoon or container numbered #2
through #9.
4. Take one drop from #1 and place it in
#2. Mix with a toothpick.
5. Repeat this process in each container.
Example: Take one drop from #2 and
add it to the nine drops of water in #3
Each dilution will be 10 times more
dilute than the previous one.
Data Table:
Container
Dilution
1
1:10
2
1:100
3
4
5
6
7
8
9
Discussion:
1. Which container is at a dilution of
1 ppm? ( #6)
2. Which container is at a dilution of
1 ppb? ( #9)
3. In which container can you no longer
see the color? (usually around #5 or #6)
4. You know the color molecules of food
coloring are there because you put them
there. How can you demonstrate their
presence? (Students could evaporate the
water, or pour onto white paper and look
for ring of color around the wet mark.)
5. If this were a toxic substance, which
spoonful would you be willing to
drink? (Depends on what it is ... there
are different standards for different
substances.)
6. Individually or in teams, use the Internet
to look up allowable total maximum
contaminant levels for different
substances. Indicate whether your
standard is for drinking water or aquatic
ecosystems. Report your findings to
your classmates.
Bring a Consumer Confidence Report
from your local water district to discuss
the local water quality.
Further activities: Bring in a pool or spa
test kit and run tests on pH and chlorine
for different water samples prepared ahead
of time. Suggestions: add several drops of
ammonia, lemon juice, detergent, baking
soda solution, etc.
Adapted from "Project Water Science," available
from the Water Education Foundation, 916- 444 -6240,
www.watereducation.org.
March /April 2005 • Southwest Hydrology • 39