Synergy in Water Pollutants
INTRODUCTION:
Chemicals that enter the water come from a myriad of sources. To date, regulatory
agencies charged with the control of such pollutants have concentrated their efforts on point
sources -- easily identified by discharge pipes or other overflow devices. Permits are granted
that limit the permissible level for each pollutant and monitoring is done periodically to
ascertain if the permit limitations are being followed. Non-point sources such as run-off from
cropland, roads, and watersheds are being given more attention recently. Soil Conservation
Services administrator several programs aimed at decreasing input of water pollutants from
non-point sources.
Because of the phenomenon known as biological magnification, water containing levels
of pollutants so low that the water is deemed potable (fit to drink) can still be a source of
problems. For example, large, long-lived fish have been found to have a concentration of PCB
that is ten million times greater than the water concentration of PCB. Two characteristics of
PCBs make them likely candidates for biological magnification. First, the PCBs are difficult for
biological processes to degrade to harmless products; the bacteria and other organisms that
usually accomplish these tasks lack the necessary enzymes to handle such man-made materials.
Because they were never exposed to such chemicals before, they did not evolve the enzymatic
capability to process these exotic substances. Second, the PCBs are fat-soluble so they
concentrate in the fat tissue of an organism and are not flushed out with the water-soluble
compounds. Thus, during an organism’s lifetime, the fat tissue increases its concentration of the
chemical and this concentrated chemical is passed onto the organisms in the next level of the
food chain. As this continues up the food chain, the final consumer retains a remarkably high
concentration of the chemical in its body fat. Thus, water that is safe to drink can be the home
to fish that greatly exceed levels for such fat-soluble compounds that are considered acceptable
for human consumption. The FDA recently lowered the acceptable level of PCB’s in
commercial fish from 5 ppm to only 2 ppm.
Metallic ions may enter the circulatory system of a fish directly from the water by gill
uptake. Active transport of necessary minerals from the water may simultaneously result in the
absorption of toxic ions that mimic the required metallic ions.
Water pollutants frequently show the phenomenon of synergy; this occurs when two
pollutants that have little effect when encountered alone, combine to multiply each other
effect’s on a living organism with dramatic results. Regulatory agencies have to be aware of the
positive synergy effects that may be shown by the water pollutants listed on the permits that
issue to a discharger; they must consider the overall, combined effects of these chemicals or the
organisms in the receiving waters will be in peril.
The effects of water pollutants on different kinds of organisms are frequently shown on
television and in our printed media. However, it is rare that a student has the opportunity to
directly view the effects of various pollutants in the laboratory; this laboratory experiment
allows you to witness a living organism’s response to six different water pollutants and then to
compare its response to various combinations of pollutants. Perhaps you will find that a
relatively harmless pollutant becomes very toxic when mixed with another pollutant. This
phenomenon of positive synergy warns us that the effects of pollutants can multiply -- not
merely add together -- when they are mixed. The second part of the exercise challenges you to
access whether positive synergy is occurring.
The living organism used in this exercise, Turbatrix aceti (vinegar eels), is a rapid
swimmer -- until the effects of the pollutant(s) take over. This is its ability to maintain directional
motion is lessened, its coordination begins to fail and it frequently makes loops of its long,
cylindrical body. When these events occur to the majority of the organisms, the lapsed time is
noted.
PROCEDURE:
Part I: Assessing the Effects of Six Different Water Pollutants
1. Prepare a control by placing two drops of distilled water in one depression of the slide
provided.
2. Add one drop of suspension of the living organism.
3. Using a dissecting microscope, observe the normal movement of this organism. These
worms should continue to remain active for 5 full minutes.
4. Now you will test the effect of six different chemicals on the directional mobility of the
worms. The 6 chemicals are:
Bottle A: Silver Nitrate
Bottle B: Mercury (II) Nitrate
Bottle C: Nickel Nitrate
Bottle D: Lead Nitrate
Bottle E: Aluminum Nitrate
Bottle F: Copper (II) Nitrate
There exists only one small bottle of each chemical. Please return each bottle to the supply table
as soon as it is used so others will have access to it without extensive hunting. To test each
chemical you will do the following:
5. Use a clean depression. Add one drop of distilled water, one drop of Bottle A (Silver Nitrate),
and lastly, one drop of the worm culture.
6. As soon as the chemical drop has been added, beginning timing. Record the time it takes for
the majority of the organisms to lose their ability to swim in one direction and to begin to form
coils instead. If this does not happen within five minutes, record a negative result for that
pollutant.
7. Repeat steps 5 and 6 with Bottle B Mercury (II) Nitrate.
8. Repeat steps 5 and 6 with Bottles C through F. These may be performed in any order.
9. Record your data in the table below.
Pollutant
Tested
Drops of
Distilled
Water
Drops of
Pollutant
Drops
of
Living
Eels
Water
(Control)
2
0
1
Silver
Nitrate
1
1 (A)
1
Mercury (II)
Nitrate
1
1 (B)
1
Time (seconds) for
Motion
Abnormalities
Class Averages
(seconds)
Nickel
Nitrate
1
1 (C)
1
Lead
Nitrate
1
1 (D)
1
Aluminum
Nitrate
1
1 (E)
1
Copper (II)
Nitrate
1
1 (F)
1
Part II: Searching for Positive Synergy between the Pollutants
1. In one of the depressions place one drop of the solution in Bottle B and one drop of the
solution in Bottle C.
2. Add one drop of the worm suspension and begin timing. Observing with a dissecting
microscope, record the time it takes for the majority of the organisms to lose their ability to
swim in one direction and to begin to form coils instead. If this does not happen within five
minutes, record a negative result for that combination of pollutants.
3. Compare this to the time achieved in the first part of the exercise when only the solution in
Bottle B was being used.
4. Repeat using one drop of the solution in Bottle B with one drop of the solutions in each of the
following bottles in turn: Bottle D, Bottle E and Bottle F.
5. Record your data in the table below.
Pollutant
Tested
Drops of
Mercury
(II)
Nitrate
Drops of
Pollutant
Drops
of
Living
Eels
Nickel
Nitrate
1 (B)
1 (C)
1
Lead
Nitrate
1 (B)
1 (D)
1
Aluminum
Nitrate
1 (B)
1 (E)
1
Copper (II)
Nitrate
1 (B)
1 (F)
1
Time (seconds) for
Motion
Abnormalities
Analyzing the Results
1. Which metal had the highest toxicity by itself?
Class Averages
(seconds)
2. What physiological effects can the metal toxin in #1 have on an organism?
3. Which metal had the second highest toxicity by itself?
4. What physiological effects can the metal toxin in #3 have on an organism?
5. Use the class average data to answer the questions below.
5A. How many times faster did Mercury + Nickel cause an effect compared to
Nickel or Mercury alone (whichever had the greatest effect)?
5B. How many times faster did Mercury + Lead cause an effect compared to
Lead or Mercury alone (whichever had the greatest effect)?
5C. How many times faster did Mercury + Aluminum cause an effect compared
to Aluminum or Mercury alone (whichever had the greatest effect)?
5D. How many times faster did Mercury + Copper cause an effect compared to
Copper or Mercury alone (whichever had the greatest effect)?
6. Which metal showed the phenomenon of positive synergy to the greatest degree
when combined with the mercury?
7. Ecologically, why is it more important to control such pollutants to prevent toxic
effects on lower organisms, represented by the worms in this exercise, instead of higher
organisms such as birds or fish?
8. How does the phenomenon of biological magnification complicate the setting of
allowable levels of pollutants in an aquatic ecosystem?
9. Why is it important to take the phenomenon of positive synergy into consideration
when setting standards for a specific body of water?