Science Buddies: "Ask an Expert"

Hello, I'm doing my 6th grade science fair project on different water purification methods using stream water and bleach, iodine and sunlight as the treatments. I love camping and wanted to see which of these methods might be the best for killing microorganisms in water that one might find while out in the wilderness. Don't worry, I won't be drinking the water! I already ran my experiment and had some trouble. I used samples of the water and treated them, then observed for movement under my microscope and compared that to movement in my control. I was careful to prevent any cross-contamination between the samples. I put one sample out in the sun for 4 hours, then observed and found no life. Then I observed the control at 4 hours and also found no life (movement). If the organisms are dying on their own in such a short period of time, then none of the conclusions about my treatments are valid. My questions are:
1) Why would they be dying on their own?
2) What can I do to keep the microorganisms in the samples healthy if I want to rerun the experiment? Maybe I need to add a food source?
I've run into a dead end and my science fair is coming up quickly! Thanks for any help you can send my way.

Hmm... cool project idea but tricky problem! I have a few thoughts.

Just to check- when you first collect the samples do you check them under the scope and see movement? You should be sure that you see organisms that seem alive before you apply any of the water treatments. If they do start out alive but die at some point, then one solution could be to check in every 10 min or so and figure out when they stop moving, then pick a time point before they die to do all your testing.

I'm not exactly sure why they seem to be dying... How different is the environment you're keeping them in compared to the stream they came from? If it's a closed container, maybe they're not getting enough oxygen. Or maybe the temperature is too different. You could try to figure out a way to contain them while keeping them in the stream, perhaps by scooping up a sample in a bucket and resting the bucket in a shallow part of the stream so that it's surrounded by water but not mixing. Does that make sense? You could apply your test conditions to a series of buckets containing isolated samples and check them under the microscope periodically (assuming your microscope is small enough to bring into the field).

Another random tip - a lot of people don't realize that you can actually use a cell phone camera to take photos through most light microscope lenses. Could be fun to take some photos of the organisms you find!

Good luck- I hope you get things figured out! Let us know what happens!

Thanks for your feedback.

Yes, I did check for movement in my samples before treating them, and saw some. I used large clean coffee cans to collect the water and am wondering if there was something in them that caused the death. This time i will use a plastic bucket. All the water was uncovered except for the 10 minutes it took me to bring it home right before testing for life. It sounds complicated to do the testing by the stream. I'm in Southern California so I don't think the water temperature at the creek was that much cooler than my house temperature, but maybe? I like the idea of pictures with a cell phone, I didn't know that! I am taking picutres by connecting my microscope to my computer!

Does anybody else have any ideas?

It will be hard to determine exactly what the cause of death of the organisms is in your samples. All of the previous suggestions are definitely good ones to try. You will want to keep all conditions as close as possible to the stream conditions. If you think there may be a large temperature difference, measure the temperature of the stream water and of the water once it is back in your home. If oxygen is the problem when you are carrying your samples back, cut a few holes in the container lids to compensate.

I also agree that it will be best to determine a time point such that your control samples still have live organisms in them when your treatments are finished. The conditions of your samples prior to and during testing must be as close as possible to the natural conditions.

Let us know how we can help you further. Best of luck!

-Pharma