Science Buddies: "Ask an Expert"

Science Fair Question: How do phosphates affect the microorganisms in creek water?

I will collect two samples of the same creek water from Beargrass Creek in Jefferson County, Louisville, KY. One will be used as a test sample. I will use the other sample as my control.
I will look at each of the samples under a microscope and record detailed observations of the microorganisms that I see.
I will pour phosphate liquid into one of the samples of creek water.
I will let the creek water with the phosphate in it sit overnight.
I will look at each sample under the microscope again and record any new detailed observations of the microorganisms that I see.
I will repeat the process exactly and end up with three trials to my experiment.
I will then conclude whether or not phosphate has any affect on microorganisms in creek water.
ANY IDEAS ON WHERE TO GET PURE PHOSPHORUS?? Or should I just use detergent and get the percentages of chemicals for it?
Thank you so much!

Hi,

Are you trying to measure the effect of agricultural field runoff or laundry detergent wastewater on a stream? If so you want to be adding a phosphate salt, NOT elemental phosphorus, to your water samples. I would be tempted to use an ammonium orthophosphate or ammonium polyphosphate or sodium tripolyphosphate for the phosphorus source. It is possible to buy elemental phosphorous from chemical supply houses such as Sigma Aldrich, but it is expensive, poisonous, and won’t do what you want it to do. You should be able to buy an ammonium phosphate fertilizer from your local hardware store rather cheaply, and get the form that would naturally occur in wastewater runoff into your local creeks.

Some info on phosphate retilizers:

http://www.extension.umn.edu/distributi ... c6288.html

http://en.wikipedia.org/wiki/Fertilizer

Some information on use of phosphates in soaps and detergents:
http://www.chemistry.co.nz/deterg_inorganic.htm

http://www.colorado.edu/conflict/full_t ... 94-54.htm/

I hope this helps.

Best regards,

Barrett L Tomlinson

Hi,

I moved your topic to the Life Sciences forum where more experts who specialize in your area will see it -- Preparing for the Science Fair is directed more toward displaying and communicating your results.

One detail that might be useful to know is that phosphate and phosphorus are not the same thing. Phosphate is an ion made of phosphorus with four oxygens attached to it with a net charge of -3. Whenever you have negative ions (anions) in a substance, there are positive ions (cations) around to balance them, so you'd never have "pure" phosphate. The cations in a phosphate compound could be sodium, hydrogen, other atomic cations, or more complicated organic molecules. The identity of the cation can affect a phosphate compound's solubility in water and perhaps other properties important to its effect on your organisms, which is why the form of phosphate you use does matter (as Barrett says).

You might also want to pay attention to whether amounts of phosphorus is fertilizers are reported as mass percentages of phosphorus or mass percentages of some phosphate compound.

These Wikipedia articles are good starting places for reading about these topics, but you will probably want to look at some of the references cited:

http://en.wikipedia.org/wiki/Phosphate
http://en.wikipedia.org/wiki/Labeling_of_fertilizers

Amanda