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Water Toxicity using Daphnia

Postby ppborax0 » Tue Jan 30, 2018 11:44 am


I am trying to help my daughter with a science experiment; measuring water toxicity using bioassays. I have looked at the procedure for this test but not sure how to process after Step #6. Need help here.

6. Weigh the sediment samples and record their weights in a data table in your lab notebook.
7. Dilute the sediment samples with spring water at different concentrations, to simulate rainwater run-off after a storm. Label each container with concentration (in grams per liter, or g/L) of sediment in the water. - If I collect 4 samples, do I make dilution for each of the 4 samples. Also what is the typical dilution (100%, 50%, 25%, 12.5%). If I take 10 grams of sediment samples, how do I make dilutions at different concentrations.

Thanks for your help.


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Re: Water Toxicity using Daphnia

Postby PharmaMan » Thu Feb 08, 2018 7:55 pm


As you suggested, I would do some dilutions at different ratios since none are provided in the procedure. I would also do different dilutions for each of the samples that you collected, unless they are all from the same exact location. To make your dilutions, I'd pick volumes of water that cover a large range. For example, if you have 10g of sample, you could dilute it in 100mL of water, which makes a 100g/L dilution (10g/0.1L). Then you could make another dilution at say 500 mL, so 10g/0.5L=20g/L dilution. Pick a few more dilutions to make, but you should have some dilutions that are very concentrated and others that are not so that you have a wide range. It appears that there is no typical dilution for this experiment.

Let us know if you have any further questions.


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