Science Buddies: "Ask an Expert"

Hello. I am doing a project where I will be testing the effects of colloidal silver on daphnia. I would also like to test how long the daphnia will stay alive in water from 3 ponds that are used by people. One is Ascarte Lake in El Paso, Texas. One is a man-made lake in Las Cruces, NM, and the other is Balmorhea State Park Pool in Texas. This one is interesting because the pool is filled with water from San Solomon Springs and fish and people seem to thrive together. I have learned that it is not possible for me to test the lake waters for the silver. I can however afford a tester that will test the conductivity of the water which indicates the presence of metals. Not quite the same thing I know but would this be an okay follow up to my experiment. I need something I can do without access to a lab. The supplies from Carolina Biologicals will fulfill the first part of the experiment very nicely but I want to follow up with testing the water from real environments. Could you give me any suggestions on a good follow up with the 3 sources I mentioned? Thank You. Xander Johnson

Hi! This sounds like a really interesting experiment! After a bit of research, it seems that Daphnia don't typically live long regardless of the water's conditions (http://ei.cornell.edu/toxicology/bioassays/daphnia/), so it may be difficult to quantify their lifespan. However, I think it is really cool that you would like to follow-up with the experiment and answer another question - other experiment ideas are listed at the bottom of the page (https://www.sciencebuddies.org/science- ... -pond-life) under the heading "Variations." Keep us updated with the results of your experiment, and good luck!