Science Buddies: "Ask an Expert"

Hi! Im doing my science experiment with polluted water.

I want to see the effects of a certain chemical on polluted dirty pond water

I want to measure how the solid volume decreases/increases. how can i measure that, besides evaporating it?

I came across TDS (Total dissolved solids), but that's about 'dissolved' solids.
One that I want to measure is the amount of solid organic compound, such as slime, algae are in there.
So TDS wont work, since those organic compounds aren't 'dissolved' in the water.

how can i measure solids in water?

thank you!

Hi Silvia,

I'm not sure if this is exactly what you are looking for, since it won't be able to distinguish between organic and inorganic compounds, but one very simple measurement you could consider doing is simple spectroscopy. Basically spectroscopy measures how much light passes through a sample, compared to a blank control. In the case of visible light (I would suggest a wavelength of 600nm), the light will be scattered by physical particles in the water, including algae, plankton, bacteria, silt, etc. You can do measurements at different wavelengths to look for different contaminating factors (in the ultraviolet wavelengths, 280nm is usually used to measure proteins, and there may be other wavelengths useful for your pollutants of interest). The benefit of this method is that it is extremely fast and easy, and certainly any university lab will have access to a spectrophotometer, and even some high school labs may have one. The drawback is that it is not very specific, so if you are interested in particular types of contaminants, it may not be the best option.

Water pollution is well outside my area of expertise, so I'm sure other experts will have some ideas for measuring specific pollutants, but this could be a good general starting point.

I hope this helps,
JMP

Hi,

I agree with JMP that a spectrophotometer would be a good way to measure water clarity. You can use the spectrophotometric method to estimate chlorophyll-a concentration and thus the amount of algae/phytoplankton that may be present.

You can also try a transparency tube, which is used to monitor water quality in streams and rivers, and whose readings "relate fairly well to lab measurements of turbidity and total suspended solids."
http://water.epa.gov/type/rsl/monitoring/155.cfm

Derek