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Thread: Measuring the level of toxicity in water

  1. #1 Measuring the level of toxicity in water 
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    Hi everyone,

    Is it possible for someone to measure the level of toxicity in water using a spectrophotometer (using transmittance rate... so higher the the rate, the less toxic it is)?

    If not, what is a way that I could possibly measure that without resorting to something too expensive?

    This is for a high school project, so a spectrophotometer is available at my school. I can also order anything from biology websites (as long as the price is not high).


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    Bullshit Intolerant PhDemon's Avatar
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    As you say the spectrophotometer measures the amount of light transmitted through water. If you assume that "toxicity" is proportional to the amount of light scattered or absorbed (i.e. not transmitted through the water) you can use the spectrophotometer data as a measure of toxicity.


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    Quote Originally Posted by lightstorm View Post
    Hi everyone,

    Is it possible for someone to measure the level of toxicity in water using a spectrophotometer (using transmittance rate... so higher the the rate, the less toxic it is)?

    If not, what is a way that I could possibly measure that without resorting to something too expensive?

    This is for a high school project, so a spectrophotometer is available at my school. I can also order anything from biology websites (as long as the price is not high).
    I am not sure what kind of spectrometer you have. If you have UV-Vis, then you have many options. However the definition of toxicity is not as rocksolid as you make it seem. Toxicity is extremely broad, from heavy metals, to nitrile, to arsenic or fluoride. If you are using spectrometry as a method, i assume you want to detect coloured toxins, usually metals. Copper or Barium have a nice color.

    A straight up measurement of your toxic water, up with a blanco or a negative will give some results. Problem with spectrometry, if you don't exactly know what you are looking for, you can only check one wavelength at a time. If your spectrometer is better, you can do all at once, and you will see a line that shows absorption per wavelength. More absorption than blanco, means more refracting chemicals. Usually more chemicals meant more toxicity.
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    lightstorm,

    how would this method actually measure toxicity? Maybe the water is full of nutrients...

    I'd go for some kind of invertebrate indicator species test (assuming your testing river/lake water or something similar).
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  6. #5  
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    Quote Originally Posted by Zwirko View Post
    lightstorm,

    how would this method actually measure toxicity? Maybe the water is full of nutrients...

    I'd go for some kind of invertebrate indicator species test (assuming your testing river/lake water or something similar).
    That only indicate thresholds, and you would also need nutriėnt concentrations. Doing UV-Vis spectrofotometry and using a template to estimate concentrations with blancs and controls seems the easiest.
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    Doesn't seem easier to me. Again, assuming an environmental sample, there is know way to determine what is actually in the water without access to some serious equipment. Simple transmittance spectrography won't tell us much of any value - it's probably in danger of assuming absorption is directly proportional to toxicity. One transmittance value versus another could mean any number of things.

    In fact, the method I pointed out is actually a quite common high school level experiment. Unless you are going to test for certain compounds or the presence of heavy metals, the only easy way to determine toxicity is to see what species live in the water.
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  8. #7  
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    Quote Originally Posted by lightstorm View Post
    Hi everyone,

    Is it possible for someone to measure the level of toxicity in water using a spectrophotometer (using transmittance rate... so higher the the rate, the less toxic it is)?

    If not, what is a way that I could possibly measure that without resorting to something too expensive?

    This is for a high school project, so a spectrophotometer is available at my school. I can also order anything from biology websites (as long as the price is not high).
    As other replies indicate, one problem is that analysis can only detect a specific list of things that you set out to test for. (In my old job people would sometimes ask to test industrial lubricating oils for "contaminants". I always had to say if you suspect a particular contaminant, yes we can look for it, but for any old unspecified contaminant it is just impossible.

    If you able to indicate what type of contamination you are most concerned about, that might help focus the discussion. For example, heavy metals? Organic fertiliser runoff? Pesticides? Bacterial contamination from sewage? All these will require different methods of detection and quantification.
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    With a spectrameter what you can test for is how much light is transmitted. There is no way to directly relate light transmission to toxicity. Perfectly potable water may be nearly opaque. The fresh waters of the Florida Everglades for example are black with disolved tannins yet are drinkable by man and beast.
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  10. #9  
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    Quote Originally Posted by Zwirko View Post
    Doesn't seem easier to me. Again, assuming an environmental sample, there is know way to determine what is actually in the water without access to some serious equipment. Simple transmittance spectrography won't tell us much of any value - it's probably in danger of assuming absorption is directly proportional to toxicity. One transmittance value versus another could mean any number of things.

    In fact, the method I pointed out is actually a quite common high school level experiment. Unless you are going to test for certain compounds or the presence of heavy metals, the only easy way to determine toxicity is to see what species live in the water.
    Using invertebrates to determine toxicity... how does that work exactly? I've seen that used before, but not sure what the process would be.

    BTW, it's a 2 part experiment. I'm experimenting an effect of a common chemical (like triclosan) on the aquatic environment with the Daphnia and then finding out the best ways to dissolve the chemical.

    So the thing I'm asking relates to the second part where I measure the amount and level of toxicity left in the environment after I run a variety of experiments to degrade the chemicals. Does that make sense?
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