Via experiments in the lab the solubility of most solvents in water has been determined. They range from almost insoluble (MBT) to chlorobenzene at 495,000 parts per billion. Other examples of lab solubilities would be benzene at 1,800,000 parts per billion. Toluene is close to that of benzene.
By lab solubilities I mean an exact amount of organic solvent in a pure litre of water. Real life and contaminated sites are nothing like that. In the real world polluters leak, drip, spill and dump all kinds of solvents into the ground and surface water. Hence determining the solubility of benzene for example in contaminated groundwater depends upon the different solvents present and their individual concentrations. What we do know is that the solubility in water of all solvents decreases as the number and concentration of other solvents increases.
These are known as Effective Solubilities and can be determined via testing the variety and concentration of all other solvents in the groundwater. These Effective Solubilities are usually a tiny fraction of the Lab Solubility of the compound on it's own in a litre of pure lab water. It's almost as if there are a pre-determined number of spaces available for organic compounds in water and hence there is competition to decide which compound ends up in the available spaces .
The significance of multiple compounds in groundwater simultaneously is as follows. Usually we think of groundwater contamination based upon the various concentrations in groundwater of these contaminants (organic pollutants). Hence the higher the number of contaminants the lower the concentration numbers but the greater the contamination.
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