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Water Solubility

By Little Pro on 2016-01-13 Views:  Update:2017-01-18

Water solubility is a measure of the amount of chemical substance that can dissolve in water at a specific temperature. The unit of solubility is generally in mg/L (milligrams per liter) or ppm (parts per million). You can often find it in the section 9 of a safety data sheet (SDS).

Regulatory Implications of Water Solubility

Water solubility is one of the most important properties affecting bioavailability and environmental fate of chemical substances. Chemicals that are water soluble are more likely to be absorbed by aquatic species such as algae and fish. Such chemicals have relatively adsorption coefficients for soils and sediments, and they bioconcentrate poorly in aquatic species. Highly water soluble substances tend to degrade more readily by processes such as photolysis or hydrolysis. [Reference]

Under REACH, this study does not need to be conducted if:

  • the substance is hydrolytically unstable at pH 4, 7 and 9 (half-life < 12 hours), or
  • the substance is readily oxidisable in water.

Testing of Poorly Soluble Substances

The purpose of an aquatic ecotoxicological test is to determine the toxicity of a substance in aqueous solution, that is, truly dissolved in the test medium. For poorly soluble substances (substances with low water solubility <100mg/L), toxicity tests are usually conducted only up to the maximum dissolved concentration under the test conditions.

If a substance has very low water solubility (i.e, <1mg/L) and a big log Kow (i.e, >3), terrestrial toxicity tests may be conducted instead of the aquatic eco-toxicological tests.

References

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