Aquatic toxicity

Water organisms are used as the standard indicators because spills and discharges often end up in water. Tests commonly use a fish, a water flea such as daphnia, and an alga, each representing a different level of the food web. The result with the lowest effect concentration, usually the most sensitive species, tends to decide the classification.

Under the GHS, hazardous to the aquatic environment is split into acute and chronic categories, and the chronic classification also takes into account whether the chemical degrades and whether it bioaccumulates. A chemical that is moderately toxic but persistent can therefore rank as more hazardous than its test numbers alone suggest.

Labels reflect this through the environment pictogram and hazard statements in the H4xx range for aquatic hazards, together with precautionary statements about avoiding release. In the United States, OSHA HazCom does not require environmental hazard classification, but many suppliers include it, and other regimes such as CLP and WHMIS handle it differently.

For workers the practical message is containment. A small amount of a highly aquatic-toxic product can affect a large volume of water. Keep spill kits, drain covers and secondary containment ready, and send waste to proper disposal.