Glossary / Ecology
EC50
EC50 is the effective concentration of a chemical that produces a specified harmful effect in 50 percent of a test population over a stated time. It is widely used to describe toxicity to aquatic organisms such as water fleas and algae.
Explanation
Unlike LC50, which counts deaths, EC50 covers sublethal effects. For water fleas the effect is often immobilization; for algae it is usually reduced growth or growth rate. The effect, the species and the exposure time are all part of the result, so an EC50 only makes sense with that context attached.
A lower EC50 means more toxic, because less chemical is needed to cause the effect. Results across fish, invertebrates and algae are compared to find the most sensitive group, which usually drives the aquatic hazard classification. Algae and invertebrates often respond at lower concentrations than fish.
EC50 values come from standardized laboratory tests that vary slightly by method, so comparisons are best made between results that used the same test. Values are normally expressed in milligrams per liter of water.
Regulators and companies use EC50 to derive predicted no-effect concentrations. A related term, PNEC, divides the lowest reliable toxicity result by an assessment factor to set a level considered protective. Keep in mind that an EC50 itself is not a safe level: it is the concentration that harms half the population.
What to do and watch for
- Read the species, effect and exposure time alongside the number.
- Compare with LC50 and other data, since the most sensitive species matters.
- Do not treat an EC50 as a safe concentration.
Where it appears on an SDS
- Section 12: Ecological information. Ecotoxicity results, listing EC50 values by species such as daphnia or algae, with test duration.
SDS content and wording vary by supplier. This page is general reference and does not replace the current SDS for your product.