Chronic toxicity, the development of adverse effects as a result of long term exposure to a contaminant or other stressor, is an important aspect of aquatic toxicology.
[1] Adverse effects associated with chronic toxicity can be directly lethal but are more commonly sublethal, including changes in growth, reproduction, or behavior.
It can manifest as direct lethality but more commonly refers to sublethal endpoints such as decreased growth, reduced reproduction, or behavioral changes such as impacted swimming performance.
NOECs and LOECs can be derived from both acute and chronic tests and are used by agencies to set water quality standards.
This includes pH, salinity, water hardness, conductivity, temperature, and amounts of dissolved organic carbon (DOC) For instance, the toxicity of copper is decreased with increasing amounts of DOC, as described by the biotic ligand model (BLM).
[5] Chronic toxicity will vary with differences in organisms, including species, size, and age.
Water quality guidelines are determined based on the results of both acute and chronic toxicity tests.