The difference between acute & chronic toxicity

Often you hear about chronic and acute toxicity when discussing effluent bioassay (biomonitoring) with test organisms. Both concepts are important for biological units that are having issues with ammonia oxidation, deflocculation, and COD/BOD removal. Over the next few posts, I am going to go into acute vs chronic toxicity with specific examples. In this post, I am going to make sure we all agree what is acute vs chronic toxicity.

Acute Toxicity - something that damages organisms immediately upon exposure. Focus on the fast kill part! Acute toxicity is often seen with pH swings, phenol, cyanides, or solvents. In bioassay tests, this is the die off of test organisms. With wastewater bacteria, acute toxicity usually comes with an immediate loss of nitrification and deflocculation. As soon as the acute toxic compound washes out or the biomass adapts, the system starts to recover.

Chronic Toxicity - a slower, accumulating toxic effect. Often we see metals that buildup in biomass as a source of chronic toxicity. You will not see the sharp change in biomass with chronic toxicity. Instead, a loss of treatment efficiency will take hold over time. In bioassay tests, chronic toxicity manifests itself as low reproduction or failure to see weight gain.