Which statement correctly describes carbon dioxide toxicity thresholds?

Which statement correctly describes carbon dioxide toxicity thresholds?

• A. CO2 toxicity can occur at concentrations greater than 20 mg/L.
• B. CO2 toxicity occurs only at concentrations below 20 mg/L.
• C. CO2 has no toxicity in water.
• D. CO2 toxicity occurs at any concentration.

Answer: (A)

High dissolved CO2 becomes toxic when its concentration rises above a level that the organism’s physiology can tolerate. In many freshwater systems, dissolved CO2 around 20 mg/L marks a threshold where adverse effects start to appear; above this, CO2 can cause respiratory stress, acid–base imbalance, and reduced oxygen transport. The toxicity threshold isn’t a fixed absolute for all species or conditions, but the idea is that CO2 toxicity occurs at higher concentrations, not at low ones. So the statement that toxicity can occur at concentrations greater than 20 mg/L best describes this relationship. CO2 is not harmless at all concentrations, nor is it limited to below 20 mg/L, and it is not free of toxicity in water.

High dissolved CO2 becomes toxic when its concentration rises above a level that the organism’s physiology can tolerate. In many freshwater systems, dissolved CO2 around 20 mg/L marks a threshold where adverse effects start to appear; above this, CO2 can cause respiratory stress, acid–base imbalance, and reduced oxygen transport. The toxicity threshold isn’t a fixed absolute for all species or conditions, but the idea is that CO2 toxicity occurs at higher concentrations, not at low ones. So the statement that toxicity can occur at concentrations greater than 20 mg/L best describes this relationship. CO2 is not harmless at all concentrations, nor is it limited to below 20 mg/L, and it is not free of toxicity in water.