The recommended control limits for fluoride levels depend on which factor?

The recommended control limits for fluoride levels are influenced significantly by the annual average of maximum daily air temperatures. This is because temperature can affect the biological activity in aquatic systems, influencing the behavior and toxicity of various substances, including fluoride. Higher temperatures can lead to increased metabolic rates in aquatic organisms, potentially magnifying the impacts of pollutants such as fluoride.

Monitoring and adjusting fluoride levels according to temperature helps ensure that aquatic environments remain safe for aquatic organisms and can support the overall health of the ecosystem.

Other factors, like naturally occurring fluoride concentrations, may also play a role in setting limits, but they don't account for the dynamic nature of temperature impacts on water quality and organism health, which makes temperature a crucial aspect in establishing and managing fluoride control measures.