Short-Term Guideline Values for Chlorine in Freshwaters.

Area of Science:

• Environmental toxicology
• Aquatic toxicology
• Water quality guidelines

Background:

• Current Australian and New Zealand freshwater guideline value for total residual chlorine (TRC) is 3 µg Cl/L.
• This value is based on acute toxicity data converted to chronic data using a default ratio, without accounting for chlorine's rapid decomposition.
• Chlorine in freshwater rapidly decomposes from hypochlorite to chloramine.

Purpose of the Study:

• To review the literature on chlorine's fate and ecotoxicity in freshwater.
• To derive revised default guideline values for hypochlorite and chloramine in freshwater.
• To recommend guideline values based on acute toxicity due to rapid chlorine decomposition.

Main Methods:

• Literature review on chlorine fate and ecotoxicity in freshwater.
• Application of species sensitivity distribution (SSD) to toxicity data.
• Derivation of guideline values for 95% species protection.

Main Results:

• Revised guideline values for 95% species protection were derived: 7 µg Cl/L for hypochlorite and 9 µg Cl/L for chloramine.
• The hypochlorite value is applicable to any TRC-containing effluent.
• The chloramine value is more appropriate for drinking water effluents where dechlorination has occurred.

Conclusions:

• Revised guideline values for TRC in freshwater are proposed, considering chlorine's decomposition.
• The proposed values are 7 µg Cl/L (hypochlorite) and 9 µg Cl/L (chloramine) for 95% species protection.
• These values are likely conservative and should be applied at the edge of the mixing zone, potentially using time-weighted averages.