Hydroxylamine-O-sulphonic acid

Toxicity to microorganisms

Description of key information

In the Activated Sludge Respiration Inhibition Test, for the test substance the EC20 (30 min) was determined as ca. 450 mg/L and the EC50 as > 1000 mg/L.

Key value for chemical safety assessment

EC50 for microorganisms:

1 000 mg/L

Additional information

For the test substance hydroxylamine-O-sulphonic acid, one reliable study is available. The test substance hydroxylamine-O-sulphonic acid was investigated in an Activated Sludge Respiration Inhibition Test (which corresponds to OECD Guideline 209) to evaluate the toxicity to microorganisms. As inoculum activated sludge from laboratory wastewater plant treating municipal sewage was used (concentration of dry substance: 1 g/L). As an outcome, for the test substance the EC20 (30 min) was determined as ca. 450 mg/L and the EC50 (30 min) as > 1000 mg/L (nominal concentration) (BASF, 2004).

 

Concerning the surrogate substance, there are three tests available on the respiration inhibition of activated sludge (BASF 1979, BASF 1984, BASF 2007).

 

Due to insufficient documentation, the two older studies (BASF 1979, 1984) have been assessed as not reliable. However, in both tests a concentration-dependent inhibition of microbial respiration was observed starting at concentrations of 0.5 - 1 mg/L. The EC20s determined in the studies were 0.6 and 1.0 mg/L.

 

In another study, the inhibition of oxygen consumption by activated sludge was investigated according to OECD 209 (BASF AG 2007). Activated sludge was obtained from a municipal wastewater treatment plant, test concentrations ranged from 0.05 to 504 mg/L (nominal). After 180 minutes incubation at 20 ± 2 °C the respiration rates were recorded. An EC10 of 0.7 mg/L was determined. At 50.4 mg/L 56% inihibition was observed (EC 50), at 504 mg/L 78% inhibition.

 

"Bis(hydroxylammonium)sulphate is known to inhibit microbial activity, also in sewage treatment plants. Other findings (e.g. Amarger & Alexander 1968), indicate an inhibition of microbial activity due to high concentrations of hydroxylamine. However, since hydroxylamine is an intermediate in the nitrification process, in lower concentrations hydroxylamine is expected to be degraded biologically to nitrite (e.g. Jetten et. al. 1997).

Taking these findings together with the data concerning transformation of bis(hydroxylammonium)sulphate, it can be assumed that the toxicity to microorganisms is associated with high concentrations of the hydroxyl-ammonium ion or hydroxylamine. In sewage treatment plants pH is buffered to pH 8 where the hydroxyl-ammonium ion is present only in very low concentrations. In addition to that, hydroxylamine (free base) is expected to  decompose rapidly due to abiotic processes. The remaining concentration is not expected to inhibit microbial activity. Hence it can be assumed that additional biological degradation occurs in the waste water treatment plant." (EU-RAR Draft 14. May 2008)

 

Reference:ECB (2008). EU-RAR Draft, Bis-(hydroxylammonium)sulphate, CAS: 10039 -54 -0,14.May 2008