Chloramide

Toxicity to aquatic plants other than algae

Description of key information

The EC50s are estimated to be 0.92 (frond number), 0.57 (dry weight) and 0.33 mg/L (total frond area) for the inhibition of growth rate relative to control cultures grown under identical conditions and expressed as monochloramine.

The EC10s are 0.18 (frond number), 0.15 (dry weight) and 0.2 mg/L (total frond area) for the inhibition of growth rate relative to control cultures grown under identical conditions and expressed as monochloramine.

Key value for chemical safety assessment

EC50 for freshwater plants:

0.33 mg/L

EC10 or NOEC for freshwater plants:

0.15 mg/L

Additional information

An acute and chronic toxicity test (Bellemain 2010) was performed on Lemna minor.

In this study, the effect of the test item monochloramine on the growth of the freshwater aquatic plant species Lemna minor was investigated in a 7 days flow-through test according to OECD Guideline 221.The study was compliant with the GLP. 

Following preliminary range-finding tests (two range finding), Lemna minor was exposed to an aqueous solution of the test item at concentrations of 0.35, 0.78, 1.49, 3.05 and 6.34 mg/L (three replicate flasks per concentration) and a control (three replicate flasks) for 7 days, under constant illumination and shaking at a temperature of 24 ± 2°C and a pH of 5.5.

After 7 days the number of fronds in each replicate was recorded, fresh and dry weight were measured.

The analytical monitoring was performed from the measurement of TRC and FRC concentrations.

TRC is the sum of the FRC (Free Residual Chlorine) and the CRC (Combined Residual Chlorine). CRC is composed of the 3 species of inorganic chloramines, mono-, di- and trichloramine). However according to the knowledge of the chemistry of chloramines and the test conditions (pH above of 8 and preparation of test solutions with a mass ratio Cl₂/N of 4.8), it is considered that monochloramine was predominant species of inorganic chloramines (CRC).

The concentration of monochloramine was then determined from the TRC and FRC concentrations by multiplying the measured CRC concentrations (Total Residual Chlorine (TRC) minus Free Residual Chlorine (FRC)) provided as eq Cl₂/L by the factor of 0.725.

During the test, measurements of monochloramine concentration were performed in the tests vessels at different times and exposition concentrations were determined by geometric average.

According to the analytical monitoring (geometric average of monochloramine), the theoretical concentrations 0.35, 0.78, 1.49, 3.05 and 6.34 mg/L correspond to the measured concentrations 0.144, 0.211, 0.420, 2.117 and 6.334 mg/L, respectively.

Thus, the obtained results were based on three endpoints: frond number, dry weight and total frond area and on the geometric mean of the measured monochloramine concentrations.

The EC50s expressed as monochloramine (based on the hypothesis that all CRC is present as monochloramine) were 1.54 (frond number), 0.96 (dry weight) and 0.56 mg/L (total frond area) for the inhibition of growth rate relative to control cultures grown under identical conditions. The EC10s expressed as monochloramine were 0.3 (frond number), 0.25 (dry weight) and 0.33 mg/L (total frond area) for the inhibition of growth rate relative to control cultures grown under identical conditions.

As the test was performed at pH 5.5, it could be expected that the solution was a mixture of monochloramine and dichloramine. Indeed according to the knowledge of the chemistry of chloramines, it was expected that the solutions had a ratio mixture of 60% monochloramine and 40% dichloramine. Therefore the EC50s values found in this study were corrected by a factor of 0.6. This hypothesis is conservativeas it was expected that toxicity was entirely due to monochloramine. EC50s calculated with this factor and the EC50s were 0.92 (frond number), 0.57 (dry weight) and 0.33 mg/L (total frond area) for the inhibition of growth rate relative to control cultures grown under identical conditions. The EC10s were 0.18 (frond number), 0.15 (dry weight) and 0.2 mg/L (total frond area) for the inhibition of growth rate relative to control cultures grown under identical conditions.

The two validity criteria of the OECD guideline 221 were fulfilled.

This study is rated as reliable without restriction according to the Klimisch scale and satisfies the guideline requirements for acute and chronic toxicity study with aquatic plants.

 

Conclusion:

Although the study of Garrivier (2009) was judged valid with restrictions, the study of Bellemain 2010 performed on Lemna minor was preferentially chosen for Classification and Labelling and for Risk Assessment of the aquatic plant/algae because it was performed under continuous flow instead of static conditions and the LC50s values were based on measured concentrations instead of nominal concentrations.

Based on these data, monochloramine is considered as very toxic to aquatic plant