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Ecotoxicological information

Toxicity to aquatic algae and cyanobacteria

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Description of key information

The decreased pH caused by the formation of HCl during hydrolysis of BCl3 is decisive for the acute toxicity to algae.

The "EC50" of pH = 4.7 is best described in pH-units and not by the concentration, in case of more or less buffered aquatic environments.

Key value for chemical safety assessment

Additional information

A degradation category approach is applied, based on the very rapid and complete degradation (hydrolysis) of boron trichloride in water to form hydrochloric acid and boric acid. The description and justification of the category is presented in Section 13. The endpoint results of the degradation products are transcribed to boron trichloride.

Relevant information for the 2 degradation products:

Hydrogen chloride:

An algae ErC50,72h value from a key study was pH = 4.7. The NOEC was 5.0. Normalized, this corresponds to 0.73 mg HCl/L respectively 0.36 mg HCl/L in non-buffered water. An ErC50,72h of ≥0.73 mg BCl3/L and a NOAEC of ≥0.39 mg BCl3/L are calculated after converting to BCl3, if not only pure water is considered.

Boric acid:

Green algae, Pseudokirchneriella subcapitata, lowest value from an acute test of reliable quality: An ErC50,72h = 300 mg B(OH)3/L. An ErC50,72h = 569 mg BCl3/L is obtained after converting to BCl3. NOEC = 154 mg BCl3/L.

Endpoint conclusion:

The decreased pH caused by the formation of HCl during hydrolysis of BCl3 is decisive for the acute toxicity to algae. An ErC50,72h of ≥0.73 mg BCl3/L and a NOAEC of ≥0.39 mg BCl3/L are calculated after converting to BCl3, if not only pure water is considered.