Boron trichloride

Endpoint summary

Additional information

A general waiver for aquatic toxicity studies is proposed according to REACH, Annex XI, 1. 'Testing does not appear to be scientifically necessary', Section 1.5. 'Grouping and read across'. Justification: See the category concept in Section 13 of IUCLID.

To enable a possible toxic action of BCl3 to aquatic organisms, the substance has to be dissolved in the aqueous medium. BCl3 hydrolysis rapidly and completely in water to form HCl and B(OH)3.

The ecotoxicity of both hydrolysis products are known and described in the IUCLID registration dossiers.

Acute toxicity:

Hydrogen chloride:

HCl exerts its action by lowering the pH. Not the concentration of HCl in mg/L is alone of relevance but also the pH is decisive, which is determined i.a. by the buffer capacity of the medium, containing minerals and other substances. H⁺ and Cl^- are naturally occurring ions.

The lowest acute LC50/EC50 with the highest pH = 4.9 was obtained for daphnids, the lowest NOEC with the highest pH = 5.5 also for Daphnia. This corresponds to EC50 ≥0.49 mg BCl3/L and NOEC ≥0.1 mg BCl3/L,if not only pure water is considered.

Boric acid:

Boric acid has generally a much lower ecotoxicity, compared to HCl. Transcribed to boron trichloride:

LC50fish = 864 mg BCl3/L

EC50Daphnia= 1440 mg BCl3/L

EC50alga = 569 mg BCl3/L

Long-term toxicity:

Hydrogen chloride:

Relevant aquatic organisms need a pH in the range of 6 to 9. If the pH is lowered by the test substance to <6, a toxicity at least to some of the aquatic organisms is foreseen. This is one of the basic assumptions in the EC directive 2006/44/EC on the quality of fresh waters needing protection or improvement in order to support fish life, which state that the pH of the fish water has to be in the range of 6 to 9. In the case of HCl it is therefore not necessary to perform long-term investigations because a toxic effect can be predicted if the pH falls below 6.

A pH of 6 corresponds theoretically to NOEClong-term = 0.036 mg HCl/L or 0.039 mg BCl3/L in pure, unbuffered water. In natural water a NOEClong-term >0.039 mg BCl3/L would be obtained, depending on the buffer capacity of the water and the species concerned.

Boric acid:

A NOEClong-term = 11 mg B(OH)3/L, transcribed to 22 mg BCl3/L is adopted.

Endpoint conclusion:

The decreased pH caused by the formation of HCl during hydrolysis of BCl3 is decisive for the toxicity to aquatic organisms, compared to that of boric acid. Toxic acute and long-term effects can be predicted if the pH is <6, caused by HCl.

A pH of 6 corresponds theoretically to a NOEClong-term = 0.036 mg HCl/L or 0.039 mg BCl3/L in pure, unbuffered water. In natural water a NOEClong-term >0.039 mg BCl3/L would be obtained, depending on the buffer capacity of the water and the species concerned.

Three times this value is considered to reflect more practical conditions of natural water and could be used for classification: NOEClong-term = 0.12 mg BCl3/L.

For a risk assessment a NOEClong-term = PNEC of pH = 6 is nevertheless considered to be the first choice for each of the aquatic organisms, as not a systemic, species specific effect is the underlying mechanism of toxicity but the acidity of the medium.