Registration Dossier

Environmental fate & pathways

Endpoint summary

Administrative data

Description of key information

Additional information

The preliminary hydrolysis study showed that at pH 4, 7 and 9 and 50±0.5ºC, more than 50% hydrolysis had occurred after 2.4 hours, equivalent to a half-life of less than 1 day under environmental conditions (25°C). Benzoic acid, the expected main degradation product, was present in the hydrolysed solutions at each test pH. Given the rapidity of the hydrolysis reaction, no further hydrolysis testing was considered necessary.

Consequently, when released into water, Dibenzoyl peroxide will rapidly be transformed into benzoic acid due to its instability. Consequently, the assessment of the bioaccumulation potential is based on both parent substance and hydrolysis product (benzoic acid).

Benzoic acid is readily biodegradable and has a low potential of bioaccumulation and adsorption due to its log Kow value at environmental pH (see Benzoic acid and Sodium benzoate, Concise International Chemical Assessment Document 26, World Health Organization, 2000)

Conducting a study on bioaccumulation is scientifically not justified, because of the following:

1) Toxicokinetic results indicate that there is no risk of bioaccumulation of neither Dibenzoyl peroxide nor benzoic acid(see section 7.1.1 “Basic Toxicokinetics”).

Benzoyl peroxide is rapidly converted to benzoic acid in the skin of both animals and humans.Absorption of the benzoic acid occurs as benzoate through the blood vessels in the dermis. This metabolite enters the blood circulation and is rapidly cleared through the kidney (Nacht, S. et al, 1981; Yeung, D., et al, 1983; Morsches, B. and Holzmann, H., 1982; Wepierre, J., et al, 1986). Topically applied benzoyl peroxide penetrates unchanged through the stratum corneum or follicular openings of excised human skin and is converted metabolically to benzoic acid within the skin (Nacht S. et al, 1981). A study in rhesus monkeys in vivo showed that this benzoic acid is systemically absorbed as benzoate and rapidly excreted in the urine in an unchanged form, without being conjugated to hippuric acid, as would be predicted to occur following oral administration.

2) A computer simulation via EPI Suite TM (using an experimental log Kow of 3.2, resulting from the Klimisch-1 -rated study (2009), see section 4.7 “Partition coefficient”) resulted in a BCF for Dibenzoyl peroxide of 60 L/kg wet-wt, which is far below the trigger value of BCF = 500 for classification with respect to chronic aquatic toxicity (see attached EPI Suite TM printout file).

Bioaccumulation Estimates (BCFBAF v3.00):

Log BCF from regression-based method = 1.778 (BCF = 60.03 L/kg wet-wt)

Log Biotransformation Half-life (HL) = -0.5728 days (HL = 0.2674 days)

Log BCF Arnot-Gobas method (upper trophic) = 1.823 (BCF = 66.58)

Log BAF Arnot-Gobas method (upper trophic) = 1.823 (BAF = 66.59)

log Kow used: 3.20 (user entered)

Based on the available information it is therefore proposed that the study on bioaccumulation of Dibenzoyl peroxide and its degradation substance can be waived, which is in accordance to the intention of the REACH regulation to minimize animal consumption by conducting unnecessary vertebrate studies.