Dibutyl phthalate

Endpoint summary

Description of key information

Environmental fate(1)

DBP may be released into the environment during its production and subsequent life cycle stages, including disposal. Emissions to water and air are expected to be the most important entry routes of DBP. General characteristics of DBP which are relevant for the exposure assessment are given below.

Degradation

The contribution of hydrolysis to the overall environmental degradation of phthalate esters, including DBP, is expected to be low. Photo-oxidation by OH radicals contributes to the elimination of DBP from the atmosphere. An atmospheric half-life of about 1.8 days has been estimated for the photo-oxidation reaction. The metabolic pathway of aerobic and anaerobic biodegradation of phthalates can be summarised as follows. First the di-ester is hydrolysed into the mono-ester by esterases with low substrate specificity. Subsequently the mono-ester is converted into phthalic acid. There is ample evidence that DBP is ready biodegradable under aerobic conditions. The same literature sources indicate that biodegradation of DBP is much slower in the anaerobic environment, e.g. sediments or deeper soil or groundwater layers.

Distribution

The Henry's law constant of 0.27 Pa.m3/mol indicates that DBP will only slowly volatilize from surface waters, i.e. virtually all of the DBP will remain in the water phase at equilibrium. The octanol/water partition coefficient (Kow) of DBP is high and consequently the equilibrium between water and organic carbon in soil or sediment will be very much in favour of the soil or sediment. A Koc of 6,340 l/kg can be calculated using the log Kow of 4.57. Despite its low volatility, DBP has been reported as particulate and as a vapour in the atmosphere. In the air DBP is transported and removed by both wet and dry deposition.

Bioaccumulation

The high Kow of DBP indicates that the substance has a potential for bioaccumulation. However, the actual degree of bioaccumulation in vivo will be determined by the metabolisation and the elimination rate of the substance. The available BCF data demonstrate a relatively low bioconcentration, but also indicate that higher BCF values are obtained when the BCF is calculated for the total amount of metabolites using 14C-labelled material. The experimental BCF of 1.8 l/kg for DBP from the recent study is used in the further risk assessment for secondary poisoning (aquatic route). In the risk characterisation attention will be paid to the possible

consequences of using a higher value. No experimental BCF data are available for terrestrial species. EUSES calculates a BCF worm of 13 kg/kg.

(1) according:

European Union Risk Assessment Report dibutyl phthalate, Volume 29, p. 6 (2003)

Editors: B. G. Hansen, S.J. Munn, R. A/Ianou, F. Berthault, J. de Bruin, M. Luotamo, C. Musset, S. Pakalin, G. Pellegrini, S. Scheen S. Vegro.

Office for Official Publications of the European Communities, ISBN 92—894—1276—3