Dibutyl terephthalate

Bioaccumulation: aquatic / sediment

Description of key information

Key study is read across to a BCF experimental study of a related substance, di(2-ethylhexyl)terephthalate, with toxicokinetic support that the metabolic breakdown products, terphthalic acid and n-butanol have low log Kow and BCF values based upon QSAR modeling. 

Key value for chemical safety assessment

BCF (aquatic species):

393 dimensionless

Additional information

An experimental BCF study is provided by read across to di(2-ethylhexyl)terephthalate (synonym DOTP), a related terephthalate substance. In that 38-d study the bioconcentration and elimination of 14C-DOTP in the soft tissues of eastern oysters, Crassostrea virginica, continuously exposed to 14C-DOTP at a nominal concentration of 50 µg/L was evaluated. The maximum bioconcentration factor for 14C-DOTP in oyster tissue was 790X and was observed on Day 3 of the exposure period. Apparent equilibrium was established between days 10 and 24. The BCF at equilibrium was 393X. Half-life of the accumulated 14C-residue content present in oyster tissues occurred between days 3 and 7 of the depuration period. Most of the 14C-residues (72.9 to 75.5%) remaining in the tissues of oysters after 14 days of depuration were the parent DOTP. The remaining 24.5 to 27.1% were metabolites and/or degradation products.

Toxicokinetic studies of dibutyl terphthalate also show that the substance is rapidly degraded to terephthalic acid and n-butanol. Both of these degradation products are readily biodegradable and exhibit low log Kow and BCF values. Based upon octanol-water partitioning coefficient QSAR results from KOWWIN (USEPA, version 1.67), terephthalic acid has an estimated log Kow of 1.76 and an experimental reference value of 2.00 (Hansch, C. et. al., 1995). n-butanol has an estimated log Kow of 0.84 and an experimental reference value of 0.88 (Hansch, C.et. al., 1995). Based upon bioconcentration and bioaccumulation factor QSAR estimates from BCFBAF (USEPA v3.00), terephthalic acid has a log BCF of 0.50 (BCF=3.16 l/kg wet-weight) from a regression based estimate, and a log BAF of 0.97 (BAF=9.4 L/kg wet-weight) by the Arnot-Gobas method at the upper trophic level. n-butanol also has a log BCF of 0.50 (BCF=3.16 l/kg wet-weight) from a regression based estimate, and a log BAF of 0.17 (BAF=1.47 L/kg wet-weight) by the Arnot-Gobas method at the upper trophic level. While the log Kow value of dibutyl terephthalate results in a high modeled BCF value using the log Kow regression approach, the Arnot-Gobas BCF and BCF models recognize the high biotransformation rate of the substance. The estimated log BCF (lower trophic level) is 2.050 (BCF=112.3 L/kg wet-weight) and the estimated log BAF (lower trophic level) is 2.203 (BAF=159.7 L/kg wet-weight). The upper trophic level estimated log BCF is 1.873 (BCF=74.66 L/kg wet-weight) and the estimated log BAF is 1.873 (BAF=74.71 L/kg wet-weight). The reduction in BCF and BAF at higher trophic levels as compared to the lower trophic level indicates that trophic dilution is occurring. Based upon this body of data, it is apparent that dibutyl terephthalate exhibits a low potential for bioaccumulation.