Compound-specific isotope analysis for aerobic biodegradation of phthalate acid esters

The degradation of three phthalic acid esters (PAEs) (dimethyl phthalate (DMP), diethyl phthalate (DEP) and di-n-butyl phthalate (DBP)) by natural microbial community under aerobic condition and their isotope fractionation were compared by using a laboratory microcosm system with natural marine sediment overlying with natural seawater. The results showed that the degradation of the three tested PAEs followed a first-order kinetics, with rate constants of 0.0541, 0.0352 and 0.00731 day(-1) for DMP, DBP and DOP, respectively, indicating that the degradation rate of PAEs is a inverse function of the length of the alkyl side chain: the longer the side chain, the slower the rate is. (13)C isotope enrichment of the three residual PAEs were evaluated with compound-specific isotope analysis (CSIA). A relatively obvious (13)C enrichment, with maximum δ(13)C shifts of Δδ(13)C(DMP)=2.05±0.21‰ (f=0.17) and Δδ(13)C(DBP)=1.92±0.23‰ (f=0.08) in the residual DMP and DBP, respectively, was observed at an advanced stage of biodegradation. No significant (13)C enrichment occurred in the residual DOP (Δδ(13)C(DOP)=0.55±0.21‰, f=0.16) within the accuracy and reproducibility for GC-C-IRMS (±0.5‰). The experimental results indicated that the degree of isotopic fractionation in the three residual PAEs appeared to be related to the number of carbon atoms, which is in the order of DMP>DBP>DOP.