Including organic mixture influence on dioxins and furans fate for toxic impact assessment in a life cycle context

Polychlorodibenzo-p-dioxins and -furans (PCDD/Fs) are always produced as undesired impurities and are found in traces in mixtures such as pentachlorophenol (PCP) pole-treating oil. PCDD/Fs were previously shown to follow the oil’s fate by affinity, but life cycle impact assessment (LCIA) has never taken into account such interactions within an organic contaminant mixture. An approach was developed to assess the potential human toxic and aquatic ecotoxic impacts of PCDD/Fs, including the influence of oil on fate.

2,3,7,8-Tetrachlorodibenzodioxin (TCDD) was used as a PCDD/Fs mixture proxy. The new TCDD fate was approximated in two steps: (1) TCDD was considered to follow the oil’s environmental fate and (2) when the oil is degraded, the fraction of nondegraded TCDD carried by oil was considered emitted from the oil’s receiving compartments and distributed into the environment. This distribution generates a new fate factor (\( \overline{\mathrm{FF}^{\prime }} \)) matrix, and characterization factors (\( \overline{\mathrm{CFs}^{\prime }} \)) are obtained by associating \( \overline{\mathrm{FFs}^{\prime }} \) to exposure and effect factors from the USEtox model. Scenario analyses on TCDD’s degradation kinetic in the oil phase and its affinity for the volatilized oil fraction were conducted, since both mechanisms are poorly documented and weak assumptions were made to model them.

The model predicts that the presence of oil increases the transfer of TCDD from air, freshwater, and natural soil into air through oil volatilization. This presence moderately changes the FF values of TCDD for an emission to air, as compared to the significant variations for emissions into freshwater and soil. The most influenced CF_eco and CF_tox are those for an emission into natural soil, which increase up to one and two order(s) of magnitude, respectively, due to oil influence (CF′_eco = 5.3E + 04 PAF.m³.d/kg and CF′_tox = 24.3 cases/kg). By reducing degradation kinetics by 50 %, both CFs′ decrease by at least 14 %, and decreasing the affinity of TCDD for volatilization through oil induces important variations of both CFs′ for emissions into freshwater and natural soil.

An innovative approach was developed to include interactions between co-contaminants, which seem to be significant in the studied situation, in an LCA context. However, the most influent mechanism highlighted by the model—the affinity of PCDD/Fs for the oil volatilized fraction—is poorly documented and modeled based on certain weak and influent assumptions. A better understanding of the PCDD/Fs’ affinity for the volatilized oil fraction is therefore a key issue.