Environmental risk assessment of natural complex substances: needs for methodology adjustments
Résumé
Natural complex substances (NCS) are under the scope of European regulations on chemicals (Biocides, PPP, REACH, CLP…). For example under REACH regulation NCS are considered as substances, either mono-, multiconstituent or UVCB. In most cases however, NCS can be considered as UVCB, hydrophobic and volatile substances. The objective of the study is to identify difficulties in environmental hazard and risk assessment of these substances and propose methodology adaptations for these chemicals. Two strategies are generally envisaged for their evaluation: one considering the NCS as a "substance" as a whole or taking its "constituent" as a basis of the assessment. The approach “substance” shows the advantage to consider the effects of all the constituents of the mixture without these needing to be totally identified. For inconvenience, certain required data have no meaning for a UVCB such as the solubility, the Kow, the bioaccumulation which are parameters intrinsically appropriate to each of the constituents. Other data can be obtained by testing the substance directly. The “constituent” approach requires an important effort for the characterization of the NCS. Besides, the addition of the effects of each constituent is not necessarily equal to the effect of the mixture as such. The approach by constituent and the characterization of these allows the use of alternative methods as the approach QSAR, by congener or category and thus the read-across between constituents. Under REACH regulation, for the tonnage band greater than 10 T/year, environmental exposure and risk have to be assessed. In this case, for environmental exposure, constituents have to be taken into account, the environment acting as a filter, the UVCB as such does not exist. It can be then decided to consider the predicted environmental concentration (PEC) of the most soluble of known constituents and to compare it with the predicted no effect concentration (PNEC) of the substance. This approach can be relatively conservative and can be refined in higher tier assessment. An example of this assessment is presented to illustrate the methodology.