Establishing and controlling dissolved concentrations of hydrophobic organics by partitioning from a solid phase

Bioavailable concentrations of hydrophobic organic substances in aqueous te sts often decrease as a result of (bio)sorption, volatilization, or degrada tion. In the present study, partitioning driven administering (PDA) is intr oduced as an approach to maintain constant exposure levels of hydrophobic o rganics in aqueous tests. The working principle of PDA is to control dissol ved concentrations by partitioning from a dominating solid phase. For this purpose, test compounds are loaded on an octadecyl Empore disk, which subse quently is placed in an aqueous test system. Stable aqueous concentrations for a range of halogenated aromatic substances (log K-OW 3.9-7.1) were esta blished within minutes to hours, and the resulting concentrations indicate that equilibrium partitioning governs the release from the disk. Furthermor e, PDA's capability to maintain stable concentrations against a depletion p rocess was demonstrated, and PDA was successfully applied to dose 1,3,5-tri bromobenzene and hexachlorobenzene in algal toxicity tests. Finally, the fe asibility to administer concentrations up to aqueous solubility, to adminis ter mixtures, and to dominate the fugacity of multicompartment systems is d iscussed.