Sorptive Capacities of Nonpolymeric Plant Lipids for Hydrophobic Chemicals Determined by Passive Dosing

Abstract

Vegetation plays an important role in the partitioning, transport, and fate of semivolatile hydrophobic organic chemicals (HOCs) in the environment. Leaf/air partition ratios (K leaf/air) of HOCs are highly variable for different plant species. The differences cannot be fully explained by the fraction of lipids in the leaves or the thickness of the cuticle. Our goal was to elucidate the importance of nonpolymeric lipids in determining K leaf/air. To do this, we extracted organic matter from 7 plant species using solvents that do not extract the polymeric lipids cutin and cutan, to yield extractable organic matter (EOM). We used passive dosing to determine the partition ratios of selected HOCs between the EOM of the leaves and our reference lipid, olive oil (K EOM/olive oil). In addition, we measured analogous partition ratios for three lipid standards. Proton nuclear magnetic resonance (NMR) spectroscopy was used to characterize the composition of lipids. Differences in K EOM/olive oil of two polychlorinated biphenyls and four chlorinated benzenes were below a factor of 2 in the plant species studied, indicating that the reported differences in K leaf/air are not caused by differences in the sorptive capacities of nonpolymeric lipids or that our EOM is not representative of all nonpolymeric leaf lipids.

Headspace Passive Dosing of Volatile Hydrophobic Organic Chemicals from a Lipid Donor—Linking Their Toxicity to Well-Defined Exposure for an Improved Risk Assessment

“…We expect the method to be applicable to chemicals with a sufficiently high air–water partition coefficient to allow equilibration via the headspace. All test chemicals in the present study have K AW > 1 L/L, while other HS-PD studies included semivolatile organic chemicals with lower K AW . − Further, the test chemicals need as a basic rule K LW > 1000 L/L and K LA > 1000 L/L in order to avoid donor depletion. HS-PD seems also suited for chronic and even multigeneration ecotoxicity testing with small aquatic and terrestrial animals , because it circumvents biofilm formation on the passive dosing donor (i.e., no direct contact with medium) during extended test durations.…”

“…We expect the method to be applicable to chemicals with a sufficiently high air-water partition coefficient to allow equilibration via the headspace. All test chemicals in the present study have K AW > 1 L/L, while other headspace passive dosing studies included semivolatile organic chemicals with lower K AW [31][32][33] . Further, the test chemicals need as a basic rule K LW > 1000 L/L and K LA > 1000 L/L in order to avoid donor depletion.…”

“…The present study introduces the use of a lipid as a passive dosing donor for the toxicity testing of liquid VHOCs at and below their saturation level. Lipid has recently been successfully applied as a partitioning donor in dedicated analytical and partitioning studies with semivolatile organic chemicals, − while other scientists used vacuum pump oil as a partitioning donor for controlling headspace concentrations in autosampler vials for calibration purposes. , The working principle of the new passive dosing method is based on equilibrium partitioning between donor and exposure medium, without a direct contact between these two phases. The test system is simple: the lipid donor is loaded by direct addition of the liquid test chemical and then used for establishing and controlling exposures below the saturation level, while the test chemical in the pure liquid form is used to establish and control exposure at the saturation level.…”

Accelerated Passive Dosing of Hydrophobic Complex Mixtures–Controlling the Level and Composition in Aquatic Tests

“…Lastly, passive dosing is increasingly used for setting and maintaining HOC exposure in aquatic tests. In passive dosing, a biocompatible polymer such as silicone is loaded with the test substance and then used as dominant partitioning donor to establish and control freely dissolved HOC concentrations in an aqueous medium. ,− This approach has been used in many types of toxicity studies, − bioaccumulation studies, , biodegradation studies, − and binding and sorption studies − and for solubility measurements. , Passive dosing has so far primarily been used for research on single compounds and simple mixtures and more recently for research on defined composed mixtures of more than 30 chemicals . For complex mixtures, passive dosing has only been used to dose crude oil and fuel oil into water near the saturation limit. − Table provides a comparison of the three dosing methods (solvent spiking, WAF, and passive dosing) based on their underlying principles.…”