A passive dosing method to determine fugacity capacities and partitioning properties of leaves

Abstract

The capacity of leaves to take up chemicals from the atmosphere and water influences how contaminants are transferred into food webs and soil. We provide a proof of concept of a passive dosing method to measure leaf/polydimethylsiloxane partition ratios (K) for intact leaves, using polychlorinated biphenyls (PCBs) as model chemicals. Rhododendron leaves held in contact with PCB-loaded PDMS reached between 76 and 99% of equilibrium within 4 days for PCBs 3, 4, 28, 52, 101, 118, 138 and 180. Equilibrium K extrapolated from the uptake kinetics measured over 4 days ranged from 0.075 (PCB 180) to 0.371 (PCB 3). The K data can readily be converted to fugacity capacities of leaves (Z) and subsequently leaf/water or leaf/air partition ratios (K and K) using partitioning data from the literature. Results of our measurements are within the variability observed for plant/air partition ratios (K) found in the literature. Log K from this study ranged from 5.00 (PCB 3) to 8.30 (PCB 180) compared to log K of 3.31 (PCB 3) to 8.88 (PCB 180) found in the literature. The method we describe could provide data to characterize the variability in sorptive capacities of leaves that would improve descriptions of uptake of chemicals by leaves in multimedia fate models.

Quantifying the Biomagnification Capability of Arctic Wolf and Domestic Dog by Equilibrium Sampling

“…In this case, the Z -value of the sample can be determined by measuring the concentration in the sample and the polymer when these are in chemical equilibrium Equilibrium sampling has, for example, been used to determine chemical bioavailability in soil . Recently, a similar technique has been applied to biological tissues, that is, to quantify the Z -value of PCBs in leaves …”

“…28 Recently, a similar technique has been applied to biological tissues, that is, to quantify the Zvalue of PCBs in leaves. 29 We herein propose a noninvasive way to quantify the BMF lim (i.e., D D /D F ) by determining the ratio of the Z-values of undigested and digested food using equilibrium sampling with silicone as the reference phase. In this study, we demonstrate the feasibility of this method for wolf and domestic dog.…”

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

“…16 We recently reported fugacity capacities and K leaf/water values for PCBs 3 and 4 for intact, dry rhododendron leaves from the same plant used in this study. 11 We converted these partition ratios into K EOM/olive oil by (i) calculating K leaf/olive oil as the product of K leaf/water and K water/storage lipid (using literature data, 37 adjusted for temperature, eq 2) and (ii) normalizing to the fraction of EOM in the rhododendron leaves (8.5%, Table s6, eq 3). K olive oil/storage lipid was assumed to be equal to 1.…”

“…The dosing for this setup could be done using a fugacity meter 39,7 or a "sandwich" in two layers of loaded silicone. 11,20…”

“…K leaf/air values derived from deposition fluxes for a range of PCBs in nine tree species differed by less than a factor of 2 . However, including other literature data for a variety of plant species, derived from deposition fluxes and empirical regressions, results in K leaf/air values spanning 3 orders of magnitude for a range of PCBs. ,,− This variability was found to be related to neither the amount of lipids present in the plants , nor the thickness of the cuticle, the waxy outer layer of the leaf. While it is possible that these differences are partly caused by the use of different methods, it has also been suggested that it could be due to differences in the quality and composition of the lipid storage compartment across plant species. , Field measurements of concentration ratios between leaves and air for chemicals with log K oa larger than 9 are less variable between plant species .…”