24 research outputs found
Importance of Passive Diffusion in the Uptake of Polychlorinated Biphenyls by Phagotrophic Protozoa
Unicellular protozoan grazers represent a size class of organisms where a transition in the mechanism of chlorobiphenyl (CB) introduction, from diffusion through surface membranes to ingestion of contaminated prey, could occur. This study compares the relative importance of these two processes in the overall uptake of polychlorinated biphenyls by protists. Uptake rates and steady-state concentrations were compared in laboratory cultures of grazing and nongrazing protozoa. These experiments were conducted with a 10-μm marine scuticociliate (Uronema sp.), bacterial prey (Halomonas halodurans), and a suite of 21 CB congeners spanning a range of aqueous solubilities. The dominant pathway of CB uptake by both grazing and nongrazing protozoa was diffusion. Organic-carbon-normalized CB concentrations (in the protozoan cell) were equivalent in grazing and nongrazing protozoa for all congeners studied. Rate constants for uptake into and loss from the protozoan cell were independently determined by using [3,3′,4,4′-(14)C]tetrachlorobiphenyl (IUPAC no. 77), 0.38 ± 0.03 min(−1) and (1.1 ± 0.1) × 10(−5) (g of organic carbon)(−1) min(−1), respectively. Magnitudes of the uptake and loss processes were calculated and compared by using a numerical model. The model result was consistent with data from the bioaccumulation experiment and supported the hypothesis that diffusive uptake is faster than ingestive uptake in phagotrophic unicellular protozoa
Physiologically Based Pharmacokinetic (PBPK) Models for Lifetime Exposure to PCB 153 in Male and Female Harbor Porpoises (Phocoena phocoena): Model Development and Evaluation
Physiologically based pharmacokinetic (PBPK) models were
developed for the most persistent polychlorinated biphenyl (PCB
153) in male and female harbor porpoises (Phocoena
phocoena) to elucidate processes such as uptake, distribution,
and elimination. Due to its limited metabolic capacities, long
life span, and top position in marine food chains, this species
is highly sensitive to pollution. The models consist of 5
compartments, liver, blubber, kidney, brain, and a compartment
which accounts for the rest of the body, all connected
through blood. All physiological and biochemical parameters
were extracted from the literature, except for the brain/blood
partition coefficient and rate of excretion, which were both fitted
to data sets used for validation of the models. These data
sets were compiled from our own analyses performed with GCMS
on tissue samples of harbor porpoises. The intake of
PCB 153 was from milk from birth to 4 months, and after weaning
fish was the main food source. Overall, these models reveal
that concentrations of PCB 153 in males increase with age but
suggest that,asthe animalsgrowolder, metabolic transformation
can be a possible pathway for elimination as well. In contrast,
the model for females confirms that gestation and lactation are
key processes for eliminating PCB 153 as body burdens
decrease with age. These PBPK models are capable of
simulating the bioaccumulation of PCB 153 during the entire
life span of approximately 20 years of the harbor porpoises