3 research outputs found
Application of Mass Balance Models and the Chemical Activity Concept To Facilitate the Use of in Vitro Toxicity Data for Risk Assessment
Practical,
financial, and ethical considerations related to conducting
extensive animal testing have resulted in various initiatives to promote
and expand the use of in vitro testing data for chemical evaluations.
Nominal concentrations in the aqueous phase corresponding to an effect
(or biological activity) are commonly reported and used to characterize
toxicity (or biological response). However, the true concentration
in the aqueous phase can be substantially different from the nominal.
To support in vitro test design and aid the interpretation of in vitro
toxicity data, we developed a mass balance model that can be parametrized
and applied to represent typical in vitro test systems. The model
calculates the mass distribution, freely dissolved concentrations,
and cell/tissue concentrations corresponding to the initial nominal
concentration and experimental conditions specified by the user. Chemical
activity, a metric which can be used to assess the potential for baseline
toxicity to occur, is also calculated. The model is first applied
to a set of hypothetical chemicals to illustrate the degree to which
test conditions (e.g., presence or absence of serum) influence the
distribution of the chemical in the test system. The model is then
applied to set of 1194 real substances (predominantly from the ToxCast
chemical database) to calculate the potential range of concentrations
and chemical activities under assumed test conditions. The model demonstrates
how both concentrations and chemical activities can vary by orders
of magnitude for the same nominal concentration
Modeling the Uptake of Neutral Organic Chemicals on XAD Passive Air Samplers under Variable Temperatures, External Wind Speeds and Ambient Air Concentrations (PAS-SIM)
The
main objective of this study was to evaluate the performance
and demonstrate the utility of a fugacity-based model of XAD passive
air samplers (XAD-PAS) designed to simulate the uptake of neutral
organic chemicals under variable temperatures, external wind speeds
and ambient air concentrations. The model (PAS-SIM) simulates the
transport of the chemical across the air-side boundary layer and within
the sampler medium, which is segmented into a user-defined number
of thin layers. Model performance was evaluated using data for polychlorinated
biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) from
a field calibration study (i.e., active and XAD-PAS data) conducted
in Egbert, Ontario, Canada. With some exceptions, modeled PAS uptake
curves are in good agreement with the empirical PAS data. The results
are highly encouraging, given the uncertainty in the active air sampler
data used as input and other uncertainties related to model parametrization
(e.g., sampler–air partition coefficients, the influence of
wind speed on sampling rates). The study supports the further development
and evaluation of the PAS-SIM model as a diagnostic (e.g., to aid
interpretation of calibration studies and monitoring data) and prognostic
(e.g., to inform design of future passive air sampling campaigns)
tool
Exploring the Role of Shelf Sediments in the Arctic Ocean in Determining the Arctic Contamination Potential of Neutral Organic Contaminants
The main objective of this study was to model the contribution
of shelf sediments in the Arctic Ocean to the total mass of neutral
organic contaminants accumulated in the Arctic environment using a
standardized emission scenario for sets of hypothetical chemicals
and realistic emission estimates (1930–2100) for polychlorinated
biphenyl congener 153 (PCB-153). Shelf sediments in the Arctic Ocean
are shown to be important reservoirs for neutral organic chemicals
across a wide range of partitioning properties, increasing the total
mass in the surface compartments of the Arctic environment by up to
3.5-fold compared to simulations excluding this compartment. The relative
change in total mass for hydrophobic organic chemicals with log air–water
partition coefficients ≥0 was greater than for chemicals with
properties similar to typical POPs. The long-term simulation of PCB-153
generated modeled concentrations in shelf sediments in reasonable
agreement with available monitoring data and illustrate that the relative
importance of shelf sediments in the Arctic Ocean for influencing
surface ocean concentrations (and therefore exposure via the pelagic
food web) is most pronounced once primary emissions are exhausted
and secondary sources dominate. Additional monitoring and modeling
work to better characterize the role of shelf sediments for contaminant
fate is recommended