Approaches for estimating PUF-air partitions coefficient for semi-volatile organic compounds: A critical comparison.

Partition coefficients between polyurethane foam (PUF) and air (K) are important when using PUF as a passive air sampler for semi-volatile organic compounds (SVOCs) and when considering the fate of SVOCs indoors where PUF is a common material. Here, K for selected SVOCs was estimated using published methods, since measured data are unavailable for most of these compounds. Estimates of K were within one order of magnitude for SVOCs having values of log octanol-air partition coefficient (K) of 5, but differed by nearly three orders of magnitude for SVOCs with log K of 12.

Modeling Human Exposure to Indoor Contaminants: External Source to Body Tissues.

Information on human indoor exposure is necessary to assess the potential risk to individuals from many chemicals of interest. Dynamic indoor and human physicologically based pharmacokinetic (PBPK) models of the distribution of nonionizing, organic chemical concentrations in indoor environments resulting in delivered tissue doses are developed, described and tested. The Indoor model successfully reproduced independently measured, reported time-dependent air concentrations of chloroform released during showering and of 2-butyoxyethanol following use of a volatile surface cleaner.

In situ air-water and particle-water partitioning of perfluorocarboxylic acids, perfluorosulfonic acids and perfluorooctyl sulfonamide at a wastewater treatment plant.

In situ measurements of air and water phases at a wastewater treatment plant (WWTP) were used to investigate the partitioning behavior of perfluorocarboxylic acids (PFCAs), perfluorosulfonic acids (PFSAs) and perfluorooctyl sulfonamide (HFOSA) and their conjugate bases (PFC(-)s, PFS(-)s, and FOSA(-), respectively). Particle-dissolved (Rd) and air-water (QAW) concentration ratios were determined at different tanks of a WWTP. Sum of concentrations of C4-12,14 PFC(A)s, C4,6,8,10 PFS(A)s and (H)FOSA were as high as 50 pg m(-3) (atmospheric gas phase), 2300 ng L(-1) (aqueous dissolved phase) and 2500 ng L(-1) (aqueous particle phase).

Understanding the atmospheric measurement and behavior of perfluorooctanoic acid.

The recently reported quantification of the atmospheric sampling artifact for perfluorooctanoic acid (PFOA) was applied to existing gas and particle concentration measurements. Specifically, gas phase concentrations were increased by a factor of 3.5 and particle-bound concentrations by a factor of 0.

TFA from HFO-1234yf: accumulation and aquatic risk in terminal water bodies.

A next-generation mobile automobile air-conditioning (MAC) refrigerant, HFO-1234yf (CF(3) CF = CH(2)), is being developed with improved environmental characteristics. In the atmosphere, it ultimately forms trifluoroacetic acid (TFA(A); CF(3)COOH), which is subsequently scavenged by precipitation and deposited on land and water as trifluoroacetate (TFA; CF(3)COO(-)). Trifluoroacetate is environmentally stable and has the potential to accumulate in terminal water bodies, that is, aquatic systems receiving inflow but with little or no outflow and with high rates of evaporation.

Estimating chemical biotransformation rates from food web concentrations.

Biotransformation is widely recognized as the most important and most uncertain determinant of bioaccumulation. A step-wise method for estimating organism-specific biotransformation half-lives from field observations and using established food web modeling is developed. As a proof of concept, the method is applied to the case of nine polycyclic aromatic hydrocarbons (PAHs) in a well-studied food web in Bohai Bay, China.

Equilibrium modeling: a pathway to understanding observed perfluorocarboxylic and perfluorosulfonic acid behavior.

Equilibrium distribution models of hydrophobic neutral partitioning of the perfluorinated carboxylic and sulfonic acids were shown, without the need for any physical chemical properties, to successfully predict the sediment-water distribution (D(SW) ) directly from independently measured equilibrium tissue distributions known as the bioconcentration factor (BCF). The constant of proportionality required by the models successfully predicted the correlation between the biotic and abiotic distributions of both sets of chemicals, thus demonstrating the applicability of the assumptions inherent in the models, that is, hydrophobically driven partitioning of the neutral species, and thus the applicability of the models themselves. Colloquially speaking, the models are thus validated as applicable to these chemicals.

Potential role of sea spray generation in the atmospheric transport of perfluorocarboxylic acids.

The observed environmental concentrations of perfluorooctanoic acid (PFOA) and its conjugate base (PFO) in remote regions such as the Arctic have been primarily ascribed to the atmospheric transport and degradation of fluorotelomer alcohols (FTOHs) and to direct PFO transport in ocean currents. These mechanisms are each capable of only partially explaining observations. Transport within marine aerosols has been proposed and may explain transport over short distances but will contribute little over longer distances.

Modeling the environmental fate of perfluorooctanoic acid and perfluorooctanoate: An investigation of the role of individual species partitioning.

A multimedia multi-species environmental fate model was developed for the conjugate pair perfluorooctanoic acid (PFOA):perfluorooctanoate (PFO). The model allows assessment of the relative contribution of each individual species, in equilibrium with each other, to the overall environmental movement of the pair. The Lake Ontario (Canada/USA) watershed system was selected for this investigation and is simulated in a single-region, seven-compartment model, including a water surface microlayer, and aqueous aerosol generation and redeposition.

A cautionary note on implications of the well-mixed compartment assumption as applied to mass balance models of chemical fate in flowing systems.

A convenient, simple, and widely used approach for modeling the fate of a chemical in a flowing environmental or biological system is to simulate the system as comprising one or more well-mixed boxes, also known as continuous stirred tank reactors (CSTRs). In principle, any desired level of accuracy can be achieved by increasing the number of boxes. However, highly segmented systems require more input data, they are more computationally intensive, and the results may be more difficult to interpret.

Experimental pKa determination for perfluorooctanoic acid (PFOA) and the potential impact of pKa concentration dependence on laboratory-measured partitioning phenomena and environmental modeling.

An accurately measured equilibrium acid dissociation constant (pKa) is essential for understanding and predicting the fate of perfluorocarboxylic acids (PFCAs) in the environment. The aqueous pKa of perfluorooctanoic acid (PFOA) has been determined potentiometrically using a standard water-methanol mixed solvent approach and was found to be 3.8 +/- 0.

Modeling bioaccumulation using characteristic times.

A new formulation of existing mass balance models for bioaccumulation is derived and applied to organisms that respire either water or air. This model employs characteristic time parameters and equations that are mathematically equivalent to those used in existing concentration-rate constant and fugacity models. The equivalence of these traditional formulations and the novel formulation is demonstrated.

Aerosol enrichment of the surfactant PFO and mediation of the water--air transport of gaseous PFOA.

Aerosol-mediated transport of perfluorooctanoate (PFO) from a water body to the atmosphere and the subsequent emission of gas-phase perfluorooctanoic acid (PFOA) was investigated. The potential for this process to facilitate long-range transport of PFOA/PFO was assessed. In a laboratory experiment, aerosols were generated and collected from deionized, fresh, and ocean waters spiked with PFO and analyzed by LC-MS/MS.

Can the unit world model concept be applied to hazard assessment of both organic chemicals and metal ions?

A unit world model that has the potential to be used for the hazard assessment of both metal ions and organic chemicals is described and discussed, with an emphasis on the problems that arise when treating metal ions. It is based on the steady-state equilibrium criterion model that is designed to simulate the fate of organic chemicals in a 100,000-km(2) region and comprises four well-mixed compartments: Air, water, soil, and sediment. To be applicable to metal ions, modifications are required.

Continued development of a mass balance model of chemical fate in a sewage treatment plant.

Chemicals that pass through a sewage treatment plant (STP) and into receiving waters lead to exposure of human and ecological receptors. Most countries require that such chemicals and especially those that are new to commerce be assessed for their treatability in STPs using a screening-level model. The STP model has been widely used for such assessments in Canada, the US and elsewhere.

Biologically mediated transport of contaminants to aquatic systems.

The prevailing view is that long-range transport of semivolatile contaminants is primarily conducted by the physical system (e.g., winds, currents), and biological transport is typically ignored.

An exploration of the role of mysids in benthic-pelagic coupling and biomagnification using a dynamic bioaccumulation model.

A mass-balance model for the uptake of organic contaminants in the opposum shrimp (Mysis relicta) is developed. The model describes the concentration in the mysid as a function of time as it grows and its lipid content changes over a two-year life span. The model can describe uptake in varying proportions from pelagic and benthic sources.

Screening level risk assessment model for chemical fate and effects in the environment.

A screening level risk assessment model is developed and described to assess and prioritize chemicals by estimating environmental fate and transport, bioaccumulation, and exposure to humans and wildlife for a unit emission rate. The most sensitive risk endpoint is identified and a critical emission rate is then calculated as a result of that endpoint being reached. Finally, this estimated critical emission rate is compared with the estimated actual emission rate as a risk assessment factor.

Environmental persistence of chemicals.

Background: The hazard criterion of persistence as it applies to chemicals in the environment is reviewed and discussed. This quantity can not be measured directly in the environment, thus it must be estimated using models that synthesise information on chemical half-lives and partitioning properties, the nature of the environment and how the chemical is released into the environment.

Main Features: It is suggested that the preferred criterion is the average residence time of the chemical in the environment, i.

Chemical partitioning to foliage: the contribution and legacy of Davide Calamari.

Background: Davide Calamari and his colleagues were among the first to appreciate that vegetation could play a key role in determining the fate and effects of organic contaminants. They conducted pioneering experiments to investigate the uptake of contaminants by plants from the atmosphere and they sought to model the observed phenomena. In the nearly two decades since there has been a marked increase in understanding of these phenomena as a result of both experimental and modelling studies.

Five-stage environmental exposure assessment strategy for mixtures: gasoline as a case study.

A five-stage strategy is suggested for conducting an exposure assessment of mixtures that may contain numerous chemical components. The stages are: (1) determination of mixture composition and variability, (2) selection of component groups within the mixture and documentation of criteria used for this selection, (3) compilation of relevant property data for each group, (4) assessment of environmental fate of each group, and (5) assessment of environmental and human exposure to each group and to the mixture as a whole. A subsequent step is the assessment of environmental and/or human risk associated with the individual and aggregate exposure to each group.

Putting science into persistence, bioaccumulation, and toxicity evaluations.

In recent decades, advances have been made in the processes used to identify substances as persistent, bioaccumulative, and toxic (PBT). Key processes have been identified, and scientifically sound assessment methods have been developed. Regulatory agencies around the world have sought practical methods for implementing policies to protect both environment and human health.

Regional differences in chemical fate model outcome.

The fate of anthropogenic substances in the environment is increasingly determined using multimedia mass balance models. It is, therefore, critical to fully understand how such models work and what their limitations are. The effects of uncertainty and variation in the chemical properties, discharges, and landscape parameters on model outcome have been examined by other researchers.