Passive sampling samplers

If the aim of an investigator is to determine equilibrium concentrations in samplers, then the residence time (tm) is a logical parameter to compare among samplers. The tm is the mean length of time that a molecule spends in a passive sampling device, where solute exchange follows first-order kinetics. Residence time is given by... 

The authors have been intimately involved in eondueting research to address many aspects of environmental contaminants for about three decades. Historically, samples of environmental matrices, particularly water and air have been collected at narrow windows of time (i.e., minutes or several hours) which are not representative of the exposure experienced by organisms. Consequently, we initiated the development of what would ultimately be the semipermeable membrane device (SPMD). The SPMD has subsequently proven to be an effective passive sampler for a wide range of hydrophobic contaminants in multiple media. To date, there are more than 180 peer reviewed publications in the open scientific literature, where SPMDs are used for a variety of applications. Some of these publications are critical of the use of passive samplers for certain applications. However, constructive criticism has greatly aided in defining information gaps and limitations of the passive sampling approach. 

Passive samplers are not useful to monitor peak concentrations, but offer a convenient way to regard for example, long term exposure of persons in an indoor environment. A more detailed description of the passive sampling technique is given in Chapter 3. 

The substance-specific kinetic constants, kx and k2, and partition coefficient Ksw (see Equations 3.1 and 3.2) can be determined in two ways. In theory, kinetic parameters characterizing the uptake of analytes can be estimated using semiempirical correlations employing mass transfer coefficients, physicochemical properties (mainly diffusivities and permeabilities in various media), and hydro-dynamic parameters.38 39 However, because of the complexity of the flow of water around passive sampling devices (usually nonstreamlined objects) during field exposures, it is difficult to estimate uptake parameters from first principles. In most cases, laboratory experiments are needed for the calibration of both equilibrium and kinetic samplers. 

Besides the advantages that passive sampling may offer, it is important to recognize that in many cases these devices measure a different fraction of contaminants than that defined for the checking of EQS compliance within the WFD. This becomes especially important when monitoring very hydrophobic chemicals (log Kow > 4), where a large fraction of the total amount present in a spot water sample is bound to colloids and particles. In contrast, most passive samplers used for monitoring hydrophobic compounds (e.g., SPMD, Chemcatcher, and silicone materials) measure only the truly dissolved fraction of these chemicals. 

Mazzella, N., J.-F. Dubemet, and F. Delmas. 2007. Determination of kinetic and equilibrium regimes in the operation of polar organic chemical integrative samplers application to the passive sampling of the polar herbicides in aquatic environments. J. Chromatogr. A 1154 42-51. 

Vroblesky, D.A. 2007. Passive diffusion samplers to monitor volatile organic compounds in groundwater. In R. Greenwood, G.A. Mills, and B. Vrana (eds), Passive Sampling Techniques in Environmental Monitoring, pp. 295-309. Amsterdam Elsevier. 

Air Sampling The relative cleanliness of air in the most critical environment is assessed using passive sampling systems such as settle plates or estimated volumetri-cally using active air samplers. Active air samplers should be designed to be isokinetic in operation to avoid disruptions to unidirectional airflow. Considerable variability has been reported among the several sampling methods employed for... 

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