Passive Sampler Development

In the following sections we highlight only selected works that have contributed toward the further development of passive samplers for SVOCs and/or HOCs. The literature related to the development and use of passive samplers for monitoring gases or VOCs in occupational environments is large. However, these publications are discussed only briefly, because lipid-containing semipermeable membrane devices (SPMDs) are primarily designed for SVOCs. 

More recently, Harner et al. (2003) coated ethylene vinyl acetate (EVA) onto glass (polymer coated glass [POG]) for use as fugacity sensors or equilibrium samplers of SVOCs in indoor and outdoor air. The EVA film fhickness was 1.1 and 2.4 qm depending on the application and as expected, SVOC sorption capacity and times to equilibrium were shown to be directly proportional to film thickness. The clearance capacity Ey volume of sample medium cleared of chemical) of a sorbent for an analyte is given by 

For a 1 xm film thickness, the surface-area (A cm )-to-sorbent-volume (V cm )-ratio (AV ) of the Harner et al. (2003) device is 1 x 10 cm with a total sorbent volume of 2.9 xL. Earlier, Wilcockson and Gobas (2001) devised a POG with a 0.05 am EVA film thickness, but it was not used for air sampling. Assuming first-order kinetics, times to 95% of equilibrium (tgs) are given by 

Shoeib and Harner (2002) and Wania et al. (2003) separately developed large capacity passive samplers for integrafively monitoring the atmospheric transport of HOCs. The sorbents used in these devices act as an infinite sink for HOC vapors, and have been used earlier to actively sample large volumes of air and 

In an effort to optimize the solvent-containing passive sampler design, Zabik (1988) and Huckins (1988) evaluated the organic contaminant permeability and solvent compatibility of several candidate nonporous polymeric membranes (Huckins et al., 2002a). The membranes included LDPE, polypropylene (PP), polyvinyl chloride, polyacetate, and silicone, specifically medical grade silicone (silastic). Solvents used were hexane, ethyl acetate, dichloromethane, isooctane, etc. With the exception of silastic, membranes were 120- um thick. Because silicone has the greatest free volume of all the nonporous polymers, thicker membranes were used. Although there are a number of definitions of polymer free volume based on various mathematical treatments of the diffusion process, free volume can be viewed as the free space within the polymer matrix available for solute diffusion. 

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Various types of detector tubes have been devised. The NIOSH standard number S-311 employs a tube filled with 420—840 p.m (20/40 mesh) activated charcoal. A known volume of air is passed through the tube by either a handheld or vacuum pump. Carbon disulfide is used as the desorbing solvent and the solution is then analyzed by gc using a flame-ionization detector (88). Other adsorbents such as siUca gel and desorbents such as acetone have been employed. Passive (diffuse samplers) have also been developed. Passive samplers are useful for determining the time-weighted average (TWA) concentration of benzene vapor (89). Passive dosimeters allow permeation or diffusion-controlled mass transport across a membrane or adsorbent bed, ie, activated charcoal. The activated charcoal is removed, extracted with solvent, and analyzed by gc. Passive dosimeters with instant readout capabiUty have also been devised (85). 

Similar to the previous section, we discuss only selected works to highlight the development of SPMDs. Also, we include some discussion of several unpublished pilot smdies (Huckins, 1989) that influenced our early development of SPMDs. These pilot studies were directed solely toward sampling the aqueous phase. The flrst application of SPMDs for sampling organic vapors did not occur until several years later (Petty et al., 1993). To our knowledge, only SPMDs, PESs and SPMEs are being applied in both air and water, because the use of many passive samplers is limited to a specific medium and exposure scenario. 

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. 

Finally, passive samplers have also been developed for ozone, primarily for use in epidemiological studies. For example, Brauer and Brook (1995) describe the application of a passive sampler in which air containing ozone diffuses through a Teflon membrane and reacts with nitrite. The sampler is then extracted and the nitrate product measured using ion chromatography. 

A colorimeter (Figure 4) has been designed specifically for analyzing >2/ ) passive samplers. It is lightweight, portable and simple to use. Features incorporated into the unit include a ten-minute timer with audible alarm to ensure complete color development of the samples before analysis, a cuvette slot which... 

Diffusive samplers have also been developed to determine SVOCs but there have been relatively few studies to date. An example is the passive flux sampler developed by Fujii et al. (2003) to determine the rate of emission of phthalate esters from materials. The sampler consisted of a circular metal disc containing activated carbon particles held within an inert matrix of PTFE. The sampler was placed on the material under test giving a diffusion length of 0.5 or 2 mm depending upon the design and adsorbed phthalate esters were extracted from the sampler with toluene and determined by GC-MS. 

To meet the need to monitor levels of 222Rn in houses, passive samplers have been developed which measure average concentrations over long periods and do not need power suplies. In the Karlsruhe dosimeter (Urban Piesch, 1981), a polycarbonate nuclear track detector foil is mounted inside a plastic cup. The mouth of the cup is closed with a filter to allow radon to enter but to exclude decay products. After exposure, the detector foil is etched and the tracks counted optically. This is a... 

A number of models has been developed to improve the understanding of the kinetics of analyte transfer to passive samplers.9,12,19,37 These models are essential for understanding how the amount of analyte accumulated in a device relates to its concentration in the sampled aquatic environment as well as for the design and evaluation of laboratory calibration experiments. Models differ in the number of phases and simplifying assumptions that are taken into account, for example, the... 

Wennrich, L., B. Vrana, P. Popp, and W. Lorenz. 2003. Development of an integrative passive sampler for the monitoring of organic water pollutants. J. Environ. Monit. 5 813-822. 

Kohoutek, J., P. Babica, L. Blaha, and B. Marsalek. 2008. A novel approach for monitoring of cyanobac-terial toxins Development and evaluation of the passive sampler for microcystins. Anal. Bioanal. Chem. 390 1167-1172. 

Systematic attempts have been made to develop passive sampling systems that accumulate chemicals, and from which reliable exposure concentrations can be calculated. The passive samplers used in such systems are usually designed either as "kinetic samplers" or as "equilibrium samplers."... 

The concept of the equilibrium sampler is analogous to that of the octanol-water equilibrium partition coefficient (fQ,w) used since the 1970s to predict the potential for persistent nonpolar contaminants to concentrate in aquatic organisms [71]. The use of equilibrium-t) e passive samplers in the aquatic environment depends on the development of a sampler-water partition coefficient (fCs ) defined as the ratio of sampler to water concentration of the compound of interest at thermod)mamic equilibrium. The other key parameter determining the utility of an equilibrium-type passive sampler is the time taken to reach an approximate equilibrium condition. A range of approaches applied in developing equilibrium-t)q)e passive samplers include polyethylene or silicon sheets of various volume to surface area ratio [72] and solid-phase microextraction techniques [73]. 

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