concentrations is observed across the length of the screened interval or the zone undergoing vertical flow. Even in wells without flow-limiting baffles, however, solute stratifi- cation can sometimes be seen by using multiple DSs. Harter and Talozi [27], using regenerated cellulose membranes, found large contrasts in salinity and nitrate concentrations over approximately 3 m intervals in 40 wells. They found non-uniform nitrate profiles in 80% of the wells they examined. Stratification of inorganic solutes in the screened inter- vals of wells has been observed in a variety of open-screened intervals using multiple regenerated cellulose passive samplers [23,41]. Stratification of VOCs has also been observed in the screened inter- vals of monitoring wells by using multiple PDB samplers at a variety of sites [41–44] (Fig. 13.4). The source of this stratification may include Well MW5, Naval Air Station North Island, California [43] 15 16 17 18 Well PW66, Naval Air Station, North Island, California [43] Depth below top of casing, in meters 7 8 9 10 11 Well 18-S, Naval Industrial Reserve Ordnance Plant, Fridley Minnesota [44] 9 10 11 12 Trichloroethene, in micrograms per liter 10,000 20,0000 4000 800 12,000 Explanation Pumped sample Passive diffusion bag (PDB) sampler 12,000600 18,000 0 Fig. 13.4. Comparison of diffusion and pumped samples in ground-water showing vertical stratification of TCE in the screened interval (modified from Refs. [43,44]). Passive diffusion samplers 303 Chapter 14 Field study considerations in the use of passive sampling devices in water monitoring Per-Anders Bergqvist and Audrone Zaliauskiene 14.1 INTRODUCTION Semipermeable membrane devices (SPMDs) are passive monitors that are being increasingly used by monitoring agencies and wastewater dischargers to measure the contents of lipophilic organic chemicals that may adversely affect water quality. Passive sampling devices can moni- tor most 75% of the organic pollutants included in the EU Water Framework Directive (WFD) priority pollutant list as well as many other compounds. Furthermore, applications and the theory underlying the use of SPMDs have been described in over 200 peer-reviewed sci- entific publications during the last two decades, making them the most comprehensively studied type of passive sampler for semivolatile or- ganic pollutants in water. The most frequently asked questions regarding the use of SPMDs for water monitoring are the following. What compartments of the envi- ronment do the SPMD extracts represent? Have lowest environmental concentrations of concern (C c ) been established for the compounds of interest? How many SPMDs are needed to detect these concentrations? What are the ranges of, and the most suitable, SPMD exposure times? What additional information should be collected about the site to en- hance the interpretation of SPMD results? What quality control (QC) measures are needed for SPMD sampling? Are SPMD calibration data available for the compounds of interest? What constitutes good SPMD practice in terms of storage, transportation, deployment, retrieval and analytical procedures? This chapter addresses these and other questions related to the field application of SPMDs (many of which are also relevant to other types of Comprehensive Analytical Chemistry 48 R. Greenwood, G. Mills and B. Vrana (Editors) Volume 48 ISSN: 0166-526X DOI: 10.1016/S0166-526X(06)48014-4 r 2007 Elsevier B.V. All rights reserved. 311 TABLE 14.2 Examples of field applications of SPMDs for monitoring organic contaminants from Vrana et al. [4] and experience of the authors Application Environment Analytes Screening of contaminants for presence or absence River HOCs Monitoring of temporal pollution trends Seawater Organochlorine pesticides, PCB Monitoring of spatial distribution and tracing pollution sources River PCBs, dioxins, PAHs, pesticides, HxCBz, PBDEs Surface water UV filter compounds Discharge from wastewater treatment plants Alkylphenol ethoxylates Seawater contaminated by discharged oilfield produced water PAHs Assessment of contaminant fate and distribution between environmental compartments Irrigation water canal PAHs Discharges from industrial sources to seawater PCBs, chlorophenols, chlorobenzenes Freshwater, wastewater treatment plants Triclosan River PCBs, PAHs, PCDDs, PCDFs and substituted benzenes Biomimetic extraction for toxicity assessment of aqueous contaminants Effluents of wastewater treatment plant Organochlorine pesticides, PCBs, PAHs P A. Bergqvist and A. Zaliauskiene 316 Chapter 15 Techniques for quantitatively evaluating aquatic passive sampling devices B. Scott Stephens and Jochen F. Mu¨ller 15.1 INTRODUCTION As the suite of available devices for passively sampling aquatic envi- ronmental pollutants has grown in recent years, groups wishing to make quantitative measurements with them have been met with simi- lar challenges. Perhaps the most pressing is the need for large amounts of publicly available, accurate, device-specific validation data for each compound of interest. With the continual advance of separation and analytical methods, the emergence of novel sequestration phases and membranes and the prioritisation of new pollutants, generating mean- ingful sampler validation databases will remain an ongoing problem. While a number of international standards have been developed specifying criteria and a set of experiments for quantitative validation of workplace passive dosimeters [1–3], validation of their aquatic en- vironmental variant has remained the work of researchers. A number of innovative approaches have been devised and several standardised devices have been presented, each with its own set of validation/ calibration data. The aim of this chapter is to illustrate the methods workers have employed for generating these different datasets and to review the techniques that have been applied to validate them in the laboratory and in situ. It should be useful to students wishing to research the techniques underlying the validation and calibration of passive sam- pling devices, particularly those considering the logistics of their own aquatic passive sampler validation studies. Comprehensive Analytical Chemistry 48 R. Greenwood, G. Mills and B. Vrana (Editors) Volume 48 ISSN: 0166-526X DOI: 10.1016/S0166-526X(06)48015-6 r 2007 Elsevier B.V. All rights reserved. 329 TABLE 15.1 Aquatic laboratory calibration systems Type Advantages Disadvantages Examples Batch depletion Simplest and earliest exposure method; only single spike addition required. Suitable for low R S samplers. For high R S samplers concentration will typically decrease significantly, but models may be able to account for this if loss through volatilisation and degradation are small. Volume likely to be insufficient to allow confirmation of water concentration for many compounds. [8,9,13,16,24–26] Negligible depletion batch exposure Simple. Single spike addition. Higher volume: R S ratio allows more stable water concentration; enables a series of samplers to be exposed to the same water throughout experiment; water samples may be taken to verify concentration. May require large-volume vessel/aquarium for high R S samplers such as SPMDs; other loss routes such as volatilisation, degradation and sorption to vessel walls are still potentially important. [11,15,27] B.S. Stephens and J.F. Mu¨ller 336 Batch renewal High level of reliability maintaining constant concentration. Very labour intensive, often requiring daily preparation and transfer of solutions. High level of waste solution generated. [16,17] Batch partition- controlled delivery Simple design. Ease of use. A few validation studies for low R S samplers such as SPME fibres exist. Few validation studies exist for high R S samplers and secondary confirmation of stable concentrations will likely be necessary. [20–23] Diffusion cell Simple system offering precise measurement of D AB for membranes and gels. Suitable only for systems in which the resistance to flux is a diffusive membrane or gel (not hydrodynamically limited). [18,19] Flow-through –partition- controlled delivery Similar advantages to batch PCD, with the addition of control of flow that may improve the efficiency of delivery. Same caveats as with PCD above. Note an increase in exposure concentration with time has been observed [30] in this type of system. [28–30] Flow-through –injection- controlled delivery Traditional method, with greatest number of validation studies. Most wasteful of water and spike compounds. Most complicated and expensive to operate. [13,14,31–34] Techniques for quantitatively evaluating aquatic passive sampling devices 337 . Zaliauskiene 316 Chapter 15 Techniques for quantitatively evaluating aquatic passive sampling devices B. Scott Stephens and Jochen F. Mu¨ller 15.1 INTRODUCTION As the suite of available devices for passively sampling. the screened interval (modified from Refs. [43,44]). Passive diffusion samplers 303 Chapter 14 Field study considerations in the use of passive sampling devices in water monitoring Per-Anders Bergqvist. of casing, in meters 7 8 9 10 11 Well 18-S, Naval Industrial Reserve Ordnance Plant, Fridley Minnesota [44] 9 10 11 12 Trichloroethene, in micrograms per liter 10, 000 20,0000 4000 800 12,000 Explanation Pumped