Article

Development of passive sampling devices for bioavailable contaminants of current and emerging concern: Waitemata Harbour case study

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  • Streamlined Environmental Ltd
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Abstract

Bioavailable contaminant concentrations are an important component in assessing environmental effects as they directly affect ecosystem health. Shellfish contaminant monitoring programmes have traditionally filled this requirement but are being phased out in some jurisdictions. Passive sampling devices (PSDs) have the potential to replace shellfish monitoring; however, there are still knowledge gaps to address before this can occur. This study assessed the suitability of three different PSDs in providing the required information to replace shellfish monitoring. PSDs were deployed at three historic mussel monitoring sites with different levels of urban influence in the Waitemata Harbour, Auckland, New Zealand. Contaminants of interest were urban heavy metals, plus current and emerging organic contaminants. PSDs provided extremely low detection limits and, for some contaminants, very strong correlations to shellfish. PSDs can currently complement shellfish in monitoring, but it is premature to make conclusions as to the suitability of PSDs in replacing shellfish monitoring until more information is available.

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... It is widely acknowledged that accurately determining the 'bioavailable' proportion of 'total' contaminant concentrations is important as this is the component that directly affects ecosystem health (see Section 8.2 for further discussion). A feasibility field study was carried out by NIWA and Auckland Council to assess whether passive sampling devices (PSDs) have the potential to replace the SCMP (see 4.2.5) in providing meaningful bioavailable concentrations of heavy metals plus selected EOCs (PBDEs, PPCP wastewater markers) and Polycyclic Aromatic Hydrocarbons (PAHs) (Stewart et al., 2015). The blueprint for this study was recent international developments in using PSDs in environmental monitoring (Allan et al., 2011;Alvarez et al., 2014;Perron et al., 2013). ...
... Results of the study showed that PSDs were capable of providing time-average water concentrations as low as pg/L (parts-per-quadrillion). Although there were some differences between uptake of some classes of EOCs in PSDs and mussels, it was confirmed that PSDs are a useful tool for estimating the bioavailability of EOCs in the aquatic environment and in some situations have the potential to replace biota in EOC bioavailability monitoring (Stewart et al., 2015). ...
... Following these examples and in a NZ first study, PSDs were recently used to measure dissolved concentrations of representative EOCs (BDEs, wastewater markers), plus PAHs and heavy metals around Auckland and to assess whether they could replace shellfish for measurement of bioavailable concentrations. Results suggest PSDs would be excellent complementary techniques to biota and sediment monitoring, however more research is necessary before they can be implemented for regulatory purposes (Stewart et al, 2015). ...
... Pharmaceutical contamination dynamics in water (Baena-Nogueras et al., 2016;Bayen et al., 2013;Borecka et al., 2015;Cantwell et al., 2016Cantwell et al., , 2017Cantwell et al., , 2018Nödler et al., 2014;Zhao et al., 2015Zhao et al., , 2017, sediments and suspended particular matter (SPM) (Lara-Martín et al., 2014;Liang et al., 2013;Stewart et al., 2014), and biota (Álvarez-Muñoz et al., 2015b;Klosterhaus et al., 2013;Meador et al., 2016) are documented in urbanized estuaries but their monitoring remains difficult to implement due to their complexity. Other types of marine sites can be selected depending on the aim of the study as coasts (bays, gulfs, beaches, etc.) (Afsa et al., 2019; Beretta et al., 2014;McEneff et al., 2014), offshore sites (Alygizakis et al., 2016;Brumovský et al., 2017), harbors (Cantwell et al., 2018;Stewart et al., 2016), mangroves (Bayen et al., 2016) lagoons and aquaculture areas (Chen et al., 2015a;Ismail et al., 2019). ...
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... ;Roig et al. 2011;Stewart et al. 2016;Edenborn et al. 2017;Swain and Sahoo 2017). 4. The current NEMA standards do not consider the different pollution management technologies of industries. ...
... [75,77,226,303,305,[327][328][329] Monitoring alongside biota Coastal waters Dioxins; FRs; PAHs; PBDEs; PCBs; pesticides LDPE including alongside PSDs (POCIS, SPME and DGT) and biota (gulf killifish, mussels and shellfish) deployed in coastal waters to evaluate the application of each method to monitor HOCs and predict concentrations in biota. [330][331][332][333][334] River and lake waters PAHs; PCBs LDPE alone and alongside SR co-deployed with biota in a range of surface waters and sediments to monitor concentrations of a range of HOCs and access the bioaccumulation prediction capacity of each device for sampled biota at various trophic levels. [229,309,335] variability greater than within laboratory variation, with still greater degrees of variation at lower concentrations. ...
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... ;Roig et al. 2011;Stewart et al. 2016;Edenborn et al. 2017;Swain and Sahoo 2017). 4. The current NEMA standards do not consider the different pollution management technologies of industries. ...
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... We also deployed passive sampling devices (PSDs) in both the main inlet (Rotokauri Drain) and outlet (Ohote Stream) to Lake Rotokauri, namely the Polar Organic Chemical Integrative Sampler (POCIS) and Diffuse Gradients in Thin Films (DGTs). These PSDs (Stewart et al., 2016), which are specific to contaminant types (polar wastewater markers and metals, respectively), provide averaged dissolved contaminant concentrations over a sustained period (in this case, 1 week -metals, 3 weeks -organics). ...
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Contaminants enter marine and estuarine environments and pose a risk to human and ecological health. Recently, passive sampling devices have been utilized to estimate dissolved concentrations of COCs, such as polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs). In the present study, the performance of three common passive samplers was evaluated for sampling PAHs and PCBs at several stations in the temperate estuary Narragansett Bay (Rhode Island, USA). Sampler polymers included polyethylene (PE), polydimethylsiloxane (PDMS) coated solid phase microextraction (SPME) fibers, and polyoxymethylene (POM). Dissolved concentrations of each contaminant were calculated using measured sampler concentrations adjusted for equilibrium conditions with performance reference compounds (PRCs) and chemical-specific partition coefficients derived in the laboratory. Despite differences in PE and POM sampler concentrations, calculated total dissolved concentrations ranged from 14-93 ng/L and 13-465 pg/L for PAHs and PCBs, respectively. Dissolved concentrations of PAHs were approximately three times greater based on POM compared to PE while dissolved concentrations of PCBs based on PE were approximately three times greater than POM. Concentrations in SPME were not reported due to the lack of detectable chemical in the amount of PDMS polymer deployed. Continued research is needed to improve and support PE and POM use for the routine monitoring of COCs. For example, a better understanding of the use of PRCs with POM is critically needed. Environ Toxicol Chem © 2013 SETAC.
Article
The technique of diffusive gradients in thin films (DGT) provides an in situ means of quantitatively measuring labile species in aqueous systems. By ensuring that transport of metal ions to an exchange resin is solely by free diffusion through a membrane, of known thickness, Delta g, the concentration in the bulk solution, C-b, can be calculated from the measured mass in the resin, M, after time, t, by C-b = M Delta g/DAt, where D is the molecular diffusion coefficient and A is the exposure surface area of the membrane. If a sufficiently thick (similar to 1 mm) diffusion layer is selected, the flux of metal to the resin is independent of the hydrodynamics in solution above a threshold level of convection. Deployment for 1 day results in a concentration factor of similar to 300, allowing metals to be measured at extremely low levels (4 pmol L(-1)). Only labile metal species are measured, the effective time window of typically 2 min being determined by the thickness of the diffusion layer. Because metals are quantified by their kinetics of uptake rather than the attainment of equilibrium, any deployment time can be selected from 1 h to typically 3 months when the resin becomes saturated. The measurement is independent of ionic strength (10 nM-1 M). For Chelex-100 as the resin, the measurement is independent of pH in the range of 5-8.3, but a subtheoretical response is obtained at pH <5 where binding to Chelex is diminished. The effect of temperature can be predicted from the known temperature dependence of the diffusion coefficient and viscosity. The application of DGT to the in situ measurement of Cd, Fe, Bin, and Cu in coastal and open seawater is demonstrated, and its more general applicability as a pollution monitoring tool and for measuring an in situ flux, as a surrogate for bioavailability, is discussed.
Article
The literature increasingly reports sampling rates (Rs) for Polar Organic Chemical Integrative Samplers (POCIS) but the data obtained come from various calibration systems that are not always well-defined (agitation, temperature, measured micropollutant concentrations in water,…). In order to obtain accurate laboratory Rs for priority and emerging substances, POCIS need to be exposed in a robust and well-defined calibration system. Thus, we built a flow-through calibration system containing tap water spiked with 56 organic micropollutants (alkylphenols and phenols, hormones, pesticides, pharmaceuticals, UV filter). POCIS were immersed for up to 28 days. Tap water micropollutant concentrations and additional parameters (temperature, pH, conductivity, dissolved organic carbon, flow velocities) were kept constant and controlled throughout the calibration experiment. Based on the observed uptake kinetics, we distinguished four types of micropollutant accumulation patterns: curvilinear accumulation (30 molecules, group 1), accumulation with an inflexion point (13 molecules, group 2), random accumulation (eight molecules, group 3), and no or very low accumulation (five molecules, group 4). Rs was calculated for 43 out of 56 micropollutants (groups 1 and 2). Calculated Rs values ranged from 0.030L/d to 0.398L/d. POCIS can supply TWA concentrations for hormones, pesticides, several pharmaceuticals, a few alkylphenols, and the UV filter. Our Rs results are generally less than two fold-different (higher or lower depending on target molecule) to the literature data using the same type of calibration system or for micropollutants with log Kow>2.65. We found a quadratic correlation between Rs and log D for betablockers, herbicides and hormones.
Article
In this work, home-made Polar Organic Chemical Integrative Samplers (POCIS) were studied for passive sampling of 15 endocrine disrupting compounds (4 alkylphenols and steroid hormones) in influent and effluent samples of wastewater treatment plants (WWTPs) as well as up- and downstream of the receiving river water. POCIS calibration at laboratory conditions was carried out using a continuous-flow calibration system. The influence of the exposure position of the POCIS within the calibration device, horizontal or vertical, to the water flow direction was evaluated. While the sampling rates of most of the target substances were not affected by the sampler position, for cis-ADT, E1, E2 and E3, the vertical position provided the highest analyte accumulation. Hence, the POCIS samplers were preferably exposed vertical to the water flow in overall experiments. Using the continuous-flow calibration device, lab-based sampling rates were determined for all the target compounds (RSBPA = 0.0326 L/d; RScisADT = 0.0800 L/d, RSE1 = 0.0398 L/d, RSEQ = 0.0516 L/d, RSTT = 0.0745 L/d, RSE2 = 0.0585 L/d, RSEE2 = 0.0406 L/d, RSNT = 0.0846 L/d, RSPG = 0.0478 L/d and RSE3 = 0.1468 L/d), except for DES, MeEE2, 4tOP, 4OP, 4NPs, where the uptake after 14 days POCIS exposure was found to be insignificant or indicated a no linear behaviour. Recoveries from POCIS extractions were in the range between 71 and 152% for most of the target analytes except for DES and E3 with around 59%. Good precision of the sampling procedure up till 20% was observed and limits of detection were at ng/L level. Two deuterated compounds ([(2)H3]-E2 and [(2)H4]-EQ) were successfully tested as performance reference compounds (PRC, [Formula: see text] = 0.0507 L/d and [Formula: see text] = 0.0543 L/d)). Finally, the POCIS samplers were tested for monitoring EDCs at two wastewater treatment plants, in Halle and Leipzig (Germany). BPA, E1, EQ, E2, MeEE2, NT, EE2, PG and E3 were quantified and their time-weighted average concentrations calculated on the basis of the lab-derived sampling rates were compared with the results based on conventional grab samples. While the influent concentration of BPA, cisADT, E1, TT, PG, EE2 reached the μg/L level, the rest of the target analytes were determined at ng/L. The analyte concentrations in the effluent never exceed ng/L level except for BPA. The concentration determined by spot sampling was partially lower (BPA, E1, TT) or comparable (EQ, E2, EE2, PG, E3) to the concentration obtained by POCIS using performance reference compounds (PRC).
Article
The implementation of strict environmental quality standards for polar organic priority pollutants poses a challenge for monitoring programs. The polar organic chemical integrative sampler (POCIS) may help to address the challenge of measuring low and fluctuating trace concentrations of such organic contaminants, offering significant advantages over traditional sampling. In the present review, the authors evaluate POCIS calibration methods and factors affecting sampling rates together with reported environmental applications. Over 300 compounds have been shown to accumulate in POCIS, including pesticides, pharmaceuticals, hormones, and industrial chemicals. Polar organic chemical integrative sampler extracts have been used for both chemical and biological analyses. Several different calibration methods have been described, which makes it difficult to directly compare sampling rates. In addition, despite the fact that some attempts to correlate sampling rates with the properties of target compounds such as log K(OW) have been met with varying success, an overall model that can predict uptake is lacking. Furthermore, temperature, water flow rates, salinity, pH, and fouling have all been shown to affect uptake; however, there is currently no robust method available for adjusting for these differences. Overall, POCIS has been applied to a wide range of sampling environments and scenarios and has been proven to be a useful screening tool. However, based on the existing literature, a more mechanistic approach is required to increase understanding and thus improve the quantitative nature of the measurements. Environ. Toxicol. Chem. © 2012 SETAC.
Article
The uptake of polar organic contaminants into polar organic chemical integrative samplers (POCIS) varies with environmental factors, such as water flow rate. To evaluate the influence of water flow rate on the uptake of contaminants into POCIS, flow-controlled field experiments were conducted with POCIS deployed in channel systems through which treated sewage effluent flowed at rates between 2.6 and 37 cm/s. Both pharmaceutical POCIS and pesticide POCIS were exposed to effluent for 21 d and evaluated for uptake of pharmaceuticals and personal care products (PPCPs) and endocrine disrupting substances (EDS). The pesticide POCIS had higher uptake rates for PPCPs and EDS than the pharmaceutical POCIS, but there are some practical advantages to using pharmaceutical POCIS. The uptake of contaminants into POCIS increased with flow rate, but these effects were relatively small (i.e., less than twofold) for most of the test compounds. There was no relationship observed between the hydrophobicity (log octanol/water partition coefficient, log KOW) of model compounds and the effects of flow rate on the uptake kinetics by POCIS. These data indicate that water flow rate has a relatively minor influence on the accumulation of PPCPs and EDS into POCIS. Environ. Toxicol. Chem. 2010;29:2461–2469. © 2010 SETAC
Article
The polar organic chemical integrative sampler (POCIS) was calibrated to monitor pesticides in water under controlled laboratory conditions. The effect of natural organic matter (NOM) on the sampling rates (R(s)) was evaluated in microcosms containing <0.1-5 mg L(-1) of total organic carbon (TOC). The effect of hydrodynamics was studied by comparing R(s) values measured in stirred (SBE) and quiescent (QBE) batch experiments and a flow-through system (FTS). The level of NOM in the water used in these experiments had no effect on the magnitude of the pesticide sampling rates (p > 0.05). However, flow velocity and turbulence significantly increased the sampling rates of the pesticides in the FTS and SBE compared to the QBE (p < 0.001). The calibration data generated can be used to derive pesticide concentrations in water from POCIS deployed in stagnant and turbulent environmental systems without correction for NOM.
Article
We review the state of the art in using passive sampling technology for environmental monitoring of waterborne organic and inorganic pollutants. We discuss strategies for sampler design, calibration, in situ sampling and quality-control issues, and advantages and challenges associated with passive sampling in aqueous environments. We then review typical applications of passive samplers in assessing the aquatic environment.
Article
The coefficients of partitioning (K(pew) ) between low-density polyethylene (LDPE) film (50-µm thickness) and water for 23 polybrominated diphenyl ether (PBDE) congeners were determined based on a regression analysis of sorption kinetics over an extended exposure period (up to 365 d). A curvilinear relationship between log K(pew) and log K(OW) (octanol-water partition coefficient) was obtained for the target BDE congeners with the turning point at log K(OW) approximately 8. Previously obtained dietary uptake efficiencies of BDE congeners in common carp (Cyprinus carpio) were also found to relate curvilinearly to log K(OW) . In addition, field-measured relative abundances of BDE-209 compiled from previous investigations conducted in the Pearl River Delta of South China were significantly (p < 0.001) higher in abiotic samples (n = 79 from 11 matrices) than in biotic samples (n = 73 from 12 matrices), suggesting the likelihood for reduced bioavailability of BDE-209 in certain biota. Finally, a molecular-scale analysis indicated that the curvilinear relationship between log K(pew) and log K(OW) can be attributed to the energy barrier that a molecule has to overcome as it attempts to diffuse into the LDPE structure, which can become significant for larger molecules. Similarly, the reduced bioavailability of BDE-209 in many biological species can be regarded as a reflection of the magnitude of molecular interactions between cell membranes and BDE-209.
Article
The effect of solution pH and levels of dissolved organic matter (DOM) on the sampling rates for model pharmaceuticals and personal care products (PPCPs) and endocrine disrupting substance (EDS) by polar organic chemical integrative samplers (POCIS) was investigated in laboratory experiments. A commercially available POCIS configuration containing neutral Oasis HLB (hydrophilic-lipophilic balance) resin (i.e. pharmaceutical POCIS) and two POCIS configurations prepared in-house containing MAX and MCX anion and cation exchange resins, respectively were tested for uptake of 21 model PPCPs and EDS, including acidic, phenolic, basic and neutral compounds. Laboratory experiments were conducted with dechlorinated tap water over a pH range of 3, 7 and 9. The effects of DOM were studied using natural water from an oligotrophic lake in Ontario, Canada (i.e. Plastic Lake) spiked with different amounts of DOM (the concentration of dissolved organic carbon ranged from 3 to 5mgL(-1) in uptake experiments). In experiments with the commercial (HLB) POCIS, the MCX-POCIS and the MAX-POCIS, the sampling rates generally increased with pH for basic compounds and declined with pH for acidic compounds. However, the sampling rates were relatively constant across the pH range for phenols with high pKa values (i.e. bisphenol A, estrone, estradiol, triclosan) and for the neutral pharmaceutical, carbamazepine. Thus, uptake was greatest when the amount of the neutral species in solution was maximized relative to the ionized species. Although the solution pH affected the uptake of some model ionic compounds, the effect was by less than a factor of 3. There was no significant effect of DOM on sampling rates from Plastic Lake. However, uptake rates in different aqueous matrixes declined in the order of deionized water>Plastic Lake water>dechlorinated tap water, so other parameters must affect uptake into POCIS, although this influence will be minor. MAX-POCIS and MCX-POCIS showed little advantage over the commercial POCIS configuration for monitoring in natural waters.
Article
In summary, we believe there are major benefits in starting global aquatic passive sampling (AQUA-GAPS) and propose the phased development of an AQUA-GAPS network of stations. The program could be started by initiating monitoring with PE samplers at accessible and relatively well studied key locations e.g., the Great Lakes, U.S. east coast, Baltic, North Seas, Mediterranean, or South China Seas. Investigators with access to ship time and buoys would be invited to participate to locate samplers and if capable, also analyze them. Although analyzing samples in a central lab would be desirable (akin to GAPS), we believe multiple laboratories could be involved provided existence of an interlaboratory quality assurance and training program. The list of POPs to be analyzed would be those readily detected by low-resolution GC-MS and for which analytical standards are readily available (e.g., legacy chlorinated pesticides, lindane, endosulfan, selected PCB congeners, chlorobenzenes, tetra- and pentaBDEs). The program would also encourage deployment of different passive devices for comparison with PE samplers. Some of the SC's regional and subregional centers for POPs located near deployment sites might want to be involved for their roles of capacity building and technology transfer.Wethus seek volunteer investigators to help conduct the initial monitoring phase including the associated costs for passive sampler deployment and analysis. With such cooperation, we can foresee improved monitoring of the global aquatic environment to enhance its and our long-term health.
Article
In order to assess the environmental impact of aquatic discharges from the offshore oil industry, polar organic chemical integrative samplers (POCIS) and semipermeable membrane devices (SPMDs) were deployed around an oil platform and at reference locations in the North Sea. Exposure to polycyclic aromatic hydrocarbons (PAH) and alkylated phenols (AP) was determined from passive sampler accumulations using an empirical uptake model, the dissipation of performance reference compounds and adjusted laboratory derived sampling rates. Exposure was relatively similar within 1-2 km of the discharge point, with levels dominated by short chained C1-C3 AP isomers (19-51 ngL(-1)) and alkylated naphthalenes, phenanthrenes and dibenzothiophenes (NPD, 29-45 ngL(-1)). Exposure stations showed significant differences to reference sites for NPD, but not always for more hydrophobic PAH. These concentrations are several orders of magnitude lower than those reported to give both acute and sub-lethal effects, although their long term consequences are unknown.
Article
Increasingly it is being realized that a holistic hazard assessment of complex environmental contaminant mixtures requires data on the concentrations of hydrophilic organic contaminants including new generation pesticides, pharmaceuticals, personal care products, and many chemicals associated with household, industrial, and agricultural wastes. To address this issue, we developed a passive in situ sampling device (the polar organic chemical integrative sampler [POCIS]) that integratively concentrates trace levels of complex mixtures of hydrophilic environmental contaminants, enables the determination of their time-weighted average water concentrations, and provides a method of estimating the potential exposure of aquatic organisms to the complex mixture of waterborne contaminants. Using a prototype sampler, linear uptake of selected herbicides and pharmaceuticals with log K(ow)s < 4.0 was observed for up to 56 d. Estimation of the ambient water concentrations of chemicals of interest is achieved by using appropriate uptake models and determination of POCIS sampling rates for appropriate exposure conditions. Use of POCIS in field validation studies targeting the herbicide diuron in the United Kingdom resulted in the detection of the chemical at estimated concentrations of 190 to 600 ng/L. These values are in agreement with reported levels found in traditional grab samples taken concurrently.
Article
In view of conflicting reports regarding the performance of DGT in low ionic strength solutions (I < 1 mM), further investigations have been carried out. Minimal washing of the diffusive gel and deployment in 1.0 and 10 mM NaNO3 solutions containing Cu and Cd gave the theoretical response of 1 for [C](DGT)/[C](SOLN), where [C](DGT) is the concentration of metal measured by DGT and [C](SOLN) is the concentration of metal measured directly in the solution by an appropriate analytical method. Erroneously high values for [C](DGT)/[C](SOLN) were obtained when these same gels were deployed at I = 0.1 mM, presumably due to a net negative charge on the gel, attributable to the presence of initiation products of polymerization. However, washing the diffusive gels completely, where the storage solution pH equaled that of deionized water, gave values of approximately 0.5 for [C](DGT)/[C](SOLN) from deployments at I = 0.1 mM, consistent with the lower measured value of the diffusion coefficients at this ionic strength. These results can be explained by the presence of a net positive charge on the gel when it is exhaustively washed, which reduces the effective diffusion coefficient of metal ions by changing their concentration at the gel-solution interface (Donnan partitioning). Diffusive gel equilibration experiments showed the presence of low capacity sites capable of binding metals irrespective of ionic strength. This binding within the diffusive gel does not affect most DGT measurements, as short (4 h) deployments at concentrations of 10 ppb gave theoretical results. Incomplete washing of the resin-gel caused a 5-15% measurement error and a decrease in precision, even at ionic strengths of 10 mM. A high level of accuracy and precision (typically <5%) was maintained during all aspects of this work, even at ionic strengths of 0.1 mM, in contrast to previous results. This is attributable to three factors: (1) exhaustive washing and conditioning protocols, (2) improvements to the DGT sampling device, and (3) low and reproducible blanks due to ultraclean handling procedures. Provided effective diffusion coefficients measured at the same ionic strength are used, the established DGT theory is obeyed irrespective of ionic strength.
Article
When using the diffusive gradients in thin-films (DGT) technique in well-stirred solutions, the diffusive boundary layer has generally been ignored on the assumption that it is negligibly thin compared to the total thickness of delta g, i.e., the sum of the thickness of the prefilter and diffusive gel. Deployment of devices with different diffusive layer thicknesses showed that the thickness of the DBL was approximately 0.23 mm in moderate to well-stirred solutions, but substantially thicker in poorly or unstirred solutions. Measurement of the distribution of Cd in the DGT resin gel at high spatial resolution (100 microm) using laser ablation inductively coupled plasma mass spectrometry showed that the effective sampling window had a larger diameter (2.20 cm) than the geometric diameter of the exposure window (2.00 cm). Lateral diffusion in the gel, which had previously been neglected, therefore increased the effective surface area of the device by approximately 20%. The concentrations measured by DGT agreed well with the known concentrations in standard solutions for all diffusion layer thicknesses, when the effective area and the appropriate diffusive boundary layer (DBL) were used. The extent of the error associated with neglecting the DBL and using the geometric window area depends on the gel layer thickness and the true thickness of the DBL, as determined by the deployment geometry and flow regime. When DGT measurements were made in well-stirred solutions using a 0.80-mm diffusive gel, the effect of neglecting the DBL and using the inappropriate geometric area offset each other, with the error being <+/-10%. For precise measurements, and especially work involving speciation or kinetic measurements, where DGT devices with different diffusive gel layer thicknesses are deployed, it is necessary to use the effective area and the appropriate DBL thickness in the full DGT equation, which allows for the use of layer-specific diffusion coefficients.
Marine sediment contaminants: Status and trends assessment 1998 to 2010. Prepared by Diffuse Sources Ltd for Auckland Council
  • G Mills
  • B Williamson
  • M Cameron
  • M Vaughan
Mills G, Williamson B, Cameron M, Vaughan M 2012. Marine sediment contaminants: Status and trends assessment 1998 to 2010. Prepared by Diffuse Sources Ltd for Auckland Council. Auckland Council technical report TR2012/041.
Shellfish contaminant monitoring programme: status and trends analysis 1987 -2011. Prepared by NIWA for Auckland Council
  • M Stewart
  • J Gadd
  • D Ballantine
  • G Olsen
Stewart M, Gadd J, Ballantine D, Olsen G 2013a. Shellfish contaminant monitoring programme: status and trends analysis 1987 -2011. Prepared by NIWA for Auckland Council. Auckland Council technical report TR2013/054. 203 p.
Stockholm Convention on Persistent Organic Pollutants (POPs) as amended in 2009. Text and Annexes
  • New Auckland
  • Zealand
Auckland, New Zealand. Science of The Total Environment 468-469: 202-210. UNEP 2009. Stockholm Convention on Persistent Organic Pollutants (POPs) as amended in 2009. Text and Annexes. 64 p.
DGT-for measurements in waters, soils and sediments
  • H Zhang
Shellfish contaminant monitoring programme: status and trends analysis 1987-2011
  • M Stewart
  • J Gadd
  • D Ballantine
  • G Olsen
Antifouling biocides in marinas: measurement of copper concentrations and comparison to model predictions for eight Auckland sites
  • J Gadd
  • M Cameron