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Development of Solid Ceramic Dosimeter for the Time Integrative Passive Sampling of Volatile Organic Compounds in Waters Riza Gabriela Bonifacio, Go-Un Nam, In-Yong Eom, and Yongseok Hong Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.7b03678 • Publication Date (Web): 26 Sep 2017 Downloaded from http://pubs.acs.org on October 1, 2017
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Development of Solid Ceramic Dosimeter for the Time Integrative Passive
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Sampling of Volatile Organic Compounds in Waters
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Riza Gabriela Bonifacio1, Go-Un Nam1, In-Yong Eom2, Yong-Seok Hong1,*
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Gyeongsan-si, Gyeongsangbuk-do, Republic of Korea 2
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Department of Environmental Engineering, Daegu University, 201 Daegudae-ro, Jillyang-eup,
Department of Chemistry, Daegu Catholic University, 330 Geumrak-ri, Hayang-eup, Gyeongsan-si, Gyeongsangbuk-do, Republic of Korea
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Corresponding author: YS. Hong, email:
[email protected], tel: 053-850-6694, fax: 053-8506699
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Abstract
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Time-integrative passive sampling of volatile organic compounds (VOCs) in water can now be
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accomplished using a solid ceramic dosimeter. A non-porous ceramic, which excludes the
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permeation of water, allowing only gas-phase diffusion of VOCs into the resin inside the
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dosimeter, effectively captured the VOCs. The mass accumulation of 11 VOCs linearly increased
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with time over a wide range of aqueous phase concentrations (16.9 to 1100 µg L-1) and the
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linearity was dependent upon the Henry’s constant (H). The average diffusivity of the VOCs in
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the solid ceramic was 1.46×10-10 m2 s-1 at 25 °C, which was 4 orders of magnitude lower than
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that in air (8.09×10-6 m2 s-1). This value was 60% greater than that in the water-permeable porous
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ceramic (0.92×10-10 m2 s-1), suggesting that its mass accumulation could be more effective than
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that of porous ceramic dosimeters. The mass accumulation of the VOCs in the solid ceramic
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dosimeter increased in the presence of salt (≥ 0.1 M) and with increasing temperature (4 to
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40 °C), but varied only slightly with DOM concentration. The solid ceramic dosimeter was
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suitable for field test and measurement of time-weighted average concentrations of VOC
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contaminated waters.
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Keywords: volatile organic compounds, time integrative passive sampling, ceramic dosimeter,
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water and groundwater monitoring, diffusion
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1. Introduction
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Volatile organic compounds (VOCs) are widely known to contaminate not only the
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atmosphere, but also water and soil systems. Most known VOCs such as benzene derivatives and
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chlorinated organics are carcinogenic1 and thus pose environmental threats and health risks.
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Although they are easily vaporized under normal atmospheric conditions, their leakage into the
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subsurface environment leads to the contamination of soil and groundwater systems2. Moreover,
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VOCs are of lower molecular weight than most persistent organic pollutants and are therefore
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more soluble and easily transported to other environments such as surface water3. The number of
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studies on VOC contamination has significantly increased over the last few decades4 suggesting
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the importance of their impact at the present time. Therefore, it is critical to detect and
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appropriately quantify these contaminants in the environment.
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Conventional water sampling involves the use of pumps or grab sampling from surface
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water and groundwater. Some of the disadvantages of this sampling method are its inability to
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monitor the contaminant concentration for long periods of time and risk of distorting the
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contaminant concentrations when purging wells in the case of groundwater sampling. These
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challenges have been met with the introduction of passive dosimetry5. Passive sampling devices
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work by the diffusion of contaminants through membranes and are driven solely by changes in
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the chemical potential. Conventional passive samplers are based on the equilibrium absorption or
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adsorption and trapping of contaminants and can only be deployed for an extended period of
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time to measure the time-weighted average (TWA) concentrations, but not for the instantaneous
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concentrations5. These equilibrium-based passive samplers have been developed, which are able
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to measure contaminant concentrations based on equilibrium partitioning6. Such samplers are
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commonly made up of polymeric materials such as polydimethylsiloxane (PDMS) and
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polyoxymethylene (POM), whose VOC absorption properties have been previously investigated7.
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On the other hand, kinetic-based passive samplers use materials with a high absorption capacity
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enclosed in an inert material such as a ceramic. For these samplers, the concentrations are
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diffusion-based and cumulative over time, which enables the measurement of the time-integrated
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concentration.
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One of these sampling devices involves the use of ceramic materials through which the
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contaminants diffuse into the contained sorbent. Several studies have proven their applicability
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for time-integrated and long-term water monitoring8–11. The ceramic holds a sorbent with a high
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absorption capacity to ensure maximum diffusion and the sorbent can vary depending on the
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contaminants of interest. Moreover, the ceramic dosimeter is inert and does not swell, unlike in
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the case of polymeric samplers. Its simplicity and robustness obviate the need for the frequent
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calibration, thereby reducing its cost and increasing its reusability. The sampling of volatile
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organic compounds (VOCs) and polycyclic aromatic hydrocarbons (PAHs) in groundwater field
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samples has been carried out using ceramic dosimeters
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Amberlite IRA-743 have been found to be suitable sorbents for VOCs and PAHs, respectively12.
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The use of bioassays has also been found to be compatible with the ceramic dosimeters using
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activated carbon sorbents for PAHs10 and dioxins13. Organophosphorus flame retardants and
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brominated hydrocarbons in river water samples have been investigated using ceramic
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dosimeters with HLB (hydrophilic-lipophilic balance) sorbents14. However, there have been no
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existing studies on the effects of physicochemical characteristics of contaminants, as well as the
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impacts of environmental variables on the dosimeter performances, which extends the
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application of the dosimeter to wider range of contaminants and environments.
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. Dowex Optipore L-493 and
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In the present study, a solid ceramic dosimeter packed with Dowex Optipore resin is
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developed to monitor the VOC contamination in aqueous systems. Eleven VOCs with a range of
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Henry’s constants (from 0.052 to 0.682) are selected, including the hydrocarbons found in fuels
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(benzene, toluene, ethylbenzene, p-xylene and 1, 3, 5-trimethylbenzene), chlorinated solvents
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and degreasers (trichloroethene, tetrachloroethene, 1,2-dichloroethane, 1,1,2-trichloroethane,
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chlorobenzene, 1,2-dichlorobenzene) to study the performance of the dosimeter in various
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environmental conditions. Unlike in previously cited reports where the ceramic is a water-
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saturated porous membrane, the ceramic employed for this study is a dense solid material which
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is impervious to water, but allows gas phase VOCs to diffuse through its micropores.
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2. Materials and Methods
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2.1 Mathematical Background
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The solid ceramic dosimeter consists of two parts, a ceramic tube and strong sorbent or
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resin inside of the tube. The diffusion of VOCs in the cylindrical tube is ubiquitously radial and
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their diffusion in the ceramic is fast due to the small thickness (1 mm) of the ceramic and, hence,
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the quasi steady state of VOC diffusion can be attained quickly. At steady-state, the diffusion
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equation becomes a function of the radius r as follows:
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d dCg r = 0, dr dr
a
