Water passive sampler calibration: accounting for changes in chemical uptake rates when exposed to variations in environmental conditions.

Dominique O'brien (2011). Water passive sampler calibration: accounting for changes in chemical uptake rates when exposed to variations in environmental conditions. PhD Thesis, School of Medicine, The University of Queensland.

       
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Author Dominique O'brien
Thesis Title Water passive sampler calibration: accounting for changes in chemical uptake rates when exposed to variations in environmental conditions.
School, Centre or Institute School of Medicine
Institution The University of Queensland
Publication date 2011-12
Thesis type PhD Thesis
Total pages 105
Total colour pages 11
Total black and white pages 94
Language eng
Subjects 11 Medical and Health Sciences
Abstract/Summary Passive sampling techniques facilitate the time-integrated measurement of pollutant concentrations through the use of a selective receiving phase. Accurate quantification using passive sampling devices rely on the implementation of methods that will negate the effects of environmental factors such as flow, salinity and temperature. The aim of this study was to: - Develop and calibrate a method for monitoring flow (i.e. the passive flow monitor abbreviated as PFM) and evaluate its sensitivity to other environmental parameters such as salinity - Evaluate the effect of flow and salinity on the uptake kinetics of a phosphate passive sampler (P-sampler) and assess whether the PFM can be used to accurately predict time averaged phosphate concentrations under various (and varying) flow and salinity conditions - Assess the use of the passive flow monitor for application with other passive sampling techniques such as the empore disk based sampler that is used for monitoring of polar organics such as herbicides and the semipermeable membrane devices. The PFM and P-sampler were co-calibrated when exposed to a range of flow velocities (0 – 27 cm s-1) and ionic strengths (0.01-0.62 mol kg-1). Further, both the PFM and P-sampler was assessed when exposed to a pulse in flow rate and or filterable reactive phosphate (FRP) concentration to assess the performance of the devices when exposed to a simulated flood event. The observed sampling rates for phosphate ranged between 0.006 and 0.20 L d-1 and were influenced by both flow and ionic strength. The empirical models established allowed the estimation of Rs from flow velocity and the mass of gypsum lost per day (rPFM) with a precision of within 8.5% when exposed to a flow of 3.5 cm s-1 or greater. Measurements of flow rates less than 3.5 cm s-1 cannot be made using the PFM. Mass loss rates of the PFMs were also shown to increase with an increase in flow and ionic strength. The study demonstrated that the increased rate of dissolution with ionic strength could be quantitatively accounted for by the change in gypsum solubility as the ionic strength of solution was changed. A calculation scheme was established for these solubilities within environmentally relevant range of temperatures 11 and ionic strengths. A comparison of the FRP concentrations determined by parallel grab sampling and the P-sampler calibrated with the PFM and direct measurement of flow rates showed that a good agreement was achieved for both the measurement of flow velocity and FRP concentration when exposed to a pulse in flow (6% overestimation) or concentration (2% underestimation). However, when the P-sampler was first exposed at the peak in the pulse event there was a significant underestimation of FRP concentrations that indicates that there is a lag in the chemical uptake into the P-sampler that should be taken into consideration when employing this sampler under highly variable conditions. The calibration of the measurement of Rs using the PFM for chemical uptake by the SDB-RPD-Empore disk in relation to the mass lost from the PFM has shown that the PFM provides an accurate measure of Rs for flow velocities from 3.5 to 16 cm s-1. Notably, for flow rates >16 cm s-1, a non linear increase in the Rs of the herbicides atrazine and prometryn was observed which indicates that the key resistance to uptake into the SDB-RPD Empore disk is associated with the diffusion through the overlying diffusion limiting membrane. Additionally, the calibration of the measurement of Rs using the PFM for the chemical uptake by semipermeable membrane device (SPMD) and polydimethyl siloxan (PDMS) provided sufficient data to establish one phase exponential associations to describe the change in the Rs of six agricultural chemicals with changes in both flow velocity and the mass lost from the PFM. Overall, the presented work has demonstrated that the PFM is a viable in situ calibration technique that can be applied in the measurement of both the average water flow velocity to which passive sampling devices have been exposed and the effect of flow and salinity on in situ sampling rates. Further, the use of the PFM as it is presented may be applied when it is not practical or safe to obtain measurements of ambient environmental conditions manually or when it is not within the financial means of the monitoring budget to employ an automated device at each deployment site and as such is a valuable addition to the passive sampling toolbox.
Keyword water pollution
passive sampling
passive flow monitor
Chemcatcher
PDMS
SPMD
Additional Notes Colour pages: 2, 34, 36, 37, 38, 42, 51, 66, 76, 94, 97

 
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Created: Mon, 19 Dec 2011, 11:48:08 EST by Miss Dominique O'brien on behalf of Library - Information Access Service