Refining the uncertainties and expansion of wastewater-based epidemiology for assessing population exposure to chemicals

O'Brien, Jake (2017). Refining the uncertainties and expansion of wastewater-based epidemiology for assessing population exposure to chemicals PhD Thesis, School of Medicine, The University of Queensland. doi:10.14264/uql.2017.420

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Author O'Brien, Jake
Thesis Title Refining the uncertainties and expansion of wastewater-based epidemiology for assessing population exposure to chemicals
School, Centre or Institute School of Medicine
Institution The University of Queensland
DOI 10.14264/uql.2017.420
Publication date 2017-03-16
Thesis type PhD Thesis
Supervisor Jochen Mueller
Phong Thai
Sarit Kaserzon
Total pages 239
Total colour pages 29
Total black and white pages 210
Language eng
Subjects 0301 Analytical Chemistry
0399 Other Chemical Sciences
1117 Public Health and Health Services
Formatted abstract
Systematic sampling and analysis of wastewater is an increasingly used tool to
complement more traditional techniques for assessing consumption of licit and illicit
chemical substances in the population. The use of wastewater sampling and
analysis contributes to a broader field that is referred to as wastewater-based
epidemiology (WBE). Both spatial and temporal analysis can be conducted
quantitatively, quickly and cost effectively using the WBE approach.

In brief, per capita exposure to a given chemical within a population is estimated by
measuring the concentration of that chemical or a metabolite in a representative
wastewater sample multiplied by the volume of wastewater represented by the
sample, divided by the population size from which the sample originates and
correcting by factors such as the excretion factor of the metabolite or chemical,
molecular weight change and potential stability of the chemical within the sewer. It
has previously been determined that the population size is the largest uncertainty for
WBE estimates.

The aim of this thesis it to therefore identify useful markers that allow population
estimation for a given wastewater sample and apply this technique including to
assess per capita exposure/release of a group of chemicals that have not been
examined in previous WBE studies.

The approach for this thesis was to systematically collect samples on a day when the
population is well defined. For this we collected samples on the 2011 Census Day in
Australia from 10 wastewater catchments ranging in size from approximately 1,500
to 500,000 people. By providing catchment maps to the Australian Bureau of
Statistics, the accurate population size for each catchment was determined.

The most obvious choice of a potentially useful population markers are endogenous
chemicals such as creatinine. Therefore, in Chapter 2, creatinine was assessed as a
population marker. It was found that there was no correlation between the mass load
of creatinine in wastewater and the population. Using laboratory-scale sewer
reactors with conditions representative of both gravity sewers and rising mains, it
was found that creatinine, while stable in collected samples, is unstable under sewer
conditions. We therefore conclude that creatinine is not suitable for predicting
differences in population size particularly when different sewer systems are
compared.

In Chapter 3, a method was developed to quantify 96 chemicals in wastewater
influent and applied to the census wastewater samples to identify potential
population size markers. Thirteen chemicals including acesulfame, caffeine, and
pharmaceuticals and personal care products were detected in all samples and found
to have a good correlation (R2 > 0.8) between mass load and population size. A
Bayesian inference model was developed which incorporated these potential
population size markers to provide a population size estimate. The model was
validated using a leave-one-out approach for all sites and comparing the population
size estimate from the model with the accurate census population data. It was shown
that for small catchments, the uncertainty of the estimate as measured by the width
of the posterior was 1.1 to 2.4 times narrower than the width of the posterior using
only the WWTP operator population size estimates. For large WWTP catchments,
the width of the posterior using the population size model was between 5 and 40
times narrower than the WWTP operator population size estimates. Additionally, it
was found that the posterior width of the model was improved with addition of more
chemicals in the model.

In Chapter 4, using laboratory-scale sewer reactors, the impact of in-sewer
degradation of the population markers identified in Chapter 3 was evaluated. It was
found that five of the fourteen markers were stable under all conditions over the 12
hour study period. Those which were unstable ranged from little degradation over the
study period and only under certain conditions to rapid degradation regardless of
sewer conditions. Additionally we assessed whether or not the degradation of these
chemicals impacted the population size estimation model by excluding the unstable
compounds from the model. We found that the uncertainty of the estimate did not
decrease through exclusion of the unstable chemicals.

In Chapter 5 we assessed whether WBE can be expanded to chemicals other than
those previously assessed (i.e. illicit drugs, alcohol and tobacco). For this a method
was developed to analyse organophosphorous flame retardants (PFRs) in
wastewater influent. Using the samples collected during census, it was estimated
that 2.1 mg person-1 day-1 enter Australian wastewater. In addition we found a good
correlation (r2 ≥ 0.87) between the population size and mass load for each of the four
main contributors (TBOEP, TCIPP, TDCIPP and TCEP).

Overall, this thesis demonstrates that the uncertainty of WBE estimates can be
improved through identifying population markers, and developing and calibrating a
population model. Additionally, we found that WBE is not limited to assessing
exposure/consumption of the chemicals previously assessed (i.e. alcohol, illicit drugs
and tobacco) and can be expanded to other chemical groups.
Keyword Wastewater
Chemical analysis
wastewater-based epidemiology
population health
modelling

Document type: Thesis
Collections: UQ Theses (RHD) - Official
UQ Theses (RHD) - Open Access
 
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Created: Thu, 09 Mar 2017, 10:54:11 EST by Jake O'brien on behalf of University of Queensland Graduate School