Analysis of exposure pathways and measures to mitigate the emanating risk of sanitation options in coastal areas of islands in the South Pacific (MSc thesis)


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Analysis of exposure pathways and measures to mitigate the emanating risk of sanitation options in coastal areas of islands in the South Pacific (MSc thesis)

Note by moderator: See earlier thread here:


Dear SuSana members,

my name is Domink Raab from BOKU university (Austria) / Lincoln University (New Zealand). I‘d like to share my master thesis, maybe it is helpful for some of you.

Title: Analysis of exposure pathways and measures to mitigate the emanating risk of sanitation options in coastal areas of islands in the South Pacific

links: data set (boku) , full text (boku) [5.4mb]

In case of questions, comments or critique feel free to post a comment.


Rural coastal areas of islands in the South Pacific are often characterized by shallow groundwater and are prone to floods. The prevalent sanitation (i.e. Single Pit System; ‘bush’, Dry, and PourFlush Toilets) may cause microbiological and chemical groundwater contamination. Floods involve the risk of spreading pathogens in the environment and may cause toilets to be inoperable. Composting Toilets (i.e. Double Vault non-Urine-Diverting Toilet) have been piloted in several island states to overcome these problems as they are built above ground and contain the excreta in watertight vaults. Urine-Diverting Dry Toilets (UDDTs; i.e. Double Vault Urine-Diverting Dry Toilet) are constructed similarly, with the difference of urine and faeces being treated separately. Both alternatives offer the possibility of reusing their output products (urine, faeces or excreta) as fertilizer.
This thesis assesses the applicability and emanating health risks of these three options under the given context. Each system was divided into its functional groups in order to identify exposure pathways and recommend measures to reduce the risk based on these entities. A focus was on the reuse-oriented systems’ reliability of treatment which determines the exposure during application of output products and consumption of products. A literature review was combined with field research in Vanuatu to approach the problem. The latter included meetings with NGOs and a governmental department, inspection of piloted Composting Toilets, identification of a pilot site to trial UDDTs, and introduction of UDDTs to chiefs and citizens to evaluate the disposition towards this system.
The prevalent system is not recommended in case it is planned to use groundwater for drinking in the future. Both alternatives are in principle suitable for the underlying conditions, whereas the treatment of UDDTs has shown to be more effective, reliable and simpler to manage as compared to Composting Toilets. The latter system is therefore not recommended. Reuse of urine and faeces imply great opportunities, but doing so includes also considerable health risks if personal protection, proper treatment and reuse practices are not adhered to.


Soil layers of small coral islands, and sandy coastal areas of larger islands in the Pacific are
usually thin and highly permeable. This makes the groundwater resources of islands belonging
to the Small Island Developing States (SIDS; Box 1) prone to contamination by the prevalent
pit-based sanitation. Small coral islands are especially of concern because their water table is
usually (very) high (i.e. shallow) which increases the risk of groundwater pollution substantially.
Especially the common practice in the Pacific to dig pits to the depth of the water table allows
the direct contamination of the groundwater (Falkland, 2002; Dillon, 1997). Groundwater conta-
mination from sanitation is generally of greater concern in urban and peri-urban areas due to
higher population densities, but ‘[m]any smaller villages however, also exhibit high bacterial
levels in groundwater or have the potential for such pollution [... which] is a major constraint to
improvements in water quality’ (Falkland, 2002, p. 17).
Islands of SIDS are further prone to natural disasters (floods, droughts, cyclones, earthquakes)
and are affected by climate change (sea level rise, changing rainfall patterns/droughts, more
severe tropical cyclones) (UN-DESA, 2017; Overmars & Gottlieb, 2009). ‘The increased
frequency in natural disasters such as floods and cyclones threatens existing infrastructure for
sanitation, and further exacerbates the spread of diseases’ (PSIDS, 2009, p. 8f). Floods may
cause toilets to overflow, spreading the contained pathogens in the environment as a result
(Stenström et al., 2011). Besides, sanitation facilities are often useless when pits are filled up
with sediments, or pits collapse due to weakened stability. Inaccessible toilets during and after
floods may induce open defecation (Uddin et al., 2013). ‘The lack of sanitation during times of
natural disaster will likely hasten the spread of communicable diseases and vector-borne
diseases’ (PSIDS, 2009, p. 9).
To overcome these shortcomings of pit-based sanitation systems, Composting Toilets have
been piloted on many pacific island states since mid-1990s (Crennan & Booth, 2007; Crennan &
Berry, 2002). These toilets contain the excreta in watertight vaults built above ground, making
them suitable for areas prone to floods and groundwater contamination. Inactivation of
pathogens is based on thermophilic composting (Berger, 2011). But the reliability of the treat-
ment is subject to debates, because ‘[t]hermophilic temperatures are seldom if ever attained
eliminating this reliable mechanism of pathogen destruction’ (Hill & Baldwin, 2012, p. 1813).
Another option are Urine-Diverting Dry Toilets (UDDTs) which are based on watertight vaults
built above ground as well. Urine and faeces are separated at the source by using a urine-di-
verting User Interface. This enables an isolated treatment of faeces (based on desiccation and
high pH) and urine (storage in airtight tanks) (Rieck et al., 2012). Both Composting Toilets and
UDDTs are reuse-oriented systems, designed to make use of the nutrients contained in excreta.
Subsistence farming plays a major role in the nutrition of people living in SIDS, but food security
is threatened by climate change (UNFCCC, 2005). Reusing nutrients of excreta is a possible
measure to increase the food security (Rieck et al., 2012). While Composting Toilets and Urine-
Diverting Dry Toilets should reduce health risks associated with floods and groundwater conta-
mination, risks may be even elevated if effective barriers (e.g. proper treatment, hand washing,
using personal protection equipment) are not in place (Schönning & Stenström, 2004).

@moderator: Although this assessment of exposure pathways is - strictly spoken - not a SSP, it covers many essential steps of it. I could not find a sub forum that fits better, but feel free to move it!

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