Sand Barriers around Latrine Pits Reduce Fecal Bacterial Leaching

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Ecotoxicology and Human Environmental Health

Sand barriers around latrine pits reduce fecal bacterial leaching into shallow groundwater: a randomized controlled trial in coastal Bangladesh Abu Mohd Naser, Solaiman Doza, Mahbubur Rahman, Kazi Matin Uddin Ahmed, Mohammed Shahid Gazi, Gazi Raisul Alam, Mohammed Rabiul Karim, Golam Kibria Khan, Mohammed Nasir Uddin, Mohammed Ilias Mahmud, Ayse Ercumen, Julia Rosenbaum, Jonathan Annis, Stephen P. Luby, Leanne Unicomb, and Thomas F. Clasen Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.8b04950 • Publication Date (Web): 17 Jan 2019 Downloaded from http://pubs.acs.org on January 18, 2019

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Environmental Science & Technology

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Sand barriers around latrine pits reduce fecal bacterial leaching into shallow groundwater:

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a randomized controlled trial in coastal Bangladesh

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Abu Mohd Naser1,2*, Solaiman Doza3, Mahbubur Rahman3, Kazi Matin Uddin Ahmed4, Mohammed Shahid Gazi3, Gazi Raisul Alam3, Mohammed Rabiul Karim3, Golam Kibria Khan3, Mohammed Nasir Uddin3, Mohammed Ilias Mahmud5, Ayse Ercumen6,7, Julia Rosenbaum8, Jonathan Annis9, Stephen P. Luby10, Leanne Unicomb3, Thomas F. Clasen1 1Department

of Environmental Health Sciences, Rollins School of Public Health, Emory University, Atlanta, GA, 30322, United States 2 Emory Global Diabetes Research Center, Hubert Department of Global Health, Rollins School of Public Health, Emory University, Atlanta, GA, 30322, United States 3International Centre for Diarrhoeal Disease Research, Bangladesh (icddr,b), Dhaka, Dhaka, 1212, Bangladesh 4Department of Geology, University of Dhaka, Dhaka, 1000, Bangladesh 5Department of Geology and Mining, University of Barisal, Barisal, 8200, Bangladesh 6Division of Epidemiology & Biostatistics, University of California Berkeley School of Public Health, Berkeley, CA, 94720, United States 7Department of Forestry and Environmental Resources, North Carolina State University, Raleigh, NC, 27695, United States 8FHI360, Washington, DC, 20009, United States 9Tetra Tech, Arlington, VA, 22202, United States 10Woods Institute for the Environment, Stanford University, Stanford, CA, 94305, United States

*Corresponding author: Abu Mohd Naser, MPH, PhD Rollins School of Public Health, Emory University 1518 Clifton Rd NE, CNR 7040-G Atlanta, GA 30322, USA email: [email protected]; Cell: 470-279-1624

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Abstract

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We evaluated the effectiveness of a sand barrier around latrine pits in reducing fecal indicator

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bacteria (FIB) leaching into shallow groundwater. We constructed 68 new off-set single pit pour

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flush latrines in Galachipa sub-district of coastal Bangladesh. We randomly assigned 34 latrines

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to include a 50-cm thick sand barrier under and around the pit and 34 received no sand barrier.

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Four monitoring wells were constructed around each pit to collect water samples at baseline and

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subsequent nine follow-up visits over 24 months. Samples were tested using the IDEXX Colilert

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method to enumerate E. coli and thermotolerant coliforms most probable number (MPN). We

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determined the difference in mean log10MPN FIB counts/100ml in monitoring well samples

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between latrines with and without a sand barrier using multilevel linear models and reported

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cluster robust standard error. The sand barrier latrine monitoring well samples had 0.38 mean

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log10MPN fewer E. coli (95% CI: 0.16, 0.59; p = 0.001) and 0.38 mean log10MPN fewer

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thermotolerant coliforms (95% CI: 0.14, 0.62; p = 0.002), compared to latrines without sand

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barriers, a reduction of 27% E. coli and 24% thermotolerant coliforms mean counts. A sand

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barrier can modestly reduce the risk presented by pit leaching.

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Abstract Art

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Introduction

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Improved sanitation is the primary barrier to human fecal organisms contaminating the

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environment. Pit latrines are the most commonly used human excreta disposal systems in low-

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income countries.1 Globally, an estimated 1.8 billion people use pit latrines as the primary means

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of sanitation.2 There are concerns, however, about the extent to which pit latrines may introduce

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fecal contamination into shallow aquifers and pose a health risk to households relying on shallow

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groundwater reserves for drinking and livelihood activities. Pit latrines that are not shared with

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other households count toward the Sustainable Development Goals (SDG) sanitation target and

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are considered a solution for “safely managed sanitation” if excreta is routinely emptied,

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transported and treated off-site.3 However, there is evidence that leaching from the latrine pit can

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occur prior to emptying, particularly when constructed in high-water table environments.2 In

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many rural areas, pit latrines are located in close proximity to community groundwater sources

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used for drinking and household chores.2 Latrine pits are either unlined or lined with bricks,

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concrete rings or other materials with gaps in the liner to allow liquids to leach out into

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surrounding soil. Latrine leachate is a known source of groundwater contamination.4

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Bangladesh has seen dramatic increases in reduction of open defecation over the past

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decade. Direct pour-flush latrine with a one-meter pit containing four concrete rings and a plastic

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pan fitted into a concrete slab is the most common latrine technology in rural Bangladesh. Much

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of the southern coastal Bangladesh is at sea level and groundwater table levels are between 1-4

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meters below the surface.5 Latrines in southern coastal Bangladesh are often installed in a way

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that untreated effluent discharges directly into unconsolidated shallow groundwater.6,7 Flooding

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due to heavy rainfall, tidal surges or cyclones increases the threat of surface and groundwater

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contamination from traditional pit latrines.8,9 4


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Slow or intermittent sand filters have been used for centuries to treat wastewater from

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sewer systems and septic tanks.10 Generally, sand filters are superior to native soils at filtering

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septic effluent.11 In areas where naturally occurring underlying soils are ill-suited for percolation

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of septic effluent, the construction of sand-lined trench has proven a viable alternative.11 When

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septic effluents percolate into the sand, a layer of bacteria (biomat) is formed in the sand surface

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exposed to the effluent.12 Once formed, the biomat reduces bacteria concentration in the filtered

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effluent; it can operate long-term if the hydraulic conductivity within the biomat is maintained.13

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We hypothesized that sand barriers constructed around pit latrines could act like a sand filter and

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reduce the spread of bacteria from latrine pits in high groundwater areas. Currently sand barriers

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surrounding the pit latrines are not used in Bangladesh, and there is a lack of field research data

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to fully understand whether sand filters can reduce pathogen leaching from pit latrines into

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shallow groundwater in tropical climates. We evaluated whether constructing a 50-cm sand

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barrier below and around the walls of an offset pour-flush latrine pit reduced leaching of fecal

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bacteria into the surrounding environment in a high groundwater coastal region of Bangladesh.

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Methods

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Study site- The study was conducted in Galachipa Upazilla (sub-district), Patuakhali

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district, Bangladesh (Figure 1). Galachipa (between 21°48' and 22°21' north latitudes and 90°15'

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and 90°37' east longitudes; area 1268 square km) is a low-lying coastal sub-district with many

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rivers and canals. The communities in these areas have limited livelihood opportunities; this is

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aggravated by regular flooding, poor infrastructure and underdeveloped communication systems.

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The groundwater table level is variable in Galachipa depending on rainfall and tidal patterns, but

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is typically very shallow, 5 meters from existing unimproved latrines, and (iii) the

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land donated by the household for pit latrine construction was not adjacent to surface water

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bodies. A statistician generated a unique household ID along with block randomization and

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prepared sealed-envelopes coded for a latrine with a sand barrier and without a sand barrier.

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Block randomization was chosen to ensure equal numbers of latrines with and without a sand

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barrier among the geographically clustered households to minimize confounding from local

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geological factors, and to ensure an equal number of latrines with and without a sand barrier in

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case construction crews had to stop installing latrines due to flooding and heavy rainfall during

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the wet season.

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Latrine, sand barrier and monitoring well construction- We selected three local contractors

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to construct the latrines, sand barriers and monitoring wells and closely supervised their work to

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conform with specifications (Supporting Information1). For all 68latrines, contractors used

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five concrete liner rings of 300 mm height for the pit (Figure S1-S4). For both latrines with and

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without sand barrier, they also placed four monitoring wells at even intervals around the pit at a

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distance of 1 meter from the outer side of the concrete rings. One meter distance was considered

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due to space limitation in the homesteads of the participating households. All monitoring wells 7



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had 6-meter depths  the top 3 meters comprised a PVC casing and the bottom 3 meters

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included a screen for the accumulation of groundwater from the surrounding soil layers. The top

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of the monitoring well was encased with a 0.3 meter x 0.3 meter concrete pad and capped to

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firmly secure the well in place and prevent any surface water runoff from leaking (Supporting

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Information1). For the latrines with a sand barrier, the contractors constructed a 50 cm sand

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barrier using locally available sand around and below the concrete rings. Therefore, the distance

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between outer side of the sand barrier and monitoring wells were 50 cm for the sand barrier

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latrines. The cost for materials for construction was US$ 282 per sand barrier latrine, and US$

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257 per latrine without sand barrier.

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We randomly selected two sand barrier latrines from each of the four unions (geographical

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administrative unit) and collected the sand samples used for the barriers for sieve analysis at the

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laboratory of Department of Geology, Dhaka University to determine the textural composition.

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Field staff also collected soil samples from the bottom of all 68 study latrines during pit hole

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excavation for analysis at the laboratory of Department of Geology, Dhaka University.

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Hydrometer analysis was used to determine the distribution of the finer soil particles at the

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bottom of the pits and assess whether the soil texture varied geographically across the study area.

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Blinding-The data collectors and the investigators were blinded to the household intervention

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status during study implementation. We had two groups of field staff. The first team was

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involved in securing informed consent, ensuring construction of the latrines as per

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randomization, and monitoring well installation. After construction, we replaced this team with a

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second team to collect study data. 8


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Baseline water sample collection: Baseline groundwater samples were collected from

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monitoring wells of all 68 study latrines before household members started using the latrine

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(Supporting Information2). Field staff purged each monitoring well 24 hours prior to sample

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collection by pumping out well water using a portable hand pump until clear water was

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discharged. 18,19 Purging was done in order to obtain aquifer water samples that were not affected

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by the conditions created by the well.18 They used a sterile disposable 1.9cm polyethylene bailer

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for collecting 500 ml water samples from each monitoring well.

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Promotion of latrine use: We selected 11 local community health promoters (CHPs) and

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trained them to deliver messages to target household members. They promoted regular latrine

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use and maintenance, and promoted protection of the monitoring wells from children and

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household activities. CHPs instructed households to demolish any previously used latrines. CHPs

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visited participating households weekly to deliver latrine use and maintenance messages. CHPs

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were not apprised of the study objectives or methods.

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Follow-up water sample collection: Following baseline groundwater sample collection, field

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staff collected water samples from each monitoring well of all 68 study latrines in months 1

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through 5, and then at 12, 15, 18 and 24 months after initiation of latrine use using the procedure

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described above for the baseline sample (Figure 2).

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Water sample transport, process and analysis- Upon collection, water samples were

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immediately poured into sterile Whirlpak® bags and transported on ice in an insulated cool box

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(at 2 to 8°C) to a field laboratory for processing within six hours of collection. 100 mL aliquots 9



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of samples were processed with Colilert®-18 media and incubated for 18 hours at 44.5°C to

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enumerate the most probable number (MPN) of E. coli and thermotolerant coliforms using the

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IDEXX QuantiTray®-2000 MPN table based on the number of fluorescent and yellow cells. 20,21

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One lab blank was run per day of sample testing. Field blanks were collected once per week per

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sample collector.

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Data analysis- We replaced the E. coli and thermotolerant coliforms MPN values where no

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contamination was detected with 0.5 (half the lower detection limit) and then converted the

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counts into log10MPN for analysis. We used multilevel mixed effect linear models using two

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random effects to address clustering at latrine and monitoring well levels to determine the

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difference in mean log10MPN counts between water samples from latrines with and without a

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sand barrier. In secondary analyses, we investigated the effect modification of sand barrier on

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water quality by including an interaction term with season (dry vs. wet) in the regression

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models. Follow-up visits conducted between May and November were considered as wet season

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visits. 14We categorized water sample contamination according to the WHO thresholds of low

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risk (100 MPN/100 ml).22 We used the cumulative approach of ordered

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logistic regression23 with the same multilevel mixed effect approach to determine the odds ratio

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of higher WHO risk categories between latrines with and without a sand barrier. In all models,

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we reported the cluster robust standard error. We performed statistical analyses in Stata, version

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15.0.

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Ethics- Selected households were informed about our study objectives and their right to discontinue participation at any point of the study period. Informed written consent was taken 10


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from all household heads prior to installing the latrines. The study protocol was approved by the

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Ethical Review Committee of icddr,b (PR-14117) and FHI360.

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Results

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Pre-intervention characteristics of study latrines: The mean members per household was

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five for latrines with and without sand barrier (Table 1). Seventy-six percent of the sand barrier

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latrine households had an unimproved private latrine compared to 79% of households without

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sand barrier. The median nearest distance between the study latrine and a previous unimproved

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latrine was 18 meters in both groups. A surface water source was present within 10 meters of

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50% of constructed sand barrier latrines, and 56% of latrines without sand barrier. We collected

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1,220 monitoring well water samples from the sand barrier latrines, and 1,212 from latrines

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without a sand barrier (Figure 2). Four monitoring wells were damaged and we were unable to

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collect water samples from them in the last four visits.

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Soil composition of latrines and sand barriers: Latrines with and without sand barriers

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had similar soil compositions at the bottom of the pits (Supporting Information Figure S5).

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The median proportion of silt was 86% for latrines with sand barrier and 84% for latrines without

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sand barrier and the median proportion of clay was 11.5% for both groups (Supporting

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Information Figure S5). The median grain size of the pit bottom soil was 0.12 mm for latrines

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with a sand barrier and 0.11 mm for latrines without a sand barrier. Sieve analysis suggests

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similarly homogenous composition of the locally produced sand barrier in all four unions. The

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proportion of sand was 87 – 93% and the grain size was 0.09 – 0.12 mm (Supporting

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Information Table S1).

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Fecal contamination of water from monitoring well: The pre-intervention (baseline)

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mean log10MPN E. coli per 100 ml was 2.3 for latrines with sand barrier and 2.0 for latrines

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without (Figure 3). The pre-intervention mean log10MPN thermotolerant coliforms per 100 mL

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was 2.6 for latrines with sand barrier and 2.4 for latrines without. Thereafter, mean log10MPN E. 12


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coli and thermotolerant coliforms counts in water samples from latrines with sand barrier were

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lower than E. coli and thermotolerant coliforms counts in samples from latrines without sand

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barrier (Figure 3). The proportions of water samples < 1 log10MPN/100 mL were 28% (95% CI:

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25.1, 30.2) for latrines with sand barrier and 21% (18.3, 22.9) for latrines without for E. coli; the

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corresponding proportions for thermotolerant coliforms were 22% (95% CI: 20.0, 24.8) and 17%

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(14.6, 18.8) (Table 2). The proportions of water samples >10 log10MPN/100 mL were 48%

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(45.4, 51.0) for latrines with sand barrier and 59% (95% CI: 56.3, 62.0) for latrines without for

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E. coli; the corresponding proportions for thermotolerant coliforms were 54% (95% CI: 50.7,

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56.4) and 65% (95% CI: 62.6, 68.0) (Table 2).

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In monitoring wells from latrines with sand barrier, we detected 1.06 mean

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log10MPN/100 mL E. coli and 1.25 mean log10MPN/100 mL thermotolerant coliforms at follow

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up visits. In monitoring wells from latrines without sand barrier, we detected 1.43 mean

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MPN/100 mL E. coli and 1.62 mean MPN/100 mL thermotolerant coliforms during follow-up.

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Compared to water samples from latrines without sand barrier, those from latrines with sand

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barrier had a 0.38 (95% CI: 0.16, 0.59; p = 0.001) mean log10MPN reduction in E. coli and 0.38

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(95% CI: 0.14, 0.62; p = 0.002) mean log10MPN reduction in thermotolerant coliforms in 100 ml

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water (Table 3), translating to 27% reduction in E. coli and 24% reduction in thermotolerant

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coliforms provided by the sand barrier.

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Compared to latrines without sand barrier, latrines with sand barrier had 0.46 (95% CI:

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0.23, 0.69; p 1 m

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distance from the pit latrine as households were unwilling to provide extra space due to space

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limitation in their homesteads. However, a similar study identified that 90% water samples in

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coastal Bangladesh had fecal contamination when collected two meter laterally from the latrine

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pit and in 86% samples had fecal contamination when collected 4 meters laterally. 26 With our

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study design, we were unable to assess whether the reduction in pit latrine leaching would 17



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improve the microbiological water quality of the water sources used by the households. We did

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not assess whether the sand barrier can reduce leaching of chemical contaminants such as

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nitrogenous and carbon compounds.

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The SDGs unify sanitation and safe water supply under a common goal; promoting pit

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latrines with sand barriers can only modestly reduce shallow groundwater contamination. Further

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modification of the sand barrier such as increasing the thickness or altering sand composition

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such as modifying pore size may increase its effectiveness and further reduce leaching.

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Environmental engineering laboratory exploration of such sand barrier modifications could be

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assessed at low cost prior to field testing. Careful modeling studies to understand the role of pit

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latrine leaching on community fecal exposure and health burden can inform whether

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interventions to lower leaching could be a pragmatic approach to support the SDG goals.

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Acknowledgements: This research was funded by the United States Agency for

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International Development (USAID) and the Swedish International Development Cooperation

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Agency (SIDA). icddr,b acknowledges with gratitude the commitment of the funders to its

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research efforts. icddr,b is also grateful to the Governments of Bangladesh, Canada, Sweden and

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the UK for providing core/unrestricted support. We are grateful to the study households who

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provided space for latrine construction. Supporting Information: Schematic cross-sectional and longitudinal view of latrines

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with and without sand barrier. Summary findings on the composition of the bottom soil of

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latrines with and without sand barrier. Sieve analysis findings of the composition of sands used

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for constructing sand barriers. Field activities and process for pit latrine, monitoring well

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installation. Methodologies for water sample collection from monitoring wells. Study dataset

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(.xls)

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Sources of Funding: United States Agency for International Development (USAID) and Swedish International Development Cooperation Agency (SIDA).

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Authors conflict of interst: None.

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Ali M, Emch M, Donnay J-P, Yunus M, Sack R. The spatial epidemiology of cholera in an endemic area of Bangladesh. Social Science & Medicine 2002; 55(6): 1015-24.

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30.

Emch M. Diarrheal disease risk in Matlab, Bangladesh. Social Science & Medicine 1999; 49(4): 519-30.

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31.

Sharmin A. Water and wastewater in Bangladesh, current status and a design of a decentralized solution. Master Thesis, Lund University, Lund, Sweden, 2016. Website; https://lup.lub.lu.se/student-papers/search/publication/8895656 (accessed November 24, 2018)

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448 449

Figure 1: Study sites in coastal Bangladesh.

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450 451 452

Figure 2: Trial profile and sample collection during field visits. Four monitoring wells were damaged and we were unable to collect water samples from them in the last four visits

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453 454 455

Figure 3: Temporal trend in mean log10MPN thermotolerant coliforms and E. coli in water samples from the latrines with and without sand barrier during all visits

25



456

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Table 1: Pre-intervention characteristics of the households with and without sand barrier latrines Characteristics

Study latrines Sand barrier latrine Latrine without sand barrier

Household members Living in compound, mean (Standard deviation) Living in household, mean (Standard deviation) latrine users per household, median (Inter-quartile range) Household environments

14 (12)

13 (10)

5 (2)

5 (2)

5 (4-6)

5 (4-6)

Households with an existing unimproved latrine, n/N (%) Distance from study latrine to nearest unimproved latrine in meters, median (IQR) Presence of surface water (e.g. pond) within 10 m of study latrine, n/N (%) Reported household feces disposal, n/N (%) Existing pit latrine

26/34 (76)

27/34 (79)

18 (10-20)

18 (10-25)

17/34 (50)

19/34 (56)

22/34 (65)

18/34 (53)

Surface water

9/34 (26)

13/34 (38)

Open place

3/34 (9)

2/34 (6)

Deep tube well

22/34 (65)

26/34 (76)

Shallow tube well

11/34 (33)

8/34 (24)

Primary household drinking water source, n/N (%)

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458 459

Table 2: Proportions of shallow groundwater samples for microbiological risks as per WHO categories

460

E. coli WHO Microbiological risk categories Low risk 10 MPN/100 mL, % (95% CI) (n/N) Very high risk >100 MPN/100 ml, % (95% CI) (n/N)

Latrines without sand barrier 21 (18.3 – 22.9) (248/1209) 79 (77.1 – 81.7) (961/1209) 59 (56.3 – 62.0) (716/1209) 34 (31.6 – 37.0) (414/1209)

Sand barrier latrines 28 (25.1 – 30.2) (337/1220) 72 (69.8 – 74.9) (883/1220) 48 (45.4 – 51.0) (588/1220) 23 (20.7 – 25.5) (281/1220)

Thermotolerant coliforms Latrines without sand barrier 17 (14.6 – 18.8) (201/1209) 83 (81.2 – 85.4) (1008/1209) 65 (62.6 – 68.0) (790/1209) 40 (36.7 – 42.3) (478/1209)

Sand barrier latrines 22 (20.0 – 24.8) (270/1220) 78 (75.4 – 80.2) (950/1220) 54 (50.7 – 56.4) (653/1220) 27 (24.8 – 29.8) (333/1220)

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Table 3: Post-intervention mean log10MPN thermotolerant coliforms and E. coli in water samples from latrines with and without sand barriers. Baseline data not included in the analyses. Latrines without sand barrier

Thermotolerant coliforms

N

Difference between latrines with and without sand barrier Sand barrier latrines

mean log10MPN

N

1.62

1220

mean log10MPN

p value

Difference in mean log10MPN₤

95% CI

p value

-0.62, -0.14

0.002

--

--

--

Difference in mean log10MPN*

95% CI

-0.38

Primary analysis 1209

All visits

1.25

Interaction with season Wet season

402

2.15

406

1.96

-0.19

-0.47, 0.10

0.194

ref

ref

ref

Dry season

807

1.36

814

0.89

-0.47

-0.73, -0.22

< 0.001

-0.28

-0.53, -0.02

0.032

1.43

1220

1.06

-0.38

-0.59, -0.16

0.001

--

--

--

E. coli

Primary analysis All visits

1209

Interaction with season Wet season

402

1.95

406

1.74

-0.21

-0.49, 0.07

0.149

ref

ref

ref

Dry season

807

1.17

814

0.71

-0.46

-0.69, -0.23

< 0.001

-0.25

-0.51, 0.01

0.063

* Difference in mean log10MPN refers to comparison between latrines without sand barrier

463 464

₤Difference

in mean log10MPN refers to comparison to reference category

Note- random effect models were used to generate the 95% confidence intervals.

465

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466


Table 4: Monitoring well sample WHO risk categories for thermotolerant coliforms and E. coli across latrines with and without sand barriers

467 Indicator bacteria

Latrines without sand barrier

Sand barrier latrines

Difference between latrines with and without sand barrier

N of wells

Low risk

Intermediate risk

High risk

Very high risk

N of wells

Low risk

Intermediate risk

High risk

Very high risk

Change in ordered logodds of higher risk category

E. coli

1209

20.5%

20.3%

25.0%

34.2%

1220

27.6%

24.2%

25.2%

23.0%

-0.51

-0.84, -0.18

0.006

Thermotolerant coliforms

1209

16.6%

18.0%

25.8%

39.5%

1220

22.1%

24.3%

26.2%

27.3%

-0.54

-0.91, -0.17

0.006

95% CI

p value

468

29


Sand Barriers around Latrine Pits Reduce Fecal Bacterial Leaching

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