Parasitic health risk associated with ecosan toilet manure, wastewater, and flood -runoff water in and around Dhaka city

Abstract

Rapid urbanization in Dhaka, Bangladesh, has led to high population density, inadequate sanitation, and increased exposure to parasitic pathogens, posing significant environmental and public health risks. This study investigates the prevalence, spatial distribution, and environmental transmission pathways of parasitic organisms in ecosan toilet manure, wastewater, and flood runoff water, with particular emphasis on ecosan sanitation systems. The research was conducted in two phases (2017–2019 and 2022–2023) to capture temporal and spatial variations in contamination. A mixed-methods approach was applied, combining quantitative laboratory analysis with qualitative field investigations. Standard parasitological techniques, including microscopy, flotation, and concentration methods, were used to quantify helminth eggs (eggs per gram, EPG) and protozoan cysts (eggs per liter, EPL). Qualitative data were collected through focus group discussions (FGDs) and key informant interviews to assess sanitation practices and hygiene behaviors. Results revealed a high level of environmental contamination, with overall parasitic prevalence exceeding 60% across all sample types. The results indicated that eco-san manure from peri-urban wards (Keraniganj and Savar) exhibited the highest helminth egg counts (135 ± 10 and 115 ± 12 EPG, respectively). Wastewater samples from urban slum areas (Kamrangirchar) showed moderate contamination levels (95 ± 9 EPL). In contrast, flood-prone wards (Badda and Demra) recorded significantly higher parasitic loads in runoff water (150 ± 15 and 165 ± 18 EPL, respectively; ANOVA, F = 72.47, p = 0.0136). GIS-based spatial analysis further identified flood-prone areas as major contamination hotspots. Multiple parasite groups were detected, including protozoa, cestodes, and nematodes, with common organisms such as Hymenolepis nana, Ascaris lumbricoides, Trichuris trichiura, Entamoeba spp., and Giardia spp. Due to methodological limitations, some organisms were reported at the genus level or categorized as “parasite-like structures.” Seasonal variation indicated increased contamination during the rainy season due to flooding and enhanced pathogen dispersion. Qualitative findings highlighted limited awareness of safe compost handling, inadequate sanitation practices, and increased exposure risks during flooding events. Overall, parasitic contamination was strongly influenced by sample type, environmental conditions, and human behavior. This study underscores the need for integrated sanitation management, improved ecosan practices, effective wastewater treatment, flood-risk mitigation, and community-based health education to reduce environmental contamination and associated health risks. The adoption of advanced molecular diagnostic techniques is recommended to enhance the accuracy of parasite identification in future research.