Resuspension and settling of helminth eggs in water: Interactions with cohesive sediments

• Published in: Water research (Oxford) Vol. 46; no. 12; pp. 3903 - 3912
• Main Authors: Sengupta, Mita E., Andersen, Thorbjørn J., Dalsgaard, Anders, Olsen, Annette, Thamsborg, Stig M.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.08.2012; Elsevier
• Subjects: Aggregation; Animals; Applied sciences; Ascaris; Cohesion; Deposition; Eggs; environmental factors; Environmental Monitoring; erodibility; Erosion; Erosion rate; Exact sciences and technology; food safety; freshwater; Geologic Sediments - parasitology; health hazards; Helminth eggs; Helminths; irrigation canals; Particle Size; Particles; Pollution; Resuspension; Sedimentation; Sediments; Settling; Settling velocity; streams; Suspensions; Thresholds; Trichuris; Water - parasitology; Water Quality; Water treatment and pollution; Aggregation; Settling velocity; Resuspension; Particles; Helminth eggs; Erosion; Irrigation; Mobility; Parasite; Environmental factor; Sediments; Modeling; Indicator; Suspended particle; Health and environment; Surface water; Water quality; Health hazards; Agriculture; Stream; Public health
• ISSN: 0043-1354; 1879-2448
• DOI: 10.1016/j.watres.2012.04.033

Helminth parasite eggs in low quality water represent main food safety and health hazards and are therefore important indicators used to determine whether such water can be used for irrigation. Through sedimentation helminth eggs accumulate in the sediment, however resuspension of deposited helminth eggs will lead to increased concentration of suspended eggs in the water. Our study aimed to determine the erodibility (erosion rate and erosion threshold) and settling velocity of Ascaris and Trichuris eggs as well as cohesive sediment at different time points after incorporation into the sediment. Cohesive sediment collected from a freshwater stream was used to prepare a sediment bed onto which helminth eggs were allowed to settle. The erodibility of both sediment and helminth eggs was found to decrease over time indicating that the eggs were incorporated into the surface material of the bed and that this material was stabilized through time. This interaction between eggs and bulk sediment was further manifested in an increased settling velocity of suspended eggs when sediment was present in the suspension as compared to a situation with settling in clean water. The incorporation into the sediment bed and the aggregation with sediment particles decrease the mobility of both helminth egg types. Our findings document that helminth eggs should not be viewed as single entities in water systems when modelling the distribution of eggs since both erodibility and settling velocity of eggs are determined by mobility of the sediment present in the water stream. Recalculation of the erosion threshold for helminth eggs and sediment showed that even at relatively low current velocities i.e. 0.07–0.12ms−1 newly deposited eggs will be mobile in open irrigation channels. These environmental factors affecting resuspension must be taken into account when developing models for sedimentation of helminth eggs in different water systems. ► Resuspension of deposited helminth eggs increases egg numbers in water. ► Helminth eggs interact both with sediment at the bed and suspended sediment. ► Erodibility of sediment and helminth eggs decreases over time. ► Consolidation of sediment bed and incorporation of eggs into the bed take place. ► Mobility of sediment determines erodibility and settling velocity of helminth eggs.