Animal Waste, Water Quality and Human Health

water), that is, whereas an illness was foodborne, the source was contaminatedwater.10.3.1 Ingestion ratesThe ingestion of water during swimming activities can be a significant factoraffecting risk. There is a dearth of empirically collected data on ingestion ofwater by swimmers. In a study of divers wearing masks, estimates based on selfreportedvolumes of water that the divers believed they had swallowed weremainly in the range of 30 mL or less, but with some reporting much largervolumes (Schijven & de Roda Husman 2006). These self-assessed volumes ofingested water were not dissimilar from the amounts of water swallowed byrecreational swimmers in a pilot study conducted in a swimming pool (Dufouret al. 2006). In that study, ingestion of water was estimated by the amount ofcyanuric acid measured in a 24 hour urine sample collected after a one hourswimming activity in a pool disinfected with chlorine isocyanurate. 5 The averageamount of water swallowed by 53 participants was about 30 mL. Swimmers lessthan 16 years old swallowed about 37 mL of water, which was more than twicethat swallowed by adults (average 16 mL). These systematic differences shouldbe taken into account in risk assessments because they directly affect exposure.10.3.2 Climate changeComparative risk analysis 373Risk of illness associated with exposure to non-human faecal pollution may besignificantly affected by global warming and climate changes. Events similar tothose which might occur under global warming conditions have been observed inrecent years (Epstein 2005, Patz et al. 2005). Weather extremes related toatmospheric and ocean warming have resulted in heat waves and extensiveflooding, and these phenomena have given a preview of what may be expectedunder full-scale global warming. In North America, weather extremes haveresulted in drought and very high temperatures, and in unusually heavyrainstorms that have caused extensive flooding. Curriero et al. (2000) havedocumented an association between extreme rainfall and waterborne diseaseoutbreaks in the United States. They showed that over 50% of the drinking-wateroutbreaks of disease in the United States were associated with rain events abovethe 90 th percentile value of total monthly precipitation. Similarly, Thomas et al.(2006) have shown that in Canada “high impact” weather events are associatedwith waterborne disease outbreaks. The association between outbreaks of diseaseand extreme rainfall events described in these studies may be a harbinger of5Similar results were obtained in a follow-up study (Evans et al. 2006).