Understanding thresholds for environmental hazards Hazard Conc entration
- Slides: 7
Understanding thresholds for environmental hazards Hazard Conc – - entration If we take a measurement of some hazard (say E. coli concentrations in drinking water) in the environment there are 3 measures which are important:
Understanding thresholds for environmental hazards Hazard Concentration Health effect Guideline value Baseline A guideline value (<1 E. coli / 100 ml) is set by the World Health Organisation. Drinking water contaminated with E. coli will affect health at concentrations above this guideline value. Exactly where depends on exposure from other pathways and pre-disposing factors that affect susceptibility to the disease. A variable baseline E. coli concentration occurs naturally in the river (e. g. from animal faeces). Naturally occurring E. coli may exceed the WHO guideline value and even cause health problems.
Baseline Monitoring Imagine a river which is used by a town for water supply. Town
Baseline Monitoring Imagine a river which is used by a town for water supply. Outlet pipe Town The outlet pipe from a cattle shed may pollute the town’s supply with E. coli.
Baseline Monitoring Imagine a river which is used by a town for water supply. Sample point Town Sample point The outlet pipe from a cattle shed may pollute the town’s supply with E. coli. Then we need to monitor E. coli counts above and below the discharge point.
Baseline Monitoring Imagine a river which is used by a town for water supply. Sample point Town Sample point The outlet pipe from a cattle shed may pollute the town’s supply with E. coli. Then we need to monitor E. coli counts above and below the discharge point. . . because we need to know the ambient E. coli level in the river already
Baseline Monitoring Otherwise we cannot tell how much the discharge is contributing to the level of pollutant in the river. Sample point Town Sample point