2. Risk calculation

2.1 Threshold effects

Threshold risks to human health are estimated by comparing actual or likely exposure levels at a given site with acceptable concentrations. This is done by calculating a ratio (risk index) between the estimated TDI exposure and the acceptable exposure. This approach is based on the existence of a threshold dose for threshold substances, i.e. a dose below which effects do not occur or have never been observed.

The equation can be written as IR = Ci / RfC, where :

• IR: risk index ;

• Ci: calculated average inhalation concentration (mg/m ³ ) ;

• RfC: chronic non-carcinogenic reference...