How to interpret the results of the risk table of application II (RI, ExCR, pRI and CI values)?

Application II reports the results of the risk assessment under the form of a table, giving risk values for – potentially – three major groups of effects (threshold, non-threshold and pseudo-threshold). A further distinction is made between systemic and local effects.

The toxicological information on the chemical determines which types of effect are considered. If a certain type of effect is not relevant for the chemical, the field(s) in the report for that type of effect will be empty. The risk metric to be retained for risk decisions and the cut-off value (value above which one should decide that there is a human health risk) for each risk metric is given in the table below.

Type of effect Risk metric Cut-off value
(Flemish soil remediation Decree)
Threshold
Systemic Highest RItotal of the reported age groups RI = 1
Local Highest RI (oral or inhalation) of the reported age groups RI = 1
Non-threshold
Systemic ExCRtotal for lifetime exposure ExCR = 1x10-5
Local ExCR (oral or inhalation) for lifetime exposure ExCR = 1x10-5
Pseudo-threshold
Systemic pRItotal for lifetime exposure pRI = 1
Local pRI (oral or inhalation) for lifetime exposure pRI = 1

The risk indices (RI or pRI) and the excess cancer risk values (ExCR) are based on the calculated exposure to the contamination. While calculating this exposure, S-Risk takes into account all scenario details (land use, time expenditure, …) the user has entered. Calculated exposures are then divided by their toxicological threshold values to obtain the final (p)RI values or are multiplied by the unit risk/slope factor to obtain the ExCR values.

Application II also reports concentration indices (CI). This is the case if legal limits or toxicological reference values are available for the environmental compartment under consideration (water, air, food products). The cut-off value for CI results is set at 1.

CI values are calculated by comparing the chemical concentration in a specific environmental compartment with the concentration limit for that compartment. These limit values do not take into account any scenario details the user has entered, and often suppose a full-time exposure of 24 hours/day, 365 days/year. This may or may not correspond to the real site scenario. Concluding:

  • A (p)RI value > 1 or an ExCR > 1×10-5 represents a risk;
  • A CI value > 1 may or may not imply a risk, depending on the exposure conditions or the type of limit value used for calculating the CI.

The way these results are further interpreted with regard to site remediation or management depends upon the procedures available in your region. For Flanders, further guidance is given in the procedures for risk assessment and detailed site investigation.

last modified on 10/06/2015 - 17:00

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