How to account for background exposure when using measured concentrations in air, food/feed or drinking water?

S-Risk FL/BRX takes into account background exposure in the risk characterization for threshold effects. For these effects, the risk is calculated using a TDI approach (see the Risk tab). Background exposures via food and drinking water are added to local oral exposure; background exposure via inhalation is added to local inhalation exposure. If you have measured concentrations, you should account for model background concentrations before entering values in S-Risk, in the following way:
 
  • Measured concentrations in outdoor or indoor air
    Subtract the background concentration used in S-Risk from the measured total air concentration. If the background concentration is higher than the measured concentration, a zero value (0) should be used as measured concentration. The chemical-specific background concentrations can be found in the substance data sheets (FL/BRX) or on the Exposure tab in the S-Risk model;
  • Measured concentrations in local food and feed
    No correction is needed. The measured value can be entered as such in S-Risk. S-Risk automatically accounts for the fraction of locally consumed food when calculating background intake from food;
  • Measured concentration in drinking water (i.e., the water that is consumed)
    If a concentration is filled in for the field “Drinking water” on the Concentrations tab, the calculated concentration in the final drinking water (i.e., the weighted average of the concentration in groundwater and supply water, whereby the weighting factor is the fraction groundwater in local consumption) is overwritten:
    • if there is no local groundwater consumption (i.e., only water from the water supply system is used):
      Subtract the background concentration used in S-Risk from the measured concentration in drinking-water. If the background concentration is higher than the measured concentration, a zero value (0) should be used as measured concentration. The chemical-specific background concentrations can be found in the substance data sheets or on the Exposure tab in the S-Risk model;
    • if there is 100% local groundwater consumption:
      In case of 100% local groundwater consumption, no correction for background is needed;
    • if there is partial local groundwater consumption:
      In case of partial local groundwater consumption, correction for background exposure is complex and is therefore approximated. It should be done for the water supply concentration and the groundwater concentration separately (as explained above). Then, the drinking water concentration should be calculated according to equation 26 in the S-Risk TGD . The chemical-specific background concentrations can be found in the substance data sheets or on the Exposure tab in the S-Risk model. The fraction local groundwater consumption is 0 by default, its value can be found on the Scenario tab.
 
In the case of non-threshold effects, background exposure is not added to local exposure. However, the above corrections are allowed as well, as the acceptable excess lifetime cancer risk is only applicable to local site contamination.
 
Overview of corrections for background exposure to be applied to measured concentrations:
Medium Correction for background exposure
Outdoor air Subtract S-Risk background concentration in outdoor air from measured value; value should be >= 0
Indoor air Subtract S-Risk background concentration in indoor air from measured value; value should be >= 0
Local food & feed Enter measured concentration without correction
Drinking water from water supply system Subtract S-Risk background concentration in drinking water from measured value; value should be >= 0
Drinking water from groundwater Enter measured concentration without correction
Drinking water partially from water supply system, partially from groundwater Approximate as explained above

 

last modified on 01/12/2016 - 09:19

FAQ Category: