How does S-Risk deal with concentrations exceeding solubility?

S-Risk deals with concentrations exceeding solubility in different ways, depending whether it relates to a soil or groundwater contamination.

It should be noted that in case of very high concentrations, approaching solubility, attention should be paid to the presence of non-aqueous phase liquids. You should consult applicable guidance documents in your region on how to deal with non-aqueous phase liquids in site assessment.

Soil concentrations

When you enter a soil concentration for an organic pollutant, S-Risk will limit the calculated concentration in soil pore water to the solubility of the chemical. You can find this value on the Chemical tab and in the substance data sheets. The concentration in soil pore water is used for the calculation of leaching to groundwater (if a groundwater concentration is not entered), volatilization to outdoor and indoor air, permeation through drinking water pipes and plant uptake (depending upon the type of plant uptake calculations). As S-Risk is not designed to calculate mobility of non-aqueous phase liquids in soil, limiting the pore water concentration to solubility is a conservative approach with regard to human health risk assessment, in most cases. The water solubility of chemicals in pure product (mixtures) is at maximum equal to the solubility of the chemical (assuming ideal behaviour). Keep in mind that permeation through drinking water pipes is potentially underestimated.

Groundwater concentrations

When you enter a groundwater concentration for an organic pollutant, S-Risk will generate a warning message if the entered concentration exceeds the solubility of the chemical:

Solubility warning dialog

The solubility value can be found on the Chemical tab and in the substance data sheets. You will, however, be able to continue data entry and run the calculations. S-Risk will use the filled-in groundwater concentration for further transfer (volatilization to outdoor and indoor air, permeation through drinking water pipes) and direct exposure (direct consumption of  groundwater as drinking water if selected as an exposure pathway, consumption of groundwater by animals if applicable) calculations. Using a groundwater concentration exceeding the solubility value will result in an overestimation of the soil air concentration and thus, in an overprediction of the transfer to outdoor and indoor air.

If inhalation from outdoor and/or indoor air are the only exposure pathways for groundwater, the solubility limit can be entered as groundwater concentration in a Tier 1 assessment. However, you should be aware that groundwater concentrations exceeding solubility point to a need for further evaluation of the data on groundwater quality in view of overall site assessment (not limited to human health risk assessment). 

last modified on 25/11/2015 - 13:40

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