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Technical issues related to the ERICA Tool (on Facilia website)

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Posted: 09/08/2010

Question on

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dose conversion coefficient formula

From:
Susan Schneider
Serco
UK Marko Černe
Jožef Stefan Institute
Slovenia

Question:
In the aqueous (ie marine and freshwater) environments, I can see how the dose rates relate to fractions of time spent in-sediment and in-water, and to water and sediment concentrations (using the distribution coefficient Kd).

Looking at Tables 14 and 15 in the ERICA Help (which I realise correspond to Tier 1 assessments, and therefore have default occupancies which maximise the exposure), it looks as though time spent on the sediment surface counts as 0.5 x in-sediment and 0.5 x in-water.  And at the water surface, it counts as all in-water.

Please can you clarify in Tier 2 how ERICA uses the input occupancies (of which there are four, in-sediment, sediment-surface, in water and water-surface).

Answer:

_In Tier 2 you can select the occupancy factors to be what you want - these are used to determine the external exposure only. The dose rate at water surface will be 50 % of that in water column. The DCCs for sediment and water are the same. For sediment-water interface the dose rate is  (\[0.5*DCC_external*sediment activity concentration\]+\[0.5*DCC_external*water activity concentration\])._ _The DCCs for sediment and water are the same._ _See response posted to question (from Marko Černe) below re how occupancies are (not) used in estimatation of internal dose rate._

ERICA Tool are the all of the DCC values estimated using the same methodology or is Monte-Carlo simulation used on for terrestrial organisms?

Answer:

The key factor in the estimation of DCC is the absorbed fraction, and this is always calculated by Monte Carlo simulation using a phantom geometry. The only difference is that, historically, in FASSET, the aquatic and terrestrial formulas were calculated by two different Monte Carlo methods, but for ERICA the Ulanovsky and Proehl sphericity method was adopted for everything, after having checked that, for aquatic organisms, both methods gave very similar results.

Answered by Jordi Vives i Batlle 23/09/2010

But note for terrestrial animals a shielding factordue to fur/feathers/skin is applied in the estimation of external dose rate. This is not used for aquatic animals.

Added by Nick Beresford 24/09Answered by Nick Beresford 09/08/2010

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Posted: 09/08/2010

Question on aquatic ecosystem occupancies

From:
Susan Schneider
Serco
UK

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