Page History

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

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Posted: 28/05/2014
From: 
Renee Silke, Canada

Biota-sediment accumulation factors?

Question
Are there any published attempts to determine biota-sediment accumulation factors for radionuclides?

Answer:
We have not supported the biota-sediment CR given it merges together both CR(biota-water) and kd and is hence even more site specific than CR(biota-water). The on-line database (http://www.wildlifetransferdatabase.org/ ) does actually contain a relatively large number of CR(biota-sediment) values. Over >95% of these values originate from Canada from grey literature predominantly associated with U-industry related studies. However, as we have reservations about this approach (and given the data are very biased to Canadian studies) we have not summarised or presented these in the IAEA/ICRP reports or associated papers.
You could access the summarised CR(biota-sediment) (view summary results option) from the on-line database. However, these values have not been as well QC’d as the CR(biota-water) values.
See also Copplestone et al. 2013 (http://dx.doi.org/10.1016/j.jenvrad.2013.05.007).

Answered by Nick Beresford (NERC-CEH), 10/09/2013

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Posted: 28/05/2014
From: 
Zoltán Dezső, Hungary

PDFs for CR values in ERICA Tool?

Question
In the documentations concerning the derivation of CR values used in the ERICA Tools (e.g Hosseini et al., 2008; Beresford et al., 2008) it is written that "where a mean and a standard deviation could be determined from the raw data being used to derive the parameter, a lognormal distribution was applied". However, in my opinion, the means and SDs given are not the geometrical ones but the arithmetical ones.
To our knowledge, the statistical description of lognormal distributions requires the use of geometrical means and GSD. For example, in case of uranium CR of trees in terrestrial environment, in the ERICA Tool the following is given: lognormal(0.006794210843500887,0.014144979928509134,0.0,Infinity), based on 521 data entries. In the IAEA Wildlife Transfer Database, for the same 521 data entries the above data are given as AM and ASD as well as a geometrical mean of 0.002929 kg/kg with geometrical SD of 3.654965.
Our questions are:
1. In case of lognormal distributions the GM gives the most probable value of the distribution and it is usually lower than the AM. Does the ERICA Tools calculate/estimate the geometrical mean based on the AM and ASD given? Furthermore, does it apply as the most probable value?
2. Similarly, in case of Tier 3 calculations, does the ERICA Tools calculate/estimate the GSD based on the AM and ASD given? Does it apply during the probability propagation calculations correctly?

Answer:
The mean and SD given in ERICA are arithmetic (not geometric) and these values are used as the inputs for assumed lognormal distributions. There may be additional information in the 'D-ERICA' report - available from https://wiki.ceh.ac.uk/x/swbbBg
Thorne, 2013 (http://dx.doi.org/10.1088/0952-4746/33/2/N1) discusses AM v's GM application in screening assessments.
See also Avila et al. 2014 (J. Radiol. Prot. 34, 261-262) (http://dx.doi.org/10.1088/0952-4746/34/1/L01) for comment on Thorne (added 26/05/2014)

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Question
In ERICA-Tool the help file documentation states that aquatic organisms have a minimum size of 1E-6 kg when calculating DCCs, but the Reference Phytoplankton has a mass of 1E-12 kg. Is it somehow possible to use the smaller reference value, or is the minimum mass upheld during assessment?

Answer:
If you select one of the default reference organisms then the DCCs should be for the mass as defined in Table 9 of the help file (i.e. 2.05E-12 kg for freshwater phytoplankton). The restrictions on size relate to organisms you can create.

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Question:
I am running an assessment using the ERICA tool, and am looking to create site-specific  organisms in  ERICA Tool. At present there appears no way to model organisms that live in trees or generally above the ground (external dose approximately equal to IN AIR). For example bats, or epiphytic lichens in trees.
Do you have any suggestions for how best to model these habitats?
One possible method would be to classify the specimen as “bird and flying insect”, but would this be acceptable?

Answer:
Yes I think this is acceptable however, you might have a problem with the limitations on sizes which can be created for organisms in air – 35 g to 2 kg.  Most/all bat species in the UK have a mass below this.  There is a limited evaluation of the impact on estimated dose for organisms outside this mass range .... select help from the ‘add organism’ screen and it should take you to correct place in the help file. Otherwise you probably need to also acknowledge that you are assuming no contribution to dose from the tree.

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Answer:
We had noticed this for a few radionuclides although there has been no subsequent discussion.
For instance the Am-241 EMCL is considerably below the WHO Guidance Level of 1 Bq/l (although the WHO GL for U-238 is 10 Bq/l).
There are also some ‘oddities’ between drinking water GLs and the concentration in water which would produce human food which would not be allowed into the foodchain, e.g. at 10 Bq/l of Cs (the WHO GL) the concentration in fish would be 25,000 Bq/kg.
Drinking water standards are obviously set to limit the dose to humans from the consumption of water (for the WHO values aim seems to be to restrict dose to <0.1mSv/a via drinking water). In the case of wildlife then the organisms are permanently in water and potentially getting a dose from sediment (which may be the largest component of dose to the most exposed organism depending upon the radionuclide).
That said we are aware that some of the ERICA EMCLs are unrealistically low, there are a few freshwater ones which are below natural background concentrations. Some of this is probably due to the pdf assigned to the sediment-water distribution coefficient (another example you’ve already come across is the prevalence of lichen as a limiting organism in terrestrial ecosystems).

Answered by Nick Beresford (CEH) and David Copplestone (Stirling University) 2/03/2012

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Dose rate equation

Question:
I am looking for the dose rate equation used by ERICA which takes into account the media. For instance, for the aquatic organism, I expect that the calculated dose rate should look something like this:

D= DCC(ext, water) [OF(water)+ 0.5xOF(water surface)+ 0.5xOF(sediment surface)]xC(water) + [OF(sediment)+ 0.5xOF(sediment surface)]xC(sediment).

However, I have not been able to find any documentation that supports this.
Furthermore, are the DCCs for water and sediment the same? Sediment is denser than water, so I expected that different DCCs should be used.

Answer:
Your equation is the correct representation of the calculation of total EXTERNAL dose rate (for the total dose rate then obviously need to include internal exposure). This does not appear to be in documentation although equations for individual elements of dose (e.g. external from sediment at the sediment interface etc.), including internal dose rate estimation, are presented in the Help file and Brown et al. 2008 paper.
You are also correct in that typical wet sediment densities tend to be greater than those for water but this difference isn't normally huge especially where the porosity, and therefore the water content, is high. In some cases you may get a factor of 2 to 3 difference between wet sediment and water but in view of all the other uncertainties this is fairly minor. For sake of simplicity using the same DCC for water and sediment isn't such a poor approximation and it gets around the problem of having to decide on an arbitrary reference density for wet sediment.

Answered by Justin Brown (NRPA, Norway) and Nick Beresford (CEH) 24/02/2012

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Double counting contribution from daughters

Question:
Seeing as the DCCs that are calculated include progeny with half-lives less than 10 days, does that mean that if I included a radionuclide with a half-life of less than 10 days in my assessment, that its contribution will be double counted?

Answer:
Simple answer is yes if you did this you would double account (this is discussed a little in Vives i Batlle et al. 2007 and Beresford et al. 2010) But if you are using the ERICA Tool (and I think the same is true of RESRAD-BIOTA, which uses a longer cut-off time than 10 d) this should not occur with the default radionuclide list. It would if, for instance, you were considering U-235 and added Th-231 to the radionuclide list (using the ‘add isotope’ option in Tier 2 or 3) as Th-231 will already be included in the U-235 DCC.

Answered by Nick Beresford 24/02/2012

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Question:
How can we best use CR (transfer) values from the marine ecosystem for the freshwater ecosystem if we do not have freshwater data?

Answer:
This was an approach used to provide some default CR values within the original parametrisation of the ERICA Tool. However, it is not one we would recommend. There are perhaps more intelligent ways the available data could be used, e.g. are ratios between CR values for given elements or organisms in marine and freshwater similar? The Wildlife transfer Database contains data for estuarine/brackish water ecosystems in addition to freshwater and marine, these may provide a better surrogate CR value for other aquatic ecosystems. However, this needs to be investigated before we would recommend such an approach.

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From:
Maria Sotiropoulou
Demokritos
Greece

Question:
How can I upload my own database?
Probably I do something wrong, because when I create my database excel file, I can see it in the Parameters Database, but I cannot choose it.
To be more specific. If I create my own DCC database and I want to compare these values, how can I do it? The only way I have found is through “My ERICA Database” files, where I change each time the DCC.xls file (that has been created in the user file). Is this the only way? Can I do this process while the tool is running,so I don’t have to create each time the same simulation?

Answer:
You can see the DCC values by selecting Database and then Parameter Database from most screens within the ERICA Tool.
If you use the Tool to create DCC values for new organisms or new radionuclides you will also see these. The DCCs in the database are broken down into radiation type and exposure route.
You can view and export the DCC values to Excel.
If you are suggesting editing the DCC database (i.e. the Excel file within “My ERICA Database”) we do not recommend this as it can lead to problems of traceability when you conduct future assessments.
If you have DCC values generated outside of the Tool, which you want to compare with those in the Tool, then why not do this in Excel? If you do not want the ERICA DCCs split into radiation type you can generate an 'overall' DCC by running the Tool. For instance, for the external DCC for soil you would input a value of 1 Bq/kg in soil and input 0 as the activity concentration in your organism(s), to determine the internal DCC input 1 Bq/kg as the organism activity concentration and 0 as the soil, water or sediment activity concentration, etc..

Answered by Nick Beresford 10/02/2011

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From:
Hildegarde Vandenhove
SCK•CEN
Belgium

Question:
Can you calculate Environmental Media Concentration Limits (EMCL) values as used in the ERICA Tool?

Answer:
You can estimate EMCL values using Tier 3 of the ERICA Tool. You need CR values with associated probability distribution functions (pdfs) for the radionuclide you are interested in (and kd values together with associated pdfs if considering an aquatic ecosystem). You need to make predictions for all reference organism assuming 1 Bq per unit media concentration; note for aquatic ecosystems you need to determine both a water and sediment EMCL separately. The EMCL is calculated by dividing your screening level dose rate (10 μGy/h default in the ERICA Tool) by the 95th percentile dose rate to the most exposed organism (i.e. the highest 95th percentile dose rate for any reference organism) assuming 1 Bq per unit media concentration.

The process of determining the EMCL using Tier 3 of the ERICA Tool is as follows:

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More infomation can be found in the ERICA Tool help file and Brown, J.E., Alfonso, B., Avila, R., Beresford, N.A., Copplestone, D., Pröhl, G., Ulanovsky A. et al. 2008. The ERICA Tool. J. Environ. Radioact., 99, 1371-1383 (http://dx.doi.org/10.1016/j.jenvrad.2008.01.008).

Answered by Cath Barnett 31/01/2011 Amended 16/04/2012

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From:
Marko Černe
Jožef Stefan Institute
Slovenia

Question:
RESRAD-BIOTA calculates the dose to biota separately from water and sediment? In ERICA we can not distinguish between sediment and water dose rates. It would be an option just to run ERICA separately for water and separately for sediment, but it is still not possible due to sediment calculation using default Kd? Is RESRAD-BIOTA more appropriate for such purpose?

Answer:
RESRAD-BIOTA does report the external dose rate from sediment (Levels 2 and 3). The ERICA Tool reports a combined external dose rate. However, you can determine the external dose rate from sediment in the ERICA Tool. To do this enter the water activity concentrations as 0. If you do this the reported dose rates will be the external dose rate from exposure to sediment only. Similarly if you want to estimate the external dose rate from water only, enter the sediment activity concentration as 0.

Answered by Nick Beresford 17/12/2010

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