|As an overarching concern, Cameco notes with some concern that the large majority of the transfer factors are derived values and question the utility of finalizing the report, given the current level of research. This draft report has highlighted many data gaps, and consequently, Cameco respectfully requests that the ICRP consider deferring publication until more transfer factors can be based upon actual values.
In the event that the ICRP proceeds to finalize the report without further research, we have included our general and specific comments below:
1. Sediment and benthic invertebrates as exposure pathways in the aquatic environment were not included and could be an essential pathway. Benthic invertebrates are a large group and food source for higher trophic levels that is missing from the aquatic exposure pathway. Benthic invertebrates are routinely monitored to measure aquatic habitat health and thus are an important group to include as an exposure pathway. Consider including the pathways analysis.
2. Only exposure from water and soil are accounted for with regard to derived transfer factors. Consider including trophic transfer of radionuclides in deriving the transfer factors.
3. Consider including a description of the data used to derive the transfer factors.
4. The majority of transfer factors that are presented for the Reference Animal and Plants terrestrial and aquatic groups are derived values from similar species, similar parameters, and predictions (e.g., review data, models, dietary data, and expert judgment) rather than based on actual data for the particular transfer factor. This calls into question the validity of the derived concentration ratios and applicability to real world scenarios for the elements of interest discussed in the report. Readers should be cautioned regarding the utility of the report given the limited data available.
5. It would be beneficial for the report to validate the transfer factors for at least a few of the parameters to provide some reasonable context to the applicability of the values to the real world, or, at minimum, discuss the differences between the derived transfer factors and reasons for such differences.
6. More discussion in the report on factors that could modify uptake should be included. This would include effects of mixtures and total dose from all sources on concentration ratios, implications of use of non-gut purged (whole-body concentration including stomach contents) whole-body concentrations on concentration ratios, use of bioavailable soil/sediment concentrations in place of total soil/sediment concentrations for some elements in regard to plant uptake, potential differences in transfer factors when exposure is elevated above reference conditions (may not be the same relationship; some species may be tolerant), and the connection between concentration ratios and potential effects on organisms (if a link can be made).
Line 234 - Expand and explain the meaning of “geochemical phase association”. Some readers may not be familiar with the use of the term “phases” associated with sediments and soils.
Line 345 - Consider revising “External exposure” to “Habitat exposure” as this is what is discussed in this point.
Paragraph 28 - This paragraph indicates that exposure pathway (ii) is not considered explicitly and that inhalation and ingestion of water may be indirectly included in transfer factors. Consider providing information on how the data used to derive transfer factors only includes these pathways and not ingestion of food sources and habitat exposure.
Paragraph 33 - Reference to Table 1.1 should be placed after “… selected” otherwise it appears as if the table is referring to the Reference Animal and Plants.
Line 445 - “Reference” should likely be replaced with “referenced”. In addition, consider explaining the value in comparing site-specific values with the reference values presented and describe what the reference values represent.
Line 533 - Explain why fresh weight (or otherwise commonly referred to as wet weight) is used rather than dry weight.
Line 857 - Elaborate on how the data was checked for quality control prior to entry into the wildlife transfer database.
Paragraph 59 - Describe the data that is included in the database (e.g., Laboratory experiments or field exposure data? Where is the data from (location, countries)? How many parameters and species (or families)? What abiotic metrics were used? Were any bioavailable fractions or phases used (soil or sediment pore water, single or sequential extraction information)? Is the data representative of reference, low, or high exposures?).
Table 3.1 - Consider excluding life stages because the values are not derived for specific life stages.
Table 3.2 - Consider removing the reference to subcategories or provide explanation as to why subcategories are required.
Line 899 - Revise to indicate that transfer to various organs/body parts is a secondary consideration because whole-body concentration ratios are primarily considered.
Paragraph 64 - State whether the datasets were from the field or laboratory.
Lines 934-936 - Elaborate on the implications to the database and resulting values from using unfiltered water and unknown soil depths. Consider the variability in soil particle size and organic carbon content associated with the data (e.g., are they skewed more to a singe type/content or evenly distributed?).
Paragraph 67 - Include a justification of the assumptions made when a lack of information in source publications was encountered, as it appears arbitrary to assign values when there is a clear lack of information. Explain where these assumptions have been used for datasets lacking primary information. In addition, the potential consequences in using the outlined assumptions should be provided, as they may grossly skew the derived values.
Line 990 - Clarify what is meant by “robust statistical analyses”.
Lines 1001-1002 - Explain why the specific activity approach is used for aquatic ecosystems rather than the data review approach. Is this other approach used in this report? If so, please outline the methods used.
Lines 1004-1040 - In Section 3.3.2, include a brief discussion on the implications of surrogate CR values to fill data gaps. Users of the derived CR values should be aware of the limitations of the values that are based on surrogate values.
Lines 1013-1015 - Explain how the “subcategory” differs from the wildlife group.
Line 1024 - Explain whether some modeling approaches are more appropriate for deriving CRs than others and whether some approaches are unacceptable.
Lines 1042-1055 - Consider removing Section 3.3.3, as it refers to and discusses information presented in Section 4. Alternatively, this section could refer instead to the concentration ratio derivation processes (e.g., derivation of baseline values (and what baseline values mean and how it is different from extracted concentration ratios) and how they may differ from what was explained previously could be included).
Line 1089 - Explain what is meant by “internal exposures” (e.g., does this mean “body burden” or “tissue concentrations”?).
Lines 1095-1098 - Environmental media may also include many modifying factors (e.g., sediment/soil composition, water quality, air quality). Consider including discussion regarding such modifying factors in this section.
Line 1103 - Consider using “exposure” instead of “contamination” in this sentence.
Line 1141 - Clarify that all concentration ratios are derived because they are calculated values and that the grey values represent values that utilized some form of surrogate value due to the lack of data.
Lines 1174-1177 - Some may disagree with this statement that “Reference Grass” fits well with the CR approach due to the uptake from the dissolved phase in pore waters. Clarify whether bioavailable fractions (the dissolved phase in pore waters) are used as the exposure measurement or if the more likely measurement of total soil concentration is used. The consideration of modifying factors and that the plant likely takes up only a portion of the total soil concentration are also worthy of consideration.
Line 1188 - Consider replacing “incorporated” with “trapped”.
Line 1195 - Consider the applicability of the term “body concentration”. Body concentration may include the stomach contents of the earthworm, which likely would influence the concentration measured. Tissue concentration may be more appropriate, as it would be assumed to free of the stomach content (from a gut purge).
Paragraph 88 - Consider suggesting the use of the relationship between the bee and the plant, which may be more relevant than the bee to soil relationship. This could be calculated pending appropriate plant (and bee) data.
Line 1244 - Consider using “derivation” instead of “application”, as the concentration ratios are “derived” based on data and “applied” to estimate concentrations in animals/plants.
Paragraph 99 - The principles of adsorption of radionuclides to the surface of eggs or larvae are likely to apply to freshwater organisms as well (e.g., fish and frog). Consider including in the freshwater section.
Paragraph 101 - Elaborate on how the set of rules to derive concentration ratios for life stages should or should not be applied in site-specific scenarios and the implications of utilizing life stage specific values.
Lines 1366-1368 - Include supporting data or rationale.
Line 1452 - Include an additional paragraph in Section 4.7 regarding the caveats of applying the presented values to real world situations and how the presented values can be compared to site-specific values (including examples) to aid the reader in the appropriate use of the values.
Line 1469 - Consider revising “derivation” to “application”.
Line 1473 - Describe what is meant by “internally consistent”.
Paragraph 116 - Since sediments and benthic invertebrates are not generally considered in the concentration ratios presented in the report, consider adding to this paragraph how concentration ratios for sediment exposure to benthic invertebrates could be derived on a site-specific basis. As well, include the potential importance of this measure in aquatic ecosystems for such parameters as selenium and that benthic invertebrates are a food source to higher trophic levels.