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APPENDIX A-1.  SUMMARY OF 1998 EXTERNAL PEER REVIEW COMMENTS AND 

DISPOSITION 

The 1998 Toxicological Review for Barium (U.S. EPA, 1998c) and all individual barium 

assessments have undergone both internal peer review performed by scientists within EPA or 

other federal agencies and a more formal external peer review performed by scientists chosen by 

EPA in accordance with U.S. EPA (1994).  The three external peer reviewers (see Authors, 

Contributors, and Reviewers) submitted written comments on the overall assessment.  A 

summary of comments made by the external reviewers and EPA’s response to these comments 

follow. 

The external peer reviewers offered editorial comments and many minor, but valuable, 

suggestions; these have been incorporated into the text to the extent feasible.  Substantive 

scientific comments are addressed below.  Several reviewers provided citations of papers they 

would like to see added to the Toxicological Review; studies that supported the hazard 

identification and dose-response assessments have been incorporated into the document. 

Comment:  One reviewer felt that the potential for children to be a high-risk population was 

generally ignored. 

Response to Comment:  As discussed in Section 4.7.1 of this document, there are limited 

data with which to assess whether children are likely to be a sensitive subpopulation. 

The available data suggest that there are potential toxicokinetic differences between 

adults and young children; however, there are no data to assess potential age-related 

toxicity differences. 

Comment:  One reviewer suggested increasing the uncertainty factor for the RfD from 3 to 10. 

He felt that the increased uncertainty factor was justified to protect against potential effects in 

children and uncertainty as to the role of dietary variability.  The other two external peer 

reviewers felt that the uncertainty factor of 3 was appropriate. 

Response to Comments:  EPA concludes that the uncertainty factor of 3 should be 

retained.  The uncertainty factor of 3 was used to account for some data base deficiencies 

and a potential difference between adults and children.  It is likely that a wide range of 

dietary variability, including low calcium intakes, was represented in the Brenniman and 

Levy (1984) study population of more than 2000 adults.  The residents, aged 18-75+ 

A-1

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