Google may use the data for their own purposes as well - like search ratings. I would not know.
If you have concerns, you should ask Google.com
I am using Disquis as a service that facilitates comments and discussions on an otherwise static site. Comments and related information such as identity of the commenter does get retained and is public - that is the point. I will not share any extra data besides what is publicly available through the comments.
Disquis could collect more data related to the comments than available on this site. If you are concerned about how Disquis uses the data related to comments, you should contact Disquis.com
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