Not that I'm aware of. Under DPA, you are allowed to retain information that is required in order for you to carry out your business. Within a blog context, retaining names and email addresses would (I imagine) be considered an integral part of operating an effective commenting/discussion system. You should also bear in mind that your visitors are not required to give you their real names and they can use a disposable email address. So it is questionable whether any of the data that you do retain could be used to identify any one specific individual.
As long as you do not use the retained data for anything else (such as mass emailing), you should be fine.