Public interest and newsworthiness: A scientist allegedly covering up the fact that DDT was killing birds was something the public had a strong interest in being informed of. Courts vary, however, as to how legitimate the public interest needs to be. Some require that there must be a "raging controversy" involving an issue related to the public good. Others are more lenient. Consult your individual state defamation section, but also keep in mind that judges will often look more favorably at the applicability of the privilege if there is a strong public interest in the accusation.
Wire Service Defense
If you republish a news item from a "reputable news service," you may be covered by a privilege called the "wire service defense." This defense to a defamation claim is distinct from the immunity provisions in the section 230 of the Communications Decency Act (commonly referred to as CDA 230 immunity), which may also cover if you republish content from a third-party. See the section on Publishing the Statements and Content of Others for more information.
Generally speaking, in states that recognize the wire service defense, it will apply if:
You republish a news item from a reputable news agency;
You did not know the information was false;
The news item on its face does not indicate any reason to doubt its veracity; and
You do not substantially alter the news items when republishing it.
In the Internet context, it is not clear how wide a net is cast by the term "reputable news agency." Traditional wire services such as the Associated Press and United Press International would likely be covered, but courts have not yet looked at the wire-service defense in light of RSS feeds and similar distribution tools.