For the most part, the information about toxic chemicals that appears on the Eco-USA site comes from the initial summary chapters of the much more detailed full-text toxicological profiles issued by the awkwardly-named yet wonderful United States Agency for Toxics Substances and Disease Registry (ATSDR). Current toxicological profiles are available on their website.
When I launched Eco-USA's predecessor back in 1996, ATSDR did not have their toxicological profiles posted on the web, or if they did, I could not find them. I decided the information was important enough that I typed up the initial summary chapters for several dozen chemicals and posted them. I believe that marked their initial appearance on the web.
In general, the excerpted material consists of text beginning with Section 1.1 of the ATSDR profiles and includes most the first chapter of each. I omitted the first few introductory paragraphs, which differ little from profile to profile; references to other chapters of the larger document; and general information not specifically related to the compound(s) in question (for example, justifications of animal testing, or discussion of the differences between regulations and recommendations).
While I've made every effort to excerpt this material accurately and in a manner which preserves the original meaning, there is no substitute for the original document. Also, please keep in mind that some of these profiles are rather old, and that the information in them may have been superseded or contradicted by more recent research.