Why would there be zero studies that study lead and have source data? What happened to those that studied lead - did they destroy their data for some reason? Are the data about lead somehow unique so that, unlike any other data, they can't be published? Did some weird catastrophe occur which erased all data regarding to lead studies, and nobody knows about it? What would be the reason that basic scientific norms would not be preserved in this case? I guess if it happened, we'd need to conduct new studies - and find people who screwed up the old ones and make sure they are not responsible for any new studies ever again, to avoid future screwups.