The PNAS article is out of reach for me, but I found this: http://www.dri.edu/newsroom/news-releases/5657-lead-pollutio...
which has the graph and a little more information than the nytimes article
Wouldn't the lead levels also be affected by variations in each year's winds?
How could they assume the lead level changes are caused by Romans? They are separated by 4600 kilometers. That seems far fetched.
This was a very timely article for me, as I just yesterday finished the epic and excellent History of Rome podcast (http://thehistoryofrome.typepad.com/). I found it extremely informative, and it really shed some light on the origins of many aspects of European history, that otherwise just seem peculiar.