A recent NYU report estimates the loss in productivity in low and middle-income countries due to the neurological effects of childhood lead exposure and its resulting impact on productivity. The authors, Teresa Attina and Leonardo Trasande, write:
We estimate a total cost of $977 billions of international dollars in low and middleincome countries, with economic losses equal to $134.7 billion in Africa (4.03% of GDP), $142.3 in Latin America and the Caribbean (2.04% of GDP), and $699.9 in Asia (1.88% of GDP).
That's equivalent to about 1.2 percent of global GDP.
The estimate focuses only on IQ loss , so is probably on the low end since it doesn't take into account the increased crime rates and cardiovascular problems also associated with childhood lead exposure.
The good news is that children's blood lead levels are down overall worldwide since the removal of lead from gasoline, though as Scientific American notes, worldwide lead consumption is actually up, driven largely by the demand for batteries.