There is on record and now a modern study on the effect of lead poisoning upon the Nightingale family and the village of Lea. There are several symptoms in children with lead poisoning. Florence writes about this in her opening of her curriculum vitae.
Lead poisoning plays havoc with reproductive organs, etc.
None of the Nightingale women ever gave birth after the girls were born away from Lea Hurst and the lead smelter. But notice should also be taken of the hat factory in the direction of Dethick, a possible source of environmental mercury. Mercury is a deadly toxin that effects the kidney, the brain, and the nervous system. It can cause kidney damage and failure, can destroy the nervous system, and acts as a carcinogen. Perhaps the most famous fictional victim of mercury poisoning is the Mad Hatter from Alice in Wonderland.