"Overexposure - Health Hazards in Photography" Susan D Shaw & Monona Rossol Allworth Press New York ISBN 0-9607118-6-4
They don't cover back pains from hulking heavy cameras about, but for all chemistry issues they are thorough.
Possibly one of the most important photography books I've bought -- after sticking my bare paws into hydroquinone based developers long enough to gain a temporary rash. I never contemplated putting selenium in the kitchen sink, however!
Regards - Ross