Cumulative Risk Assessment & Joint Toxicity: Mercury Vapor, Methyl Mercury & Lead.
Mark Richardson PhD. 2010

Concurrent exposure to Pb, MeHg and Hg0 does occur in the US population. A large proportion
- 1/3rd - of the US population is concurrently exposed to Hg0, methyl Hg and Pb on a daily basis.
All of these substances share the following characteristics:

• All are absorbed in large proportion into systemic circulation;
• All cross the blood-brain and placental barriers;
• All cause neurological toxicity;
• Exposure to all of these substances currently exceed individual reference exposure
levels for many in the US population.

85.7 million Americans currently exceed the California EPA’s reference blood Pb level of 1 ug
Pb per deciliter of blood (1 ug/dL or 10 ug/L). For Hg0, 101.5 million Americans currently
exceed the urine Hg concentration associated with the reference exposure level of 0.06 ug/m3
recently developed in Canada. For methyl Hg, 1.8 million Americans exceed the reference
blood level of 8 ug/L established in Canada for protection or neurological outcomes, particularly
relating to neurodevelopmental effects in the fetus.
The weight of available evidence suggests that risks posed by concurrent exposure to combinations of these 3 substances should be assessed as additive.