Many heavy metals increase the apparent toxicity of low levels of mercury.
Mercury toxicity: Genetic susceptibility and synergistic effects
B.E. Haley. Medical Veritas, 2 (2005) 535–542.
This article discusses mercury intoxication and several normally appearing factors that increase the susceptibility to mercury toxicity. Boys with autism represent a subset of the population that is more susceptible to the toxic effects of mercury and thimerosal because they are not efficient excretors of these toxic materials. Research confirms that a lead toxic person would be more susceptible to mercury toxicity than a healthy, non-toxic person researchers routinely observed that many heavy metals increase the apparent toxicity of low levels of mercury. In other words, the synergistic effects of other heavy metals, diet, antibiotics, etc. on mercury toxicity make it impossible to define a “safe level of mercury exposure.”