Tungsten also known as wolfram is a chemical element with the chemical symbol W and atomic number 74.
Tungsten is the only metal from the third transition series that is known to occur in biomolecule, where it is used in a few species of bacteria. It is the heaviest element known to be used by any living organism. However, tungsten interferes with molybdenum and copper metabolism, and is somewhat toxic to animal life
Lead is a main-group element with the symbol Pb (from Latin: plumbum) and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metal. Metallic lead has a bluish-white color after being freshly cut, but lead soon tarnishes to a dull grayish color when exposed to air. Lead has a shiny chrome-silver luster when it is melted into a liquid.
But lead is a poisonous substance to animals. It damages the nervous system and causes brain disorders. Excessive lead also causes blood disorders in mammals. Like the element mercury another heavy metal, lead is a potent neurotoxin that accumulates both in soft tissues and the bones.
Tungsten and lead are the two most commonly used elements for cost-effective radiation shielding. Testing, both on prototypes and actual products exposed to a 120 kV X-ray source, has proven that tungsten-filled polymer products (in varying densities) provide radiation shielding and attenuation up to and including a one-to-one equivalency to lead.