Which of the following statements about mercury is false?
a. methyl mercury compounds are unusual in that they cannot cross the body's blood-brain barrier.
b. significant amounts of mercury are released into the environment during the smelting of other metals.
c. human exposure to mercury is primarily by eating marine animals containing high levels of mercury.
d. methyl mercury compounds are more toxic forms of mercury that readily enter the food web.
e. methyl mercury compounds persist in the environment for a long time.