Mercury fundamentals

1a. Which of the following forms of mercury has the longest residence time in the atmosphere? Circle exactly one answer

(A) Hg⁰
(B) Hg²⁺
(C) Hg_p (That is, mercury absorbed on particulate matter.)
(D) MeHg

Answer: (A) or (C)

1b. Human exposure to mercury primarily occurs from which of the following forms? Circle exactly one answer.

(A) Hg⁰
(B) Hg²⁺
(C) Hg_p (That is, mercury absorbed on particulate matter.)
(D) MeHg

2. Why do the vaccines given to young children in developing countries still contain mercury, given all that we know about the effects of mercury on the developing human brain? (1 paragraph answer)