We tend to use 'about' for either a situation or a person. "I am really concerned about Lyn - she is facing tremendous difficulties." "I'm very concerned about the situation." We use 'for' to reference a person. "I am concerned for Lin. She is really ill." But it is really odd to be concerned 'for' a situation. To be concerned 'about' is more impersonal. To be concerned 'for' is to express the personal, emotional aspect. Subtle difference.