I'm unsure about the Weeping Figs' inclusion in the list, although I do expect NASA has considered this - but, don't Weeping Figs contain lactose, which becomes air born when dried into a dust, and isn't anaphylactic shock a potential consequence of lactose dust inhalation?
Or is it that the impact of Weeping Figs lactose content is minimal when compared to the benefits of the plant, overall - perhaps the lactose is why it is able to filter air so well, anyway?