The final Agent Orange raid in Vietnam took place in 1970. The apparent toxic fallout from those clouds is a crop of human miseries including cancers, miscarriages and birth defects that may persist for decades. The offensive substance referred to in this quotation is:

Answer: (d) Dioxin used as defoliants

Agent Orange was a herbicide mix (2,4-D and 2,4,5-T) contaminated with dioxin (TCDD). The dioxin caused the cancers and birth defects.

The idea

Agent Orange was a plant-killer, sprayed from aircraft to strip the leaves off forests so that soldiers could not hide under them. The herbicide itself was not the main poison. During manufacture it was contaminated with dioxin, one of the most toxic man-made chemicals, and dioxin breaks down very slowly.

Herbicide mix sprayed over forests → Leaves fall (defoliation) → Dioxin in the mix settles in soil and water → Enters fish and people → Cancers and birth defects for decades

Why the others are wrong

(a) DDT is an insecticide; Agent Orange was sprayed on forests, not insects.

(b) It was a military defoliant to strip jungle cover, not an aid-programme farm input.

(c) It was not for malaria control.

The trap

(b) sounds half-right because Agent Orange WAS a herbicide mix — but the harm came from its dioxin, and it was used to defoliate, not to grow crops.

Also know

The name came from the orange stripe on the storage drums. Dioxins also form when plastic (PVC) and waste are burnt and when paper is bleached with chlorine. They are listed under the Stockholm Convention as pollutants produced unintentionally.