‘The final Agent Orange raid in Vietnam took place in 1970;... areas have begun to bloom again. But 19 years after the war’s end, it seems plain that Agent Orange is killing and maiming human beings, something it never intended to do. The apparent toxic fall out 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 the above quotation is

The passage refers to Agent Orange, the US military defoliant used in Vietnam whose primary formulation was a 1:1 mixture of the herbicides 2,4‑D and 2,4,5‑T. Industrial production of 2,4,5‑T was contaminated with the highly toxic dioxin 2,3,7,8‑TCDD, and this dioxin contamination has been linked to cancers, miscarriages and birth defects in exposed populations. Major defoliation missions with Agent Orange ended around 1970, and the health fallout described in the quote matches the known effects of dioxin‑contaminated defoliants rather than DDT or malaria insecticide programs [2].

Sources

1. [1] https://www.nal.usda.gov/sites/default/files/agent-orange/05245.pdf
2. [2] https://www.ncbi.nlm.nih.gov/books/NBK594243/