DN6

DN6 was a pesticide developed in the early 1960s by Smithers to end famine. Arnold Farrow discovered that it worked so effectively that, if used, widely it would have caused serious harm to Earth's ecology. Forester, who had heavily invested in DN6, murdered Farrow to cover up his findings. His crimes were exposed thanks to the secret help of the Doctor and his companions, but not before Barbara Wright was briefly poisoned by DN6. (DW: Planet of Giants)