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