Noun
dieldrin (countable and uncountable, plural dieldrins)
(organic chemistry) A cyclodiene insecticide, related to aldrin, that is a persistent organic pollutant.
Coordinate terms: aldrin, endrin
Aldrin has been recovered after four years, both as traces and, more abundantly, as converted to dieldrin. Source: Internet
In any event, aldrin is slightly more toxic than dieldrin. Source: Internet