answer:
It has been shown that having earthworms present in petroleum polluted soil will decrease the levels of these chemicals over time.
There are a number of papers that discuss the effect that earthworms have on bioremediation of soil, both in combination with other presences like compost, and alone.
Here is an abstract of one article, called "Effects of Lumbricus terrestris, Allolobophora chlorotica and Eisenia fetida on microbial community dynamics in oil-contaminated soil" From the journal Soil Biology & Biochemistry. 2005, vol. 37, no11, pp. 2065-2076 [12 page(s) (article)] (1 p.1/4)
