Involvement of Fenton reaction in DDT degradation by brown-rot fungi

In this study, the ability of the brown-rot fungi (BRF) Fomitopsis pinicola and Daedalea dickinsii to degrade DDT (1,1,1-trichloro-2,2-bis (4-chlorophenyl) ethane) was investigated. F. pinicola and D. dickinsii degraded approximately 63% and 47% of total DDT in potato dextrose broth (PDB) medium, respectively. Degradation of DDT by D. dickinsii resulted in several metabolic products; DDD (1,1-dichloro-2,2-bis (4-chlorophenyl) ethane), DDE (1,1-dichloro-2,2-bis (4-chlorophenyl) ethylene), and DDMU (1-chloro-2,2-bis (4-chlorophenyl) ethylene), whereas degradation by F. pinicola produced only one metabolic product, DDD. Investigation was done to find out whether the Fenton reaction was involved in the degradation process. More DDT was degraded in medium lacking FeSO4 than in that containing FeSO4, suggesting that these fungi lack the benzoquinone-driven Fenton reaction cycle system. In addition, F. pinicola and D. dickinsii produced only very low levels of hydroxyl radicals (1.2 and 5.1 μM, respectively), which provides further evidence that these fungi lack the Fenton reaction cycle system. The addition of mannitol as a hydroxyl radical scavenger did not inhibit DDT degradation. Hydroxyl radical production increased when the medium was supplemented with Fe2+. Higher levels of hydroxyl radicals enhanced DDT degradation by D. dickinsii, but not by F. pinicola. These results indicate that F. pinicola and D. dickinsii have different mechanisms for degrading DDT from that reported for the BRF Gloeophyllum trabeum, in which the Fenton reaction is an important factor in DDT degradation.