Enhancing the mineralization of [U-14C]dibenzo-p-dioxin in three different soils by addition of organic substrate or inoculation with white-rot fungi

The potential for aerobic mineralization of [U-14C]dibenzo-p-dioxin (DD) was investigated in samples of three different agricultural soils already contaminated with polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) by industrial activities. The influence of amendments, i.e. wheat straw and compost, and of soil treatment by inoculation with lignolytic fungi, grown on wheat straw substrate, was tested. All the soils tested contained an indigenous DD-mineralizing microflora. The soil characterized by the highest organic matter content and the highest content of soil microbial biomass displayed the best DD mineralization of 36.6% within 70 days, compared with the two organic-matter-poor soils with an endogenous DD mineralization of 19.5% and 23.3% respectively. Amendments with compost increased DD mineralization up to 28% in both soils with low organic matter and microbial biomass content, but did not affect mineralization in the organic-matter-rich soil. Addition of wheat straw had no constant influence on DD mineralization in the soils tested. The best DD mineralization resulted from inoculation with lignolytic white-rot fungi (Phanerochaete chrysosporium, Pleurotus sp. Florida, Dichomitus squalens) and with an unidentified lignolytic fungus, which was isolated originally from a long-term PCDD/F-contaminated soil. A mineralization of up to 50% within 70 days was reached by this treatment. The influence of inoculated fungi on mineralization differed between the soils investigated.