CHARACTERISTICS OF PAHS INTRINSIC DEGRADATION IN TWO COKE FACTORY SOILS

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are the most commonly found pollutants in former coke site grounds. These organic pollutants are particularly a concern because of their possible toxic, carcinogenic or mutagenic properties. Biodegradation is one possible pathway for PAHs elimination from soils. This study aims to evaluate intrinsic degradation potential of PAHs in soils taken from two former coke sites, differing by their contamination levels and by their physico-chemical characteristics (organic carbon and metal contents).PAHs biodegradation kinetics as observed in both soil types distinguishes between two steps: a first step showing a rapid but short PAHs abiotic degradation, followed by a second step which is characterized by a much slower PAHs decrease pattern, progressively smoothing along time. These patterns lead to a significant decrease in the bulk PAHs content of 35% and 46% respectively for site 1 and site 2 soils after 12 months. In this experiment, PAHs degradation seems to be altered neither by the conditions of the medium (availability of carbon, phosphorus, nitrogen, moisture, oxygen …), nor by any decrease in bacterial degrading activity, but rather by lack of PAHs' bioavailability and recalcitrance of some degradation products. If the occurrence of metals and organic carbon does not alter the bulk yield of PAHs' degradation, it does modify the degradation pattern, insofar as bacterial processes seem to need longer to set when metals and organic carbon are present in higher amounts.