Potential of the soil microbial biomass C to tolerate and degrade persistent organic pollutants

A 12-day incubation experiment with the addition of glucose to soils contaminated with persistent organic pollutants (POPs) was carried out in order to estimate the potential microbial activities and the potential of the soil microbial biomass C to degrade 1,1,1-trichloro-2,2-bis(p-chlorophenyl) ethane (DDT), polychlorinated biphenyls (PCB) and polycyclic aromatic hydrocarbons (PAHs). The microbial activities were affected in different ways depending on the type of pollutant. The soil organic matter also played an important role. The microbial activities were affected particularly by high concentrations of PAHs in the soils. Soil microorganisms in the PAHs contaminated soil used the added glucose to a lesser extent than in the non-contaminated soil, which in the contaminated soil resulted in a higher microbial biomass content during the first day of incubation. DDT, DDD and DDE, and PCB affected the soil microbial activities differently and, in comparison with control soils, decreased the microbial biomass C during the incubation. The increased microbial activities led to a significant decrease of PAH up to 44.6% in the soil long-term contaminated with PAHs, and up to 14% in the control soil after 12 days of incubation. No decrease of PAHs concentrations was observed in the soil which was previously amended with sewage sludges containing PAHs and had more organic matter from the sewage sludges. DDT and its derivates DDD and DDE decreased by about 10%, whereas the PCB contents were not affected at all by microbial activities. Studies on the microbial degradation of POPs could be useful for the development of methods focused on the remediation of the contaminated sites. An increase of soil microbial activities caused by addition of organic substrates can contribute to the degradation of pollutants in some soils. However, in situ biodegradation may be limited because of a complex set of environmental conditions, particularly of the soil organic matter. The degradability and availability of POPs for the soil microorganisms has to be estimated individually for each contaminated site.