PAH DECREASE IN SOIL SAMPLES FROM DIFFERE NT POLLUTED INDUSTRIAL SITES BY ACTIVATING THE AUTOCHTHONOUS MICROFLORA

In: pot experiments under field conditions the-PAM decrease in ten dif ferent soil samples from former industrial sites with:differing PAH. l oad were investigated over a period of:74 and 168 weeks,:15 but of 16. PAH according to OS EPA; (without acenaphthylene) were determined. Ea sily degradable organic matter, mineral fertilizers, synthetic surfact ants and in some experiments also lime were added to the soil samples in varying amounts. Depending on the nature and quantity of the amendm ents,the biological activity and: (co-)metabolic decomposition of PAH by: soil. microorganisms could considerably be increased. In the diffe rent soil samples a decrease of the initial PAH contents between 12 an d 90% was achieved within 74 weeks. Even from 74 up to 168 weeks for s ome soil samples a remarkable further decrease of the PAH contents cou ld be observed. The decrease bf the extractable PAH with lime is mainl y caused by microbial decomposition and formation of nonextractable re sidues. This behavior can befitted by two coupled exponential function s, one for an initial phase of rapid decomposition and the other for a :subsequent phase of slow decomposition Therefore two different proces ses (I, II) determine the decrease df PAH. In the first week of the ex periment the decomposition rates for process:I amount-to 4,2-88,3 and for process II to 9,06-5,3 mg PAH . kg(-1) soil . week(-1); in the 168 th week they are no longer determinable for process I and amount to 0, 05-2,3 mg . kg(-1) . week(-1) for process II. Higher initial PAH conte nts often led to higher relative PAH decreases, but also to absolute h igher contents of residues. The persistence of PAH is mainly determine d by their bioavailability. PAH degradation is increased by the soil t reatments. The addition of easily degradable organic matter (C/N ratio < 20).in a quantity of 30g . kg(-1) (w/w) combined with the addition of nitrate and-a;surfactant most effectively increased the degradation of PAH; Raising the pH of a very strongly acidic:soil Sample revealed a maximum PAH decomposition at a pH of 6.