In the first part of this work, a methodology for the analysis of polycyclic aromatic hydrocarbons (PAHs) in soils has been optimized and a new methodology for the analysis of their hydroxylated metabolites (OHPAHs) has been entirely developed and applied. For the analysis of PAHs, two extraction methods (Soxhlet and Microwave assisted extraction (MAE)), four clean-up methods involving column chromatography and solid phase extraction (SPE) based on different adsorbents and a final analysis with gas chromatography coupled to mass spectrometry (GC/MS) were tested. The results showed that MAE followed by SPE based on silica or by column chromatography based on alumina/silica and GC/MS analysis constituted a great methodology for PAHs analysis. It presented great sensitivity, low detection limits (DL) and quantification limits (QL) and good resolution for the analysis of the selected analytes. It has also been validated by means of a certificate reference material to ensure traceability of the experimental results. On the other hand, a new methodology was developed for the analysis of OH-PAHs, which consisted in MAE, followed by SPE based on molecularly imprinted polymers (MIPs) and the final analysis by high performance liquid chromatography coupled to fluorescence detection (HPLC/FLD). During the development of the methodology, several parameters involved in the different steps of the analysis were optimized. Different temperature and mixtures of extraction solvents were tested for MAE, the volume and nature of eluting solvents were tested for SPE MIPs and the chromatographic and detection conditions were optimized for HPLC/FLD. The new methodology was also compared with a more conventional one consisting in MAE-silylation-GC/MS as well as with other reported methodologies in the literature, showing comparable or greater sensitivity, DL, QL and reproducibility (RSD). The new methodology also presented advantages in terms of lack of interferences during the analysis as a result of the use of the highly selective clean-up by SPE MIPs, which also allowed shortening the sample pretreatment. This was the first time that MIPs technology was applied for soil clean-up purposes for the analysis of PAHs hydroxylated metabolites. In the second part of the work, an experiment to assess the effect of mixed pollutants was carried out. In particular, the influence of different concentrations of heavy metals on the degradation of some PAHs by soil bacterial communities was studied along 60 days. Among the scientific community, there are not many studies regarding the effect of mixed pollutants in real matrices, whereas the studies of their interaction are usually conducted for the isolated compounds (heavy metals or PAHs) and under in vitro conditions. To give an answer to this problem, a group of microcosms’ experiments were prepared as a reresentation of the native environment at laboratory scale, adding mixtures of PAHs and heavy metals under controlled experimental conditions. After the analyses of such microcosms were performed, results showed that the presence of heavy metals had a significant influence on PAHs biodegradation. As a general observation, higher concentrations of heavy metals led to lower biodegradation of PAHs of 3-4 rings (Phe, Fluo and Pyr). On the other hand, no important effect on biodegradation of higher molecular weight PAHs (BbF and BaP) was observed at the different levels of heavy metals. Thus, results showed that there was a significant influence of heavy metals on PAHs biodegradation as a result of the interaction of both compounds in a complex soil matrix. Finally, a hydroxylated metabolite of phenanthrene, 9-OHPhe, was detected and quantified in the same microcosms’ experiments applying the new developed methodology previously mentioned. The results seemed to indicate that the formation mechanism of 9-OHPhe in such microcosms might not be affected by the different concentrations of heavy metals.