Influence of xenobiotic contaminants on landfill soil microbial activity and diversity
Introduction
In Spain the most habitual practice for elimination of urban solid wastes has been its storage in municipal solid waste landfills. Although many old landfills are now sealed, these landfills continue to be potentially sources of significant environmental contamination. Moreover, the generation of contaminated leachate remains as inevitable consequence of the practice of waste disposal in landfills (Banar et al., 2006), with groundwater pollution being the most significant concern arising from leachate migration (El-Fadel et al., 1997). Degradation of the old landfill material is a slow process, lasting over 30 years.
Among the most hazardous compounds accumulated in soil and leachate, heavy metals, nitroaromatic compounds (NACs,) polycyclic aromatics (PAHs), and pesticides are the most dangerous. These compounds originated from household and industrial wastes can be found in most municipal landfills. Depending on their composition and on soil characteristics, these products may cause dramatic changes in aquifer geochemistry and landfill microbiology (Röling et al., 2001, Sastre et al., 2003).
Through knowledge of microbial community structure in polluted landfills, the capabilities of the microbial populations and their effect on the environment may be used as tools for predicting and monitoring natural degradation (Jain et al., 2005). Although bacteria capable of degrading pollutants usually play central roles in bioremediation, other organisms (i.e. fungi, protozoa and plants) can also affect the process (Demmerová et al., 2005). Techniques used to study landfill microbiology include traditional and emerging genetic molecular tools (Arias et al., 2005). The genetic diversity of microbial communities may now be monitored using profiling techniques such as denaturing gradient gel electrophoresis (DGGE). This technique allows the analysis of many samples simultaneously, and provides information relating to microbial communities. The construction of clone libraries and the sequencing of 16S rRNA gene sequences is another molecular technique frequently used to obtain phylogenetic information of the microorganisms present in a sample.
The aim of the present work was to study how the presence of different pollutants, including hydrocarbons, polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) affect the microbial activity and diversity in a municipal solid waste landfill at Torrejón de Ardoz (Madrid), Spain.
Section snippets
Municipal landfill characteristics
Samples were taken from a municipal solid waste (MSW) landfill placed in Torrejón de Ardoz (Madrid), a city located in the Spanish central region. The original landfill received urban and industrial wastes and was capped in 1982. Over the past 10 years new residues have been stored on the site, constituting solid urban, industrial and inert wastes which have not undergone any pre-treatment prior to dumping.
Soil sampling and processing
Four samples, T2 (40° 26′ 18.72″ N, 3° 28′ 30.66″ W), T2B (40° 26′ 12.60″ N, 3° 28′
Physical, chemical and biological analysis
Soil samples were collected in situ at four different zones of a solid waste landfill in which toxic compounds were detected. Organic pollutants were measured in the samples. The concentrations of total hydrocarbons, PAHs and PCBs determined in the T2, T2B, T8 and T9 soil areas are shown in Table 1. As can be observed in the table, although pollutants have been found in the four zones of the landfill, the highest values for hydrocarbons and PCBs were detected in the areas T9 (189.91 ppm and
Acknowledgments
This work has been supported by the Comunidad de Madrid EIADES project (S-0505/AMB/0296) and the CICYT project (CGL2006-12730-C03-02).
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