Effects of pesticides and pharmaceuticals on soil and water bacterial communities

Studying soil and water ecosystems using a microbial ecology approach, which analyses the diversity and functioning of microbial communities, can help in evaluating the impact of environmental stressors, such as xenobiotics. In fact, soil and water microorganisms play an important role in maintaining ecosystem environmental quality. For instance, the ability of soil and water to recover from chemical contamination is primarily dependent on the presence of a microbial community with the ability to remove it. Furthermore the microbial community characteristics of an ecosystem can indicate changes in resource availability and the presence of pollution. In this way, the microbial community represents an important key to understanding the impacts of environmental and anthropogenic factors on ecosystems. This thesis focuses on two groups of xenobiotics frequently detected in soil and water: pesticides and pharmaceuticals. The effects of s-triazine and phenylurea herbicides (terbuthylazine, simazine and linuron) and pharmaceuticals (such as the antiviral drug Tamiflu and two macrolide antibiotics, erythromycin and josamycin) on microbial communities in soil, surface and groundwater were studied. The researches was carried out utilizing innovative molecular techniques in order to identify the natural microbial populations involved in the chemical degradation and evaluate the direct and indirect effects of the herbicides and pharmaceuticals on the microbial community structure and functioning. For this purpose several investigations involving the selected chemicals in soil and water ecosystems were carried out: - Research activity regarding s-triazine groundwater contamination caused by diffuse sources. Although the groundwater was considered to have been without life for a long period and unable to recover from herbicide contamination, the experiments performed showed the presence of an autochthonous bacterial community able to degrade the herbicide terbuthylazine. Moreover some bacterial strains such as Janthinobacterium lividum, Advenella incenata and Rhodococcus wratislaviensis, with the capability of growing on various s-triazines were isolated. Among the three isolates, Rhodococcus wratislaviensis was also capable of mineralising the triazine-ring. Finally, an oligonucleotide probe was designed to detect this strain in soil and water samples by applying the in situ fluorescence hybridization technique. This probe can be very useful for monitoring the presence of active R. wratislaviensis populations with the potential to degrade s-triazines in contaminated aquifers and agricultural soils. The research activity was accomplished thanks to active cooperation between IRSA-CNR in Rome and Madrid Complutense University. - Research activity regarding soil herbicide contamination caused by point sources. The experiments aimed at evaluating the effects of the co-presence of herbicides (linuron and terbuthylazine) and wood amendments on soil bacterial communities. These amendments have recently been proposed for their adsorption capacity, which prevents the mobility of pesticides caused by point sources of contamination. The herbicide degradation and the microbial activity in the presence/absence of pine and oak amendments were assessed and compared. The amendments did not negatively affect bacterial community functioning in terms of dehydrogenase activity. The use of wood amendments can thus be effective in limiting the mobility of herbicides in soils. However the capacity of pine-amended soils to adsorb linuron and terbuthylazine was so high that it hampered herbicide degradation and this should be taken into account since it can modify the persistence of these herbicides. This research was performed by IRSA-CNR together with Spanish CSIC. - Research on the assessment of the effects of pharmaceutical waste disposal on bacterial communities in soil and groundwater. The research regarded an open quarry contaminated by pharmaceutical residuals (erythromycin and josamycin) owing to its previous improper use for disposal of pharmaceutical waste by a factory producing macrolide antibiotics. The microbiological community characteristics (bacterial abundance, diversity, viability and activity), proposed as microbial indicators, together with chemical investigations of soil and groundwater samples, made it possible to evaluate the quality state of the site. - Research on the effects of the antiviral drug Tamiflu (recommended for the treatment of cases of avian and swine influenza) on the bacterial community of a surface ecosystem. The role of the bacterial community in the antiviral degradation was demonstrated in microcosm experiments and some bacterial groups, analyzed by fluorescence in situ hybridization, were found to increase in number when there was a halving of the pharmaceutical. This research was performed by IRSA-CNR together with Bologna University. - Research on variations in bacterial community structure in soil, surface water and groundwater in the presence of herbicides (terbuthylazine, simazine and linuron) or pharmaceuticals (Tamiflu). The research shows that fluorescence in situ hybridization was a useful tool for following the dynamics of individual microbial populations in the ecosystems considered and highlighted the presence of particular groups presumably involved in chemical degradation.