MICROCOSM EXPERIMENTS FOR EVALUATING NATURAL BIOREMEDIATION OF CONTAMINATED ECOSYSTEMS

Microorganisms play a key role not only in biogeochemical cycles and ecosystem energy flow but also in maintaining ecosystem environmental quality. In fact, natural microbial communities harbour an amazing physiological versatility and catabolic potential for the breakdown of an enormous number of organic molecules, including synthetic compounds, thanks to their great adaptability to different conditions. They are able to colonize contaminated sites and metabolize some recalcitrant xenobiotics, for example pesticides and pharmaceuticals. In this way, microbial communities represent an important key to understanding the impacts of environmental and anthropogenic factors on ecosystems. Pollution may influence soil and water quality and productivity, but little is known on the effects on microbial communities, and consequent impacts on its functioning. Miniaturized ecosystems (microcosms) provide the advantage of allowing researchers to investigate under controlled conditions the effects of selective pressures, such as xenobiotic occurrence, on natural microbial communities. In this work we report the results of several microcosm studies, using natural soil and water samples, in which the environmental fate of several pesticides and pharmaceuticals in soil and water ecosystems has been evaluated. The natural attenuation capability of autochthonous microbial communities versus chemical contamination was evaluated comparing microbiologically active microcosms treated with each chemical with others previously sterilized. The degradation experiments were conducted under different natural conditions (e.g. temperature, light, humidity, etc.), including the occurrence of more stressors (e.g. co-presence of excess of nutrients or of other contaminants) in order to evaluate the fate and the effects of the chemicals in different environmental scenarios. The disappearance time of 50 % of the parent compound applied (DT50) was assessed for each chemical and condition. The overall results show the key role of microorganisms in the degradation of all chemicals studied and encourage the use of the microcosm approach for assessing more realistic environmental exposure scenarios and establishing the casual relationship between degradation and the role of microbial communities in chemical disappearance from the environment.