Some Physiological, Microbial, and Toxicological Aspects of the Removal of Phenanthrene by Hydroponic Cultures of Alfalfa (Medicago sativaL.)

Abstract

Alfalfa (Medicago sativa L.) and other plants bearing an important root system have been shown to be effective in the removal of organic compounds, including polycyclic aromatic hydrocarbons (PAHs). Phenanthrene is one of the main contaminants arising from the petrochemical industry and is included in the USEPA's list of priority toxic pollutants. Hydroponic cultures of alfalfa were employed as a model system to evaluate their capability of removing phenanthrene and to study the plantpollutant interaction without the interference of a soil matrix. The removal of phenanthrene was followed over a period of 30 days. The half-life of phenanthrene in hydroponics (initial concentration 50 mg L -1 ) was reduced 2.7 times when plants were present. Growth index, chlorophyll content of leaves, and peroxidase activity of the roots of plants exposed to phenanthrene were lower than the corresponding values of nonexposed plants. Phenanthrene produced an acute negative effect on the total bacterial counts but also caused an increase in degraders/total bacteria ratio. The Ames Salmonella plate incorporation assay was employed to screen for potential genotoxic metabolites, which could be generated by metabolic activation of the parent compound. None of the samples exhibited a positive response. While lack of a positive response to this test is not a definitive evidence of the absence of genotoxic substances, these results suggest that the plant-assisted removal of phenanthrene merits further investigation.

Root Exudates Impact on Phenanthrene Availability

“…Indeed, rhizospheric conditions increase the microbial population and enhance its activity creating optimal degradation conditions for organic pollutant mineralization Muratova et al, 2003). Efficient degradation has been observed under hydroponic conditions (Chaîneau et al, 2000;Flocco et al, 2002) but published results obtained on real polluted soils have led to contradictory conclusions (Genney et al, 2004). In order to improve and optimize phytoremediation of PAH we propose to study the rhizospheric processes controlling PAH degradation.…”

Soil variables that determine lead accumulation in Bidens pilosa L. and Tagetes minuta L. growing in polluted soils

“…Despite phytoextraction being a method that is currently being used in many parts of the world, studies related to this are scarce in Argentina, especially those using native species for toxic metal removal (Arreghini et al, 2006;Bonfranceschi et al, 2009;Flocco et al, 2002;Salazar and Pignata, 2014;Torri et al, 2009;Zubillaga et al, 2012).…”

Lead accumulation in plants grown in polluted soils. Screening of native species for phytoremediation

“…Many of these problems, however, can be avoided if extensive knowledge is obtained regarding species selection and the establishment of optimal working conditions by considering the above factors. Despite phytoremediation being a method that is currently being used in many parts of the world, studies related to this are scarce in Argentina, especially those using native species for heavy metals removal (Arreghini et al, 2006;Bonfranceschi et al, 2009;Flocco et al, 2002;Torri et al, 2009). …”