Characterizing Rhizodegradation of the Insecticide Bifenthrin in Two Soil Types

Rhizodegradation is a process by which plant-supplied substrates stimulate microbial populations in plant root zones (rhizospheres) to cause removal of undesirable levels of contaminants in soil. This study characterized rhizodegradation of the insecticide bifenthrin in Armour silt loam and Sullivan fine sandy loam soils that were planted with switchgrass, big bluestem, and alfalfa. After six weeks in soils, plate dilution frequency assays (PDFA) of bacterial populations were higher in all planted soils than in unplanted ones. Planted Sullivan soils contained higher bacteria than corresponding Armour soils and alfalfa rhizospheres of both soil types contained highest bacteria. Bacterial populations generally increased between week 6 and week 10, before declining in each treatment at week 12. Carbon utilization patterns (CUP) of bacterial communities, measured as color development on BIOLOG plates, were higher in planted soils than in unplanted ones. Principal Component Analysis (PCA) constructed patterns based on different extents of color development;these patterns were used to relate microbial communities in the different treatments. Gas chromatography (GC-ECD) showed that significantly more bifenthrin dissipated in planted soils than unplanted ones. Different levels of bifenthrin were recovered in planted soils but the differences were generally not significant. Data are being evaluated further to provide a basis for the development of strategies for enhancing rhizodegradation of soils contaminated with bifenthrin.

Phytoremediation of Soil Contaminated with Crude Oil Using Mucuna Bracteata

This study examines the ability of Mucuna bracteata DC. to remediate soil contaminated with increasing levels of crude oil up to 20%. It also investigates the effect of fertilizer application on crude oil degradation. Changes in crude oil concentrations, pH and moisture of the soil in eight experimental pots were tracked over a period of 9 weeks. The crude oil levels in soil were analysed as Total Petroleum Hydrocarbons (TPHs) using the UV-Vis spectrophotometer. The study revealed the capacity of Mucuna bracteata to phytoremediate soil contaminated with crude oil in all experimental pots though the plant died at 20% contamination towards the end of the experiment. The plant survived up to 15% contamination with that in the fertilized pot showing better physiological conditions. In all instances, fertilized pots showed higher rates of crude oil reduction. The amounts of crude oil degraded in fertilized pots were also higher except at 20% contamination. The soil pH varied over a narrow range throughout the experimental period. Moisture of soil contaminated with 15% and 20% crude oil was higher than that contaminated with 5% and 10% crude oil. Mucuna bracteata showed signs of phytoextraction which can be subject to further study. This study contributed a new candidate of phytoremediation for soil contaminated with high level of crude oil.