Efficiency of Opuntia ficus in the phytoremediation of a soil contaminated with used motor oil and lead,compared to that of Lolium perenne and Aloe barbadensis

Industrial pollutants such as heavy metals and hydrocarbons in soils represent a serious concern due to their persistence and negative effects on the environment, affecting cellular processes in living organisms and even causing mutations and cancer. The main objectives of this work were to evaluate the efficiency of Opuntia ficus in the phytoremediation of a soil polluted with used motor oil. Two other species, one with different and one with similar characteristics, relatively, were used for comparison purposes: Lolium perenne and Aloe barbadensis. The effect of the plants on lead solubility and bioaccumulation, the biomass production of each specie and the microbial counts and bacterial identification for each experiment was studied. Total petroleum hydrocarbons (TPH) were measured every 5 weeks throughout the 20-week phytoremediation experiment. At the end of the experiment soluble Pb, Pb extracted by the plant species, microbiological counts, total biomass and bacterial species in soil were analyzed. Even though Lolium perenne showed the highest TPH removal (47%), Opuntia ficus produced the highest biomass and similar removal (46%). Since Opuntia ficus requires low amounts of water and grows fast, it would be a suitable option in the remediation of soils polluted with hydrocarbons and/or heavy metals.     

Mineralization of 14C-labelled maize in alkaline saline soils

The turnover of organic material determines the availability of plant nutrients in unfertilized soils, and this applies particularly to the alkaline saline soil of the former Lake Texcoco in Mexico. Uniformly labelled [¹⁴C] maize and its neutral detergent fibre (NDF) fraction, mainly containing cellulose and hemi-cellulose, were added to these soils to investigate dynamics of C and N and the importance of the NDF fraction. Soil with electrolytic conductivity (EC) of 1.2, 3.2, 24.6 and 32.7 dS m^–1 was incubated aerobically, while CO₂ and ¹⁴CO₂ production, and inorganic N dynamics (NH₄ ⁺, NO₂ ^–, NO₃ ^–) were monitored. The amount of ¹⁴C-labelled maize mineralized after 97 days was >500 mg C kg^–1 dry soil (D.S.) of the 1000 mg C kg^–1 D.S. added in soils with EC 24.6 dS m^–1, but only 257 mg C kg^–1 D.S. in soil with EC 32.7 dS m^–1. The decomposition of the NDF fraction showed a lag, greatest in the soil with the largest EC and the amount of ¹⁴C-labelled NDF fraction mineralized after 97 days was > 300 mg C kg^–1 D.S. in soils with EC 3.2 dS m^–1, but in the soil with EC 32.7 dS m^–1 it was only 118 mg C kg^–1D.S. Application of ¹⁴C-labelled maize and the NDF fraction induced a priming effect, most accentuated at the onset of the incubation. The ratio between the amount of CO₂ produced due to the priming effect and the ¹⁴CO₂ produced was 16-times larger when 250 mg maize-C kg^–1 D.S. was added and only 3-times when 2000 mg maize-C kg^–1 D.S. was added. Oxidation of NO₂ ^– occurred in soil with EC 32.7 dS m^–1 as witnessed by decreases in concentration of NO₂ ^– and increases in concentration of NO₃ ^–. It was found that EC affected the decomposition of maize, the NDF fraction and the priming effect. Decomposition of cellulose and oxidation of NO₂ ^– occurred in soil with EC 32.7 dS m^–1 although cellulolytic micro-organisms and autotrophic NO₂ ^– oxidizers could previously not be isolated from this soil.