An increasing number of pesticides have been used in agriculture for protecting the crops from pests, weeds, and diseases but as much as 80 to 90% of applied pesticides hit non-target vegetation and stay as pesticide residue in the environment which is potentially a grave risk to the agricultural ecosystem. This review gives an overview of the pollution in agricultural soils by pesticides, and the remediation techniques for pesticide-contaminated soils. Currently, the remediation techniques involve physical, chemical, and biological remediation as well as combined ways for the removal of contaminants. The microbial functions in rhizosphere including gene analysis tools are fields in remediation of pesticide-contaminated soil which has generated a lot of interest lately. However, most of those studies were done in greenhouses; more research work should be done in the field conditions for proper evaluation of the efficiency of the proposed techniques. Long-term monitoring and evaluation of in situ remediation techniques should also be done in order to assess their long-term sustainability and practical applications in the field.
Raya (Brassica juncea) and spinach (Spinacia oleracea), grown as leafy vegetables, are known to accumulate large amounts of heavy metals in their shoots and roots because of their high biomass and root proliferation. In a pot experiment, a sandy loam soil was polluted with cadmium (Cd) at rates of 0, 5, 10, 20, 40 and 80 mg kg−1 soil to assess the accumulation pattern and its effect on the dry matter yield and mineral composition of these vegetables. There was a decrease in dry matter yield due to the phytotoxic effect of Cd. The rate of Cd application at which a significant decline in root and shoot dry matter yield occurred varied depending on the vegetable. It was 20 mg Cd kg−1 soil in the shoots for both crops. However, the roots of raya were found to be more tolerant of Cd toxicity than those of spinach, as is evident from the fact that a significant decline in dry matter yield occurred at 20 and 10 mg Cd kg−1 soil, respectively. Since no visual toxic symptoms were observed on the leaves of raya in any of the treatments, it is clear that the metal may accumulate in this vegetable without visual evidence of its presence. However, at application levels beyond 40 mg kg−1 soil, toxicity symptoms, in the form of interveinal chlorosis of the leaf lamina followed by necrosis and leaf rolling, were clearly evident in the case of spinach. The reduction in root and shoot growth corresponded with the amounts of extractable Cd in the soils. The total content of Cd in the crops increased gradually as the rate of applied Cd rose and the roots accumulated much higher amounts than the shoots. The relationship of Cd with Zn and Fe was synergistic in both roots and shoots at the lower rates, but antagonistic at higher Cd application rates for both the crops, while in the case of Mn and Cu, the relationship was negative and antagonistic.
Several million metric tons of mining wastes, called stamp sands, were generated in the Upper Peninsula of Michigan during extensive copper (Cu) mining activities in the past. These materials, containing large amounts of Cu, were discharged into various offshoots of Lake Superior. Due to evidences of Cu toxicity on aquatic organisms, in due course, the materials were dredged and dumped on lake shores, thus converting these areas into vast, fallow lands. Erosion of these Cu-contaminated stamp sands back to the lakes is severely affecting aquatic life. A lack of uniform vegetation cover on stamp sands is facilitating this erosion. Understanding the fact that unless the stamp sands are fertilized to the point of sustaining vegetation growth, the problem with erosion and water quality degradation will continue, amending the stamp sands with locally available biosolids and composts, was considered. The purpose of the reported study was to assess potential effects of such organic fertilizer amendments on soil quality. As the first step of a combined laboratory and greenhouse study, a 2-month-long incubation experiment was performed to investigate the effects of biosolids and compost addition on the soil nutrient profile of stamp sands and organic matter content. Results showed that both biosolids and compost amendments resulted in significant increase in nitrogen and phosphorus concentrations and organic matter contents of stamp sands. Sequential extraction data demonstrated that Cu was mostly present as bound forms in stamp sands, and there was no significant increase in the plant available fraction of Cu because of fertilizer application.
Copper mining in the Upper Peninsula of Michigan in the mid-19th century generated millions of tons of mining waste, called stamp sand, which was deposited into various offshoots of Lake Superior. The toxic stamp sand converted the area into barren, fallow land. Without a vegetative cover, stamp sand has been eroding into the lakes, adversely affecting aquatic life. Our objective was to perform a greenhouse study, to grow cold-tolerant oilseed crops camelina (Camelina sativa) and field pennycress (Thlaspi arvense) on stamp sand, for the dual purpose of biofuel production and providing a vegetative cover, thereby decreasing erosion. Camelina and field pennycress were grown on stamp sands in columns, using compost to supply nutrients. A greenhouse study in wooden panels was also done to evaluate the effectiveness of camelina in reducing erosion. Results show that camelina significantly reduced erosion and can also be used commercially for generating biodiesel. A 25-fold reduction in Cu content in the surface run-off was observed in the panels with camelina compared to those of the control. Stamp sand-grown camelina seeds contained 20% and 22.7% oil and protein respectively, and their fatty acid composition was similar to previous studies performed on uncontaminated soils.
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