Abstract
The aim of this research was to evaluate the impact of chromium (III) nitrate on soil microbial activities and growth performance and phytoremediation potentials of two staple leguminous crops, namely cowpea (Vigna unguiculata) and groundnut (Arachis hypogea). Pristine sandy loam soil samples were polluted with nitrate salts of chromium (III) at four different levels (50, 100, 200 and 400 mg/kg) in triplicates. There was a significant (P < 0.05) retarding effect of this metal on the study parameters. A consistent decrease in the total bacterial count in response to increase in dosage of the metal salt was observed. Chromium was also observed to significantly (P<0.05) affect the microbial metabolism as indicated by the decline in microbial respiration shown by the lowering of CO2 evolution in the test samples. There was a reduction in the general growth performance of the two test plants treated with different levels of chromium when compared with the control. Phytoaccumulation experiment showed that only cowpea roots accumulated the pollutant from the 400 mg/kg treated soil, with no metal salt presence in aerial parts of the plants. This chromium-removal potential demonstrated by cowpea makes it a better candidate than groundnut for the phytoremediation of chromium-contaminated soils. Key words: Chromium (III) nitrate, microbial activities, cowpea, groundnut, phytoremediation.
Highlights
Chromium (Cr) is one of the naturally occurring elements found in rocks, soils, and in volcanic dust and gases
In both control and 50 mg/kg treated soil, all the cowpea seeds sown in each pot germinated whereas in the other levels, there was a concomitant reduction in the number of germinated seeds as the dose increased
This work has brought the following to limelight: (1) The retardative effects of chromium (III) on soil microbial population and metabolism
Summary
Chromium (Cr) is one of the naturally occurring elements found in rocks, soils, and in volcanic dust and gases. It occurs in two main forms in the environment, namely, chromium (III) and chromium (VI). Chromium is a toxic non-essential metal for microorganisms and plants. Chromium (III) may react with carboxyl and sulfhydryl groups of enzymes causing alterations in their structure and activities. It modifies DNA polymerase and other enzyme activities as a result of the displacement of magnesium ions by chromium ions (Snow, 1994)
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