Abstract
Two species of radishes, Raphanus sativus and Raphanus raphanistrum, were grown in the laboratory in the same substrate consisting of a smectite-type clay, which was watered at the beginning of the experience with 50 ml of a solution containing either none or 1000, 2000 or 4000 mg/L of AgNO3, respectively. Occurrence of the toxic metal in the substrate outlines higher element uptakes by the cultivated species Raphanus sativus than by the wild species Raphanus raphanistrum, except for the highest degree of Ag pollution. After a one-month growth in the Ag-polluted substrate, Raphanus sativus was depleted in most of the major, trace and rare-earth elements, except for Al, Fe, Th, Ag and U that increased in the radishes from substrate polluted by 2000 mg/L of AgNO3, and Sr, Co, Ni, U and Ag that increased in the radishes from substrate polluted by 4000 mg/L of AgNO3. Raphanus raphanistrum was enriched in all elements except Si, Na, Rb and K in the polluted substrate. The uptake was monitored by a cation-exchange process in the rhy-zosphere between mineral particles and the watering solution in the presence of various enzymes with specific activities that induced a variable uptake with the REEs being even fractionated. These activities most probably depend on combined factors, such as the plant species, and the chemical and physical properties of the substrate. The results obtained here reveal also that accumulation of nutrient elements and others in the plants is not uniform at a given Ag pollution of the substrate and therefore at a given Ag contamination in the same plant species.
Highlights
The main anthropogenic source of heavy metals is presently in the metallurgic activities that often produce punctual elevated concentrations relative to the natural background [1]
R. sativus incorporates 9.8 times more Ag than R. raphanistrum when grown in the unpolluted substrate, 3.2 times more Ag when grown in the substrate polluted by 1000 mg/L AgNO3, 4.2 times more Ag when grown in the substrate polluted by 2000 mg/L, and 3 times less Ag when grown in the most polluted substrate at 4000 mg/L (Table 1)
The highest Ag uptake was by the cultivated Raphanus sativus, the highest “contamination” in the plant occurred at the addition of 2000 mg/L AgNO3 to the substrate and, surprisingly, the lowest plant contamination occurred at an addition of the highest AgNO3 pollution at 4000 mg/L
Summary
The main anthropogenic source of heavy metals is presently in the metallurgic activities that often produce punctual elevated concentrations relative to the natural background [1]. Heavymetal accumulation raises important questions about their potential impact on the soil mineral and organic components, as well as on their uptake by plants that are grown on metal-polluted soils and are potentially consumed by humans. They exert toxic effects in soils by contributing to biochemical reactions with the organisms, the typical responses being growth inhibition, suppression of oxygen consumption and impairments of the reproduction cycle. Many laboratory studies have been published in the recent decades to determine the response of microorganisms to contaminants released into soils by human activity, e.g., [2,3,4]. Many of these studies were focused on the inhibitory effect including the reduction of the number, amount and activity of the microorganims, e.g., [5,6], as well as on the significant reduction of the microbial activity, its diversity and structure [7,8,9,10,11,12]
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