Remobilization of toxic heavy metals adsorbed to bacterial wall-clay composites

Abstract

Significant quantities of Ag(I), Cu(II), and Cr(III) were bound to isolated Bacillus subtilis 168 walls, Escherichia coli K-12 envelopes, kaolinite and smectite clays, and the corresponding organic material-clay aggregates (1:1, wt/wt). These sorbed metals were leached with HNO3, Ca(NO3)2, EDTA, fulvic acid, and lysozyme at several concentrations over 48 h at room temperature. The remobilization of the sorbed metals depended on the physical properties of the organic and clay surfaces and on the character and concentration of the leaching agents. In general, the order of remobilization of metals was Cr < Ag < Cu. Cr was very stable in the wall, clay, and composite systems; pH 3.0, 500 ,uM EDTA, 120-ppm [mg liter-'] fulvic acid, and 160-ppm Ca remobilized less than 32% (wt/wt) of sorbed Cr. Ag (45 to 87%) and Cu (up to 100%) were readily removed by these agents. Although each leaching agent was effective at mobilizing certain metals, elevated Ca or acidic pH produced the greatest overall mobility. The organic chelators were less effective. Lysozyme digestion of Bacillus walls remobilized Cu from walls and Cu-wall-kaolinite composites, but Ag, Cr, and smectite partially inhibited enzyme activity, and the metals remained insoluble. The extent of metal remobilization was not always dependent on increasing concentrations of leaching agents; for example, Ag mobility decreased with some clays and some composites treated with high fulvic acid, EDTA, and lysozyme concentrations. Sometimes the organic material-clay composites reacted in a manner distinctly different from that of their individual counterparts; e.g., 25% less Cu was remobilized from wall-and envelope-smectite composites than from walls, envelopes, or smectite individually in 500 ,uM EDTA. Alternatively, treatment with 160-ppm Ca removed 1.5 to 10 times more Ag from envelope-kaolinite composites than from the individual components. The particle size of the deposited metal may account for some of the stability changes; those metals that formed large, compact aggregates (Cr and Ag) as seen by transmission electron microscopy were less likely to be remobilized. In summary, it is apparent that remobilization of toxic heavy metals in sediments, soils, and the vadose zone is a complicated issue. Predictions based on single inorganic or organic component systems are too simplistic.

Interactions of chromium with microorganisms and plants

“…CrO 23 4 ) and thus cannot be trapped by the anionic components of bacterial envelopes [26]. However, cationic Cr(III) derivatives bind tightly to Salmonella lipopolysaccharides [27], Bacillus subtilis and E. coli cell walls [28], and capsular polymers of Bacillus licheniformis [29].…”

Antimicrobial and mechanical properties of acrylic resins with incorporated silver–zinc zeolite – part I

“…Antimicrobial cations, such as silver and zinc, may be lodged within the void spaces of the zeolites and be exchanged over time with other cations from their environment 14,[20][21][22] . As this ion availability occurs, the free cations come into contact with the environmental microorganisms, suppressing their development by inactivating vital microbial enzymes, interrupting RNA replication and blocking their respiration by an oxidative process [23][24][25][26][27][28][29][30][31] . The efficacy of antimicrobial zeolites against aerobic and anaerobic bacteria and fungi has been demonstrated 20,24,32,33 .…”

Undesirable Effects of Some Topical Antiseptics Chemical, pharmacological and dermatological aspects

“…Silver nitrate is a widely used antiseptic also used in different concentrations for cauterizing and wound healing properties. AgNO 3 Silver ion reacts with the thiol group in vital enzymes and inactivates them [38,39] or interacts with DNA, resulting in marked enhancement of pyrimidine dimerization by photodynamic reaction and possible prevention of DNA replication [39][40][41]. Structural changes in the cell envelope and the presence of some small electron-dense granules formed with silver and sulfur have also been demonstrated in bacterial [42,43].…”