Release, Transport and Toxicity of Engineered Nanoparticles - Reviews of Environmental Contamination and Toxicology - page 22

Complete inhibition of E. coli growth was observed at 10 ʼg/mLAg NPs (Li
et al. 2010 ).AgNPsresultedinleakageofreducingsugarsandproteins,andledto
inactivation of membrane-bound enzymes, suggesting that they had the ability to
destroymembranepermeability(Table 5 ). This resulted from the potential of Ag +
ions to disturb the proton gradient across the cell membrane, ultimately causing cell
death. Moreover, AgNPs also interact with free sulphr-, oxygen- and nitrogen-
containing compounds, leading to loss of their function. At a concentration of 50 ʼg/
mL AgNPs, many pits and gaps were observed in bacterial cells as seen through
TEM(Transmissionelectronmicroscope)andSEM(Scanningelectronmicroscope)
analyses. The conclusions were that AgNPs may damage the structure of bacterial
cellmembranesandsuppresstheactivityofmembranousenzymes(Lietal. 2010 ).
Choietal.( 2010 ) conducted a differential toxicity study to determine the effects
ofnanosilver(15-21nm)onplanktonicandbioilmculturesbyusing E. coli . Silver
nanoparticle aggregation and penetration was observed after 1 h of exposure at two
bactericidal concentrations (viz., 38 and 10 mg/L) (Table 5 ) (Choi et al. 2010 ).
Similarly,Battinetal.( 2009 ) performed a surface water study of TiO 2 nanoparticles
(20and10nm)withaexposureconcentrationof5mg/L.Theaimofthestudywas
toevaluatetoxicityonplanktonicandbioilmsofthenaturalmicrobialcommunity.
Cellmembranedamagewasobservedasamajortoxiceffect(Table 5 ). Moreover,
toxic effects resulted from both individual nanoparticles and from their aggregates
(Battinetal. 2009 ).
Adamsetal.( 2006 ) reported an antibacterial effect of nano TiO 2 , SiO 2 and ZnO
water suspensions against B. subtilis and E. coli . They observed that the antibacte-
rial effects were highest for SiO 2 andlowestforZnO(SiO 2 < TiO 2 <ZnO)(Table 5 ).
B. subtilis was more susceptible to the above-mentioned nanoparticles than was E.
coli . TiO 2 showedatoxicityrangeof1,000-5,000mg/L.Thiswideresponsemay
haveresultedfromparticlesizeandlight-dependentreactiveoxygenspecies(ROS)
generation by these TiO 2 nanoparticles.BulkSiO 2 is not toxic, whereas nano SiO 2
showed toxicity at concentrations higher than that of TiO 2 and ZnO. The ZnO
nanoparticle resulted in 99% growth inhibition of B. subtilis ata10mg/Lconcentra-
tion; on the other hand, only 48% growth reduction was observed in E. coli cells at
a 1,000 mg/L concentration. SiO 2 and ZnO showed similar antibacterial effects,
eitherinlightordarkconditions,indicatingthatlightisinsigniicantinincreasing
the toxicity of these nanoparticles. Testing under dark conditions may have had
someunexplainedeffectsontoxicity(Adamsetal. 2006 ).
Gram negative triple membrane disorganization was observed with ZnO (1.4-
14 nm) nanoparticles in E. coli (Brayneretal. 2006 ). The interaction of this organ-
ism with ZnO nanoparticles revealed 100% inhibition of bacterial growth at a
concentration of 10 −2 -3.0×10 −3 M. An increase in bacterial colonies was seen at
lowerconcentrations(1.5×10 −3 and 10 −3 M) of ZnO nanoparticles. These results are
presumed to result from metabolic utilization of Zn 2+ ions as an oligoelement.
Cellular internalization and increased membrane permeability has also been
observed through transmission electron microscopy (Table 5 ). In this study, the
authors concluded that lower concentrations of ZnO nanoparticles do not cause
harmtobacterialcells(Brayneretal. 2006 ).