112
catalase, and peroxidase but increment in urease activity of soil containing titanium
oxide nanoparticles. In contrast, Chai et al. (2015) reported that nano-titanium oxide
decreased urease activity. The multiple exposure effect of titanium oxide was also
evaluated on microbial nitrifying communities by Simonin et al. (2016). Authors
found that titanium oxide nanomaterials affected the diversity of ammoniumoxidizing bacterial communities and negative impact on nitrification enzymes.
Cai et al. (2014) found that titanium oxide declined the nitrogen fixation and
methane oxidation by disrupting the gene expression of bacteria but increased the
organic material degrading microbial community population. Ge et al. (2012)
reported that soil protease activity was found significantly enhanced with the exposure of titanium oxide and zinc oxide nanoparticles due to increase in extracellular
protease production by Streptomycetaceae and Streptomyces class bacteria.
4.5.5 Zinc Oxide Nanoparticles
Zinc oxide nanoparticles have shown their wide application in remediation of pollutant due to photocatalytic activity. Zinc oxide nanoparticles have been applied in
different products like paints, plastic, ceramics, glass, cement, rubber, lubricants,
pigments, batteries sunscreen creams, and cosmetics. The total volume of zinc oxide
nanoparticles is increasing in the environment due to the use of these products
(Daughton and Ternes 1999). Zinc is present in the dissolution form (Zn
2+
) or zinc
oxide and in the agglomerated form in the soil or water (Wu et al. 2010). A detailed
review on the toxicity of zinc oxide has been covered by Ma et al. (2013). Zinc
oxide nanoparticles showed inconsistency in toxicity concentration toward E. coli
with same size of particles. The zinc oxide nanoparticles in ultrapure water with
20 nm size showed inhibitory concentration (IC 50 ) less than 0.1 ppm to E. coli,
whereas similar size (10–30 nm) zinc oxide nanoparticles in media showed IC 50
500 mg.l
−1
to wild E. coli (Li et al. 2011; Premanathan et al. 2011). 100% inhibition
of E. coli has been reported by 10–70 nm particle size zinc oxide nanoparticle
(Brayner et al. 2006; Jiang et al. 2009 and Liu et al. 2009).
The coating on nanoparticles also affected the toxicity of nanoparticles. It has
been reported that zinc oxide showed less toxicity in the presence of tannic acid in
comparison to alginic, fulvic, and humic acid (Li et al. 2010). They reported that the
presence of organic acid reduced the bioavailability of free Zn
2+
ions in surround
matrix. Further, Li et al. (2011) proved that the presence of free Zn
2+
is mainly
responsible for their toxicity by experimentation of different media types. Ge et al.
(2011) found that zinc oxide nanoparticles decrease the microbial biomass and soil
bacterial diversity and significantly change the soil enzymes activity. In addition to
bacteria, zinc oxide nanoparticles also showed toxicity to yeast. In the short-term
experiment, Kasemets et al. (2009) found that within 24 h exposure, 30–70 nm sized
zinc oxide nanoparticles showed more toxicity in comparison to bulk zinc oxide to
the yeast Saccharomyces cerevisiae with EC 50 of 131 and 158 ppm. While, Lipovsky
et al. (2011) found only 1 ppm zinc oxide nanoparticles inhibited 95% growth of
H. Chhipa
catalase, and peroxidase but increment in urease activity of soil containing titanium
oxide nanoparticles. In contrast, Chai et al. (2015) reported that nano-titanium oxide
decreased urease activity. The multiple exposure effect of titanium oxide was also
evaluated on microbial nitrifying communities by Simonin et al. (2016). Authors
found that titanium oxide nanomaterials affected the diversity of ammoniumoxidizing bacterial communities and negative impact on nitrification enzymes.
Cai et al. (2014) found that titanium oxide declined the nitrogen fixation and
methane oxidation by disrupting the gene expression of bacteria but increased the
organic material degrading microbial community population. Ge et al. (2012)
reported that soil protease activity was found significantly enhanced with the exposure of titanium oxide and zinc oxide nanoparticles due to increase in extracellular
protease production by Streptomycetaceae and Streptomyces class bacteria.
4.5.5 Zinc Oxide Nanoparticles
Zinc oxide nanoparticles have shown their wide application in remediation of pollutant due to photocatalytic activity. Zinc oxide nanoparticles have been applied in
different products like paints, plastic, ceramics, glass, cement, rubber, lubricants,
pigments, batteries sunscreen creams, and cosmetics. The total volume of zinc oxide
nanoparticles is increasing in the environment due to the use of these products
(Daughton and Ternes 1999). Zinc is present in the dissolution form (Zn
2+
) or zinc
oxide and in the agglomerated form in the soil or water (Wu et al. 2010). A detailed
review on the toxicity of zinc oxide has been covered by Ma et al. (2013). Zinc
oxide nanoparticles showed inconsistency in toxicity concentration toward E. coli
with same size of particles. The zinc oxide nanoparticles in ultrapure water with
20 nm size showed inhibitory concentration (IC 50 ) less than 0.1 ppm to E. coli,
whereas similar size (10–30 nm) zinc oxide nanoparticles in media showed IC 50
500 mg.l
−1
to wild E. coli (Li et al. 2011; Premanathan et al. 2011). 100% inhibition
of E. coli has been reported by 10–70 nm particle size zinc oxide nanoparticle
(Brayner et al. 2006; Jiang et al. 2009 and Liu et al. 2009).
The coating on nanoparticles also affected the toxicity of nanoparticles. It has
been reported that zinc oxide showed less toxicity in the presence of tannic acid in
comparison to alginic, fulvic, and humic acid (Li et al. 2010). They reported that the
presence of organic acid reduced the bioavailability of free Zn
2+
ions in surround
matrix. Further, Li et al. (2011) proved that the presence of free Zn
2+
is mainly
responsible for their toxicity by experimentation of different media types. Ge et al.
(2011) found that zinc oxide nanoparticles decrease the microbial biomass and soil
bacterial diversity and significantly change the soil enzymes activity. In addition to
bacteria, zinc oxide nanoparticles also showed toxicity to yeast. In the short-term
experiment, Kasemets et al. (2009) found that within 24 h exposure, 30–70 nm sized
zinc oxide nanoparticles showed more toxicity in comparison to bulk zinc oxide to
the yeast Saccharomyces cerevisiae with EC 50 of 131 and 158 ppm. While, Lipovsky
et al. (2011) found only 1 ppm zinc oxide nanoparticles inhibited 95% growth of
H. Chhipa