20.2.4 Microbial and Ecotoxicological Assessment of Both
Pilot Test Phases
In both studies, Němeček et al. (2014 and 2015), the authors also provided detailed
microbial and ecotoxicological assessment of the whole 21-month period of the pilot
test duration. Using standard approaches such as microbial cultivation tests and
inhibition of bioluminescence of Vibrio fischeri, the authors assessed the possible
ecotoxicological impact of nZVI. The impact on autochthonous microbial population was also monitored by phospholipid fatty acid analysis (PLFA) and 16S rRNA
454 pyrosequencing. Overall, the authors did not observe any negative effect on the
microbial population in the groundwater after the nZVI application and even growth
stimulation of Gram-positive bacteria was observed in the soil samples using PLFA.
Notwithstanding the acute toxicity of nZVI detected during the in vitro tests
(Semerád et al. 2018), the lack of negative or less pronounced toxic effect during in
situ application corresponds with the findings of several other authors (Semerád and
Cajthaml 2016). Bacterial stimulation was probably caused by the elimination of
highly toxic Cr(VI) from the aquifer and thus by the decrease of overall toxicity
during the first abiotic phase. Additionally, in the second phase, after nine months
from nZVI application the microbial growth was stimulated by the addition of
cheese whey and the increase of anaerobic bacteria contributed to the biotic reduction of residual Cr(VI). The direct or indirect effect of biotic reduction was clearly
long-term and persisted even after ten months from the whey injection even when the
substrate was completely depleted.
20.3 Locality 2
20.3.1 Sampling and Site Monitoring
The second locality is polluted by Cr(VI) and chlorinated ethenes originating from
historical degreasing and chromium coating activities. The initial levels of contamination in the groundwater reached values from 4.4 to 57 mg/L for Cr(VI) and from
400 to 6526 μg/L for the sum of chlorinated ethenes at the beginning of the pilot test.
Similarly to locality 1, the aquifer is situated in Quaternary sands and gravels with
silty admixture and is covered by a layer of clay and clayey loam with a thickness of
5 m. The saturated zone of the aquifer is approximately 4 m thick and the hydraulic
conductivity of the aquifer is 7.6 Â 10
À4 m/s. The groundwater discharges into the
neighboring river at the distance of 430 m from the contaminated site. Physicochemical parameters of the groundwater reached values of pH 6.9–7.0, total organic
carbon ˂1.0 to 5.4 mg/L, the total dissolved solids from 0.9 to 1.2 g/L, and oxidationreduction potential ranging from +130 to À490 mV. Samples of the groundwater
were collected during the whole pilot application from seven different monitoring
20 Nano-Bioremediation: Nanoscale Zero-Valent Iron for Inorganic and. . .
429
Pilot Test Phases
In both studies, Němeček et al. (2014 and 2015), the authors also provided detailed
microbial and ecotoxicological assessment of the whole 21-month period of the pilot
test duration. Using standard approaches such as microbial cultivation tests and
inhibition of bioluminescence of Vibrio fischeri, the authors assessed the possible
ecotoxicological impact of nZVI. The impact on autochthonous microbial population was also monitored by phospholipid fatty acid analysis (PLFA) and 16S rRNA
454 pyrosequencing. Overall, the authors did not observe any negative effect on the
microbial population in the groundwater after the nZVI application and even growth
stimulation of Gram-positive bacteria was observed in the soil samples using PLFA.
Notwithstanding the acute toxicity of nZVI detected during the in vitro tests
(Semerád et al. 2018), the lack of negative or less pronounced toxic effect during in
situ application corresponds with the findings of several other authors (Semerád and
Cajthaml 2016). Bacterial stimulation was probably caused by the elimination of
highly toxic Cr(VI) from the aquifer and thus by the decrease of overall toxicity
during the first abiotic phase. Additionally, in the second phase, after nine months
from nZVI application the microbial growth was stimulated by the addition of
cheese whey and the increase of anaerobic bacteria contributed to the biotic reduction of residual Cr(VI). The direct or indirect effect of biotic reduction was clearly
long-term and persisted even after ten months from the whey injection even when the
substrate was completely depleted.
20.3 Locality 2
20.3.1 Sampling and Site Monitoring
The second locality is polluted by Cr(VI) and chlorinated ethenes originating from
historical degreasing and chromium coating activities. The initial levels of contamination in the groundwater reached values from 4.4 to 57 mg/L for Cr(VI) and from
400 to 6526 μg/L for the sum of chlorinated ethenes at the beginning of the pilot test.
Similarly to locality 1, the aquifer is situated in Quaternary sands and gravels with
silty admixture and is covered by a layer of clay and clayey loam with a thickness of
5 m. The saturated zone of the aquifer is approximately 4 m thick and the hydraulic
conductivity of the aquifer is 7.6 Â 10
À4 m/s. The groundwater discharges into the
neighboring river at the distance of 430 m from the contaminated site. Physicochemical parameters of the groundwater reached values of pH 6.9–7.0, total organic
carbon ˂1.0 to 5.4 mg/L, the total dissolved solids from 0.9 to 1.2 g/L, and oxidationreduction potential ranging from +130 to À490 mV. Samples of the groundwater
were collected during the whole pilot application from seven different monitoring
20 Nano-Bioremediation: Nanoscale Zero-Valent Iron for Inorganic and. . .
429