storage. Following the dehydration, the experimental tissue was dipped in xylene
and embedded in paraffin wax. The material was further trimmed and the sections
were made using Spencer’s microtome. Deparaffinization and washing in absolute
alcohol was done before staining with Delafield’s haematoxylin. Later, the stained
slide was washed till they appeared blue for the naked eye. Finally, the tissues
stained with Eosin were dehydrated, cleared in xylene and mounted in DPX
mountant (Sharma and Satyanarayan 2011).
16.2.5 Determination of Metallothionein
Due to various contaminants present in the soil ecosystem, organisms which dwell in
the soil are dependent on the detoxification system. This happens in earthworms by
eliciting certain biomolecules, which are called the biomarkers of soil pollution. One
such biomarker is the metal-binding protein metallothionein as reported by Dedeke
et al. (2016), Suriya et al. (2012), Homa et al. (2005), Dallinger-Marianne et al.
(2000) and Gastaldi et al. (2007). Metallothionein is a protein of low molecular
weight whose concentration is reported to increase in the tissues due to the exposure
to heavy metals. The biomarker is estimated as per the procedure of Linde-Arias
et al. (2008).
16.3 Results and Discussion
Earthworms were found to bioremediate the soil contaminated with pollutants such
as heavy metals (Rorat et al. 2017). During the bioremediation of high density
polyethylene (HDPE)-coated paper cups, the combined action of the earthworms
with the microbes were reported (Arumugam et al. 2015). The concentration of
heavy metals such as Fe, Cu, Cd, Zn and Mn ions was less in Eudrilus eugeniae
worked vermicompost (Fig. 16.1a–e).
The concentration of Cd has reduced by about 82%, 98% and 96% in DSC1,
DSV1 and DSV2, respectively, and about 70% in DSC2. Such higher accumulation
of Cd is reported to be due to the higher uptake of the metal and very low excretion
of the same (Spurgeon and Hopkin 1999). A similar trend is noticed for Mn, Fe, Zn
and Cu. This may be attributed to the higher concentration of the sludge which could
have been toxic to the organisms.
Figure 16.2a, b depicts the accumulation of heavy metals in earthworm tissues
subjected to vermicomposting. Increase in the Mn concentration is noticed in DSV1
and DSV2 (12.63–156 mg/kg). A similar trend is noticed for all heavy metals. From
the reduction in the heavy metal content of the worm-worked vermicompost sample,
an increase in the same is noticed in the tissue samples.
Similarly, Shahmansouri et al. (2005) have studied the bioaccumulation of
Iranian and Australian earthworms in sewage sludge vermicompost using Eisenia
272
S. Sugumar et al.
and embedded in paraffin wax. The material was further trimmed and the sections
were made using Spencer’s microtome. Deparaffinization and washing in absolute
alcohol was done before staining with Delafield’s haematoxylin. Later, the stained
slide was washed till they appeared blue for the naked eye. Finally, the tissues
stained with Eosin were dehydrated, cleared in xylene and mounted in DPX
mountant (Sharma and Satyanarayan 2011).
16.2.5 Determination of Metallothionein
Due to various contaminants present in the soil ecosystem, organisms which dwell in
the soil are dependent on the detoxification system. This happens in earthworms by
eliciting certain biomolecules, which are called the biomarkers of soil pollution. One
such biomarker is the metal-binding protein metallothionein as reported by Dedeke
et al. (2016), Suriya et al. (2012), Homa et al. (2005), Dallinger-Marianne et al.
(2000) and Gastaldi et al. (2007). Metallothionein is a protein of low molecular
weight whose concentration is reported to increase in the tissues due to the exposure
to heavy metals. The biomarker is estimated as per the procedure of Linde-Arias
et al. (2008).
16.3 Results and Discussion
Earthworms were found to bioremediate the soil contaminated with pollutants such
as heavy metals (Rorat et al. 2017). During the bioremediation of high density
polyethylene (HDPE)-coated paper cups, the combined action of the earthworms
with the microbes were reported (Arumugam et al. 2015). The concentration of
heavy metals such as Fe, Cu, Cd, Zn and Mn ions was less in Eudrilus eugeniae
worked vermicompost (Fig. 16.1a–e).
The concentration of Cd has reduced by about 82%, 98% and 96% in DSC1,
DSV1 and DSV2, respectively, and about 70% in DSC2. Such higher accumulation
of Cd is reported to be due to the higher uptake of the metal and very low excretion
of the same (Spurgeon and Hopkin 1999). A similar trend is noticed for Mn, Fe, Zn
and Cu. This may be attributed to the higher concentration of the sludge which could
have been toxic to the organisms.
Figure 16.2a, b depicts the accumulation of heavy metals in earthworm tissues
subjected to vermicomposting. Increase in the Mn concentration is noticed in DSV1
and DSV2 (12.63–156 mg/kg). A similar trend is noticed for all heavy metals. From
the reduction in the heavy metal content of the worm-worked vermicompost sample,
an increase in the same is noticed in the tissue samples.
Similarly, Shahmansouri et al. (2005) have studied the bioaccumulation of
Iranian and Australian earthworms in sewage sludge vermicompost using Eisenia
272
S. Sugumar et al.