with the pesticides, such as factory workers and agriculturalists, who are involved in the manufacture and application
(Carvalho et al. 2017).
Pesticides are applied on the field either in the form of
powder, solution or emulsion, from where approximately 2–
25% of pesticides move away from the target, whereas about
80–90% volatilizes into the atmosphere in the period of few
days (Aktar et al. 2009). Pesticides can be leached by surface
run-off and end up in water bodies. As a general rule, the high
volatility or instability of the pesticides lead to the farthest
deposition of it from the application site. Synthetic pesticides,
which are non-biodegradable, can persist in the soil for weeks
to years and have been classified as persistent organic pollutants (POPs). First-generation organochloride pesticides were
especially persistent, hence because of this reason and
development of pest resistance urged their replacement by
organophosphates, which are less persistent in the environment (Caravalho et al. 2017). However, the problem is that
many animals across related phylogenies share similar physiologies and are also affected by the pesticides. Animals such
as bees, shrimps and crabs are direct non-target casualties of
pesticide application. Both target (pests) and non-target species are consumed within the food chain and concentrate
within the biomass in higher trophic levels and have been
termed as biological magnification. Overuse of pesticides
cause population of beneficial soil bacteria to decline, which
are responsible for long-term fixing of nutrients, e.g. nitrogen
fixating bacteria (Aktar et al. 2009). Ultimately pesticides
make their way to humans, where they have been related with
diseases such as cancer, obesity and endocrine disruption
(Caravalho et al. 2017). Phasing out of POPs was agreed upon
in the Stockholm Convention, which includes several notorious pesticides such as dichloro diphenyl trichloroethane
(DDT) and endosulfan, which are detrimental to both the
environment and human health.
The concept behind augmenting soil nutrition and thus
increasing crop productivity is also as old as agriculture.
Ancient people used mulch, manure and guano as a means of
fertilizer. Nutritional requirements of plants can be broadly
divided into macronutrients, primary among them being,
nitrogen (N), phosphorus (P) and potassium (K), collectively
called NPK requirement. Micronutrients include a multitude
of minerals and elements, which are needed in much smaller
dosage and are plant specific. Fertilizers can be classified on
the basis of different number of nutrients present in the
product. Single or straight fertilizers contain either N, P or
K. Binary fertilizers contain two nutrients of any of the
above type, whereas NPK fertilizer contains all the three
(Erisman et al. 2008). Although fertilizers, unlike pesticides,
are non-toxic and nutrient rich, yet they pose a considerable
risk to the environment. Ecologically, they are responsible
for disturbing the delicate nutrient cycle via nutrient loading,
as well as being a source for pollutant by-products. Most of
the fertilizers used are washed away with surface water from
rain or irrigation and end up in water bodies. Fertilizers
contain a large amount of phosphate, which coincidentally is
a limiting factor in such aquatic ecosystems. This causes an
exponential increase in the cyanobacterial and algal population, which is detrimental to the aquatic ecosystem, as it
prevents sunlight from penetrating deeper into the water
body. The eventual death of cyanobacterial and algal population causes significant oxygen depletion in the water body
in a process known as eutrophication. Nutrient loading from
estuaries into oceans can also cause oxygen depletion in a
similar manner and lead to dead zones or areas of significant lower dissolved oxygen with reduced biodiversity.
Cyanobacterial blooms can release toxins, which can accumulate and magnify within the ecosystem (Schmidt et al.
2013).
The fertilizer industry is also considered a source of
radionuclide and heavy metals such as mercury, cadmium,
arsenic, lead, copper and nickel which lead to contamination
and accumulation in soil and plant biota such as fruits and
vegetables, from where they can affect humans (Atafar et al.
2010; Savci 2012). Out of all the nitrogen fertilizers widely
used, only 50% is used by the plants, while 2–20% is
evaporated, 15–25% reach with soil organic compounds,
whereas remaining 10% contaminates groundwater (Savci
2012). In case of such fertilizers, they are converted to
nitrates via microbial nitrification. These excess nitrates can
percolate into ground water or leach into any water bodies in
the catchment areas. Physiologically an excess of nitrates
cause methemoglobin, affecting infants, aged and sick.
The effect of chemical fertilizers on soil is not immediately obvious, due to complex chemical and microbial profile, which offers it a buffering capability. However,
prolonged fertilizers misuse or overuse can overwhelm this
mechanism (Savci 2012). Particularly, fertilizers high in
sodium and potassium have a negative impact on soil profile,
pH and prevent uptake of micronutrients by plants (Savci
2012). Excessive fertilizers use can cause a breakdown
between the microbial symbiotic relations with plant roots.
Volatilization or decomposition of fertilizers has also been
linked with emission of nitrogen oxides into the atmosphere,
which is not only a potent greenhouse gas, but can also cause
acid rain, thereby affecting the soil pH even more. Figure 1
is a very simplistic model of the nitrogen cycle and how
nutrient loading may lead to most of it being unassimilated
and reaching aquatic bodies unintentionally, where it might
lead to algal blooms.
154
N. Sarkar et al.
(Carvalho et al. 2017).
Pesticides are applied on the field either in the form of
powder, solution or emulsion, from where approximately 2–
25% of pesticides move away from the target, whereas about
80–90% volatilizes into the atmosphere in the period of few
days (Aktar et al. 2009). Pesticides can be leached by surface
run-off and end up in water bodies. As a general rule, the high
volatility or instability of the pesticides lead to the farthest
deposition of it from the application site. Synthetic pesticides,
which are non-biodegradable, can persist in the soil for weeks
to years and have been classified as persistent organic pollutants (POPs). First-generation organochloride pesticides were
especially persistent, hence because of this reason and
development of pest resistance urged their replacement by
organophosphates, which are less persistent in the environment (Caravalho et al. 2017). However, the problem is that
many animals across related phylogenies share similar physiologies and are also affected by the pesticides. Animals such
as bees, shrimps and crabs are direct non-target casualties of
pesticide application. Both target (pests) and non-target species are consumed within the food chain and concentrate
within the biomass in higher trophic levels and have been
termed as biological magnification. Overuse of pesticides
cause population of beneficial soil bacteria to decline, which
are responsible for long-term fixing of nutrients, e.g. nitrogen
fixating bacteria (Aktar et al. 2009). Ultimately pesticides
make their way to humans, where they have been related with
diseases such as cancer, obesity and endocrine disruption
(Caravalho et al. 2017). Phasing out of POPs was agreed upon
in the Stockholm Convention, which includes several notorious pesticides such as dichloro diphenyl trichloroethane
(DDT) and endosulfan, which are detrimental to both the
environment and human health.
The concept behind augmenting soil nutrition and thus
increasing crop productivity is also as old as agriculture.
Ancient people used mulch, manure and guano as a means of
fertilizer. Nutritional requirements of plants can be broadly
divided into macronutrients, primary among them being,
nitrogen (N), phosphorus (P) and potassium (K), collectively
called NPK requirement. Micronutrients include a multitude
of minerals and elements, which are needed in much smaller
dosage and are plant specific. Fertilizers can be classified on
the basis of different number of nutrients present in the
product. Single or straight fertilizers contain either N, P or
K. Binary fertilizers contain two nutrients of any of the
above type, whereas NPK fertilizer contains all the three
(Erisman et al. 2008). Although fertilizers, unlike pesticides,
are non-toxic and nutrient rich, yet they pose a considerable
risk to the environment. Ecologically, they are responsible
for disturbing the delicate nutrient cycle via nutrient loading,
as well as being a source for pollutant by-products. Most of
the fertilizers used are washed away with surface water from
rain or irrigation and end up in water bodies. Fertilizers
contain a large amount of phosphate, which coincidentally is
a limiting factor in such aquatic ecosystems. This causes an
exponential increase in the cyanobacterial and algal population, which is detrimental to the aquatic ecosystem, as it
prevents sunlight from penetrating deeper into the water
body. The eventual death of cyanobacterial and algal population causes significant oxygen depletion in the water body
in a process known as eutrophication. Nutrient loading from
estuaries into oceans can also cause oxygen depletion in a
similar manner and lead to dead zones or areas of significant lower dissolved oxygen with reduced biodiversity.
Cyanobacterial blooms can release toxins, which can accumulate and magnify within the ecosystem (Schmidt et al.
2013).
The fertilizer industry is also considered a source of
radionuclide and heavy metals such as mercury, cadmium,
arsenic, lead, copper and nickel which lead to contamination
and accumulation in soil and plant biota such as fruits and
vegetables, from where they can affect humans (Atafar et al.
2010; Savci 2012). Out of all the nitrogen fertilizers widely
used, only 50% is used by the plants, while 2–20% is
evaporated, 15–25% reach with soil organic compounds,
whereas remaining 10% contaminates groundwater (Savci
2012). In case of such fertilizers, they are converted to
nitrates via microbial nitrification. These excess nitrates can
percolate into ground water or leach into any water bodies in
the catchment areas. Physiologically an excess of nitrates
cause methemoglobin, affecting infants, aged and sick.
The effect of chemical fertilizers on soil is not immediately obvious, due to complex chemical and microbial profile, which offers it a buffering capability. However,
prolonged fertilizers misuse or overuse can overwhelm this
mechanism (Savci 2012). Particularly, fertilizers high in
sodium and potassium have a negative impact on soil profile,
pH and prevent uptake of micronutrients by plants (Savci
2012). Excessive fertilizers use can cause a breakdown
between the microbial symbiotic relations with plant roots.
Volatilization or decomposition of fertilizers has also been
linked with emission of nitrogen oxides into the atmosphere,
which is not only a potent greenhouse gas, but can also cause
acid rain, thereby affecting the soil pH even more. Figure 1
is a very simplistic model of the nitrogen cycle and how
nutrient loading may lead to most of it being unassimilated
and reaching aquatic bodies unintentionally, where it might
lead to algal blooms.
154
N. Sarkar et al.