Insecticides are substances used to kill insects.

They include ovicides and larvicides used against insect eggs

and larvae, respectively. Insecticides are used in agriculture, medicine, industry and by consumers.
Insecticides are claimed to be a major factor behind the increase in the 20th-century's agricultural productivity.
Nearly all insecticides have the potential to significantly alter ecosystems; many are toxic to humans and/or
animals; some become concentrated as they spread along the food chain.
Insecticides can be classified into two major groups: systemic insecticides, which have residual or long term
activity; and contact insecticides, which have no residual activity.
The mode of action describes how the pesticide kills or inactivates a pest. It provides another way of
classifying insecticides. Mode of action can be important in understanding whether an insecticide will be toxic
to unrelated species, such as fish, birds and mammals.
Insecticides may be repellent or non-repellent. Social insects such as ants cannot detect non-repellents and
readily crawl through them. As they return to the nest they take insecticide with them and transfer it to their
nestmates. Over time, this eliminates all of the ants including the queen. This is slower than some other
methods, but usually completely eradicates the ant colony.
Insecticides are distinct from non-insecticidal repellents, which repel but do not kill.

Type of activity

Systemic insecticides

Systemic insecticides become incorporated and distributed systemically throughout the whole plant. When
insects feed on the plant, they ingest the insecticide. Systemic insecticides produced by transgenic plants are
called plant-incorporated protectants (PIPs). For instance, a gene that codes for a specific Bacillus
thuringiensis biocidal protein was introduced into corn (maize) and other species. The plant manufactures the
protein, which kills the insect when consumed.

Contact insecticides

Contact insecticides are toxic to insects upon direct contact. These can be inorganic insecticides, which are
metals and include the commonly used sulfur, and the less commonly used arsenates, copper and fluorine
compounds. Contact insecticides can also be organic insecticides, i.e. organic chemical compounds,
synthetically produced, and comprising the largest numbers of pesticides used today. Or they can be natural
compounds like pyrethrum, neem oil etc. Contact insecticides usually have no residual activity.
Efficacy can be related to the quality of pesticide application, with small droplets, such as aerosols often
improving performance.
Synthetic insecticides

Organochlorides
known organochloride, DDT, was created by Swiss scientist Paul Müller. For this discovery, he was awarded
the 1948 Nobel Prize for Physiology or Medicine.[6] DDT was introduced in 1944. It functions by opening
sodium channels in the insect's nerve cells.[7] The contemporaneous rise of the chemical industry facilitated
large-scale production of DDT and related chlorinated hydrocarbons.

Organophosphates

Organophosphates are another large class of contact insecticides. These also target the insect's nervous
system. Organophosphates interfere with the enzymes acetylcholinesterase and other cholinesterases,
disrupting nerve impulses and killing or disabling the insect. Organophosphate insecticides and chemical
warfare nerve agents (such as sarin, tabun, soman, and VX) work in the same way. Organophosphates have a
cumulative toxic effect to wildlife, so multiple exposures to the chemicals amplifies the toxicity.[8] In the US,
organophosphate use declined with the rise of substitutes.[9]
Carbamates

Carbamate insecticides have similar mechanisms to organophosphates, but have a much shorter duration of
action and are somewhat less toxic.

Pyrethroids

Pyrethroid pesticides mimic the insecticidal activity of the natural compound pyrethrin, the biopesticide found in
Pyrethrum (Now Chrysanthemum and Tanacetum) species. These compounds are nonpersistent sodium
channel modulators and are less toxic than organophosphates and carbamates. Compounds in this group are
often applied against household pests.[10]

Neonicotinoids

Neonicotinoids are synthetic analogues of the natural insecticide nicotine (with much lower acute mammalian
toxicity and greater field persistence). These chemicals are acetylcholine receptor agonists. They are
broad-spectrum systemic insecticides, with rapid action (minutes-hours). They are applied as sprays,
drenches, seed and soil treatments. Treated insects exhibit leg tremors, rapid wing motion, stylet withdrawal
(aphids), disoriented movement, paralysis and death.[11] Imidacloprid may be the most common. It has recently
come under scrutiny for allegedly pernicious effects on honeybees[12] and its potential to increase the
susceptibility of rice to planthopper attacks.[13]

Butenolides

Butenolide pesticides are a novel group of chemicals, similar to neonicotinoids in their mode of action, that
have so far only one representative: flupyradifurone [fr]. They are acetylcholine receptor agonists, like
neonicotinoids, but with a different pharmacophore.[14] They are broad-spectrum systemic insecticides, applied
as sprays, drenches, seed and soil treatments. Although the classic risk assessment considered this
insecticide group (and flupyradifurone specifically) safe for bees, novel research[15] have raised concern on
their lethal and sublethal effects, alone or in combination with other chemicals or environmental factors.[16][17]

Ryanoids/diamides

Diamides are synthetic ryanoid analogues with the same mode of action as ryanodine, a naturally occurring
insecticide extracted from Ryania speciosa (Salicaceae). They bind to calcium channels in cardiac and skeletal
muscle, blocking nerve transmission. The first insecticide from this class to be registered was Rynaxypyr,
generic name chlorantraniliprole.[18]

Insect growth regulators

Insect growth regulator (IGR) is a term coined to include insect hormone mimics and an earlier class of
chemicals, the benzoylphenyl ureas, which inhibit chitin (exoskeleton) biosynthesis in insects[19] Diflubenzuron
is a member of the latter class, used primarily to control caterpillars that are pests. The most successful
insecticides in this class are the juvenoids (juvenile hormone analogues). Of these, methoprene is most widely
used. It has no observable acute toxicity in rats and is approved by World Health Organization (WHO) for use
in drinking water cisterns to combat malaria. Most of its uses are to combat insects where the adult is the pest,
including mosquitoes, several fly species, and fleas. Two very similar products, hydroprene and kinoprene, are
used for controlling species such as cockroaches and white flies. Methoprene was registered with the EPA in
1975. Virtually no reports of resistance have been filed. A more recent type of IGR is the ecdysone agonist
tebufenozide (MIMIC), which is used in forestry and other applications for control of caterpillars, which are far
more sensitive to its hormonal effects than other insect orders.

Biological pesticides

More natural insecticides have been interesting targets of research for two main reasons, firstly because the
most common chemicals are losing effectiveness, and secondly due to their toxic effects upon the
environment.[20] Many organic compounds are already produced by plants for the purpose of defending the
host plant from predation, and can be turned toward human ends.
Four extracts of plants are in commercial use: pyrethrum, rotenone, neem oil, and various essential oils[21]
A trivial case is tree rosin, which is a natural insecticide. Specifically, the production of oleoresin by conifer
species is a component of the defense response against insect attack and fungal pathogen infection.[22] Many
fragrances, e.g. oil of wintergreen, are in fact antifeedants.

Other biological approaches

Plant-incorporated protectants

Transgenic crops that act as insecticides began in 1996 with a genetically modified potato that produced the
Cry protein, derived from the bacterium Bacillus thuringiensis, which is toxic to beetle larvae such as the
Colorado potato beetle. The technique has been expanded to include the use of RNA interference RNAi that
fatally silences crucial insect genes. RNAi likely evolved as a defense against viruses. Midgut cells in many
larvae take up the molecules and help spread the signal. The technology can target only insects that have the
silenced sequence, as was demonstrated when a particular RNAi affected only one of four fruit fly species.
The technique is expected to replace many other insecticides, which are losing effectiveness due to the spread
of insecticide resistance.[23] Spider venom peptide fractions are another class of potential transgenic traits
which could expand the mode of action repertoire and help to answer the resistance question.[24]

Enzymes[edit]

Many plants exude substances to repel insects. Premier examples are substances activated by the enzyme
myrosinase. This enzyme converts glucosinolates to various compounds that are toxic to herbivorous insects.
One product of this enzyme is allyl isothiocyanate, the pungent ingredient in horseradish sauces.

The myrosinase is released only upon crushing the flesh of horseradish. Since allyl isothiocyanate is harmful
to the plant as well as the insect, it is stored in the harmless form of the glucosinolate, separate from the
myrosinase enzyme.[25]

Bacterial[edit]

Bacillus thuringiensis is a bacterial disease that affects Lepidopterans and some other insects. Toxins
produced by strains of this bacterium are used as a larvicide against caterpillars, beetles, and mosquitoes.
Toxins from Saccharopolyspora spinosa are isolated from fermentations and sold as Spinosad. Because these
toxins have little effect on other organisms, they are considered more environmentally friendly than synthetic
pesticides. The toxin from B. thuringiensis (Bt toxin) has been incorporated directly into plants through the use
of genetic engineering.

Other[edit]

Other biological insecticides include products based on entomopathogenic fungi (e.g., Beauveria bassiana,
Metarhizium anisopliae), nematodes (e.g., Steinernema feltiae) and viruses (e.g., Cydia pomonella
granulovirus).[citation needed]

Synthetic insecticide and natural insecticides[edit]

A major emphasis of organic chemistry is the development of chemical tools to enhance agricultural
productivity. Insecticides represent a major area of emphasis. Many of the major insecticides are inspired by
biological analogues. Many others are not found in nature.

Environmental harm[edit]

Effects on nontarget species[edit]

Some insecticides kill or harm other creatures in addition to those they are intended to kill. For example, birds
may be poisoned when they eat food that was recently sprayed with insecticides or when they mistake an
insecticide granule on the ground for food and eat it.[8] Sprayed insecticide may drift from the area to which it is
applied and into wildlife areas, especially when it is sprayed aerially.[8]

DDT[edit]

The development of DDT was motivated by desire to replace more dangerous or less effective alternatives.
DDT was introduced to replace lead and arsenic-based compounds, which were in widespread use in the early
1940s.[26]
DDT was brought to public attention by Rachel Carson's book Silent Spring. One side-effect of DDT is to
reduce the thickness of shells on the eggs of predatory birds. The shells sometimes become too thin to be
viable, reducing bird populations. This occurs with DDT and related compounds due to the process of
bioaccumulation, wherein the chemical, due to its stability and fat solubility, accumulates in organisms' fatty
tissues. Also, DDT may biomagnify, which causes progressively higher concentrations in the body fat of
animals farther up the food chain. The near-worldwide ban on agricultural use of DDT and related chemicals
has allowed some of these birds, such as the peregrine falcon, to recover in recent years. A number of
organochlorine pesticides have been banned from most uses worldwide. Globally they are controlled via the
Stockholm Convention on persistent organic pollutants. These include: aldrin, chlordane, DDT, dieldrin, endrin,
heptachlor, mirex and toxaphene.[citation needed]

Runoff and Percolation[edit]

Solid bait and liquid insecticides, especially if improperly applied in a location, get moved by water flow. Often,
this happens through nonpoint sources where runoff carries insecticides into larger bodies of water. As snow
melts and rainfall moves over and through the ground, the water picks applied insecticides and deposits them
in to larger bodies of water, rivers, wetlands, underground sources of previously potable water, and percolates
in to watersheds.[27] This runoff and percolation of insecticides can effect the quality of water sources, harming
the natural ecology and thus, indirectly effect human populations through biomagnification and
bioaccumulation.

Pollinator decline[edit]

Insecticides can kill bees and may be a cause of pollinator decline, the loss of bees that pollinate plants, and
colony collapse disorder (CCD),[28] in which worker bees from a beehive or Western honey bee colony abruptly
disappear. Loss of pollinators means a reduction in crop yields.[28] Sublethal doses of insecticides (i.e.
imidacloprid and other neonicotinoids) affect bee foraging behavior.[29] However, research into the causes of
CCD was inconclusive as of June 2007.[30]

Bird decline[edit]

Besides the effects of direct consumption of insecticides, populations of insectivorous birds decline due to the
collapse of their prey populations. Spraying of especially wheat and corn in Europe is believed to have caused
an 80 per cent decline in flying insects, which in turn has reduced local bird populations by one to two thirds.[31]

Alternatives[edit]

Instead of using chemical insecticides to avoid crop damage caused by insects, there are many alternative
options available now that can protect farmers from major economic losses.[32] Some of them are:
1. Breeding crops resistant, or at least less susceptible, to pest attacks.[33]
2. Releasing predators, parasitoids, or pathogens to control pest populations as a form of
biological control.[34]
3. Chemical control like releasing pheromones into the field to confuse the insects into not being
able to find mates and reproduce.[35]
4. Integrated Pest Management: using multiple techniques in tandem to achieve optimal results.[36]
 5. Push-pull technique: intercropping with a "push" crop that repels the pest, and planting a "pull"
crop on the boundary that attracts and traps it.[37]
A fertilizer (American English) or fertiliser (British English; see spelling differences) is any material of natural
or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct
from liming materials or other non-nutrient soil amendments. Many sources of fertilizer exist, both natural and
industrially produced.[1] For most modern agricultural practices, fertilization focuses on three main macro
nutrients: Nitrogen (N), Phosphorus (P), and Potassium (K) with occasional addition of supplements like rock
dust for micronutrients. Farmers apply these fertilizers in a variety of ways: through dry or pelletized or liquid
application processes, using large agricultural equipment or hand-tool methods.
Historically fertilization came from natural or organic sources: compost, animal manure, human manure,
harvested minerals, crop rotations and byproducts of human-nature industries (i.e. fish processing waste, or
bloodmeal from animal slaughter). However, starting in the 19th century, after innovations in plant nutrition, an
agricultural industry developed around synthetically created fertilizers. This transition was important in
transforming the global food system, allowing for larger-scale industrial agriculture with large crop yields. In
particular nitrogen-fixing chemical processes such as the Haber process at the beginning of the 20th century,
amplified by production capacity created during World War II led to a boom in using nitrogen fertilizers. In the
later half of the 20th century, increased use of nitrogen fertilizers (800% increase between 1961 and 2019)
have been a crucial component of the increased productivity of conventional food systems (more than 30% per
capita) as part of the so-called "Green Revolution".[2]
Synthetic fertilizer used in agriculture has wide-reaching environmental consequences. According to the
Intergovernmental Panel on Climate Change (IPCC) Special Report on Climate Change and Land, production
of these fertilizers and associated land use practices are key drivers of global warming.[2] The use of fertilizer
has also led to a number of direct environmental consequences: agricultural runoff which leads to downstream
effects like ocean dead zones and waterway contamination, soil microbiome degradation,[3] and accumulation
of toxins in ecosystems. Indirect environmental impacts include: the environmental impacts of fracking for
natural gas used in the Haber process, the agricultural boom is partially responsible for the rapid growth in
human population and large-scale industrial agricultural practices are associated with habitat destruction,
pressure on biodiversity and agricultural soil loss.
In order to mitigate environmental and food security concerns, the international community has included food
systems in Sustainable Development Goal 2 which focuses on creating a climate-friendly and sustainable food
production system.[4] Most policy and regulatory approaches to address these issues focus on pivoting
agricultural practices towards sustainable or regenerative agricultural practices: these use less synthetic
fertilizers, better soil management (for example no-till agriculture) and more organic fertilizers.

Mechanism[edit]

Fertilizers enhance the growth of plants. This goal is met in two ways, the traditional one being additives that
provide nutrients. The second mode by which some fertilizers act is to enhance the effectiveness of the soil by
modifying its water retention and aeration. This article, like many on fertilizers, emphasises the nutritional
aspect. Fertilizers typically provide, in varying proportions:[20]
● three main macronutrients:
○ Nitrogen (N): leaf growth
○ Phosphorus (P): Development of roots, flowers, seeds, fruit;
○ Potassium (K): Strong stem growth, movement of water in plants, promotion of flowering
and fruiting;
● three secondary macronutrients: calcium (Ca), magnesium (Mg), and sulfur (S);
● micronutrients: copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), zinc (Zn), boron (B). Of
occasional significance are silicon (Si), cobalt (Co), and vanadium (V).
The nutrients required for healthy plant life are classified according to the elements, but the elements are not
used as fertilizers. Instead compounds containing these elements are the basis of fertilizers. The
macro-nutrients are consumed in larger quantities and are present in plant tissue in quantities from 0.15% to
6.0% on a dry matter (DM) (0% moisture) basis. Plants are made up of four main elements: hydrogen, oxygen,
carbon, and nitrogen. Carbon, hydrogen and oxygen are widely available as water and carbon dioxide.
Although nitrogen makes up most of the atmosphere, it is in a form that is unavailable to plants. Nitrogen is the
most important fertilizer since nitrogen is present in proteins, DNA and other components (e.g., chlorophyll). To
be nutritious to plants, nitrogen must be made available in a "fixed" form. Only some bacteria and their host
plants (notably legumes) can fix atmospheric nitrogen (N2) by converting it to ammonia. Phosphate is required
for the production of DNA and ATP, the main energy carrier in cells, as well as certain lipids.

Microbiological considerations[edit]

Two sets of enzymatic reactions are highly relevant to the efficiency of nitrogen-based fertilizers.
Urease
The first is the hydrolysis (reaction with water) of urea. Many soil bacteria possess the enzyme urease, which
catalyzes conversion of urea to ammonium ion (NH4+) and bicarbonate ion (HCO3−).
Ammonia oxidation
Ammonia-oxidizing bacteria (AOB), such as species of Nitrosomonas, oxidize ammonia to nitrite, a process
termed nitrification.[21] Nitrite-oxidizing bacteria, especially Nitrobacter, oxidize nitrite to nitrate, which is
extremely mobile and is a major cause of eutrophication.

Classification[edit]

Fertilizers are classified in several ways. They are classified according to whether they provide a single
nutrient (e.g., K, P, or N), in which case they are classified as "straight fertilizers." "Multinutrient fertilizers" (or
"complex fertilizers") provide two or more nutrients, for example N and P. Fertilizers are also sometimes
classified as inorganic (the topic of most of this article) versus organic. Inorganic fertilizers exclude
carbon-containing materials except ureas. Organic fertilizers are usually (recycled) plant- or animal-derived
matter. Inorganic are sometimes called synthetic fertilizers since various chemical treatments are required for
their manufacture.[22]

Single nutrient ("straight") fertilizers[edit]

The main nitrogen-based straight fertilizer is ammonia or its solutions. Ammonium nitrate (NH4NO3) is also
widely used. Urea is another popular source of nitrogen, having the advantage that it is solid and
non-explosive, unlike ammonia and ammonium nitrate, respectively. A few percent of the nitrogen fertilizer
market (4% in 2007)[23] has been met by calcium ammonium nitrate (Ca(NO3)2 • NH4 • 10H2O).
The main straight phosphate fertilizers are the superphosphates. "Single superphosphate" (SSP) consists of
14–18% P2O5, again in the form of Ca(H2PO4)2, but also phosphogypsum (CaSO4 • 2H2O). Triple
superphosphate (TSP) typically consists of 44–48% of P2O5 and no gypsum. A mixture of single
superphosphate and triple superphosphate is called double superphosphate. More than 90% of a typical
superphosphate fertilizer is water-soluble.
The main potassium-based straight fertilizer is muriate of potash (MOP). Muriate of potash consists of 95–99%
KCl, and is typically available as 0-0-60 or 0-0-62 fertilizer.

Multinutrient fertilizers[edit]

These fertilizers are common. They consist of two or more nutrient components.
Binary (NP, NK, PK) fertilizers
Major two-component fertilizers provide both nitrogen and phosphorus to the plants. These are called NP
fertilizers. The main NP fertilizers are monoammonium phosphate (MAP) and diammonium phosphate (DAP).
The active ingredient in MAP is NH4H2PO4. The active ingredient in DAP is (NH4)2HPO4. About 85% of MAP
and DAP fertilizers are soluble in water.
NPK fertilizers
Main article: Labeling of fertilizer
NPK fertilizers are three-component fertilizers providing nitrogen, phosphorus, and potassium. There exist two
types of NPK fertilizers: compound and blends. Compound NPK fertilizers contain chemically bound
ingredients, while blended NPK fertilizers are physical mixtures of single nutrient components.
NPK rating is a rating system describing the amount of nitrogen, phosphorus, and potassium in a fertilizer.
NPK ratings consist of three numbers separated by dashes (e.g., 10-10-10 or 16-4-8) describing the chemical
content of fertilizers.[24][25] The first number represents the percentage of nitrogen in the product; the second
number, P2O5; the third, K2O. Fertilizers do not actually contain P2O5 or K2O, but the system is a conventional
shorthand for the amount of the phosphorus (P) or potassium (K) in a fertilizer. A 50-pound (23 kg) bag of
fertilizer labeled 16-4-8 contains 8 lb (3.6 kg) of nitrogen (16% of the 50 pounds), an amount of phosphorus
equivalent to that in 2 pounds of P2O5 (4% of 50 pounds), and 4 pounds of K2O (8% of 50 pounds). Most
fertilizers are labeled according to this N-P-K convention, although Australian convention, following an N-P-K-S
system, adds a fourth number for sulfur, and uses elemental values for all values including P and K.[26]

Micronutrients[edit]

Micronutrients are consumed in smaller quantities and are present in plant tissue on the order of
parts-per-million (ppm), ranging from 0.15 to 400 ppm or less than 0.04% dry matter.[27][28] These elements are
often required for enzymes essential to the plant's metabolism. Because these elements enable catalysts
(enzymes), their impact far exceeds their weight percentage. Typical micronutrients are boron, zinc,
molybdenum, iron, and manganese.[20] These elements are provided as water-soluble salts. Iron presents
special problems because it converts to insoluble (bio-unavailable) compounds at moderate soil pH and
phosphate concentrations. For this reason, iron is often administered as a chelate complex, e.g., the EDTA or
EDDHA derivatives. The micronutrient needs depend on the plant and the environment. For example, sugar
beets appear to require boron, and legumes require cobalt,[1] while environmental conditions such as heat or
drought make boron less available for plants.[29]

Application[edit]

Fertilizers are commonly used for growing all crops, with application rates depending on the soil fertility,
usually as measured by a soil test and according to the particular crop. Legumes, for example, fix nitrogen
from the atmosphere and generally do not require nitrogen fertilizer.

Liquid vs solid[edit]

Fertilizers are applied to crops both as solids and as liquid. About 90% of fertilizers are applied as solids. The
most widely used solid inorganic fertilizers are urea, diammonium phosphate and potassium chloride.[38] Solid
fertilizer is typically granulated or powdered. Often solids are available as prills, a solid globule. Liquid
fertilizers comprise anhydrous ammonia, aqueous solutions of ammonia, aqueous solutions of ammonium
nitrate or urea. These concentrated products may be diluted with water to form a concentrated liquid fertilizer
(e.g., UAN). Advantages of liquid fertilizer are its more rapid effect and easier coverage.[20] The addition of
fertilizer to irrigation water is called "fertigation".[36]

Urea[edit]

Main article: urea

Urea is highly soluble in water and is therefore also very suitable for use in fertilizer solutions (in combination
with ammonium nitrate: UAN), e.g., in 'foliar feed' fertilizers. For fertilizer use, granules are preferred over prills
because of their narrower particle size distribution, which is an advantage for mechanical application.
Urea is usually spread at rates of between 40 and 300 kg/ha (35 to 270 lbs/acre) but rates vary. Smaller
applications incur lower losses due to leaching. During summer, urea is often spread just before or during rain
to minimize losses from volatilization (a process wherein nitrogen is lost to the atmosphere as ammonia gas).
Because of the high nitrogen concentration in urea, it is very important to achieve an even spread. Drilling
must not occur on contact with or close to seed, due to the risk of germination damage. Urea dissolves in
water for application as a spray or through irrigation systems.
In grain and cotton crops, urea is often applied at the time of the last cultivation before planting. In high rainfall
areas and on sandy soils (where nitrogen can be lost through leaching) and where good in-season rainfall is
expected, urea can be side- or top-dressed during the growing season. Top-dressing is also popular on
pasture and forage crops. In cultivating sugarcane, urea is side-dressed after planting, and applied to each
ratoon crop.
Because it absorbs moisture from the atmosphere, urea is often stored in closed containers.
Overdose or placing urea near seed is harmful.[39]

Slow- and controlled-release fertilizers[edit]

A controlled-release fertiliser (CRF) is a granulated fertiliser that releases nutrients gradually into the soil (i.e.,
with a controlled release period).[41] Controlled-release fertilizer is also known as controlled-availability fertilizer,
delayed-release fertilizer, metered-release fertilizer, or slow-acting fertilizer. Usually CRF refers to
nitrogen-based fertilizers. Slow- and controlled-release involve only 0.15% (562,000 tons) of the fertilizer
market (1995).

Foliar application[edit]

Foliar fertilizers are applied directly to leaves. This method is almost invariably used to apply water-soluble
straight nitrogen fertilizers and used especially for high-value crops such as fruits. Urea is the most common
foliar fertilizer.[20]
Chemicals that affect nitrogen uptake[edit]

N-Butylthiophosphoryltriamide, an enhanced efficiency fertilizer.

Various chemicals are used to enhance the efficiency of nitrogen-based fertilizers. In this way farmers can limit
the polluting effects of nitrogen run-off. Nitrification inhibitors (also known as nitrogen stabilizers) suppress the
conversion of ammonia into nitrate, an anion that is more prone to leaching. 1-Carbamoyl-3-methylpyrazole
(CMP), dicyandiamide, nitrapyrin (2-chloro-6-trichloromethylpyridine) and 3,4-Dimethylpyrazole phosphate
(DMPP) are popular.[42] Urease inhibitors are used to slow the hydrolytic conversion of urea into ammonia,
which is prone to evaporation as well as nitrification. The conversion of urea to ammonia catalyzed by
enzymes called ureases. A popular inhibitor of ureases is N-(n-butyl)thiophosphoric triamide (NBPT).

Overfertilization[edit]

Careful use of fertilization technologies is important because excess nutrients can be detrimental.[43] Fertilizer
burn can occur when too much fertilizer is applied, resulting in damage or even death of the plant. Fertilizers
vary in their tendency to burn roughly in accordance with their salt index.

Environmental effects[edit]

Use of fertilizers are beneficial in providing nutrients to plants although they have some negative
environmental effects. The large growing consumption of fertilizers can affect soil, surface water, and
groundwater due to dispersion of mineral use.[49]
For each ton of phosphoric acid produced by the processing of phosphate rock, five tons of waste are
generated. This waste takes the form of impure, useless, radioactive solid called phosphogypsum. Estimates
range from 100,000,000 and 280,000,000 tons of phosphogypsum waste are produced annually worldwide.[57]
Water[edit]

Phosphorus and nitrogen fertilizers when commonly used have major environmental effects. This is due to
high rainfalls causing the fertilizers to be washed into waterways.[58] Agricultural run-off is a major contributor to
the eutrophication of fresh water bodies. For example, in the US, about half of all the lakes are eutrophic. The
main contributor to eutrophication is phosphate, which is normally a limiting nutrient; high concentrations
promote the growth of cyanobacteria and algae, the demise of which consumes oxygen.[59] Cyanobacteria
blooms ('algal blooms') can also produce harmful toxins that can accumulate in the food chain, and can be
harmful to humans.[60][61]
The nitrogen-rich compounds found in fertilizer runoff are the primary cause of serious oxygen depletion in
many parts of oceans, especially in coastal zones, lakes and rivers. The resulting lack of dissolved oxygen
greatly reduces the ability of these areas to sustain oceanic fauna.[62] The number of oceanic dead zones near
inhabited coastlines are increasing.[63] As of 2006, the application of nitrogen fertilizer is being increasingly
controlled in northwestern Europe[64] and the United States.[65][66] If eutrophication can be reversed, it may take
decades[citation needed] before the accumulated nitrates in groundwater can be broken down by natural processes.

Nitrate pollution[edit]

Only a fraction of the nitrogen-based fertilizers is converted to plant matter. The remainder accumulates in the
soil or is lost as run-off.[67] High application rates of nitrogen-containing fertilizers combined with the high water
solubility of nitrate leads to increased runoff into surface water as well as leaching into groundwater, thereby
causing groundwater pollution.[68][69][70] The excessive use of nitrogen-containing fertilizers (be they synthetic or
natural) is particularly damaging, as much of the nitrogen that is not taken up by plants is transformed into
nitrate which is easily leached.[71]
Nitrate levels above 10 mg/L (10 ppm) in groundwater can cause 'blue baby syndrome' (acquired
methemoglobinemia).[72] The nutrients, especially nitrates, in fertilizers can cause problems for natural habitats
and for human health if they are washed off soil into watercourses or leached through soil into
groundwater.[citation needed]

Soil[edit]

Acidification[edit]

See also: Soil pH and Soil acidification

Nitrogen-containing fertilizers can cause soil acidification when added.[73][74] This may lead to decrease in
nutrient availability which may be offset by liming.

Accumulation of toxic elements[edit]

Cadmium[edit]

The concentration of cadmium in phosphorus-containing fertilizers varies considerably and can be

problematic.[75] For example, mono-ammonium phosphate fertilizer may have a cadmium content of as low as
0.14 mg/kg or as high as 50.9 mg/kg.[76] The phosphate rock used in their manufacture can contain as much as
188 mg/kg cadmium[77] (examples are deposits on Nauru[78] and the Christmas islands[79]). Continuous use of
high-cadmium fertilizer can contaminate soil (as shown in New Zealand)[80] and plants.[81] Limits to the
cadmium content of phosphate fertilizers has been considered by the European Commission.[82][83][84]
Producers of phosphorus-containing fertilizers now select phosphate rock based on the cadmium content.[59]

Fluoride[edit]

Phosphate rocks contain high levels of fluoride. Consequently, the widespread use of phosphate fertilizers has
increased soil fluoride concentrations.[81] It has been found that food contamination from fertilizer is of little
concern as plants accumulate little fluoride from the soil; of greater concern is the possibility of fluoride toxicity
to livestock that ingest contaminated soils.[85][86] Also of possible concern are the effects of fluoride on soil
microorganisms.[85][86][87]

Radioactive elements[edit]

The radioactive content of the fertilizers varies considerably and depends both on their concentrations in the
parent mineral and on the fertilizer production process.[81][88] Uranium-238 concentrations can range from 7 to
100 pCi/g in phosphate rock[89] and from 1 to 67 pCi/g in phosphate fertilizers.[90][91][92] Where high annual rates
of phosphorus fertilizer are used, this can result in uranium-238 concentrations in soils and drainage waters
that are several times greater than are normally present.[91][93] However, the impact of these increases on the
risk to human health from radinuclide contamination of foods is very small (less than 0.05 mSv/y).[91][94][95]

Other metals[edit]

Steel industry wastes, recycled into fertilizers for their high levels of zinc (essential to plant growth), wastes
can include the following toxic metals: lead[96] arsenic, cadmium,[96] chromium, and nickel. The most common
toxic elements in this type of fertilizer are mercury, lead, and arsenic.[97][98][99] These potentially harmful
impurities can be removed; however, this significantly increases cost. Highly pure fertilizers are widely
available and perhaps best known as the highly water-soluble fertilizers containing blue dyes used around
households, such as Miracle-Gro. These highly water-soluble fertilizers are used in the plant nursery business
and are available in larger packages at significantly less cost than retail quantities. Some inexpensive retail
granular garden fertilizers are made with high purity ingredients.

Trace mineral depletion[edit]

Attention has been addressed to the decreasing concentrations of elements such as iron, zinc, copper and
magnesium in many foods over the last 50–60 years.[100][101] Intensive farming practices, including the use of
synthetic fertilizers are frequently suggested as reasons for these declines and organic farming is often
suggested as a solution.[101] Although improved crop yields resulting from NPK fertilizers are known to dilute
the concentrations of other nutrients in plants,[100][102] much of the measured decline can be attributed to the use
of progressively higher-yielding crop varieties that produce foods with lower mineral concentrations than their
less-productive ancestors.[100][103][104] It is, therefore, unlikely that organic farming or reduced use of fertilizers
will solve the problem; foods with high nutrient density are posited to be achieved using older, lower-yielding
varieties or the development of new high-yield, nutrient-dense varieties.[100][105]
Fertilizers are, in fact, more likely to solve trace mineral deficiency problems than cause them: In Western
Australia deficiencies of zinc, copper, manganese, iron and molybdenum were identified as limiting the growth
of broad-acre crops and pastures in the 1940s and 1950s.[106] Soils in Western Australia are very old, highly
weathered and deficient in many of the major nutrients and trace elements.[106] Since this time these trace
elements are routinely added to fertilizers used in agriculture in this state.[106] Many other soils around the world
are deficient in zinc, leading to deficiency in both plants and humans, and zinc fertilizers are widely used to
solve this problem.[107]

Changes in soil biology[edit]

Further information: soil biology

High levels of fertilizer may cause the breakdown of the symbiotic relationships between plant roots and
mycorrhizal fungi.[108]]

Contribution to climate change[edit]

The greenhouse gases carbon dioxide, methane and nitrous oxide are produced during the manufacture of
nitrogen fertilizer. The effects can be combined into an equivalent amount of carbon dioxide. The amount
varies according to the efficiency of the process. The figure for the United Kingdom is over 2 kilograms of
carbon dioxide equivalent for each kilogram of ammonium nitrate.[114][needs update] Nitrogen fertilizer can be
converted by soil bacteria to nitrous oxide, a greenhouse gas.[115] Nitrous oxide emissions by humans, most of
which are from fertilizer, between 2007 and 2016 have been estimated at 7 million tonnes per year,[116] which is
incompatible with limiting global warming to below 2C.[117]

Atmosphere[edit]

Through the increasing use of nitrogen fertilizer, which was used at a rate of about 110 million tons (of N) per
year in 2012,[118][119] adding to the already existing amount of reactive nitrogen, nitrous oxide (N2O) has become
the third most important greenhouse gas after carbon dioxide and methane. It has a global warming potential
296 times larger than an equal mass of carbon dioxide and it also contributes to stratospheric ozone
depletion.[120] By changing processes and procedures, it is possible to mitigate some, but not all, of these
effects on anthropogenic climate change.[121]
Methane emissions from crop fields (notably rice paddy fields) are increased by the application of
ammonium-based fertilizers. These emissions contribute to global climate change as methane is a potent
greenhouse gas.[122][123]
Pesticides are substances that are meant to control pests.[1] The term pesticide includes all of the following:
herbicide, insecticides (which may include insect growth regulators, termiticides, etc.) nematicide, molluscicide,
piscicide, avicide, rodenticide, bactericide, insect repellent, animal repellent, antimicrobial, fungicide,[2] and
lampricide.[3] The most common of these are herbicides which account for approximately 80% of all pesticide
use.[4] Most pesticides are intended to serve as plant protection products (also known as crop protection
products), which in general, protect plants from weeds, fungi, or insects. As an example, the fungus Alternaria
solani is used to combat the aquatic weed Salvinia.
In general, a pesticide is a chemical (such as carbamate) or biological agent (such as a virus, bacterium, or
fungus) that deters, incapacitates, kills, or otherwise discourages pests. Target pests can include insects, plant
pathogens, weeds, molluscs, birds, mammals, fish, nematodes (roundworms), and microbes that destroy
property, cause nuisance, or spread disease, or are disease vectors. Along with these benefits, pesticides also
have drawbacks, such as potential toxicity to humans and other species.

Definition[edit]
The Food and Agriculture Organization (FAO) has defined pesticide as:
any substance or mixture of substances intended for preventing, destroying, or controlling any pest, including
vectors of human or animal disease, unwanted species of plants or animals, causing harm during or otherwise
interfering with the production, processing, storage, transport, or marketing of food, agricultural commodities,
wood and wood products or animal feedstuffs, or substances that may be administered to animals for the
control of insects, arachnids, or other pests in or on their bodies. The term includes substances intended for
use as a plant growth regulator, defoliant, desiccant, or agent for thinning fruit or preventing the premature fall
of fruit. Also used as substances applied to crops either before or after harvest to protect the commodity from
deterioration during storage and transport.[5]
Pesticides can be classified by target organism (e.g., herbicides, insecticides, fungicides, rodenticides, and
pediculicides[6] – see table), chemical structure (e.g., organic, inorganic, synthetic, or biological (biopesticide),[7]
although the distinction can sometimes blur), and physical state (e.g. gaseous (fumigant)).[7] Biopesticides
include microbial pesticides and biochemical pesticides.[8] Plant-derived pesticides, or "botanicals", have been
developing quickly. These include the pyrethroids, rotenoids, nicotinoids, and a fourth group that includes
strychnine and scilliroside.[9]: 15 
Many pesticides can be grouped into chemical families. Prominent insecticide families include
organochlorines, organophosphates, and carbamates. Organochlorine hydrocarbons (e.g., DDT) could be
separated into dichlorodiphenyl ethanes, cyclodiene compounds, and other related compounds. They operate
by disrupting the sodium/potassium balance of the nerve fiber, forcing the nerve to transmit continuously. Their
toxicities vary greatly, but they have been phased out because of their persistence and potential to
bioaccumulate.[9]: 239–240  Organophosphate and carbamates largely replaced organochlorines. Both operate
through inhibiting the enzyme acetylcholinesterase, allowing acetylcholine to transfer nerve impulses
indefinitely and causing a variety of symptoms such as weakness or paralysis. Organophosphates are quite
toxic to vertebrates and have in some cases been replaced by less toxic carbamates.[9]: 136–137  Thiocarbamate
and dithiocarbamates are subclasses of carbamates. Prominent families of herbicides include phenoxy and
benzoic acid herbicides (e.g. 2,4-D), triazines (e.g., atrazine), ureas (e.g., diuron), and Chloroacetanilide (e.g.,
alachlor). Phenoxy compounds tend to selectively kill broad-leaf weeds rather than grasses. The phenoxy and
benzoic acid herbicides function similar to plant growth hormones, and grow cells without normal cell division,
crushing the plant's nutrient transport system.[9]: 300  Triazines interfere with photosynthesis.[9]: 335  Many
commonly used pesticides are not included in these families, including glyphosate.
The application of pest control agents is usually carried out by dispersing the chemical in an (often
hydrocarbon-based) solvent-surfactant system to give a homogeneous preparation. A virus lethality study
performed in 1977 demonstrated that a particular pesticide did not increase the lethality of the virus, however,
combinations that included some surfactants and the solvent clearly showed that pretreatment with them
markedly increased the viral lethality in the test mice.[10]
Pesticides can be classified based upon their biological mechanism function or application method. Most
pesticides work by poisoning pests.[11] A systemic pesticide moves inside a plant following absorption by the
plant. With insecticides and most fungicides, this movement is usually upward (through the xylem) and
outward. Increased efficiency may be a result. Systemic insecticides, which poison pollen and nectar in the
flowers, may kill bees and other needed pollinators.[12]
In 2010, the development of a new class of fungicides called paldoxins was announced. These work by taking
advantage of natural defense chemicals released by plants called phytoalexins, which fungi then detoxify using
enzymes. The paldoxins inhibit the fungi's detoxification enzymes. They are believed to be safer and
greener.[13]

Uses[edit]

Pesticides are used to control organisms that are considered to be harmful, or pernicious to their
surroundings.[25] For example, they are used to kill mosquitoes that can transmit potentially deadly diseases
like West Nile virus, yellow fever, and malaria. They can also kill bees, wasps or ants that can cause allergic
reactions. Insecticides can protect animals from illnesses that can be caused by parasites such as fleas.[25]
Pesticides can prevent sickness in humans that could be caused by moldy food or diseased produce.
Herbicides can be used to clear roadside weeds, trees, and brush. They can also kill invasive weeds that may
cause environmental damage. Herbicides are commonly applied in ponds and lakes to control algae and
plants such as water grasses that can interfere with activities like swimming and fishing and cause the water to
look or smell unpleasant.[26] Uncontrolled pests such as termites and mold can damage structures such as
houses.[25] Pesticides are used in grocery stores and food storage facilities to manage rodents and insects that
infest food such as grain. Each use of a pesticide carries some associated risk. Proper pesticide use
decreases these associated risks to a level deemed acceptable by pesticide regulatory agencies such as the
United States Environmental Protection Agency (EPA) and the Pest Management Regulatory Agency (PMRA)
of Canada.
DDT, sprayed on the walls of houses, is an organochlorine that has been used to fight malaria since the
1950s. Recent policy statements by the World Health Organization have given stronger support to this
approach.[27] However, DDT and other organochlorine pesticides have been banned in most countries
worldwide because of their persistence in the environment and human toxicity. DDT use is not always
effective, as resistance to DDT was identified in Africa as early as 1955, and by 1972 nineteen species of
mosquito worldwide were resistant to DDT

Benefits[edit]

Pesticides can save farmers' money by preventing crop losses to insects and other pests; in the U.S., farmers
get an estimated fourfold return on money they spend on pesticides.[35] One study found that not using
pesticides reduced crop yields by about 10%.[36] Another study, conducted in 1999, found that a ban on
pesticides in the United States may result in a rise of food prices, loss of jobs, and an increase in world
hunger.[37]
There are two levels of benefits for pesticide use, primary and secondary. Primary benefits are direct gains
from the use of pesticides and secondary benefits are effects that are more long-term.[38]
Primary benefits[edit]

Controlling pests and plant disease vectors

● Improved crop yields
● Improved crop/livestock quality
● Invasive species controlled
Controlling human/livestock disease vectors and nuisance organisms
● Human lives saved and disease reduced. Diseases controlled include malaria,[38] with millions of
lives having been saved or enhanced with the use of DDT alone.[39]
● Animal lives saved and disease reduced
Controlling organisms that harm other human activities and structures
● Drivers view unobstructed
● Tree/brush/leaf hazards prevented
● Wooden structures protected[38]

Health effects

Pesticides may cause acute and delayed health effects in people who are exposed.[42] Pesticide exposure can
cause a variety of adverse health effects, ranging from simple irritation of the skin and eyes to more severe
effects such as affecting the nervous system, hearing,[43] mimicking hormones causing reproductive problems,
and also causing cancer.[44] A 2007 systematic review found that "most studies on non-Hodgkin lymphoma and
leukemia showed positive associations with pesticide exposure" and thus concluded that cosmetic use of
pesticides should be decreased.[45] There is substantial evidence of associations between organophosphate
insecticide exposures and neurobehavioral alterations.[46][47][48][49] Limited evidence also exists for other negative
outcomes from pesticide exposure including neurological, birth defects, and fetal death.[50]
The American Academy of Pediatrics recommends limiting exposure of children to pesticides and using safer
alternatives:[51]
Owing to inadequate regulation and safety precautions, 99% of pesticide-related deaths occur in developing
countries that account for only 25% of pesticide usage.[52]
One study found pesticide self-poisoning the method of choice in one third of suicides worldwide, and
recommended, among other things, more restrictions on the types of pesticides that are most harmful to
humans.[53]
A 2014 epidemiological review found associations between autism and exposure to certain pesticides, but
noted that the available evidence was insufficient to conclude that the relationship was causal.

Prevention[edit]

Minimizing harmful exposure to pesticides can be achieved by proper use of personal protective equipment,
adequate reentry times into recently sprayed areas, and effective product labeling for hazardous substances
as per FIFRA regulations. Training high-risk populations, including agricultural workers, on the proper use and
storage of pesticides, can reduce the incidence of acute pesticide poisoning and potential chronic health
effects associated with exposure. Continued research into the human toxic health effects of pesticides serves
as a basis for relevant policies and enforceable standards that are health protective to all populations.

Environmental effects

Pesticide use raises a number of environmental concerns.Over 98% of sprayed insecticides and 95% of
herbicides reach a destination other than their target species, including non-target species, air, water and
soil.[20] Pesticide drift occurs when pesticides suspended in the air as particles are carried by wind to other
areas, potentially contaminating them. Pesticides are one of the causes of water pollution, and some
pesticides are persistent organic pollutants and contribute to soil and flower (pollen, nectar) contamination.[69]
Furthermore, pesticide use can adversely impact neighboring agricultural activity, as pests themselves drift to
and harm nearby crops that have no pesticide used on them.[70]
In addition, pesticide use reduces biodiversity, contributes to pollinator decline,[71][72][73] destroys habitat
(especially for birds),[74] and threatens endangered species.[20] Pests can develop a resistance to the pesticide
(pesticide resistance), necessitating a new pesticide. Alternatively a greater dose of the pesticide can be used
to counteract the resistance, although this will cause a worsening of the ambient pollution problem.
The Stockholm Convention on Persistent Organic Pollutants, listed 9 of the 12 most dangerous and persistent
organic chemicals that were (now mostly obsolete) organochlorine pesticides.[6][75] Since chlorinated
hydrocarbon pesticides dissolve in fats and are not excreted, organisms tend to retain them almost indefinitely.
Biological magnification is the process whereby these chlorinated hydrocarbons (pesticides) are more
concentrated at each level of the food chain. Among marine animals, pesticide concentrations are higher in
carnivorous fishes, and even more so in the fish-eating birds and mammals at the top of the ecological
pyramid.[76] Global distillation is the process whereby pesticides are transported from warmer to colder regions
of the Earth, in particular the Poles and mountain tops. Pesticides that evaporate into the atmosphere at
relatively high temperature can be carried considerable distances (thousands of kilometers) by the wind to an
area of lower temperature, where they condense and are carried back to the ground in rain or snow.[77]
In order to reduce negative impacts, it is desirable that pesticides be degradable or at least quickly deactivated
in the environment. Such loss of activity or toxicity of pesticides is due to both innate chemical properties of the
compounds and environmental processes or conditions.[78] For example, the presence of halogens within a
chemical structure often slows down degradation in an aerobic environment.[79] Adsorption to soil may retard
pesticide movement, but also may reduce bioavailability to microbial degraders.

Alternatives[edit]

Alternatives to pesticides are available and include methods of cultivation, use of biological pest controls (such
as pheromones and microbial pesticides), genetic engineering, and methods of interfering with insect
breeding.[20] Application of composted yard waste has also been used as a way of controlling pests.[82] These
methods are becoming increasingly popular and often are safer than traditional chemical pesticides. In
addition, EPA is registering reduced-risk conventional pesticides in increasing numbers.
Cultivation practices include polyculture (growing multiple types of plants), crop rotation, planting crops in
areas where the pests that damage them do not live, timing planting according to when pests will be least
problematic, and use of trap crops that attract pests away from the real crop.[20] Trap crops have successfully
controlled pests in some commercial agricultural systems while reducing pesticide usage;[83] however, in many
other systems, trap crops can fail to reduce pest densities at a commercial scale, even when the trap crop
works in controlled experiments.[84]
Release of other organisms that fight the pest is another example of an alternative to pesticide use. These
organisms can include natural predators or parasites of the pests.[20] Biological pesticides based on
entomopathogenic fungi, bacteria and viruses causing disease in the pest species can also be used.[20]
Interfering with insects' reproduction can be accomplished by sterilizing males of the target species and
releasing them, so that they mate with females but do not produce offspring.[20] This technique was first used
on the screwworm fly in 1958 and has since been used with the medfly, the tsetse fly,[85] and the gypsy
moth.[86] However, this can be a costly, time-consuming approach that only works on some types of insects.[20]