The impact of pesticides consists of the effects
of pesticides on non-target species.
Pesticides are chemical preparations used
to kill fungal or animal pests.
Over 98% of sprayed insecticides and 95% of
herbicides reach a destination other than
their target species, because they are sprayed
or spread across entire agricultural fields.
Runoff can carry pesticides into aquatic environments
while wind can carry them to other fields,
grazing areas, human settlements and undeveloped
areas, potentially affecting other species.
Other problems emerge from poor production,
transport and storage practices.
Over time, repeated application increases
pest resistance, while its effects on other
species can facilitate the pest's resurgence.Each
pesticide or pesticide class comes with a
specific set of environmental concerns.
Such undesirable effects have led many pesticides
to be banned, while regulations have limited
and/or reduced the use of others.
Over time, pesticides have generally become
less persistent and more species-specific,
reducing their environmental footprint.
In addition the amounts of pesticides applied
per hectare have declined, in some cases by
99%.
However, the global spread of pesticide use,
including the use of older/obsolete pesticides
that have been banned in some jurisdictions,
has increased overall.
== Agriculture and the environment ==
The arrival of humans in an area, to live
or to conduct agriculture, necessarily has
environmental impacts.
These range from simple crowding out of wild
plants in favor of more desirable cultivars
to larger scale impacts such as reducing biodiversity
by reducing food availability of native species,
which can propagate across food chains.
The use of agricultural chemicals such as
fertilizer and des magnify those impacts.
While advances in agrochemistry have reduced
those impacts, for example by the replacement
of long-lived chemicals with those that reliably
degrade, even in the best case they remain
substantial.
These effects are magnified by the use of
older chemistries and poor management practices.
== History ==
While concern for ecotoxicology began with
acute poisoning events in the late 19th century;
public concern over the undesirable environmental
effects of chemicals arose in the early 1960s
with the publication of Rachel Carson′s
book, Silent Spring.
Shortly thereafter, DDT, originally used to
combat malaria, and its metabolites were shown
to cause population-level effects in raptorial
birds.
Initial studies in industrialized countries
focused on acute mortality effects mostly
involving birds or fish.Data on pesticide
usage remain scattered and/or not publicly
available (3).
The common practice of incident registration
is inadequate for understanding the entirety
of effects.Since 1990, research interest has
shifted from documenting incidents and quantifying
chemical exposure to studies aimed at linking
laboratory, mesocosm and field experiments.
The proportion of effect-related publications
has increased.
Animal studies mostly focus on fish, insects,
birds, amphibians and arachnids.Since 1993,
the United States and the European Union have
updated pesticide risk assessments, ending
the use of acutely toxic organophosphate and
carbamate insecticides.
Newer pesticides aim at efficiency in target
and minimum side effects in nontarget organisms.
The phylogenetic proximity of beneficial and
pest species complicates the project.One of
the major challenges is to link the results
from cellular studies through many levels
of increasing complexity to ecosystems.The
concept (borrowed from nuclear physics) of
a half-life has been utilized for pesticides
in plants, and certain authors maintain that
pesticide risk and impact assessment models
rely on and are sensitive to information describing
dissipation from plants.
Half-life for pesticides is explained in two
NPIC fact sheets.
Known degradation pathways are through: photolysis,
chemical dissociation, sorption, bioaccumulation
and plant or animal metabolism.
A USDA fact sheet published in 1994 lists
the soil adsorption coefficient and soil half-life
for then-commonly used pesticides.
== Specific pesticide effects ==
== Air ==
Pesticides can contribute to air pollution.
Pesticide drift occurs when pesticides suspended
in the air as particles are carried by wind
to other areas, potentially contaminating
them.
Pesticides that are applied to crops can volatilize
and may be blown by winds into nearby areas,
potentially posing a threat to wildlife.
Weather conditions at the time of application
as well as temperature and relative humidity
change the spread of the pesticide in the
air.
As wind velocity increases so does the spray
drift and exposure.
Low relative humidity and high temperature
result in more spray evaporating.
The amount of inhalable pesticides in the
outdoor environment is therefore often dependent
on the season.
Also, droplets of sprayed pesticides or particles
from pesticides applied as dusts may travel
on the wind to other areas, or pesticides
may adhere to particles that blow in the wind,
such as dust particles.
Ground spraying produces less pesticide drift
than aerial spraying does.
Farmers can employ a buffer zone around their
crop, consisting of empty land or non-crop
plants such as evergreen trees to serve as
windbreaks and absorb the pesticides, preventing
drift into other areas.
Such windbreaks are legally required in the
Netherlands.Pesticides that are sprayed on
to fields and used to fumigate soil can give
off chemicals called volatile organic compounds,
which can react with other chemicals and form
a pollutant called tropospheric ozone.
Pesticide use accounts for about 6 percent
of total tropospheric ozone levels.
== Water ==
In the United States, pesticides were found
to pollute every stream and over 90% of wells
sampled in a study by the US Geological Survey.
Pesticide residues have also been found in
rain and groundwater.
Studies by the UK government showed that pesticide
concentrations exceeded those allowable for
drinking water in some samples of river water
and groundwater.Pesticide impacts on aquatic
systems are often studied using a hydrology
transport model to study movement and fate
of chemicals in rivers and streams.
As early as the 1970s quantitative analysis
of pesticide runoff was conducted in order
to predict amounts of pesticide that would
reach surface waters.There are four major
routes through which pesticides reach the
water: it may drift outside of the intended
area when it is sprayed, it may percolate,
or leach, through the soil, it may be carried
to the water as runoff, or it may be spilled,
for example accidentally or through neglect.
They may also be carried to water by eroding
soil.
Factors that affect a pesticide's ability
to contaminate water include its water solubility,
the distance from an application site to a
body of water, weather, soil type, presence
of a growing crop, and the method used to
apply the chemical.
=== United States regulations ===
In the US, maximum limits of allowable concentrations
for individual pesticides in drinking water
are set by the Environmental Protection Agency
(EPA) for public water systems.
(There are no federal standards for private
wells.)
Ambient water quality standards for pesticide
concentrations in water bodies are principally
developed by state environmental agencies,
with EPA oversight.
These standards may be issued for individual
water bodies, or may apply statewide.
=== United Kingdom regulations ===
The United Kingdom sets Environmental Quality
Standards (EQS), or maximum allowable concentrations
of some pesticides in bodies of water above
which toxicity may occur.
=== European Union regulations ===
The European Union also regulates maximum
concentrations of pesticides in water.
== Soil ==
The extensive use of pesticides in agricultural
production can degrade and damage the community
of microorganisms living in the soil, particularly
when these chemicals are overused or misused.
The full impact of pesticides on soil microorganisms
is still not entirely understood; many studies
have found deleterious effects of pesticides
on soil microorganisms and biochemical processes,
while others have found that the residue of
some pesticides can be degraded and assimilated
by microorganisms.
The effect of pesticides on soil microorganisms
is impacted by the persistence, concentration,
and toxicity of the applied pesticide, in
addition to various environmental factors.
This complex interaction of factors makes
it difficult to draw definitive conclusions
about the interaction of pesticides with the
soil ecosystem.
In general, however, long-term pesticide application
can disturb the biochemical processes of nutrient
cycling.Many of the chemicals used in pesticides
are persistent soil contaminants, whose impact
may endure for decades and adversely affect
soil conservation.The use of pesticides decreases
the general biodiversity in the soil.
Not using the chemicals results in higher
soil quality, with the additional effect that
more organic matter in the soil allows for
higher water retention.
This helps increase yields for farms in drought
years, when organic farms have had yields
20-40% higher than their conventional counterparts.
A smaller content of organic matter in the
soil increases the amount of pesticide that
will leave the area of application, because
organic matter binds to and helps break down
pesticides.Degradation and sorption are both
factors which influence the persistence of
pesticides in soil.
Depending on the chemical nature of the pesticide,
such processes control directly the transportation
from soil to water, and in turn to air and
our food.
Breaking down organic substances, degradation,
involves interactions among microorganisms
in the soil.
Sorption affects bioaccumulation of pesticides
which are dependent on organic matter in the
soil.
Weak organic acids have been shown to be weakly
sorbed by soil, because of pH and mostly acidic
structure.
Sorbed chemicals have been shown to be less
accessible to microorganisms.
Aging mechanisms are poorly understood but
as residence times in soil increase, pesticide
residues become more resistant to degradation
and extraction as they lose biological activity.
== Effect on plants ==
Nitrogen fixation, which is required for the
growth of higher plants, is hindered by pesticides
in soil.
The insecticides DDT, methyl parathion, and
especially pentachlorophenol have been shown
to interfere with legume-rhizobium chemical
signaling.
Reduction of this symbiotic chemical signaling
results in reduced nitrogen fixation and thus
reduced crop yields.
Root nodule formation in these plants saves
the world economy $10 billion in synthetic
nitrogen fertilizer every year.Pesticides
can kill bees and are strongly implicated
in pollinator decline, the loss of species
that pollinate plants, including through the
mechanism of Colony Collapse Disorder, in
which worker bees from a beehive or western
honey bee colony abruptly disappear.
Application of pesticides to crops that are
in bloom can kill honeybees, which act as
pollinators.
The USDA and USFWS estimate that US farmers
lose at least $200 million a year from reduced
crop pollination because pesticides applied
to fields eliminate about a fifth of honeybee
colonies in the US and harm an additional
15%.On the other side, pesticides have some
direct harmful effect on plant including poor
root hair development, shoot yellowing and
reduced plant growth.
== Effect on animals ==
Many kinds of animals are harmed by pesticides,
leading many countries to regulate pesticide
usage through Biodiversity Action Plans.Animals
including humans may be poisoned by pesticide
residues that remain on food, for example
when wild animals enter sprayed fields or
nearby areas shortly after spraying.Pesticides
can eliminate some animals' essential food
sources, causing the animals to relocate,
change their diet or starve.
Residues can travel up the food chain; for
example, birds can be harmed when they eat
insects and worms that have consumed pesticides.
Earthworms digest organic matter and increase
nutrient content in the top layer of soil.
They protect human health by ingesting decomposing
litter and serving as bioindicators of soil
activity.
Pesticides have had harmful effects on growth
and reproduction on earthworms.
Some pesticides can bioaccumulate, or build
up to toxic levels in the bodies of organisms
that consume them over time, a phenomenon
that impacts species high on the food chain
especially hard.
=== Birds ===
The US Fish and Wildlife Service estimates
that 72 million birds are killed by pesticides
in the United States each year.
Bald eagles are common examples of nontarget
organisms that are impacted by pesticide use.
Rachel Carson's book Silent Spring dealt with
damage to bird species due to pesticide bioaccumulation.
There is evidence that birds are continuing
to be harmed by pesticide use.
In the farmland of the United Kingdom, populations
of ten different bird species declined by
10 million breeding individuals between 1979
and 1999, allegedly from loss of plant and
invertebrate species on which the birds feed.
Throughout Europe, 116 species of birds were
threatened as of 1999.
Reductions in bird populations have been found
to be associated with times and areas in which
pesticides are used.
DDE-induced egg shell thinning has especially
affected European and North American bird
populations.
From 1990 to 2014 the number of common farmland
birds has declined in the European Union as
a whole and in France, Belgium and Sweden;
in Germany, which relies more on organic farming
and less on pesticides the decline has been
slower; in Switzerland, which does not rely
much on intensive agriculture, after a decline
in the early 2000s the level has returned
to the one of 1990.
In another example, some types of fungicides
used in peanut farming are only slightly toxic
to birds and mammals, but may kill earthworms,
which can in turn reduce populations of the
birds and mammals that feed on them.Some pesticides
come in granular form.
Wildlife may eat the granules, mistaking them
for grains of food.
A few granules of a pesticide may be enough
to kill a small bird.The herbicide paraquat,
when sprayed onto bird eggs, causes growth
abnormalities in embryos and reduces the number
of chicks that hatch successfully, but most
herbicides do not directly cause much harm
to birds.
Herbicides may endanger bird populations by
reducing their habitat.
=== Aquatic life ===
Fish and other aquatic biota may be harmed
by pesticide-contaminated water.
Pesticide surface runoff into rivers and streams
can be highly lethal to aquatic life, sometimes
killing all the fish in a particular stream.Application
of herbicides to bodies of water can cause
fish kills when the dead plants decay and
consume the water's oxygen, suffocating the
fish.
Herbicides such as copper sulfite that are
applied to water to kill plants are toxic
to fish and other water animals at concentrations
similar to those used to kill the plants.
Repeated exposure to sublethal doses of some
pesticides can cause physiological and behavioral
changes that reduce fish populations, such
as abandonment of nests and broods, decreased
immunity to disease and decreased predator
avoidance.Application of herbicides to bodies
of water can kill plants on which fish depend
for their habitat.Pesticides can accumulate
in bodies of water to levels that kill off
zooplankton, the main source of food for young
fish.
Pesticides can also kill off insects on which
some fish feed, causing the fish to travel
farther in search of food and exposing them
to greater risk from predators.The faster
a given pesticide breaks down in the environment,
the less threat it poses to aquatic life.
Insecticides are typically more toxic to aquatic
life than herbicides and fungicides.
=== Amphibians ===
In the past several decades, amphibian populations
have declined across the world, for unexplained
reasons which are thought to be varied but
of which pesticides may be a part.Pesticide
mixtures appear to have a cumulative toxic
effect on frogs.
Tadpoles from ponds containing multiple pesticides
take longer to metamorphose and are smaller
when they do, decreasing their ability to
catch prey and avoid predators.
Exposing tadpoles to the organochloride endosulfan
at levels likely to be found in habitats near
fields sprayed with the chemical kills the
tadpoles and causes behavioral and growth
abnormalities.The herbicide atrazine can turn
male frogs into hermaphrodites, decreasing
their ability to reproduce.
Both reproductive and nonreproductive effects
in aquatic reptiles and amphibians have been
reported.
Crocodiles, many turtle species and some lizards
lack sex-distinct chromosomes until after
fertilization during organogenesis, depending
on temperature.
Embryonic exposure in turtles to various PCBs
causes a sex reversal.
Across the United States and Canada disorders
such as decreased hatching success, feminization,
skin lesions, and other developmental abnormalities
have been reported.
=== Humans ===
Pesticides can enter the body through inhalation
of aerosols, dust and vapor that contain pesticides;
through oral exposure by consuming food/water;
and through skin exposure by direct contact.
Pesticides secrete into soils and groundwater
which can end up in drinking water, and pesticide
spray can drift and pollute the air.
The effects of pesticides on human health
depend on the toxicity of the chemical and
the length and magnitude of exposure.
Farm workers and their families experience
the greatest exposure to agricultural pesticides
through direct contact.
Every human contains pesticides in their fat
cells.
Children are more susceptible and sensitive
to pesticides, because they are still developing
and have a weaker immune system than adults.
Children may be more exposed due to their
closer proximity to the ground and tendency
to put unfamiliar objects in their mouth.
Hand to mouth contact depends on the child's
age, much like lead exposure.
Children under the age of six months are more
apt to experience exposure from breast milk
and inhalation of small particles.
Pesticides tracked into the home from family
members increase the risk of exposure.
Toxic residue in food may contribute to a
child’s exposure.
The chemicals can bioaccumulate in the body
over time.
Exposure effects can range from mild skin
irritation to birth defects, tumors, genetic
changes, blood and nerve disorders, endocrine
disruption, coma or death.
Developmental effects have been associated
with pesticides.
Recent increases in childhood cancers in throughout
North America, such as leukemia, may be a
result of somatic cell mutations.
Insecticides targeted to disrupt insects can
have harmful effects on mammalian nervous
systems.
Both chronic and acute alterations have been
observed in exposees.
DDT and its breakdown product DDE disturb
estrogenic activity and possibly lead to breast
cancer.
Fetal DDT exposure reduces male penis size
in animals and can produce undescended testicles.
Pesticide can affect fetuses in early stages
of development, in utero and even if a parent
was exposed before conception.
Reproductive disruption has the potential
to occur by chemical reactivity and through
structural changes.
== Persistent organic pollutants ==
Persistent organic pollutants (POPs) are compounds
that resist degradation and thus remain in
the environment for years.
Some pesticides, including aldrin, chlordane,
DDT, dieldrin, endrin, heptachlor, hexachlorobenzene,
mirex and toxaphene, are considered POPs.
Some POPs have the ability to volatilize and
travel great distances through the atmosphere
to become deposited in remote regions.
Such chemicals may have the ability to bioaccumulate
and biomagnify and can bioconcentrate (i.e.
become more concentrated) up to 70,000 times
their original concentrations.
POPs can affect non-target organisms in the
environment and increase risk to humans by
disruption in the endocrine, reproductive,
and respiratory systems.
== Pest resistance ==
Pests may evolve to become resistant to pesticides.
Many pests will initially be very susceptible
to pesticides, but following mutations in
their genetic makeup become resistant and
survive to reproduce.
Resistance is commonly managed through pesticide
rotation, which involves alternating among
pesticide classes with different modes of
action to delay the onset of or mitigate existing
pest resistance.
== Pest rebound and secondary pest outbreaks
==
Non-target organisms can also be impacted
by pesticides.
In some cases, a pest insect that is controlled
by a beneficial predator or parasite can flourish
should an insecticide application kill both
pest and beneficial populations.
A study comparing biological pest control
and pyrethroid insecticide for diamondback
moths, a major cabbage family insect pest,
showed that the pest population rebounded
due to loss of insect predators, whereas the
biocontrol did not show the same effect.
Likewise, pesticides sprayed to control mosquitoes
may temporarily depress mosquito populations,
however they may result in a larger population
in the long run by damaging natural controls.
This phenomenon, wherein the population of
a pest species rebounds to equal or greater
numbers than it had before pesticide use,
is called pest resurgence and can be linked
to elimination of its predators and other
natural enemies.Loss of predator species can
also lead to a related phenomenon called secondary
pest outbreaks, an increase in problems from
species that were not originally a problem
due to loss of their predators or parasites.
An estimated third of the 300 most damaging
insects in the US were originally secondary
pests and only became a major problem after
the use of pesticides.
In both pest resurgence and secondary outbreaks,
their natural enemies were more susceptible
to the pesticides than the pests themselves,
in some cases causing the pest population
to be higher than it was before the use of
pesticide.
== Eliminating pesticides ==
Many alternatives are available to reduce
the effects pesticides have on the environment.
Alternatives include manual removal, applying
heat, covering weeds with plastic, placing
traps and lures, removing pest breeding sites,
maintaining healthy soils that breed healthy,
more resistant plants, cropping native species
that are naturally more resistant to native
pests and supporting biocontrol agents such
as birds and other pest predators.
In the United States, conventional pesticide
use peaked in 1979, and by 2007, had been
reduced by 25 percent from the 1979 peak level,
while US agricultural output increased by
43 percent over the same period.Biological
controls such as resistant plant varieties
and the use of pheromones, have been successful
and at times permanently resolve a pest problem.
Integrated Pest Management (IPM) employs chemical
use only when other alternatives are ineffective.
IPM causes less harm to humans and the environment.
The focus is broader than on a specific pest,
considering a range of pest control alternatives.
Biotechnology can also be an innovative way
to control pests.
Strains can be genetically modified (GM) to
increase their resistance to pests.
However the same techniques can be used to
increase pesticide resistance and was employed
by Monsanto to create glyphosate-resistant
strains of major crops.
In the United States in 2010, 70% of all the
corn that was planted was resistant to glyphosate;
78% of cotton, and 93% of all soybeans
