Pesticide Residues
A pesticide is
any product that kills or controls various types of pests where a pest is
defined as a plant or animal that is harmful to man or the environment. Most of
us recognize that certain insects, weeds, and rodents that are pests, but the
use of pesticides is not limited to the control of these pests, where other
harmful pests can include birds, snails, fungi, algae, and bacteria which needs
specific concerns while controlling them. Inability to control pests has had a
tremendous impact on world history, i.e. Millions of people died from bubonic
plague (the infamous Black Death) before it was discovered that rat fleas
carried the disease. A similar number have died from malaria, which is
transmitted by mosquitoes. The Irish potato famine in the 1850s was caused by a
fungus that destroyed that country’s major food source, resulting in many
deaths and prompting mass migrations to the United States. Today, bubonic
plague is of little concern, the potato fungus is an insignificant problem, and
malaria has been greatly reduced in the world. The use of pesticides is the
primary reason these problems are no longer a threat.
But pesticides
are also potentially toxic to humans, which may induce adverse health effects
including cancer, immune or nervous systems and it may cause effects on
reproduction. Thus, it needs proper investigations before it can be authorized
for use where pesticides should be tested for all possible health effects and
the results should be analyzed by experts to assess any risks to humans. Scientific
studies of the potential health effects of hazardous chemicals, such as
pesticides, allow them to be classified as carcinogenic (can cause cancer),
neurotoxic (can cause damage to the brain), or teratogenic (can cause damage to
a fetus). This process of classification, called “hazard identification,” is
the first step of “risk assessment”. These problem creating compounds after usage
are called pesticide residues.
Thus pesticide residues
are the deposits of pesticide’s active ingredient, its metabolites or breakdown
products present in some component of the environment after its application, spillage
or dumping. Residue analysis provides a measure of the nature and level of any chemical
contamination within the environment and of its persistence. It is often difficult
to correlate pesticide residues in the environment with effects on fauna and/or
ecological processes. They can, however, show whether an animal or site has been
exposed to chemicals and identify the potential for future problems. All pesticides
are subject to degradation and/or metabolism once released into the environment.
The rates of degradation and dissipation vary greatly from pesticide to pesticide
and situation to situation.
Type
of Pesticides
There are various
kinds of pesticides in use based on the type of pest and intensity of the pest
attack which can be summarized as:
Organochlorines
Mobility of
organochlorines in soil is generally limited; although it is greater in sandy soil.
They tend to be bound in clay soils with limited leaching. Residues of the parent
compound or metabolites can be found in soil, sediment, vegetable samples and in
vertebrates/invertebrates for extended periods. Their solubility in water is low,
although residues can be detected in water where there is extreme contamination
and, particularly, on suspended matter in water.
E.g. lindane
(gamma isomer of benzene hexachloride), dieldrin, DDT (p-p’ isomer), heptachlor,
endosulfan
Organophosphates
Organophosphates have
a fairly limited environmental persistence and residues in living specimens generally
are not detected, or only as metabolites in specific cases. Water solubility is
variable but higher than with the organochlorines; residues generally break down
quite quickly in water (hydrolysis) which is not generally detected except where
the contamination is quite recent. Soil residues are similarly short-lived. Residues
are probably only of interest for 5–15 days after spraying unless in shaded areas
or where the concentrations applied are high.
E.g. fenitrothion,
fenthion.
Carbamates
Residues of parent
compounds are generally not environmentally persistent; metabolites are rapidly
excreted by vertebrates where wWater solubility is moderate; greater for the metabolites.
Most carbamates are relatively stable in water of neutral pH. Stability and mobility
in soil varies between compounds. Environmental residues are probably only of interest
for 10–20 days after spraying, although in certain soils and in water, extended
monitoring may be required.
E.g. aldicarb, carbaryl,
propoxur.
Pyrethroids
Pyrethroids are insecticides
and generally non-persistent in the environment. It is being rapidly degraded in
the presence of strong sunlight, where residues are probably only of interest for
5–7 days after spraying, unless in shaded areas and where the concentrations applied
are particularly high. Proper and accurate detection of residues requires a specialist
laboratory.
E.g. Cypermethrin,
permethrin, deltamethrin.
Insect
Growth Regulators
Benzoyl urea IGRs
generally act by inhibition of chitin synthesis and moulting, thus interfering with
the formation of the insect cuticle. They are increasingly used for the control
of leaf-eating insects (mandibulate herbivores) in forestry, ornamentals and fruit.
Their low water solubility and adsorption by soil reduces their environmental impact
and in general use, residues are only likely to be detected in soil. There may be
some, limited non-target effects in treated areas. There are also IGRs which act
as juvenile hormone mimics, disrupting or preventing maturation of immature invertebrates.
E.g. diflubenzuron
– benzoyl urea IGR, teflubenzuron – benzoyl urea IGR, triflumuron – benzoyl
urea IGR, methoprene – terpenoid IGR (juvenile hormone mimic) and fenoxycarb –
bridged diphenyl carbamate IGR (juvenile hormone analogue).
Herbicides
Although of relatively
low acute toxicity to most animals, herbicides can indirectly affect a variety of
species through the removal of vegetative cover. Environmental persistence of the
herbicides varies; some are readily absorbed by and degraded in soil (e.g. paraquat)
whilst others are more persistent and, with relatively high water solubility, considered
to be quite mobile (e.g. triazine materials) where residues transferring (leaching)
to waterways are a recognized problem. Residues in wildlife are generally transient
with rapid metabolism and excretion. The significance of residues depends upon the
applied material e.g. with 2,4-D, residues decline quite quickly with a half-life
of <7 days in soil; with the triazine herbicides or with products such as linuron/diuron,
persistence is considerably greater and residues can be present for months. The
persistence of sulphonyl urea herbicides varies although at the extremely low rates
they are applied under normal use, the residues present are particularly low and
the analysis can be difficult.
E.g., 2-4-D, atrazine,
linuronm, chlorsulfuron
Fungicides
Some fungicides can
have adverse environmental effects but, although they are used extensively in the
field for cereal production, their use patterns suggest limited scope for environmental
contamination except as the result of disposal (e.g. from large-scale dip treatment
operations) or accidental contamination (spillage, etc.). Water solubility and stability
are variable; some fungicide residues can be detected in water for periods of days
through to months.
E.g. carbendazim, chlorothalonil, metalaxyl
Soil
Fumigants
Materials such as
methyl bromide (use now heavily restricted under the Montreal Protocol) and 1,3-
dichloropropene are examples of materials used as soil fumigants. Under controlled
use, soil fumigants do not pose a substantial environmental problem unless they
are allowed to contaminate watercourses (methyl bromide is highly soluble in water,
13.4 g l-1 at 25 ºC, 1,3-dichloropropene is less soluble, 2 g l-1
at 20 ºC). The materials are volatile and
dissipate to atmosphere on aeration of the soil.
The use of toxic
pesticides to manage pest problems has become a common practice around the
world. Pesticides are used almost everywhere, not only in agricultural fields,
but also in homes, parks, schools, buildings, forests, and roads. It is
difficult to find somewhere where pesticides aren't used from the can of bug
spray under the kitchen sink to the airplane crop dusting acres of farmland;
our world is filled with pesticides. In addition, pesticides can be found in
the air we breathe, the food we eat, and the water we drink.
The presence of
minute residues of pesticides in food has caused some people to ask, “Is our
food supply safe? “due to the recently increased
attention on chemical residues in food. Current evidence strongly indicates
that US foods are safe where Food and Drug Administration (FDA) officials
recently stated that “pesticide residues occurring in foods in the U.S. pose a
very minor if not negligible risk to public health.” However, public
perceptions of risks from pesticides differ markedly from this official
viewpoint and the product that we buy everyday are not coming from USA and they
also differ from actual risks attributable to these products.
Pesticides and Human Health
Pesticides have
been linked to a wide range of human health hazards, ranging from short-term
impacts such as headaches and nausea to chronic impacts like cancer,
reproductive harm, and endocrine disruption. Acute dangers - such as nerve,
skin, and eye irritation and damage, headaches, dizziness, nausea, fatigue and
systemic poisoning - can sometimes be dramatic, and even occasionally fatal. Chronic
health effects may occur years after even minimal exposure to pesticides in the
environment, or result from the pesticide residues which we ingest through our
food and water. A July 2007 study conducted by researchers at the Public Health
Institute, the California Department of Health Services, and the UC Berkeley
School of Public Health found a six fold increase in risk factor for autism
spectrum disorders (ASD) for children of women who were exposed to
organochlorine pesticides.
Pesticides can
cause many types of cancer in humans where some of the most prevalent forms
include leukemia, non-Hodgkins lymphoma, brain, bone, breast, ovarian,
prostate, testicular and liver cancers. In February 2009, the Agency for Toxic
Substances and Disease Registry published a study that found that children who
live in homes where their parents use pesticides are twice as likely to develop
brain cancer versus those that live in residences in which no pesticides are
used. Studies by the National Cancer Institute found that American farmers, who
in most respects are healthier than the population at large, had startling
incidences of leukemia, Hodgkins disease, non-Hodgkins lymphoma, and many other
forms of cancer.
There is also
mounting evidence that exposure to pesticides disrupts the endocrine system,
wreaking havoc with the complex regulation of hormones, the reproductive
system, and embryonic development. Endocrine disruption can produce infertility
and a variety of birth defects and developmental defects in offspring,
including hormonal imbalance and incomplete sexual development, impaired brain
development, behavioral disorders, and many others. Examples of known endocrine
disrupting chemicals which are present in large quantities in our environment
include DDT (which still persists in abundance more than 20 years after being
banned in the U.S.), lindane, atrazine, carbaryl, parathion, and many others.
Multiple Chemical
Sensitivity (MCS) is a medical condition characterized by the body's inability
to tolerate relatively low exposure to chemicals. This condition, also referred
to as Environmental Illness, is triggered by exposure to certain chemicals
and/or environmental pollutants. Exposure to pesticides is a common way for
individuals to develop MCS, and once the condition is present, pesticides are
often a potent trigger for symptoms of the condition. The variety of these
symptoms can be dizzying, including everything from cardiovascular problems to
depression to muscle and joint pains. Over time, individuals suffering from MCS
will begin to react adversely to substances that formerly did not affect them. For
individuals suffering from MCS, the only way to relieve their symptoms is to
avoid those substances that trigger adverse reactions. For some individuals,
this can mean almost complete isolation from the outside world.
Do
We Need Pesticides?
Supporters argue
that pesticide use is necessary to keep the cost of food production low and to
maintain an abundant, affordable supply of fruits and vegetables in the market.
However, opponents argue that since pesticide-free agriculture has never been tried
on a large enough scale, we really do not know if the cost of food production
would increase, or by how much. Researchers have studied the profitability of
farms that do not use synthetic pesticides and found that results can vary
depending on the kind of crop and region of the country. There are other
advantages of using pesticides. For example, pesticides can help prevent some
types of food poisonings. Food that is damaged by insects is more easily
attacked by mold. Pesticides that prevent insect-damage also help prevent the
growth of a mold that produces a natural, but potent cancer-causing poison
called aflatoxin in food.
Best Practices in Minimizing Pesticide Residue in Your
Foods
Wash your food.
To remove pesticides, as well as for general health, it is a good idea to wash
food with clean, potable water before it is cooked or eaten.
Peel, if
possible. Peeling helps reduce the levels of pesticides that may be on the
surface. Peeling does not remove all pesticide residues, since some residues
are absorbed into the food.
Trim the fat from
meats. Some pesticides collect in animal fat. Trimming excess fat from meats
helps to reduce the amount of such pesticides that would be eaten.
Cooking helps
reduce some of the pesticide residues in food that are not removable by washing
or peeling.
Eat a varied diet
rich in fruits and vegetables. Specific pesticides are used for specific food
crops. Eating a diet with many different fruits, vegetables and grains is a
healthy practice in itself. It also prevents eating an unbalanced amount of a
particular food or the pesticide residues that it may carry.
If still
concerned, consider buying food that has been grown using "Integrated Pest
Management" or "Certified Organic Methods" Buying food grown
using less or no synthetic chemicals may help reduce the intake of pesticide
residues. However, that even organically grown food is not guaranteed to be
totally free of pesticide residues.
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