Flashcards in Q 2 Text Deck (53)
The US Environmental Protection Agency's definition of a pesticide is as follows:
The purpose of a pesticide is usually to kill or repel some form of life.
"A pesticide is any substance or mixture of substances intended for preventing, destroying, repelling, or mitigating any pest. Though often misunderstood to refer only to insecticides, the term pesticide also applies to herbicides, fungicides, and various other substances used to control pests."
Pesticide formulations contain both "active" and "inert" ingredients. Active ingredients are what kill the pest, and inert ingredients help the active ingredients to work more effectively
Pesticide formulations contain both "___" and "____" ingredients. _____ ingredients are what kill the pest, and _____ ingredients help the active ingredients to work more effectively
Active and Inert
The two largest classes of synthetic pesticides are ________ and ________,
insecticides, which are designed to kill insects, and herbicides, which are designed to kill plants.
3 other types of pesticides that aren't the main two.
Other classes of pesticides include fungicides (for molds and fungi), rodenticides (for mammals), and antimicrobials (for microorganisms such as bacteria and viruses). Antimicrobial pesticides are used as preservatives, sterilizers, and disinfectants in home, institutional, and commercial environments.
A common insecticide used to kill fleas on cats is imidacloprid. This insecticide is also used to control insects such as aphids, whiteflies, termites and a range of other soil insects, and some beetles. It is also very toxic to honey bees.
Imidacloprid is toxic to the nervous system, causing an overstimulation of acetylcholine and consequent paralysis and death in insects.
The total use of pesticides in the United States is about __ billion pounds a year, ___ billion pounds of which is used in agriculture.
carbofuran (n-methyl carbamate) is a broad-spectrum insecticide used on rice, alfalfa, table and wine grapes, cotton, potatoes, and soybeans. Carbofuran insecticide inhibits cholinesterase, causing an increase in the neurotransmitter acetylcholine. Elevated acetylcholine levels cause tremor, paralysis, and death in insects, and can have similar effects on wildlife, such as birds, as well as humans. Due to its toxicity to humans and mammals, the US EPA moved to ban all use of carbofuran in 2008.
____ was banned in 2008 by the US EPA due to its toxicity to humans and mammals.
One of the first pesticides was sulfur, used by the Chinese in around 1000 BC to control bacteria and mold (fungus). Sulfur is still widely used today. For example, it is used in fungicides to control diseases on both agricultural and ornamental plants, and in the wine industry, sulfur is used to control unwanted bacterial growth in empty wine barrels and is commonly added to wine to kill unwanted yeast
One of the first pesticides was _____, used by the Chinese in around 1000 BC
The Chinese also pioneered the use of arsenic-containing compounds to control insects. Arsenic has a long history of use both as an insecticide and herbicide, and also as a medicine. Arsenic trioxide was used as a weed killer (herbicide) in the late 1800s, and lead arsenate, containing both lead and arsenic, was used as an insecticide, particularly in orchards, prior to the development of synthetic pesticides following WWII
Plants have provided several other important nonsynthetic pesticides. In the late 1600s _____.
an extract from tobacco leaves, was recognized as a potent insecticide and is now in limited use as a pesticide
4 non-synthetic pesticides?
nicotine, rotenone, pyrethrums, strychnine.
Synthetic chemistry advanced rapidly in the ____s and by the early ____s, a range of new pesticides had been developed, including organochlorine insecticides like DDT.
In 1937 the first _________ compounds were synthesized by a group of German chemists.
4 most common synthetic insecticides?
The most prominent classes of insecticides are organochlorines, organophosphates, carbamates, and pyrethroids.
While organochlorines have the advantage of being cheap to manufacture and are effective against target species, they have serious unintended consequences. Organochlorines disrupt the movement of ions such as calcium, chloride, sodium, and potassium into and out of nerve cells. Depending on the specific structure of the organochlorine chemical, it may also affect the nervous system in other ways. At one time organochlorines were thought to be ideal because they are very stable, slow to degrade in the environment, dissolve in fats (and are therefore readily taken up by insects), and seemingly harmless to mammals. Unfortunately it eventually became clear that the attributes of persistence and fat solubility were actually very undesirable: the organochlorines passed up the food chain, where they bioaccumulated in the fat of large animals and humans and were passed on to nursing young.
Organophosphates and Carbamates
Organophosphates were initially developed in the 1940s as highly toxic biological warfare agents (nerve gases). Modern derivatives, including sarin, soman, and VX, were stockpiled by various countries and now present some difficult disposal problems. Researchers created many different organophosphates in their search for insecticides that would target selected species and would be less toxic to mammals. When the organophosphate parathion was first used as a replacement for DDT, it was believed to be better as it was more specific. Unfortunately there were a number of human deaths because workers failed to appreciate the fact that parathion's short term (acute) toxicity is greater than DDT's.
One of the newer classes of insecticide, synthetic pyrethroids are loosely based upon the naturally occurring pyrethrum found in chrysanthemum flowers. Synthetic pyrethroids were first developed in the 1980s, but the naturally occurring pyrethrum was first commercially used in the 1800s. Their use has increased significantly over the last 20 years. The chemical structure of pyrethroids is quite different from that of organochlorines, organophosphates, and carbamates but the primary site of action is also the nervous system. Pyrethroids affect the movement of sodium ions (Na+) into and out of nerve cells, causing the nerve cells to become hypersensitive to neurotransmitters. Structural differences between various pyrethroids can change their toxic effects on specific insects and even mammals.
Synthetic pyrethroids are more persistent in the environment than natural pyrethrum, which is unstable in light and breaks down very quickly in sunlight.
Herbicides are used to kill or damage plants and are the most rapidly growing type of pesticide. Prior to the 1930s, herbicides were nonspecific and often very toxic to humans as well as other animals. In the 1930s, researchers discovered several chemicals that selectively killed plants while developing new insecticides. These chemicals are now widely used to increase food production by killing weeds that choke out or compete with food crops.
The most well known herbicides are the chlorophenoxy compounds that include 2,4-D
The most well known herbicides are the chlorophenoxy compounds that include 2,4-D
85 and 2,4,5-T.
This herbicide mixture, sometimes called Agent Orange in the 1960s, was widely used to kill broadleaf plants in agricultural fields, along roadsides, and on rights of way for power lines. It was also extensively used as a chemical warfare agent to kill unwanted vegetation, for example in jungles. The mechanism of action of this class of chemicals is poorly understood, but the herbicides appear to interact with plant growth hormones. (See Pesticides - History for discussion of the contamination of 2,4,5-T with dioxin.)
Paraquat and diquat
Paraquat and the related chemical diquat are nonselective herbicides that are also toxic to mammals. Occupational or accidental exposure to paraquat can occur by ingestion, skin exposure, or inhalation, all of which can cause serious illness or death. While seldom used in the United States at this time, paraquat is still widely used in developing countries. At one time it was used in marijuana plant eradication programs, but it was discontinued when a number of fatalities were observed in smokers of paraquat-contaminated marijuana
Fungicides were developed to control the fungi and mold that may grow on crops, stored foods and seeds, and in our bodies. Control of plant fungus in agriculture is important not only because fungi can damage crops, but also because some fungi produce toxic chemicals (mycotoxins)
hexachlorobenzene and Mercury
In the 1940s and 50s, hexachlorobenzene, a synthetic fungicide, was widely used to protect seed grain from fungal rot. Mercurial compounds were also applied to seed grains to protect them from soil fungus. Both of these chemicals caused severe illness when people ate treated grains intended for planting as crops. These two fungicides are now rarely used and have been replaced by less-toxic ones, but careful harvest and storage procedures for seeds are necessary to prevent potential contamination of food supplies.
_______ _______ ______ reduces the need to use dangerous fungicides on growing plants.
Integrated Pest Management
One of the first anticoagulant rodenticides was warfarin
Rodenticides are a broad class of pesticides designed to kill small mammals such as rats and mice. Some rodenticides are anticoagulants and work by inhibiting bloodclotting; these are often used to control rat populations. One of the first anticoagulant rodenticides was warfarin, which is related to plant-derived coumadin (from spoiled sweet clover). Inthe 1950s rats developed resistance to warfarin, which prompted scientists to develop more potent anticoagulants, which are termed second-generation anticoagulants. Other rodenticides include fluoroacetic acid and zinc phosphide (which are both very toxic), and thiourea-based compounds.
One of the problems of rodenticides is that they may also harm wildlife that mistake pesticide-containing baits or pellets for food. Wildlife, such as wolves or birds of prey, may also be harmed by eating rodents or other animals that have been poisoned. The primary alternative to using chemical rodenticides is trapping
Molluscicides are used to control slugs and snails. Mollusks are a group of invertebrate animals that include shellfish, cephalopods (such as squid and octopus), slugs, and snails.
The most commonly used active ingredient in molluscicides is metaldehyde
The World Health Organization estimates that there are ___ million cases of pesticide poisoning each year and up to ______ thousand deaths, primarily in developing countries.
Federal Insecticide, Fungicide, and Rodenticide Act(FIFRA)
Congress passed the first federal act specifically dealing with pesticides in 1947. This act, the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA), allowed the US Department of Agriculture to regulate appropriate labeling of pesticides. Unfortunately, this law did not provide sufficient protection for consumers or workers. Rachel Carson's Silent Spring, published in 1962, explored the harmful effects of pesticides, especially DDT, on people, wildlife, and the environment and marked a turning point in our understanding of the effects of chemicals on human and environmental health
In _____ the US Environmental Protection Agency was formed and given authority to register pesticides based on evaluating and weighing estimated risks and benefits.
Mercury exists in different forms with very different properties; thus each section of this chapter is divided into ______ mercury, the common silvery liquid, and _______ mercury (usually methyl mercury, Hg-CH ), which is generated from inorganic ₃ mercury by bacteria and accumulates in some commonly consumed species of fish.
in Roman mythology, in which the winged messenger ________, who was noted for his cleverness, cunning and eloquence, was both the god of merchants and commerce as well as of thieves and vagabonds
Inorganic Mercury also known as ______ or ______
and what it is
Elemental mercury, also known as quicksilver or metallic mercury,
is a silvery liquid at room temperature. It has a low boiling point, a high vapor pressure (e.g. evaporates) at room temperature, and a high density, weighing 13.6 times as much as water. Stone, iron, lead, and even humans can float on its surface (see Putman, 1972). Its toxicity has been recognized since Roman times when slaves mined it in Almaden, Spain; this mine remains active today as a major mercury source. While all rock types contain some mercury, cinnabar contains the greatest concentration of inorganic mercury (>80%). Elemental mercury is produced from cinnabar by condensing the vapor of heated ore. In the United States elemental mercury is produced primarily as a byproduct of mining.
Its toxicity has been recognized since Roman times when slaves mined it in Almaden, Spain; this mine remains active today as a major mercury source.
rock type with highest content of mercury >80%
The first reported use of organic mercury compounds in chemical research occurred in 1863. Their synthesis immediately led to the recognition of their extremely high toxicity relative to inorganic mercury forms, and by 1866 two chemists had died from organic mercury poisoning. Therapeutic applications of organic mercurials in the treatment of CNS syphilis, which began in 1887, led to non-occupational poisoning; the use of organic mercury-based medicines ceased soon after because of their extremely high toxicity. The use of synthetic organic mercurials as antifungal dressings for agricultural seeds began in 1914. Their use in this industry has resulted in scattered case reports of acute poisoning associated with the chemical manufacture, application, and inadvertent consumption of either the treated grain or of animals fed with the treated grain. The use of organic mercurials in agriculture has resulted in large-scale poisoning episodes worldwide, such as occurred in Iraq.
Organic mercury is ______ toxic then inorganic
options: less, more, equally
Minimata, Japan: Late 1950's
Minamata, Japan: Mercury and Fish In the late 1950s
the subtle and serious consequences of methyl mercury exposure became evident in Minamata, Japan. Initially, health experts were baffled by early signs of uncoordinated movement and numbness around the lips and extremities, followed by constriction in visual fields in fishermen and their families. Developmental effects were clearly evident in infants who exhibited subtle to severe disabilities. This spectrum of adverse effects was finally related to methyl mercury exposure from consumption of contaminated fish. Minamata Bay was contaminated with mercury and methyl mercury from a factory manufacturing the chemical acetaldehyde. Mercury was used in the manufacturing process, and both mercury and methyl mercury were discharged into Minamata Bay. The fish in the bay accumulated increasing amounts of methyl mercury, which was subsequently passed to the fish-consuming residents of the area. This was one of the first modern lessons of the consequences of the bioaccumulation of methyl mercury.
Seed Grain in Iraq
Mercury-coated Seed Grain in Iraq
The toxic antifungal properties of organic mercury compounds were beneficial when applied to seed grain, but when humans consumed these seeds there were tragic consequences. During much of the 20th century, seeds were coated with organomercury compounds to reduce their destruction by fungus in the soil. Often these seeds were colored pink to indicate they were coated with an antifungal agent and were for planting only, not consumption. During the early 1970s, a severe drought in Iraq resulted in a loss of seed grain and people struggled with malnutrition. Pinkcolored mercury-coated seed grain was shipped to Iraq for planting. Unfortunately, the local population could not read the foreign language on the seed bags nor recognize the pink seeds as hazardous. Bread made from these seeds was pink, tasty, and toxic, particularly to the developing child. Many people died or were tragically disabled for life, giving the world another lesson in communication and mercury toxicity.
Inorganic Mercury: How it works
When mercury vapor from elemental mercury is inhaled, it is readily and rapidly absorbed into the blood stream, easily crossing the blood-brain barrier and the placenta. Ingestion of elemental mercury is far less hazardous than inhalation of mercury vapor due to its poor absorption in the gut. After entering the brain, mercury is oxidized and will not transfer back across the blood-brain barrier, thus continued exposure to mercury vapor results in the accumulation of mercury in the nervous system.
Organic Mercury: How it works
While there are many synthetic organic mercury compounds, the most important organic mercury is the naturally occurring form methyl mercury (MeHg). In the environment, inorganic mercury is biotransformed to MeHg primarily through microbial methylation in sediments of fresh and ocean waters. Once produced, MeHg readily enters the aquatic food chain and bioaccumulates in tissues of aquatic organisms. Because MeHg is stored throughout the life of aquatic organisms, it is transferred up the food chain and results in the highest concentrations in larger, long-lived, predatory species such as swordfish, pike, and ocean tuna. The bulk of mercury in fish is stored in muscle, and almost all of the mercury in muscle is MeHg. The concentration of MeHg in fish depends on the age and trophic level of the particular fish, and can be quite substantial (> 1000 µg/kg (ppm)). For example, the total mercury in the edible tissues of shark and swordfish can average as high as 1200 µg/kg. The use of organomercurials as fungicides and paint preservatives and in medicinal applications has ceased; therefore, fish and marine mammal consumption is the primary source of human MeHg exposure
Inorganic Mercury: Health Affects
Elemental mercury in the form of mercury vapor is readily and rapidly absorbed into the blood stream when inhaled and easily crosses the blood-brain barrier and the placenta. Oral ingestion of elemental mercury is far less hazardous than inhalation of mercury vapor due to its poor absorption in the gut. Acute, high level exposure to mercury vapor can result in respiratory, cardiovascular, neurological, and gastrointestinal effects, and even death.
Both acute, high-dose exposure and chronic, low-dose exposure to mercury vapor can result in increasing and irreversible neurological effects. Symptoms include tremors and loss of feeling in the hands (paresthesia or stocking-glove sensory loss), emotional instability, insomnia, memory loss, and neuromuscular weakness. Exposure to mercury vapor may precipitate tremor, drowsiness, depression, and irritability; such symptoms form the basis for the expression "mad as a hatter" and the character the Mad Hatter in Lewis Carroll's Alice's Adventures in Wonderland. Decreased performance on memory tests and verbal concept formation have also been documented in industry workers exposed to mercury vapor. Neurotoxic effects such as dizziness, weakness, insomnia, numbness, and tremor were observed in a 12-year-old girl exposed to spilled mercury.
Organic Mercury: Health Affects
The devastating health consequences of methyl mercury (MeHg) exposure were well documented from several tragic incidents (see the case studies section). Historically, MeHg exposure played a very important role in drawing worldwide attention to the consequences of industrial pollution, not just for workers but also for the general public. In the 1950s, the consequences of MeHg exposure to the people of Minamata and Niigata, Japan were recognized. In both cases MeHg exposure resulted from consumption of fish from waters receiving industrial effluent discharge containing mercurials, which demonstrated conclusively that MeHg poisoning could occur through food-chain transfer of MeHg. By 1974 over 2,150 cases of what was then called Minamata disease had been established in the Minamata region alone. Observations of an abnormally high incidence of cerebral palsy-like symptoms with involvement of the visual, sensory, and auditory systems among children from the Minamata region also heralded a new concern over the potential developmental toxicity of industrially derived MeHg. However, as with the adult cases of MeHg poisoning, establishing a causal relationship between environmental MeHg and cases of observed infantile developmental toxicity was difficult because the affected children had not eaten fish and there were no identified neurological effects in their mothers, based on evaluations at that time. The susceptibility and the sensitivity of the fetus to MeHginduced neurotoxicity were later documented in other studies
MEHG affects development?
The accumulated evidence leaves no doubt that MeHg is a serious developmental toxicant in humans, especially to the nervous system. While the toxicological and behavioral outcomes resulting from high-concentration in utero exposures are not in debate, questions regarding risks and mechanisms of action following low concentration, chronic in utero exposures remain.
A US National Research Council report states that "over _______ newborns annually might be at risk for adverse neurodevelopmental effects from in utero exposure to MeHg (methyl mercury)
Common Sources of Mercury
• Switches in gas furnaces, heaters, etc.
• Major household appliances (tilt switches in freezers, dryers, etc.)
• Irons (tilt switches)
• Automobile switches
• Bilge pumps, sump pumps, etc. (float switches)
• Dental amalgam
• Measuring devices and lab equipment, such as barometers, manometers, etc.
• Medical equipment and supplies
• Fluorescent lights
• Novelty items
• Film pack batteries
In the 2nd century BCE, Dioscorides noted, "Lead makes the mind give way." In modern times, lead has been heavily used in paint and as a gasoline additive. Even low levels of lead exposure cause subtle brain damage in children; this was recognized and acted upon only in the last thirty years. It is now well documented that even blood lead levels below 10 µg/dL can harm the developing brain. Lead has no beneficial biological effects.
Lead is naturally present in soil and water at very low levels, but people have caused extensive distribution of lead in the environment. Lead's physical properties of low melting point, easy malleability, corrosion resistance, and easy availability make it well suited to applications both ancient and modern. It is found alongside gold and silver, making lead both a by-product and a contaminant during the smelting of these precious metals. The earliest recorded lead mine dates from 6500 BC, in Turkey.
History of Lead
Significant production of lead began about 3000 BC, and large mines in Spain and Greece contributed to the global atmospheric redistribution of lead. The Roman Empire was the first society to use lead widely; in fact, the word plumbing is derived from plumbum, Latin for lead, which also gave rise to the chemical symbol for lead, Pb. Lead is slightly sweet to taste, making it a good additive for fine Roman wine that was then shipped all over Europe. Even in those times, there were reports that lead caused severe colic, anemia, and gout. Some historians believe that lead poisoning hastened the fall of the Roman Empire.
It is estimated that ___ million tons of lead were released into the atmosphere from gasoline in the United States alone.
How it works: Lead
The absorption, distribution, and subsequent health effects of lead illustrate the basic principles of toxicology. Foremost is the sensitivity of children to the adverse effects of even low levels of lead exposure. There are many reasons that children are more sensitive to lead. Children are much smaller than adults and will receive a much higher dose by weight given the same exposure. They also absorb lead at a higher rate: adults absorb only 5-10% of orally ingested lead, while children absorb approximately 50% and can absorb much more depending on nutrition. Both children and pregnant women absorb more lead because their bodies have a greater demand for calcium and iron. Lead substitutes for calcium and is thus readily absorbed, particularly if a diet is low in calcium and iron. Children in low-income families, who often have poor diets and live in older housing containing lead, are most vulnerable to the developmental effects of lead. The same is true for pregnant women, whose bodies need more calcium.
Lead distributes in several compartments within the body, each with a different halflife. When lead enters the bloodstream it attaches to red blood cells and has a half-life of about 25 days in blood. Lead readily crosses the placenta, thus exposing the developing fetus and fetal nervous system to lead. Lead is also stored in the muscle, where it has a longer half-life of about 40 days. Calcium requirements for children are high in part because of rapid bone growth. Lead readily substitutes for calcium and is stored in bone, which is visible in x-rays of children with very high lead exposure (fortunately this is very rare now, at least in the United States). In normal circumstances, bone turnover or half-life is very long, so the half-life of lead in the bone is about 20 years. However, if bone turnover is increased, the lead in the bone is mobilized into the blood. This can occur during pregnancy or in older women subject to osteoporosis.
We accumulate lead over a lifetime, but particularly when we are young, so that as adults our bone and teeth contain approximately 95% of the total lead in the body. As we shall see, the short half-life of lead in the blood made tooth lead levels an important indicator of childhood lead exposure and a vital marker to use in correlating exposure with developmental effects.
Health Affects: Lead
Lead is one of the most intensively studied hazardous agents of the 20th century. The more toxicologists and other researchers investigated the health effects of lead, the more they realized that even very low levels of lead exposure were hazardous (Gilbert and Weiss, 2006). The most common biomarker of lead exposure is the blood lead level, usually measured in micrograms (µg) per one tenth of a liter of blood (dL) or µg/dL. For example, many regulatory agencies set 40 µg/dL as a level of concern for adult male workers. Typically, at this level workers would be removed from the environment responsible for the exposure and ideally some determination would be made as to the cause of the exposure.The blood level of concern for children has dropped steadily as shown in the graph below, and some believe that there is sufficient data on the health effects below 10 µg/dL that the CDC should significantly lower the blood lead action level (Gilbert and Weiss, 2006).