Pesticide profiles : Toxicity, environmental impact and fate - Chapter 2 pps

No developmental effects were seen in the offspring of rats given doses ofallethrin as high as 195 mg/kg/day 2.. Also, no birth defects were observed in theoffspring of rabbits given dos

Trang 1

Section II Pesticide profiles

L1190 CH02 pgs Page 13 Friday, July 2, 1999 3:58 PM

Trang 2

chapter two

Pyrethroids and other botanicals

2.1 Class overview and general description

Background

Pyrethroids and other botanical pesticides are grouped together not becausethey have similar toxicological properties, like the organophosphates or carba-mates, but because they all have biological origins Pesticides may be extractedfrom naturally occurring materials or they can be synthesized in commercial lab-oratories The most common natural materials come from plants Some plants havedeveloped, over long periods of time, substances that deter plant-eating insects.The plants use these compounds as protection from insects Researchers haveisolated a number of compounds from plants that are effective insecticides or

fungicides Development of these botanical pesticides is one of the fastest growingareas in the pesticide industry

The World Health Organization, in 1967, stated that “all of the most poisonousmaterials so far known are, in fact, of natural origin” (1) Whether this is still true

or not is unimportant; however, the comment points out that just because something

is found in nature does not mean that it is harmless (1) Pesticides extracted fromplants or synthesized to mimic compounds found in plants are powerful and effectivecontrol agents

Plant-derived pesticides fall into several different broad classifications By farthe largest group of such pesticides consists of pyrethrum and its related syntheticcompounds, pyrethroids Pyrethrum comes from chrysanthemums There are cur-rently over 20 pyrethroids and they constitute the single largest group of naturalinsect chemical control agents in the world (2)

Another class of botanicals is the rotenoids They are found in several plants

in the bean family Rotenone is one of six compounds in this group It is used as

a fish poison A third important category of botanicals, the nicotinoids, comes fromtobacco and several other plants Nicotine is the most commonly used compound

in the group The fourth group of botanicals includes the compounds strychnineand scilliroside These and several other compounds in the group are used tocontrol rodents

The latter three groups of botanicals will not be discussed in detail here, thoughthey will be briefly described at the end of the overview in this chapter Only thepyrethroids will be discussed at length in this chapter

The generalized structure of the pyrethroids is shown in Figure 2.1, and thevarious pyrethroids are listed in Table 2.1

Trang 3

Uses of pyrethroids and other botanicals

Currently, there are no estimates of the national or regional use patterns ofbotanically derived pesticides in the United States

This group of pesticides interferes with the balance of sodium ions in the nervejunctions of target and non-target organisms, rendering them inactive (2) The pes-ticide provides a “knockdown” dose to insects but is generally not strong enough

to kill them Compounds in this group are toxic to insects but not as toxic to mammals

because of their ability to break down the pyrethroids into metabolite compoundsthat are easily excreted

Pyrethrins and pyrethroids are commonly combined with other insecticides toenhance their efficacy against insects The synthetic pyrethroids are more potent thanthe natural compounds

Acute toxicity

Pyrethroids are slightly to moderately toxic to animals The LD50 of allethrin is

1100 mg/kg in male rats and 370 mg/kg in mice (2) Cypermethrin is moderatelytoxic, with an LD50 of 187 to 326 mg/kg in male rats (2)

Exposure to high doses of pyrethroids can be fatal There was one instance when

a man died after eating a meal cooked in 10% cypermethrin concentrate mistakenlyused for cooking oil He had symptoms of nausea that progressed to stomach pains,

Figure 2.1 Generic pyrethroid structure.

Table 2.1 Pyrethroids

Allethrin* Fenfluthrin Barthrin Fenvalerate Bioallethrin Flucythrinate*

Bioresmethrin Fluorocyphenothrin Cismethrin Fluvalinate*

Cyphenothrin Kadethrin Cyflurthin Permethrin*

Cyhalothrin Pyrethrin I Cypermethrin* Pyrethrin II Deltamethrin Resmethrin*

Esfenvalerate* Tetramethrin Fenproponate

Note: * indicates that a profile for this compound

is included in this chapter.

Trang 4

to diarrhea, to convulsions, to unconsciousness, and then to coma Death thenoccurred due to respiratory failure (2).

For humans, dermal contact with large amounts of these compounds, such asdeltamethrin, may result in numbness, burning and itching of the skin, and intoxi-cation (2)

Chronic toxicity

Long-term studies of pyrethroids showed that several of them can cause livereffects (2) In a chronic feeding study with rats, doses of 125 mg/kg/day of resmethrinproduced some pathological liver changes in addition to increased liver weights (3).Rats fed large doses of pyrethrins over two years showed liver damage (2)

Reproductive effects

In laboratory animal studies on about half of the pyrethroids, there were nosignificant reproductive effects However, in experiments with two pyrethroids, per-methrin and resmethrin, there were some reproductive effects High oral doses of

250 mg/kg/day of permethrin during days 6 to 15 of pregnancy reduced the fertility

of female rats (2) A three-generation rat study using resmethrin showed slightincreases in premature stillbirths and a decrease in pup weight at the 25-mg/kg/daydose (2)

Therefore, botanical compounds at low doses are unlikely to cause reproductiveeffects in humans

Teratogenic effects

Available evidence suggests that pyrethroids will be unlikely to cause teratogeniceffects No developmental effects were seen in the offspring of rats given doses ofallethrin as high as 195 mg/kg/day (2) Also, no birth defects were observed in theoffspring of rabbits given doses of resmethrin as high as 100 mg/kg/day (4).Mutagenic effects

Laboratory animal experiments with various pyrethroids (compounds such asesfenvalerate, permethrin, and resmethrin) showed no mutagenic effects (5,6)

Trang 5

Fate in humans and animals

Pyrethroid compounds are metabolized and excreted rapidly in animals Forexample, rats eliminated over 99% of cypermethrin within a few hours (2) Also,when an oral dose of 10 mg/kg resmethrin was given to laying hens, 90% of thedose was eliminated via urine and feces within 24 hours (10)

Humans also eliminate pyrethroid compounds such as cypermethrin relativelyquickly The “urinary excretion of cypermethrin metabolites was complete 48 hoursafter the last of five daily tracer doses of 1.5 mg” (2)

Ecological effects

Effects on birds

The majority of the pyrethroid compounds are practically nontoxic to birds The

LD50 of allethrin in mallard ducks is 2000 mg/kg and the LD50 of cypermethrin inmallard ducks is 4640 mg/kg (7,8)

Effects on aquatic organisms

Pyrethroid compounds are very highly toxic to fish and aquatic invertebrates

The LC5 of bioallethrin in coho salmon is 0.0026 mg/L, and the 96-hour LC50 ofcypermethrin in rainbow trout is 0.00082 mg/L (7) Also, the acute LC50 for Daphnia magna, a small freshwater crustacean, is 0.0002 mg/L (8) In addition, pyrethroidcompounds tend to bioaccumulate in fish A bioconcentration factor of 1200× wasdetermined in a flow-through study investigating the accumulation of cypermethrin

in rainbow trout (8) In another study, the bioaccumulation factor of esfenvalerate

in rainbow trout was found to be about 400× (11)

Effects on other organisms ( non-target species )

The majority of pyrethroids are highly toxic to bees (8,12)

Environmental fate

Breakdown in soil and groundwater

Pyrethroid compounds have a strong tendency to adsorb to soil particles andare moderately persistent For example, permethrin has a half-life of 3 to 6 weeks(13) and esfenvalerate has a half-life ranging from 15 days to 3 months (11) However,one of the pyrethroids, cypermethrin, has low persistence in sunlight inasmuch as

it photodegrades rapidly with a half-life of 8 to 16 days (8) Because of the pyrethroidcompounds’ tendency to bind to soil, they are unlikely to cause groundwater con-tamination

Breakdown in water

Pyrethroid compounds are relatively insoluble in water They readily adsorb tosediment and soils and, therefore, concentrations of pyrethroids in silty waterdecrease rapidly

Trang 6

EC (cypermethrin) was applied to strawberry plants Results revealed that 40% ofthe applied cypermethrin remained after 1 day, 12% remained after three days, and0.5% remained after 7 days (14) In another study, permethrin was neither phytotoxicnor poisonous to most plants when used directly However, some injury occurred

on certain ornamental plants (15)

General properties of other botanicals

Rotenoids

The rotenoids are extracted mainly from two species, Derris and Lonchocarpus,members of the bean family These compounds are found in over 65 species oflegumes Rotenoids are found in leaves, stems, roots, and seeds of these plants Parts

of the plant may contain up to 40% of the compound (2)

Rotenoids are highly toxic to fish and some insects; however, they are onlymoderately toxic to mammals (16) Refer to the rotenone profile for further informa-tion

Nicotinoids

Three compounds make up the bulk of this category: nicotine, nornicotine,and anabasine Nicotine is by far the most widely used of the group and is alsothe most potent The active compounds in this group have been extracted fromfive different families of plants (2) Nicotine is extracted with steam or water fromthe different plants, though most commonly from tobacco It is a moderately tohighly toxic compound with an acute oral LD50 of 50 to 60 mg/kg (17) Thecompound affects the nerve’s ability to function properly, much like the organo-phosphate and carbamate insecticides, resulting in similar symptoms Nicotine cancause twitching and difficulties with breathing, convulsions, and death The use

of nicotinoids has been declining They are being replaced with equally effectivesynthetic insecticides Additionally, they are nonpersistent, and are ineffective incold weather (16)

Botanical rodenticides

Three compounds are found in this group: strychnine, scilliroside, and ricin.Strychnine comes from the plant Strychnos nux-vomica, scilliroside comes from thered squill bulb, and ricin comes from castor beans

Trang 7

Trade or other names

Trade names for allethrin include Alleviate, Pynamin, d-allethrin, d-cisallethrin,Bioallethrin, Esbiothrin, Pyresin, Pyrexcel, Pyrocide, and trans-allethrin

Regulatory status

Pesticides containing allethrin are toxicity class III — slightly toxic, and bear the

Signal Word CAUTION on the product label Containers of technical grade d-transallethrin bear the Signal Word WARNING Allethrin is a General Use Pesticide

-(GUP)

Introduction

Allethrin is a nonsystemicinsecticide that is used almost exclusively in homesand gardens for control of flies and mosquitoes, and in combination with otherpesticides to control flying or crawling insects Another structural form, the d-trans-isomer of allethrin, is more toxic to insects and is used to control crawling insects inhomes and restaurants It is often used to control parasites living within animalsystems It is available as mosquito coils, mats, oil formulations, and as an aerosolspray

Allethrin is a pyrethroid, a synthetic compound that duplicates the activity ofthe pyrethrin plant It has stomach and respiratory action and paralyzes insects beforekilling them Unless stated otherwise, information in this profile refers to unpurifiedallethrin

Toxicological effects

Acute toxicity

Allethrin is slightly toxic by dermalabsorption and ingestion Short-term dermal

exposure to allethrin may cause itching, burning, tingling, numbness, or a feeling ofwarmth, but not dermatitis (2) Exposure to large doses by any route may lead tonausea, vomiting, diarrhea, hyperexcitability, incoordination, tremors, convulsivetwitching, convulsions, bloody tears, incontinence, muscular paralysis, prostration,and coma

Allethrin is a central nervous system stimulant Heavy respiratory exposurecaused incoordination and loss of bladder control in mice and rats (2)

The toxicity of allethrin varies with the amounts of different isomers present.The oral LD50 for allethrin is 1100 mg/kg in male rats, 685 mg/kg in female rats, 480mg/kg in mice, and 4290 mg/kg in rabbits (7,12) For d-allethrin, the oral LD50 is

1320 mg/kg in rats The dermal LD50 is greater than 2500 mg/kg in rats (12,19)

Trang 8

Mutagenic effects

Allethrin has been found to be mutagenic under certain conditions in strains ofthe bacterium Salmonella typhinurium (18) However, tests of d-allethrin (bioallethrin)for DNA damage and mutation were negative (19) Thus, allethrin appears to havelittle or no mutagenic activity

no detectable effect in dogs (19)

Following oral administration, allethrin is readily absorbed and metabolized inmammalian systems to less toxic compounds that may be more easily eliminated bythe body (12)

Ecological effects

Effects on birds

Allethrin is practically nontoxic to birds The oral LD50 for allethrin is 2030 mg/kg

in bobwhite quail and greater than 2000 mg/kg in mallards (12,19) The dietary LD50

is 5620 ppm for d-allethrin in mallards and bobwhite quail (19)

The pyrethroid insecticides, including allethrin, are toxic to fish Fish sensitivity

to the pyrethroids may be explained by their relatively slow metabolism and ination of these compounds The half-lives for elimination of several pyrethroids bytrout are all greater than 48 hours (20,21) Generally, the lethality of pyrethroids tofish increases with increasing ability to dissolve in fat (22) The LC50 (96-hour) forchannel catfish is 30 mg/L

elim-The toxicity of allethrin compounds ranges from an LC50 of 0.0026 mg/L ford-allethrin in coho salmon to an LC50 of 0.08 mg/L for s-bioallethrin in fatheadminnows (19)

Allethrin is slightly toxic to bees (19) Its LD50 is 0.003 to 0.009 mg per bee (19)

Environmental fate

No data are currently available

Trang 9

Breakdown in water

In pond waters and in laboratory degradation studies, pyrethroid concentrations

decrease rapidly due to sorption to sediment, suspended particles and plants bial and photodegradation also occur (19)

Solubility in water: Allethrin and d-allethrin are insoluble in water (12)

Solubility in other solvents: alcohol v.s.; hexane v.s.; xylene v.s., petroleum etherv.s (12)

Melting point: 4°C (12)

Vapor pressure: 16 mPa @ 30°C (12)

Partition coefficient (octanol/water): 91,300 (12)

Adsorption coefficient: Not available

Trang 10

Trade names include Ammo, Arrivo, Barricade, Basathrin, CCN52, Cymbush,

Cymperator, Cynoff, Cypercopal, Cyperguard 25EC, Cyperhard Tech, Cyperkill,

Cypermar, Demon, Flectron, Fligene CI, Folcord, Kafil Super, NRDC 149, Polytrin,

PP 383, Ripcord, Siperin, Stockade, and Super

Regulatory status

Many products containing cypermethrin are classified as Restricted Use

Pesti-cides (RUPs) by the EPA because of cypermethrin’s toxicity to fish RUPs may be

purchased and used only by certified applicators Cypermethrin is classified toxicity

class II — moderately toxic Some formulations are toxicity class III — slightly toxic

Pesticides containing cypermethrin bear the Signal WordWARNING or CAUTION

on the product label, depending on the particular formulation

Introduction

Cypermethrin is a synthetic pyrethroid insecticide used to control many pests,

including moth pests of cotton, fruit, and vegetable crops It is also used for crack,

crevice, and spot treatment to control insect pests in stores, warehouses, industrial

buildings, houses, apartment buildings, greenhouses, laboratories, and on ships,

railcars, buses, trucks, and aircraft It may also be used in non-food areas in schools,

nursing homes, hospitals, restaurants, and hotels, in food processing plants, and as

a barrier treatment insect repellent for horses Technical cypermethrin is a mixture

of eight different isomers, each of which may have its own chemical and biological

properties Cypermethrin is light stable It is available as an emulsifiable concentrate

or wettable powder

Acute toxicity

Cypermethrin is a moderately toxic material by dermalabsorption or ingestion

(2,8) Symptoms of high dermal exposure include numbness, tingling, itching,

burn-ing sensation, loss of bladder control, incoordination, seizures, and possible death

(2,8) Pyrethroids like cypermethrin may adversely affect the central nervous system

(2,8) Symptoms of high-dose ingestion include nausea, prolonged vomiting, stomach

pains, and diarrhea that progresses to convulsions, unconsciousness, and coma

Cypermethrin is a slight skin or eye irritant, and may cause allergic skin reactions (8)

The oral LD50 for cypermethrin in rats is 250 mg/kg (in corn oil) or 4123 mg/kg

(in water) (2,8) The EPA reports an oral LD50 of 187 to 326 mg/kg in male rats and

150 to 500 mg/kg in female rats (8) The oral LD50 varies from 367 to 2000 mg/kg

in female rats, and from 82 to 779 mg/kg in mice, depending on the ratio of cis/trans

-isomers present (2) This wide variation in toxicity may reflect different mixtures of

isomers in the materials tested The dermal LD50 in rats is 1600 mg/kg, and in rabbits

is greater than 2000 mg/kg (2,8)

Chronic toxicity

No adverse effects on reproduction were observed in a three-generation study

with rats given doses of 37.5 mg/kg/day,the highest dose tested (8)

Trang 11

Teratogenic effects

Cypermethrin is not teratogenic (2) No birth defects were observed in the

off-spring of rats given doses as high as 70 mg/kg/day nor in the offspring of rabbits

given doses as high as 30 mg/kg/day (8)

Mutagenic effects

Cypermethrin is not mutagenic, but tests with very high doses on mice caused

a temporary increase in the number of bone marrow cells with micronuclei Other

tests for mutagenic effects in human, bacterial, and hamster cell cultures and in live

mice have been negative (2)

Carcinogenic effects

EPA has classified cypermethrin as a possible human carcinogen because

avail-able information is inconclusive It caused benign lung tumors in female mice at the

highest dose tested (229 mg/kg/day); however, no tumors occurred in rats given

high doses of up to 75 mg/kg/day (8)

Organ toxicity

Pyrethroids like cypermethrin may cause adverse effects on the central nervous

system Rats fed high doses (37.5 mg/kg) of the cis-isomer of cypermethrin for 5

weeks exhibited severe motor incoordination, while 20 to 30% of rats fed 85 mg/kg

died 4 to 17 days after treatment began (2) Long-term feeding studies have shown

increased liver and kidney weights and adverse changes in liver tissues in test

animals (8)

Pathological changes in the cortex of the thymus, liver, adrenal glands, lungs,

and skin were observed in rabbits repeatedly fed high doses of cypermethrin (23)

In humans, urinary excretion of cypermethrin metabolites was complete 48 hours

after the last of five doses of 1.5 mg/kg/day (2) Studies in rats have shown that

cypermethrin is rapidly metabolized by hydroxylation and cleavage, with over 99%

being eliminated within hours The remaining 1% becomes stored in body fat This

portion is eliminated slowly, with a half-life of 18 days for the cis-isomer and 3.4

days for the trans-isomer (2)

Ecological effects

Effects on birds

Cypermethrin is practically nontoxic to birds Its acute oral LD50 in mallard ducks

is greater than 4640 mg/kg (8) The dietary LC50 in mallards and bobwhite quail is

greater than 20,000 ppm (8) No adverse reproductive effects occurred in mallards

or bobwhite quail given 50 ppm, the highest dose tested (8)

Cypermethrin is very highly toxic to fish and aquatic invertebrates The LC50

(96-hour) for cypermethrin in rainbow trout is 0.0082 mg/L, and in bluegill sunfish

is 0.0018 mg/L (20) Its acute LC50 in Daphnia magna, a small freshwater crustacean,

is 0.0002 mg/L (20)

Trang 12

Cypermethrin is metabolized and eliminated significantly more slowly by fishthan by mammals or birds, which may explain this compound’s higher toxicity infish compared to other organisms (20).

The half-lives for elimination of several pyrethroids by trout are all greater than

48 hours, while elimination half-lives in birds and mammals range from 6 to 12 hours(20,23)

The bioconcentration factor for cypermethrin in rainbow trout was 1200 timesthe ambient water concentration, indicating that there is a moderate potential toaccumulate in aquatic organisms (8) Elimination of half of the accumulated amount

of the compound took nearly 8 days After 14 days, 70 to 80% of the material hadbeen eliminated from the organisms (8)

Cypermethrin is highly toxic to bees (8,24)

Environmental fate

Cypermethrin has a moderate persistence in soils Under laboratory conditions,cypermethrin degrades more rapidly on sandy clay and sandy loam soils than onclay soils, and more rapidly in soils low in organic material (8) In aerobic conditions,its soil half-life is 4 days to 8 weeks (8,12,25) When applied to a sandy soil underlaboratory conditions, its half-life is 2.5 weeks (26) Cypermethrin is more persistentunder anaerobic conditions (8)

It photodegrades rapidly with a half-life of 8 to 16 days Cypermethrin is alsosubject to microbial degradation under aerobic conditions (8)

Cypermethrin is not soluble in water and has a strong tendency to adsorb to soilparticles It is therefore unlikely to cause groundwater contamination (12)

Breakdown in water

In neutral or acid aqueous solution, cypermethrin hydrolyzes slowly, with

hydrolysis being more rapid at pH 9 (basic solution) Under normal environmentaltemperatures and pH, cypermethrin is stable to hydrolysis with a half-life of greaterthan 50 days and to photodegradation with a half-life of greater than 100 days (8)

In pond waters and in laboratory degradation studies, pyrethroid concentrationsdecrease rapidly due to sorption to sediment, suspended particles and plants Micro-bial degradation and photodegradation also occur (22,27)

Breakdown in vegetation

When applied to strawberry plants, 40% of the applied cypermethrin remainedafter 1 day, 12% remained after 3 days, and 0.5% remained after 7 days, with a lightrain occurring on day 3 (14)

When cypermethrin was applied to wheat, residues on the wheat were 4 ppm

immediately after spraying and declined to 0.2 ppm 27 days later No cypermethrinwas detected in the grain Similar residue loss patterns have been observed on treatedlettuce and celery crops (28)

Trang 13

Solubility in water: 0.01 mg/L @ 20°C; insoluble in water (12)

Solubility in other solvents: methanol v.s.; acetone v.s.; xylene v.s (12)

Melting point: 60–80°C (pure isomers) (12,2)

Vapor pressure: 5.1 × 10–7 nPa @ 70°C (12)

Partition coefficient (octanol/water): 4,000,000 (25)

Trade names for the older fenvalerate compounds include Ectrin, Pydrin, marton, Sumifly, Sumiflower, and Sumitick Trade names for the new product, esfen-valerate, include Asana XL, Halmark, and Sumi-alfa The compound may also belisted as S-fenvalerate

San-Regulatory status

Most products containing esfenvalerate are General Use Pesticides (GUPs) Theemulsified concentrate formulation is a Restricted Use Pesticide (RUP) because of

Figure 2.4 Esfenvalerate.

Trang 14

possible adverse effects in aquatic organisms Esfenvalerate is a moderately toxic

pesticide in EPA toxicity class II; products containing it must contain the Signal WordWARNING on the label

Introduction

Esfenvalerate is a synthetic pyrethroid insecticide used on a wide range of pestssuch as moths, flies, beetles, and other insects It is used on vegetable crops, treefruit, and nut crops It may be mixed with a wide variety of other types of pesticidessuch as carbamate compounds or organophosphates Esfenvalerate has replaced thenaturally occurring compound fenvalerate (to which it is almost identical) for use

in the U.S

Much of the data for fenvalerate is applicable to the pesticide esfenvaleratebecause the two compounds contain the same components The only differences inthe two products are the relative proportions of the four separate constituents (iso-mers) Esfenvalerate has become the preferred compound because it requires lowerapplications rates than fenvalerate, is less chronically toxic, and is a more powerfulinsecticide The compound contains a much higher percentage of the one insecticid-ally active isomer (84% for esfenvalerate and 22% for fenvalerate)

of acute poisoning included dizziness, burning, and itching (which was worsened bysweating and washing) Severe cases of direct contact caused blurred vision, tightness

in the chest, and convulsions (2) The changes appear to be reversible

In rats, high acute exposure to esfenvalerate produced muscle incoordination,tremors, convulsions, nerve damage, and weight loss The compound may producenausea, vomiting, headache, and temporary nervous system effects such as weak-ness, tremors, and incoordination at acute exposure levels in humans Esfenvalerate

is a strong eye irritant, producing tearing or blurring of vision

Chronic toxicity

Rats fed fenvalerate at concentrations of approximately 12.5 mg/kg/day for 2years had no compound-related changes in the blood or urine (12) In other studiessignificant reduction in body weight was the main adverse effect seen in both ratsand mice of both sexes

In a three-generation rat study, low doses (up to 12.5 mg/kg/day) of fenvalerateproduced no toxicity in the fetus Some maternal toxicity was noted in the second

Trang 15

generation at the higher dose When pregnant mice and rabbits were fed low dietarylevels of fenvalerate (2.5 mg/kg/day) on days 6 to 15 of gestation, there was maternaltoxicity in both species It seems that during pregnancy, the females are more sensi-tive to fenvalerate than they would otherwise be, even though the toxicity is notreflected in any effect on the fetus (5) There are no specific data available foresfenvalerate, but it is not expected to cause reproductive effects at low doses.

Cows treated with 0.1 or 0.5 g fenvalerate on their skin had 0.03 to 0.06% of theapplied chemical in the milk When the cows received fenvalerate orally at very lowlevels, about 0.50% of the dose appeared in the milk

Fenvalerate does not appear to be metabolized by bovine rumen, but it isdegraded further down the digestive tract (32) This happens rapidly with less than0.02% of the parent compound found in the urine and 20% of the major metabolite

present Higher concentrations of the parent compound are present in the feces Inthe rat, fenvalerate is rapidly broken down and almost completely eliminated withinseveral days One study indicated mammals eliminated 96% in the feces in 6 to 14days (32)

While the data presented here are for fenvalerate, esfenvalerate behaves in thesame manner (33)

Ecological effects

Effects on birds

Esfenvalerate is slightly toxic to birds Oral LD50 values for the compound are

1312 mg/kg in bobwhite quail and greater than 2250 mg/kg in mallard ducks (12).Effects on aquatic organisms

Based on laboratory studies, fish are very sensitive to esfenvalerate It has a hour LC50 of 0.0003 mg/L in bluegill, 0.0003 mg/L in rainbow trout, 0.001 mg/L in

Trang 16

96-carp, and 0.0002 mg/L in killfish (5) The LC50 in Daphnia magna, an aquatic

inver-tebrate, is 0.001 mg/L The pesticide is very highly toxic to these species Waterturbidity, such as would be found in the field, tends to reduce the toxicity of thiscompound (5)

Bioaccumulation factors in rainbow trout are about 400 times the background(ambient water concentration of the pesticide) levels (5)

Esenvalerate is highly toxic to bees The compound tends to repel bees for a day

or two after application, causing bee visitations to drop during that time (5) Sincemost intoxicated bees die in the field before they can return to contaminate the hive,the brood is not exposed except by direct spray Dried spray residues are not expected

to pose a significant threat to bees (5)

Environmental fate

Under field conditions, esfenvalerate is moderately persistent with a half-life

ranging from about 15 days to 3 months, depending on soil type (25) In a soillaboratory study, 17% of the applied chemical was lost in 90 days

Esfenvalerate and its breakdown products are relatively immobile in soil andthus pose little risk to groundwater (11) The compound’s ability to bind to soilincreases with increasing organic matter It is very insoluble in water Fenvaleratehas not been found in over 100 tested groundwater supplies (34)

Solubility in water: <0.3 mg/L at 25°C, insoluble in water (12)

Solubility in other solvents: v.s in hexane, acetone, chloroform, and methanol @

20°C (12)

Trang 17

Melting point: 59–60°C (12)

Vapor pressure: 0.067 mPa @ 25°C (12)

Partition coefficient (octanol/water): 1,660,000 (12)

DuPont Agricultural Products

Walker’s Mill, Barley Mill Plaza

Trade names include AASTAR, AC 222705, Cybolt, Fuching Jujr, OMS 2007, andPay-Off

Regulatory status

Flucythrinate is a highly toxic pesticide in EPA toxicity class I Pesticides taining flucythrinate must bear the Signal Word DANGER on the product labelbecause of its high oral toxicity and potential to cause eye irritation For someapplications flucythrinate may be classified as a Restricted Use Pesticide (RUP) bythe EPA RUPs may be purchased and used only by certified applicators

con-Introduction

Flucythrinate is a synthetic pyrethroid used to control insect pests in apples,

cabbage, field corn, head lettuce, and pears, and to control Heliothis spp in cotton,

which is its primary use It is available in emulsifiable concentrate, water-dispersiblegranules, and wettable powder formulations The AASTAR product also contains

Figure 2.5 Flucythrinate.

Trang 18

phorate, and it may also be found in formulation with chlorpyrifos, dimethoate,

methomyl, or phenthoate Unless otherwise stated, the information presented here refers

to the technical product.

Acute toxicity

Flucythrinate is highly toxic via the oral route The oral LD50 for technical rinate is 81 mg/kg in male rats (35), 67 mg/kg in female rats, and 76 mg/kg in mice (12).Flucythrinate is moderately toxic via the dermal route with a reported dermal

flucyth-LD50 in rabbits of greater than 1000 mg/kg and in guinea pigs of greater than 2000mg/kg (36)

Flucythrinate can cause mild to severe skin irritation (35) It failed to produceallergic reactions in guinea pigs (2,36) Skin application on human volunteers causedmore severe paresthesia (i.e., abnormal sensations such as burning or tingling) onthe earlobes than on the forearms This condition lasted for approximately 24 hoursafter application on earlobes and 4 to 5 hours on forearms (36) When 13.8 mg/cm2

was applied to the forearms of volunteers, paresthesia appeared 4 to 5 hours laterand lasted for 3 days (36) Flucythrinate may also cause extreme eye irritation (36).Flucythrinate is moderately toxic via the inhalation route The 4-hour inhalation

LC50 for technical flucythrinate in rats is 4.85 mg/L (12)

Chronic toxicity

Rats fed 15 mg/kg/day for 28 days showed severe motor symptoms (involuntarymuscular movement), and rats fed 7.5 mg/kg/day showed moderate motor symp-toms In both cases, symptoms disappeared within 48 hours after resumption of anormal diet (2) Symptoms exhibited by animals in other short-term feeding studiesinclude vomiting, diarrhea, incoordination, excessive salivation and urination, andhypersensitivity (2)

No adverse effects were observed when rats and dogs were fed flucythrinate for

90 days at doses of up to 3 mg/kg/day for rats and 3.75 mg/kg/day for dogs (35).Dogs fed 7.5 mg/kg/day for 2 years exhibited vomiting and decreased body weightgain Rats fed 6 mg/kg/day for 2 years also exhibited decreased body weight gain (2)

In a three-generation reproductive study, rats given 1.5, 3, or 6 mg/kg/dayshowed reduced parental and pup weights, and decreased pup survival Reducedlitter size occurred at 3 and 6 mg/kg/day (2,35) It is unlikely that reproductiveeffects due to flucythrinate will be seen under normal circumstances in humans

Teratogenic effects

Flucythrinate does not cause birth defects (12) No teratological effects wereobserved in studies with rats or rabbits (12) The highest dose tested was 8.0mg/kg/day for rats and 60 mg/kg/day for rabbits (35)

Mutagenic effects

Ames tests using several strains of bacteria exposed to concentrations as high

as 1000 µg/plate and a rat dominant-lethal test at up to 10.0 mg/kg showed noevidence that flucythrinate causes mutations (2,35)

Trang 19

Flucythrinate is rapidly metabolized in mammals (12) When flucythrinate wasadministered orally to rats, 15 to 24% was eliminated in the urine, and 37 to 65.6%was eliminated in the feces during the first 24 hours Within 8 days, 95.8 to 100% ofthe dose was eliminated in either urine or feces A large amount of the chemicalrecovered in the feces was unaltered flucythrinate, suggesting that this portionpassed through the gut without being absorbed into the bloodstream (36) Metabo-lites of flucythrinate are considered to be of no toxicological significance (11)

The pyrethroid insecticides are very highly toxic to fish with 96-hour LC50 valuesgenerally below 0.001 mg/L in many species tested (12,20) Fish sensitivity to thepyrethroids may be explained by their relatively slow metabolism and elimination

of these compounds The half-lives for elimination of several pyrethroids by troutare all greater than 48 hours, while elimination half-lives for birds and mammalsrange from 6 to 12 hours (21) Flucythrinate accumulated in the edible tissues ofbluegill sunfish to 487 times the concentration in surrounding waters (37)

The compound is highly toxic to bees, with a reported topical application tact) LD50 of 0.078 µg per bee (12)

(con-Environmental fate

Flucythrinate is of low to moderate persistence with reported field half-lives of

21 to 60 days (25) Observed persistence will vary according to soil type and othervariables Most residues will be found within the top 3 inches of soil (37) It is nearlyinsoluble in water and has a very strong tendency to bind to soil particles (25).Therefore, it is unlikely to be mobile or to contaminate groundwater

Định dạng
Số trang	39
Dung lượng	655,38 KB