APPENDIX II-CO:  Dangerous Inerts: Trimethylbenzene Added to Piperonyl Butoxide, Cox, “Piperonyl Butoxide,” Journal of Pesticide Reform, v.22,no.2, Summer 2002.

 

This appendix is copied from:

http://www.pesticide.org/PiperonylButoxide.pdf

 

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I N S E C T I C I D E S Y N E R G I S T F A C T S H E E T

Caroline Cox is NCAP’s staff scientist.

BY CAROLINE COX

Piperonyl butoxide (PBO) is an

insecticide synergist, a chemical that

is used to make insecticides more potent.

(See Figure 1 for PBO’s molecular

structure.) The discovery of PBO’s

properties as a synergist occurred in

the 1940s, following the development

of aerosol cans to apply insecticides.1

PBO is now frequently used, particularly

in aerosol products. About 1700

insecticide products contain PBO,2 8

percent of the over 20,000 pesticide

products3 registered in the U.S.

Major U.S. manufacturers of PBO

pesticides include MGK (McLaughlin

Gormley King Company), Prentiss, Inc.

and S.C. Johnson & Son, Inc.1

PBO is often used as a synergist

with pyrethrins (JPR 22(1):14-20) and

the chemically related synthetic pyrethroids.

4 However, it also can synergize

a variety of other pesticides, including

the insecticides fipronil,5 parathion,6

PIPERONYL BUTOXIDE

Piperonyl butoxide (PBO) is a synergist used to increase the potency of insecticides like pyrethrins and pyrethroids.

According to the U.S. Environmental Protection Agency (EPA), PBO is one of the most commonly used ingredients in

household pesticide products.

PBO acts as a synergist by inhibiting the activity of a family of enzymes called P450s. These enzymes have many

functions, including breakdown of toxic chemicals and transformation of hormones.

Symptoms of PBO exposure include nausea, diarrhea, and labored breathing.

EPA classifies PBO as a “possible human carcinogen” because it caused liver tumors and cancers in laboratory tests.

In a study conducted by PBO manufacturers, PBO caused atrophy of the testes in male rats. Other researchers found

behavioral changes (a decrease in home recognition behavior) in the offspring of exposed mothers.

PBO affects a variety of hormone-related organs, including thyroid glands, adrenal glands and the pituitary gland.

PBO reduces the immune response of human lymphocytes, cells in our blood that help fight infections.

Concentrations of less than one part per million of PBO reduce fish egg hatch and growth of juvenile fish. PBO also

inhibits hormone-related enzymes in fish and slows the breakdown of toxic chemicals in their tissues. PBO is very

toxic to earthworms and highly toxic to aquatic animals.

taining products are

made indoors every

year in the U.S, and

almost 60 million

applications outdoors.

10

In addition to

these household

uses, other significant

uses include

use in public health

pest control, commercial

indoor pest control, buildings

that house animals, commercial landscape

maintenance, and lettuce

production.12

Mode of Action

Piperonyl butoxide acts as a synergist

by slowing the breakdown in

insects of certain insecticides. The first

step in the breakdown of many drugs,

pesticides, and other compounds is

oxidation by a family of enzymes called

the P450 mono-oxygenases. PBO inhibits

the activity of these enzymes. If

the breakdown product is less toxic

than the insecticide itself, the insecticide

remains toxic longer when PBO

dichlorvos,7 linalool, and D-limonene,8

the insect growth regulators methoprene,

hydroprene, and fenoxycarb,8

as well as alpha-naphthylthiourea (formerly

used as a rodenticide).9

Use

In a household pesticide use survey

done for the U.S. Environmental

Protection Agency (EPA), products contained

PBO more frequently than any

other ingredient. Over 12 percent of

the products used by households in

the survey contained PBO.10 A recent

Minnesota survey had similar results.11

The EPA survey estimates that almost

300 million applications of PBO-con-

Figure 1

Piperonyl Butoxide

2-(2-butoxyethoxy)ethyl 6-propylpiperonyl ether

O

O

O

O

O

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Raid Flea Killer Plus (EPA Reg. No. 4822-273) contains

butane, propane, and isobutane as “inert” propellants.

1 Butane, isobutane, and propane can cause

headache, dizziness, numbness, sleepiness, mental confusion,

poor coordination, and memory loss. They are

extremely flammable” and “will be easily ignited by

heat, sparks, or flame.”2,3,4

Pyrenone® Crop Spray (EPA Reg. No. 432-1033) and

Prentox® PyronylTM Fogging & Contact Spray (EPA Reg.

No. 655-675) contain a petroleum solvent.5,6 This solvent

is called hydrotreated kerosene and its Chemical

Abstract Service number is 64742-47-8.7 This solvent has

caused skin tumors when applied to the skin of laboratory

mice.8 Exposure to this solvent also causes dizziness,

nausea, and headache. Breathing droplets of this

solvent can cause aspiration pneumonia.6

Scourge® Insecticide with SBP-1382®/PBO 1.5%+4.5%

Forla II (EPA Reg. No. 432-719) contains an aromatic

petroleum solvent with Chemical Abstract Services number

64742-94-59 also called solvent naphtha. This solvent

contains two aromatic hydrocarbons, naphthalene and 1,2,4-

trimethylbenzene.10 Naphthalene is classified by EPA as a

possible human carcinogen because it causes lung tumors

in mice following inhalation. Naphthalene exposure also

causes headache, restlessness, lethargy, nausea, diarrhea,

and anemia. Anemia in newborns can be caused by exposure

during pregnancy.11 1,2,4-Trimethyl benzene is irritating

to eyes and skin. It can depress the central nervous

system and cause headache, fatigue, nausea, and anxiety.

It has also caused asthmatic bronchitis.12

1. S.C. Johnson & Son, Inc. 2000. Material safety data sheet: Raid® Flea

Killer Plus. Racine, Wisconsin. 800-725-6737.

2. Hazardous Substance Data Bank. 2002. Butane. http://toxnet.nlm.nih.gov.

3. Hazardous Substance Data Bank. 2002. Isobutane. http://

toxnet.nlm.nih.gov.

4. Hazardous Substance Data Bank. 2001. Propane. http://toxnet.nlm.nih.gov.

5. Aventis. 2001. Material safety data sheet: Pyrenone® Crop Spray.

www.cdms.net/ldat/mp0GC000.pdf.

6. Prentiss, Inc. 1998. Material safety data sheet: Prentox® Pyronyl Fogging &

Contact Spray. www.prentiss.com/msds/pdf/655_675.pdf.

7. National Institute for Occupational Safety and Health. Undated. The registry

of toxic effects of chemical substances: Kerosene (petroleum),

hydrotreated. www.cdc.gov/niosh/rtecs/oa53fc00.html.

8. International Agency for Research on Cancer. 1989. Occupational exposures

in petroleum refining. IARC Monographs 45:39. http://193.51.164.11/

htdocs/monographs/Vol45/45-01.htm.

9. Aventis. 2000. Material safety data sheet: Scourge® Insecticide with

SBP-1382®/PBO 1.5%+4.5% Forla II. www.cdms.net/ldat/mp57D000.pdf.

10. Shell Chemical Company. 2002. Material safety data sheet: Shellsol®

A150. www.euapps.shell.com/MSDS/GotoMsds.

11. Hazardous Substance Data Bank. 2002. Naphthalene. http://

toxnet.nlm.nih.gov.

12. Hazardous Substance Data Bank. 2002. 1,2,4-trimethylbenzene. http://

toxnet.nlm.nih.gov.

EXAMPLES OF HAZARDOUS “INERTSIN PRODUCTS

CONTAINING PIPERONYL BUTOXIDE

inhibits the P450 enzymes.13

P450 enzymes have important biological

functions. In addition to detoxification

of synthetic compounds, they

also transform sex hormones, vitamins,

and other naturally occurring

molecules.13

Inert Ingredients

Like most pesticides, commercial

PBO-containing insecticides contain ingredients

other than PBO many of

which, according to U.S. pesticide law,

are called “inert.”14 Except for acute

toxicity testing, all toxicology tests required

for registration of PBO products

were conducted with PBO, not

with the combination of ingredients

found in commercial products.15

Most inert ingredients are not identified

on product labels, and little

information about them is publicly

available.

For more information about the

hazards of some of the inert ingredients

in PBO products see “Examples

of Hazardous ‘Inerts’,” below.

Exposure Symptoms

Symptoms caused by ingestion of

PBO include nausea, cramps, vomiting,

and diarrhea.16 Symptoms caused

by breathing PBO include tearing, salivation,

and labored breathing.17 Accumulation

of fluids in the lungs can

occur.18 PBO can also cause temporary

eye and skin irritation.16

Effects on the Nervous

System

PBO causes behavioral changes in

young laboratory animals. A researcher

at the Tokyo Metropolitan Research

Laboratory of Public Health observed

behavior of mice after they had been

fed PBO for six weeks. He found that

exposed rats traveled longer distances

and turned more frequently than unexposed

animals. (See Figure 2.) The

effects on travel distance occurred at

all doses tested in this experiment.19

PBO also reduces the activity of the

Figure 2

PBO Changes Behavior

Source: Tanaka, T. 1993. Behavioral

effects of piperonyl butoxide in male mice.

Toxicol. Lett. 69: 155-161.

Unexposed Exposed

25

20

15

10

5

0

Distance travelled (meters in 10 minutes)

Note: Lines above

bars are standard

errors.

In a laboratory study, PBO affected motor

activity at every dose level tested.

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enzyme cholinesterase. This enzyme

plays a role in transmitting nerve impulses

from one nerve cell to another

or to muscle cells.20 In a long-term

feeding study with rats, researchers

from the laboratory mentioned in the

previous paragraph found that female

rats fed PBO had 30 percent less blood

cholinesterase activity than unexposed

rats.21

In addition, PBO can increase the

neurotoxicity of other compounds. For

example, pharmacologists at Virginia

Commonwealth University fed rats

PBO and methylmercury, a neurotoxic

metal. They found that rats fed the

combination developed neurological

symptoms more frequently than rats

fed methylmercury alone.22

Effects on the Digestive

System

Researchers at the National Institute

of Hygienic Sciences (Japan) found that

long-term exposure to PBO caused

intestinal ulcers in rats. Intestinal bleeding

was also more common in exposed

rats than in unexposed ones.23

Effects on the Larynx

The larynx is susceptible to damage

from breathing PBO-contaminated

air. A study conducted by a manufacturers’

task force found damage at

all dose levels tested.24 (See Figure 3.)

The damage consisted of metaplasia,

transformation of cells to an atypical

form, and hyperplasia, an abnormal

increase in the number of cells in an

organ.25

Effects on the Liver and

Kidney

In laboratory toxicology studies,

PBO often affects the liver. For example,

in the study of the digestive

system mentioned above, liver weights

in all exposed rats were greater than

in unexposed rats. The researchers also

observed liver damage.23 Other researchers

in the same laboratory found

that liver damage occurred following

as little as one week of exposure.26 In

a study with dogs conducted by a

manufacturers’ task force, liver damage

occurred at all dose levels tested.27

A similar study with a lower dose level

found liver damage at all but the Piperonyl butoxide exposure increases cholesterol levels.

Figure 4

Exposure to Piperonyl Butoxide Increases Cholesterol Levels

Source: U.S. EPA. Office of Prevention, Pesticides and Toxic Substances. 1988. EPA Reg. No.:

4816-72. Piperonyl butoxide. Review of a chronic feeding/oncogenicity study submitted by the

Piperonyl Butoxide Task Force. Memo from J. Doherty, Hazard Evaluation Division, to P. Hutton

and G. Werdig, Registration Division. Washington, D.C., Apr. 28.

0 30 100 500

200

100

0

Cholesterol concentration(as percent of level in unexposed animals;males and females combined)

Amount of piperonyl butoxide consumed for 25 weeks

(milligrams per kilogram of body weight per day)

Figure 3

Breathing Piperonyl Butoxide Damages the Larynx

Source:

U.S. EPA. Office of Prevention, Pesticides and Toxic Substances. 1994. EPA Id# 067501.

Piperonyl butoxide. Review of a series 82-4 subchronic inhalation toxicity study in rats. Memo

from J. Doherty, Health Effects Division, to A. Dixon and B. Sidwell, Special Review and

Reregistration Division. Washington, D.C., June 22.

Piperonyl butoxide damaged the larynx at all dose levels tested.

100

80

60

40

20

0

Percent of animals with larynx lesions(metaplasia and hyperplasia,

males and females combined)

0 0.2 0.4 0.6

Piperonyl butoxide concentration (milligrams per liter)

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lowest level.27 Liver damage also occurred

in studies with mice.28

Researchers from the Tokyo Metropolitan

Research Laboratory studied effects

of PBO on kidneys. In a threemonth

feeding study with rats, they

found kidney damage at all dose levels

tested. Damage included atrophy

and dilation of kidney structures.29

Effects on the

Circulatory System

Long-term feeding of PBO caused

anemia in rats in a study conducted

by researchers from the Tokyo Metropolitan

Research Laboratory of Public

Health. The amount of hemoglobin (an

oxygen-carrying molecule in blood)

was lower in exposed rats than unexposed

ones at all dose levels tested.30

In another study by the same group

of researchers, a three-month exposure

to PBO increased the blood levels

of cholesterol in rats. Cholesterol

levels at the highest dose were about

double the level in unexposed rats.31

A study by a manufacturers’ task

force also found that PBO increased

cholesterol. Rats exposed in a longterm

study had higher cholesterol levels

than unexposed rats at all but the

lowest dose tested.32 (See Figure 4.)

Carcinogenicity

Since 1995, EPA has classified piperonyl

butoxide as carcinogen (a

chemical that causes cancer). EPA’s

classification of piperonyl butoxide is

“Group C,” a possible human carcinogen.

EPA based its evaluation on a

study of mice conducted by a

manufacturers’ task force. The study

found that piperonyl butoxide caused

liver tumors and cancer.33,34 (See

Figure 5.)

PBO also caused liver cancer in

mice in a study conducted by researchers

from the Tokyo Metropolitan Research

Laboratory. At the highest dose

level, almost half of the mice tested

developed liver cancer.35

PBO has also caused cancer in rats.

A study conducted by PBO manufacturers

found the incidence of lymph

and thyroid tumors increased with increasing

exposure to PBO.36 A second

study, by the Japanese researchers

mentioned above, found that PBO

Figure 5

Exposure to Piperonyl Butoxide Causes Cancer

Source: U.S. EPA. Office of Prevention, Pesticides and Toxic Substances. 1995.

Carcinogenicity peer review of piperonyl butoxide. Memo from J. Doherty and E. Rinde , Health

Effects Division, to R. Keigwin, Registration Division, and A. Dixon and B. Sidwell, Special

Review and Reregistration Division. Washington, D.C., June 7.

35

30

25

20

15

10

5

0

EPA classifies PBO as a carcinogen because it causes liver tumors and cancer.

Percent of animals with liver tumors and cancer(both sexes combined)

0 100 200 300

Amount of piperonyl butoxide consumed

(milligrams per kilogram of body weight per day)

caused liver cancer.37

A contaminant of PBO causes cancer.

The contaminant is safrole, which

the National Toxicology Program classifies

as “reasonably anticipated to be

a human carcinogen.”38 Researchers at

the UFR de Pharmacie (France) found

safrole in all of the PBO samples they

tested. The samples were provided

by European manufacturers.39

In addition, PBO can increase the

carcinogenicity of other cancer-causing

chemicals. Researchers at Harvard

Medical School and the National Cancer

Institute found that the combination

of Freon (a refrigerant that was

also used as a propellant in aerosol

pesticides) and PBO was more carcinogenic

than either chemical alone.40

The liver carcinogen N-hydroxy-2-

acetylaminofluorene also is more carcinogenic

when combined with PBO

than it is alone.41

However, the carcinogenicity of PBO

is still controversial to some reviewers.

The World Health Organization, in a

1995 review, identified five other

studies that found no evidence that

PBO exposure caused cancer.42

Mutagenicity

(Genetic Damage)

While some tests for genetic damage

have shown that PBO “does not demonstrate

any significant potential for

mutagenicity,”43 this synergist does

cause genetic damage in other tests.

In 1995, researchers from the Tokyo

Metropolitan Research Laboratory of

Public Health studied PBO’s effects

on a cell culture derived from human

embryo cells. They found that

PBO caused mutations in a gene

called OuaR. Also, PBO caused mutations

in K-ras, a gene “believed to

be involved in neoplastic [tumorous]

changes.”44

Another study from the same

laboratory found that PBO caused sister

chromatid exchanges in cultures of

cells from hamster ovaries.45 (Sister

chromatid exchanges are exchanges of

genetic material within a chromosome.46)

PBO’s contaminant safrole also

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caused sister chromatid exchanges in

this study.45

In addition, a study conducted by a

PBO manufacturer found that the frequency

of a mutation called HGPRT

was 2 to 4 times higher in hamster

ovary cells exposed to PBO than in

unexposed cells. However, EPA agreed

with the study authors that this was

not of biological significance.”47

Effects on Reproduction

In laboratory tests, PBO has adversely

affected a variety of reproductive

functions.

Atrophy of the testes was observed

in a two-year feeding study with rats

conducted by a manufacturers’ task

force,48 along with some decreases in

weight of the seminal vesicles (spermproducing

structures).49 (See Figure 6.)

Increased incidence of testicular atrophy

occurred at all dose levels tested.

However, because the average weight

of the testes did not decrease, EPA

concluded that “the data did not

provide conclusive evidence.”48

A series of studies at the Tokyo

Metropolitan Research Laboratory

found other effects on reproduction.

The offspring of mice that were fed

PBO before, during, and after pregnancy

weighed less than the offspring

of unexposed mice. This decrease occurred

at all the dose levels tested in

this experiment. In addition, PBO

caused changes in the home recognition

olfactory behavior of the offspring

of exposed mothers. In a test where

the mice had a choice of entering a

compartment with wood chips from

their home cage or entering a compartment

with fresh (unused) chips,

the offspring of exposed mothers were

less likely to enter the compartment

that smelled like home than the offspring

of unexposed mothers. This

behavioral change occurred at all but

the lowest dose level tested.50

A three-generation study by researchers

from the same laboratory

found that litter size and weight were

less for exposed mothers than for unexposed

ones. (Animals were fed PBO

continuously from an age of 5 days in

the first generation through the weaning

of the third generation.) Also, nursing

pups of exposed mothers weighed

less than pups with unexposed

mothers. In the third generation, several

behaviors, including the olfactory

home-recognition behavior mentioned

above, were also affected by PBO exposure.

The effects on the weight of

nursing pups occurred at all dose levels

tested, the behavioral effects occurred

at all but the lowest dose

level.51

A third study from the same laboratory

used a different kind of exposure.

In this study, pregnant mice were

given a single dose of PBO on the

ninth day of their pregnancy. The

weight of fetuses from exposed mothers

was less than the weight of fetuses

from unexposed mothers. This

effect occurred at all dose levels tested

for female fetuses and all but the lowest

dose level for males. The number

of fetal deaths was also higher for exposed

mothers. These increased fetal

deaths occurred at all but the lowest

dose level tested. These researchers

also found that the frequency of fetuses

with defective or missing fingers

was higher for mothers exposed at all

but the lowest dose level.52

A study conducted by a manufacturers’

task force found that the incidence

of a bone defect was higher

in the offspring of rats exposed during

pregnancy than in the offspring of

unexposed rats. The incidence was

dose-related and was 2 to 4 times

higher for exposed rats than for unexposed

ones. However, EPA concurred

with the study author’s conclusions

that these effects were not related to

treatment.”53

Effects on the Immune

System

Medical researchers first documented

PBO’s ability to inhibit normal

functions of the immune system in

1979. Physicians from the State University

of New York (Buffalo) showed

that PBO inhibited the immune response

of human blood cells called

lymphocytes. PBO caused stronger inhibition

(25 percent) than the seven

other pesticide chemicals tested.54

In a recent (1999) study, researchers

from the University of Applied Sciences

Figure 6

Exposure to Piperonyl Butoxide Causes Atrophied Testes

Source: U.S. EPA. Office of Prevention, Pesticides and Toxic Substances. 1988. EPA Reg. No.:

4816-72. Piperonyl butoxide. Review of a chronic feeding/oncogenicity study submitted by the

Piperonyl Butoxide Task Force. Memo from J. Doherty, Hazard Evaluation Division, to P. Hutton

and G. Werdig, Registration Division. Washington, D.C., Apr. 28. p. R12-R13.

Number of animals with bilateral testicular atrophy(both right and left testes damaged)

30

20

10

0

Piperonyl butoxide caused atrophied testes in a long-term feeding study of rats.

Amount of piperonyl butoxide consumed

(milligrams per kilogram of body weight per day)

0 30 100 500

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(Germany) found similar results: PBO

caused about a 50 percent reduction

in the immune response of human

lymphocytes.55 (See Figure 7.)

Effects on Hormones

The impact of environmental contaminants

on the normal function of

human and animal hormone systems

has been a significant concern in the

last decade.56 Hormones are biologically

active molecules that control all

responses and functions of the body.

Dramatic changes in the activity of cells

in humans and other animals “are

caused by extremely small amounts”

of hormones or other chemicals that

disrupt this system.57

Since the P450 enzymes inhibited

by PBO break down steroids (a class

of chemicals that includes many sex

hormones),13 it is not surprising that

PBO can have this kind of hormonal

effect. A study conducted by a task

force of PBO manufacturers showed

that long-term exposure of rats to PBO

damages hormone-related organs. In

exposed animals, thyroid glands were

larger than in unexposed animals. Also,

adrenal glands in exposed females

were larger than in unexposed females,

and pituitary glands were smaller in

exposed males.58

Increasing Exposure to

Potentially Toxic Chemicals

PBO can increase exposure of

people and other species to toxic

chemicals in several different ways.

First, this synergist affects the

amount of certain toxic chemicals that

are absorbed through skin. Veterinarians

at North Carolina State University

found that PBO exposure increased

the absorption of the insecticide carbaryl

through skin. When exposure to

PBO occurred, skin absorption was

about double the rate without PBO

exposure. The veterinarians believe

that the increased absorption was

caused by PBO’s ability to irritate the

skin.59

Second, PBO can inhibit the activity

of P450 enzymes in the nose that

would otherwise detoxify chemicals

that are inhaled. Researchers from the

Lovelace Respiratory Institute showed

that high levels of detoxifying enzymes

occur in the noses of many species,

and some of these enzymes are

inhibited by PBO.60

Finally, PBO can inhibit the breakdown

of toxic chemicals in the soil by

inhibiting the enzymes in microorganisms

that usually do the detoxification.

For example, researchers at the

Institute for Environmental Studies (Illinois)

found that about 1 1/2 times as

much benzidine, a carcinogen, persisted

for a month when the soil was

treated with both benzidine and PBO

as persisted when the treatment used

only benzidine.61

Exposure

Because PBO is frequently used for

household pesticide treatments, people

are frequently exposed. A recent (2002)

study of pregnant women conducted

by researchers from Columbia University

documented how often this exposure

occurs. In this study, women from

northern Manhattan and the South

Bronx (New York) wore personal air

monitors for two days and left the

monitor near their beds at night. The

monitoring found PBO in air samples

from over 80 percent of women in the

study. PBO was the fourth most com-

Contamination of Food

PBO is regularly found on food.

The U.S. Department of Agriculture has

found PBO on spinach,63 peas, sweet

potatoes,64 tomatoes, peaches,

squash,65 strawberries,66 bell peppers,67

grapes, and pineapples.68

Effects on Birds

According to a study conducted by

a manufacturers’ task force, PBO

adversely affected reproduction in mallard

ducks. PBO affected the number

of eggs laid, the number of eggs that

cracked while being hatched, and the

Figure 7

Piperonyl Inhibits Immune System Function

Proliferation of lymphocytes in response tostimulation by phytohemagglutinin(percent of unexposed cells)

100

80

60

40

20

0

Unexposed

Source: Diel, F. et al. 1999. Pyrethroids and piperonyl-butoxide affect human T-lymphocytes in

vitro. Toxicol. Lett. 107: 65-74.

Piperonyl butoxide reduces the activity of immune system cells in human blood.

Exposed

“The monitoring

found PBO in air

samples from

over 80 percent

of the women in

the study.”

monly detected pesticide. PBO concentrations

were highest in homes that

had been treated with insecticide aerosol

spray cans or “bombs.”62

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thickness of the eggshells.69

Researchers from the Indian Institute

of Chemical Technology found

that PBO inhibited “important detoxification

enzymes” in the kidney, lung,

brain, and heart of pigeons. These enzymes

protect the cell against chemically

induced damages” so that inhibition

of their activity could make the

birds more susceptible to a variety of

toxic chemicals.70

Effects on Fish

In terms of its acute toxicity (ability

to cause mortality in a time period up

to 96 hours long), PBO is classified as

moderately toxic” to fish. Concentrations

between 3 and 7 parts per million

(ppm) are sufficient to kill fish.69

PBO affects the ability of fish to

successfully reproduce at much lower

concentrations than are required for

mortality. In a study conducted by a

manufacturers’ task force, concentrations

of less than 1 ppm reduced egg

hatch and larval growth in the fathead

minnow, a standard test fish.69

PBO also increases the toxicity to

fish of a variety of pesticides. For example,

studies done by the New York

Department of Environmental Conservation

found that, compared to fish

exposed to the insecticide resmethrin

alone, mortality was higher and swimming

stamina less in fish exposed to

both PBO and resmethrin.71,72 PBO

also increased bioconcentration of the

insecticide phenothrin in a study of

carp conducted by the Sumitomo

Chemical Co., Ltd.73 Other studies (by

researchers at the University of Wisconsin-

Milwaukee and the Illinois Natural

History Survey) found that PBO

decreased the ability of fish to detoxify

the pesticides rotenone, aldrin, methoxychlor,

and trifluralin.74,75

PBO increases the toxicity of other

chemicals to fish. A study from the

University of Utrecht (The Netherlands)

found that PBO slowed the transformation

of the dioxin 2,8-DCDD (a

chemical relative of the notorious

2,3,7,8-TCDD) into a form that goldfish

can eliminate.76 This resulted in

higher bioaccumulation of the dioxin.

(See Figure 8.) Researchers at the Medical

College of Wisconsin found that

PBO inhibited the breakdown of di-2-

ethylhexyl phthalate77 (DEHP, a chemical

that causes cancer and genetic damage)

78 and nonyl phenol (an estrogen

mimic that disrupts normal hormone

function) in rainbow trout.79

In addition, PBO can disrupt fish

hormone systems. Researchers from

Oregon State University showed that

PBO strongly inhibits the activity of

an enzyme called progesterone-6ß-hydroxylase

in rainbow trout livers.80 (See

Figure 8.) Progesterone regulates egg

maturation in fish.81

Effects on Other Aquatic

Animals

PBO is “highly” acutely toxic to

water fleas, shrimp and oysters. Studies

conducted by a manufacturers’ task

force found that concentrations of less

than one ppm killed all three of these

species.69

Another of the task force’s studies

found adverse effects on water flea

reproduction at concentrations as low

as 12 parts per billion.69 Supporting

these results, a study from North Carolina

State University found that exposure

of water fleas to PBO altered the

transformation of the sex hormone

testosterone. Less than one ppm

inhibited most enzymes that transform

testosterone over 60 percent.82

Effects on Insects

In addition to making other insecticides

more toxic to pest insects, PBO

can increase the toxicity of insecticides

to beneficial insects, such as honey

bees and water beetles.83,84

PBO also has more unexpected effects.

Researchers from the University

of South Australia showed that PBO

exposure of fruit flies increased the

genetic damage caused by X-rays and

the mutagenic chemical heliotrine.85

U.S. Dept. of Agriculture researchers

showed that PBO inhibits the activity

of enzymes involved in the breakdown

or synthesis of insect sex pheromones,

86 chemicals insects use for

communication between males and

Figure 8

Effects of Piperonyl Butoxide on Fish

Sources:

Sijm, D.T.H.M., G. Schaap, and A. Opperhuizen. 1993. The effect of the biotransformation

inhibitor piperonyl butoxide on the bioconcentration of 2,8-dichlorodibenzo-p-dioxin and

pentachlorobenzene in goldfish. Aquat. Toxicol. 27: 345-360.

Miranda, C.L., M.C. Henderson, and D.R. Buhler. 1998. Evaluation of chemicals as inhibitors of

trout cytochrome P450s. Toxicol. Appl. Pharmacol. 148: 237-244.

100

80

60

40

20

0

Piperonyl butoxide can disrupt fish hormone systems and increase the concentration of toxic

chemicals in fish tissues.

Bioconcentration

of a dioxin

Activity of a hormonetransforming

enzyme

Bioconcentration factor(concentration in fish/concentration in water)

150

100

50

0

Unexposed Exposed Unexposed Exposed

Activity of progesterone-6Â-hydroxylase(percent of the activity in unexposed cells)

NORTHWEST COALITION FOR ALTERNATIVES TO PESTICIDES/NCAP

P. O. B O X 1 3 9 3, E U G E N E, O R E G O N 9 7 4 4 0 / ( 5 4 1 ) 3 4 4 - 5 0 4 4

JOURNAL OF PESTICIDE REFORM/ SUMMER 2002 • VOL. 22, NO. 2

19

females.87

Toxicity to Earthworms

University of Kentucky researchers

tested the acute toxicity of a variety of

chemicals to a common earthworm,

Eisenia foetida. They found that piperonyl

butoxide was “very toxic” to

this earthworm.88

Effects on Plants

Although it is perhaps unexpected

for a chemical usually used as an insecticide

synergist, PBO can affect plant

physiology. For example, researchers

at Ibaraki University (Japan) found that

PBO inhibited P450 enzymes in rice

leaves that produce phytoalexins, compounds

that inhibit the germination of

disease-causing fungus spores.89 PBO

causes flowering in asparagus, also by

inhibiting P450 enzymes.90

PBO also increases herbicide damage

to plants. It increases the damage

to corn caused by the sulfonylurea

herbicides primisulfuron91 and

tribenuron,92 the thiocarbamate herbicide

EPTC,93 and the triazine herbicides

atrazine, terbutryn, and prometryn.

94 Similar increases in the toxicity

of sulfonylurea herbicides have

been documented in soybeans,

lambsquarter, and a variety of weedy

grasses.95,96

Persistence

Outdoors: PBO’s half-life (the time

required for half of applied PBO to

break down or move away from the

application site) is about 4 days in

field tests of agricultural soils conducted

by a manufacturers’ task force.

In the same tests, conducted in California,

Georgia, and Michigan, PBO

persisted (measured as the time required

for all applied PBO to dissipate)

up to 30 days.97

The manufacturers’ task force also

measured PBO’s half-life and persistence

in water and aquatic sediments.

In water tested in California, Arkansas,

and Mississippi, the half-life was

about a day. In sediments, the halflife

was up to 24 days and PBO

persisted up to 120 days.97

Indoors: There is less information

available about PBO’s persistence indoors,

but a study from Justus Liebig

University (Germany) found that PBO

persisted for at least two weeks after

a cockroach treatment on toys and in

dust in a kindergarten.98

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