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PUBLIC HEALTH STATEMENT 

HYDRAULIC FLUID 

CAS#: 55957-10-3; 68937-40-6; 50815-84-4; 

55962-27-1; 66594-31-8; 63848-94-2; 

107028-44-4; 28777-70-0 

Division of Toxicology September 1997 

This Public Health Statement is the summary 

chapter from the Toxicological Profile for 

Hydraulic Fluid. It is one in a series of Public 

Health Statements about hazardous substances and 

their health effects. A shorter version, the 

ToxFAQsTM, is also available. This information is 

important because this substance may harm you. 

The effects of exposure to any hazardous substance 

depend on the dose, the duration, how you are 

exposed, personal traits and habits, and whether 

other chemicals are present. For more information, 

call the ATSDR Information Center at 1-888-422­

8737. 

This public health statement tells you about 

hydraulic fluids and the effects of exposure. 

The Environmental Protection Agency (EPA) 

identifies the most serious hazardous waste sites in 

the nation. These sites make up the National 

Priorities List (NPL) and are the sites targeted for 

long-term federal cleanup. Hydraulic fluids have 

been found in at least 10 of the 1,428 current or 

former NPL sites. However, it's unknown how 

many NPL sites have been evaluated for these 

substances. As more sites are evaluated, the sites 

with hydraulic fluids may increase. This is 

important because exposure to these substances may 

harm you and because these sites may be sources of 

exposure. 

When a substance is released from a large area, 

such as an industrial plant, or from a container, such 

as a drum or bottle, it enters the environment. This 

release does not always lead to exposure. You are 

exposed to a substance only when you come in 

contact with it. You may be exposed by breathing, 

eating, or drinking the substance or by skin contact. 

If you are exposed to hydraulic fluids, many factors 

determine whether you'll be harmed. These factors 

include the dose (how much), the duration (how 

long), and how you come in contact with it. You 

must also consider the other chemicals you're 

exposed to and your age, sex, diet, family traits, 

lifestyle, and state of health. 

1.1 WHAT IS HYDRAULIC FLUID? 

Hydraulic fluids are a very large class of materials 

that are used in machines and equipment to transfer 

pressure from one point to another. They are used 

in many ways including all fluids for car automatic 

transmissions, brakes, and power steering. 

Hydraulic fluids are also used in many machines 

like tractors and other farm equipment, forklift 

trucks, bulldozers, and other construction 

equipment, and airplanes. In industry, hydraulic 

fluids are used in machines that push, lift, pull, turn, 

and hold things. This profile covers only three of 

the many types of hydraulic fluids: (1) mineral oil, 

(2) organophosphate ester, and (3) polyalphaolefin. 

These types are among the most commonly used 

today. The trade names of typical hydraulic fluids 

covered in this profile include Durad®, Fyrquel®, 

Skydrol®, Houghton-Safe®, Pydraul®, Reofos®, 

Reolube®, and Quintolubric®. Hydraulic fluids 

used in cars are not specifically covered in this 

profile. 

Some hydraulic fluids have a bland oily smell, 

while others have no smell. Mineral oil and 

polyalphaolefin hydraulic fluids are mixtures that 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

Agency for Toxic Substances and Disease Registry 

www.atsdr.cdc.gov/ Telephone: 1-888-422-8737 Fax: 770-488-4178 E-Mail: atsdric@cdc.gov 
 

 

 

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PUBLIC HEALTH STATEMENT 

HYDRAULIC FLUID 

CAS#: 55957-10-3; 68937-40-6; 50815-84-4; 

55962-27-1; 66594-31-8; 63848-94-2; 

107028-44-4; 28777-70-0 

Division of Toxicology September 1997 

have oil in them and will burn. Oil-in-water 

hydraulic fluids (a special type of mineral oil 

hydraulic fluid) do not burn because they contain 

water. Organophosphate ester hydraulic fluids are 

mostly made without oil and will not burn unless 

there is a flame directly on them; once the flame is 

removed, these fluids will stop burning. Because 

they do not burn, organophosphate ester hydraulic 

fluids are used in airplanes and other places where 

fires are very undesirable. 

Mineral oil hydraulic fluids are produced from 

crude oil. Organophosphate ester and 

polyalphaolefin hydraulic fluids are manufactured. 

All hydraulic fluids contain many ingredients which 

reduce wear, make the fluid flow better, and make it 

thinner when it is cold. More than 200 million 

gallons of hydraulic fluids are sold each year in the 

United States. 

1.2 WHAT HAPPENS TO HYDRAULIC 

FLUID WHEN IT ENTERS THE 

ENVIRONMENT? 

Hydraulic fluids can enter the environment from 

spills and leaks in machines that use them and from 

leaky storage tanks. If spilled on soil, some of the 

ingredients in the hydraulic fluids mixture may stay 

on the top, while others may sink into the 

groundwater. How fast the ingredients move 

through soil depends on many things. These 

include how much is spilled, how much rain falls on 

the spill, and the type of soil (for example, 

hydraulic fluids will move quickly in sandy soil, but 

will move slower in heavy clay). In water, some 

ingredients of hydraulic fluids will transfer to the 

bottom and stay there. Fish may contain some 

hydraulic fluid ingredients if they live near places 

that make or use a lot of it. Eventually, the 

ingredients of hydraulic fluids are degraded in the 

environment, but complete degradation may take 

more than a year. Scientists know a little about how 

some of the ingredients in hydraulic fluids break 

down in the environment, but they know almost 

nothing about how toxic these breakdown products 

are. 

1.3 HOW MIGHT I BE EXPOSED TO 

HYDRAULIC FLUID? 

Exposures to hydraulic fluids occur mainly in 

workers using hydraulic equipment and in people 

who work on cars or tractors that use the fluids. 

Most people are exposed when fluids spill or leak 

on the skin, when the fluid is changed, or when the 

fluid reservoirs are filled. Low levels of hydraulic 

fluids may occur in the air near machines that use 

them. Understanding environmental levels of 

hydraulic fluids is very difficult because the 

ingredients in hydraulic fluids are used in many 

products other than hydraulic fluids. For example, 

mineral oil is an ingredient in both motor oil and 

mineral oil hydraulic fluids. In the environment, 

mineral oil from both sources would appear to be 

the same. Polyalphaolefin hydraulic fluids have 

chemical components and potential applications 

similar to mineral oil hydraulic fluids. 

The ingredients in organophosphate ester hydraulic 

fluids also have many uses, but are usually not 

detected in the environment. They do not have as 

many uses as mineral oils and polyalphaolefins. 

When detected, concentrations of organophosphate 

esters range from 1 to 20 parts per billion (ppb) in 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

Agency for Toxic Substances and Disease Registry 

www.atsdr.cdc.gov/ Telephone: 1-888-422-8737 Fax: 770-488-4178 E-Mail: atsdric@cdc.gov 
 

 

 

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PUBLIC HEALTH STATEMENT 

HYDRAULIC FLUID 

CAS#: 55957-10-3; 68937-40-6; 50815-84-4; 

55962-27-1; 66594-31-8; 63848-94-2; 

107028-44-4; 28777-70-0 

Division of Toxicology September 1997 

water, 0.0002 to 1.31 ppb in drinking water, and 

less than 100 to greater than 6,300,000 ppb in 

sediments. In general, organophosphate esters are 

found near places where they are manufactured. 

People most likely to be exposed to hydraulic fluids 

include car, truck, tractor, industrial equipment, and 

airplane mechanics and repair technicians, and 

maintenance workers in heavy industry like car 

assembly plants, foundries, steel mills, paper mills, 

and plants that manufacture appliances or other 

large or small household or commercial items. 

Polyalphaolefin hydraulic fluids are often used in 

military equipment. 

1.4 HOW CAN HYDRAULIC FLUID ENTER 

AND LEAVE MY BODY? 

Very little is known about how mineral oil 

hydraulic fluids, polyalphaolefin hydraulic fluids, 

and organophosphate ester hydraulic fluids enter 

and leave your body. Some information exists 

about how some of the chemical components in the 

organophosphate ester hydraulic fluids enter and 

leave your body. 

We know that chemical components of mineral oil 

hydraulic fluids can enter the body if you swallow 

them or they come in contact with your skin 

because health effects have occurred in people after 

they swallowed or had prolonged skin contact with 

certain mineral oil hydraulic fluids. Health effects 

have occurred in animals after they breathed, 

swallowed, or had skin contact with 

organophosphate ester hydraulic fluids. We do not 

know if mineral oil hydraulic fluids or 

polyalphaolefin hydraulic fluids will enter your 

body from your lungs if you breathe them as vapor 

or oil mist. 

We know that some chemical components of 

organophosphate ester hydraulic fluids can enter 

your body from your lungs if you breathe them. 

Some organophosphate esters rapidly enter your 

body. Certain components of organophosphate 

ester hydraulic fluids are found in blood and urine 

within 1 hour of having them on your skin. Within 

6 hours after animals swallow large amounts of 

certain components of organophosphate ester 

hydraulic fluids, they enter the blood and are found 

throughout the body, especially in fat. 

Organophosphate esters leave the body in the urine 

and feces within several days. 

1.5 HOW CAN HYDRAULIC FLUID AFFECT 

MY HEALTH? 

This toxicological profile discusses only three 

classes of hydraulic fluids: mineral oil hydraulic 

fluids, polyalphaolefin hydraulic fluids, and 

organophosphate ester hydraulic fluids. The classes 

are based on the major chemicals found in the 

hydraulic fluids. However, hydraulic fluids are 

often complex mixtures of many chemical 

components. A particular hydraulic fluid can differ 

in its chemical components from another hydraulic 

fluid even if the two fluids are in the same class. 

Thus, effects of exposure may differ. 

Very little is known about how mineral oil 

hydraulic fluids and polyalphaolefin hydraulic 

fluids will affect your health. There are reports of 

health effects in people exposed to these classes of 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

Agency for Toxic Substances and Disease Registry 

www.atsdr.cdc.gov/ Telephone: 1-888-422-8737 Fax: 770-488-4178 E-Mail: atsdric@cdc.gov 
 

 

 

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PUBLIC HEALTH STATEMENT 

HYDRAULIC FLUID 

CAS#: 55957-10-3; 68937-40-6; 50815-84-4; 

55962-27-1; 66594-31-8; 63848-94-2; 

107028-44-4; 28777-70-0 

Division of Toxicology September 1997 

hydraulic fluids. After drinking mineral oil 

hydraulic fluid, a child developed pneumonia and 

bleeding in the intestines and then died. A man 

whose hands and forearms were heavily exposed to 

mineral oil hydraulic fluids in his job developed 

weakness in his hands. This effect was probably 

caused by one of the organophosphate ester 

additives of the mineral oil hydraulic fluid. The 

skin and eyes of animals were red and swollen after 

contact with certain mineral oil hydraulic fluids and 

polyalphaolefin hydraulic fluids. Animals breathing 

very high levels of polyalphaolefin hydraulic fluids 

became drowsy and had congested lungs and 

trouble breathing. We do not know if mineral oil 

hydraulic fluids or polyalphaolefin hydraulic fluids 

will cause birth defects, reproductive effects, or 

cancer. 

There have been reports of people being poisoned 

from swallowing cooking oil or medicines 

contaminated with organophosphate esters. 

Outbreaks of brain, nerve, and muscle problems due 

to organophosphate contamination have happened 

in the United States and other countries. If you get 

certain organophosphate ester hydraulic fluids on 

your skin, it may be irritated and turn red. There 

are no reports of people breathing or swallowing 

this type of fluid. Studies in animals suggest that if 

you breathe or swallow large amounts of certain 

organophosphate ester hydraulic fluids, you may 

have nervous system problems. Certain 

organophosphate ester hydraulic fluids affect the 

nervous system of animals in two different ways. 

The first type of effect occurs within a few hours of 

breathing, swallowing, or skin contact. The 

organophosphate ester part of the hydraulic fluid 

rapidly inhibits the activity of important enzymes in 

the nervous system causing multiple symptoms 

including tremors, sweating, diarrhea, and difficulty 

breathing. The second effect involves damage to 

nerves. The symptoms of this type of damage are 

general weakness, weakness of the arms and legs, 

and paralysis. These symptoms of nerve damage 

can occur several weeks after exposure has stopped. 

If you have been exposed once to organophosphate 

ester hydraulic fluids, the symptoms of enzyme 

inhibition will disappear before the weakness 

occurs. Not all types of these fluids cause both 

types of nervous system damage. In animal studies, 

not all animals that have symptoms of enzyme 

inhibition have nerve damage. Both of these types 

of nervous system damage can occur after one or 

several exposures. 

Cows eating grass containing organophosphate ester 

hydraulic fluid had difficulty producing milk for 

their young. We do not know if this will also occur 

in people. We do not know if organophosphate 

ester hydraulic fluids will cause birth defects, affect 

fertility, or cause cancer. 

The Department of Health and Human Services 

(DHHS), the International Agency for Research on 

Cancer (IARC), and EPA have not classified 

mineral oil hydraulic fluids, polyalphaolefin 

hydraulic fluids, and organophosphate ester 

hydraulic fluids for carcinogenic effects. 

1.6 IS THERE A MEDICAL TEST TO 

DETERMINE WHETHER I HAVE BEEN 

EXPOSED TO HYDRAULIC FLUID? 

Hydraulic fluids themselves cannot be measured in 

blood, urine, or feces, but certain chemicals in them 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

Agency for Toxic Substances and Disease Registry 

www.atsdr.cdc.gov/ Telephone: 1-888-422-8737 Fax: 770-488-4178 E-Mail: atsdric@cdc.gov 
 

 

 

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PUBLIC HEALTH STATEMENT 

HYDRAULIC FLUID 

CAS#: 55957-10-3; 68937-40-6; 50815-84-4; 

55962-27-1; 66594-31-8; 63848-94-2; 

107028-44-4; 28777-70-0 

Division of Toxicology September 1997 

can be measured. Aliphatic hydrocarbons, which 

are major components of mineral oil hydraulic 

fluids and polyalphaolefin hydraulic fluids, can be 

detected in the feces. Certain components of 

organophosphate ester hydraulic fluids leave the 

body in urine. Some of these fluids inhibit the 

enzyme cholinesterase. Cholinesterase activity in 

blood can be measured. Because many other 

chemicals also inhibit cholinesterase activity in 

blood, this test is not specific for organophosphate 

ester hydraulic fluids. This test is not available at 

most doctor's offices, but can be arranged at any 

hospital laboratory. 

1.7 WHAT RECOMMENDATIONS HAS THE 

FEDERAL GOVERNMENT MADE TO 

PROTECT HUMAN HEALTH? 

Federal government recommendations exist to 

protect people's health from mineral oil hydraulic 

fluids. 

Mineral oil is the major chemical component of 

mineral oil hydraulic fluids. Mineral oil belongs to a 

larger class of chemicals called petroleum 

distillates. The Occupational Safety and Health 

Administration (OSHA) regulates petroleum 

distillate and mineral oil mist levels in workplace 

air. The occupational exposure limits for an 8-hour 

workday, 40-hour workweek are 2,000 milligrams 

per cubic meter (mg/m3) in air for petroleum 

distillates and 5 mg/m3 for mineral oil mists. The 

National Institute for Occupational Safety and 

Health (NIOSH) recommends an exposure limit of 

350 mg/m3 of petroleum distillates for a 10-hour 

workday, 40-hour workweek. 

1.8 WHERE CAN I GET MORE 

INFORMATION? 

If you have any more questions or concerns, please 

contact your community or state health or 

environmental quality department or: 

Agency for Toxic Substances and Disease Registry 

Division of Toxicology 

1600 Clifton Road NE, Mailstop F-32 

Atlanta, GA 30333 

Information line and technical assistance: 

Phone: 888-422-8737 

FAX: (770)-488-4178 

ATSDR can also tell you the location of 

occupational and environmental health clinics. 

These clinics specialize in recognizing, evaluating, 

and treating illnesses resulting from exposure to 

hazardous substances. 

To order toxicological profiles, contact: 

National Technical Information Service 

5285 Port Royal Road 

Springfield, VA 22161 

Phone: 800-553-6847 or 703-605-6000 

Reference 

Agency for Toxic Substances and Disease Registry 

(ATSDR). 1997. Toxicological profile for hydraulic 

fluid. Atlanta, GA: U.S. Department of Health and 

Human Services, Public Health Service. 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

Agency for Toxic Substances and Disease Registry 

www.atsdr.cdc.gov/ Telephone: 1-888-422-8737 Fax: 770-488-4178 E-Mail: atsdric@cdc.gov