A Small Dose of Solvents

Solvents: Quick Facts

Use: varied - recreational (alcohol) to industrial (gasoline, degreasers)

Source: synthetic chemistry, petroleum products; plant oils

Recommended daily intake: none (not essential)

Absorption: intestine, inhalation (major), skin

Sensitive individuals: fetus, children

Toxicity/symptoms: nervous system, reproductive system, and death

General facts: long history of use (alcohol), high volatility of solvent results in inhalation exposure of vapors

Environmental concerns: volatile organic compounds react with sunlight to produce smog; solvents may contaminate groundwater

Recommendations: avoid, use proper workplace protection

Also see our page, Solvents - Chemical Profiles and External Links

Case Studies


Anesthetics

"I also attended on two occasions the operating theatre in the hospital at Edinburgh, and saw two very bad operations, one on a child, but I rushed away before they were completed. Nor did I ever attend again, for hardly any inducement would have been strong enough to make me do so; this being long before the blessed days of chloroform. The two cases fairly haunted me for many a long year."  - Charles Darwin, Autobiography (1993)

An effective anesthetic agent must be easy to use, quickly render the patient unconscious, and not produce any toxicity. Dr. William T.G. Morton first publicly demonstrated the use of ether as an effective anesthetic agent at the Massachusetts General Hospital on October 16, 1846 before a crowd of skeptical physicians. Ether (CH3CH2)2O was first discovered in 1275 by Raymundus Lullius, a Spanish chemist. Its hypnotic effects were soon appreciated (and enjoyed by some), but for many decades ether was only used occasionally to treat medical ailments. The success of surgical procedures did not improve until the introduction of antiseptic procedure and infection control some 20 years later. Ether was replaced by cyclopropane in 1929, which in turn was replaced by halothane in1956. While anesthetic agents are desirable for the patient, exposure to hospital staff is highly undesirable and an important occupational consideration.

n-Hexane


n-Hexane is a simple and common hydrocarbon found in solvents, degreasing agents, glues, spray paints, gasoline, silicones, and other common substances. A common workplace exposure to n-hexane is from degreasing agents, which usually contain a mixture of solvents. In 1997 a 24-year-old male automotive technician went to his doctor complaining of numbness and tingling of the toes and fingers. Further neurological evaluation revealed reduced sensation in the forearms and diminished reflexes. For the previous 22 months this worker had used, on a daily basis, aerosol cans of brake cleaner that contained 50-60% hexane (composed of 20%-80% n-hexane), 20-30% toluene, and 1-10% methyl ethyl ketone. He used this degreasing agent to clean brakes, small tools, and even car engines, commonly using latex gloves while at work. His condition improved when exposure to the cleaning agent was stopped. 2,5-hexanedione, a urinary metabolite of n-hexane that is thought to be the toxic agent responsible for the nervous system effects, can be measured and used to estimate exposure to n-hexane. A subsequent study found that automotive technicians were indeed exposed to n-hexane. Degreasing products typically contain a mixture of solvents that are readily absorbed when inhaled or allowed to pass through the skin. The latex gloves used by this worker offered little protection. More information on this case study can be found at MMWR (2001).

Introduction and History



Solvents are a broad class of compounds that we are commonly exposed to when we pump gas at the gas station, change the car oil, paint the house, glue something back together, drink alcohol, or use anesthetic when we undergo surgery. Solvents are highly volatile in air and are readily absorbed by the lungs when the vapors are inhaled. The small molecular weight of most solvents and their high fat solubility means they are easily absorbed across the skin. Occupational exposure to solvents is common, with an estimated 10 million workers in the United States exposed either though inhalation or skin contact. Acute exposure can result in loss of coordination, reduced speed of response, and a general feeling of drunkenness. Long-term exposure can result in decreased learning and memory, reduced ability to concentrate, changes in personality, and even structural changes in the nervous system.

Some people find the effects of solvents on the nervous system desirable and purposely inhale (sniff) solvents to induce a form of intoxication. In the United States approximately 15% of high school students have tried solvent inhalation at least once. Solvents available for inhalation and abuse are common in the home. Home products that may contain solvents included paints, paint remover, varnishes, adhesives, glues, degreasing and cleaning agents, dyes, marker pens, printer inks, floor and shoe polishes, waxes, pesticides, drugs, cosmetics, and fuels, just to name a few.

In general there are few benefits to solvent exposure and it should be avoided. The one important exception is the use of solvents to induce unconsciousness prior to surgery. As mentioned above, the solvent ether was discovered centuries ago but not used in surgery until the 1840s. Some physicians and dentists first became aware of the effects of ether during "ether frolics" while attending school. Nitrous oxide was also experimented with around the same time but was not widely adopted by dentists and surgeons until the 1860s. Despite its liver toxicity, chloroform was also used as an anesthetic particularly in England and Scotland starting in the late 1840s. Anesthetic agents changed little until the accidental discovery of cyclopropane in 1929. With the increased use of electronic equipment in the surgery area, the flammability of the anesthetic agents became an important issue. In 1956, halothane was discovered by researchers in England, ushering in a new era in anesthesiology.

The use of solvents greatly expanded with the Industrial Revolution, which resulted in solvents' widespread release into the environment. Solvents such as volatile organic compounds (VOCs) readily evaporate into air, for example, when oil-based paint dries. Industrial release also occurs during manufacture or spills.

Solvent contamination of drinking water is not uncommon and is a public health issue. VOCs that enter groundwater become trapped until released during use. Human exposure occurs from drinking contaminated water or from bathing. Solvents such as benzene and trichloroethylene are commonly found at hazardous waste sites and may endanger nearby groundwater.



Biological Properties


From a biological perspective the most important properties of solvents are their volatility, high fat solubility (lipophilicity), and small molecule size. Solvents with these characteristics are termed volatile organic compounds (VOCs). Under normal working conditions solvents readily evaporate into the air, from where they enter the lungs. The high lipid solubility and small molecule size means they are quickly absorbed across lung membranes and enter the blood supply. Blood from the lung moves directly to the brain and other body organs before reaching the liver, where metabolism of the solvent occurs. With ongoing exposure, equilibrium is reached between the amount in the body and the concentration of the solvent in the air.

Solvents are also well absorbed following oral or skin exposure. Most solvents are quickly absorbed from the gut, although the presence of food may delay absorption. Alcohol is a good example of a solvent typically consumed orally. The skin offers little barrier to solvents. Skin exposure to solvents can result in local irritation and increased blood levels of the solvent.

Solvents are eliminated from the body by metabolism or exhalation. The more volatile and fat-soluble the solvent, the greater its concentration in exhaled air. Exhaled air can be used to estimate solvent concentrations in the blood, as in breath analysis for alcohol exposure. Metabolism of solvents occurs primarily in the liver by P450 enzymes. In most cases the metabolism results in reduced toxicity and increased elimination of the resulting products. For example, the toxicity of toluene is reduced when liver enzymes change the compound so that it does not readily cross cell membranes. However, the toxicity of benzene is increased when it is changed to a compound that can attack the blood-forming cells of the bone marrow, causing leukemia.

There is considerable variability in people's ability to metabolize solvents. Subtle genetic differences can increase or decrease an individual's ability to metabolize certain solvents, resulting in increased or decreased toxicity. The liver is also prone to damage by some solvents, such as carbon tetrachloride (CCl4). This damage can actually be made worse by prior exposure to alcohol.

Products that are mostly solvent:
Gasoline
Diesel fuel
Charcoal lighter fluid
Lantern fuel
Lubricating oils
Degreasing agents
Paint strippers
Paint thinner
Turpentine
Nail polish remover
Rubbing alcohol

Products that are partially solvent based:
Glues
Adhesives
Oil-based paints
Furniture polishes
Floor polishes and waxes
Spot removers
Metal and wood cleaners
Correction fluid
Computer disk cleaner
Varnishes and shellacs
Wood and concrete stains

Health Effects


The majority of us are exposed to low levels of solvents every day. Millions of workers around the world are exposed on a daily basis to high levels of solvents that can adversely affect health. Workers often come in contact with more than one solvent during a day's work. Health hazards from solvent exposure range from mild to life-threatening depending on the compound involved and the level and duration of exposure. It should also not be forgotten that many solvents are highly flammable.

Acute effects often involve the central nervous system because of the rapid absorption of the solvent from the lungs and direct distribution to the brain. The immediate effects may result in drowsiness or mild impairment of judgment . In most situations these effects are not serious and will end quickly once exposure stops. In some circumstances a slight lapse of judgment could be disastrous. A person responding to a hazardous materials spill or perhaps a fire must take appropriate precautions to limit exposure to any solvents that could impair her or his judgment and thus increase risk of injury.

Chronic exposure to solvents can result in a range of organ-system effects. Damage to the peripheral nervous system results in a tingling sensation and loss of feeling in the hands and feet, increased reaction time, and decreased coordination. Reproductive effects included decreased and damaged sperm, which causes a loss in fertility. Liver and kidney damage is possible from a range of solvents. Cancer is also caused by a number of different solvents, such as benzene and carbon tetrachloride.

There is no doubt that repeated exposure to high levels of solvent can result in permanent damage to the nervous system. These changes may result in impaired learning and memory, decreased attention spans, and other psychological effects. There is also considerable data indicating that chronic low-level exposure to solvents can result in a cluster of symptoms variously referred to as painter's syndrome, organic solvent syndrome, or chronic solvent encephalophathy. The painter's syndrome was first described in Scandinavia in the late 1970s and became a recognized occupational disease in these countries. The cluster of symptoms includes headache, fatigue, sleep disorders, personality changes, and emotional instability, which progress to impaired intellectual function and ultimately, dementia. Early symptoms are often reversible if exposure is stopped.

Health Effects of Solvents

Reproductive hazard

methoxyethanol, 2-ethoxyethanol, methyl chloride

Developmental hazard

alcohol (Ethyl Alcohol)

Liver or kidney damage

Toluene, carbon tetrachloride, 1,1,2-2-tetrachloroethane, Chloroform

Nervous system damage

n-hexane, perchloroethylene, n-butyl mercaptan

Carcinogenic

carbon tetrachloride, Trichloroethylene, 1,1,2,2-tetrachloroethane, perchloroethylene, Methylene Chloride, Benzene

Visual system hazard

methanol

The easy availability of solvents in commercial and household products, combined with the rapid onset of nervous systems effects, encourages the use of solvents as an intoxicating drug. The recreational inhalation of solvents can produce euphoria, visual and auditory hallucinations, and sedation. As mentioned above, repeated exposure to high levels of solvents results in permanent brain damage. Children who accidentally drink furniture polish or other solvent-based household products are vulnerable to nervous system effects and possibly pneumonitis.

Reducing Exposure


From a health perspective there are few redeeming features of solvents except for their use as anesthetics. Clearly the simple recommendation is to avoid exposure unless administered for some medical reason. In the workplace, appropriate ventilation and personal safety equipment should be in place at all times. There are numerous national and international regulations on solvent exposure in the workplace. Substitution of less-toxic solvents in processes and products can reduce the risk of injury.

Regulatory Standards


In workplaces, standards and exposure recommendation are complex because they must address both level and duration of exposure. Below are some of the common terms used in establishing exposure recommendations.

STEL - Short term exposure limits (15 minute exposure) -protects against loss of consciousness or loss of performance, allows short-term exposure in emergency situations
TLV - Threshold Limit Value
TWA - Time Weighted Average (acceptable for 8-hr day, 40-hr week)
TLV-C - Threshold Limit Value-C (ceiling not to be exceeded)

Recommendation and Conclusions


Solvents are common around the home and workplace. As with most toxic substances, the best policy is to substitute less-toxic products whenever possible, and to reduce exposure through ventilation or protective equipment when substitutes are not available. Inhalation of solvents is particularly dangerous because of the rapid exchange in the lungs and quick access to the nervous system. Solvent inhalation produces predictable short-term effects but the long effects of repeated solvent exposure are not well characterized.

References


Charles Darwin. The Autobiography of Charles Darwin 1809-1882. Charles Darwin, Nora Barlow (Editor), W.W. Norton & Company, New York, NY, 1993.

MMWR (2001). n-Hexane - Related Peripheral Neuropathy Among Automotive Technicians - California, 1999-2000. Vol 50, No 45;1011, 11/16/2001. Online: <http://www.cdc.gov/mmwr/PDF/wk/mm5045.pdf> (accessed: 16 April 2009).

Dick, FD. (2006). "Solvent neurotoxicity." Occup Environ Med. 63(3): 221-226. doi: 10.1136/oem.2005.022400.

Feldman, RG, Ratner, MH, and Ptak, T. (1999). "Chronic toxic encephalopathy in a painter exposed to mixed solvents." Environ Health Perspect. 107(5): 417-422.

Breaking News


News on solvents from *Environmental Health News*

Scientific studies


  • No labels