[Histonet] RE: Histonet Digest, Vol 94, Issue 35 XYLENE

[Steve McClain]

It seems there is a debate on three or more issues, 
one being the validation of a test where xylene was the processing standard 
another being the safety of xylene where an employee is allergic or sensitized to xylene,
a third on poor lab design and poor ventilation,
 another on the safety of xylene as a potential toxin.

>From a dermatology perspective, formaldehyde is a great risk as a sensitizer.
Latex gloves are a greater risk for allergy than xylene- latex allergies are common among persons with nut allergies.
Allergies to the Limonene oils were/are also common.
Xylene  may induce bronchospasm and I assume the employee under discussion has issues in this regard.

If an employee were to have an issue, I suppose I would re-train them and assign them to other duties or help them find another job. 

Apparently there are others whose emotions run high on this subject.
Xylene is toxic, yet may be handled with relative safety assuming adequate ventilation.
In the absence of adequate ventilation one should refuse to handle any volatile liquids at all and find a new job.
I fail to see what there is to be emotional about xylene.
Xylene can be detected by most ordinary human noses at about 0.01 to 1ppm, or 1/100th to 1/10,000th of the acceptable 8 hour exposure limits.
OSHA and the CDC have fairly well established standards for workplace exposure.
For the CDC information- see http://www.atsdr.cdc.gov/mmg/mmg.asp?id=291&tid=53

In my own lab we designed for sufficient air exchange so I do not smell any fumes.
However, we have 3000 cubic feet per minute fans pulling fumes out of the grossing and solvent areas of the lab including stainers, coverslippers, processors and grossing benches.
And we keep containers closed whenever possible.

Steve A. McClain, MD
631 361 4000

Here are part of the CDC  data published on that website.
Medical Management Guidelines for Xylene 
(C6H4)(CH3)2

 PDF Version, 47 KB


CAS#: 1330-20-7 
UN#: 1307

Synonyms include dimethylbenzene, methyl toluene, xylol, and mixed xylenes.

Persons exposed only to xylene vapor do not pose substantial risks of secondary contamination. Persons whose clothing or skin is contaminated with liquid xylene can cause secondary contamination by direct contact or through off-gassing vapor. 
Xylene is a clear, colorless liquid. It is volatile, readily producing flammable and toxic concentrations at room temperature. Its vapor is heavier than air and may accumulate in low-lying areas. Xylene's odor generally provides adequate warning of hazardous concentrations. 
Xylene is rapidly absorbed after inhalation and ingestion. Exposure via ingestion and inhalation produces systemic toxicity. Xylene is slowly absorbed through intact skin, but percutaneous absorption may contribute to total body burden. 
General Information 

Description

Xylene exists as three isomers (ortho-, meta-, and para-xylene), which can be found singly or, more commonly, mixed in varying proportions. Commercial grade xylene, in which m-xylene is usually the major constituent, is a clear, colorless liquid with a sweet, aromatic odor. It is generally referred to as Mixed, Total or Technical-Grade Xylene. There is a fourth structural isomer, ethylbenzene (C6H5)(C2H5) that may be present as a congener, but is not toxicologically distinct to a significant degree. Xylene is flammable at room temperature; therefore, it constitutes a fire hazard. It is insoluble in water, but mixes readily with many organic solvents. Xylene is less dense than water and will float on the surface of water.

Routes of Exposure

Inhalation

Most exposures to xylene occur by inhalation and xylene is readily absorbed from the lungs. Xylene's odor threshold is about 1 ppm, which is 100 times less than the OSHA PEL and generally provides adequate warning of acutely hazardous concentrations. Irritation of eye and throat occur at about 200 ppm. Xylene vapor is heavier than air and may cause asphyxiation in enclosed, poorly ventilated, or low-lying areas.

Children exposed to the same levels of xylene vapor as adults may receive a larger dose because they have greater lung surface area:body weight ratios and increased minute volumes:weight ratios. In addition, they may be exposed to higher levels than adults in the same location because of their short stature and the higher levels of xylene vapor found nearer to the ground. 

Skin/Eye Contact

Xylene vapor is only mildly irritating to mucous membranes; however, xylene splashed in the eyes can result in corneal injury. Repeated or prolonged skin contact with liquid xylene can defat the skin, causing it to crack and peel. Percutaneous absorption is slow through intact skin; however, xylene absorbed through the skin may contribute to body burden.

Children are more vulnerable to toxicants absorbed through the skin because of their relatively larger surface area:body weight ratio.

Ingestion

Acute systemic toxicity can result from ingestion of xylene.

Sources/Uses

Xylene is among the 30 most abundantly produced chemicals in the United States. It is obtained primarily from crude petroleum. It is widely used as a degreasing agent and as a thinner and solvent in paints, inks, adhesives, and many other products. It is commonly found as a solvent in pesticide products.

Standards and Guidelines

OSHA PEL (permissible exposure limit) = 100 ppm (averaged over an 8-hour workshift) NIOSH IDLH (immediately dangerous to life or health) = 900 ppm

Physical Properties 
Description: Clear, colorless liquid

Warning properties: Adequate; sweet, aromatic odor at 1 ppm 

Molecular weight: 106.2 daltons

Boiling point (760 mm Hg)*: 292ºF (144ºC), 269ºF (139ºC), and 281ºF (138ºC)

Freezing point*: -13ºF (-25ºC), -54ºF (-48ºC), and 56ºF (13ºC)

Specific gravity*: 0.88, 0.86, and 0.86 (water = 1)

Vapor pressure*: 5, 6, and 6.5 mm Hg at 68ºF (20ºC)

Gas density: 3.8 (air = 1)

Water solubility: insoluble

Flammability*: 63ºF (17ºC), 81ºF (27ºC), 81ºF (27ºC)

Flammable range: 1.0% to 7.0% (concentration in air)

*ortho-, meta-, and para-xylene, respectively.

Incompatibilities
Xylene reacts with strong oxidizers and strong acids.

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Health Effects 


Xylene is irritating to the skin, eyes, and respiratory tract. It can cause systemic toxicity by ingestion or inhalation. The most common route of exposure is via inhalation. 
Symptoms of xylene poisoning include CNS effects (headache, dizziness, ataxia, drowsiness, excitement, tremor, and coma), ventricular arrythmias, acute pulmonary edema, respiratory depression, nausea, vomiting, and reversible hepatic impairment. 
The mechanism by which xylene produces toxicity is not known... see website http://www.atsdr.cdc.gov/mmg/mmg.asp?id=291&tid=53