Pentachlorophenol

Pentachlorophenol
File:Pentachlorophenol.svg
IUPAC name 2,3,4,5,6-Pentachlorophenol
Other names Santophen, Pentachlorol, Chlorophen, Chlon, Dowicide 7, Pentacon, Penwar, Sinituho, Penta
style="background: #F8EABA; text-align: center;" colspan="2" | Identifiers
CAS number	87-86-5 Y
PubChem	992
ChemSpider	967
SMILES
style="background: #F8EABA; text-align: center;" colspan="2" | Properties
Molecular formula	C6HCl5O
Molar mass	266.34 g mol−1
Appearance	White crystalline solid
Density	1.978 g/cm3 at 22 °C
Melting point	190-191 °C
Boiling point	309-310 °C (dec.)
Solubility in water	0.020 g/L at 30 °C
Y (what is this?)  (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Pentachlorophenol (PCP) is an organochlorine compound. First produced in the 1930s, it is marketed under many trade names. It can be found in two forms: PCP itself or as the sodium salt of PCP, which dissolves easily in water. In the past, PCP has been used as a herbicide, insecticide, fungicide, algaecide, disinfectant and as an ingredient in antifouling paint. Some applications were in agricultural seeds (for nonfood uses), leather, masonry, wood preservation, cooling tower water, rope and paper mill system. Its use has been significantly declined due to the high toxicity of PCP and its slow biodegradation.

There are two general methods for preserving wood. The pressure process method involves placing wood in a pressure-treating vessel where it is immersed in PCP and then subjected to applied pressure. In the non-pressure process method, PCP is applied by spraying, brushing, dipping, and soaking. Utility companies save millions of dollars in replacement poles, because the life of these poles increases from approximately 7 years for an untreated pole to about 35 years for a preservative-treated pole.

Synthesis

PCP can be produced by the chlorination of phenol in the presence of catalyst (anhydrous aluminium or ferric chloride) and a temperature of up to approximately 191 °C. This process does not result in complete chlorination and commercial PCP is only 84-90% pure. The main contaminants include other polychlorinated phenols, polychlorinated dibenzo-p-dioxins, and polychlorinated dibenzofurans. Some of these species are even more toxic than the PCP itself.

Exposure

People may be exposed to PCP in occupational settings through the inhalation of contaminated workplace air and dermal contact or with wood products treated with PCP. Also, general population exposure may occur through contact with contaminated environment media, particularly in the vicinity of wood treatment facilities and hazardous wastes sites. In addition, some other important routes of exposure seem to be the inhalation of contaminated air, ingestion of contaminated ground water used as a source of drinking water, ingestion of contaminated food, and dermal contact with soils or products treated with the chemical.

Toxicity

Short-term exposure to large amounts of PCP can cause harmful effects on the liver, kidneys, blood, lungs, nervous system, immune system, and gastrointestinal tract. Elevated temperature, profuse sweating, uncoordinated movement, muscle twitching, and coma are additional side effects.

Contact with PCP (particularly in the form of vapor) can irritate the skin, eyes, and mouth. Long-term exposure to low levels such as those that occur in the workplace can cause damage to the liver, kidneys, blood, and nervous system. Finally exposure to PCP is also associated with carcinogenic, renal, and neurological effects. The U.S. Environmental Protection Agency Toxicity Class classifies PCP in group B2 (probable human carcinogen).

Monitoring of human exposure

Pentachlorophenol may be quantitated in plasma or urine as an index of excessive exposure. This is usually performed by gas chromatography with electron-capture or mass spectrometric detection. Since urine contains predominantly conjugated PCP in chronic exposure situations, prior hydrolysis of specimens is recommended. The current ACGIH biological exposure limits for occupational exposure to PCP are 5 mg/L in an end-of-shift plasma specimen and 2 mg/g creatinine in an end-of-shift urine specimen.

Fate in humans and animals

PCP is quickly absorbed through the gastrointestinal tract following ingestion. Accumulation is not common, but if it does occur, the major sites are the liver, kidneys, plasma protein, spleen and fat. Unless kidney and liver functions are impaired, PCP is quickly eliminated from tissues and blood, and is excreted, mainly unchanged or in conjugated form via the urine. Single doses of PCP have half-lives in blood of 30 to 50 hours in humans. Biomagnification of PCP in the food chain is not thought to be significant due to the fairly rapid metabolism of the compound by exposed organisms.

Releases to the environment

PCP has been detected in surface waters and sediments, rainwater, drinking water, aquatic organisms, soil, and food, as well as in human milk, adipose tissue, and urine. As PCP is generally used for its properties as a biocidal agent, there is considerable concern about adverse ecosystem effects in areas of PCP contamination.

Releases to the environment are decreasing as a result of declining consumption and changing use methods. However, PCP is still released to surface waters from the atmosphere by wet deposition, from soil by run off and leaching, and from manufacturing and processing facilities. PCP is released directly into the atmosphere via volatilization from treated wood products and during production. Finally, releases to the soil can be by leaching from treated wood products, atmospheric deposition in precipitation (such as rain and snow), spills at industrial facilities and at hazardous waste sites.

Environmental fate

After PCP is released into the atmosphere it is transformed via photolysis. The main biodegradative pathway for PCP is reductive dehalogenation. In this process, the compound PCP is broken down to tetrachlorophenols, trichlorophenols, and dichlorophenols. Another pathway is methylation to pentachloroanisole (a more lipid soluble compound). These two methods eventually lead to ring cleavage and complete degradation.

In shallow waters, PCP is also quickly removed by photolysis. In deep or turbid water processes such as sorption and biodegradation take place. In reductive soil and sediments, PCP can be degraded within 14 days to 5 years, depending on the anaerobic soil bacteria that are present. However, adsorption of PCP in soils is pH dependent because it increases under acidic conditions and it decreases in neutral and basic conditions.

Pentachlorophenol by country

New Zealand

PCP was used in New Zealand as a timber preservative and antisapstain treatment and it was no longer used after 1988.

It was also sold as a moss killer to the general public (by Shell, at least) in the form of a 115g/L aqueous solution and labelled as a poison.

United States

Since the early 1980s, the purchase and use of PCP in the U.S has not been available to the general public. Nowadays most of the PCP used in the U.S is restricted to the treatment of utility poles and railroad ties. In the United States, any drinking water supply with a PCP concentration exceeding the MCL, 1 ppb, must be notified by the water supplier to the public. Disposal of PCP and PCP contaminated substances are regulated under RCRA as a F-listed hazardous waste.

References

http://cfpub.epa.gov/ncer_abstracts/index.cfm/fuseaction/display.abstractDetail/abstract/5235/report/F describes an EPA study that used the fungus phanerochaete chrysosporium to aid in bioremediation of pentachlorophenol in soil.

External links

• Non-CCA Wood Preservatives: Guide to Selected Resources - National Pesticide Information Center
• EPA on Pentachlorophenol
• atsdr.cdc.gov/ on Pentachlorophenolcs:Pentachlorfenol

pt:Pentaclorofenol