CHAPTER 38

PERSPECTIVES ON SPECIFIC SUBSTANCES: PENTACHLOROPHENOL Richard Lawuyi and Merv Fingas Emergencies Science Division, Environment Canada, Environmental Technology Centre, River Road, Ottawa, Ontario

38.1

OVERVIEW OF PRODUCT AND INDUSTRIAL USES Pentachlorophenol (PCP) and its salts are purely anthropogenic substances that are widely used for wood and leather preservation due to their broad spectrum of antimicrobial characteristics. Industrially, their application as fungicides, bacteriacides, herbicides, insecticides, ovicides, algicides, and molluscicides is well known. Pentachlorophenol enters the environment and works its way into the soil, surface water, groundwater, sediments, food, and air primarily from treated utility poles and fences, during production, from treatment facilities, hazardous waste sites, and accidental spills, and from its use as a pesticide. The major contaminants in commercial pentachlorophenol can be very toxic and include polychlorodibenzodioxins, polychlorodibenzofurans, polychlorodiphenyl ethers, and chlorophenols. Many toxicologists have reported that short-term, high-level exposure, which often occurs during accidental spills, can damage the liver, kidneys, nervous system, and blood and cause death in humans. Other researchers have shown that these exposures cause a decrease in the number of offspring in animals. The use of PCP is now restricted in both Canada and the United States.

38.1.1

Modern Industrial Uses

While pentachlorophenol is no longer manufactured in Canada, it is still imported and used as a preservative for utility poles, paints, adhesives, textiles, leather, and furs. Other uses such as pest control and preserving fence posts and crossties were stopped in 1990. The environmental impact of pentachlorophenol and its uses are being reviewed by regulatory agencies. 38.1

38.2

CHAPTER THIRTY-EIGHT

38.2

INTRODUCTION PCP and its salts were introduced into commerce in 1936 and were one of the most heavily used substances in North America for many years. They were used primarily as a timber preservative to control molds, wood-boring insects, termites, and a variety of fungal rots. Their widespread use was due to their solubility in both aqueous and organic solvents. They were so successful that their use was extended to other applications such as in petrochemical drilling fluids, paints, oils, leather, masonry, paper mill systems, agricultural seeds, rope, and in cooling tower water. Unfortunately, PCP often contains impurities that are toxic not only to fungi and bacteria but also to other living organisms. Its environmental impact includes effects on human health as well as on plants and other environmental organisms, such as aquatic species and wildlife. Its impurities include the less chlorinated phenols, polychlorinated phenoxy phenols, polychlorinated dibenzo-p-dioxins, and polychlorinated furans. By the late 1980s, pentachlorophenol and its impurities had become so ubiquitous in the environment that its use has now been restricted.

38.2.1

Spill Profile

PCP and its salts enter the environment through a variety of sources, primarily during wood treatment, spills, discharge at dump sites, other disinfecting uses, as well as during manufacture. Most spills are due to one or more of the following causes (Environment Canada, 2000): 1. 2. 3. 4. 5.

Overflow Leaks from containers, pipes, underground storage tanks, and valves and fittings Intentional discharges Process upsets Unknown causes

The annual spill frequency of PCP from 1982 to 1992 is shown in Fig. 38.1. As can be seen, there were very few spills—a total of 31 in 11 years. The frequency of spills has been decreasing since 1987, when there were major concerns in Canada about the byproducts of PCP. Once it is introduced into the environment, PCP transport is very fast. The sodium salt is very soluble in water, while PCP itself is soluble in organic solvents. Transport often occurs through runoff from treatment sites, as well as from leaching and volatilization.

38.2.2

Priority List Ranking

Pentachlorophenol is very toxic and more persistent in the soil than most organic compounds and the spill number, spill volume, and supply volume are much less. It is ranked tenth, just below potassium chloride, on Environment Canada’s priority substance list of hazardous chemicals (Fingas et al., 1991). This is shown in Table 38.1. The primary objective of the list was to determine the minimum number of hazardous substances that were most frequently spilled. The list was developed by a simple ranking of: (1) reported spill frequency, (2) supply volumes, (3) historical spill volumes, and (4) toxicity data, stability, accumulation, and persistence.

PERSPECTIVES ON SPECIFIC SUBSTANCES: PENTACHLOROPHENOL

38.3

NUMBER OF SPILLS

7 6 5 4 3 2 1 0

82 83 84

85 86 87 88 YEAR

89 90

91 92

FIGURE 38.1 PCP—Annual spill frequency (1982–1992).

38.3

PHYSICAL AND CHEMICAL PROPERTIES AND GUIDELINES SUMMARY

OH Cl

Cl

Cl

Cl Cl

38.3.1

Physical State Properties

Pentachlorophenol is a colorless to light or dark brown crystalline solid or powder with a weak or phenolic odor, but with a strong pungent odor when heated. Common name: Pentacholorphenol (PCP) Molecular formula: Cl5C6OH Molecular weight: 266.35 CAS number: 87-86-5 UN number: 2020 STCC number: 4961380 Labels: Poisonous and infectious substances

38.4

CHAPTER THIRTY-EIGHT

TABLE 38.1 Priority List Ranking of Hazardous Chemicals

Chemical Ammonia Chlorine Tetraethyl lead Styrene PCBs Sulfuric acid Sodium cyanide Hydrochloric acid Potassium chloride Pentachlorophenol Phenol Zinc sulfate Phosphorus Toluene MTBE

Ranking

Number of spills

Spill quantity (t)

Supply quantity (kt)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

107 36 4 24 334 155 3 123 31 19 10 3 16 13 1

470 120 72 5,000 89 13,000 83 3,300 12,000 110 14 68 46 110 1

3,700 1,700 26 630 — 3,700 12 170 — 1.5 68 1,500 68 430 500

RTECS number: SM6300000 Synonyms and trade names (RTECS On-Line, 2000) Antimicrobial* Block Penta Chem-Tol Chion Chlon Chlorophen Cryptogil Dow Pentachlorophenol DP-2* Antimicrobial Dowicide 7 Dowicide EC-7* Dowicide-G Dura Treet II Durotox EP 30 Fungifen GLAZD* Glazed Penta Grundier arbezol Lauxtol Lauxtol A Laustrol Liroprem Monsanto Penta PCP Penchlorol* Penta Penta EC 30* Penta Ready* Penta WR* Pentacon* Penta Pres 1-10*

PERSPECTIVES ON SPECIFIC SUBSTANCES: PENTACHLOROPHENOL

38.5

Penwar* Permasan Permatox PKHF POL NU Preventol Santobrite* Santophen 20* Sinituho* Weedone* Woodtreat A * Discontinued names. Grades and Purities: Pentachlorophenol (PCP) is available in two main grades: (1) technical grade which is about 86% pure, being contaminated by a mixture of mostly polychlorodibenzodioxins and phenol ethers; and (2) a pure quality grade consisting of 99% PCP. The main impurities are chlorinated phenols and polychlorodibenzodioxins. PCP is available in solution or as a dry powder. For example, technical grade pentachlorophenol contains traces of hexa, hepta, and octachlorodibenzo-p-dioxins; hexa-, hepta-, and octachlorodibenzofurans; and hexachlorobenzene. Grade Technical Special

38.3.2

Purity 86% 99%

Physical Data

Pentachlorophenol is a colorless to light or dark brown crystalline solid or powder with a weak or phenolic odor, but a strong, pungent odor when hot. It melts at between 187 and 189⬚C and boils with decomposition at 310⬚C. The odor threshold in water is 1.6 mg / L and the taste threshold in water is 30 ␮g / L. It is soluble in alcohol, ether, benzene, and slightly soluble in water. It is stable at room temperature, in closed containers, and under normal conditions. Photodegradation can occur in sunlight. It is also available as sodium pentachlorophenate. Appearance: White, monoclinic, crystalline solid; technical grade dark grey to brown (Verschueren, 1996) Usual shipping state: Solid (Transport Canada, 1994) Physical state at room temperature and pressure: Solid (Verschueren, 1996) Boiling point: 309 to 310⬚C (decomposes) Melting point: 188 to 191⬚C Vapor pressure: 0.00011 mm Hg at 25⬚C or 0.100 Pa Specific gravity (kg / m3): 1.98 Relative vapor density (air ⴝ 1): 9.2 Fire properties: Flammability: Depends on the solvent; substance itself is not flammable Behavior in fire: Produces toxic gases and vapor Decomposition temperature (⬚C): ⬎191 Decomposition products: Hydrogen chloride, chlorinated phenols, and carbon monoxide Flash point: –

38.6

CHAPTER THIRTY-EIGHT

Flammable limits: Not flammable Autoignition temperature: – Extinguishing: Dry chemical, foam or carbon dioxide, water spray Keep containers cool with water spray Reactivity: Stable Other properties: Molecular weight: 266.35 Solubility in water: Slightly soluble, 0.5 mg / 100 mL (0⬚C) 1.4 mg / 100 mL (20⬚C) 3.5 mg / 100 mL (50⬚C) 8.5 mg / 100 mL (70⬚C) Solubility in organic solvents: Alcohol, ether, and benzene Log octanol / water partition coefficient: 5.01 Refractive index (20⬚C): 1.3689 Henry’s law constant (Pa 䡠 m3 / mol): 0.284; 0.00248; 0.0127; 0.277; 0.079 Molar volume (cm3 / mol): 207.9 Summary of Chemical Properties and Behavior. As a group, the phenols are the aromatic counterparts of the alcohols although they are far more acidic. The phenoxide anion is stabilized by the delocalization of electrons into the aromatic ring. Any substitution by electron withdrawing groups such as chlorine increases the acidity. The pKa of PCP at 25⬚C is 4.7, while that of ethanol is 16.00. Some substituted phenols such as the nitrophenols are even more acidic than the carboxylic acids. At pH 4, PCP is fully protonated and highly lipophilic, while at pH 9, it is ionized and least toxic.

38.3.3

Main Hazards

Pentachlorophenol is a poison that is highly toxic by skin absorption, inhalation, and ingestion and irritating to the eyes, skin, throat, and lungs. Repeated exposure can cause skin rashes. Ingestion can result in severe systematic poisoning. Acute exposures may cause rapid heartbeat, rapid breathing, hypertension, fevers, muscular weakness, anorexia, sweating, dizziness, and nausea. High doses can cause unconsciousness, convulsions, and death due to cardiac arrest. Excessive skin exposure has caused human death. Chronic exposure can cause chloracne and bronchitis. Liver and kidney damage have been found in animals. When heated or during a fire (above 200⬚C), PCP emits toxic fumes of hydrogen chloride, chlorine, chlorinated hydrocarbons, and chlorodibenzodioxins.

38.3.4

Human Health

TLV: 0.5 mg / m3 (skin) TWA: 0.5 mg / m3 (8-hour) (skin) IDLH: 150 mg / m3 Probable human carcinogen (U.S. EPA) Possibly carcinogenic to humans (IARC, 1994) Exposure Effects Contact and inhalation: The main routes of exposure are inhalation, skin absorption, ingestion, and eye contact. Exposure will cause irritation of the skin, throat, eyes, and

PERSPECTIVES ON SPECIFIC SUBSTANCES: PENTACHLOROPHENOL

38.7

lungs. Acute exposure may cause rapid heartbeat, rapid breathing, hypertension, fevers, sweating, dizziness, nausea, muscular weakness, and anorexia. High doses may cause seizures, unconsciousness, or death. Chronic effects include chloracne and bronchitis. Liver and kidney damage have been found in animals. Environment: PCP is toxic to plants, fungi, bacteria, algae, fish, and aquatic life. Behavior in air: PCP tends to associate with particulate matter in air and eventually settles on the ground. PCP vapor is lost by photolysis, or by reaction with hydroxyl radicals. Behavior in water: PCP will dissociate in water at ambient pH levels. The dissociated species will photodegrade (half-life of hours to days). Adsorption to sediments can occur. Photolysis can occur in water.

38.3.5

Emergency Response

Symptoms: Irritating to the eyes, throat, skin, and nose. Exposure can cause weakness, nausea, vomiting, shortness of breath, headaches, dizziness, fever, and high temperature. Local: Skin contact is irritating and could provide efficient way for the chemical to enter the body and cause systemic poisoning. Skin rashes may occur. Respiratory: Acute exposure is irritating. Respiratory tract irritation. It may cause rapid breathing, rapid heartbeat, high blood pressure, fevers, muscular weakness, sweating, dizziness, and nausea. Large doses may cause unconsciousness, seizures, and death. Gastrointestinal: Ingestion may cause severe systemic poisoning. Treatment: Inhalation: At the spill site, move patient to fresh air and call for medical assistance. Monitor for respiratory distress. If breathing has stopped, give artificial respiration (not mouth to mouth) or CPR if indicated. If breathing is labored, give oxygen. If cough or difficulty in breathing develops, evaluate for respiratory tract irritation, bronchitis, or pneumonitis. During transportation, continue to administer oxygen by 40% venturi mask. In the emergency room, continue giving oxygen. Monitor arterial blood gas. Evaluate for pulmonary involvement. Observe for liver or kidney damage. Skin: At the spill site, wash exposed areas extremely thoroughly with soap and water and remove contaminated clothing. Shower thoroughly. In the emergency room, treat as skin irritant. Prolonged exposure may cause acneiform dermatitis. Eyes: At the spill site, flush eyes with water for 15 minutes. Hold eyelids open while washing and continue to irrigate. Continue eye irrigation during transportation. In the emergency room, continue giving oxygen (Mediflow lens if available); determine nature and degree of corneal damage. Notify ophthalmologist. Ingestion: At the spill site, give large quantities of water. Induce vomiting. During transportation, observe vital signs. In the emergency room, induce vomiting or lavage. Observe for liver or kidney damage. Observe urine for pentachlorophenol. Hazards and toxicity: For emergency response to a spill of pentachlorophenol, the immediate concerns are shown in the following box.

38.8

CHAPTER THIRTY-EIGHT

Immediate Concerns Hazard: Material itself is not flammable, but may be mixed with flammable solvents in commercial formulations. Toxic gases and vapors, e.g., hydrogen chloride gas, chlorinated phenols, chlorodibenzodioxins, furans, and carbon dioxide are released when product is heated. Humans: Poison. Irritating to eyes, nose, and throat. May cause weakness, nausea, vomiting, shortness of breath, chest pain, headaches, dizziness, and increased temperature and heartbeat. May cause death or permanent injury after exposure to small quantities. Possible human carcinogen. Environment: Toxic to fish and plant life. Could disrupt stable ecological relationships among localized populations. Adverse effects on various animals and plant species. Protection: Wear self-contained breathing apparatus and totally encapsulated suits, rubber gloves, boots, and goggles.

38.3.6

Spill Control

Spills or leaks: Keep all unprotected personnel clear of area. Wear protective clothing. Evacuate area. Ventilate area. Contain spill with earth and sand. Prevent spilled material from entering drains, sewers, waterways, and soil. Inform appropriate authorities if a major spill occurs. Absorb small quantities on paper towels. Do not allow to enter confined space or sewer. Fire: PCP is not flammable, even though it may be mixed with flammable solvents in commercial preparations. Use dry chemical or carbon dioxide, water spray, or foam to fight fires. Use water spray to keep fire-exposed containers cool, disperse vapors, and protect workers trying to fight the fires. Water spray may be used to flush spills away from exposures. Wear goggles and self-contained breathing apparatus. When heated to decomposition, toxic fumes of hydrogen chloride, carbon dioxide, dioxins, and furans are produced.

38.3.7

Countermeasures

Emergency control procedures: Soil: Stop or reduce discharge if safe to do so. Contact manufacturer or supplier for help. Notify Canutec and provincial authorities. Contain spill with earth, sand, or other noncombustible absorbent material and place into containers for later disposal. Construct barriers to contain spill or divert spill to impermeable holding area. Remove material by manual or mechanical means. Recover undamaged containers. Remove contaminated soil for disposal. Water: Stop or reduce discharge if safe to do so. Contact manufacturer or supplier for help. Notify Canutec and provincial authorities.

PERSPECTIVES ON SPECIFIC SUBSTANCES: PENTACHLOROPHENOL

38.9

Contain discharge by damming or water diversion. Dredge or vacuum pump to remove liquids, contaminants, and contaminated bottom sediments.

38.4

INDUSTRIAL ASPECTS AND PRODUCTION IN THE UNITED STATES, CANADA, AND WORLDWIDE The pentachlorophenol market is quite small and has been declining for some time for environmental reasons. PCP prices have been very stable. The main producers worldwide are Vulcan (U.S.A.), Idacon (U.S.A.), Rhone-Poulenc, and Chapman (CIS, 1995). The global market for pentachlorophenol has been estimated at about 25,000 tons / year. In 1994, the imports of pentachlorophenol to Canada jumped by more than 110% probably due to extra demand for utility poles after many years of austerity. The main buyers of pentachlorophenols are listed here.

38.4.1

Main Buyers in Canada

Bell Pole Bios KMS (GMI) Canada Cedar Pole Preservers Goodfellow Newfoundland Hardwoods Northern Pressure Treated Wood Northern Wood Preservers Stella-Jones Trans Canada Pole Wood Preservation Industries

38.4.2

Carseland, AB L’Annonciation, QC Galloway, BC Delson, QC Clarenville, NF Kirkland Lake, ON Thunder Bay, ON Prince George, BC, Truro, NS, Cochrane, AB, and Delson, QC Thornton, ON Mascouche, QC

Manufacture of Pentachlorophenol

The most common method for manufacturing pentachlorophenol is the progressive chlorination of phenols in the presence of Lewis acid catalysts. Another method specific for 2,4,5trichlorophenol and pentachlorophenol is by hydrolysis of chlorobenzenes such as pentaand hexachlorobenzene. In general, the hydrolysis method always produces more impurities. The final product is a mixture often containing a couple or more of the following compounds: Dichlorophenol Trichlorophenol Tetrachlorophenol Hexachlorobenzene Tetrachlorodibenzodioxin Hexachlorodibenzodioxin Heptachlorodibenzodioxin

38.10

CHAPTER THIRTY-EIGHT

Octachlorodibenzodioxin Pentachlorodibenzofuran Hexachlorodibenzofuran Heptachlorodibenzofuran Octachlorodibenzofuran Heptachlorohydroxydiphenyl ether Octachlorohydroxydiphenyl ether

38.5

CHEMISTRY Pentachlorophenol, while essentially an aromatic alcohol, is a rather acidic substance because the pentachlorophenate anion is resonance stabilized by the aromatic ring resulting in increased stability for this anion. The electron-withdrawing chlorines also delocalize the negative charge (electrons) on the oxygen, thus making the proton easily removable and hence much more acidic (pKa ⫽ 4.7).

38.5.1

Formation of Dioxins and Furans

When heated, PCP will form chlorinated diphenyl ethers which can further react to produce chlorinated dioxins and furans. This is why wood treated with PCP should only be burned at controlled temperatures so that dioxins and furans are not produced. The reactions are illustrated in Figs. 38.2 to 38.5. 38.5.2

Acid–Base Reactions

Pentachlorophenols are extremely acidic and will react with bases to produce a salt, sodium pentachlorophenate, and water. PCP can also be converted to esters and several other aromatic and alcoholic derivatives. In a fire, formation of dioxins and furans is also possible, as shown in Fig. 38.4. 38.5.3

Formation of Other Ethers

Pentachlorophenol will also take part in nucleophilic displacement reactions to produce the nontoxic conjugates such as sulfates and anisoles. This is the principal process for the elimination of PCP in fish and many mammals (Kobayashi et al., 1977; Glickman et al., 1977).

38.6

ENVIRONMENTAL FATE AND EFFECTS Pentachlorophenol is extremely toxic to the environment and is still the subject of much research and many government regulations. It has a broad spectrum of bactericidal activities and will kill many algae and fungi. It also has phytotoxic properties. In aquatic environments, the LC50 for fish is 0.03 to 0.6 mg / L, causing renal and hepatic lesions at lesser concentrations. Pentachlorophenol has been found to be widespread in the soil and surface water in areas where utility poles are used due to washing of the poles by rain and snow and exposure to

38.11

PERSPECTIVES ON SPECIFIC SUBSTANCES: PENTACHLOROPHENOL OH

OH

Cl

Cl

Cl

Cl

+ Cl

Cl

Cl

Cl

Cl

Cl h e a t/light

Cl

Cl

Cl O

Cl

Cl OH

Cl

Cl

Cl

Cl

he a t/ligh t

Cl

f

Cl

Cl

O

Cl +

O

Cl Cl

HCl

Cl

Cl d ib e nzo -p -d io x in

FIGURE 38.2 Formation of polychlorodibenzo-p-dioxins.

wind. Pentachlorophenol has been detected in air, rainwater, and snow and at hazardous waste sites in Canada and the United States and continues to be an exposure risk chemical. Formation of polychlorodibenzo-p-dioxins and dibenzofurans could occur as a result of environmental transformation. Levels of pentachlorophenol in the soil decrease through biodegradation and in the air, by photodegradation. PCP has a high adsorption coefficient (Koc ⬃ 3000 to 4000) and it is therefore strongly adsorbed to the soil particles and sediments. It will also bioconcentrate to a small extent in fish and animals. It is also known to volatilize from water surfaces and soil. The environmental fate of pentachlorphenol is shown in Fig. 38.6.

38.12

CHAPTER THIRTY-EIGHT

OH

Cl 2 OH

OH

OH Cl Cl

+

Cl

+

Cl

Cl

Cl 2

OH Cl

Cl

Cl

Cl Cl

Pentachlorophenol FIGURE 38.3 Manufacture of pentachlorophenol.

38.13

PERSPECTIVES ON SPECIFIC SUBSTANCES: PENTACHLOROPHENOL OH

OH

Cl

Cl

Cl

Cl

+ Cl

Cl

Cl

Cl

Cl

Cl h e a t/lig h t

Cl

Cl

Cl O

Cl

Cl OH

Cl

Cl

Cl

Cl

h e a t/lig h t

Cl

Cl

Cl O

Cl +

HCl

Cl

Cl Cl

Cl d ib e n z o f u r a n

FIGURE 38.4 Formation of polychlorodibenzofuran.

38.7 38.7.1

BEHAVIOR Solubility in Aqueous and Organic Solvents

The solubilities of PCP and its salts tend to complement each other. While PCP is readily soluble in most organic solvents such as oils, hydrocarbons, ethers, alcohols (ethanol 470 to 520 g / L), and esters, it is only slightly soluble in water (14 mg / L at 20⬚C). On the other hand, sodium pentachlorophenate, its salt, is very soluble in water (330 g / L at 25⬚C) and only slightly in organic solvents. The solubilities of PCP and its salts are pH-dependent. For

38.14

CHAPTER THIRTY-EIGHT OH

ONa

Cl

Cl

Cl

Cl + H 2O

NaOH Cl

Cl

Cl Cl

Cl Cl

OH Cl Cl 5 H Cl + 6 C O 2 + H 2 O Fire Cl

Cl Cl

FIGURE 38.5 Reactions of pentachlorophenol with NaOH and in fires.

VOLATILIZATION INTO THE AIR FROM SOIL AND WATER SURFACES SORPTION TO SOIL ELEMENTS WATER PARTICULATES AND SEDIMENTS

COVALENT BONDING TO SOIL ELEMENTS OH Cl

Cl

Cl

Cl Cl PHOTODEGRADATION -bonds and rings breaking by radicals formation

BIODEGRADATION -dechlorination -hydroxylation -methylation -mineralization

FIGURE 38.6 Environmental fate of pentachlorophenol.

PLANTS AND ANIMALS UPTAKE

PERSPECTIVES ON SPECIFIC SUBSTANCES: PENTACHLOROPHENOL

38.15

example, the solubility of sodium or potassium pentachlorophenate in water increases from 79 mg / L at pH 5 to ⬎4 g / L at pH 8.0. High concentrations of these salts would, of course, have profound and adverse effects during exposure at high pHs. Differences in lipid solubilities also reflect different bioaccumulation potentials. Clearly, the highly lipophilic pentachlorophenol will be more prone to bioaccumulate than the salts. The toxic contaminants, such as tri-, tetra-, and other chlorophenols isomers, dibenzofurans, dioxins, hexachlorobenzene, and phenoxyphenols, which are often present in the technical grades, are also lipophilic. In terms of transport, during precipitation, the readily soluble pentachlorophenate salts will most likely be dissolved and washed away in runoff from spill and wood-treatment sites to rivers, lakes, and streams or leached through the soil to groundwater, while the lipophilic PCP will easily adsorb to soil material and sediments (Wan, 1992).

38.7.2

Sorption

The adsorption of pentachlorophenol by soils strongly depends on the chemical and physical properties of the soil, pH of the soil–water systems, the chemical species, and their affinity for the soil surface (Callahan, 1979). Soil properties that can affect adsorption are grain size, soil pH, clay, and organic carbon content. The organic matter includes mostly biodegradation products and humic and fulvic acids that usually cover the surface of soil particles. High organic matter content tends to increase adsorption. Clay soil consists of fine particles with large surface area and large solid–water interfaces on which PCP molecules can adhere. The measured adsorption coefficient (Koc) is 3,000 to 4,000. The type of chemical species present will also influence adsorption. Pentachlorophenol behaves like a weak organic acid (pKa ⫽ 4.74, same as acetic acid). It ionizes in solution according to the following equilibrium: C6Cl5OH → ← C6Cl5O⫺ ⫹ H⫹

(38.1)

The equilibrium constant for the reaction increases with temperature and pH. At low pH, the undissociated form of PCP is the predominant species, while at high pH, the reverse exists, the pentachlorophenate being the predominant species. At low pH, the adsorption coefficient is high because the undissociated PCP is strongly adsorbed onto the soil particles by virtue of its affinity. On the other hand, at high pH above the pKa, the pentachlorophenate ions (PCP⫺) that have little affinity for the soil surface predominate and adsorption is greatly reduced. Another reason is that pentachlorophenate is more soluble at high pH than at lower pH. When PCP in solution is added to the soil, the PCP molecules adsorb on to the surface of the soil particles until an equilibrium is reached at the liquid and soil particle interface. The model that is often used for solid–liquid systems is the Freundlich equation: q ⫽ KƒC1 / n

(38.2)

where: q ⫽ the amount of chemical adsorbed per unit weight of adsorbent Kƒ and 1 / n are constants C ⫽ the equilibrium concentration in the liquid phase These adsorption isotherms seem to follow the Freundlich behavior. The solute sorption at pH 7 is much greater than at pH 10. The adsorption isotherms vary for different types of soils. The adsorption capacity in medium sand seems to be the least, while that of loam is the highest.

38.16

CHAPTER THIRTY-EIGHT

38.7.3

Volatilization

PCP solution is not a volatile substance even though it is easy to detect in the air where ever it is being used (the vapor pressure is 0.00011 mm at 20⬚C; methanol is 92 mm at 20⬚C). One reason is that most aqueous solutions are at pH 7 when PCP is already in ionized form. Transport by evaporation is therefore not an important process (Callahan, 1979). However, it has been shown to volatilize in special pesticide formulations such as aerosols or mists. Significant quantities have been detected in air and precipitation (Boyd, 1989; Weiss et al., 1982a). PCP has been found to evaporate at high temperatures and humidity, and volatilization is a probable means of transference into the air (Kozak et al., 1979).

38.7.4

Biodegradation and Persistence

The microbial degradation of pentachlorophenol has been well studied and the pathways determined (Boyd, 1989; Haggblom and Valo, 1995). The consensus is that, although it is rather persistent in the soil and groundwater, it is degradable by photochemical, microbiological, or chemical processes. PCP has been biodegraded by different strains of bacteria and fungi to produce differing products, and a number of these bacteria have been isolated. The degradation pathways seem to differ with different microbial groups (Tabak et al., 1981). A number of these are aerobic, while others are obligately anaerobic. Polychlorinated phenols are degraded primarily by initial dechlorination, followed by hydroxylation and reductive dechlorinations. Ring cleavage often occurs after most of the chlorines have been removed. Chlorinated catechols, quinones, and hydroquinones are the central intermediates in the biodegradation of PCP. Methylation of PCP produces anisoles, which are more hydrophobic, more resistant to degradation, and may bioaccumulate. In many organisms, PCP is rapidly bioaccumulated and excreted. Biomagnification does not occur in the food chain. Biodegradation is the predominant process for PCP removal from the environment. PCP has been known to persist in soils for 15 days to more than 60 days, depending on the type of soil. In warm, moist soils PCP was still detectable after 12 months. The half-life of PCP in water ranged from 0.15 to 15 days; in the presence of bacteria alone it was 5 to 12 hours.

38.7.5

Photodegradation

PCP readily absorbs sunlight in the UV region (wavelength ⫽ 320 nm). Irradiation of a dilute aqueous solution of PCP with sunlight or UV light has been found to be an effective means of degradation, yielding chlorinated phenols, trichlorobenzoquinones, and nonaromatic fragments such as dichloromaleic acid (Callahan, 1979; Weiss et al., 1982b; Ghoshal et al., 1992). Octachlorodibenzo-p-dioxin and furans have also been detected when PCP and sodium pentachlorophenate were irradiated. Photodegradation is definitely significant in PCP removal from the environment.

38.7.6

Spills on Land

When pentachlorophenol solution in oil or the aqueous solution of the sodium salt is spilled on land, after initial settling, some overland flow will occur depending on the quantity spilled. The pentachlorophenol oil solution will mostly be adsorbed to the soil while the aqueous solution will be much less adsorbed. Leaching to groundwater can occur in both cases. Little evaporation will occur, but some biodegradation and photodegradation will, depending on the moisture content, pH, organic matter content, and the bacteria strains. Some of the spill will, however, be washed off in runoffs during precipitation to rivers and streams.

PERSPECTIVES ON SPECIFIC SUBSTANCES: PENTACHLOROPHENOL

38.17

One incident involving a PCP spill occurred when telephone poles were resprayed. In 1975, a company sprayed the base of a number of telephone poles to prevent rot. In one month, 15 fish kills were reported. The fish kills were all found to be caused by the washoff from the sprayed poles. The poles were all close to the stream where the kill occurred, heavy rains having washed the solution some distance to the stream. 38.7.7

Spills on Water

When released into water bodies, PCP will readily dissociate at ordinary pHs (for PCP, pKa ⫽ 4.74) to produce the pentachlorophenate, sodium, and hydrogen ions in the water (Paasivirta et al., 1990). Any undissolved PCP will eventually end up in the sediments. Some photolysis and biodegradation will occur. Evaporation will be negligible. An incident of PCP pollution occurred after a 4-in. rainfall at a lumber treatment site. The treatment tank, containing 10,000 ppm penta- and tetrachlorophenol, overflowed into a stream, killing 5,000 adult coho salmon.

38.8 38.8.1

HUMAN AND ENVIRONMENTAL TOXICITY Toxicological Profile

The toxic effects of PCP are due not only to the undissociated PCP but also to other impurities, such as the polychlorinated dioxins, furans, and ethers (Ahlborg and Thunberg, 1980; Rao, 1978). PCP formulations in oil are therefore more toxic than in aqueous media. Acute Effects during Spills. PCP causes severe irritation of the eyes, skin, and upper respiratory tract. Even at moderate concentrations, coughing, violent sneezing, pain in the nose and throat, dizziness, convulsions, and unconsciousness can develop, and in extreme cases PCP can be fatal. Acute toxicity is the result of uncoupling of mitochondrial oxidative phosphorylation (Eisler, 1989; ATSDR, 1992). The eventual stimulation of cell activities can produce heat stress. Other acute effects include increase in alkaline phosphatase, blood urea nitrogen, and serum creatinine. Excessive exposure can cause damage to the liver, kidneys, skin, blood, gastrointestinal tract, nervous and immune system, and death. Many deaths have been reported as a result of unnecessary exposure and improper handling of treated lumber and sawdust. Some symptoms of poisoning are general weakness, vomiting, nausea, abdominal pain, headaches, anorexia, intense thirst, pain in the extremities, tachycardia (rapid heartbeat), tachypnea (rapid breathing), hypertension, and fevers (Wood, 1983). Chronic Exposure. Acute effects are often pronounced during chronic exposure as in occupational settings. These include conjunctivitis, chronic sinusitis, bronchitis, dermatitis, and polyneuritis. The presence of impurities such as dioxins and furans can cause chloracne (ATSDR, 1992; Choudhry et al., 1986). Many animal studies have shown that the immune system is adversely affected on prolonged exposure (Bevenue and Beckman, 1967; Roszell and Anderson, 1994). Increased susceptibility to tumor growth was observed in mice fed diets containing 50 to 500 ppm PCP. Exposure of newborn guppies to the toxicant caused decreased growth, increased mortality, and delayed sexual maturity (Crandall and Goodnight, 1962). When administered to pregnant rats in doses of 5 to 50 mg / kg bw / d, symptoms of fetotoxicity were observed (Schwetz, 1974). These include dilated ureters, resorptions, subcutaneous edema, and anomalies in the bone structure. Evidence of carcinogenicity for some PCP mixtures has also been found in mice. Mice fed diets with 100 to 200 ppm technical grade PCP showed increased incidences of he-

38.18

CHAPTER THIRTY-EIGHT

mangiosarcomas and hepatocellular neoplasms. Another group of male and female mice given up to 600 ppm PCP showed increased incidences of adrenal medullary and hepatocellular neoplasms. However, no consensus on its carcinogenicity has been reached, and so far the weight of evidence supports it not being carcinogenic.

38.9

SURVEY OF PAST SPILLS, LESSONS LEARNED, AND COUNTERMEASURES APPLIED After the fish kill incident noted in Section 38.7.6, the company complied with the order to stop spraying. As a result of the incident noted in Section 38.7.7 and similar incidents, Environment Canada encouraged the use of enclosed tanks or putting roofs over open tanks. It was also recommended that drainage areas be constructed to collect overflow in secondary tanks for holding purposes.

38.10

CONCLUSIONS Pentachlorophenol has a variety of uses. It is an effective bacteriacide, algicide, fungicide, insecticide, and herbicide. It is used in adhesives, rubber, paints, oils, textiles, carpet shampoos, gaskets for food containers, beehives, and poultry products. There is no doubt that the persistence of PCP and its impurities has been of concern since the late 1970s. As with many chlorinated organics, the long-term effects of this substance and its contaminants have not been clearly defined, even though some are known. It is now shown that although PCP is readily metabolized in animal tissues and in the environment, many of its metabolites, such as the anisoles and impurities such as dioxins, furans, and diphenyl ethers, are even more toxic or persistent. Not much is known about the toxicity of the tetra-, tri-, and dichlorophenol precursors. Use of PCP as a pesticide is now restricted. Monitoring of PCP in the environment should continue due to its widespread contamination of the marine and terrestrial ecosystems.

38.11

REFERENCES Ahlborg, U. G., and T. M. Thunberg. 1980. ‘‘Chlorinated Phenols: Occurrence, Toxicity, Metabolism and Environmental Impact,’’ CRC Critical Review of Toxicology, vol. 7, pp. 1–35. Agency for Toxic Substances and Disease Registry (ATSDR). 1992. Toxicological Profile for Pentachlorophenol: U.S. Department of Health and Human Services. Bevenue, A., and H. Beckman. 1967. ‘‘Pentachlorophenol: A Discussion of Its Properties and Its Occurrence as a Residue in Human and Animal Tissues,’’ Residue Reviews, vol. 19, pp. 83–134. Boyd, S. A. 1989. ‘‘Chlorophenols in Soils,’’ in Reactions and Movement of Organic Chemicals in Soils, ed. B. L. Sawhney and K. Brown, Soil Science Society of America, Madison, WI, pp. 209–228. Callahan, M. A. 1979. Water-Related Environmental Fate of 129 Priority Pollutants, 440 / 4-79-029b pp. 87–94. Camford Information Services, Inc. (CIS). 1995. ‘‘Pentachlorophenol,’’ CPI Product Profiles, CIS, Scarborough, ON. Choudhry, H., J. Coleman, L. T. De Rosa, and J. F. Stara. 1986. ‘‘Pentachlorophenol: Health and Environmental Effects Profile,’’ Toxicology and Industrial Health, vol. 2, pp. 483–571. Crandall, C. A., and C. J. Goodnight. 1962. ‘‘Effects of Sublethal Concentrations of Several Toxicants on the Growth of the Common Guppy, Lebistes reticulatus,’’ Limnology and Oceanography, vol. 7, pp. 233–239.

PERSPECTIVES ON SPECIFIC SUBSTANCES: PENTACHLOROPHENOL

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Eisler, R. 1989. ‘‘Pentachlorophenol Hazards to Fish, Wildlife and Invertebrates: A Synoptic Review,’’ USD / Contaminants Hazard Reviews, vol. 85, pp. 1–17. Environment Canada. 2000. NATES—National Analysis of Trends in Emergencies Systems, Hull, QC. Fingas, M., N. Laroche, G. Sergy, B. Mansfield, G. Cloutier, and P. Mazerolle. 1991. ‘‘A New Chemical Spill Priority List,’’ in Proceedings of the Eighth Technical Seminar on Chemical Spills, Environment Canada, Ottawa, ON. Ghoshal, S., S. K. Banerji, and R. K. Bajpai. 1992. ‘‘Role of Photodegradation in Pentachlorophenol Decontamination in Soils,’’ Annals of the New York Academy of Sciences, vol. 665, no. 7, pp. 412– 422. Glickman, A. H., C. N. Statham, A. Wu, and J. J. Lech. 1977. ‘‘Studies on the Uptake, Metabolism and Disposition of Pentachlorophenol and Pentachloroanisole in Rainbow Trout,’’ Toxicology and Applied Pharmacology, vol. 41, p. 649. Haggblom, M. M., and R. J. Valo. 1995. ‘‘Bioremediation of Chlorophenols Wastes,’’ in Microbial Transformation and Degradation of Toxic Organic Chemicals, ed. L. Y. Young and C. E. Cerniglia, Wiley-Liss, New York, NY, pp. 389–434. International Agency for Research on Cancer (IARC). 1994. IARC Monographs on the Evaluation of Carcinogenic Risk of Chemicals to Man, IARC, World Health Organization, Lyon, France. Kobayashi, K., S. Kimura, and E. Shimizu. 1977. ‘‘Studies on the Metabolism of Chlorophenols in Fish—IX. Isolation and Identification of Pentachlorophenols-␤-glucuronide Accumulated in Bile of Goldfish,’’ Bulletin of Japanese Society of Scientific Fisheries, vol. 43, pp. 601–607. Kozak, V. P., G. V. Simsiman, G. Chesters, D. Stensby, and J. Harkin. 1979. Reviews of the Environmental Effects of Pollutants: XI Chlorophenols, EPA-600 / 1-79-012, U.S. EPA Health Effects Research Laboratory, Cincinnati, OH. Paasivirta, J., H. Hakala, J. Knuutinen, T. Otollinen, J. Sarkka, L. Welling, R. Paukku, and R. Lammi. 1990. ‘‘Organic Chlorine Compounds in Lake Sediments. III. Chlorohydrocarbons, Free and Chemically Bound Chlorophenols,’’ Chemosphere, vol. 21, pp. 1355–1370. Rao, K. R., ed. 1978. Pentachlorophenol Chemistry, Pharmacology, and Environmental Toxicology, Plenum Press, New York, NY. Roszell, L. E., and R. S. Anderson. 1994. ‘‘Inhibition of Phagocytosis and Superoxide Production by Pentachlorophenol in Two Leukocyte Subpopulations from Fundulus heteroclitus,’’ Marine Environmental Research, vol. 38, pp. 195–206. RTECS On-Line. 2000. Registry of Toxic Effects of Chemical Substances, Department of Health and Human Services, Centers for Disease Control and National Institute for Occupational Safety and Health, Washington, DC. Schwetz, B. A. 1974. ‘‘The Effect of Purified and Commercial Grade Pentachlorophenol on Rat Embryonal and Fetal Development,’’ Toxicology and Applied Pharmacology, vol. 28, pp. 151–161. Tabak, H. H., S. A. Quave, C. A. Mashni, and E. F. Barth. 1981. ‘‘Biodegradability Studies with Organic Priority Pollution Compounds,’’ Journal of the Water Pollution Control Federation, vol. 53, pp. 1503– 1518. Transport Canada. 1994. Transport of Dangerous Goods Regulations (TDG), Ottawa, ON. Verschueren, K. 1996. Handbook of Environmental Data on Organic Chemicals, 3d ed., Van Nostrand Reinhold, New York, NY, pp. 1464–1480. Wan, M. T. 1992. ‘‘Utility and Railway Right-of-Way Contaminants in British Columbia: Chlorophenols,’’ Journal of Environmental Quality, vol. 21, pp. 225–231. Weiss, U., P. Moza, I. Scheunert, A. Hague, and F. Korte. 1982a. ‘‘Fate of Pentachlorophenol-14C in Rice Plants under Controlled Conditions,’’ Journal of Agricultural and Food Chemistry, vol. 30, pp. 1186–1190. Weiss, U., I. Scheunert, W. Klein, and F. Korte. 1982b. ‘‘Fate of Pentachlorophenol-14C under Controlled Conditions,’’ Journal of Agricultural and Food Chemistry, vol. 30, pp. 1191–1194. Wood, S. 1983. ‘‘Pentachlorophenol Poisoning,’’ Journal of Occupational Medicine, vol. 25, pp. 527– 530.