Metabolism of pentachlorophenol

Urinary pentachlorophenol in general population of central China: reproducibility, predictors, and associations with oxidative stress biomarkers

Pentachlorophenol (PCP) is a ubiquitous environmental persistent organic pollutant and a Group 1 carcinogen. Human exposure level of PCP was reported to be relatively higher in China than in many other countries, because sodium pentachlorophenate was abused as molluscicide in China. PCP can induce oxidative stress; however, the relationship of PCP exposure with oxidative stress biomarkers (OSBs) in human beings has rarely been documented. In this study, 404 first-morning urine samples (including repeated samples in three days donated by 74 participants) were collected from 128 healthy adults (general population without occupational exposure to PCP) in autumn and winter of 2018, respectively, in Wuhan, central China. Urinary concentrations of PCP and three select OSBs [including 8-OHG (abbreviation of 8-hydroxy-guanosine), 8-OHdG (8-hydroxy-2'-deoxyguanosine), and 4-HNEMA (4-hydroxy-2-nonenal mercapturic acid), which reflect oxidative damage of RNA, DNA, and lipid, respectively] were determined. PCP was detectable in 100% of the urine samples (specific gravity-adjusted median concentration: 0.44 ng/mL; range: 0.02-14.2 ng/mL). Interday reproducibility of urinary PCP concentrations was excellent (intraclass correlation coefficient: 0.88) in three days. Significant differences in PCP concentrations were found among different age groups; the group of participants aged 20-45 y (median: 0.72 ng/mL) had higher concentrations than those in the elders (aged 45-60 y and > 60 y). Spatial disparity was observed in autumn, and urban residents had higher PCP concentrations than rural residents (median: 0.60 vs. 0.31 ng/mL), whereas such disparity was not found in winter. There were no season-, sex-, or BMI-related differences between the corresponding subgroups. The urinary PCP concentrations were found to be associated with increases in 8-OHdG and 8-OHG rather than 4-HNEMA. An interquartile range increase in urinary PCP concentration was associated with a 23.5% (95% CI: 9.18-39.6) increase in 8-OHdG and a 21.3% (95% CI: 9.18-32.4) increase in 8-OHG, implied that PCP exposure at environmental relevant dose might be associated with nucleic acid oxidative damage in the general population. This pilot study reported associations between PCP exposure and OSBs in human beings. Future studies are needed to elucidate the mediating roles of OSBs in the association between PCP exposure and certain adverse health outcomes.

Assessment of Pentachlorophenol Exposure in Humans using the Clearance Concept

1 Pentachlorophenol (PeCP), a widely-used wood preservative, is a ubiquitous compound which has been found to be carcinogenic in mice. The objective of this study is to assess the average net daily intake of PeCP in cohorts of individuals who are: (1) not specifically exposed to PeCP, (2) residents of homes made of PeCP-treated logs and (3) occupationally exposed to PeCP.

2 The average net daily intake was calculated using a basic pharmacokinetic principle, the clearance (CL) concept: net daily intake equals CL (in 1 d-1) times the average steady-state concentration of PeCP in plasma ( Css). Css values reported in the literature were used for the calculations.

3 Because the two definitive studies on PeCP toxicokinetics in humans have given conflicting results, kinetic information from human exposure to PeCP was reviewed. Plasma clearance was estimated from retrospective analysis of urine and plasma concentrations measured in people after long-term exposure to PeCP. An overall clearance of 0.425 1 d-1 was obtained.

4 In groups of individuals who are not specifically exposed to PeCP, net daily intake estimated in eight countries varied from 5 μg (Nigeria) to 37 μg (The Netherlands). Net intake was between 51 μg d-1 and 157 μg d-1 in residents of homes made of PeCP-treated logs. In individuals occupationally exposed to PeCP, net daily intake varied widely (from 35 μg to about 24 000 μg) depending on the type of work.

Extraction of pentachlorophenol from soils using environmentally benign lactic acid solutions

Soil contamination with pentachlorophenol (PCP) is widespread across the globe. Soil washing/extraction is a common technique to remove this compound. Several soil washing/extraction solutions have been used but a majority of them have the problem of persistence in the environment due to their low biodegradability. Our aim was to investigate mixed solutions of lactic acid and water as potential alternatives to surfactant solutions or organic solvent systems used for the removal of PCP from three soils: montmorillonite, a natural sediment (with organic matter), and the same sediment without organic matter (ignited sediment). This study included the optimization of the concentration of lactic acid in water for maximum extraction efficiency and the determination of linear desorption constants for removal of PCP from the three soils with lactic acid. The effect of soil/sediment organic matter on the extraction efficiency was also studied. Initial experiments showed that 24h was the optimum extraction time. High extraction efficiencies were obtained for montmorillonite (40-80%) and ignited sediment ( approximately 90%). The natural sediment exhibited low PCP extraction due to presence of organic matter, while high desorption coefficient values ( approximately 23 L/kg) were obtained for the ignited sediment. For all soils, a decrease in extraction was observed at higher concentrations of lactic acid. The specific surface area of soil/sediment was also found to be an important factor affecting the extraction of PCP.

Pentachlorophenol and other chlorinated phenols are substrates for human hydroxysteroid sulfotransferase hSULT2A1

Pentachlorophenol (PCP) is a persistent chemical contaminant that has been extensively investigated in terms of its toxicology and metabolism. Similar to PCP, other chlorinated phenol derivatives are also widely present in the environment from various sources. Even though some of the chlorine-substituted phenols, and particularly PCP, are well-known inhibitors of phenol sulfotransferases (SULTs), these compounds have been shown to undergo sulfation in humans. To investigate the enzymatic basis for sulfation of PCP in humans, we have studied the potential for PCP as well as the mono-, di-, tri-, and tetra-chlorinated phenols to serve as substrates for human hydroxysteroid sulfotransferase, hSULT2A1. Our results show that all of these compounds are substrates for this isoform of sulfotransferase, and the highest rates of sulfation are obtained with PCP, trichlorophenols, and tetrachlorophenols. Much lower rates of sulfation were obtained with isomers of monochlorophenol and dichlorophenol as substrates for hSULT2A1. Thus, the sulfation of polychlorinated phenols catalyzed by hSULT2A1 may be a significant component of their metabolism in humans.

Pentachlorophenol Poisoning

Despite being banned in many countries and having its use severely restricted in others, pentachlorophenol (PCP) remains an important pesticide from a toxicological perspective. It is a stable and persistent compound. In humans it is readily absorbed by ingestion and inhalation but is less well absorbed dermally. Its distribution is limited, its metabolism extensive and it is eliminated only slowly. Assessment of the toxicity of PCP is confounded by the presence of contaminants known to cause effects identical to those attributed to PCP. However, severe exposure by any route may result in an acute and occasionally fatal illness that bears all the hallmarks of being mediated by uncoupling of oxidative phosphorylation. Tachycardia, tachypnoea, sweating, altered consciousness, hyperthermia, convulsions and early onset of marked rigor (if death occurs) are the most notable features. Pulmonary oedema, intravascular haemolysis, pancreatitis, jaundice and acute renal failure have been reported. There is no antidote and no adequate data to support the use of repeat-dose oral cholestyramine, forced diuresis or urine alkalinisation as effective methods of enhancing PCP elimination in poisoned humans. Supportive care and vigorous management of hyperthermia should produce a satisfactory outcome. Chronic occupational exposure to PCP may produce a syndrome similar to acute systemic poisoning, together with conjunctivitis and irritation of the upper respiratory and oral mucosae. Long-term exposure has also been reported to result in chronic fatigue or neuropsychiatric features in combination with skin infections (including chloracne), chronic respiratory symptoms, neuralgic pains in the legs, and impaired fertility and hypothyroidism secondary to endocrine disruption. PCP is a weak mutagen but the available data for humans are insufficient to classify it more strongly than as a probable carcinogen.

Characterization of metabolic activation of pentachlorophenol to quinones and semiquinones in rodent liver

Pentachlorophenol (PCP), a widely used biocide, induces liver tumors in mice but not in rats. Metabolic activation of PCP to chlorinated quinones and semiquinones in liver cytosol from Sprague-Dawley rats and B6C3F1 mice was investigated in vitro (1) with microsomes in the presence of either beta-nicotinamide adenine dinucleotide phosphate (NADPH) or cumene hydroperoxide (CHP), (2) with CHP in the absence of microsomes, and (3) with horseradish peroxidase (HRP) and H2O2. Mono-S- and multi-S-substituted adducts of tetrachloro-1,4-benzoquinone (Cl4-1,4-BQ) and Cl4-1,2-BQ and their corresponding semiquinones [i.e. tetrachloro-1,4-benzosemiquinone (Cl4-1,4-SQ) and tetrachloro-1,2-benzosemiquinone (Cl4-1,2-SQ)] were measured by gas chromatography-mass spectrometry (GC-MS). Qualitatively, the metabolites of PCP were the same in both rats and mice for all activation systems. Induction of PCP metabolism by either 3MC or PB-treated microsomes was observed in NADPH- but not in CHP-supported systems. In rats, the amount of induction was comparable with either 3MC or PB. 3MC was a stronger inducer than PB in mice and also induced a greater amount of metabolism than in rats. This suggests that induction of specific P450 isozymes may play a role in the toxicity of PCP to mice. Both HRP/H2O2 and CHP led to production of the full spectrum of chlorinated quinones and semiquinones, confirming the direct oxidation of PCP. CHP (with or without microsomes) converted PCP into much greater quantities of quinones and semiquinones than did microsomal P450/NADPH or HRP/H2O2 in both species. This implies that, under conditions of oxidative stress, endogenous lipid hydroperoxides may increase PCP metabolism sufficiently to enhance the toxicity and carcinogenicity of PCP.

Inhibitory effect of pentachlorophenol on gap junctional intercellular communication in rat liver epithelial cells in vitro

To understand the initiating/promoting actions of pentachlorophenol (PCP), a non-mutagenic hepatocarcinogen, and its metabolite, tetrachlorohydroquinone (TCHQ), we investigated the effects of each chemical on gap junctional intercellular communication (GJIC) in rat liver epithelial cells (WB cells) by the scrape-loading and dye transfer method. After treatment with PCP, the GJIC was initially inhibited at 4 h but was restored in 6-8 h, followed by a second phase of inhibition between 16 and 24 h. Both the first and second inhibitions were concentration-dependent and were restored by 2-4 h after removal of PCP. The phosphorylation state of connexin 43 (CX43) and its localization on the plasma membrane were unchanged up to 24 h after treatment; however, this was accompanied by a decrease in the CX43 protein level. No inhibitory effect was apparent on the GJIC of cells treated with TCHQ. These results suggest that PCP may play a critical role of promoting activity via non-mutagenic mechanisms.

Dosimetry of chlorinated quinone metabolites of pentachlorophenol in the livers of rats and mice based upon measurement of protein adducts

The dosimetry of chlorinated quinones arising from metabolism of pentachlorophenol (PCP), in the livers of male Sprague-Dawley rats and B6C3F1 mice was investigated via measurements of cysteinyl protein adducts and estimates of the second-order reaction rate constants between the quinones and the proteins. We had previously shown that adducts of tetrachloro-1,4-benzoquinone (Cl4-1,4-BQ) and tetrachloro-1,2-benzosemiquinone (Cl4-1,2-SQ) were observed at the highest levels in the livers of Sprague-Dawley rats to which PCP had been administered by gavage (5-40 mg/kg body wt) (Biomarkers 1, 232-243, 1996). In the current study we observed that adducts of Cl4-1,4-BQ and tetrachloro-1,2-benzoquinone (CL4-1,2-BQ) were predominant in the livers of B6C3F1 mice receiving 20 mg PCP/kg body wt. The second-order rate constants, representing in vitro reactions between Cl4-1,2-BQ and Cl4-1,4-BQ and various cysteine residues of hepatic proteins of liver cytosol and liver nuclei, were estimated to be 0.012-1.96 L(g protein)(-1) hr(-1) in rats and 0.082-1.67 L(g protein)(-1) hr(-1) in mice. The estimated tissue doses of the quinones to liver cytosol decreased in the order rat Cl4-1,4-BQ > mouse Cl4-1,4-BQ > mouse Cl4-1,2-BQ and to liver nuclei in the order mouse Cl4-1,2-BQ > mouse Cl4-1,4-BQ > rat Cl4-1,4-BQ. The corresponding doses of Cl4-1,2-SQ could not be inferred due to our inability to estimate the second-order rate constants. After aggregating the estimated contributions of all quinone species, mice had a fourfold greater dose to liver nuclei than rats, whereas rats had a threefold greater dose to liver cytosol. The increased nuclear dose to mouse liver compared to that of the rat suggests that the mouse is at greater risk to hepatic DNA damage from PCP-derived quinones. Investigation of the time course of levels of unconjugated tetrachlorohydroquinone (Cl4HQ) in the livers indicated that about 0.4% of Cl4HQ was oxidized to Cl4-1,4-BQ in both rats and mice.

Biomarkers of human exposure to pesticides

For centuries, several hundred pesticides have been used to control insects. These pesticides differ greatly in their mode of action, uptake by the body, metabolism, elimination from the body, and toxicity to humans. Potential exposure from the environment can be estimated by environmental monitoring. Actual exposure (uptake) is measured by the biological monitoring of human tissues and body fluids. Biomarkers are used to detect the effects of pesticides before adverse clinical health effects occur. Pesticides and their metabolites are measured in biological samples, serum, fat, urine, blood, or breast milk by the usual analytical techniques. Biochemical responses to environmental chemicals provide a measure of toxic effect. A widely used biochemical biomarker, cholinesterase depression, measures exposure to organophosphorus insecticides. Techniques that measure DNA damage (e.g., detection of DNA adducts) provide a powerful tool in measuring environmental effects. Adducts to hemoglobin have been detected with several pesticides. Determination of chromosomal aberration rates in cultured lymphocytes is an established method of monitoring populations occupationally or environmentally exposed to known or suspected mutagenic-carcinogenic agents. There are several studies on the cytogenetic effects of work with pesticide formulations. The majority of these studies report increases in the frequency of chromosomal aberrations and/or sister chromatid exchanges among the exposed workers. Biomarkers will have a major impact on the study of environmental risk factors. The basic aim of scientists exploring these issues is to determine the nature and consequences of genetic change or variation, with the ultimate purpose of predicting or preventing disease.

Pentachlorophenol-induced oxidative DNA damage in mouse liver and protective effect of antioxidants

8-Hydroxydeoxyguanosine (8-OH-dG) was determined as a marker of oxidative DNA damage in male B6C3F1 mice treated with the hepatocarcinogen pentachlorophenol (PCP). A single oral administration of PCP (0-80 mg/kg) significantly and dose-dependently increased the 8-OH-dG level specifically in the liver at 6 hr. Repeated doses (0-80 mg/kg) over 5 days caused a further increase. Elevation of the 8-OH-dG level caused by a single dose of PCP (60 mg/kg) was not affected by ip injection of buthionine sulfoximine (2 mmol/kg), an inhibitor of GSH synthesis, or aminotriazole (1 g/kg), an inhibitor of catalase, showing no clear evidence for enhancement by the oxidative stress due to reduction of antioxidative factors under these experimental conditions. However, examination of the effects of natural antioxidants on repeated PCP treatment (60 mg/kg/day, for 5 days) revealed that oral administration of vitamin E and diallyl sulfide 3 hr before each PCP challenge significantly protected against elevation of hepatic 8-OH-dG levels. beta-Carotene did not have any effect. Ellagic acid, epigallocatechin gallate and vitamin C demonstrated partial protection. These findings indicate that PCP causes oxidative DNA damage in the target organ liver which can be blocked by a number of antioxidant agents.

Growth responses of achlorophyllous Euglena gracilis to selected concentrations of cadmium and pentachlorophenol

The growth response of a wild achlorophyllous Euglena gracilis mutant was studied during exposure to cadmium and pentachlorophenol (PCP). Cadmium gradually reduced the growth rate and terminal cell density; PCP only lengthened the initial lag phase relative to control cultures. Flow cytometry showed that cadmium altered the cell cycle by delaying late S and G2/M phases; PCP did not disturb the cell cycle, but markedly affected DNA staining: the intercalating dyes ethidium bromide and propidium iodide showed little staining compared to controls. However, replication and transcription processes were not altered by PCP, as cell division occurred normally. Cells surviving after PCP treatment apparently developed an adaptative response during the lag phase.

Disposition and metabolism of radiolabelled pentachloroanisole in rats and rabbits

Male Sprague-Dawley rats and New Zealand White rabbits were administered 14C-labelled pentachloroanisole (PCA) in corn oil by gavage as single doses of 25 mg/kg and were then placed in individual metabolism cages for as long as 4 days. Peak blood level of radioactivity occurred 6 hr after administration of the dose to rats and between 3 and 4 hr in rabbits; the blood elimination half-life ranged from 8 to 15 hr in rats and averaged 6 hr in rabbits. Rats excreted an average of 54.2% of the administered radiolabel in the urine and 32.4% in the faeces during the 96 hr following the dose; rabbits excreted an average of 84.2 and 13.1% of the radiolabel in the urine and faeces, respectively, during this time. Examination of the metabolites in the rat showed that 60% of the urinary radioactivity was attributable to tetrachlorohydroquinone (TCH), 3% to free pentachlorophenol (PCP) and 29% to conjugated PCP; faecal metabolites were PCP (85.7%), TCH (4.3%) and polar metabolite(s) (10%). In the rabbit, 58% of the urinary radioactivity was attributable to TCH, 8% to free PCP and 34% to conjugated PCP. Faecal metabolites consisted of PCP and conjugated material.

Toxicokinetics and biotransformation of pentachlorophenol in the sea urchin (Strongylocentrotus purpuratus)

1. The toxicokinetics and biotransformation of pentachlorophenol (PCP) were determined in the purple sea urchin (Strongylocentrotus purpuratus). 2. In a static chamber, urchins (n = 9) were individually exposed to 50 micrograms/l of [U-14C]PCP for 24 h to determine bioconcentration and the absorption rate constant (Ka), elimination rate constant (Ke), and elimination half-life (t1/2). Determination was by direct quantitation of radioactivity in the exposure water. 3. After exposure, urchins were placed in a flow-through chamber for 24 h to allow depuration of retained residues, which were identified by hplc and quantified by lsc. The Ka and Ke, calculated using a simplified model, were 0.12 +/- 0.06 h and 0.43 +/- 0.22 h, respectively, whilst the 24-h total concentration factor was 316.3 +/- 209.7, and the t1/2 was 1.6 +/- 0.8 h. 4. Whereas urchins depurated 40.6% of retained residues, only a small amount of PCP was excreted unchanged (17.0%), as the more polar conjugates pentachlorophenyl-beta-D-glucoside (72.4%) and pentachlorophenylsulphate (10.6%) were also formed.

Human pentachlorophenol poisoning

Pentachlorophenol (PCP) was, and still is, one of the most frequently used fungicides and pesticides. Its toxicity is due to interference with oxidative phosphorylation. Acute and chronic poisoning may occur by dermal absorption, inhalation or ingestion. Chronic poisoning occurs mainly in sawmill workers or people living in log homes treated with PCP-containing wood protecting formulations. Quantitative determination of PCP in urine and serum is useful to detect occupational or subclinical exposure. The clinical features of acute and chronic PCP poisoning can be classified systematically into effects on the skin, metabolism (fever), the haematopoietic tissue, the respiratory system, the central and peripheral nervous system, the kidney and the gastrointestinal tract. Although PCP is not classified as a human carcinogen, some epidemiological observations suggest that exposure to chlorophenols in general and PCP solutions in particular may result in an increased risk for certain malignant disorders such as nasal carcinoma and soft tissue sarcoma. There is concern that contamination of PCP-solutions with products such as chlorodibenzo-p-dioxins is the real cause of this suspected carcinogenicity. No specific antidote exists for the treatment of (acute) PCP poisoning. The basis of the treatment of acute poisoning is intensive supportive care with prevention of dangerous rise in temperature. Use of PCP-based products as indoor wood preservatives poses an unacceptable risk to human health.

Toxicokinetics and biotransformation of pentachlorophenol in the topsmelt (Atherinops affinis)

The toxicokinetics and biotransformation of pentachlorophenol (PCP) were determined in the topsmelt (Atherinops affinis). In a static system, topsmelt (n = 9) were exposed to 50 micrograms/L of [U-14C]PCP for 24 hours to determine the absorption rate constant (Ka), the whole-body bioconcentration (at steady-state conditions), the elimination rate constant (Ke), and the elimination half-life (t1/2). Kinetics were determined by direct quantitation of radioactivity in the exposure water. Following exposure, fish were placed in a flow-through metabolism chamber for 24 hours to allow depuration of retained residues, which were collected on XAD-4 resin. Excreted residues were identified and quantified by high-pressure liquid co-chromatography, fraction collection, and liquid scintillation counting. The Ka and Ke, calculated using a simplified model, were 0.012 +/- 0.005/h and 0.014 +/- 0.003/h, respectively, while the 24 hour total concentration factor was 278.0 +/- 182.0 and the t1/2 was 52.7 +/- 11.2. During 24 hours of exposure to clean seawater, topsmelt depurated 32.9% of retained residues, and while PCP was primarily excreted unchanged (64.9%), significant amounts of both pentachlorophenylsulfate (18.9%) and pentachloro-beta-D-glucuronide (16.2%) were also formed.

Pentachlorophenol carcinogenicity: extrapolation of risk from mice to humans

1. Pentachlorophenol (PCP) has been found to be carcinogenic in mice. The objective of this study was to extrapolate to humans the risk of cancer from data obtained in mice using information on disposition, serum protein binding and metabolism of PCP across species. 2. A review of the literature indicates that neither PCP nor a mutagenic metabolite, tetrachlorohydroquinone (TCHQ), has been specifically identified as responsible for the carcinogenicity. In addition, the occurrence of TCHQ as a metabolite of PCP in humans is still questionable. Therefore, cancer risk assessment is performed on the assumption that PCP itself is responsible for the carcinogenicity. 3. For interspecies extrapolation, a new method in which interspecies differences in clearance and serum protein binding are taken into account is used. The method gives estimates of equivalent human doses of PCP which are up to 4 times smaller than those obtained using body surface area. For both interspecies extrapolation methods, the estimated virtually-safe doses of PCP are smaller than the average daily intakes reported in groups of subjects nonspecifically exposed to PCP. Corresponding extra risks of cancer for lifetime exposure are from 20 to 140 times greater than the acceptable extra risk (10(-6)). The results obtained with this approach indicate that PCP is a possible public health hazard.

Disposition, bioavailability, and serum protein binding of pentachlorophenol in the B6C3F1 mouse

The toxicokinetics of pentachlorophenol (PCP) were studied in B6C3F1 mice, a strain in which PCP was previously found to be carcinogenic. In a crossover design, doses of 15 mg/kg were given intravenously (bolus) and orally (gastric intubation) to six animals. Concentrations of PCP in blood, urine, and feces were measured by capillary gas chromatography with electron-capture detection. After intravenous administration, the values of clearance and volume of distribution were 0.057 +/- 0.007 L/hr/kg and 0.43 +/- 0.06 L/kg, respectively. These two parameters exhibited low intermouse variability (coefficients of variation less than 14%). The elimination half-life was 5.2 +/- 0.6 hr. After oral administration, the PCP peak plasma concentration (28 +/- 7 micrograms/ml) occurred at 1.5 +/- 0.5 hr and absorption was complete (bioavailability = 1.06 +/- 0.09). The elimination half-life was 5.8 +/- 0.6 hr. Only 8% of the PCP dose was excreted unchanged by the kidney. PCP was primarily recovered in urine as conjugates. A portion of the dose was recovered in urine as the mutagen, tetrachlorohydroquinone (5%) (TCHQ), and its conjugates (15%). For both PCP and TCHQ, sulfates accounted for 90% or more of the total conjugates (glucuronides and sulfates).

Induction of micronuclei in V79 Chinese hamster cells by tetrachlorohydroquinone, a metabolite of pentachlorophenol

Tetrachlorohydroquinone, a metabolite of the fungicide pentachlorophenol, induced significant dose-related increases in micronuclei in V79 Chinese hamster cells without exogenous metabolic activation. The lowest observed effective dose was 10 microM, where the relative survival was about 62%. At the highest dose tested, 20 microM, the relative survival was about 8% and the frequency of cells with micronuclei was about 6 times the solvent control frequency. The induction of micronuclei by tetrachlorohydroquinone was significantly inhibited by the hydroxyl radical scavenger dimethyl sulfoxide at 5% (v/v).

Disposition and biotransformation of pentachlorophenol in the red abalone (Haliotis rufescens)

1. The disposition and biotransformation of pentachlorophenol (PCP) in the red abalone (Haliotis rufescens) have been determined. 2. In a flow-through system, three abalones were exposed to 1.2 mg/l of [U-14C]PCP for 5 h to determine bioconcentration and tissue distribution. Retained residues were quantified from radioactivity, while excreted residues were identified and quantified by h.p.l.c. and determination of radioactivity. 3. The 5-h total concentration factor ranged from 16.0 to 21.5; individual tissue concentrations ranged from 133.4 nmol/g in gill to 17.5 nmol/g in gonad. Due to its large size, the foot muscle received the largest amount of total retained residue (47.4%). 4. During a 13-h recovery period the abalones depurated 72.2% of retained residues; however, residue concentration in gonad increased over 100%. PCP was primarily excreted unchanged (89.3%), but small amounts of pentachloro-beta-D-glucoside (7.9%), pentachloroanisole (1.3%), pentachlorophenylsulphate (0.9%), and tetrachloro-p-hydroquinone (0.6%) were also formed.

Pentachlorophenol toxicokinetics after intravenous and oral administration to rat

1. The toxicokinetics of pentachlorophenol (PCP) were studied in rats. Doses of 2.5 mg/kg were given i.v. (bolus, five rats) and orally (gastric intubation, five rats). Concentrations in plasma, urine and faeces were measured by capillary g.l.c. with electron-capture detection. 2. After i.v. administration, the clearance and volume of distribution at steady state were 0.026 +/- 0.003 l/h per kg and 0.25 +/- 0.02 l/kg, respectively. These two parameters exhibit low inter-rat variability (coefficients of variation less than 15%). The half-life of the initial decline of PCP plasma concn. was less than 1.3 h, while the second phase half-life was 7.11 +/- 0.87 h. 3. After oral administration the peak plasma concn. (7.3 +/- 2.8 micrograms/ml) occurred between 1.5 and 2 h and absorption was complete (bioavailability = 0.91-0.97). No distinct distribution phase was observed and the elimination half-life was 7.54 +/- 0.44 h. 4. PCP clearance is essentially metabolic since only 5.3 +/- 0.2% dose is eliminated unchanged by the kidney. About 60% dose was recovered in urine, mainly as conjugated PCP and conjugated tetrachlorohydroquinone (TCHQ). 5. For both routes of administration, about 10% dose was recovered in faeces as PCP and/or metabolites, which indicates that biliary excretion contributes to total elimination.

Induction of mutation in V79 Chinese hamster cells by tetrachlorohydroquinone, a metabolite of pentachlorophenol

Tetrachlorohydroquinone (TCHQ) and tetrachlorocatechol (TCC), two metabolites of the environmental mutagen and carcinogen pentachlorophenol, were tested without exogenous activation in V79 Chinese hamster cells for the induction of mutation at the hypoxanthine phosphoribosyl transferase (HPRT) locus to 6-thioguanine resistance (TGr) and at the Na/K-ATPase locus to ouabain resistance (OuaR). Treatment was for 24 h at 37 degrees C. TCHQ produced statistically significant increases in the frequency of TGr mutants. The lowest observed effective dose (LOED) was 20 microM, where the relative cloning efficiency was 63%. The relationship between the dose of TCHQ and the frequency of TGr mutants was approximately linear over the range of 0-60 microM with an estimated slope (+/- 95% confidence limits) of 1.1 +/- 0.3 mutants per 10(6) clonable cells per microM. At the highest tested dose of TCHQ, 60 microM, the relative cloning efficiency was reduced to 7%. In contrast to TCHQ, TCC was unable to induce TGr mutants at doses up to 120 microM. The relative cloning efficiency at this dose was 5%. Both TCHQ and TCC were unable to induce OuaR mutants. The results suggest that TCHQ is at least partly responsible for the genotoxic activity of pentachlorophenol. TCHQ can produce reactive oxygen species, which may cause large genetic damage such as deletions, resulting in mutation to TGr but not to OuaR.

Effects of hexachlorobenzene and its metabolites pentachlorophenol and tetrachlorohydroquinone on serum thyroid hormone levels in rats

Effects of administration of equimolar doses of hexachlorobenzene (HCB) and its metabolites pentachlorophenol (PCP) and tetrachlorohydroquinone (TCHQ) on serum thyroxine (TT4) and triiodothyronine (TT3) levels in rats were studied. Furthermore, it was investigated whether the observed effects were related to the serum levels of HCB or PCP. Rats received either corn oil (controls) or HCB, PCP or TCHQ in a single equimolar intraperitoneal dose of 0.056 mmol/kg. Results indicated that HCB did not alter serum TT4 and TT3 levels for a period up to 96 h after dosing. In contrast, PCP and TCHQ were both capable of reducing serum TT4 levels with a maximum effect between 6 and 24 h after exposure. TCHQ was more effective in repressing TT3 than TT4 blood levels. Dose-response experiments were carried out in order to obtain insight into the sensitivity of the observed effects. Rats received different doses of PCP or TCHQ intraperitoneally. The reductions of TT4 levels by PCP were inversely related to serum PCP levels in exposed animals, based on the toxicokinetics and dose-response profiles. Furthermore, PCP serum levels after HCB administration appeared too low to cause an effect. The results of this study indicate that not HCB itself, but rather its metabolites PCP and TCHQ may be involved in reduced serum thyroid hormone levels after HCB administration.

Simultaneous assay of pentachlorophenol and its metabolite, tetrachlorohydroquinone, by gas chromatography without derivatization

A sensitive capillary gas chromatographic method was developed for the simultaneous determination of pentachlorophenol and its major metabolite, tetrachlorohydroquinone, in plasma, urine and feces. The method involved a simple one-step liquid-liquid extraction with diethyl ether and electron-capture detection gas chromatography on a fused-silica capillary column coated with 50% methylsilicone-50% trifluoropropylsilicone. The detection limit of both compounds was 50 ng/ml in plasma (from an initial volume of 0.1 ml), 100 ng/ml in urine and 100 ng/g in feces. Optimal conditions for both chemical and enzymatic hydrolysis were defined to measure conjugates of both pentachlorophenol and tetrachlorohydroquinone in urine. Tetrachlorohydroquinone was found to be unstable in plasma and urine; means to prevent its degradation during sample collection and storage by addition of ascorbic acid and ethylenediaminetetracetic acid are presented. This chromatographic method was shown to be precise, accurate and specific. It was successfully applied to toxicokinetic studies in rat.

The effect of pentachlorophenol and its metabolite tetrachlorohydroquinone on cell growth and the induction of DNA damage in Chinese hamster ovary cells

It is shown that p-tetrachlorohydroquinone (TCH), the metabolite of the environmental chemical pentachlorophenol (PCP), is more toxic to cultured CHO cells than PCP, and that it causes DNA single-strand breaks and/or alkali-labile sites at concentrations of 2-10 microgram/ml as demonstrated by the alkaline elution technique.

Metabolic studies on pentachlorophenol (PCP) in rats

1. The metabolism of pentachlorophenol in rats was studied. 2. Metabolites isolated from rat urine and identified were: 2,3,4,5-tetrachlorophenol, 2,3,4,6-tetrachlorophenol, 2,3,5,6-tetrachlorophenol, tetrachlorocatechol, tetrachlororesorcinol, trichlorohydroquinone, tetrachlorohydroquinone, and traces of trichloro-1,4-benzoquinone, and tetrachloro-1,4-benzoquinone.

The effects of pentachlorophenol (PCP) at the toad neuromuscular junction

1. Effects of PCP at the frog neuromuscular junction were studied in vitro in sciatic nerve sartorius muscle of the toad Pleurodema-thaul. 2. Within the concentration 0.003-0.1 mM, PCP caused a dose-time-dependent block of evoked transmitter release acompanied by an increase in the rate of spontaneous quantal release. 3. PCP induced an increase in miniature endplate potential (MEPP) frequency and it was not antagonized in a Ca2(+)-free medium, indicating that it does not depend upon Ca2+ influx from the external medium, but may act by releasing Ca2+ from intraterminal stores. 4. The present data, together with previous results concerning PCP at eighth sympathetic ganglia indicate that 3,4-diaminopyridine (3,4-DAP) counteracts the effects of PCP on synaptic transmission. This result suggests that PCP interfering Ca2+ influx occurs during depolarization of motor nerve terminals.

Identification of multiple glutathione S-transferases from Daphnia magna

1. Six anionic glutathione S-transferases (GST) were purified from the crustacean, Daphnia magna, by means of affinity chromatography, that are responsible for ca. 40% of cytosolic GST activity. 2. Electrophoresis in the presence of sodium dodecyl sulfate (SDS) revealed the presence of three proteins, with molecular weights of 27,500, 28,000, and 30,200. 3. Separation under nondenaturing conditions revealed six proteins, all of which exhibited GST activity, with molecular weights ranging from 55,000 to 61,700. 4. Ethacrynic acid is a competitive inhibitor of activity towards CDNB of all six GSTs, binding each with similar affinities. 5. Chlorinated phenols are also competitive inhibitors of the enzyme, with the degree of inhibition being directly correlated with the lipophilicity of the compounds. 6. Analysis of inhibition of separated isoforms reveals that form 4 is most strongly inhibited by these chlorinated phenols, with forms 5 and 6 being inhibited to a lesser degree.

Pentachlorophenol: health and environmental effects profile

Pentachlorophenol is used as an industrial wood preservative for utility poles, crossarms, fence posts, and other purposes (79%);for NaPCP (12%); and miscellaneous, including mill uses, consumer wood preserving formulations and herbicide intermediate (9%) (CMR, 1980). As a wood preservative, pentachlorophenol acts as both a fungicide and insecticide (Freiter, 1978). The miscellaneous mill uses primarily involve the application of pentachlorophenol as a slime reducer in paper and pulp milling and may constitute ∼6% of the total annual consumption of pentachlorophenol (Crosby et al., 1981). Sodium pentachlorophenate (NaPCP) is also used as an antifungal and antibacterial agent (Freiter, 1978). Pentachlorophenol also is used as a general herbicide (Martin and Worthing, 1977).

Photolysis and microbial degradation are the important chemical removal mechanisms for pentachlorophenol in water. In surface waters, pentachlorophenol photolyzes rapidly (ECETOC, 1984; Wong and Crosby. 1981; Zepp et al., 1984); however, the photolytic rate decreases as the depth in water increases (Pignatello et al., 1983). Pentachlorophenol is readily biodegradable in the presence of accli-mated microorganisms; however, biodegradation in natural waters requires the presence of microbes that can become acclimated. A natural river water that had been receiving domestic and industrial effluents significantly biodegraded pentachlorophenol after a 15-day lag period, while an unpolluted natural river water was unable to biodegrade the compound (Banerjee et al., 1984). Even though pentachlorophenol is in ionized form in natural waters, sorption to organic particulate matter and sediments can occur (Schellenberg et al., 1984), with desorption contributing as a continuing source of pollution in a contaminated environment (Pierce and Victor, 1978). Experimentally determined BCFs have shown that pentachlorophenol can significantly accumulate in aquatic organisms (Gluth et al., 1985; Butte et al., 1985; Statham et al., 1976; Veith et al., 1979a,b; Ernst and Weber, 1978), which is consistent with its widespread detection in fish and other organisms.

Direct photolysis may be an important environmental sink for pen tachlorophenol present in the atmosphere. The detection of pen tachlorophenol in snow and rain water (Paasivirta et al., 1985; Bevenue et al., 1972) suggests that removal from air by dissolution is possible.

Soil degradation studies indicate that pentachlorophenol is biodegrad able; microbial decomposition is an important and potentially domin ant removal mechanism in soil (Baker et al., 1980; Baker and Mayfield, 1980; Edgehill and Finn, 1983; Kirsch and Etzel, 1973; Ahlborg and Thunberg, 1980). The degree to which pentachlorophenol leaches in soil is dependent on the type of soil. In soils of neutral pH, leaching may be significant, but in acidic soils, adsorption to soil generally increases (Callahan et al. , 1979; Sanborn et al. , 1977). The ionized form of pentachlorophenol may be susceptible to adsorption in some soils (Schellenberg et al., 1984). In laboratory soils, pen tachlorophenol decomposes faster in soils of high organic content as compared with low organic content, and faster when moisture content is high and the temperature is conducive to microbial activity. Half- lives are usually ∼2-4 weeks (Crosby et al., 1981).

Monitoring studies have confirmed the widespread occurrence of pentachlorophenol in surface waters, groundwater, drinking water and industrial effluents (see Table 2). The U.S. EPA's National Urban Runoff Program and National Organic Monitoring Survey reported frequent detections in storm water runoff and public water supplies (Cole et al., 1984; Mello, 1978). Primary sources by which pen tachlorophenol may be emitted to environmental waters may be through its use in wood preservation and the associated effluents and its pesticidal applications. Pentachlorophenol can be emitted to the atmosphere by evaporation from treated wood or water surfaces, by releases from cooling towers using pentachlorophenol biocides or by incineration of treated wood (Skow et al., 1980; Crosby et al., 1981). Pentachlorophenol has been detected in ambient atmospheres (Caut reels et al., 1977), in snow and rain water (Paasivirta et al,. 1985; Bevenue et al., 1972) and in emissions from hazardous waste incinera tion (Oberg et al., 1985). The U.S. Food and Drug Administration's Total Diet Study (conducted between 1964 and 1977) found pen tachlorophenol residues in 91/4428 ready-to-eat food composites (See Tables 4 and 5). The average American dietary intake of pen tachlorophenol during 1965-1969 was estimated to range from <0.001-0.006 mg/day (Duggan and Corneliussen, 1972). The most likely source of pentachlorophenol contamination in many food prod ucts may be the exposure of the food to pentachlorophenol-treated wood materials such as storage containers (Dougherty, 1978).

Acute toxicity data indicated that salmonids are more sensitive to the toxic effects of pentachlorophenol than other fish species, with LC50values of 34-128 μ g/l for salmonids and 60-600 μ g/l for other species. More recent data showed that carp larvae, bluegills, channel catfish and knifefish also had LC50values < 100 μ gl (see Table 10). The most sensitive marine fishes were pinfish larvae, the goby, Gobius minutus, and eggs and larvae of the flounder, Pleuronectes platessa, all with LC50values <100 μ g/l (Adema and Vink, 1981). The most sensitive freshwater invertebrate species were the chironomid, Chironomus gr. thummi (Slooff, 1983) and the snail, Lymnaea luteola (Gupta et al., 1984). The most sensitive marine invertebrates were the Eastern oyster (Borthwick and Schimmel, 1978), larvae of the crusta ceans, Crangon crangon and Palaemon elegans (VanDijk et al. , 1977), and the copepod, Pseudodiaptomus coronatus (Hauch et al., 1980), all with LC50values <200 μ g/l.

In chronic toxicity tests, the lowest concentration reported to cause adverse effects was 1.8 μ g/l (NaPCP), which inhibited growth of sockeye salmon (Webb and Brett, 1973). The marine species tested displayed similar thresholds for chronic toxicity.

Both acute and chronic toxicity increased at lower pH, probably because a lower pH favors the un-ionized form of pentachlorophenol, which is taken up more readily and is therefore more toxic than ionized pentachlorophenol (Kobayashi and Kishino, 1980; Spehar et al., 1985).

Data concerning the effects of pentachlorophenol on aquatic plants were highly variable. Therefore, it was difficult to draw conclusions from these data.

Pentachlorophenol did not appear to bioaccumulate in aquatic or ganisms to very high concentrations. BCFs for pentachlorophenol were <1000 for most species tested. The highest BCF was 3830 for the polychaete, Lanice conchilega (Ernst, 1979). Some species appear to have an inducible pentachlorophenol-detoxification mechanism, as evidenced in several experiments in which pentachlorophenol tissue levels peaked in 4-8 days and declined thereafter despite continued exposure (Pruitt et al., 1977; Trujillo et al., 1982). A study by Niimi and Cho (1983) indicated that uptake of waterborne pentachlorophenol from gills was much greater than uptake from food, indicating that bioconcentration of pentachlorophenol through the food chain is unlikely. Biomonitoring data of Lake Ontario fishes showed that similar pentachlorophenol levels were found in predators andforage species.

Studies with experimental ecosystems have indicated that ecological effects may occur at pentachlorophenol levels as low as those causing chronic toxicity in sensitive species in single-species tests. The lowest concentration that caused adverse effects in these studies was 15.8 μ g/l, which caused a reduction in numbers of individuals and species in a marine benthic community (Tagatz et al., 1978).

Pentachlorophenol is readily absorbed from the gastrointestinal tract of rats, mice, monkeys and humans (Braun et al. , 1977, 1978; Ahlborg et al., 1974; Braun and Sauerhoff, 1976). Peak plasma concentrations are reached within 12-24 hours after oral administration to monkeys (Braun and Sauerhoff, 1976), but 4-6 hours after oral administration to rats (Braun et al., 1977). After oral administration, the highest concentration of radioactivity was found in the liver and gastrointesti nal tract of monkeys (Braun et al., 1977). In rats and mice, tet rachlorohydroquinone was identified in the urine (Jakobson and Yllner, 1971; Braun et al., 1977; Ahlborg et al., 1974) as well as unmetabolized pentachlorophenol and glucuronide-conjugated pen tachlorophenol. Although Ahlborg et al. (1974) reported that oxidative dechlorination of pentachlorophenol occurs in humans, as evidenced by the presence of tetrachlorohydroquinone in the urine of workers occupationally exposed (probably by inhalation), analysis of human urine after ingestion of pentachlorophenol revealed the presence of conjugated pentachlorophenol and unmetabolized pentachlorophenol (Braun et al., 1978).

The primary route of excretion after oral administrtation of all species studied is in the urine (Braun et al. , 1977, 1978; Ahlborg et al., 1974; Larsen et al., 1972; Braun and Sauerhoff, 1976). Although urinary excretion followed second-order kinetics in rats (Larsen et al., 1972; Braun et al., 1977) except in females receiving a single high dose (100 mg/kg) of pentachlorophenol, urinary excretion of pentachlorophenol in humans and monkeys followed first-order kinetics (Braun and Sauerhoff, 1976; Braun et al., 1978). Enterohepatic circulation played an importation role in the pharmacokinetics of pen tachlorophenol. The half-life of pentachlorophenol in the plasma is longer in female rats and monkeys than it is in male rats and monkeys (Braun et al. , 1978; Braun and Sauerhoff, 1976).

Because many preparations of pentachlorophenol are contaminated with small but measurable amounts of highly toxic substances, such as dibenzodioxins, special attention must be paid to the composition of the pentachlorophenol solution tested. In studies where technical and purified pentachlorophenol have been evaluated (Schwetz et al., 1974; Goldstein et al., 1977; Kimbrough and Linder, 1978; Knudsen et al., 1974; Johnson et al., 1973; Kerkvliet et al., 1982), only the results of the experiments using purified pentachlorophenol were reported in detail. Oral exposure to pentachlorophenol was not carcinogenic in mice (BRL, 1968; Innes et al., 1969) or rats (Schwetz et al., 1977), regardless of the composition of the pentachlorophenol solution tested. Although there are a few studies that suggest pentachlorophenol may be mutagenic in B. subtilis (Waters et al., 1982; Shirasu, 1976), in yeast, Saccharomyces cerevisiae (Fahrig et al., 1977) and in mice, as evidenced by the coat-color spot test (Fahrig et al., 1977), no evidence of mutagenicity was reported in S. typhimurium (Anderson et al. , 1972; Simmon et al., 1977; Lemma and Ames, 1975; Moriya et al. , 1983; Waters et al., 1982; Buselmaier et al., 1973) or in E. coli (Simmon et al., 1977; Fahrig, 1974; Moriya et al., 1983; Waters et al., 1982) with or without metabolic activation.

Three teratogenicitylreproductive toxicity studies (Schwetz et al., 1974, 1977; Courtney et al., 1976) indicate that pentachlorophenol is fetotoxic in rats at oral dose levels ≥5 mg/kg/day. At the highest dose tested (500 ppm) in a fourth teratogenicity/reproductive toxicity study (Exon and Koller, 1982), there was a statistically nonsignificant decrease in litter size. The lowest dose tested (5 mg/kg/day) by Schwetz et al. (1977) was the lowest dose at which any evidence offetotoxicity, as indicated by delayed ossification, was observed. No adverse fetal or reproductive effects were reported at ≤3 mg/kg/day (Schwetz et al., 1977; Exon and Koller, 1982). In subchronic and chronic toxicity studies, adverse effects occurred primarily in the liver (Kerkvliet et al., 1982; Johnson et al., 1973; Knudsen et al. , 1974; Goldstein et al. , 1977; Kimbrough and Linder, 1978; Schwetz et al., 1977), the kidney (Johnson et al., 1973; Kimbrough and Linder, 1978; Schwetz et al., 1977) and the immune system (Kerkvliet et al., 1982). Knudsen et al. (1974) reported increased liver weights in female rats and centrilobu lar vacuolization in male rats exposed to diets containing ≧50 ppm commercial pentachlorophenol, which contained 282 ppm dioxins. In the remaining studies, increased liver weight (Johnson et al., 1973) and increased pigmentation of hepatocytes (Schwetz et al., 1977) were observed at oral doses of≥10 mg/kg/day (∼90%), and SGPT levels significantly increased in rats ingesting 30 mg/kg/day pentachloro phenol (∼90%) for 2 years (Schwetz et al., 1977). Increased kidney weight unaccompanied by renal histopathology was reported in rats exposed to dietary concentration ≧20 ppm of pentachlorophenol (>99%) for 8 months (Kimbrough and Linder, 1978) and in rats ingesting 30 mg/kg/day (∼90%) for 90 days (Johnson et al., 1973). Increased pigmentation of the renal tubular epithelial cells was re ported in rats ingesting 10 or 30 mg/kg/day pentachlorophenol for 2 years (Schwetz et al., 1977). Although decreased immunocompetence was reported in mice exposed to dietary levels of 50 or 500 ppm of pentachlorophenol (>99%) for 34 weeks (Kerkvliet et al., 1982), the decrease was statistically significant only at the higher dose.

An ADI of 0.03 mg/kg/day or 2.1 mg/day for a 70 kg human was derivedfrom the NOAEL of 3 mg/kg/day in rats in the chronic dietary study by Schwetz et al. (1977). An uncertainty factor of 100 was used. An RQ of 100 was derived based on the fetotoxic effects of pen tachlorophenol in rats in the study by Schwetz et al. (1974). Based on guidelines for carcinogen risk assessment (U.S. EPA, 1984b) and inadequate evidence for animal carcinogenicity or absence of human cancer data, pentachlorophenol is classified as Group D, meaning that it is not classified as a human carcinogen.

Pharmacokinetics of pentachlorophenol in man

Pentachlorophenol (PCP) was given orally to three volunteers at single doses of 3.9, 4.5, 9, and 18.8 mg. Daily urinary excretion of PCP and PCP conjugated to glucuronic acid was monitored using gas chromatography with electron capture detection (GC/ECD). Based on first-order elimination kinetics an elimination half-life of 20 days was derived. To eliminate interference by the uncontrolled absorption of PCP from the environment 0.98 mg 13C-PCP was taken by one of the volunteers. PCP levels in urine and plasma were determined using mass spectrometry (GC/MS) with negative chemical ionization. An elimination half-life of 17 days was found in both urine and blood. The collected data were used to calculate the clearance of PCP: a value of 0.07 ml/min was found. The long elimination half-life of PCP is explained by the low urinary clearance due to the high plasma protein binding (greater than 96%) and the tubular reabsorption. The pH-dependency of the elimination of PCP was investigated, and a distinct increase in the daily excretion was observed following alkalinization by oral administration of sodium bicarbonate. In order to elucidate the role of the enterohepatic circulation as a possible pool for PCP in humans, the bile of cholelithiasis patients with postoperative T-drainage was investigated for PCP and compared with the corresponding urine and plasma levels, but no accumulation of PCP in the enterohepatic circulation could be observed. The daily elimination and plasma levels of PCP in a group of individuals without a specific exposition were found to range from 10 to 48 micrograms/day and 19 to 36 micrograms/1, respectively.

DNA-damaging properties and cytotoxicity in human fibroblasts of tetrachlorohydroquinone, a pentachlorophenol metabolite

The DNA-damaging potential of pentachlorophenol (PCP) and its metabolite tetrachlorohydroquinone (TCH) was investigated. TCH was found to bind covalently to calf-thymus DNA and to cause single-strand breaks in PM2 DNA. No DNA-damaging effects were observed for PCP. Exposure of human fibroblasts to PCP and TCH showed that TCH is more toxic, when colony-forming ability after exposure to the agent is used as a measure of toxicity. In the evaluation of the mutagenic and carcinogenic potential of PCP the metabolite TCH should be taken into consideration.

Determination of total pentachlorophenol in the urine of workers. A method incorporating hydrolysis, an internal standard and measurement by liquid chromatography

Free pentachlorophenol (PCP) represents a small and variable fraction of total PCP excreted in the urine of exposed workers. A method incorporating hydrolysis is essential to be able to relate PCP excretion to absorbed dose. 3,5-Dichloro-2,4,6-tribromophenol (DTP) is added as an internal standard to a urine sample which is then acidified and steam-distilled. The distillate is made alkaline and extracted with methylene chloride to remove interferences. The distillate is then acidified and the phenols extracted into methylene chloride. The extract is evaporated, redissolved in acetonitrile and the PCP is measured using high pressure liquid chromatography (HPLC) using a 15 X 0.46 cm Spherisob-ODS 5 microns column with isocratic elution (H2O:CH3CN:CH3CO2H, 45:55:0.3 v/v). Detection is by fixed wavelength detector at 313 nm and calculation by the method of internal standardization. The biological threshold value used to trigger action to reduce exposure is 7 mg/l (corrected to a specific gravity of 1.024).

Biotransformation of the fungicides hexachlorobenzene and pentachloronitrobenzene

This overview of the metabolism of the fungicides hexachlorobenzene (HCB) and pentachloronitrobenzene (PCNB) indicates similarities in their pathways of biotransformation. Several metabolites of HCB and PCNB, such as chlorinated benzenes, the mercapturic acid, thiophenols, thioanisoles and phenols are identical. Both Fungicides initially react with glutathione, with elimination or of the chlorine of the nitro group respectively. The conjugate, S-(pentachlorophenyl)glutathione, is further metabolized by cleavage of the glutamate and glycine results and acetylation of the amino group of the cysteinyl moiety, to give the mercapturic acid N-acetyl-S-(pentachlorophenyl)cysteine, a major metabolite of HCB and PCNB in rats and rabbits respectively, which is further metabolized to simpler sulphur-containing products.

Chlorinated phenols: occurrence, toxicity, metabolism, and environmental impact

Pentachlorophenol and the lower chlorinated phenols, tetra- and trichlorophenols, have gained an increasing use as fungicides, herbicides, insecticides, and precursors in the synthesis of other pesticides since the early 1930s. World-wide production totals about 200,000 tons. Production and use of chlorinated phenols have caused industrial hygiene problems but, otherwise, have not been recognized to create more than limited environmental problems. The introduction of modern analytical techniques, however, has revealed the ubiquitous occurrence of chlorophenols in the environment, and the discovery of chlorinated dimers, such as dibenzo-p-dioxins and dibenzofurans, as impurities in commercial chlorophenol formulations, has made a reevaluation of the chlorinated phenols necessary. The present article reviews recent studies on the toxicity and metabolism in mammals and aquatic organisms and the degradation of the chlorophenols under various conditions in the environment. Finally, the hazards of burning of chlorophenol wastes are discussed, as well as health considerations with regard to humans and the environment.

Effects of pentachlorophenol and 2,4,6-trichlorophenol on the disposition of sulfobromophthalein and respiration of isolated liver cells

The effect of pentachlorophenol (PCP) and 2,4,6-tricholorphenol (2,4,6-T) on the disposition of the hepatodiagnostic dye, sulfobromophthalein (BSP) has been studied in isolated liver cells. PCP (4-6 microM) as well as 2,4,6-T (50-100 microM) interferes with the disposition of BSP. The main effect apparently occurs at the secretion step as both drugs severely impair the release of the glutathione conjugate of BSP into the medium. As a consequence, BSP and its conjugate accumulate in the cell. High doses of PCP did not increase the release of lactate dehydrogenase from the hepatocytes. Concentrations of the two phenols which interfere with the secretion of BSP also completely uncouple the oxidative phosphorylation of hepatocellular mitochondria. The dysfunction of liver cells described here may therefore be explained by the effect of PCP and 2,4,6-T on the energy production of the cells. The higher toxicity of PCP as compared to 2,4,6-T observed in our system corresponds well with the higher LD50 of the latter compound.

Effects of pentachlorophenol on rat liver changes induced by hexachlorobenzene, with special reference to porphyria, and alterations in mixed function oxygenases

Hexachlorobenzene (HCB, 1000 ppm) and 500 ppm pentachlorophenol (PCP) were fed separately or in combination to female Wistar rats. A control group was provided with standard food without HCB or PCP. Subgroups of 4 rats were killed after 1, 2, 4, 6 and 8 weeks. No significant difference was found between the amounts of HCB accumulated in the livers of the HCB and HCB + PCP fed rats. Administering HCB together with PCP caused a noticeable accumulation of PCP in the liver, compared to the results after administering HCB and PCP separately. In the HCB and HCB + PCP fed groups liver weight increased continuously during the experiments. Microsomal cytochrome P-450, NADPH-cytochrome c reductase, ethoxyresorufin O-de-ethylase, aminopyrine N-demethylase, and glucuronyl transferase increased to a maximum in 2-4 weeks in HCB and HCB + PCP fed rats. Pentachlorophenol accelerates the onset of HCB porphyria, in other words it increases the total urinary porphyrin excretion and causes an earlier disturbance of the porphyrin pattern.

Studies on the toxicology of hexachlorobenzene. IV. Sulphur-containing metabolites

After administration of hexachlorobenzene rats excrete sulphur-containing conjugates from which pentachlorothiophenol can be split off. In the present study we describe the identification of pentachlorothiophenol and pentachlorothioanisol in the livers of animals treated with hexachlorobenzene. In order to clarify the further fate of these two substances, we administered them to rats, and isolated the conversion products excreted in the urine and feces. The metabolites of pentachlorothiophenol and pentachlorothioanisol are excreted in both conjugated and free form. From extracts of the excreta, we isolated tetra- and trichlorobenzene with two or three sulphur-containing substituents on the ring, analogous compounds in which thiol groups were converted into sulphoxide and sulphone groups, as well as analogous compounds with a phenolic oxygen in addition to sulphur, and sulphur-containing compounds in which clorine was replaced by hydrogen. Following administration of the sulphoxide and of the sulphone of pentachlorothioanisol under analogous conditions, pentachlorothiophenol and pentachlorothioanisol and their metabolites were detected in the excreta of the animals. No evidence was obtained that the parent compounds are excreted in the unchanged form.

Metabolism of pentachlorophenol in vivo and in vitro

Pentachlorophenol has earlier been shown to be metabolized in mammals to tetrachloro-p-hydroquinone. The metabolite possesses pronounced inhibitory activity on bacterial beta-glucuronidase but not on beta-glucuronidase from liver. Indirect evidence for the occurrence of both pentachlorophenol and tetrachloro-p-hydroquinone as conjugates with glucuronic acid in the urine from pentachlorophenol-treated rats is now presented. Bovine liver beta-glucuronidase has been utlizied to split the conjugates present. The in vivo metabolism of pentachlorophenol has also been studied in rats treated with phenobarbital and beta-diethylaminoethylidiphenyl propylacetate (SKF 525-A). In vitro metabolism has been studied using liver microsomes from rats pretreated with pehnobarbital. Quantitative analysis of the compounds occurring in extracts of urine or extracts from the microsomal incubates was performed by means of mass fragmentography. Pretreatment with phenobarbital increased the metabolism of pentachlorophenol to tetrachloro-p-hydroquinone both in vivo and in vitro. SKF 525-A, however, inhibited the metabolism in vitro but enhanced the metabolism in vivo when given less frequently than every 6th h. Dechlorination of pentachlorophenol is mediated by microsomal enzymes that can be induced by phenobarbital. SKF 525-A does not inhibit the dechlorination in vivo but does so in vitro.

Effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin on the in vivo and in vitro dechlorination of pentachlorophenol

The metabolism of pentachlorophenol has been studied in the rat after pretreatments with phenobarbital, 3-methyl cholanthrene or 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). In addition to the previously identified metabolite, tetrachloro-p-hydroquinone, trichloro-p-hydroquinone has been identified in urine as a metabolite. The formation of the latter represents a type dechlorination different from that of the formation of tetrachlorohydroquinone. The inducing agents, 3-methylcholanthrene and TCDD have similar effects on the dechlorination and increase the formation of tetrachloro-p-hydroquinone more pronounced than does phenobarbital. In contrast to phenobarbital they also increase the formation of trichloro-p-hydroquinone and the total elimination of pentachlorophenol and its metabolites. The in vivo findings are supported by in vitro studies with microsomes from rats pretreated with phenobarbital or TCDD. Use of the inhibitor beta-diethylaminoethyl-diphenyl propylacetate (SKF 525-A) in vitro showed a more pronounced inhibition on microsomes from phenobarbital-treated rats than on microsomes from untreated or TCDD-treated rats. Gas chromatography-mass spectrometry have been used for the identification and quantification of pentachlorophenol and its metabolites.

Metabolism of tetrachlorophenols in the rat

The three isomers of tetrachlorophenol were administrated intraperitoneally to rats and the urinary excretion products studied. Tetrachloro-p-hydroquinone was identified as a major metabolite of 2,3,5,6-tetrachlorophenol, constituting about 35% of the dose given. Trichloro-p-hydroquinone was identified as a minor metabolite of both 2,3,4,5- and 2,3,4,6-tetrachlorophenol. 2,3,5,6-tetrachlorophenol was eliminated within 24 h, 2,3,4,6-tetrachlorophenol within 48 h while only 60% of the given dose of 2,3,4,5-tetrachlorophenol could be recovered within 72 h. The acute toxicity of the tetrachlorophenols and tetrachloro-p-hydroquinone was studied in mice upon oral and intraperitoneal administration. 2,3,5,6-tetrachlorophenol (LD50p.o. 109 mg . kg-1) was the most toxic compound followed by 2,3,4,6- and 2,3.4,5-tetrachlorophenol (LD50p.o. 131 and 400 mg . kg-1, respectively). Tetrachloro-p-hydroquinone proved to have low oral toxicity (LD50p.o. 500 mg . kg-1) but was more toxic than the tetrachlorophenols when administered intraperitoneally. The oral LD50 for pentachlorophenol, under identical experimental conditions was found to be 74 mg . kg-1.

Subcellular distribution, a factor in risk evaluation of pentachlorophenol

Pentachlorophenol (PCP) is a potent uncoupler of mitochondrial phosphorylation in vitro and also interferes with microsomal detoxication functions in vitro. This favours flavin mediated oxygenation compared with flavin cytochrome P-450 dependent reactions. Gas chromatographic analysis of subcellular fractions, obtained by zonal centrifugation showed markedly lower PCP concentration in mitochondria and a high accumulation in microsomes compared with cytosol. This increases the likelihood that PCP in vivo causes a malfunction in microsomal detoxication.

Inhibition of beta-glucuronidase by chlorinated hydroquinones and benzoquinones

An earlier study of the metabolism of pentachlorophenol has shown that a metabolite, tetrachloro-p-hydroquinone, possessed pronounced inhibitory action on the activity of beta-glucuronidase from bacterial origin. Several other chlorinated hydroquinones and benzoquinones have now been studied with regard to their ability to inhibit beta-glucuronidase of various origin in vitro and in vivo. All the studied chlorinated hydroquinones and benzoquinones were found to be potent inhibitors of beta-glucuronidase of bacterial origin. D-glucaric acid-1.4-lactone was included for comparison and was found to be less active than the other studied compounds. The inhibition was found to be competitive in nature. No inhibitory effect of the benzo- and hydroquinones studied in vitro or in vivo could be demonstrated on beta-glucuronidase from livers. The result calls for precaution when using bacterial beta-glucuronidase to split urinary conjugates of glucuronic acid.