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Molecular cloning and characterization of pentachlorophenol-degrading monooxygenase genes of Pseudomonas sp. from the chemostat.

Pseudomonas sp. strain IST 103 (PCP103) capable of utilizing pentachlorophenol (PCP) was determined by utilization of a carbon source and release of the hydroxylating enzyme PCP-4 monooxygenase. The metabolites were extracted from the culture medium and analyzed by high-performance liquid chromatography. The enzyme purified to apparent homogeneity from an extract of PCP-grown cells indicated that a fraction of DEAE-cellulose ion exchange chromatography of molecular size of 30,000 kDa determined by gel filtration chromatography and SDS-polyacrylamide gel electrophoresis was responsible for dechlorination of PCP. The plasmid isolated from the bacterium was subjected to Shotgun cloning by restriction digestion by BamHI, HindIII, and SalI, ligated to pUC19 vector, and transformed into Escherichia coli XLBlue1alpha. The recombinant clones having higher potentiality to degrade PCP were selected by utilization of a carbon source and release of intermediary metabolites during degradation of PCP as the sole source of carbon and energy. The recombinant clones, which contained an insert of 3.0 kb of SalI and HindIII sites, were sequenced and compared with gene sequences deposited in GenBank by BLAST search; this indicated homology with the thdf gene of monooxygenase of thiophene and furan. Southern blot analysis performed by developing gene probes indicated the presence of the PCP monooxygenase gene in plasmids of the bacterium.

Base Sequence↗

Toxic effects of pentachlorophenol and other pollutants on the mineralization of acetate in several soils.

The mineralization of [14C]acetate was studied in bottles with fresh soil and groundwater. Addition of toxicants inhibited the formation of 14CO2 and dose-effect curves were obtained. The acetate mineralization was not inhibited by zinc, cadmium, K2Cr2O7, chloropyrifos, and paraquat in an acid sandy soil at 1000 mg/kg dry soil. The IC10 is the toxicant concentration which inhibits 10% of the initial mineralization rate. The IC10 concentrations for 3,4-dichloroaniline, triphenyltin, and orthoxylene were 48, 96, and 730 mg/kg, respectively, in the acid sandy soil. The IC10 of pentachlorophenol was measured in samples from the acid sandy soil and in several other soil and subsoil samples. The geometrical mean of the 13 IC10 values was 16 mg pentachlorophenol/kg. A statistical method was used to calculate the PCP concentration above which 5% of the most sensitive acetate-mineralizing communities in all soils are influenced. The best estimate of this concentration is 0.3 mg PCP/kg but to be on the safe side the 95% confidence level of this concentration is 25 micrograms/kg.

Acetates↗

Effects of pentachlorophenol and biotic interactions on soil fauna and decomposition in humus soil.

In a laboratory experiment, effects of chemical stress (pentachlorophenol, PCP, at concentrations of 0, 50, and 500 mg/kg) and biotic interactions (nematodes in the presence or absence of collembolas and enchytraeids) on the community structure of soil animals and decomposition processes were studied. PCP was strongly adsorbed to humus that contained 65% organic matter. Numbers of fungal-feeding nematodes decreased significantly at the highest PCP concentration, while no effects were found in bacterial feeders. There were differences in the numbers of nematodes between different animal combinations, but at the highest PCP concentration, collembolas and enchytraeids had no effect on them. Numbers of collembola Willemia anophtalma were lowered at the highest PCP concentration, although PCP was not acutely toxic at this concentration. The highest PCP concentration was acutely toxic to enchytraeids, and for an unknown reason all of them died in the main experiment. Both ATP content of the soil and soil respiration were reduced at the highest PCP concentration, while no differences were found between animal treatments. Amounts of NH4-N and PO4-P in the soil increased with increasing PCP concentration. It was concluded that in the presence of simple animal communities, harmful chemicals like PCP regulate the community structure of soil animals as well as decomposition and nutrient mobilization.

Acholeplasma laidlawii↗

Lethal body residues for pentachlorophenol in zebra mussels (Dreissena polymorpha) under varying conditions of temperature and pH.

Pentachlorophenol (PCP) toxicity was measured in the zebra mussel under varying conditions of pH (6.5, 7.5, or 8.5) and temperature (10, 17, or 25 degrees C). Toxicity decreased significantly with increasing pH at all temperatures. At a given pH level, toxicity increased significantly with increasing temperature. PCP was most toxic at pH 6.5, 25 degrees C and least toxic at pH 8.5, 10 degrees C. Toxicokinetic parameters were determined at trace PCP concentrations under each combination of pH and temperature. Increasing temperature generally increased the PCP uptake clearance (ku) although elimination rate constants (kd) were unaffected. The effect of pH on toxicokinetic parameters was inconsistent but ku tended to decrease as pH and ionization of PCP increased. Lethal body residues (LR50s), estimated from kinetic parameters determined at trace PCP concentrations and the LC50 values, varied by a factor of 122 as a function of environmental conditions while LC50s varied by a factor of 381. LR50s were also estimated from the measured PCP tissue concentrations and varied by a factor of 8 across conditions. Calculated LR50s were always higher than measured LR50s, determined under identical conditions, by at least a factor of five. However, when LR50 values were recalculated using ku values measured at the LC25 concentration, the resulting adjusted LR50s varied only by a factor of 2.5 across the range of conditions studied and were more consistent with measured LR50 values. Thus, variance in the PCP concentration required to produce toxicity is reduced when LR50s are used in place of LC50s. Further, the method by which lethal residues (LR50 values) are determined can significantly affect the results and their interpretation.

Algorithms↗

Modifications of the topical Japanese medaka (Oryzias latipes) embryo larval assay for assessing developmental toxicity of pentachlorophenol and p, p'-dichlorodiphenyltrichloroethane.

One method currently available for investigating developmental toxicity in teleost species is the Japanese medaka embryo larval assay (MELA). In the present study, the MELA was modified to evaluate repeated topical exposures to pentachlorophenol (PCP) and p, p'-dichlorodiphenyltrichloroethane (DDT) and to identify sensitive stages of embryonic development. A single topical exposure using embryos at 48 h postfertilization resulted in a statistically significant increase in embryo mortality at 688 and 1250 ng PCP/egg compared with controls. In contrast, the toxicity following exposure to 11, 36, 78, 120, 208, and 400 ng DDT/egg was expressed only in larvae after hatching. Results further demonstrate that the MELA can be optimized to accommodate repeated daily topical exposures starting at 48 h postfertilization and ending at 120 h postfertilization. In addition, the neurula stage (24 h postfertilization) represented the most sensitive embryonic stage following a single topical exposure of PCP. However, no differences were observed in the sensitivity of embryonic stages following DDT exposure. The modified MELA was also used to evaluate sediment extracts contaminated with DDT metabolites obtained from the Tensas River, Louisiana. Results indicate that there is a low potential for developmental toxicity using the present extraction and exposure scenario even though elevated levels of DDE and toxaphene currently exist in several adult fish species at this site. The MELA as a screen for evaluating the potential for developmental toxicity of contaminated sediments is discussed.

Administration, Topical↗

Sublethal effects of pentachlorophenol in abalone (Haliotis rufescens) veliger larvae as measured by (31)P-NMR.

Toxicity tests with larval marine organisms are widely used as water quality-monitoring tools. Often employing a single morphological endpoint, they provide only limited insight into toxic action mechanisms. Since mechanistic observations can provide more sensitive endpoints of toxicity, the goal of this study was to modify existing in vivo (31)P-NMR techniques to evaluate the effects of pentachlorophenol (PCP) on high-energy phosphates in veliger larvae of the red abalone (Haliotis rufescens), a species and life stage commonly used in developmental toxicity tests. Fluxes of phosphoarginine (PA), nucleoside triphosphates (NTPs), sugar phosphates (SPs), and inorganic phosphate (P(i)), as well as in intracellular pH (pH(i)), were monitored via NMR using a flow-through exposure system. The exposure protocol included 1 h of clean seawater, 2 h of PCP (1.2 mg L(-1)) exposure, and 2 h of recovery in clean seawater. During PCP exposure, veligers displayed maximum declines in PA and NTP resonance intensities to 38+/-10% (P<0.01) and 61+/-16% (P<0.05) of reference values (represented by the average resonance intensities taken from 1 h of preexposure spectral acquisition). Inorganic phosphate concentrations rose to 302+/-63% (P<0.01), and pH(i) declined from a reference period average of 7.12+/-0.03 to 7.04+/-0.04 (P<0.05). On exposure to clean seawater, veligers recovered within 2 h, returning to 196+/-53, 89+/-12, and 89+/-13% of the reference intensities for P(i), PA, and NTPs, respectively (P>0.05 for all values), while pH(i) increased to 7.08+/-0.11. When compared with adult abalone, veliger larvae responded similarly to PCP, differing mainly in their rapid recovery (2 h for larvae versus 6 h adults) and more severe acidification (a 0.08 pH unit decline versus a 0.03 pH unit decline). This report describes an application of NMR for small (> or =200 micro) marine organisms using commonly available vertical-bore NMR magnets; it should prove adaptable for use with other similar larval forms.

Animals↗

Protein synthesis in cadmium- and pentachlorophenol-tolerant Euglena gracilis.

This work is a preliminary characterization of two adapted Euglena gracilis cell lines, one to cadmium and the other to pentachlorophenol. Growth curve analyses indicate that tolerance to one pollutant did not protect against the second pollutant. These suggest that metabolic pathways that are induced by one pollutant are specific for this pollutant. This specificity is detectable at the level of gene expression.

Animals↗

Pentachlorophenol exposure in women with gynecological and endocrine dysfunction.

Exposure to wood preservatives containing pentachlorophenol (PCP) was detected in 65 women who consulted the Endocrinological Department of the University Hospital of Obstetrics and Gynecology, Heidelberg, Germany, because of gynecological problems. Blood PCP levels ranged from 20.7 to 133 microg per liter of serum. One hundred and six women with similar clinical conditions, corresponding age and body weight, no PCP exposure in history, and PCP levels below 20 microg per liter of serum served as control group. Significant associations were found between serum PCP concentrations, age, and different parameters of the endocrine system. PCP may act centrally on a hypothalamic or suprahypothalamic level which may result in mild ovarian and adrenal insufficiency. PCP may, therefore, play a role in the increasing infertility problem.

Adrenal Cortex Hormones↗

Percutaneous absorption of pentachlorophenol from soil.

Pentachlorophenol (PCP) is one of the most heavily used pesticides. About 80% of PCP is used for wood preservation, whereas the remainder is used as an herbicide, fungicide, and disinfectant. PCP is a probable human carcinogen, based on animal studies. Illness and death have been reported where PCP is in direct contact with skin. PCP is the most ubiquitous compound found when the general population is screened for pesticide residue. PCP is found in soil as well as other environmental sources. Our objective was to determine the skin bioavailability of PCP from soil and from the control vehicle acetone. In vivo in the Rhesus monkey, percutaneous absorption of PCP was 24.4 +/- 6.4% of applied dose from soil and 29.2 +/- 5.8% of applied dose from acetone vehicle for a 24-hr exposure period. This amount of absorption makes PCP one of the more extensively absorbed compounds to date. Additionally, the 14C half-life was 4.5 days following both intravenous and skin administration of [14C]PCP. These data suggest high bioavailability and an extended biological interaction period with the long half-life. In vitro percutaneous absorption with human cadaver skin and human plasma receptor fluid underestimated the in vivo absorption. Receptor fluid accumulation was 0.6 +/- 0.09% and 1.5 +/- 0.2% for two skin sources for PCP in acetone vehicle and 0.01 +/- 0.00% and 0.00 +/- 0.08% for two skin sources with soil vehicle. Skin content after skin surface wash ranged from 2.6 to 3.7% for acetone vehicle and 0.07-0.11% for soil vehicle. Overall accountability for in vitro dose ranged from 81 to 96%.

Acetone↗

Oxidative DNA damage and cell proliferation in the livers of B6C3F1 mice exposed to pentachlorophenol in their diet.

Pentachlorophenol (PCP), which has been used as a wood preservative, was reported to be a liver carcinogen in mice. To investigate the initial effects of PCP administration under the same conditions of exposure as in the carcinogenic study, we examined oxidative stress and cell proliferation, along with other hepatotoxicological parameters, in the livers of B6C3F1 mice fed PCP in their diet at doses of 0.03, 0.06, and 0.12% for up to 4 weeks. We observed significant increases of 8-OHdG levels in hepatic nuclear DNA at doses of 0.03% and above at 2 and 4 weeks. Likewise, dose-dependent increases in the labeling index of cells were detected by counting those that had incorporated 5-bromo-2'-deoxyuridine throughout the experimental period. Also, we found significant elevations of the liver weights, concurrent with increases in hepatic DNA content in the treated mice, which again were dose-related. Serum aspartic transferase activity at doses of 0.06% and above were significantly increased despite these changes being slight. Also, histopathological examination provided no evidence of necrotic changes, but severe hepatocyte swelling in the treated mouse livers. These data indicate that PCP might be able to induce cell proliferation in the mouse liver, as well as induce oxidative DNA damage, suggesting both changes may play an important role in hepatocarcinogenesis.

Animals↗

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.

Animals↗

Pentachlorophenol dermal absorption and disposition from soil in swine: effects of occlusion and skin microorganism inhibition.

Residue of the environmentally relevant biocide pentachlorophenol (PCP) is found mainly in soil, making dermal contact one of the primary routes for PCP exposure. To quantify exposure effects on dermal absorption and systemic disposition, [14C-UL]PCP was dosed nonocclusively or occlusively at 40 micrograms/cm2 in a soil-based mixture in an in vivo swine model. Additionally, antibiotics were also codosed with occlusive PCP in soil to examine the impacts of skin microbial PCP biodegradation on total dermal absorption. Under nonocclusive, occlusive, and occlusive-antibiotic conditions, total radiolabel absorption by 408 hr was 29.08, 100.72, and 86.21% dose, respectively. Tissue accumulation of PCP and its labeled metabolite(s) was very significant in swine since one-half to two-thirds of the absorbed dose was still present in tissues by 17 days after PCP dermal exposure. High 14C concentrations were found in liver, kidney, lung, ovary, and uterus. Urine and fecal routes were equally important for label excretion from the body. Occlusion enhanced total dermal absorption and changed the shape of the absorption profiles in the blood and plasma. Skin microorganism inhibition retarded 14C dermal absorption, altered local and systemic tissue distribution, and increased plasma/blood concentration ratios, suggesting skin microbial PCP degradation might play an important role in the altered absorption and disposition by occlusion. This study demonstrated significant dermal absorption and extensive tissue persistence of PCP after soil exposure. Occlusion and skin microflora growth may greatly impact dermal absorption, cutaneous disposition, and systemic toxic input. Therefore, exposure-specific PCP absorption and disposition profiles must be taken into consideration in risk analysis.

Animals↗

Effects of molybdate and pentachlorophenol on the sulfation of dehydroepiandrosterone.

Pentachlorophenol (PCP) and molybdate have been shown to inhibit the sulfoconjugation of various chemicals in rats and therefore are useful to examine the role of sulfoconjugation on the toxicity of a chemical. PCP inhibits sulfation by competing with substrates for phenol-sulfotransferases, but not hydroxysteroid-sulfotransferases. In contrast, molybdate decreases sulfation by limiting sulfate availability and thereby decreasing the synthesis of 3'-phosphoadenosine 5'-phosphosulfate (PAPS), which is the obligate cosubstrate for sulfation. Therefore, it was of interest to determine whether PCP or molybdate is effective in decreasing the in vivo sulfation of dehydroepiandrosterone (DHEA), which is a substrate for hydroxysteroid-sulfotransferases. PCP (40 micromol/kg ip) or molybdate (7.5 mmol/kg po) was given 45 min and 4 h, respectively, prior to the start of DHEA infusion. The effects of these two sulfation inhibitors on DHEA sulfation were dependent on the rate of DHEA infusion in rats. PCP had different effects on the sulfation of various infusion rates of DHEA in rats. PCP had little effect on the sulfation after the two lowest infusion rates of DHEA (12.5 and 25 mg/kg) and actually increased (233%) DHEA-sulfate serum concentrations with the highest DHEA infusion rate (50 mg/kg). Although molybdate had little affect on the sulfation of the lowest DHEA infusion rate, it significantly decreased (50-85%) DHEA-sulfate serum concentrations with the two higher DHEA infusion rates. These data indicate that molybdate, unlike PCP, decreases the sulfation of DHEA and may be a useful tool to decrease the sulfation of other substrates of hydroxysteroid-sulfotransferases.

Animals↗

Degradation of pentachlorophenol by the white rot fungus Phanerochaete chrysosporium grown in ammonium lignosulphonate media.

Removal and degradation of pentachlorophenol (PCP) by Phanerochaete chrysosporium in static flask cultures was studied using ammonium lignosulphonates (LS), a waste product of the papermill industry, as a carbon and nitrogen source. After 3 days, cultures of P. chrysosporium grown in either a 2% LS (nitrogen-sufficient) medium or a 0.23% LS and 2% glucose (nitrogen-deficient) medium removed 72 to 75% of PCP, slightly less than the 95% removal seen using nitrogen-deficient glucose and ammonia medium. PCP dehalogenation occurred despite the fact that extracellular enzyme (LiP) activity, measured by a veratryl alcohol oxidation assay and by PCP disappearance in cell-free extracts, was inhibited by LS. This inactivation of LiP likely contributed to the lower percent of PCP dehalogenation observed using the LS media. In order to better understand the relationship between PCP disappearance and dehalogenation, we measured the fate of the chlorine in PCP. After 13 days, only 1.8% of the initial PCP added was recoverable as PCP. The remainder of the PCP was either mineralized or transformed to breakdown intermediates collectively identified as organic halides. The largest fraction of the original chlorine (58%) was recovered as organic (non-PCP) halide, most of which (73%) was associated with the cell mass. Of the remaining chlorine, 40% was released as chloride ion, indicating a level of dehalogenation in agreement with previously reported values.

Basidiomycota↗

Dechlorination of pentachlorophenol by membrane bound enzymes of Rhodococcus chlorophenolicus PCP-I.

Dechlorination (para-hydroxylation) of pentachlorophenol (PCP) and tetrachloro-para-hydroquinone (TeCH) and O-methylation of TeCH were demonstrated in cell extracts of Rhodococcus chlorophenolicus PCP-I. PCP para-hydroxylating activity was membrane bound, whereas TeCH dechlorinating enzyme was soluble. The PCP para-hydroxylating enzyme was solubilized by Triton X-100 and the requirement for both FAD and NADPH was shown. The dechlorinating activities were inducible in contrast to the constitutive TeCH O-methylating activity. The PCP para-hydroxylation was inhibited by its product TeCH, by anoxic conditions, and by different inhibitors of P450. Participation of this cytochrome in the PCP hydroxylation was confirmed by the appearance of a carbon monoxide dependent peak of absorbance at 457 nm in the membrane fraction prepared from PCP degrading cells.

Biodegradation, Environmental↗

Toxicological assessment of biotransformation products of pentachlorophenol: Tetrahymena population growth impairment.

Pentachlorophenol (PCP) is a widespread contaminate of soils and ground water throughout North America. Earlier studies have indicated that microbial biodegradation leads to the formation of intermediate metabolites which are more toxic than the parent compound. Microbial degradation is by three general pathways: dechlorination, methylation, and oxidation. The relative toxicity of PCP and 25 of its identified intermediates of microbial transformation was evaluated in the static Tetrahymena pyriformis population growth assay. Dechlorination of chlorophenols resulted in a decrease in toxicity because of a decrease in both hydrophobicity and reactivity. Moreover, dechlorination of chloroanisoles resulted in a decrease in toxicity due to a decrease in hydrophobicity. Since there was a decrease in reactivity, methylation of chlorophenols resulted in a decrease in toxicity. Oxidation of chlorophenols resulted in enhanced toxicity owing to increased reactivity and concomitant decreased hydrophobicity.

Animals↗

Distribution of hydrophobic ionizable xenobiotics between water and lipid membranes: pentachlorophenol and pentachlorophenate. A comparison with octanol-water partition.

We have studied distribution of pentachlorophenol (PCP)--a major environmental pollutant--between egg-phosphatidylcholine (egg-PC) membranes and water. The objectives were (1) to compare the membrane-water partition of the un-ionized (HA) and ionized (A) PCP, and (2) to establish similarities and differences between the partition of PCP into lipid membranes and into octanol. The studies were made with egg-PC liposomes. It is shown that the distribution isotherms can be understood in terms of the Langmuir-Stern-Grahame adsorption model. The model is applicable to both the HA and A species; it takes into account the electrostatic interactions at the membrane-water interface charged by the adsorbed pentachlorophenate. Relationships between the membrane surface adsorption and bulk partition characteristics were presented and used to relate the partition of PCP into egg-PC membranes to those for octanol-water systems. Results (egg-PC membranes): bulk distribution coeff. gamma HA = 2.9 x 10(5), gamma A = 1.6 x 10(4), association constant KmHA = 2.9 x 10(5) M-1, KmA = 0.7 x 10(5) M-1, adsorption site area PsHA = 0.6 nm2, PsA = 3.5 nm2, and linear partition coeff. Beta mHA = 550 microns, beta mA = 30 microns. Comparable to gamma HA and gamma A for octanol-water are P(ow)(HA) approximately 1.3 x 10(5) and P(ow)(A) approximately 30. The major difference is in the distribution of ionized PCP which is several hundred times greater for egg-PC membranes compared to octanol. The difference is associated with the properties of the membrane-water interface.

Membranes, Artificial↗

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.

Animals↗