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PubMed1994

Effect of mixtures of chlorophenols, surfactants, and aniline on growth of Pseudomonas fluorescens.

Industrial wastewater often contains a mixture of chemical substances and knowledge of joint action of toxicants is therefore important when the toxicity of an effluent is evaluated or reduction of the toxicity is needed. In this study, the joint action of three pairs of toxicants, selected on the basis of their expected different modes of toxic actions, was tested for inhibition of the growth of the bacteria Pseudomonas fluorescens: pentachlorophenol and aniline, the surfactants nonylphenolethoxylate and tetrapropylenebenzenesulfonate, and pentachlorophenol and 2, 4-dichlorophenol. The joint effect of pentachlorophenol and aniline did not differ significantly from additivity, whereas less than additive responses were observed for mixtures of nonylphenolethoxylate and tetrapropylenbenzenesulfonate. A more than additive response was observed for mixtures of pentachlorophenol and 2,4-dichlorophenol at some concentration levels, while at others additive responses were found. It was concluded that joint actions other than additivity may occur between commonly known toxic substances, and that the modes of toxic action of the substances studied can explain the different types of joint action observed in this study. Further, test strategy followed proved useful in the evaluation of the joint toxicity of binary mixtures.

Aniline Compounds↗
PubMed1999

A comparison of the ability of forest and agricultural soils to mineralize chlorinated aromatic compounds.

Soils were sampled from two agricultural fields, two relatively pristine forests, and one suburban forest in Ontario, Canada. The ability of these soils to mineralize 2,4-dichlorophenoxyacetate, 3-chlorobenzoate, 4-chlorophenol, 2,4-dichlorophenol, pentachlorophenol, and atrazine was determined using 14C-labeled substrates. Direct pre-exposure was necessary before atrazine mineralization could be detected; however, it was not necessary for degradation of any of the other chemicals. 2,4-dichlorophenoxyacetate and pentachlorophenol mineralization was much higher in the agricultural soils relative to the pristine forest soils, but 3-chlorobenzoate and 2,4-dichlorophenol mineralization rates showed the opposite trend. Mineralization of 4-chlorophenol was about equivalent in all soils. Suburban forests soils were indistinguishable from agricultural soils with respect to their degradation of 2,4-dichlorophenoxyacetate and chlorobenzoate. Additionally, they were better able than any of the soils to withstand the toxic effects of pentachlorophenol. Pentachlorophenol mineralization was highly variable in the pristine forest soils, ranging from about 6 to 50%. Abiotic factors such as pH, soil type, and organic and moisture content did not account for these significant site differences. The selective forces responsible for these differences, and the possible differences in microbial populations are discussed.

Agriculture↗
PubMed2006

Spatial and geographical variations of urban, suburban and rural atmospheric concentrations of phenols and nitrophenols.

GOAL, SCOPE AND BACKGROUND: Atmospheric sampling (gas and particles) of 5 phenols (phenol, m-cresol, p-cresol, o-cresol, pentachlorophenol) and 15 nitrophenols (3-methyl-2-nitrophenol, 3-nitrophenol, 4-methyl-2-nitrophenol, 5-methyl-2-nitrophenol, 2-methyl-3-nitrophenol, 3-methyl-4-nitrophenol, 2,6-dinitrophenol, bromoxynil, 2,5-dinitrophenol, 2,6-dinitropcresol, 2,4-dinitrophenol, ioxynil, DNOC, 3,4-dinitrophenol, dinoseb) on XAD-2 resin (20 gr) and glass fibre filters, respectively, were performed in 2002 by using 'Digitel DA80' high volume sampiers. These measurements were undertaken in order to show spatial and geographical variations of concentrations and the role of traffic in the emissions of these compounds to the atmosphere. METHODS: Sampling were performed in Strasbourg (eastern France), in its vicinity (Schiltigheim) and in Erstein. Sites were chosen to be representative of urban (Strasbourg), suburban (Schiltigheim) and rural (Erstein) conditions. Field campaigns were undertaken simultaneously in urban and suburban sites during all the seasons during 4 hours at a flow rate of 60 m3 h(-1), which gives a total of 240 m3 of air per sample. Period of sampling varied between 06h00 to 10h00, 11h00 to 15h00 and 18h00 to 22h00 in order to evaluate a variation of concentration during automobile traffic between urban, suburban and rural areas. Gas and particle samples were separately Soxhlet extracted for 12 h with a mixture of CH2Cl2 / n-hexane (50:50 v/v), concentrated to about 1 mL with a rotary evaporated and finally dried under nitrogen. Dry extracts were dissolved in 1 mL of CH3CN. Before analysis, extracts were sylilated by using MTBSTFA. Analysis was performed by GC/MSD in the SIM mode. RESULTS AND DISCUSSION: Partitioning of phenolic compounds between gas and particle phases seems to be mainly correlated with vapour pressure. Among phenolic compounds analysed, phenol, p-cresol, pentachlorophenol and 2.4-dinitrophenol were detected in all samples and emissions from traffic seems to be the major source for the presence of these compounds to the atmosphere. No increase of concentrations in autumn tend to confirm this hypothesis since, with the use of domestic heating in colder months, increases of PAHs concentrations were observed and these compounds are known to be emitted by all combustion processes, Pentachlorophenol is a special case since this molecule is only used as wood preservative. Its presence in all atmospheric samples, whatever the locations and the period of time is the consequence of its persistence. CONCLUSIONS AND PERSPECTIVES: These measurements demonstrate that phenols and nitrophenols are emitted to the atmosphere and further measurements, in order to confirm their sources, their behaviour and their potential impact to the air quality and to human health should be undertaken especially since the literature collected is relatively old. Concentrations of pentachlorophenol measured are very low and, due to its toxicity, further investigations should be undertaken.

Air Movements↗
PubMed1995

Pesticide residues in urine of adults living in the United States: reference range concentrations.

We measured 12 analytes in urine of 1000 adults living in the United States to establish reference range concentrations for pesticide residues. We frequently found six of these analytes: 2,5-dichlorophenol (in 98% of adults); 2,4-dichlorophenol (in 64%); 1-naphthol (in 86%); 2-naphthol (in 81%); 3,5,6- trichloro-2-pyridinol (in 82%); and pentachlorophenol (in 64%). The 95th percentile concentration (95th PC) for 2,5-dichlorophenol (indicative of p-dichlorobenzene exposure) was 790 micrograms/liter; concentrations ranged up to 8700 micrograms/liter. 2,4-Dichlorophenol concentrations ranged up to 450 micrograms/ liter, and the 95thPC was 64 micrograms/liter. 1-Naphthol and 2-naphthol (indicative of naphthalene exposure) had 95thPCs of 43 and 30 micrograms/liter, respectively; concentrations of 1-naphthol ranged up to 2500 micrograms/liter. Chlorpyrifos exposure was indicated by 3,5,6-tricholoro-2-pyridinol concentrations of 13 (95thPC) and 77 micrograms/liter (maximum observed). Pentachlorophenol had a 95thPC of 8.2 micrograms/liter. Other analytes measured included 4-nitrophenol (in 41%); 2,4,5-trichlorophenol (in 20%); 2,4,6-trichlorophenol (in 9.5%); 2,4-dichlorophenoxyacetic acid (in 12%); 2-isopropoxyphenol (in 6.8%); and 7-carbofuranphenol (in 1.5%). The 95thPCs of these analytes were < 6 micrograms/liter. p-Dichlorobenzene exposure is ubiquitous; naphthalene and chlorpyrifos are also major sources of pesticide exposure. Exposure to chlorpyrifos appears to be increasing. Although pentachlorophenol exposure is frequent, exposure appears to be decreasing. These reference range concentrations provide information about pesticide exposure and serve as a basis against which to compare concentrations in subjects who may have been exposed to pesticides.

2,4-Dichlorophenoxyacetic Acid↗
PubMed1976

Studies on the toxicology of hexachlorobenzene. II. Identification and determination of metabolites.

Female rats were dosed intraperitoneally with 14C-hexaxhlorobenzene. The drug was administered on 2 or 3 occasions. The total doses amounted to 260 and 390 mg/kg 14C-hexachlorobenzene, respectively. Urine and feces from the animals were collected over a period of 4 weeks after the first injection. Both excreta and some tissues of the animals were examined for their content of radioactivity and for hexachlorobenzene and its metabolites. Gas chromatography, isotope dilution analysis, and combined gas chromatography-mass spectrometry were used to identify the metabolites of hexachlorobenzene. In urine pentachlorophenol, tetrachlorohydroquinone, and pentachlorothiophenol were present as major metabolites. One of the isomers of tetrachlorothiophenol was present as a minor metabolite. In the feces pentachlorophenol and pentachlorothiophenol only were identified. At the end of the experiment, carbon-14 excreted with urine and feces amounted to 7% and 27%, respectively, of the radioactivity administered. More than 90% of carbon-14 excreted in urine was contained in the major metabolites. In the feces about 30% of the excreted radioactivity was bound to metabolites and about 70% was contained in the unchanged drug, while in the tissues of the animals only pentachlorophenol was detected in measurable amounts, accounting for 10% of label in blood and less than 0.1% of carbon-14 determined in body fat. Total radioactivity contained in the metabolites detected in the animal body and in the excreta at the end of the experiment accounted for about 16% of the administered radioactivity.

Animals↗
PubMed2004

Formation and emission of chloroanisoles as indoor pollutants.

GOAL, SCOPE AND BACKGROUND: Complaints by residents of frame-houses about musty odour in the houses has become an increasing problem within the last years. An additional problem is that the odour is transferred to clothes and skin. The persons themselves do not recognize the smell after a while because of adaptation. Serious social problems are the result. For a long time, the smell was explained to be from mould due to construction-based humidity problems. However, in an increasing number of houses, no indications were found for elevated levels of mould growth. METHODS: Air and material samples were taken from 5 houses, which show typical musty odours, and analysed with respect to chlorophenols and chloroanisoles. Additionally, some samples were analysed for lindane and its metabolites, because lindane was commonly used together with pentachlorophenol (PCP) for wood protection. RESULTS AND DISCUSSION: Meticulous analysis resulted in the identification of chloroanisoles, mainly 2,3,4,6-tetrachloroanisole. These substances are known from corky wines and from contamination of food from pentachlorophenol (PCP) treated pallets and result from microbiological metabolic processes. Pentachlorophenol was commonly used to protect wood from fungi in Germany mainly in the later 60s and 70s. Details of these processes, as well as effective methods to identify chloroanisoles in the problem houses, are described. CONCLUSIONS: Chloroanisoles formed by metabolism of PCP have been well known to contaminate food or wine. Here, they were identified and are probably responsible for the musty odours in the frame houses. Since it is quite clear that these substances were not components of building materials used in the houses, an explanation for chloroanisole formation is proposed. Localized dampness probably favours microbial growth associated with metabolic conversion of chlorophenols to the corresponding chloroanisoles, primarily 2,3,4,6-tetrachloroanisol, which spread throughout the buildings, resulting in the observed odours. RECOMMENDATIONS AND OUTLOOK: The group of chloroanisoles has been recognized as important indoor pollutants as they possess musty odours at extremely low concentrations, e.g. for 2,4,6-trichloroanisole in a range of 5-10 ppt in air (Staples 2000). On the basis of currently available toxicological data, exposure of the occupants to the concentrations of chloroanisoles measured is not associated with a health risk. No correlation could be observed between concentrations of chloroanisoles and PCP in house dust and indoor air. However, chloroanisoles are good indicators for possible PCP-treatment of wood in frame houses and their detection should initiate investigations on PCP contamination. Research is continuing to identify the microorganisms involved and to devise a remediation procedure for affected houses.

Air Pollution, Indoor↗
PubMed1998

Mutagenic interactions of model chemical mixtures.

Although current methodology for human health risk assessment assumes additive interactions among the contaminants of a complex mixture, chemical interactions may occur which produce synergistic or antagonistic effects. In this study, the mutagenic response of three f2p4l compounds, benzo(a)pyrene (B(a)P), pentachlorophenol (PCP) and 2,4,6-trinitrotoluene (TNT), were tested individually and in binary and tertiary solutions, using the Salmonella/microsome assay with each of three bacterial tester strains (TA97a, TA98, and TA100). For all strains, B(a)P was mutagenic with metabolic activation (Arochlor 1254-induced Sprague-Dawley rat liver S9 fraction), TNT was mutagenic without metabolic activation, and pentachlorophenol was inactive both with and without metabolic activation. In binary and tertiary solutions, pentachlorophenol had no effect on the mutagenicity of B(a)P or TNT, independent of metabolic activation. For strain TA97a, the mutagenicity of B(a)P with metabolic activation was slightly decreased in the presence of TNT; the mutagenicity of TNT without metabolic activation was slightly decreased in the presence of B(a)P and PCP; and the mutagenicity of the tertiary solution (496 revertants/10 ug) with metabolic activation was lower than the mutagenicity of B(a)P alone (729 revertants/10 ug). The mutagenicity of B(a)P in strain TA98 with activation was inhibited by the addition of TNT. Studies conducted using several concentrations of TNT or B(a)P indicate that the inhibition of B(a)P mutagenicity was increased as the concentration of TNT increased. Assays performed using four concentrations of S9 indicated the inhibition of B(a)P mutagenicity was relatively unaffected by the level of S9. The data suggest that an interaction in the presence of TNT limits the concentration of B(a)P that is capable of reaching or binding with bacterial DNA.

Animals↗
PubMed2002

Factors influencing nominal effective concentrations of chemical compounds in vitro: medium protein concentration.

Quantitative data used to characterise biological activities of chemicals in vitro (e. g. EC50 values) are generally based on nominal concentrations and thus depend on factors influencing the availability of a compound. In this study, the impact of protein binding on the availability of chemicals in vitro is theoretically investigated and experimentally examined using a bovine sperm cell assay to measure the cytotoxic potency of selected compounds at different medium protein concentrations. In agreement with theoretical considerations, linear correlations between EC50 values and medium albumin concentrations were determined with 2,4-dichlorophenol, pentachlorophenol, p,p'-DDT and mercuric chloride. Ratios of EC50 values measured in the presence and absence of 4% (w/v) albumin varied between 500 (hexachlorophene), 258 (pentachlorophenol) and almost 1 (potassium cyanide, dextropropoxyphene). Calculated molar ratios of substance bound to albumin ranged from 0.05 (arsenic trioxide) and 0.1 (potassium cyanide) to 2.5 and 4.7 moles/mole for malathion and xylene, respectively. The fractions bound at 4% albumin varied between 11 and 15% for dextropropoxyphene and potassium cyanide, respectively, and more than 99% for hexachlorophene, pentachlorophenol and mercuric chloride. The results clearly demonstrate that the differing impact of protein binding on the bioavailability of chemicals considerably influences their nominal and relative potencies in the presence of albumin.

Animals↗
PubMed2000

Evolution of a metabolic pathway for degradation of a toxic xenobiotic: the patchwork approach.

The pathway for degradation of the xenobiotic pesticide pentachlorophenol in Sphingomonas chlorophenolica probably evolved in the past few decades by the recruitment of enzymes from two other catabolic pathways. The first and third enzymes in the pathway, pentachlorophenol hydroxylase and 2,6-dichlorohydroquinone dioxygenase, may have originated from enzymes in a pathway for degradation of a naturally occurring chlorinated phenol. The second enzyme, a reductive dehalogenase, may have evolved from a maleylacetoacetate isomerase normally involved in degradation of tyrosine. This apparently recently assembled pathway does not function very well: pentachlorophenol hydroxylase is quite slow, and tetrachlorohydroquinone dehalogenase is subject to severe substrate inhibition.

Amino Acid Sequence↗
PubMed1988

Degradation and O-methylation of chlorinated phenolic compounds by Rhodococcus and Mycobacterium strains.

Three polychlorophenol-degrading Rhodococcus and Mycobacterium strains were isolated independently from soil contaminated with chlorophenol wood preservative and from sludge of a wastewater treatment facility of a kraft pulp bleaching plant. Rhodococcus sp. strain CG-1 and Mycobacterium sp. strain CG-2, isolated from tetrachloroguaiacol enrichment, and Rhodococcus sp. strain CP-2, isolated from pentachlorophenol enrichment, mineralized pentachlorophenol and degraded several other polychlorinated phenols, guaiacols (2-methoxyphenols), and syringols (2,6-dimethoxyphenols) at micromolar concentrations and were sensitive to the toxic effects of pentachlorophenol. All three strains initiated degradation of the chlorophenols by para-hydroxylation, producing chlorinated para-hydroquinones, which were then further degraded. Parallel to degradation, strains CG-1, CG-2, and CP-2 also O-methylated nearly all chlorinated phenols, guaiacols, syringols, and hydroquinones. O-methylation of chlorophenols was a slow reaction compared with degradation. The preferred substrates of the O-methylating enzyme(s) were those with the hydroxyl group flanked by two chlorine substituents. O-methylation was constitutively expressed, whereas degradation of chlorinated phenolic compounds was inducible.

Anisoles↗
PubMed1986

Excretion of metabolites of hexachlorobenzene in the rat and in man.

From the urine of rats treated with hexachlorobenzene (HCB), 21 metabolites were separated by capillary gas chromatography. Sulfur-containing metabolites were present in larger numbers and greater amounts than phenolic compounds. In studies on the origin of pentachlorophenol in man, HCB was determined in adipose tissue and pentachlorophenol in urine, and in 48 out of 60 females, 80-90% of the daily urinary pentachlorophenol appeared to be formed from HCB.

Adult↗
PubMed1990

Induction of prophage lambda by chlorophenols.

Chlorinated phenols, which are used primarily as wood preservatives and fungicides, are present in most air, water, and soil samples in industrialized areas as well as in the urine of most people. We have examined the ability of phenol and the 19 isomers of chlorophenol to induce DNA damage using the Microscreen prophage-induction assay in Escherichia coli. Seven of the isomers (2,3,4,-tri, 2,4,5-tri, 3,4,5-tri, 2,3,4,5-tetra, 2,3,6-tri, 2,4,6-tri, and pentachlorophenol) induced prophage lambda in the presence of S9, with the first three being approximately 10 times more potent than the last three. The more potent isomers have either one or no chlorine atom ortho to the OH group; whereas the less potent isomers have two chlorine atoms ortho to the OH group. Although none of the 20 compounds is mutagenic in Salmonella, the prophage-induction results agree with findings by others that most of these seven isomers are clastogenic, are associated with cancer and chromosomal aberrations in humans (pentachlorophenol), and are carcinogenic in rodents (2,4,6-tri and pentachlorophenol). A likely basis for the genotoxicity of the seven isomers involves the metabolism of the parent isomer to a chlorohydroquinone, which can form a chlorobenzosemiquinone in the presence of oxygen. These two metabolites can produce free radicals that can cause DNA strand breaks, resulting in prophage induction in E. coli or, possibly, the chromosomal aberrations/cancer associated with human exposure to chlorophenols.

Bacteriophage lambda↗
PubMed2002

Lethal body residue of chlorophenols and mixtures of chlorophenols in benthic organisms.

The lethal body residue (LBR) of a few chlorophenol congeners were measured in the oligochaete worm Lumbriculus variegatus, and the LBR of pentachlorophenol was measured also in a midge, Chironomus riparius larvae. LBR is defined as the concentration of the compound in the organism, on molar basis, to cause death, and the LBR(50) is defined as the calculated LBR value to cause a 50% mortality in population after a given time. Groups of 30 or 40 organisms were exposed to different chlorophenol concentrations in artificial soft fresh water to achieve differential mortality. Exposure times were either 24 h or 48 h. In addition to exposures with individual congeners, mixtures of chlorophenols were also tested. After each exposure, the surviving organisms were collected and the body burden of chlorophenols was measured by gas chromatography with electron capture detection. The measured body burden was related to the percent mortality in the group. The trichlorophenols and pentachlorophenol have a 48-h LBR(50) of 0.45-0.66 micromol/g wet weight in L. variegatus. The 48-h LBR(50) of pentachlorophenol for C. riparius was 0.15 micromol/g wet weight, indicating a slight difference in the sensitivity of these two species. The 48-h LBR(50) of 2,3,4,6-tetrachlorophenol is 0.91 micromol/g wet weight, and the value for 2,6-dichlorophenol is 1.2 micromol/g wet weight in L. variegatus. The 48-h LBR(50)s of the chlorophenol mixtures ranged from 0.50 to 0.83 micromol/g wet weight, demonstrating an additive toxicity.

Animals↗
PubMed1989

The presence of chlorophenols and their conjugates in Finnish human adipose and liver tissues.

The concentrations of 2,4,6-trichlorophenol, 2,3,4,6-tetrachlorophenol, pentachlorophenol and their conjugates were analysed in tissues of 58 people from the southern and northern parts of Finland, none of whom were known to be occupationally exposed. The tissue samples consisted of 44 adipose and 13 liver samples. The ages of the donors varied from 3 months to 91 years. Only very small residues of chlorophenols were found: the median concentration of tetra- or pentachlorophenol in adipose tissue samples was 0.002 micrograms g-1 fat, ranging from a trace amount to 0.031 micrograms g-1, while none of the samples contained measurable amounts of trichlorophenol. In liver samples, the median concentration of pentachlorophenol was 0.004 micrograms g-1. Only two liver samples were positive for tetrachlorophenol and none for trichlorophenol. The age, smoking habit or fish intake of the donor did not have any relation to the chlorophenol concentration found in the tissue sample.

Adipose Tissue↗
PubMed1976

Screening by negative chemical ionization mass spectrometry for environmental contamination with toxic residues: Application to human urines.

A screening procedure based on solvent extraction with minimal clean up followed by examination with negative chemical ionization mass spectrometry has been developed for organochlorine residues and related compounds with masses greater than 130 daltons. The procedure has been made quantitative for analysis of pentachlorophenol residues. A limited survey of human urines indicated extensive contamination of the subjects, studied at parts per billion and higher levels, with pentachlorophenol, 2, 4, 5-trichlorophenoxy acetic acid, other polychlorophenoxy acids, and numerous unknown compounds. In an attempt to define the source of the contamination, the screening procedure was applied to samples of environmental substrates. The results suggest the food chain as one significant source of the contamination. A preliminary study of organochlorine compounds in human seminal fluid showed pentachlorophenol and other organochlorine residues in every sample, a result which suggests that this area may merit additional monitoring.

Humans↗
PubMedDate not supplied

Organochlorine and organophosphorus residues in the fat of domestic farm animal species, Ontario, Canada 1986-1988.

During the period 1986-1988 a total of 602 samples of animal products were analysed for organochlorine and organophosphorus pesticides and industrial organic pollutants. Samples of abdominal fat were collected from avian, bovine, caprine, lupine, ovine and porcine species together with hen eggs. The following six compounds were identified in animal tissues: DDE, dieldrin, lindane, PCB, pentachlorophenol and tetrachlorophenol. Pentachlorophenol was the most frequently found contaminant, being identified in 35% of samples, and DDE was the second in 21%. All other contaminants were present in less than 10% of samples. The residues of all six compounds detected were added to give a combined residue. Forty-three per cent of samples had non-detectable residues. A further 31% had combined residues adding to less than 0.01 mg/kg. The highest combined residues ranged between 0.1 and 1.0 mg/kg and were present in 2.8% of samples. One egg sample had a residue of 0.16 mg/kg that exceeded the 0.1 mg/kg maximum residue limit for pentachlorophenol. Residues of chlordane and its metabolites, heptachlor and its epoxide, endosulphan and its sulphate metabolite, dicofol, HCB and mirex were below their detection limits in all samples and no residues of the organophosphorus insecticide listed as applied to livestock were found in meat, fat or egg tissues.

Abdomen↗
PubMed2000

Responses of transgenic mouse lines p53(+/-) and Tg.AC to agents tested in conventional carcinogenicity bioassays.

The haplo-insufficient p53 knockout (p53+/-) and zetaglobin v-Ha-ras (Tg.AC) transgenic mouse models were compared to the conventional two rodent species carcinogen bioassay by prospectively testing nine chemicals. Seven of the chemicals classified as carcinogens in the conventional bioassay induced tumors in the liver or kidneys of B6C3F1 mice, and one (pentachlorophenol) also induced tumors in other tissues. Only three chemicals, furfuryl alcohol, pyridine, and pentachlorophenol, induced tumors in rats. The tumorigenic effect of pyridine was seen in F344 rats but not in Wistar strain rats. None of the chemicals induced tumors in the p53+/- transgenic mice, which is consistent with the absence of genotoxicity of these chemicals. Only two of the seven nongenotoxic carcinogens were positive in the Tg.AC model (lauric acid diethanolamine and pentachlorophenol). These results show that these transgenic models do not respond to many chemicals that show strain- or species-specific responses in conventional bioassays.

Administration, Oral↗
PubMed1997

Environmental xenobiotics may disrupt normal endocrine function by interfering with the binding of physiological ligands to steroid receptors and binding proteins.

The disruption of the reproductive system of male and female animals in the wild has been attributed to environmental chemicals (xenobiotics). The effects seen mirror alterations one might anticipate if the steroid hormone-dependent processes that regulate these systems were impaired. To determine whether xenobiotics (present at a concentration of 100 microM) exert their action through steroid-mediated pathways, we examined their ability to inhibit the binding of [3H]physiological ligands (present at a concentration of 7 nM) to the androgen and estrogen receptors, rat androgen-binding protein (ABP), and human sex hormone-binding globulin (hSHBG). The gamma- and delta-isomers of hexachlorocyclohexane, congeners of dichlorodiphenyl-trichloroethane (DDT; p,p'-DDT; p,p'-DDE; o,p'-DDT), dieldrin, atrazine, and pentachlorophenol, caused a statistically significant inhibition of specific binding of [3H]5 alpha-DHT to the androgen receptor that ranged from 100% (p,p'-DDE) to 25% (dieldrin). Methoxychlor, o,p'-DDT1, pentachlorophenol, and nonylphenol significantly reduced [3H]17 beta-estradiol binding to the estrogen receptor by 10, 60, 20, and 75%, respectively. The binding of [3H]5 alpha-DHT to ABP was inhibited 70% by the delta-isomer of hexachlorocyclohexane, but the gamma-isomer did not reduce binding significantly. Methoxychlor, p,p'-DDT, atrazine, and nonylphenol reduced [3H]5 alpha-DHT binding to ABP by approximately 40%. Nonylphenol reduced the binding of [3H]5 alpha-DHT to hSHBG by 70%. Hexachlorocyclohexane reduced [3H]5 alpha-DHT binding to hSHBG by 20%, but the stereospecific effects observed with ABP did not occur. o,p'-DDT and pentachlorophenol resulted in a statistically significant 20% inhibition of [3H]5 alpha-DHT binding to hSHBG. Some xenobiotics resulted in dissociation of [3H]ligands from their binding proteins that was statistically identical to that caused by the unlabeled natural ligand, whereas others resulted in slower or more rapid dissociation rates.

Androgen-Binding Protein↗