The genetic toxicity of 3,3′,4,4′-tetrachloroazobenzene and 3,3′,4,4′-tetrachloroazoxybenzene: discordance between acute mouse bone marrow and subchronic mouse peripheral blood micronucleus test results

3,3′,4,4′-Tetrachloroazobenzene (TCAB) and 3,3′,4,4′-tetrachloroazoxybenzene (TCAOB) are dioxin-like chemicals that were investigated for toxicity in 13-week gavage studies in male and female B6C3F₁ mice and F344N rats by the National Toxicology Program. As part of the comprehensive toxicological investigation of these chemicals, peripheral blood smears from mice treated 5 days per week for 13 weeks with 0.1–30 mg/kg/day TCAB or TCAOB were analyzed for the frequency of micronucleated (MN) normochromatic erythrocytes (NCE). Both chemicals produced significant increases in MN-NCE in male and female mice. In contrast to these positive results in subchronic exposure studies, no significant increases were seen in acute bone marrow MN tests in male mice administered three daily injections of 50–200 mg/kg/day TCAB and TCAOB. The results with TCAB and TCAOB suggest that the routine integration of MN tests with subchronic toxicity studies may allow detection of mutagenic activity for some chemicals that fail to elicit responses in short-term, high dose tests. In addition, the integration of mutagenicity tests into general toxicity tests reduces the use of laboratory animals and the cost of the testing.     

3,3',4,4'-tetrachlorobiphenyl: metabolism by the chick embryo in ovo and toxicity of hydroxylated metabolites

The metabolism of 3,3',4,4'-tetrachlorobiphenyl (TCB) has been studied in the chicken in ovo by analysis of bile from chick embryos. Four percent of the [14C]TCB dose injected into the air sac on day 13 of incubation was detected in the bile by day 19. An increase of more lipophilic TCB metabolites was observed by HPLC analysis after hydrolysis of the bile. TCB and three phenolic TCB metabolites were identified and quantified in the hydrolyzed bile: TCB (14 ng/gall bladder), 5-hydroxy-3,3',4,4'-tetrachlorobiphenyl (234 ng/gall bladder), 4-hydroxy-3,3',4',5-tetrachlorobiphenyl (45 ng/gall bladder) and 2-hydroxy-3,3',4,4'-tetrachlorobiphenyl (3 ng/gall bladder). The presence of two other TCB metabolites in the bile, a dihydroxy-tetrachlorobiphenyl and a dihydroxy-trichlorobiphenyl was also indicated. The method used in the present study is well suited for studies of metabolism in avian embryos in ovo. The three TCB metabolites identified all proved to be at least two orders of magnitude less toxic than TCB in a chick embryo test. These metabolites were also shown to bind with significantly lower affinity than TCB to the Ah receptor. TCB, 5-hydroxy-3,3',4,4'-tetrachlorobiphenyl, 4-hydroxy-3,3',4',5-tetrachlorobiphenyl and 2-hydroxy-3,3',4,4'-tetrachlorobiphenyl gave Kd values of 16, 33, 45 and 37 nM, respectively, in the Ah receptor test.     

Effect of 3,3',5' triiodo-L-Thyronine (rT3) on the serum concentration of thyroid hormones in rats

50, 100 or 150 micrograms/100 g body weight/day of very pure 3,3',5' triiodo-L-thyronine (rT3), obtained from a new synthetic method, was intraperitoneally administered in male Wistar rats for 5 weeks. Serum total thyroxine (T4), free thyroxine (FT4) and total 3,5,3' triiodo-L-thyronine (T3) concentrations were increased with all the doses of rT3. Free T3 (FT3) was also but non-significantly elevated. Different assumptions are put forward in order to explain this rT3 effect.     

Influence of Feeding Schedule on Chronopharmacological Aspects of Gentamicin in Mice

The effects of the time of day of drug administration on the subchronic toxicity and pharmacokinetics of gentamicin, as well as the role of feeding schedule on circadian rhythms, were investigated in mice. ICR male mice were housed in a light-dark (LD) cycle (12:12) with food and water ad libitum (ALF) or under a time-restricted feeding (TRF) schedule (feeding time: 8 h during the light phase) for 1 day or 14 days before drug administration. The animals were given a single subcutaneous dose of gentamicin 180 mg/kg for the kinetic studies and subcutaneous doses of gentamicin 180 mg/kg/day for 14 days or 220 mg/kg/day for 18 days for the subchronic toxicity studies. A significant dosing-time dependency was shown for mortality and body weight loss, with higher values at midlight and lower ones at the middark (p > 0.05). A significant circadian rhythm was also found for gentamicin kinetics in ALF mice, with the highest clearance at middark and the lowest one at midlight (p > 0.01). The kinetic rhythm of gentamicin coincided well with the toxicity rhythm of the drug. The TRF schedule had a marked influence on the rhythms of gentamicin kinetics and toxicity, showing lowest clearance and higher toxicity at middark. The rhythm of subchronic toxicity of gentamicin seems to be due, at least in part, to the rhythm in kinetics and is strongly influenced by the feeding schedule. Thus, the timing of dosing is an important factor in the kinetics and the subchronic toxicity of gentamicin administration in mice, and the manipulation of feeding schedule can modify the rhythm of the toxicity by changing the rhythm of gentamicin kinetics.     

Increased retinoic acid metabolism following 3,3',4,4',5,5'-hexabromobiphenyl injection

Young male Wistar rats received single i.p. injections of 3,3',4,4',5,5'-hexabromobiphenyl. In rats dosed with 40 mg/kg, food consumption and growth as well as liver retinol and retinyl palmitate concentrations decreased, while serum retinol and liver weight increased within 28 days following the injection. In rats receiving a 20-mg/kg dose, food consumption, growth, liver weight, and serum retinol were not affect, although liver retinol and retinyl palmitate concentrations declined to 23 and 21% of their respective control values. Vitamin A metabolism was studied in liver microsomes prepared from rats sacrificed 7 days after the 20-mg/kg injection. The rate of retinoic acid hydroxylation via the cytochrome P-450 system to 4-hydroxyretinoic acid plus the subsequent oxidation to 4-ketoretinoic acid was significantly elevated. Retinoic acid conjugation by UDP-glucuronyl transferase was also significantly increased. These changes corresponded with increased activities of cytochrome P-450-dependent aryl hydrocarbon hydroxylase and UDP-glucuronyltransferase conjugation of p-nitrophenol. These results provide a direct link between enzyme induction due to xenobiotics and specific steps in the vitamin A metabolic pathway.     

Increased thyroxine turnover after 3,3',4,4',5,5'-hexabromobiphenyl injection and lack of effect on peripheral triiodothyronine production

Juvenile male Wistar rats were injected i.p. with 0, 20, or 40 mg/kg 3,3',4,4',5,5'-hexabromobiphenyl and blood samples collected periodically up to 28 days. A dose-dependent depression of the serum thyroxine level was detected, while the circulating triiodothyronine concentration was not affected by the biphenyl congener. Thyroxine turnover in vivo 7 days after injection of the 20 mg/kg dose revealed significant increases of various clearance parameters relative to controls. The fractional clearance rate (day-1) increased by 84%, the daily metabolic clearance rate (mL.kg-1.day-1) increased by 128%, and the daily thyroxine disposal rate (ng.kg-1.day-1) increased by 41%. Also, the thyroxine distribution space (mL/kg) increased by 21%. These results indicated greater thyroxine binding in major organs as well as a marked increase in the peripheral metabolism of thyroxine. The increased thyroxine metabolism is explained by a 4.8-fold induction of uridine 5'-diphosphoglucuronyltransferase activity in liver microsomes. The type I 5'-deiodinase activity in liver homogenates and endogenous concentrations of the cofactor for this reaction, glutathione, were not affected by the biphenyl. This result means that homeostatic mechanisms involving thyroxine conversion to triiodothyronine do not explain the maintenance of serum T3 under these conditions.     

Chiral overcrowded alkenes; asymmetric synthesis of (3S,3'S)-(M, M)-(E)-(+)-1,1',2,2',3,3',4,4'-octahydro-3,3',7,7'-tetramethyl-4, 4'-biphenanthrylidenes

An asymmetric synthesis route towards (3S,3'S)-(M,M)-(E)-(+)-1,1',2, 2',3,3',4,4'-octahydro-3,3',7,7'-tetramethyl-4,4'-biphenanthrylidene was developed using the Evans procedure as a key step. The absolute configurations of the title compound and of its parent ketone were determined by CD spectroscopy and could be correlated with the stereochemical results of the asymmetric alkylation. Furthermore, a comparison was made with the known (3R,3'R)-(P,P)-(E)-(-)-1,1',2,2', 3,3',4,4'-octahydro-3,3',7,7'-dimethyl-4,4'-biphenanthrylidene. Finally, the X-ray crystallographic analysis of (3S,3'S)-(M, M)-(E)-(+)-1,1',2,2',3,3',4,4'-octahydro-3,3',7,7'-tetramethyl-4, 4'-biphenanthrylidene is presented.     

Simultaneous determination of 3,3',4',5,7-pentamethylquercetin and its possible metabolite 3,3',4',7-tetramethylquercetin in dog plasma by liquid chromatography-tandem mass spectrometry and its application to preclinical pharmacokinetic study

A sensitive, simple and rapid ultra fast liquid chromatography (UFLC)-ESI-MS/MS method was established for the simultaneous determination of 3,3',4',5,7-pentamethylquercetin (PMQ) and its possible metabolite 3,3',4',7-tetramethylquercetin (TMQ) in dog plasma using 4',5,7-trimethylapigenin (TMA) as the internal standard. The plasma sample was pretreated with acetonitrile for protein precipitation and the analytes were separated on an Ultimate XB-CN column (5 μm, 2.1 mm × 150 mm) with the mobile phase consisting of acetonitrile and water (2:1, v/v). Detection was performed on a triple-quadrupole tandem mass spectrometer under a positive multiple reaction-monitoring mode (MRM). The mass transition ion-pair was followed as m/z 373.1-312.1 for PMQ, 359.1-344.0 for TMQ and 313.1-298.1 for TMA. The validated concentration ranged from 1.272 to 3060 ng/mL for PMQ and from 10.35 to 1725 ng/mL for TMQ. The lower limit of quantifications for PMQ and TMQ were 1.272 ng/mL and 10.35 ng/mL, respectively. The developed-method was successfully applied for the pharmacokinetic study of PMQ and its metabolite TMQ in dogs following a single oral dose.     

Structural basis of species differences between human and experimental animal CYP1A1s in metabolism of 3,3',4,4',5-pentachlorobiphenyl

Coplanar polychlorinated biphenyls included in dioxin-like compounds are bio-accumulated and adversely affect wildlife and human health. Although many researchers have studied the metabolism of PCBs, there have been few reports of the in vitro metabolism of 3,3',4,4',5-pentachlorobiphenyl (PCB126), despite the fact that it has the highest toxicity among PCB congeners. Cytochrome P450 (CYP) 1A1 proteins can metabolize some dioxins and PCBs by hydroxylation, but the activities of human and rat CYP1A1 proteins are very different. The mechanism remains unclear. From our results, rat CYP1A1 metabolized PCB126 into 4-OH-3,3',4',5-tetrachlorobiphenyl and 4-OH-3,3',4',5,5'-pentachlorobiphenyl, but human CYP1A1 did not metabolize. Homology models of the two CYP proteins, and docking studies, showed that differences in the amino acid residues forming their substrate-binding cavities led to differences in the size and shape of the cavities; only the cavity of rat CYP1A1 allowed PCB126 close enough to the haem to be metabolized. Comparison of the amino acid residues of other mammalian CYP1A1 proteins suggested that rats have a unique metabolism of xenobiotics. Our results suggest that it is necessary to be careful in human extrapolation of toxicity data estimated by using the rat as an experimental animal, especially in the case of compounds metabolized by CYP1A1.     

Comparison of particulate 3,3',5,5'-tetramethylbenzidine and 3,3'-diaminobenzidine as chromogenic substrates for immunoblot

In horseradish peroxidase (EC: 1.11.1.7)-dependent immunoblot assays, particulate 3,3',5,5'-tetramethylbenzidine (TMB) is shown to be a more efficient immunoblot substrate than the standard substrate 3,3'-diaminobenzidine (DAB), because TMB is easily prepared, stable, and less carcinogenic than is DAB. Assays of antibody in a serially diluted human immunodeficiency virus (HIV) control serum (CDC reference CAT# VS2151) have the same sensitivity limits with both DAB and TMB (1:312,500). Complete, working substrate solutions of H2O2/TMB/enhancer and of H2O2/DAB were stored at room temperatures and at 48 degrees C respectively. Periodic tests showed the TMB substrate system to be functional after four weeks at 48 degrees C and after eight weeks at room temperature, while the DAB system was functional after one week at 48 degrees C and after four weeks at room temperature. The stability, safety, and convenience of the commercially available TMB kits make this substrate ideal for immunoblot tests.     

Effect of dietary selenium on the promotion of hepatocarcinogenesis by 3,3', 4,4'-tetrachlorobiphenyl and 2,2', 4,4', 5,5'-hexachlorobiphenyl

Polychlorinated biphenyls (PCBs) are persistent organic pollutants that have promoting activity in the liver. PCBs induce oxidative stress, which may influence carcinogenesis. Epidemiological studies strongly suggest an inverse relationship between dietary selenium (Se) and cancer. Despite evidence linking Se deficiency to hepatocellular carcinoma and liver necrosis, the underlying mechanisms for Se cancer protection in the liver remain to be determined. We examined the effect of dietary Se on the tumor promoting activities of two PCBs congeners, 3,3', 4,4'-tetrachlorobiphenyl (PCB-77) and 2,2', 4,4', 5,5'-hexachlorobiphenyl (PCB-153) using a 2-stage carcinogenesis model. An AIN-93 torula yeast-based purified diet containing 0.02 (deficient), 0.2 (adequate), or 2.0 mg (supplemental) selenium/kg diet was fed to Sprague-Dawley female rats starting ten days after administering a single dose of diethylnitrosamine (150 mg/kg). After being fed the selenium diets for 3 weeks, rats received four i.p. injections of either PCB-77 or PCB-153 (150 micromol/kg) administered every 14 days. The number of placental glutathione S-transferase (PGST)-positive foci per cm(3) and per liver among the PCB-77-treated rats was increased as the Se dietary level increased. Unlike PCB-77, rats receiving PCB-153 did not show the same Se dose-response effect; nevertheless, Se supplementation did not confer protection against foci development. However, the 2.0 ppm Se diet reduced the mean focal volume, indicating a possible protective effect by inhibiting progression of preneoplastic lesions into larger foci. Cell proliferation was not inhibited by Se in the liver of the PCB-treated groups. Se did not prevent the PCB-77-induced decrease of hepatic Se and associated reduction in glutathione peroxidase (GPx) activity. In contrast, thioredoxin reductase (TrxR) activity was not affected by the PCBs treatment or by Se supplementation. These findings indicate that Se does not inhibit the number of PGST-positive foci induced during promotion by PCBs, but that the size of the lesions may be inhibited. The effects of Se on altered hepatic foci do not correlate with its effects on GPx and TrxR.     

Vitamin A metabolism in rats chronically treated with 3,3',4,4',5,5'-hexabromobiphenyl

Chronic dietary administration of 3,3',4,4',5,5'-hexabromobiphenyl (HBB), 1 mg/kg diet, caused a decrease in retinol (20-fold) and retinyl esters (23-fold) in the livers of female rats, but resulted in a 6.4-fold increase in retinol and 7.4-fold increase in retinyl esters in the kidneys. Liver acyl-CoA:retinol acyltransferase and retinyl palmitate hydrolase activities were reduced while serum concentration of retinol was unaffected by HBB feeding. Metabolism of a physiological dose of [11-3H]retinyl acetate (10 micrograms), was examined in rats fed either vitamin A-adequate diet, or marginal amounts of vitamin A, or vitamin A-adequate diet containing HBB. A 13-fold greater amount of the administered vitamin A was found in kidneys of HBB-treated rats. In rats fed adequate or low amounts of vitamin A, kidney radioactivity was primarily in the retinol fraction, while in HBB-fed rats the radioactivity was associated mostly with retinyl esters. Fecal and urinary excretion of radioactivity was greatly increased in HBB-treated rats. Chronic HBB feeding results in a loss of ability of liver to store vitamin A, and severely alters the uptake and metabolism of vitamin A in the kidneys. We conclude that HBB causes major disturbances in the regulation of vitamin A metabolism.     

3,3',4,4',5-Pentachlorobiphenyl (PCB 126) impacts hepatic lipid peroxidation, membrane fluidity and beta-adrenoceptor kinetics in chick embryos

Polychlorinated biphenyls (PCB) and other aryl hydrocarbon receptor (AHR) agonists induce oxidative stress and alter membrane lipid peroxidation and fluidity. This study tested the hypothesis that PCB-induced changes in membrane properties impact membrane beta-adrenoceptor (beta-AR) affinity and capacity in chick embryo hepatocytes. Embryos were injected into the air cell with 1.6 microg 3,3',4,4',5-pentachlorobiphenyl (PCB 126)/kg egg at day 0, and incubated to day 19 when livers were removed. This dose resulted in hepatic PCB 126 levels of 0.67 ng/g liver or 10.2 ng/g liver lipid; levels in untreated embryos were non-detectable. Hepatic microsomal EROD activity was elevated by approximately 12-fold and embryo mortality was significantly increased compared with the untreated group. Hepatic lipid peroxidation increased and membrane order (steady-state fluorescence anisotropy values) decreased with in ovo PCB 126 exposure. Consistent with changes in membrane structure, hepatic beta-AR affinity for CGP 12177 significantly decreased (Kd increased) without changes in receptor numbers. This study demonstrates that in ovo exposure to PCB 126 in chick eggs significantly impacted embryo survival, and this was correlated with altered hepatic membrane structure and ultimately membrane function.     

The interaction of 3,3',4',5-tetrachlorosalicylanilide with phosphatidylcholine bilayers.

1. The interaction of the germicide 3,3',4',5-tetrachlorosalicylanilide (T4CS) with vesicles and dispersions of egg phosphatidylcholine has been studied by gel permeation chromatography, electron microscopy, electron spin resonance spin labelling and ion permeability measurements. 2. Incorporation of T4CS into vesicles of egg phosphatidylcholine gives rise to a large increase in the permeability rate of the paramagnetic cation N,N-dimethyl-N-(1'-oxyl-2',2',6',6'-tetramethyl-4'-piperidyl)-2-hydroxyethylammonium chloride through the lipid bilayer but has no significant effect on the vesicle sizes as measured by gel permeation chromatography or electron microscopy. 3. ESR studies using a spin-labelled fatty acid have demonstrated the presence of two different environments for the spin label when T4CS is incorporated into phosphatidylcholine bilayers. These two environments are identified as (a) highly ordered areas of the bilayer, rich in T4CS and (b) areas with very similar ordering to that in pure egg phosphatidylcholine. 4. The effectiveness of very low concentrations of the germicide in increasing vesicle permeability is explained in terms of its clustering to give rigid patches, rich in T4CS, rather than being evenly distributed throughout the bilayer. It is proposed that the increased ion permeability arises from leakage at the interfaces between the rigid and flexible regions of the lipid bilayer. 5. Comparisons between the effective levels of T4CS in phosphatidylcholine vesicles and its minimum inhibitory concentration with a Gram-positive bacterium confirm the validity of phospholipid vesicles as a model for studies of germicidal activity.     

Gas-liquid chromatographic determination of the distribution of 3,3',4,4'-tetrachlorobiphenyl in the adult female rat following short-term oral administration

A gas-liquid chromatographic assay using electron-capture detection was developed for the quantitation of 3,3',4,4'-tetrachlorobiphenyl (TCBP) in the serum, urine, brain, liver, adipose tissue, and feces of the rat. The sample preparation involves extraction of 3,3',4,4'-TCBP with hexane under neutral or alkaline conditions (and washing with concentrated acid for feces only). Aqueous standards are used for calibration of the assay, except for adipose tissue. The lower limit of quantitative sensitivity of the assay for 3,3',4,4'-TCBP is 25 ng/mL for serum and urine and 125 ng/g for brain, liver, adipose tissue, and feces, which can be extended to 5 ng/mL and 25 ng/g, respectively, by analyzing a larger aliquot of the hexane extract. The overall accuracy is greater than 95% for serum, urine, brain and feces and 86% for liver, and the within-day coefficient of variation does not exceed 8.6%. 3,3',4,4'-TCBP was administered orally to adult, female, Sprague-Dawley rats in the dosage regimens: 0.2, 0.5 and 2 mg X kg-1 X day-1 for 10 days and 5 mg X kg-1 X day-1 for 4 days. 3,3',4,4'-TCBP distributed preferentially into adipose tissue and liver, where the xenobiotic concentration was greater in adipose tissue. The adipose tissue and hepatic 3,3',4,4'-TCBP concentrations were dependent on both the absolute dose and dosing schedule of the xenobiotic. Only trace concentrations, usually below the lower limit of quantitation, were detected in the serum, brain and kidney. Fecal excretion of 3,3',4,4'-TCBP was greater than urinary excretion for the 5 mg X kg-1 X day-1 X 4-day regimen.     

Effect of 3,3',4',5-tetrachlorosalicylanilide on reduction of excess sludge and nitrogen removal in biological wastewater treatment process

A metabolic uncoupler, 3,3',4',5-tetrachlorosalicylanilide (TCS), was used to reduce excess sludge production in biological wastewater treatment processes. Batch experiments confirmed that 0.4 mg/l of TCS reduced the aerobic growth yield of activated sludge by over 60%. However, the growth yield remained virtually constant even at the increased concentrations of TCS when cultivations were carried out under the anoxic condition. Reduction of sludge production yield was confirmed in a laboratory-scale anoxic-oxic process operated for 6 months. However, it was found that ammonia oxidation efficiency was reduced by as much as 77% in the presence of 0.8 mg/l of TCS in the batch culture. Similar results were also obtained through batch inhibition tests with activated sludges and by bioluminescence assays using a recombinant Nitrosomonas europaea (pMJ217). Because of this inhibitory effect of TCS on nitrification, the TCS-fed continuous system failed to remove ammonia in the influent. When TCS feeding was stopped, the nitrification yield of the process was resumed. Therefore, it seems to be necessary to assess the nitrogen content of wastewater if TCS is used for reducing sludge generation.     

Computational study of conformational and chiroptical properties of (2R,3S,4R)-(+)-3,3',4,4',7-flavanpentol

Conformational analysis of (2R,3S,4R)-(+)-3,3',4,4',7-flavanpentol, a flavonoid compound displaying both antioxidant and pro-oxidant properties, is performed by molecular mechanics and density functional theory calculations both in the gas phase and in methanol solution by using the Polarizable Continuum Model. Nine different conformations are identified. Absorption (UV) and circular dichroism (CD) spectra and optical rotations are calculated by means of time dependent density functional theory (TDDFT) and compared with experiments. The effects of a complex environment formed by water and proline-rich peptide molecules on the conformational characteristics of (2R,3S,4R)-(+)-3,3',4,4',7-flavanpentol and therefore on its UV and CD spectra are investigated by atomistic molecular dynamics simulations.     

Mix-G200益生菌粉安全性毒理学评价

目的通过对Mix-G200益生菌粉的安全性毒理学进行研究,为以后的应用提供科学依据。方法采用雌雄小鼠急性毒性试验、小鼠骨髓细胞微核试验、小鼠精子畸形试验、Ames试验和大鼠30天喂养试验等对Mix-G200益生菌粉进行安全性试验研究。结果急性经口毒性试验表明,Mix-G200益生菌粉对雌雄小鼠的急性经口LD50均大于21500 mg/kg,以急性毒性半数致死量毒性分级,属无毒级物质。小鼠骨髓细胞微核试验、小鼠精子畸形试验、Ames试验结果均为阴性。30天喂养试验结果表明,大鼠生长情况良好,血液学检查、生化学检查、主要脏体以及组织学检查结果与对照组相比,差异均无统计学意义。结论 Mix-G200益生菌粉未见遗传毒性,使用Mix-G200益生菌粉是安全可靠的。     

Degradation of 4,4'-dichlorobiphenyl, 3,3',4,4'-tetrachlorobiphenyl, and 2,2',4,4',5,5'-hexachlorobiphenyl by the white rot fungus Phanerochaete chrysosporium.

The white rot fungus Phanerochaete chrysosporium has demonstrated abilities to degrade many xenobiotic chemicals. In this study, the degradation of three model polychlorinated biphenyl (PCB) congeners (4,4'-dichlorobiphenyl [DCB], 3,3',4,4'-tetrachlorobiphenyl, and 2,2',4,4',5,5'-hexachlorobiphenyl) by P. chrysosporium in liquid culture was examined. After 28 days of incubation, 14C partitioning analysis indicated extensive degradation of DCB, including 11% mineralization. In contrast, there was negligible mineralization of the tetrachloro- or hexachlorobiphenyl and little evidence for any significant metabolism. With all of the model PCBs, a large fraction of the 14C was determined to be biomass bound. Results from a time course study done with 4,4'-[14C]DCB to examine 14C partitioning dynamics indicated that the biomass-bound 14C was likely attributable to nonspecific adsorption of the PCBs to the fungal hyphae. In a subsequent isotope trapping experiment, 4-chlorobenzoic acid and 4-chlorobenzyl alcohol were identified as metabolites produced from 4,4'-[14C]DCB. To the best of our knowledge, this the first report describing intermediates formed by P. chrysosporium during PCB degradation. Results from these experiments suggested similarities between P. chrysosporium and bacterial systems in terms of effects of congener chlorination degree and pattern on PCB metabolism and intermediates characteristic of the PCB degradation process.     

Acute and sub-acute toxicity of an insect pheromone, N-heneicosane and combination with insect growth regulator, diflubenzuron, for establishing no observed adverse effect level (NOAEL)

Aedes aegypti mosquito is one of the most notorious vectors of dangerous diseases like dengue hemorrhagic fever and chikangunya. One method of control of the vectors is by the use of semiochemicals or pheromones. The pheromone n-heneicosane (C21) has been proved to be effective in attracting the female Aedes aegypti to lay eggs in the treated water and the growth of the larva is controlled by insect growth regulator diflubenzuron (DB). This study was planned to assess the safety of C21 alone and the combination with DB. Acute toxicity tests were carried out using two doses, viz., 1600 and 3200 mg/kg and two routes of exposure oral and intra-peritoneal. Dermal toxicity test was carried out in both male and female rats at the dose of 3200 mg/kg. Primary skin irritation test was carried out in rabbits. Sub-acute (90 days) dermal toxicity studies in male and female rats at the dose of 1 and 2 mg/kg via the per-cutaneous route were also studied. Sub-acute (90 days) toxicity test through the oral route was carried out, at doses 125, 250 and 500 mg/kg in male and female rats. The calculated LD50 by ip route and dermal route was more than 5 g/kg in mouse and rats of both the sexes. In the primary skin irritation test no significant changes were noted. In the sub-acute toxicity studies even 500 mg/kg dose was not able to produce toxic response in rats when they were dosed daily for 90 days. The established no observed adverse effect level (NOAEL) was more than 500 mg/kg.