Methods for measuring mutagenicity in urine of rats dosed with [14C]di(2-ethylhexyl)phthalate.

Di(2-ethylhexyl)phthalate (DEHP) is extensively used as a plasticizer for vinyl plastic articles. It has been found to be positive in an NCI rodent bioassay but has generally given negative results in in vitro genotoxicity tests. We therefore decided to test the urine of rats fed [14C]DEHP for mutagenic activity in the Ames Salmonella test. The recovery of radioactivity from the urine of rats dosed with [14C]DEHP was examined by solvent extraction and XAD-2 resin absorption procedures. Both of these procedures were inadequate for quantitative recovery of urinary metabolites required for subsequent mutagenicity testing using the Ames Salmonella/microsome procedure. Recoveries of less than 5% were observed using standard solvent extraction techniques whereas the XAD-2 adsorption technique gave about 67% at high resin/urine ratios. Treatment of the urine with beta-glucuronidase/aryl sulfatase did not affect these recoveries. The direct urine plating procedure represents a viable alternative to the above concentration procedures for this phthalate ester. The effects of L-histidine and the beta-glucuronidase/aryl sulfatase preparation on the background reversion frequencies of the Ames tester strains is discussed.

Bacterial mutagenicity testing of urine from rats dosed with 2-ethylhexanol derived plasticizers.

Di-(2-ethylhexyl)phthalate (DEHP) produced hepatocellular carcinomas in rodents at high doses in a NTP/NCI bioassay. DEHP has not shown evidence of genotoxic activity in in vitro mutagenicity tests. We extended these studies by examining the mutagenicity of urine from rats dosed with DEHP, 2-ethylhexanol (2-EH), and several other 2-EH derived plasticizers, i.e. di-(2-ethylhexyl)adipate (DEHA), di-(2-ethylhexyl)terephthalate (DEHT) and tri-(2-ethylhexyl)trimellitate (TEHT). A modified Ames Salmonella/microsome assay was used to determine mutagenicity. Urine was pooled from male Sprague--Dawley rats dosed daily for 15 days with 2000 mg/kg of each test substance with the exception of 2-EH which was given at 1000 mg/kg. Direct plating procedures were used to determine the presence of mutagens in urine. Urine from rats dosed with 8-hydroxyquinoline was used as a positive control. There was no evidence that mutagenic substances were excreted in the urine by rats dosed with either DEHP, DEHA, DEHT, TEHT or 2-EH as determined in the presence or absence of rat liver microsomes, and with or without treatment with beta-glucuronidase/aryl sulfatase. Our findings indicate that the above test compounds were not converted to urinary metabolites that were mutagenic. These observations provide no evidence for a genotoxic mechanism for DEHP carcinogenicity in rodents.

Biologic monitoring of workers exposed to silver.

The smelting and refining of silver and the preparation of silver salts for use in photosensitized products can lead to occupational exposures to silver. Our objectives in this study were to determine the absorption and elimination of silver by workers exposed to different species of silver, to estimate the body burden of silver and to relate these findings to the potential development of argyria. Workers potentially exposed to silver (n = 37) and a similar number of controls (n = 35) participated in this study. Blood, urine, feces and hair samples were collected and were analyzed for total silver content by atomic absorption spectroscopy. The mean concentration of silver in the blood, urine and feces of silver workers was 0.011 microgram/ml, less than 0.005 microgram/g and 15 microgram/g, respectively; and of controls was less than 0.005 microgram/ml, less than 0.005 microgram/g and 1.5 microgram/g, respectively. The concentration of silver in hair was markedly higher for the silver workers than for controls (130 +/- 160 vs 0.57 +/- 0.56 microgram/g, respectively). The importance of these latter findings was questionable since airborne particles of silver can bind to hair and lead to apparent high values. Since silver is eliminated predominantly in the feces, fecal measurements were used as an index of exposure and as a means of calculating body burdens. Human exposure to metallic silver at the TLV (0.1 mg/m3) is expected to lead to a fecal excretion of about 1 mg of silver per day.(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolic fate and disposition of [14C]hydroquinone given orally to Sprague-Dawley rats.

Hydroquinone (HQ) is used widely in industry and in commerce and is considered to have a low degree of toxicity. Although the metabolism of HQ has been studied elsewhere, a complete materials balance has not been reported. We investigated the metabolism of HQ in naive and HQ pretreated male Sprague-Dawley rats. [14C]HQ was administered by gavage in single doses of 5, 30, or 200 mg/kg to naive rats. HQ was given repeatedly by gavage to male rats at 200 mg/kg for 4 consecutive days followed by a single dose with 200 mg/kg of [14C]HQ. In separate studies rats were fed 5.6% unlabeled HQ in the diet for 2 days or were dosed by gavage with 311 mg/kg [14C]HQ. The excretion patterns of [14C]HQ and its metabolites were similar for rats dosed singly or repeatedly. Rats given a single dose of 200 mg/kg of [14C]HQ excreted 91.9% of the dose in the urine within 2-4 days; 3.8% was excreted in the feces, about 0.4% was excreted in expired air, and 1.2% remained in the carcass. Radioactivity was widely distributed throughout the tissues with higher concentrations in the liver and kidneys. A decrease in 14C tissue concentrations occurred from 48 to 96 h. The only radiolabeled compounds in the urine were HQ (1.1-8.6% of the dose), hydroquinone monosulfate (25-42%), and hydroquinone monoglucuronide (56-66%). Similar findings were observed for rats given HQ in the feed. There were no significant increases from controls for absolute or relative liver weights, liver microsomal protein concentrations, cytochrome b-5, cytochrome P-450 or cytochrome c reductase activity in rats dosed repeatedly with 200 mg/kg HQ. Cytochrome P-450 values were slightly but significantly decreased in rats dosed repeatedly with HQ compared with controls.

Pulmonary and percutaneous absorption of 2-propoxyethyl acetate and 2-ethoxyethyl acetate in beagle dogs.

A comparison was made of the absorption and elimination rates of 2-propoxyethyl acetate (PEA) and 2-ethoxyethyl acetate (EEA) following inhalation, dermal application or IV administration. Male beagle dogs were exposed to 50 ppm PEA or EEA for 5 hr, and breath samples were collected during the exposure and a 3-hr recovery period. Both compounds were rapidly absorbed through the lungs. After 10 min of exposure, the concentrations of the parent compounds in the expired breath were 5 to 10 ppm (80-90% absorption) and reached plateau values at about 3 hr of 13 ppm for PEA (74% absorption) and 16 ppm for EEA (68% absorption). Post-exposure breath samples declined exponentially to 0.5 ppm and 2 ppm after 3 hr for PEA and EEA, respectively. Expired concentrations of PEA were slightly, but significantly (p less than 0.025), lower than those of EEA at corresponding times during the exposure. After IV dosing with 1 mg/kg [ethyl-1,2-14C]PEA, the urine contained 61% and 88% of the dose in 4 and 24 hr, respectively. [14C]EEA was eliminated more slowly, with 20% and 61% of the dose appearing in the urine in 4 and 24 hr, respectively. Blood elimination half-lives were 1.6 hr for [14C]PEA and 7.9 hr for [14C]EEA. Only trace amounts of 14CO2 (less than 1%) or volatile materials (less than 0.1%) were detected in the expired air with either compound. For studies of percutaneous absorption, [14C]PEA or [14C]EEA was added to undiluted compound and applied in a glass cell to a shaved area on a dog's thorax for 30 or 60 min.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of the urinary metabolites of 5-amino-1-naphthol in the rat.

The metabolic fate of [14C]5-amino-1-naphthol (5A1N) was investigated in Sprague-Dawley rats. [14C]5A1N was administered by gastric intubation to male rats at doses 1, 37 and 135 mg/kg body weight. In a separate experiment the rats were also dosed with 150 mg/kg of unlabeled 5A1N daily for 4 consecutive days. Between 74% and 85% of the administered dose was excreted in the urine. Over 98% of the urinary radioactivity was characterized as unchanged 5A1N, 5-acetamido-1-naphthol (5AA1N) and glucuronic and sulfuric acid conjugates of both 5A1N and 5AA1N. Unchanged 5A1N and 5AA1N accounted for less than 3% of the dose. The amount of 5A1N converted to 5AA1N and its conjugates varied inversely with the dose. Two minor metabolites were not identified. Rats dosed repeatedly with 150 mg/kg of 5A1N showed no significant change in metabolite excretion patterns compared to rats dosed singly. These findings indicate that in the rodent model the metabolism of 5A1N was dose dependent, and occurred predominantly by phase II reactions involving N-acetylation and conjugation with glucuronic and sulfuric acids. N-Acetylation predominated at lower doses and O-sulfate conjugation at higher doses. There was no evidence for the formation of N-hydroxylated metabolites over the dose range studied.

Further studies on ketone neurotoxicity and interactions.

Ethyl n-butyl ketone (EBK, 3-heptanone) has not been reported to produce neurotoxicity in previous studies when it was given by oral or inhalation routes. In the present study, EBK given by gavage at 2 g/kg/day, 5 days/week for 14 weeks produced a typical central-peripheral distal axonopathy characterized by "giant" axonal swelling and neurofilamentous hyperplasia. This dose approximates the single dose LD50 (2.76 g/kg) of EBK determined by Smyth et al., (J. Ind. Hyg. Toxicol. 31, 60-62, 1949). Large multiple doses (1.5 g/kg/day, 5 days/week, 14 weeks) of methyl ethyl ketone (MEK) given by gavage potentiated EBK neurotoxicity but 5-methyl-2-octanone did not. MEK modestly increased the urinary excretion of two neurotoxic gamma-diketones, 2,5-heptanedione, and 2,5-hexanedione, when MEK was given by gavage with EBK. When rats were exposed to EBK (700 ppm) and MEK (700 or 1400 ppm) in combination by inhalation exposure, serum 2,5-heptanedione levels were increased approximately 2.5 times. This effect was absent at MEK levels of 70 ppm. The serum from rats exposed to EBK or EBK/MEK combinations did not contain 2,5-hexanedione. The toxicity of EBK appears to involve the metabolism of EBK to two neurotoxic gamma-diketones, 2,5-heptanedione and 2,5-hexanedione. Combined EBK/MEK exposure modestly increased gamma-diketone levels in the serum and urine suggesting that MEK potentiates EBK neurotoxicity by stimulating the metabolism of EBK to neurotoxic metabolites. The magnitude of the doses used in the present study to produce neurotoxicity and the absence of neurotoxicity in previous subchronic studies suggest that the neurotoxic hazard of EBK is low.