Bryan D. Hardin

Reproductive toxicity of the glycol ethers

The glycol ethers are an important and widely used class of solvents. Recent studies have demonstrated that ethylene glycol monomethyl ether (EGME), ethylene glycol dimethyl ether (EGdiME), ethylene glycol monoethyl ether (EGEE), and ethylene glycol monoethyl ether acetate (EGEEA) are teratogenic. Other studies have demonstrated that testicular atrophy or infertility follow treatment of males with EGME, ethylene glycol monomethyl ether acetate (EGMEA), EGEE, EGEEA, diethylene glycol dimethyl ether (diEGdiME), and diethylene glycol monoethyl ether (diEGEE). Experimental data are reviewed and structure-activity relationships are speculated upon.

Teratogenicity of 2-Ethoxxethanol by Dermal Application

ABSTRACTUndiluted 2-ethoxyethanol or water (control) was applied to the skin of pregnant Sprague-Dawley rats on days 7–16 of gestation (sperm = day 1). Applications were made 4 times daily in volumes of 0.25 or 0.50 ml 2-ethoxyethanol. Females exhibited ataxia following treatment of the high-dose group, and weight gain was significantly (p<0.001) reduced in the last half of gestation. Litters were collected by caesarian section on day 21 of gestation, and fetuses were examined for external defects. Half of the fetuses were cleared and stained in alizarin red S for skeletal examinations, and half were examined for visceral defects by the Wilson technique. Intrauterine death was 100% in the high-dose group. In the lower dosage group, there was a significant increase in the number of pregnant females with 100% dead implants (p<0.001), a significant reduction in the number of live fetuses per litter (p<0.001), a significant reduction in fetal body weight (p<0.001), and a significant increase in the incidence ...

Developmental toxicity of nine selected compounds following prenatal exposure in the mouse: naphthalene-, p-nitrophenol, sodium selenite, dimethyl phthalate, ethylenethiourea, and four glycol ether derivatives

Ethylene glycol dimethyl ether (EGdiME), diethylene glycol dimethyl ether (diEGdiME), triethylene glycol dimethyl ether (triEGdiME), diethylene glycol diethyl ether (diEGdiEE), ethylenethiourea (ETU), sodium selenite (SS), dimethyl phthalate (DMP), naphthalene (NAP), or p-nitrophenol (PNP) were administered by gavage for eight consecutive days to female CD-1 mice. Weight loss was insensitive as an index of sublethal adult toxicity and was inadequate for determining a maximum tolerated dose. LD50 values indicate that SS, NAP, and PNP were more toxic (8.4, 353.6, and 625.7 mg/kg, respectively) than the polyglycol ethers, ETU, and DMP (LD50 values ranged from 2525.8 to 6281.9 mg/kg). Each of the compounds was administered on d 7 through 14 to pregnant animals at a single dose estimated to be at or just below the threshold of adult lethality. In such a reproductive study, each of the compounds could be categorized on the basis of the pattern of maternal lethality and fetotoxicity which it produced. The number of dams with complete resorptions was significantly increased after administration of ETU, and no mice in the EGdiME-, diEGdiME-, or triEGdiME-treated groups delivered any viable offspring. Maternal lethality was significant in the EGdiME, triEGdiME, PNP, and NAP groups. There was a slight reduction in the average number of live pups per litter in the diEGdiEE- and PNP-treated groups and a significant reduction in the NAP group. The number dead per litter was increased with diEGdiEE. SS and DMP had no effect on maternal or fetal survival at the doses administered. Individual pup weight at d 1 postpartum was only significantly reduced by diEGdiEE, and no gross congenital abnormalities were detected in neonates from any treatment group. These results provide guidelines for the subsequent toxicity testing of these chemicals.

Evaluation of propylene oxide for mutagenic activity in 3 in vivo test systems.

Propylene oxide (CAS No. 75-56-9) was tested for mutagenic activity following vapor exposure using 3 in vivo test systems. Rat dominant lethal and mouse sperm-head morphology assays were conducted using males exposed to propylene oxide at 300 ppm in a dynamic exposure chamber for 7 h per day on 5 consecutive days. A sex-linked recessive lethal test in Drosophila melanogaster employed a 24-h static exposure to propylene oxide at 645 ppm. Male mice were killed 1, 3, 5, 7, and 9 weeks post-exposure for evaluation of sperm-head morphology. Propylene oxide exposure did not result in an increase in abnormal forms. Male rats were mated with 2 virgin females per week for 6 weeks following exposure. A statistically significant increase in preimplantation losses and a statistically significant reduction in the number of living implants in the first post-exposure week did not appear to be treatment related. A highly significant increase in sex-linked recessive lethal mutations was observed in two germ cell stages (mature sperm and developing spermatocytes). These results warrant continued caution in potential human exposure to propylene oxide.

Developmental toxicity of diethylene glycol monomethyl ether (diEGME)

Diethylene glycol monomethyl ether (diEGME) was one of 15 glycols tested in CD-1 mice using a short-term in vivo reproductive toxicity assay (Chernoff/Kavlock test). Because results were strongly suggestive of potential reproductive toxicity, a teratology study was conducted in Sprague-Dawley rats. Time-mated females were orally dosed on Days 7-16 of gestation with diEGME in distilled water. Doses of 0, 1000, 1495, 2235, 3345, and 5175 mg/kg/day were used in a preliminary dose-finding study. At 5175 mg/kg/day, two of nine rats died, five of five litters were totally resorbed, and maternal extra gestational body weight gain was reduced. At 3345 mg/kg/day, six of nine litters were resorbed but there were no deaths and extra gestational body weight gain was not affected. Visceral and skeletal examinations revealed a dose-related increase in malformations, primarily of the ribs and cardiovascular system. Subsequently, pregnant rats were similarly dosed with 0, 720, or 2165 mg/kg/day. Neither dose was maternally toxic, but fetal body weights and the number of live implantations were significantly reduced at 2165 mg/kg/day. Rib malformations were seen in 9.1% (control), 42.9% (720 mg/kg/day, p less than 0.05), and 80.0% (2165 mg/kg/day, p less than 0.001) of litters. Cardiovascular malformations occurred in 0.0, 4.8, and 71.4% (p less than 0.001) of litters. Diethylene glycol monomethyl ether thus was teratogenic in rats at all doses tested, producing a dose-dependent series of malformations similar to those produced by other members of the glycol ether family.

Pattern of Response of Intact Drosophila to Known Teratogens

Drosophila, as the test organism, was used to assess 17 chemicals. The teratogenic potential of 15 of these chemicals is well established from animal studies or human epidemiology. The test involves examination of adult flies following treatment during larval stages of development. Flies are examined for abnormal external morphology. The incidence of abnormalities in treated and control populations is compared using the Chi-square test. All 17 chemicals were active to varying degrees in the test system. Most chemicals produced a unique response yielding individual patterns of abnormalities. These results suggest that Drosophila may have the potential to become a valuable teratogen screen, but further, more rigorous examination–particularly with nonteratogens–is required.

The Concentration of No Toxicologic Concern (CoNTC) and Airborne Mycotoxins

The threshold of toxicologic concern (TTC) concept was developed as a method to identify a chemical intake level that is predicted to be without adverse human health effects assuming daily intake over the course of a 70-yr life span. The TTC values are based on known structure–activity relationships and do not require chemical-specific toxicity data. This allows safety assessment (or prioritization for testing) of chemicals with known molecular structure but little or no toxicity data. Recently, the TTC concept was extended to inhaled substances by converting a TTC expressed in micrograms per person per day to an airborne concentration (ng/m3), making allowance for intake by routes in addition to inhalation and implicitly assuming 100% bioavailability of inhaled toxicants. The resulting concentration of no toxicologic concern (CoNTC), 30 ng/m3, represents a generic airborne concentration that is expected to pose no hazard to humans exposed continuously throughout a 70-yr lifetime. Published data on the levels of mycotoxins in agricultural dusts or in fungal spores, along with measured levels of airborne mycotoxins, spores, or dust in various environments, were used to identify conditions under which mycotoxin exposures might reach the CoNTC. Data demonstrate that airborne concentrations of dusts and mold spores sometimes encountered in agricultural environments have the potential to produce mycotoxin concentrations greater than the CoNTC. On the other hand, these data suggest that common exposures to mycotoxins from airborne molds in daily life, including in the built indoor environment, are below the concentration of no toxicologic concern.

Reproductive and Developmental Toxicity of N,N-Diethyl-m-toluamide in Rats

N,N-Diethyl-m-toluamide (mDET, DEET) is widely used as a topical insect repellent. It is the active ingredient in many consumer formulations, which usually contain 10-25% mDET in an alcohol base. More concentrated consumer products are also available, including some that are pure technical grade mDET. Persons living or employed in mosquito-infested areas may have very high seasonal exposures to mDET. Because contradictory reports had been published on the reproductive and developmental toxicity of mDET, a series of studies was conducted in male and female Sprague-Dawley rats. All treatments were administered by daily subcutaneous injections of undiluted mDET. A dose finding study was done using 12 time-mated females per group treated on Gestational Days (GD) 6-15 with 0.50, 0.62, 0.78, 0.92, or 1.2 ml mDET/kg/day. No females survived 10 days of mDET dosing with 1.2 ml/kg/day. Deaths occurred in all other groups except the low dose (0.50 ml/kg/day). Pregnant females treated on GD 6-15 with 0 or 0.30 ml/kg/day were used for the teratology study. Half of each group was euthanized on GD 20: the second half was singly housed in nesting boxes and allowed to deliver litters. Live pups were counted and weighed soon after birth on Postnatal Day (PD) 0 and again on PD 3, 9, and 14. Proven fertile males were treated 5 days/week for 9 weeks with 0, 0.30, 0.73, 1.15, or 1.80 ml mDET/kg/day for a male dose-finding study. Each group consisted of 20 males. No males survived the 1.80 ml/kg/day. Deaths occurred in all remaining dose groups except the 0.30 ml/kg/day and control group. Immediately following the final treatment of the male dose study, 11 males were randomly selected from the 0.30 and 0.73 ml/kg/day groups. They were cohabited for 7 days with 4 females per male during post-treatment Weeks 1 and 2. Half of the females were euthanized 12-14 days after the last day of cohabitation for a dominant lethal study; the remaining females were singly housed in nesting boxes and allowed to deliver litters. Live pups were counted and weighted on PD 0 and 3. There was no evidence of reproductive or developmental toxicity in any of these assays, but there were signs of neurotoxicity in treated adult male and female rats, which may relate to reports of neurotoxicity in humans heavily exposed to mDET-containing insect repellents.

Calcium homeostasis in pregnant rats treated with ethylene glycol monomethyl ether (EGME)

The industrial solvent ethylene glycol monomethyl ether (EGME) is a known teratogen that has been reported to alter calcium metabolism in guinea pigs during chronic exposure. Because of the tremendous demand of reproduction on maternal calcium stores, the effects of EGME on calcium and vitamin D metabolism during gestation were examined. Timed pregnant rats were treated by gavage with 0, 50, or 100 mg/kg EGME in 10 ml/kg distilled water on Days 9-15 of gestation (sperm = Day 1) and examined on Days 16 and 21. Virgin rats were treated for 7 days with 0 or 100 mg/kg EGME and examined 5 days later. EGME exposure did not affect body or kidney weight in virgin or pregnant rats, but liver weight was reduced in near-term pregnant rats treated with 100 mg/kg EGME. EGME (50 mg/kg) reduced litter size and fetal body weight and caused a significant number of live fetuses to have visceral abnormalities. EGME (100 mg/kg) caused all fetuses to be resorbed. In nonpregnant rats, 100 mg/kg did not affect serum 1,25-dihydroxyvitamin D (1,25(OH)2D3), 25-hydroxyvitamin D, ionic calcium, total calcium, or parathyroid hormone. EGME appeared to have a dose-dependent effect on calcium and vitamin D metabolism during gestation. On Day 21 of gestation, total calcium and ionic calcium were increased and 1,25(OH)2D3 was reduced in rats treated with EGME compared with nontreated controls. However, significant alterations in calcium homeostasis were evident only in dams that completely resorbed their litters. The changes in calcium and vitamin D metabolism during gestation appear to be secondary to the EGME-induced loss of litters.