Toxicology and Industrial Health

A preliminary study of dermal and respiratory exposure to chlorpyrifos (Dursban^R TC) during structural treatments was conducted with eight workers from a commercial pest control company. The compound was applied by sub-slab and soil injection to four houses, with each application involving two workers. Crawl space applications were included in three of the jobs. Field sampling extended over the entire workday, and included personal air samples and dermal exposure evaluation with patches and handwashes. A fluorescent tracer was added to the formulation for qualitative determination of skin deposition patterns. Pre-exposure and complete 72 hour urine samples were also collected. Total dermal exposure averaged 5.94 mg/hr. The major contributors were the upper legs (38%) and the forearms (34%). Accidents occurred during two of the four applications observed, and the two workers involved in the accidents were the most highly exposed individuals. The mean estimated absorbed daily dose was 9.5 ug/kg/day, with approximately 73% contributed by the dermal route. Thus, under these work conditions the Threshold Limit Value is not an appropriate guide for worker safety. The principal urinary metabolite of chlorpyrifos, 3,5,6-trichloro-2-pyridinol, was found in measurable quantities in all urine samples. Urinary metabolite levels collected 24–48 hr post-exposure were highly correlated (R² = 0.86) with total absorbed dose estimates. The high variability among individual excretion patterns suggests against the use of urine spot sampling, but longer collections may prove useful in the development of a Biological Exposure Index for chlorpyrifos.

The developmental toxicology of 13 industrial alcohols (methanol, ethanol, 1-propanol, isopropanol, 1-butanol, 2-butanol, tertiary-butanol, 1-pentanol, 1-hexanol, 2-ethyl-1-hexanol, 1-octanol, 1-nonanol, and 1-decanol), and the behavioral teratogenicity of 4 of these alcohols, were assessed in a series of experiments. The results of individual alcohols have been published previously, but the present paper summarizes the results in view of structure-activity relationships among these alcohols. The alcohols were administered by inhalation for 7 hours per day (6 hours/day for 1-decanol) on gestation days 1–19 to groups of approximately 15 pregnant Sprague-Dawley rats. For developmental toxicology evaluations, dams were sacrificed on gestation day 20. Fetuses were serially removed, weighed, sexed, and examined for external malformations. The frequency of visceral malformations and variations was determined in one-half of the fetuses, and the frequency of skeletal deviations was determined in the other half. Behavioral teratology endpoints were investigated in groups of 15 pregnant rats exposed to one of four alcohols (ethanol, 1-propanol, 1-butanol, and tertiary-butanot) and also involved groups of 18 male rats which were exposed to the same concentrations of each alcohol for 6 weeks, and then mated to untreated females. In the behavioral teratology evaluations, all litters were culled to eight pups and fostered to unexposed mothers. Offspring were tested from days 10–90 on a series of behavioral tests designed to evaluate neuromotor integrity, activity levels, learning, and memory. Additionally, brains were removed from 10 offspring per group at 21 days of age, and were dissected into cerebrum, cerebellum, brainstem, and midbrain; these samples were assayed for steady-state levels of protein and the neurotransmitters acetylcholine, dopamine, norepinephrine, 5-hydroxytryptamine (serotonin), substance P, B-endorphin, and met-enkephalin.

Congenital malformations were noted for methanol, 1-propanol, isopropanol, and 1-butanol, but only at concentrations in excess of 5000 ppm. These concentrations also produced toxicity in the maternal animals; thus, there was little evidence of selective developmental toxicity among the alcohols. Although sporadic behavioral and neurochemical deviations were detected, no consistent pattern of effects was seen for any of the alcohols we tested. It should be noted that alcohols with chain lengths longer than the butyl series could not be generated as vapors at sufficiently high concentrations to produce observable toxicity in the maternal animals. This limits the generality of these findings to the possible developmental effects of these alcohols when taken through other routes of exposure. Thus, rats are unlikely to exhibit developmental toxicity if exposed to these alcohols within current occupational limits. One adverse finding of note from this series of studies was an apparently reversible infertility observed in male rats exposed to a high concentration of 1-propanol, a finding which should be replicated.

The effects of low levels of hydrogen sulfide (H₂S) on mammalian growth and development are unknown although it has long been postulated that H₂S can inhibit critical developmental functions through the cleavage of disulfide bonds and chelation of essential metal ions. Gravid rat dams exposed to H₂S (≤75 PPM) from day 6 of gestation until day 21 postpartum (PP) demonstrated normal reproductive parameters until parturition. At parturition, however, delivery time was extended in a dose dependent manner with a maximum increase of 42% at 75 PPM. Maternal liver cholesterol content was elevated significantly on day 21 postpartum following exposure to 75 PPM H₂S each day for 6 weeks. Pups which were exposed in utero and neonatally to day 21 postpartum developed with a subtle decrease in time of ear detachment and hair development and with no other observed change in growth and development throughday 21 postpartum.

Male and female F-344 rats were exposed at 0, 25, or 247 ppm triethylamine (TEA) vapor, 6 hr per day, 5 days per week for up to 28 weeks in order to characterize the subchronic organ system toxicity. Rats were weighed biweekly and scheduled sacrifices were performed following about 30, 60, and 120 days of exposure. No statistically significant treatment-related effects on organ weights, hematology, clinical chemistry, or electrocardiographic indices were observed. Body weight gain was not affected by TEA treatment. No physiologic or pathologic evidence of cardiotoxicity was seen in rats exposed to either TEA concentration for up to 28 weeks. No gross or histopathologic lesions attributable to TEA exposure were noted in any of the organs examined, including the nasal passages. This latter finding is in marked contrast to previously reported findings from this laboratory in which squamous metaplasia, suppurative rhinitis, and lymphoid hyperplasia were found in the respiratory epithelium of F-344 rats exposed to the structurally related chemical, diethylamine, under the same conditions as this study (Lynch et al., 1986).

There industrial organophosphorus compounds were tested for their ability to cause organophosphorus compound-induced delayed neurotoxicity (OPIDN) in the adult hen. The compounds tested were tributyl phosphate (TBP), tributoxyethyl phosphate (TBEP), and dibutylphenyl phosphate (DBPP). The acute oral LD₅₀ of TBP and DBPP were estimated to be 1,863 and 1,500 mg/kg, respectively, and the dose equal to the LD₅₀ was used as a test dose. The acute oral LD₅₀ of TBEP was greater than 5,000 mg/kg and 5,000 mg/kg was used as a test dose. An oral dose of 750 mg tri-o-cresyl phosphate (TOCP) was used as a positive control. For the acute delayed neurotoxicity test, hens were given two test doses of the test materials 21 days apart and killed 21 days after the second dose. None of the hens given TBP, TBEP, or DBPP exhibited nerve damage or clinical signs which distinguished them from untreated control animals. A single dose of TOCP resulted in paralysis and a histopathological profile typical of a distal neuropathy. For the assay of the inhibition of esterases, hens were killed 24 hours after a single dose equal to the greater of either the LD₅₀ or 5000 mg/kg. TOCP administration resulted in over 90% inhibition of brain neurotoxic esterase (NTE), but none of the other three compounds inhibited NTE to an extent (<70%) which would be expected to result in OPIDN. Administration of TOCP, TBEP, or DBPP resulted in approximately a 70% decrease in plasma butyrylchol-inesterase (BuChE) activity. TBP caused a 2–3 fold increase in BuChE activity. TBEP administration resulted in about 45% inhibition of acetycholinesterase (AChE) in brain. These results indicate that TBP, TBEP, and DBPP are all unlikely to cause OPIDN with any single sublethal dose.

A promising screening test for neurotoxicity has been developed using a computer tracking system and a species of nematode, Caenorhabditis elegans. The animals are viewed in dark-field illumination by a video camera interfaced directly to a microcomputer. Several hundred nematodes are tracked simultaneously and rates of locomotion and frequency of change of direction are reported in real time. This system can rapidly obtain reliable data on a variety of behavioral parameters relating to locomotion and response to sensory stimulation. Initial testing has examined the effects of six chemicals on locomotion. Four metals (copper, beryllium, mercury, and lead) and two organophosphate pesticides (malathion and vapona) have been studied. Copper and beryllium were chosen as chemicals that have not been shown to be neurotoxins and the other four chemicals were chosen as substances known to be neurotoxins. Our findings indicate that the rate of movement of exposed nematodes compared to the rate of movement of vehicle controls may prove to be useful as an indicator of neurotoxicity.

Catalytic reforming is a refining process that converts naphthenes to aromatics by dehydrogenation to make higher octane gasoline blending components. A portion of this wide boiling range hydrocarbon stream can be separated by distillation and used for other purposes. One such application is a mixture of predominantly 9-carbon aromatic molecules (C9 aromatics, primarily isomers of ethyltoluene and trimethylbenzene), which is removed and used as a solvent—High Flash Aromatic Naphtha. A program was initiated to assess the toxicological properties of High Flash Aromatic Naphtha since there may be human exposure through inhalation or external body contact. The current study was conducted to assess the potential for developmental toxicity in the mouse and for reproductive toxicity in the rat.

In the developmental toxicity study in CD-I mice, exposure of dams by inhalation to near lethal levels (1500 ppm) resulted infetal mortality, reduced weight, delayed ossification, and an increased incidence of cleft palate. At 500 ppm, a level at which maternal weight gain was slightly reduced, fetal weight gain was also reduced, but there was no other evidence of developmental effects. The lowest exposure level (100 ppm) did not cause any maternal or developmental toxicity.

There was no consistent evidence of reproductive toxicity in rats, even at exposure levels which resulted in significantly reduced parental weight gain. In addition, when parental exposure was stopped on GD (gestation day) 20, birth weights as well as posh natal survival were generally similar to control values, even in the 1500 ppm exposure group. Postnatal weight gain was also similar to controls early in weaning, but, if maternal exposure was reinitiated, weight gain was reduced in the high exposure group. However, when exposure was continued until delivery, pups in the high exposure group exhibited reduced litter size, birth weight and poor survival. Thus it was likely that the reduction in fetal weight, seen in the developmental toxicity study in mice, was transient and had no postnatal consequences if maternal exposure was terminated at any time prior to delivery.

The developmental toxicity of 2,4-Pentanedione (2,4-PD; CAS No. 123-54-6), a widely used industrial chemical, was investigated by vapour exposure, because of its widespread use, and potential for human exposure. Timed-pregnant Fischer 344 rats were exposed on gestational days (gd) 6 to 15 inclusive to analytically measured concentrations (as mean ± SD) of 53 ± 1.6, 202 ± 4.7 and 398 ± 5.7 ppm 2,4-PD vapour. At sacrifice (gd 21) foetuses were examined for external, visceral and skeletal variations and malformations. There was no maternal mortality, and body weight was reduced only at 398 ppm. Histological examination of maternal brains from the 398 ppm group showed no abnormalities. No treatment-related effects were seen on number of corpora lutea; total, nonviable or viable implants per litter; pre-or post-implantation losses; or foetal sex ratio. Reduced foetal body weight per litter was seen at 398 ppm (males and females and all foetuses) and 202 ppm (males and all foetuses). There was no concentration-related, or statistically significant, increase in the incidence of individual malformations, malformations by category (external, visceral or skeletal), or total malformations. Partial foetal atelectasis was increased at 398 ppm, and the increased incidence of 17 skeletal variants (out of 79 observed) indicated a consistent pattern of fototoxicity at 398 ppm. In summary, at 398 ppm there was maternal toxicity (reduced body weight) and foetotoxicity (reduced body weight and ossification) and at 202 ppm there was foetotoxicity (reduced body weight). Embryotoxicity or teratogenicity were not seen at any concentration. The no-observable-effects concentration was 53 ppm for both maternal and developmental toxicity.

Petroleum middle distillates (PMDs) elicit skin tumors in mouse epidermal carcinogenesis studies. The response is characterized by a long latency with only a small percentage of animals developing tumors. Although the carcinogenic activity of certain other petroleum hydrocarbons largely depends upon the presence of polycyclic aromatic hydrocarbons (PAHs), many PMDs contain relatively low concentrations of PAHs. PMDs are also irritating to mouse skin, and chronic irritation may be involved in the development of skin tumors. This study was conducted to investigate the patterns of cutaneous irritation elicited by topical application of PMDs having compositional differences. The three PMDs selected for study were a steam cracked gas oil (SCGO), a lightly refined paraffinic oil (LRPO), and a jet fuel (JF). Male C3H/HeNCr1BR mice (25/group) were treated topically (37.5 μl 2x/week for 13 weeks) with 10%, 50% or 100% (undiluted) concentrations of each PMD. Catalytically cracked clarified oil (CCCO, 10%), a potent carcinogen to mouse skin, was also tested. The vehicle was a noncarcinogenic mineral oil with a viscosity of 90 SUS.

Cutaneous changes were evaluated by gross observations and light microscopy. Cutaneous irritation was the only significant toxic response in this study. Neither the vehicle nor any of the 10% PMD concentrations produced significant cutaneous irritation. The 10% CCCO and 50% PMD treatments all elicited slight to moderate proliferative and inflammatory changes in mouse skin. Ulcers were also observed microscopically in mice treated with 10% CCCO and 50% SCGO. The 100% SCGO treatment produced evidence of necrosis on Days 1–7 but not later in the study despite continued treatment. In contrast, the irritating effects of 100% LRPO were not evident until 2–3 weeks of study, and at study completion were characterized by moderately severe inflammatory and proliferative changes. The effects of 100% JF were qualitatively similar to 100% LRPO but less marked. Thus, the SCGO caused a different pattern of cutaneous responses than either LRPO or JF. The possible relationships of these cutaneous changes to epidermal carcinogenesis are being studied further.

The interaction of Freon 113 (1,1,2-trichloro-1,2,2-trifluoro-ethane) and hypoxia on the heart conduction system was studied using electrocardiogram monitoring of isolated perfused rat hearts. Freon 113 (0.2 mM) alone elicited significant atrioventricular conduction delay (p > 0.05) and heart rate decrease (p > 0.01), which were significantly enhanced by hypoxia (75% oxygen decrease), for instance, resulting in 2:1 AV block. The data suggest that arrhythmogenicity of Freon 113 on the heart conduction system may be enhanced synergistically by hypoxia.