o-Phthalaldehyde is a high-level chemical disinfectant that is commonly used for disinfection of dental and medical instruments as an alternative to glutaraldehyde, which is a known skin and respiratory sensitizer. o-Phthalaldehyde was nominated by the National Institute for Occupational Safety and Health for toxicologic characterization based on its proposed use as a safer alternative to glutaraldehyde for chemical disinfection, its increasing use, the lack of adequate and publicly available toxicologic data, and because many human case reports document incidences of skin and respiratory sensitization following occupational exposure. Inhalation was chosen as the route of exposure for these studies because inhalation is a major route of human occupational exposure. Male and female Sprague Dawley (Hsd:Sprague Dawley SD) rats and B6C3F1/N mice were exposed to o-phthalaldehyde (99.7% pure) by whole-body inhalation for 3 months.
Groups of 10 male and 10 female rats and mice were exposed to o-phthalaldehyde at concentrations of 0, 0.44, 0.88, 1.75, 3.5, or 7.0 ppm, 6 hours plus T90 (17 minutes) per day, 5 days per week for 14 weeks; additional groups of 10 male and 10 female clinical pathology study rats were exposed to the same concentrations for 23 days.
All rats exposed to 7.0 ppm died by the end of week 2 of the study, and seven males and two females exposed to 3.5 ppm died by week 7 of the study. All mice exposed to 7.0 ppm died during week 1 of the study, and five males and four females exposed to 3.5 ppm died by week 6 of the study. Clinical observations in rats and mice included abnormal breathing, sneezing, and thinness, with increasing frequency in higher exposure groups. In rats, clinical observations also included black discoloration of the appendages (pinnae and/or feet), which was noted throughout the study in male and female rats exposed to 3.5 ppm or greater. Clinical observations in mice also included alopecia. Mean body weights of all surviving exposed groups of male rats and 1.75 and 3.5 ppm female rats were significantly less than those of the chamber controls. Mean body weights of all surviving exposed groups of male and female mice were significantly less than those of the chamber controls, and 3.5 ppm males lost weight during the study.
In the hematopoietic system of rats, decreases in lymphocyte counts in males and females coincided with increases in neutrophil counts. These alterations in lymphocyte and neutrophil counts were consistent with stress and inflammation. Decreased lymphocyte counts corresponded to lymphoid atrophy in the thymus and spleen. Within the erythron, the erythrocyte counts, hemoglobin concentrations, hematocrit values, and packed cell volumes were significantly elevated in both male and female rats at all time points. Erythron increases at the earlier time points were consistent with a physiological hemoconcentration, while increases at study termination may have been due to hypoxia with a resultant secondary erythrocytosis.
In the hematopoietic system of mice, the total leukocyte and lymphocyte counts, as well as neutrophil and eosinophil counts, were increased in males at study termination. Similarly, female mice had increased total leukocyte, neutrophil, and eosinophil counts. The increases in the leukon were generally consistent with inflammation. Hemoglobin concentrations, erythrocyte counts, hematocrit values, and packed cell volumes were decreased in male and female mice. The decreases in the erythron were most likely due to bone marrow suppression as a result of the chronic inflammation in the respiratory tract.
Inhalation exposure to o-phthalaldehyde resulted in a spectrum of lesions at sites of contact within the respiratory tract (nose, larynx, trachea, and lung), skin, and eye that were generally consistent with an irritant effect. In general, exposure of rats and mice to o-phthalaldehyde resulted in lesions throughout the respiratory tract that included necrosis, inflammation, regeneration, hyperplasia, and metaplasia, ranging from minimal to moderate in severity. In general, histologic findings occurred at deeper sites within the respiratory tract with increasing exposure concentration. The first site of contact, the nose, was most affected, with many lesions occurring at the lowest exposure concentration (0.44 ppm) in male and female rats and mice. Laryngeal lesions occurred at all exposure concentrations in rats and at 0.88 ppm or greater in mice. Tracheal findings were first noted at a variety of exposure concentrations. Lung findings were most prevalent at the two highest exposure concentrations (3.5 and 7.0 ppm) in rats and mice. In the skin, there were significant increases in adnexa degeneration and epithelial parakeratosis in both male and female rats and mice. In the eye, there were significant increases in suppurative inflammation of the anterior chamber and cornea, as well as corneal necrosis in male and female rats.
Rats exposed to o-phthalaldehyde exhibited lower cauda epididymis, epididymis, and testis weights. In rats, total sperm/cauda exhibited a negative trend and sperm motility was lower. There were no histopathologic correlates identified that could explain the observed responses in sperm parameters, or the weight changes in the testis or epididymis. However, in the higher dose groups where morbidity and mortality were observed, testicular and epididymal histopathologic lesions were noted. In the testes, these lesions included significant increases in the incidences of elongated spermatid degeneration, apoptosis of the germinal epithelium, and interstitial cell atrophy. In the epididymis of male rats, there were significant increases in the incidences of exfoliated germ cells and apoptosis of the epithelium. The mice also displayed decreased sperm motility, and some testicular and epididymal histopathologic lesions, including significantly increased incidences of exfoliated germ cells of the epididymal duct, as well as multifocal cellular depletion of the germinal epithelium, and interstitial cell atrophy of the testis.
o-Phthalaldehyde was mutagenic in Salmonella typhimurium strain TA100 in the absence of exogenous metabolic activation (S9 mix); no mutagenicity was seen in TA100 with S9 or in TA98 or Escherichia coli WP2 uvrA/pKM101, with or without S9. Following 3 months of inhalation exposure to o-phthalaldehyde, no increases in the frequencies of micronucleated reticulocytes were observed in male or female Sprague Dawley rats. In B6C3F1/N mice following 3 months of inhalation exposure to o-phthalaldehyde, a small increase in micronucleated reticulocytes was seen in male mice exposed to 3.5 ppm, but no significant increases in micronuclei were seen in erythrocytes of male mice or in reticulocytes or erythrocytes of female mice. A small increase in the percentage of reticulocytes was seen in female mice at the highest dose tested (3.5 ppm).
Under the conditions of these 3-month inhalation studies, there were treatment-related lesions in male and female rats and mice. The major targets from o-phthalaldehyde exposure in rats and mice included the respiratory system (nasal cavity, larynx, trachea, and lung), skin, eye, testis, and epididymis. The most sensitive measure of o-phthalaldehyde inhalation toxicity in male and female rats and mice was significantly increased incidences of nasal cavity lesions (lowest-observable-effect concentration = 0.44 ppm). A no-observed-effect concentration was not reached in rats or mice of either sex.
National Toxicology Program (NTP). 2018. NTP technical report on the toxicity studies of o-phthaladehyde (CASRN 643-79-8) administered by inhalation to Sprague Dawley (Hsd:Sprague Dawley SD) rats and B6C3F1/N mice. Research Triangle Park, NC: National Toxicology Program. Toxicity Report 84. https://doi.org/10.22427/NTP-TOX-84