Vinylidene chloride is used as an intermediate in organic synthesis reactions and is widely used in the production of a variety of polymers. Most of the vinylidene chloride in the plastics industry is used in the production of copolymers with polyvinylidene polymers that have a broad spectrum of application, including in films for household and industrial food packaging, as coatings on a variety of products, in flame-resistant fiber and carpet backing, as binders in paints, and to fabricate filaments, pipes, pipe liners, and gaskets. The highest potential for human exposure to vinylidene chloride is at its point of production and formulation, and occupational exposure may occur via inhalation or dermal contact. The general population is exposed via inhalation and ingestion of contaminated drinking water. Vinylidene chloride was nominated for study by the Agency for Toxic Substances and Disease Registry because of the potential for human exposure, and because there was insufficient critical information concerning its health effects and a need to fill critical data gaps. Male and female F344/N rats and B6C3F1/N mice were exposed to vinylidene chloride (greater than 99.9% pure) by inhalation for 2 weeks, 3 months, or 2 years. Genetic toxicology studies were conducted in Salmonella typhimurium and Escherichia coli, L5178Y mouse lymphoma cells, Drosophila melanogaster, and mouse peripheral blood erythrocytes.
Two-week study in rats
Groups of five male and five female rats were exposed by whole body inhalation to vinylidene chloride vapor at concentrations of 0, 25, 50, 100, 200, or 400 ppm, 6 hours plus T90 (12 minutes) per day, 5 days per week for 16 days. All male and nine of 10 female rats in the 200 and 400 ppm groups were found dead by day 2; one female in the 400 ppm group was found dead on day 4. All other rats survived until the end of the study except one 25 ppm male was removed from the study due to chylothorax (nonexposure-related condition). The mean body weight gain of 100 ppm females was significantly less than that of the chamber controls. Prior to death, all females and nine of 10 males exposed to 200 or 400 ppm became lethargic, while all females and four of five males exposed to 400 ppm developed ataxia. Kidney weights of all surviving groups of exposed males and females were significantly greater than those of the chamber controls. Centrilobular necrosis of the liver was associated with early deaths in male and female rats exposed to 200 or 400 ppm, and centrilobular cytoplasmic alteration of hepatocytes occurred in all exposed male and female rats that survived to terminal kill. The incidences of renal tubule casts in the renal papillae of 200 and 400 ppm rats were significantly increased.
Two-week study in mice
Groups of five male and five female mice were exposed by whole body inhalation to vinylidene chloride vapor at concentrations of 0, 25, 50, 100, 200, or 400 ppm, 6 hours plus T90 (12 minutes) per day, 5 days per week for 17 days. All male mice exposed to 100 ppm or greater died within the first 4 days of exposure. All females exposed to 200 or 400 ppm were found dead following exposure on day 1. One 50 ppm male and one 100 ppm female were removed dead before exposure on day 5. Mean body weights of 25 and 50 ppm male mice were less than those of the chamber control group. Lethargy and abnormal breathing occurred in 50 and 100 ppm males. In all surviving groups of exposed females, lung weights were significantly greater than those of the chamber controls, and the liver weights of 50 and 100 ppm females were significantly greater than those of the chamber controls. Necrosis of the respiratory epithelium of the nose occurred in all mice exposed to 200 or 400 ppm and in all 100 ppm males. Centrilobular necrosis of the liver occurred in all males and females exposed to 100 ppm or greater; in addition, regeneration occurred in the four 100 ppm females that survived to the end of study. Proximal renal tubule necrosis and granular casts occurred in the kidney in all exposed males.
Three-month study in rats
Groups of 10 male and 10 female rats were exposed by whole body inhalation to vinylidene chloride vapor at concentrations of 0, 6.25, 12.5, 25, 50, or 100 ppm, 6 hours plus T90 (10 minutes) per day, 5 days per week for 14 weeks. Additional clinical pathology groups of 10 male and 10 female rats were exposed to the same concentrations for 23 days. All rats survived until the end of the study. Mean body weights of exposed groups were similar to those of the chamber control groups. Sorbitol dehydrogenase activities were increased in 100 ppm females on day 3 and in 100 ppm males and 50 and 100 ppm females on day 23. Alanine aminotransferase activities were increased on day 3 in 50 and 100 ppm male rats and on day 23 in 100 ppm male rats. Kidney weights of 12.5 ppm or greater females were significantly greater than those of the chamber controls. In males, sperm motility was decreased and spermatid/g testis and total spermatid/testis were lower at 100 ppm than those of the chamber control groups. No treatment-related effects were observed in females. These data suggest that vinylidene chloride may be a reproductive toxicant in male, but not female rats.
A combination of lesions in the nasal epithelium of male and female rats including olfactory epithelium atrophy, mineralization, and necrosis and turbinate atrophy occurred with generally increasing severity with increasing exposure concentration. In the liver, the incidences of centrilobular cytoplasmic alteration were significantly increased in males exposed to 12.5 ppm or greater, and cytoplasmic vacuolization occurred in all 50 and 100 ppm females.
Three-month study in mice
Groups of 10 male and 10 female mice were exposed by whole body inhalation to vinylidene chloride vapor at concentrations of 0, 6.25, 12.5, 25, 50, or 100 ppm (females only), 6 hours plus T90 (10 minutes) per day, 5 days per week for 14 weeks. Two 50 ppm males and four 100 ppm females died during the first week of the study. The mean body weights of all exposed groups of females and of males exposed to 12.5 ppm or greater were significantly less than those of the chamber control groups. Exposure concentration-related decreases in the erythrocyte counts, hemoglobin concentrations, and hematocrit values occurred at the end of the study in 12.5, 25, and 50 ppm male mice. Female mice had decreased erythrocyte counts in the 50 and 100 ppm groups. In addition, hemoglobin concentration and the hematocrit value were decreased in 50 ppm female mice. Absolute kidney weights of all exposed groups of males were significantly less than that of the chamber control group. Absolute and relative liver weights of 12.5 ppm or greater females and absolute and relative kidney and lung weights of 100 ppm females were significantly greater than those of the chamber controls. In males, decreased cauda epididymis weights at 25 and 50 ppm and total sperm/cauda epididymis in all vinylidene chloride-exposed groups were observed. No treatment-related effects were observed in females. These data suggest that vinylidene chloride may be a reproductive toxicant in male, but not female mice.
In male mice, the incidences and severities of nephropathy were significantly increased in the 12.5, 25, and 50 ppm groups, and two 50 ppm males had renal tubule necrosis and protein casts. The incidence of respiratory epithelium squamous metaplasia of the larynx was significantly increased in the 50 ppm males. In female mice, laryngeal lesions consisted of necrosis and respiratory epithelium hyperplasia and squamous metaplasia and occurred primarily in the 100 ppm group. Exposure-related lung lesions were limited to 100 ppm female mice and consisted of bronchial epithelium necrosis and histiocytic inflammation. The incidences of nasal necrosis of the respiratory epithelium and atrophy of the turbinate were significantly increased in 100 ppm females. The incidences of necrosis and hypertrophy of the liver were significantly increased in 100 ppm females, and necrosis occurred in two 50 ppm males.
Two-year study in rats
Groups of 50 male and 50 female rats were exposed by whole body inhalation to vinylidene chloride vapor at concentrations of 0, 25, 50, or 100 ppm, 6 hours plus T90 (10 minutes) per day, 5 days per week for 105 weeks. Survival of exposed groups of males was similar to that of the chamber control group. Survival of 100 ppm females was significantly less than that of the chamber controls. Mean body weights of exposed groups of male and female rats were similar to those of the chamber control groups throughout the study.
In male rats, the incidences of malignant mesothelioma occurred with a positive trend and were significantly increased in all exposed groups compared to the chamber control group. Malignant mesothelioma occurred in one 25 ppm female and one 50 ppm female. Global gene expression analysis was performed to identify overrepresented pathways involved in mesotheliomas from vinylidene chloride-exposed F344/N rats compared to spontaneous mesotheliomas in control F344/N rats.
The incidence of C-cell adenoma of the thyroid gland was significantly increased in 100 ppm females, and the incidence of C-cell carcinoma was significantly increased in 25 ppm females. The incidences of adenoma or carcinoma (combined) were significantly increased in 25 and 100 ppm females.
The incidence of mononuclear cell leukemia was significantly increased in 100 ppm females.
Renal tubule carcinomas were observed in several vinylidene chloride exposed males; these neoplasms are rare in male F344/N rats.
The only exposure-related primary nasal neoplasm observed in rats was adenoma in the respiratory epithelium. Exposure concentration-related increased incidences of turbinate atrophy and hypertosis, olfactory epithelium respiratory metaplasia, respiratory epithelium hyperplasia, and chronic active inflammation occurred in all exposed groups of male and female rats, and the severities of the lesions generally increased with increasing exposure concentration.
The incidences of alveolar epithelium hyperplasia in the lung were significantly increased in all exposed groups of male rats; the severities increased with increasing exposure concentration.
In the liver of rats, increased incidences of chronic inflammation, diffuse fatty change, and cystic degeneration in males and females and necrosis in females occurred.
Two-year study in mice
Groups of 50 male and 50 female mice were exposed by whole body inhalation to vinylidene chloride vapor at concentrations of 0, 6.25, 12.5, or 25 ppm, 6 hours plus T90 (10 minutes) per day, 5 days per week for 105 weeks. Survival of 6.25 ppm males was significantly greater than that of the chamber controls. Survival of 25 ppm males and 6.25 and 25 ppm females was significantly less than that of the chamber control groups. Mean body weights of 12.5 and 25 ppm males were at least 10% less than those of the chamber control group after weeks 17 and 13, respectively, and those of 25 ppm females were at least 10% less after week 21. Exposure-related clinical findings included thinness and abnormal breathing in 25 ppm males and abnormal breathing, thinness, and ventral torso mass in all exposed groups of females.
The incidences of renal tubule adenoma, renal tubule carcinoma, and renal tubule adenoma or carcinoma (combined) were significantly increased in all exposed groups of males; the incidences of renal tubule hyperplasia were also significantly increased in all exposed groups of males.
The incidences of hemangioma (all organs) in all exposed groups of females were increased compared to that in the chamber controls, and the incidence of hemangioma or hemangiosarcoma (combined) in 25 ppm females was significantly greater than that in the chamber controls.
The incidences of hepatocellular adenoma in 12.5 ppm females, hepatocellular carcinoma in 25 ppm females, and hepatocellular adenoma or carcinoma (combined) in 12.5 and 25 ppm females were significantly greater than those in the chamber control group. In addition, hepatocholangiocarcinoma occurred in all exposed groups of females. The incidences of hepatocholangiocarcinoma in exposed groups of males were increased compared to that in the concurrent chamber control group and exceeded the historical control range for inhalation studies. In females, this neoplasm is much less common than in males; it has not been observed in 300 inhalation controls or 948 controls from all routes of exposure. In males, hepatocholangiocarcinoma has been reported in two of 299 inhalation controls and in 10 of 949 from all routes of exposure. The incidences of hepatocellular adenoma in 12.5 ppm females, hepatocellular carcinoma in 25 ppm females, and hepatocellular adenoma or carcinoma (combined) in 12.5 and 25 ppm females were significantly greater than those in the chamber control group. In addition, hepatocholangiocarcinoma occurred in all exposed groups of females. The incidences of hepatocholangiocarcinoma in exposed groups of males were increased compared to that in the concurrent chamber control group and exceeded the historical control range for inhalation studies. In females, this neoplasm is much less common than in males; it has not been observed in 300 inhalation controls or 948 controls from all routes of exposure. In males, hepatocholangiocarcinoma has been reported in two animals from 299 inhalation studies and in 10 male mice from all routes of exposure.
The incidence of alveolar/bronchiolar carcinoma was significantly increased in 12.5 ppm females.
In 25 ppm females, the incidence of carcinoma of the small intestine (ileum) exceeded the historical control ranges for inhalation studies and all routes of administration.
Turbinate atrophy, hyperostosis, and olfactory epithelium respiratory metaplasia occurred in the nose of the vast majority of exposed male and female mice, and the severity of these lesions increased with increasing exposure concentration. The incidences of olfactory epithelium hyaline droplet accumulation in 12.5 and 25 ppm males and 25 ppm females and respiratory epithelium hyperplasia in 25 ppm females were significantly increased compared to chamber controls.
Genetic toxicology
Vinylidene chloride was not mutagenic in any of several strains of Salmonella typhimurium when testing occurred with or without exogenous metabolic activation using a preincubation protocol. However, when tested in a closed system as a vapor, vinylidene chloride was mutagenic in mouse lymphoma L5178Y tk+/- cells in the presence of exogenous metabolic activation provided by induced male rat liver S9 mix and questionable without S9. In vivo, no increase in sex-linked recessive lethal mutations was seen in germ cells of adult male Drosophila melanogaster exposed via feeding or injection to vinylidene chloride. No increase in the frequency of micronucleated erythrocytes was observed in peripheral blood of male or female B6C3F1/N mice exposed to vinylidene chloride by inhalation for a period of 3 months.
Conclusions
Under the conditions of this 2-year inhalation study, there was clear evidence of carcinogenic activity (see summary of the peer review panel comments and the public discussion on this Technical Report in Appendix M) of vinylidene chloride in male F344/N rats based on increased incidences of malignant mesothelioma. Increased incidences of renal tubule carcinoma and respiratory epithelium adenoma in the nose of male rats were also considered to be related to vinylidene chloride exposure. There was some evidence of carcinogenic activity of vinylidene chloride in female F344/N rats based on increased incidences of C-cell adenoma or carcinoma in the thyroid gland and systemic mononuclear cell leukemia. Occurrences of malignant mesothelioma may have been related to vinylidene chloride exposure. There was clear evidence of carcinogenic activity of vinylidene chloride in male B6C3F1/N mice based on increased incidences of renal tubule adenoma and carcinoma. Increased incidences of hepatocholangiocarcinoma may have been related to vinylidene chloride exposure. There was clear evidence of carcinogenic activity of vinylidene chloride in female B6C3F1/N mice based on increased incidences of systemic hemangioma or hemangiosarcoma (combined). Hepatocholangiocarcinoma and hepatocellular adenoma or carcinoma (combined) in the liver of female mice were also considered to be related to vinylidene chloride exposure. Increased incidences of alveolar/bronchiolar carcinoma in the lungs and carcinoma of the small intestine may have been related to treatment.
Exposure to vinylidene chloride caused increases in the incidences of nonneoplastic lesions in the nose of rats and mice, the liver of rats, the lung of male rats, and the kidney of male mice.
National Toxicology Program (NTP). 2015. NTP technical report on the toxicology and carcinogenesis studies of vinylidene chloride (CASRN 75-35-4) in F344/N rats and B6C3F1/N mice (inhalation studies). Research Triangle Park, NC: National Toxicology Program. Technical Report 582. https://doi.org/10.22427/NTP-TR-582