Methylene chloride can cause slight irritation and mild central nervous system (CNS) depression. Slight irritation of the nose and throat were noted in one study after exposure to 500 ppm for 1 hour. However, in another study, no irritation was noted following exposures to concentrations from 515 ppm (1 hour) to 986 ppm (2 hrs).

No effects were seen when volunteers were exposed to 213 ppm for 60 minutes. Mild CNS effects (headache, dizziness) were seen in volunteers exposed to concentrations as low as 200 ppm for 2-3 hours or 986 ppm for 1 hour. Other signs of mild CNS depression such as dizziness, nausea, inability to concentrate, and reduced coordination have been reported in numerous case reports, usually when methylene chloride was used in poorly ventilated areas. In more severe cases, methylene chloride has caused serious CNS depression including unconsciousness and respiratory failure as well as pulmonary edema and death.

Metabolism of methylene chloride to carbon monoxide (which binds to red blood cells forming carboxyhemoglobin) may cause heart problems.

The liquid is a moderate to severe irritant. If methylene chloride is sealed to the skin by gloves, shoes or tight clothing, serious irritation may result. In one case, a worker developed second and third degree burns after collapsing and laying unconscious for about 30 minutes in methylene chloride. Absorption through the skin can occur, but it is not reported to be significant.

A vapour concentration of 500 ppm caused mild irritation after one hour. Liquid and concentrated vapours may cause moderate to severe irritation. Liquid may cause temporary corneal damage.

Methylene chloride has relatively low toxicity if ingested, based on limited human information and animal studies. Ingestion of about 1-2 pints (about 500-1000 mL) of a paint remover containing methylene chloride caused severe burns and swelling in the throat of a man. The man became unconscious one and a half hours after ingesting the paint remover and hospitalization was required. He recovered but continued to have stomach problems 6 months after the event.

A group of employees exposed to an average concentration of 475 ppm (8 hour TWA) for more than 10 years was compared to a similar non-exposed group. There was no difference in liver, cardiac or neurologic health when the two groups were compared.

SKIN: Repeated or prolonged skin contact may result in dermatitis (redness and irritation).

NEUROLOGICAL: Long-term (months, years) exposure to methylene chloride has caused neurological effects. In one case, a worker developed memory loss, speech problems and balance problems after regular exposure for about three years to an estimated airborne concentration of 500-1000 ppm methylene chloride. In another case, a worker developed delirium (auditory hallucinations), memory loss, blurred vision and confusion. The worker had worked with a solution containing 78% methylene chloride in a vat room for 12 hour periods over 4 years. In both of these case reports, the authors attribute the effects to the metabolism of methylene chloride to carbon monoxide.

In three studies, there was no increase in cancer among workers with long-term exposure to dichloromethane (methylene chloride).

IARC evaluation of the carcinogenicity of dichloromethane (methylene chloride) to humans: Inadequate evidence. Overall IARC evaluation of carcinogenic risk: Group 2B (possibly carcinogenic to humans).

The US National Toxicology Program (NTP) identifies this chemical as one which may reasonably be anticipated to be a carcinogen.

In a case study, eight men had histories of infertility and testicular or prostatic discomfort. These men all worked in a process where they had mixed skin and inhalation exposure to methylene chloride. The average airborne concentration was 68 ppm (range 3.3 to 154.4 ppm). Biological monitoring also indicated exposure to methylene chloride. Four of the eight men were tested for sperm count. In all four, there was a significant reduction in the motile sperm count. These case reports suggest that methylene chloride may inhibit sperm production. However, the men were exposed to other chemicals at the same time, and additional research is required to confirm these findings. Testicular atrophy was seen in one animal study. Methylene chloride has been detected in human breast milk.

In animal studies, slight fetotoxicity was noted, but no embryotoxic or teratogenic effects were seen. The fetotoxicity was observed at doses which were maternally toxic. A study of women working in a pharmaceutical factory found an increased risk of spontaneous abortions associated with exposure to several chemicals including methylene chloride. Another study of women working with glue found methylene chloride in the fetal tissues. This observation indicates methylene chloride crosses the placental barrier.

Because methylene chloride can be metabolized to carbon monoxide, other exposures to carbon monoxide (e.g. smoking, vehicle exhaust) should be monitored. Animal evidence indicates that exposure to ethanol may potentiate the effects of methylene chloride.

Animal evidence suggest that methylene chloride is well absorbed through the lungs, intestine and skin. It is converted to carbon monoxide and carbon dioxide in the body. The carbon monoxide results in increased levels of blood carboxyhemoglobin. Methylene chloride does not appear to accumulate in the body and is rapidly excreted.