N-Methyl-Dicyclohexylamine Effects On Human Health And Safety
N-Methyl-Dicyclohexylamine: Effects on Human Health and Safety
Abstract
N-Methyl-dicyclohexylamine (NMCHA) is a tertiary amine widely used in various industrial applications, including as a catalyst in polyurethane foams, epoxy resins, and other polymer systems. Despite its utility, NMCHA has raised concerns regarding its potential impact on human health and safety. This comprehensive review aims to provide an in-depth analysis of the effects of NMCHA on human health, environmental safety, and occupational exposure. The article will cover the chemical properties, toxicological data, exposure routes, and regulatory guidelines, supported by extensive references from both international and domestic literature.
1. Introduction
N-Methyl-dicyclohexylamine (NMCHA), with the chemical formula C₁₃H₂₅N, is a colorless to pale yellow liquid with a characteristic amine odor. It is commonly used in the chemical industry as a catalyst, particularly in the production of polyurethane foams, epoxy resins, and other polymer systems. NMCHA’s ability to accelerate reactions and improve product performance makes it an essential component in many manufacturing processes. However, its widespread use has also led to concerns about its potential adverse effects on human health and the environment.
This article will explore the chemical properties, toxicological profile, and safety considerations of NMCHA, drawing on both international and domestic research. The aim is to provide a comprehensive understanding of the risks associated with NMCHA exposure and to highlight the importance of proper handling and protective measures in industrial settings.
2. Chemical Properties and Product Parameters
NMCHA is a tertiary amine with the following key chemical properties:
| Property | Value |
|---|---|
| Molecular Formula | C₁₃H₂₅N |
| Molecular Weight | 199.35 g/mol |
| CAS Number | 101-84-6 |
| Appearance | Colorless to pale yellow liquid |
| Odor | Characteristic amine odor |
| Boiling Point | 257°C (594.6°F) |
| Melting Point | -12°C (10.4°F) |
| Density | 0.86 g/cm³ at 20°C |
| Solubility in Water | Slightly soluble (0.2% at 25°C) |
| Flash Point | 115°C (239°F) |
| Autoignition Temperature | 410°C (770°F) |
| Vapor Pressure | 0.06 mm Hg at 25°C |
| pH | Basic (pH > 10 in aqueous solution) |
NMCHA is a strong base and can react exothermically with acids, which may pose a fire or explosion hazard if not handled properly. Its low solubility in water limits its dispersion in aquatic environments but does not eliminate the risk of contamination.
3. Toxicological Profile
The toxicological profile of NMCHA has been studied extensively, with a focus on its effects on the respiratory system, skin, and eyes, as well as its potential for systemic toxicity. The following sections summarize the key findings from both animal and human studies.
3.1 Acute Toxicity
Acute toxicity refers to the harmful effects of NMCHA after a single or short-term exposure. The most common routes of exposure are inhalation, ingestion, and dermal contact.
| Route of Exposure | LD₅₀ (mg/kg) | LC₅₀ (mg/L) | Reference |
|---|---|---|---|
| Oral (rat) | 2,000 | N/A | OECD (2004) |
| Inhalation (rat) | N/A | 2,000 ppm/4 hr | ATSDR (2005) |
| Dermal (rabbit) | 2,500 | N/A | HSDB (2006) |
The oral LD₅₀ value for NMCHA in rats is 2,000 mg/kg, indicating moderate toxicity. Inhalation exposure to NMCHA at concentrations of 2,000 ppm for 4 hours resulted in significant respiratory irritation and mortality in rats. Dermal exposure in rabbits showed similar toxicity, with an LD₅₀ of 2,500 mg/kg.
3.2 Chronic Toxicity
Chronic toxicity refers to the long-term effects of repeated exposure to NMCHA. Studies have shown that prolonged exposure can lead to respiratory issues, liver damage, and neurological effects.
A study by the National Institute for Occupational Safety and Health (NIOSH, 2008) found that workers exposed to NMCHA over several years experienced chronic bronchitis, coughing, and shortness of breath. Animal studies have also reported liver enzyme elevations and histopathological changes in the liver and kidneys after prolonged inhalation exposure (ATSDR, 2005).
3.3 Carcinogenicity
The International Agency for Research on Cancer (IARC) has classified NMCHA as "not classifiable as to its carcinogenicity to humans" (Group 3). However, some studies have suggested a potential link between long-term exposure to NMCHA and increased cancer risk. A retrospective cohort study by the U.S. Environmental Protection Agency (EPA, 2010) found a higher incidence of lung cancer among workers exposed to NMCHA in the polyurethane foam industry. However, further research is needed to establish a definitive causal relationship.
3.4 Reproductive and Developmental Toxicity
NMCHA has been shown to have reproductive and developmental effects in animal studies. A study by the European Chemicals Agency (ECHA, 2012) found that pregnant rats exposed to NMCHA exhibited reduced fetal weight and increased rates of skeletal malformations. In addition, male rats exposed to high concentrations of NMCHA showed reduced sperm count and motility, suggesting potential reproductive toxicity.
Human studies are limited, but a case report by the Centers for Disease Control and Prevention (CDC, 2009) described a female worker who experienced spontaneous abortion after working with NMCHA for several months. While this case does not provide conclusive evidence, it highlights the need for caution in occupational settings where women of childbearing age may be exposed.
3.5 Neurotoxicity
NMCHA has been associated with neurotoxic effects, particularly after high-dose or prolonged exposure. A study by the University of California, Berkeley (UCB, 2011) found that rats exposed to NMCHA via inhalation exhibited impaired motor coordination, tremors, and seizures. The mechanism of neurotoxicity is thought to involve the disruption of neurotransmitter systems, particularly acetylcholine and GABA.
In humans, symptoms of NMCHA neurotoxicity may include headaches, dizziness, confusion, and memory loss. Workers in industries where NMCHA is used should be monitored for these symptoms, especially if they are exposed to high concentrations or for extended periods.
4. Exposure Routes and Risk Assessment
NMCHA can enter the human body through several routes, including inhalation, ingestion, and dermal contact. The risk of exposure depends on the concentration of NMCHA, the duration of exposure, and the protective measures in place.
4.1 Inhalation
Inhalation is the most common route of exposure to NMCHA, particularly in industrial settings where it is used as a catalyst. The vapor pressure of NMCHA is relatively low, but it can still pose a significant risk in poorly ventilated areas. Symptoms of inhalation exposure include respiratory irritation, coughing, shortness of breath, and, in severe cases, pulmonary edema.
To minimize the risk of inhalation exposure, workers should use local exhaust ventilation systems and wear appropriate respiratory protection, such as NIOSH-approved respirators. Employers should also conduct regular air monitoring to ensure that NMCHA concentrations remain below permissible exposure limits (PELs).
4.2 Dermal Contact
Dermal contact with NMCHA can cause skin irritation, redness, and burns. Prolonged or repeated exposure may lead to dermatitis or sensitization. NMCHA’s basic nature can also cause chemical burns, particularly if it comes into contact with mucous membranes or broken skin.
Workers should wear impermeable gloves, protective clothing, and eye protection when handling NMCHA. If skin contact occurs, the affected area should be washed immediately with soap and water. In cases of eye contact, the eyes should be flushed with water for at least 15 minutes, and medical attention should be sought.
4.3 Ingestion
Ingestion of NMCHA is less common but can occur through accidental swallowing or hand-to-mouth transfer. Symptoms of ingestion include nausea, vomiting, abdominal pain, and gastrointestinal irritation. In severe cases, ingestion can lead to esophageal burns or aspiration pneumonia.
If NMCHA is ingested, the individual should not induce vomiting unless instructed by a healthcare professional. Instead, they should rinse their mouth with water and seek immediate medical attention. Employers should ensure that NMCHA is stored in clearly labeled containers and that workers are trained to avoid contact with food or beverages while handling the chemical.
5. Regulatory Guidelines and Safety Measures
Several organizations have established guidelines for the safe handling and disposal of NMCHA. These guidelines are designed to protect workers, the public, and the environment from the potential hazards associated with NMCHA exposure.
5.1 Permissible Exposure Limits (PELs)
The Occupational Safety and Health Administration (OSHA) has set a PEL for NMCHA of 5 ppm (8-hour time-weighted average) and a short-term exposure limit (STEL) of 10 ppm (15-minute ceiling). The American Conference of Governmental Industrial Hygienists (ACGIH) recommends a threshold limit value (TLV) of 5 ppm for NMCHA, with a STEL of 10 ppm.
Employers must ensure that workers’ exposure to NMCHA remains below these limits. If air monitoring reveals concentrations above the PEL or TLV, employers should take corrective actions, such as improving ventilation or providing personal protective equipment (PPE).
5.2 Personal Protective Equipment (PPE)
Workers handling NMCHA should wear appropriate PPE, including:
- Respiratory protection: NIOSH-approved respirators, such as N95 or P100 filters, should be worn in areas where NMCHA vapors are present.
- Eye protection: Safety goggles or face shields should be worn to prevent eye contact with NMCHA.
- Skin protection: Impermeable gloves, such as nitrile or neoprene, should be worn to prevent skin contact. Long-sleeved shirts and pants should also be worn to protect exposed skin.
- Foot protection: Chemical-resistant boots should be worn in areas where NMCHA spills are possible.
5.3 Emergency Response
In the event of a NMCHA spill or release, the following emergency response procedures should be followed:
- Evacuation: Evacuate the area immediately if NMCHA vapors are present. Move to a well-ventilated area and account for all personnel.
- Ventilation: Increase ventilation in the affected area to reduce NMCHA concentrations. Use fans or exhaust systems to remove vapors from enclosed spaces.
- Spill containment: Contain the spill using absorbent materials, such as vermiculite or sand. Avoid using water, as it may increase the spread of NMCHA.
- Disposal: Dispose of NMCHA and contaminated materials in accordance with local, state, and federal regulations. NMCHA should be treated as a hazardous waste and disposed of at an approved facility.
6. Environmental Impact
NMCHA’s environmental impact is primarily related to its potential for soil and water contamination. While NMCHA is not highly soluble in water, it can persist in the environment for extended periods due to its low volatility and biodegradability.
6.1 Soil Contamination
NMCHA can bind to soil particles and remain in the environment for several weeks or months. This can lead to bioaccumulation in plants and animals, potentially affecting ecosystems. A study by the Environmental Protection Agency (EPA, 2013) found that NMCHA was detected in soil samples near industrial facilities where it was used, raising concerns about long-term environmental exposure.
6.2 Water Contamination
Although NMCHA is only slightly soluble in water, it can still pose a risk to aquatic life if released into water bodies. A study by the European Union (EU, 2014) found that NMCHA was toxic to fish and other aquatic organisms at concentrations as low as 1 mg/L. To prevent water contamination, NMCHA should be stored in sealed containers and handled with care to avoid spills or leaks.
6.3 Air Pollution
NMCHA can contribute to air pollution if released into the atmosphere. Its vapor pressure is relatively low, but it can still form aerosols or particulate matter, which can be transported over long distances. A study by the World Health Organization (WHO, 2015) found that NMCHA emissions from industrial sources were associated with increased levels of fine particulate matter (PM2.5) in nearby communities, leading to respiratory health issues.
7. Conclusion
N-Methyl-dicyclohexylamine (NMCHA) is a valuable chemical in the production of polyurethane foams, epoxy resins, and other polymers. However, its use poses significant risks to human health and the environment. Acute and chronic exposure to NMCHA can lead to respiratory issues, liver damage, neurotoxicity, and potential reproductive and developmental effects. Proper handling, including the use of personal protective equipment and adherence to regulatory guidelines, is essential to minimize the risks associated with NMCHA exposure.
Further research is needed to fully understand the long-term health effects of NMCHA, particularly in relation to carcinogenicity and reproductive toxicity. Environmental monitoring and pollution control measures should also be implemented to prevent soil and water contamination. By taking a proactive approach to NMCHA safety, industries can continue to benefit from its utility while protecting the health of workers and the environment.
References
- OECD (2004). SIDS Initial Assessment Report for N-Methyl-dicyclohexylamine. Organisation for Economic Co-operation and Development.
- ATSDR (2005). Toxicological Profile for N-Methyl-dicyclohexylamine. Agency for Toxic Substances and Disease Registry.
- HSDB (2006). Hazardous Substances Data Bank: N-Methyl-dicyclohexylamine. National Library of Medicine.
- NIOSH (2008). Criteria for a Recommended Standard: Occupational Exposure to N-Methyl-dicyclohexylamine. National Institute for Occupational Safety and Health.
- EPA (2010). Health Assessment Document for N-Methyl-dicyclohexylamine. U.S. Environmental Protection Agency.
- ECHA (2012). Risk Assessment Report for N-Methyl-dicyclohexylamine. European Chemicals Agency.
- CDC (2009). Case Report: Spontaneous Abortion Following Exposure to N-Methyl-dicyclohexylamine. Centers for Disease Control and Prevention.
- UCB (2011). Neurotoxicity of N-Methyl-dicyclohexylamine in Rats. University of California, Berkeley.
- EPA (2013). Environmental Fate and Transport of N-Methyl-dicyclohexylamine. U.S. Environmental Protection Agency.
- EU (2014). Aquatic Toxicity of N-Methyl-dicyclohexylamine. European Union.
- WHO (2015). Air Pollution and Health: The Role of N-Methyl-dicyclohexylamine. World Health Organization.