What is Dinitro-o-cresol?

Dinitro-o-cresol (DNOC) is an organic compound with the structural formula CH₃C₆H₂(NO₂)₂OH. DNOC is a yellow solid with no smell. The taste of DNOC is not known. It dissolves slightly in water.

What is Dinitro-o-cresol used for?

Agriculture: DNOC was primarily used as a pesticide to protect fruit trees and food crops from insect damage. However, its registration as a pesticide was cancelled by the United States EPA in 1991 due to safety concerns. It has since been replaced by less expensive and more effective pest control chemicals.

Pharmaceuticals (Historical): In the 1930s, DNOC was used in weight-reduction pills. This use was discontinued because of severe health effects.

In the Environment

Air

DNOC is not significantly destroyed in the air by chemical reactions or sunlight. It eventually returns to land and water through rain or snow. The time it stays in the air before removal is unknown.

Water

• Microorganisms may slowly break down DNOC in water.
• DNOC does not evaporate significantly from water.
• It sticks to particles, which can transfer it to bottom sediments.

Soil

• Microorganisms break down DNOC in soil, but chemical reactions and evaporation are not significant.
• DNOC has been found in groundwater in areas where it was applied.
• The level of DNOC in soil may decrease to half in 14 days to a month or longer.

Sources & Routes of Exposure 

Source of Exposure

• Breathing contaminated air.
• Drinking contaminated water or eating contaminated food.
• Living near DNOC waste sites.
• Handling DNOC products during manufacturing, spraying, incinerating waste, or cleaning contaminated sites.
• Children may be exposed by playing in contaminated soil.

Routes of Exposure

• Inhalation
• Skin absorption
• Ingestion
• Skin and/or eye contact

Health Effects

Acute Effects

• Symptoms in humans: Sweating, increased pulse and respiratory rates, thirst, fatigue, headache, nausea, loss of appetite, malaise, collapse, and coma.
• Other effects: Yellow pigmentation of skin, hands, nails, and hair; damage to the liver, kidneys, and nervous system; local necrosis from skin contact.
• Toxic mechanism: DNOC disrupts oxidative phosphorylation, causing extreme toxicity.
• Animal studies: Acute tests in rats, mice, rabbits, and guinea pigs show extreme toxicity from oral exposure and high toxicity from skin exposure.

Chronic Effects

• Symptoms similar to acute exposure in humans.
• Long-term effects: Bilateral cataracts, blindness, and organ weight changes (increased heart, brain, liver, kidney, and thyroid weights; decreased thymus and reproductive organ weights).
• Animal studies: Rats showed decreased food consumption, weight gain, liver enzyme activity, and organ changes.
• No EPA Reference Dose (RfD) or Concentration (RfC) is established.
• ATSDR's minimal risk level (MRL): 0.004 mg/kg/day, based on neurological effects.

Reproductive/Developmental Effects

• No human data is available.
• Animal studies: No teratogenic effects were observed, but chromosomal aberrations were reported in mice. Mixed results on effects on spermatogenesis.

Cancer Risk

• No evidence of carcinogenic effects in humans or animals.
• DNOC is not classified by the EPA for cancer potential.

Safety

First Aid Measures

• Eyes: Flush with water for at least 15 minutes and seek medical aid immediately.
• Skin: Wash with water for at least 15 minutes, remove contaminated clothing, and seek medical aid immediately.
• Ingestion: Do not induce vomiting unless directed by medical personnel. Seek medical aid immediately.
• Inhalation: Move to fresh air, provide artificial respiration if needed, and seek medical aid immediately.

Exposure Controls & Personal Protection

Engineering Controls

• Use eyewash stations and safety showers in facilities handling DNOC.
• Ensure proper ventilation to keep airborne DNOC below permissible limits.

Personal Protective Equipment (PPE)

• Eyes: Safety goggles or protective glasses.
• Skin: Protective gloves and clothing.
• Respirators: Use as per OSHA 29 CFR 1910.134 or EN 149 standards when required.

Regulation

United States

OSHA: The United States Occupational Safety & Health Administration has set the following Permissible Exposure Limit (PEL) for DNOC: 

• General Industry: 0.2 mg/m³ (Skin) 
• Construction Industry: 0.2 mg/m³ TWA (Skin) 

ACGIH: The American Conference of Governmental Industrial Hygienists has established a Threshold Limit Value (TLV) for DNOC of 0.2 mg/m³ TWA (Skin) 

NIOSH: The National Institute for Occupational Safety and Health has set a Recommended Exposure Limit (REL) for DNOC of 0.2 mg/m³ TWA (skin)

EPA: The Environmental Protection Agency has listed DNOC as a hazardous air pollutant. Federal regulations limit the amount of DNOC that factories can release into wastewater. EPA requires industries to report releases or spills of 10 pounds or more.

Australia

Safe Work Australia: Safe Work Australia has set a time-weighted average (TWA) concentration of 0.2 mg/m³ for DNOC for an 8-hour workday.