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Health and Environmental Impacts

Inhalation is the principal route by which an individual is exposed to nPB. Exposure can also occur by absorption through the skin.

No federal or Massachusetts agency has established safe exposure limits for workers using nPB. In 2005, the American Conference of Governmental Industrial Hygienists (ACGIH) set a Threshold Limit Value (TLV) of 10 ppm as a time weighted average (TWA). The California Occupational Safety and Health Standards Board set a limit of 5 ppm (TWA) in 2009. Neither of these exposure limits, however, reflects recent reports of nervous system damage in workers exposed to levels of nPB as low as 1.28 ppm, or the potential of nPB to cause cancer.  Based on this recent evidence, employers and workers should err on the side of caution by keeping exposures to nPB as low as possible, and preferably below 1 ppm. As a result of the emerging evidence regarding health effects associated with nPB, in 2011, ACGIH has issued a Notice of Intended Change regarding its nPB TLV.

 Acute (Short-Term) Health Effects

The following effects have been reported among workers with high exposures to nPB:

  • Eye, nose, throat, or lung irritation
  • Headache, fatigue, dizziness, nausea, malaise

 Chronic (Long-Term) Health Effects

Neurotoxicity:

Peripheral and central nervous system toxicity have been observed in workers exposed to nPB, and in animals. In several studies, exposed workers exhibited the following symptoms:

  • Joint pain or leg weakness and pain leading to difficulty with standing and walking (stumbling);
  • Muscle twitching or numbness, tingling, and prickling in the hands or feet, loss of vibration sense;
  •  Anxiety, apathy, insomnia, and memory and concentration difficulties.

Symptoms persisted for months and, in some cases, years after exposure.

Developmental and Reproductive Effects: 

The National Toxicology Program’s (NTP) Center for the Evaluation of Risks to Human Reproduction (CERHR) released a report on nPB in 2003. This expert panel concluded that nPB was a developmental and reproductive toxicant based on animal studies. As reviewed in this report, nPB affected a number of reproductive endpoints that can result in impaired fertility or sterility in both females and males. nPB also caused delayed growth in the offspring of animals exposed during pregnancy. While no epidemiological study has examined the developmental and reproductive effects of nPB in humans, some case studies of female workers occupationally exposed to nPB reported altered menstrual periods. These effects have not been observed in all studies.

Liver Toxicity:

Based on evidence in studies using mice, exposures may harm the liver.

Hematological Effects:

Studies of workers indicate that exposures can result in lowered red blood cell count.

 Cancer:

Results from a 2-year inhalation cancer study conducted by NTP show that nPB can cause malignant large intestinal tumors in female rats, possibly rare intestinal tumors in male rats and malignant lung/bronchial tumors in female mice.The NTP study also suggests that cancerous tumors of the skin, pleura (e.g., mesothelioma), and pancreas in rats may be related to nPB exposure. Because nPB is a new solvent, and cancer takes a long time to develop, studies of cancer associated with nPB exposure among workers or the public have not been conducted.