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398 13 Nanoaerosol

or integumentary system and leach into the bloodstream. Contrary to neutral nano-
aerosols of the same size; charged nanoaerosol particles have a much greater prob-
ability of depositing into the lungs [9]. Similar to the effects of fine aerosol,
nanoaerosol can cause inflammation, fibrosis, and lung tumors if the exposure at
workplaces passes certain threshold and long-lasting. Increased surface area and
decreased particle diameter are believed to be the cause of the increased toxicity of
granular nanomaterials in the lungs. Lung toxicity, evidenced by inflammation and
tissue damage, was also proven to be induced by fibrous nanomaterials such as carbon
nanotubes (CNTs). Despite of the evidences provided by tests using rate, mice, and
hamsters, not everybody agrees with the mechanisms of tumor development.
Effects on the skin or a relevant skin penetration were not well quantified.
However, the barrier function of the skin could be breached by the presence of skin
lesions, strong mechanical strain or small-sized nanoparticles (<5–10 nm). For
example, a human case of allergic response to nanomaterials was described by a
person exposed to dendrimers in Japan [57]. A 22-year old student involved in
synthesis of dendrimers developed erythema multiforme-like contact dermatitis on
his hands. Conventional treatments and anti-histamines could not stop the disease
from progressing to other areas of the body. After 3 weeks of hospitalization, he
recovered, but it appeared again when he reentered the same laboratory.
At this moment, there is no legal standard that sets the occupational exposure
threshold of nanoaerosol. The development of risk assessment of exposure to
nanoaerosol has been limited by the lack of standard methods and compact
instrumentation for long term monitoring. Accurate risk assessment requires
advanced nanoaerosol sampling and characterization techniques for the analysis of
both physical and chemical properties of nanoaerosol. Nonetheless, occupational
exposure limits for nanomaterials are set by different organizations. Proposed
occupational exposure limits for engineered nanoaerosol are summarized in
Table 13.1.

Table 13.1 Proposed occupational exposure limits of nanoaerosols
Nanoaerosol Occupational exposure Parameters
limit
Titanium dioxide 0.1 mg/m 3 0.1 risk level particles\100 nm
General dust 3 mg/m 3
Photocopier toner 0.6 mg/m 3 Tolerable risk
0.06 mg/m 3 2009 acceptable risk
0.006 mg/m 3 2018 acceptable risk
Biopersistent granular 20,000 particles/cm 3 Density > 6,000 kg/m 3
materials (e.g., metal oxides) 40,000 particles/cm 3 Density < 6,000 kg/m 3
Carbon Nanotubes (CNTs) 0.01 f/cm 3 Exposure risk ratio for asbestos
Fibrous 0.01 f/cm 3 3:1; length 75,000 nm
Multi-walled CNTs 0.0025 mg/m 3 Nanocyl product only [40]
Source Schulte et al. [47]