Lessons Learned from Unintentional Aerosols - Safety of Nanomaterials along Their Lifecycle - page 104

Motor vehicles are a particularly important source of nanoparticles. As detailed
in a recent Health Effects Institute Report (Johnston et al. 2013), investigators devel-
oped an experimental instrument, the nano aerosol mass spectrometer (NAMS),
which focused on nanoparticles smaller than 30 nm. They also analyzed the primary
constituents of these particles and gathered data near a major roadway intersection.
Nanoparticles are formed during transformations of mobile and stationary
sources in the atmosphere. For example, sulfur dioxide is converted into sulfurous
and sulfuric acid. They typically result in many UFPs. We know that nanoparticles
are abundant in diesel emissions but further research in laboratories and in human
populations is needed to fully understand the extent of diesel nanoparticle emissions
and especially their impact on human health.
No current regulations focus exclusively on nanoparticles (UFPs). Inevitably,
regulatory standards are mass based because sampling devices measure that param-
eter. Neither appropriate air samplers nor data exist which permit rational standards
focusing on nanoparticle emissions from gasoline or diesel engines. Another prob-
lem is that some diesel particles contain volatile material as well as solids, and most
sampling techniques fail to capture and measure the volatile fraction.
5.4.3 o CCuPational e xPosures
Smith et al. have extensive data on exposures of employees who drive trucks (Smith
et al. 2006, 2012). Importantly, the most significant exposures of truck drivers occur
not in their cabs while driving, but while loading and unloading materials at truck
terminals. Frequently, engines continue to run and these sheltered or semisheltered
areas may not have adequate air circulation to dispose off truck exhaust. Their data
show that diesel particles contribute to the exposure of truck drivers and that these
particles contain significant numbers of nanoparticles.
Diesel emissions have changed dramatically over the last three or four decades.
Changes have been made in engine design, fuels, and after-treatment. The result has
been a dramatic decrease in the mass of emissions. However, decreases in nanopar-
ticles have been less dramatic.
Fumes, particularly metal fumes, consist of particles produced by materials that
have become gaseous. As they cool, they form liquids and solids. Such nanoparticles
are prominent in welding fume. These fumes consist primarily of UFPs and may
lead to well-characterized responses such as metal or polymer fume fever (Drinker
et al. 1927; Gordon et al. 1992).
5.4.4 C oal d ust
Underground coal mining is associated with serious lung diseases. The literature
suggests that respirable particles are responsible. There is increasing evidence that
regulations in the United States designed to prevent Coal Workers' pneumoconiosis
(CWP) may no longer be adequate. Recent CDC data show that younger individuals,
such as those working in underground mines in West Virginia and Kentucky, are
getting serious lung diseases related to their occupational exposure. A key element
is the increasing use of powerful machinery and the way it produces both higher