from the diesel sample on the basis of size. Only low levels of EC (# 15 :g/m3 ) were found in electric-powered (i.e., nondieselized) coal mines when impactors with submicrometer cutpoints were used for air sampling [47]. Guidance on air sampling is discussed in a following section. In addition to selectivity, potential health effects were considered when an EC surrogate was proposed [34, 48, 49]. Diesel particles and other types of insoluble fine particles are inhaled deeply into the lungs, where they can induce an inflammatory response. Further, EC particles increase the long-term retention [50, 51] of adsorbed genotoxins and other chemical toxins because the particles have a high affinity for them [52]. The adsorbed organic fraction results from rapid cooling of the exhaust mixture, which causes enrichment of some species on the particle surface [53–55]. Enrichment by this mechanism is associated with compounds of moderate to low volatility [54, 55]. For example, PAHs having four or more rings are generally associated with particulate matter [56]; this is important because these higher-ring condensates are expected to be the most carcinogenic or mutagenic [57, 58]. In combination with an inflammatory response induced by the particles, genotoxic agents may promote tumorigenesis. Ultrafine particles (< 0.10 :m) may pose an even greater health risk. Results of toxicological studies on solid particles having aerodynamic diameters in this size range indicate ultrafine particles are especially toxic, even those not having an organic fraction and consisting of materials considered relatively nontoxic (e.g., carbon black, titanium dioxide). In a recent study (see reference [23], Donaldson et al.) of rats, a 10-fold increase in inflammation was seen with exposures to ultrafine particles, relative to the same mass of fine particles. This is significant because, by mass, the majority of diesel particles are in the fine particle range, and most are in the ultrafine range by number (see reference [28], Kittleson et al.). Given the physical and chemical nature of EC particles emitted by diesel engines, monitoring and controlling exposures to these particles is prudent.
2.
ANALYTICAL METHOD a. Background A monitoring method for diesel particulate matter was published as Method 5040 in the NIOSH Manual of Analytical Methods (NMAM). The method is based on a thermal-optical analysis technique for particulate carbon. Both OC and EC are determined by the method, but EC is a better surrogate of exposure. Rationale for use of an EC surrogate is summarized in the previous section (see Analyte Choice). Method updates have been published [59, 60] to include data (e.g., round robin results) obtained since the initial publication (1996) of the method. NMAM 5040 has been used in numerous industrial hygiene surveys, [36–43] and it was recently applied to an ongoing epidemiological study (NIOSH/National Cancer Institute [NCI]) of miners. Details on method operation and performance are provided in this chapter. Recently proposed exposure criteria also are discussed.
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