Lead, respirable particles

Dichlorobenzidine is not a volatile chemical. In the air, it may exist as dust particles or boimd to particulate matter. The absorption of 3,3 -dichlorobenzidine from such respirable particles into the body depends, in part, on the size of the particle. Large particles tend to deposit in the upper airways and are subsequently cleared by ciliary action with little absorption across limg tissues. However, the ciliary action transports the particles to the epiglottis where they are often swallowed, leading to gastrointestinal absorption. Smaller particles can penetrate more deeply into the respiratoiy tree, where 3,3 -dichloro-benzidine absorption may be significant. 

To counter the fine lead pigment particles that become airborne, a respirator with an organic vapor and particulate cartridge is strongly suggested for use by the operator. The cartridges should be capable of removing lead particulate and associated fumes, and removal efficiencies should be documented with actual test data, a fresh air mask could also be used. 

Before we examine the oxidation pathways available to aromatic systems, it is first instructive to review the most notorious role of these compounds in combustion chemistry their propensity to lead to soot formation. Soot is a byproduct of fuel-rich combustion, and soot particles can affect respiration and general health in humans." Soot production is a result of polycyclic aromatic hydrocarbon (PAH) formation in flames as reactive hydrocarbon radical intermediates combine to grow... 

As lead in automotive emissions has been found largely in the fine particle fraction (22, 23), it is reasonable to expect a similar size distribution pattern for manganese from automotive sources. This would explain the strong association between MN and PB in the factor analyses reported here. This probably also explains the association of MN (TSP samples) with several factors at low loadings, rather than with a single factor as the TSP samples would include the mass of respirable as well as coarse manganese. When the concentration of the tracers in coarse particles (calculated as the differences in concentration between the TSP and RSP samples) were included with the RSP data for factor analysis, a factor on which 20% of the total variance (No. 5, Table I) was loaded was obtained. 

At this time the evidence that hyperoxic-induced lung injury was due to excessive oxygen free radical production was still largely indirect. The next major event which specifically addressed this question was the important experiments of Crapo and colleagues in the early 1980 s [10]. These studies conducted with lung tissue were similar to those performed earlier in liver [11] and heart [12]. Crapo and co-workers found that superoxide production, measured as CN-insensitive respiration, was increased in lung slices when exposed to 100% O2 rather than air [10]. This work was extended to the measurement of O2 production in submitochondrial particles [13]. Clearly then exposure of tissues to elevated concentrations of O2 leads to ROS production, the extent of which, in association with local antioxidant defences, will determine the redox balance of the tissue. 

Figure 15.6. Photosynthesis and respiration, (a) A well-balanced ecosystem may be characterized by a stationary state between photosynthetic production, P (rate of production of organic material) and heterotrophic respiration, R (rate of destruction of organic matter). Photosynthetic functions and respiratory functions may become vertically segregated in a lake or in the sea. In the surface waters the nutrients become exhausted by photosynthesis, (b) The subsequent destruction (respiration) of organism-produced particles after settling leads to enrichment of the deeper water layers with these nutrient elements and a depletion of dissolved oxygen. The relative compositional constancy of the aquatic biomass and the uptake (P) and release (R) of nutritional elements in relatively constant proportions (see equation 3) are responsible for a co-variance of carbon, nitrate, and phosphate in lakes (during stagnation period) and in the ocean an increase in the concentration of these elements is accompanied by a decrease in dissolved oxygen, (c, d) The constant proportions AC/AN/AP/AO2 typically observed in these waters are caused by the stoichiometry of the P-R processes.

The metallic element whose concentration in air is most clearly ascribable to man s activities is lead. The level of lead found varies from about 0.1 iig/vn in sparsely populated areas to about 10 /xg/m in areas where automobile traflBc is at a maximum. In a study conducted at Los Angeles, two sites were monitored on either side of a freeway which had approximately 200,000 cars per day as a traflBc level 21), One site was downind a preponderance of the time. If the concentrations at the downwind site are divided by the concentrations of the site that was usually upwind, one can see, in Table XII, ratios that vary from 1.03 (where the percentage of favorable wind was 28) to 4.3 (where the favorable wind percentage was 68). In Table XIII are shown the results obtained when a massive respirable particulate sampler was field tested. The collector was built for EPA by Battelle Columbus. Particles greater than 20 /xm are eliminated with a cyclone. The first stage collects particles by impaction... 

Biological, chemical, and physical effects of airborne metals are a direct function of particle size, concentration, and composition. The major parameter governing the significance of natural and anthropogenic emissions of environmentally important metals is particle size. Metals associated with fine particulates are of concern particles larger than about 3-fjim aerodynamic equivalent diameter are minimally respirable, are ineffective in atmospheric interactions, and have a short air residence time. Seventeen environmentally important metals are identified arsenic, beryllium, cadmium, chromium, copper, iron, mercury, magnesium, manganese, nickel, lead, antimony, selenium, tin, vanadium, and zinc. This report reviews the major sources of these metals with emphasis on fine particulate emissions. 

There is much debate about these particular tests and their appropriateness. However, the concept of the use of aerodynamic particle size testing as a compendial test is now well established. Both impactor testing and impingers testing have a role in the development of MDIs, because they are useful tools in studying aerosol clouds and can provide information that leads to formulation optimization (at least in terms of respirable dose). It should be emphasized that these data should not be taken in isolation, and other appropriate particle-sizing techniques should also be used. A more complete discussion of this topic can be found in Chapter 11. 

The combustion of MMT and its rapid photodecomposition lead to the emission of manganese phosphate, manganese sulfate and manganese oxides, especially Mn304. About 99% of Mn304 particles have mass median aerodynamic diameters of <5 jm and are respirable (Lynam etal. 

It is clear that chemical processes do not involve just alteration of particles that fall to the sediment-water interface. Rather, these systems are dominated by cycling between oxidized and reduced chemical forms within the sediment column. Heterotrophic respiration leads to the oxidation of organic mattei releasing C, N, and P into solution, and the reduction of O2, Fe, Mn, and S. The latter three elements are then subject to transport, both in dissolved and solid forms, back toward the sediment-water interface, where they may be reoxidized either abiotically or by lithotrophic bacteria. The burial of reduced Fe, Mn, and S is a slow leak from these rapid internal cycles (Figure 6). 

Particles up to about 10 pm aerodynamic equivalent diameter (AED) in size are respirable and can reach deeper regions of the lung, where clearance times may be long. Particles between 10 pm and 100 pm AED are of little concern for the inhalation pathway, but they can contribute to other exposure pathways after deposition. Particles greater than 100 pm AED deposit very quickly. While this could lead to a localized contamination in the immediate vicinity of the accident, it would not represent a significant mechanism for internal exposure. 

Our eoneems with the induction and exaceibation of respiratoiy diseases encompass bronchitis, emphysema, asthma, and other nonoecupational diseases. (Pneumoconiosis and silicosis are eonsidered diseases due to occupational exposure, rather than to inhalation of ambient air.) The pollutants principally indicted are ozone, sulfur dioxide, nitrogen dioxide, suspended particulate matter, and mixtures of these pollutants. Concern over the effects of suspended partieulate matter on human health is particularly focused on what are called respirable or inhalable partieles, usually detined as particles less than 10 mn in size. Lead dust is the exeeption to the mle that particles must be inhaled to be hazardous to health. Lead... 

Another study carried out in 1981-1982 dealt with lead levels in the MZMC, both in total suspended particles (TSP) and in the respirable fraction (RF) (Grana-Garcia 1983). The author mentions that the lead content in TSP were lowest during the rainy season (August to October) and confirms the observations of Jauregui and Sanchez (1987). However, even in the rainy season, lead concentrations found in the TSP in this study were above the value accepted in Mexico of 1.5 xg/m (see Table 7). 

Table 7. Lead in total suspended particles (TSP) and respirable fraction (RF) in the air of Mexico City...

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