Air Quality Guidelines Global Update 2005 - World Health ...

PARTICULATE MATTER
modulating biological response. Using aqueous extracts of filter-collected PM10
obtained from Utah Valley before, during and after closure of a local steel mill,
Frampton et al. (212) avoided the issue of water solubility vs insolubility as a
modulating factor in examining effects of these extracts on human respiratory
epithelial cells in vitro in terms of oxidant capacity, cytotoxicity and induction of
pro-inflammatory cytokine expression. The extract with the lowest metal content,
specifically soluble iron, copper and zinc, showed no cytotoxicity, minimal
induction of cytokines and lowest oxidant generation ability compared to extracts
from filters having higher metal content. However, when metals were removed
from the extract prior to exposure there was still an effect of the extracts on at
least one endpoint, namely phagocytic activity of macrophages. Thus, the soluble
metals were probably not the only component responsible for the observed effects.
There is additional evidence for effects of soluble metals that may relate to
health outcomes associated with PM exposure. When ambient PM samples from
St Louis, Washington, DC, Düsseldorf and Ottawa were tested for toxicity, the
observed greater response to the PM from Ottawa was postulated to be due to its
higher content of water-soluble metals (213). Other studies have indicated that
zinc in PM may be responsible for various pulmonary effects, such as inflammation,
necrosis and airway hyperreactivity (214–217). Human bronchial epithelial
cells exposed to PM extracts collected in Taiwan, China showed a correlation
between cytokine production and metal content, with effects on some cytokines
correlating with chromium and manganese and others with iron and chromium
(194). In a study using residual oil fly ash, particles with higher zinc content resulted
in greater pulmonary inflammation and airway responsiveness than did
particles with higher nickel or vanadium content (217). In a similar study, human
bronchial epithelial cells were exposed to concentrated fine fraction PM
(132). The greatest correlation to the biomarker of response, namely NF-ĸB (an
indicator of cellular stress), was seen with residual oil sources, using nickel and
vanadium as markers. Mice with induced allergic airway disease were found to
have increased pro-inflammatory cytokines following exposure to PM2.5 recovered
from ambient air filters from different areas, but only PM having a higher
metal content (specifically zinc, magnesium, lead, copper, cadmium and arsenic)
resulted in increased airway responsiveness (218). These apparent differences in
responses to various particles in differing model systems suggest that the endpoint
examined is critical in deriving conclusions as to the toxicity of specific
metals, and also that effects may be linked to the specific valence state of metals.
Secondary inorganic sulfates and nitrates
Schlesinger & Cassee (219) provided an extensive review of the toxicology of
secondary inorganic aerosols, namely sulfates and nitrates (including acidic species),
in relation to health outcomes considered in epidemiological studies on
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