Basis for a particle size-selective TLV for sulfuric acid aerosols

PM source apportionment for short-term cardiac function changes in ApoE-/- mice

Daily rates of cardiovascular mortality and morbidity are have been associated with daily variations in fine particulate matter (aerodynamic diameter < or = 2.5 microm, PM2.5), but little is known about the influences of the individual source-related PM2.5 categories or the temporal lags for the effects. We investigated heart rate (HR) and HR variability (HRV) data collected during a 5-month study involving 6 hr/day, 5 day/week exposures of normal (C57) mice and a murine model for atherosclerotic disease (ApoE-/-) in Sterling Forest (Tuxedo, New York, USA). The mice were exposed to concentrated ambient particles (PM2.5 concentrated 10-fold, producing an average of 113 microg/m3). Daily 6-hr PM2.5 air samples were analyzed by X-ray fluorescence, permitting attribution to major PM source categories [secondary sulfate (SS), resuspended soil (RS), residual oil (RO) combustion, and other, largely due to motor vehicle traffic]. We examined associations between these PM2.5 components and both HR and HRV for three different daily time periods: during exposure, the afternoon after exposure, and late at night. For HR there were significant transient associations for RS during exposure, and for SS in the afternoon after exposure. For HRV, there were comparable associations with RO in the afternoon after exposure and for both SS and RS late at night. The biologic bases for these associations and their temporal lags are not known but may be related to the differential solubility of the biologically active PM components at the respiratory epithelia and their access to cells that release mediators that reach the cardiovascular system. Clearly, further research to elucidate the underlying processes is needed.

Airway hyper-responsiveness and the prevalence of work-related symptoms in workers exposed to irritants

The association between exposure to airway irritants and the presence of work-related symptoms and whether this association was modified by airway hyper-responsiveness, smoking, and allergy by history was studied in 668 workers of synthetic fiber plants. A Dutch version of the British Medical Research Council (BMRC) questionnaire with additional questions on allergy and work-related symptoms was used to assess symptoms, and a standardized histamine challenge test of airway hyper-responsiveness (AHR) was employed. Work-related symptoms were defined as having more than usual eye and respiratory symptoms during work. On the basis of job titles and working department, the exposure status of all workers was characterized into seven groups: (1) reference group; (2) white collars; (3) SO2, HCl, SO4(2-); (4) polyester vapor; (5) oil mist and oil vapor; (6) polyamide and polyester vapor; and (7) multiple exposure. The association between exposure groups and work-related symptom prevalence was estimated by means of multiple logistic regression. The overall prevalence of the work-related symptoms were: cough 9%; phlegm 6%; dyspnea 7%; wheeze 2%; eye symptoms 16%; nasal symptoms 15%. Exposure to airway irritants was significantly associated with work-related symptoms, independent of AHR, smoking, allergy by history, and chronic respiratory symptoms. The association of exposure group with work-related symptoms was stronger for subjects with AHR than for subjects with no AHR. The association with dyspnea and/or wheeze was also stronger for smokers than for nonsmokers and ex-smokers. In contrast, the association between exposure and a higher prevalence of work-related symptoms was stronger in subjects with no history of allergy than in subjects with history of allergy. This is most likely due to the relatively high prevalence of background symptoms in (nonexposed) allergic subjects. It is concluded that exposure to irritants in the working environment might lead to respiratory symptoms, even if exposure levels are relatively low.

Exposure assessment: input into risk assessment

The validity of a risk assessment can be no better than that of the exposure assessment upon which it is based. The general paucity of relevant exposure data, combined with the limited appreciation by most risk assessors of the critical dimensions and metrics of exposure, often leads to an overreliance on exposure models of questionable validity. The problems of identifying and interpreting relevant metrics of exposure for epidemiologic studies and risk assessments are illustrated through the presentation of three case studies. The first examines the effects of ozone on respiratory mechanical function and demonstrates that the appropriate averaging time is greater than or equal to 6 hr, rather than 1 hr, as is implied by the current ambient air quality standard. The second case study examines the effects of sulfur oxides and particulate matter in ambient air on morbidity and mortality. It indicates that the effects are most closely associated with the acidity of the aerosol, providing a basis for an index of exposure more relevant than those currently used, i.e., sulfur dioxide and nonspecific gravimetric mass concentration of particulate matter. The third case study examines the effects of lead on blood pressure. It shows that blood lead in concentrations below 35 micrograms/dL correlates with blood pressure in both humans and animals independently of other known causal factors for blood pressure elevation. It also examines the variable relations between levels of lead in blood and in environmental media to illustrate the potential problems which can arise from the use of biological markers, such as lead in blood, as indices of exposure.