The effects of both ambient air pollution and socioeconomic position (SEP) on health are well documented. A limited number of recent studies suggest that SEP may itself play a role in the epidemiology of disease and death associated with exposure to air pollution. Together with evidence that poor and working-class communities are often more exposed to air pollution, these studies have stimulated discussion among scientists, policy makers, and the public about the differential distribution of the health impacts from air pollution. Science and public policy would benefit from additional research that integrates the theory and practice from both air pollution and social epidemiologies to gain a better understanding of this issue. In this article we aim to promote such research by introducing readers to methodologic and conceptual approaches in the fields of air pollution and social epidemiology; by proposing theories and hypotheses about how air pollution and socioeconomic factors may interact to influence health, drawing on studies conducted worldwide; by discussing methodologic issues in the design and analysis of studies to determine whether health effects of exposure to ambient air pollution are modified by SEP; and by proposing specific steps that will advance knowledge in this field, fill information gaps, and apply research results to improve public health in collaboration with affected communities.

Seasonal variability in stable carbon (S'XZ) and nitrogen (b15N) isotope ratios was observed in suspended particulate matter of the Delaware estuary. Two major pools of organic matter were found in the estuary-phytoplankton growing in situ and a mixture of planktonic and terrestrial detritus. In general, the 6°C and 615N of suspended particulate matter reflected planktonic dominance. With the background chemical and physical information available for the estuary, it is evident that biogeochemical processes influence isotopic distributions in the estuary to a greater extent than does physical mixing. During spring, we postulate that isotopic fractionation of ammonium assimilated at concentrations >20 PM resulted in more negative 615N values for organic matter fixed by phytoplankton. As algal growth proceeded, the 615N of seston reached a maximum (+ 1 SY&) because phytoplankton were using a pool of NH,+ enriched in 15N as a result of previous fractionation during assimilation. Similarly, maximal 813C values were related to high rates of primary productivity associated with algal growth. Decreased isotopic fractionation occurred at high rates of production, implying that diffusion of CO, across the cell membrane became increasingly rate limiting.The 613C values in bottom sediments were equivalent to those in suspended particulate matter, but a 2Y60 difference in 615N was found between suspended and bottom sediments. With nitrogen isotopic differences between water-column seston and surficial sediments, we estimate that 15-30% of planktonic production is deposited in the sediments during spring. If this organic matter is remineralized in late summer and fall, it could support up to 20% of primary production at that time.Differences exist among natural abundances of stable carbon isotopes (813C) and stable nitrogen isotopes (615N) in organic matter from terrestrial and anthropogenic I Present address: Department of Oceanography, Texas A&M University, College Station 77843.

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Elevated temperatures are associated with mortality risk in these Latin American cities, with the strongest associations in São Paulo, the hottest city. The elderly are an important population for targeted prevention measures, but vulnerability by sex and education differed by city.

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Daily counts of non-accidental deaths in Santiago, Chile, from 1988 to 1996 were regressed on six air pollutantsfine particles (PM 2.5 ), coarse particles (PM 10-2.5 ), CO, SO 2 , NO 2 , and O 3 . Controlling for seasonal and meteorological conditions was done using three different modelsa generalized linear model, a generalized additive model, and a generalized additive model on previously filtered data. Single-and two-pollutant models were tested for lags of 1-5 days and the average of the previous 2-5 days.The increase in mortality associated with the mean levels of air pollution varied from 4 to 11%, depending on the pollutants and the way season of the year was considered. The results were not sensitive to the modeling approaches, but different effects for warmer and colder months were found. Fine particles were more important than coarse particles in the whole year and in winter, but not in summer. NO 2 and CO were also significantly associated with daily mortality, as was O 3 in the warmer months. No consistent effect was observed for SO 2 . Given particle composition in Santiago, these results suggest that combustion-generated pollutants, especially from motor vehicles, may be associated with increased mortality. Temperature was closely associated with mortality. High temperatures led to deaths on the same day, while low temperatures lead to deaths from 1 to 4 days later. IMPLICATIONSSignificant statistical associations were found between daily mortality in Santiago for 1988-1996 and several measures of ambient air pollution (PM 2.5 , PM 10-2.5 , CO, NO 2 , and O 3 ). The risks for PM 2.5 , NO 2 , and CO were comparable. PM 10-2.5 and O 3 were significant only during the warmer months. SO 2 did not show a consistent statistically significant risk. The results suggest that combustion sources may be responsible for increased mortality in Santiago.

Abstract--Previous work has suggested that apparent old ~4C ages for oceanic DOC are the result of mixing of different organic carbon fractions. This report provides direct evidence for a contemporary ~4C age of a high-molecular-weight (HMW) fraction of colloidal organic carbon (-> 10 kD). Colloidal organic matter, COM~0 (from 10 kDaltons (kD) to 0.2/zm), isolated from the upper water column of the Gulf of Mexico and the Middle Atlantic Bight (MAB) region, generally has a contemporary age (i.e., younger than a few decades), while COMI (from 1 kD to 0.2 pm), is apparently old: 380-4500 y BP. Thus, HMW COM~0 (3-5% of DOC) from the upper water column is derived from living particulate organic matter (POM) and cycles rapidly, while a significant fraction of low-molecular-weight (-< 1 kD) DOM is likely more refractory, and cycles on much longer time scales. The presence of pigment biomarker compounds in COMI from the upper water column points to selected phytoplankton species as one of the sources of COM. Terrestrial carbon as another source of COM is suggested from the inverse correlation between A ~4C and 6 ~3C values, as well as the increasing 613C values with increasing salinity. 2~l'h-derived turnover times of COM~0 and COM~ from both the Gulf of Mexico and MAB are consistently short, 1-20 and 3-30 days, respectively. These short residence times support the hypothesis that ~4C ages of colloidal fractions of DOC are the result of COM fractions being a mixture of several endmembers with fast and slow turnover rates.

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