HUMIC-LIKE SUBSTANCES IN AIR-POLLUTION PARTICULATES CORRELATE WITH CONCENTRATIONS OF TRANSITION-METALS AND OXIDANT GENERATION

We tested the hypotheses that (1) an incomplete oxidation of carbon-ba sed fossil fuels during their combustion produces humic-like substance s (HLS), which can be present in air pollution particulates and confer a capacity to complex metals; (2) air pollution particulates collecte d on PM(10) filters can be associated with concentrations of first-row transition metals; (3) particulates can catalyze the production of fr ee radicals by cycling these transition metals through two stable vale nce states; and (4) concentrations of transition metals and oxidant ge neration by air pollution particulates increase with the content of HL S associated with these particles. HLS were isolated by alkali extract ion. The content of these substances in combustion products of coal, d iesel, oil, and wood was 3.1 +/- 0.8%, 4.7 +/- 1.0%, 1.0 +/- 0.1%, and 8.2 +/- 0.6%, respectively. Similarly, filters with sequestered air p ollution particulates contained HLS ranging from 0.0 to 7.1%. Elementa l analysis of these materials isolated from both products of fuel comb ustion and sequestered particulate disclosed values of C, H, N, and O consistent with an MLS. There were correlations between HLS content an d ionizable concentrations of metals, quantified using inductively cou pled plasma emission spectroscopy, associated with particulates seques tered on filters. Similarly, HLS content correlated with the absorbanc e of oxidized products of deoxyribose, demonstrating an affiliation be tween these substances and free radical generation by sequestered part iculate. We conclude that HLS, a potential organic metal chelator, can be isolated from air pollution particulates. Concentrations of acid-s oluble transition metals and in vitro oxidant generation correlated wi th the content of these substances collected on filters.