Environ. Sci. Technol. 2001, 35, 3139-3143
Photolytic Behavior of Polycyclic Aromatic Hydrocarbons in Diesel Particulate Matter Deposited on the Ground S A D A O M A T S U Z A W A , * ,† LULWA NASSER-ALI,‡ AND PHILIPPE GARRIGUES§ National Institute of Advanced Industrial Science and Technology, AIST west, 16-1 Onogawa, Tsukuba, Ibaraki 305-8569, Japan, Kuwait Institute for Scientific Research, P.O. Box 24885, 13109 Safat, Kuwait, and Universite´ de Bordeaux I, 33405 Talence Cedex, France
To clarify the photolytic behavior of polycyclic aromatic hydrocarbons (PAHs) in diesel particulate matter (DPM) deposited on the ground, we determined the rate constants and half-lives for the photodegradation of benzo[a]pyrene (BaPy), phenanthrene (Phe), fluoranthene (Flrt), pyrene (Py), and chrysene (Ch) in air for three probable cases: (1) DPM is placed on an inert surface, (2) DPM is mixed with soil, and (3) PAHs are leached from DPM and adsorbed to soil. We found that BaPy and Phe degraded relatively quickly in case 1. However, in case 2, these PAHs degraded more slowly due to the effect of the presence of soil. Flrt, Py, and Ch were stable. In case 3, photodegradation of adsorbed PAHs in soil was strongly inhibited as a function of soil depth. Although these findings were obtained at extreme light intensities, they may occur under real world conditions. Conversion factors for obtaining rate constants and half-lives for PAHs on the ground under sunlight are presented. We conclude that under the average intensity of sunlight in Tokyo, photodegradation of PAHs in DPM deposited on an inert surface is very slow.
Introduction Polycyclic aromatic hydrocarbons (PAHs) are a group of major contaminants in the environment, and their presence in air, water, soil, ice, sediments, plants, and animals has been reported (1-8). The main source of PAHs in the environment is incomplete combustion of organic substances. Automobile engines (mainly diesel engines), electric power plants, heating facilities, waste incinerators, and forest fires produce much PAH. The toxicity (carcinogenicity, mutagenicity, estrogen disturbance) of specific PAHs associated with atmospheric particulate matter is a worldwide concern. The PAH concentration in the air surrounding large cities remains high due to an increase in the number of diesel cars, which emit large amounts of particulate matter (9, 10). The PAH concentration in urban soil is also high due to the deposition * Corresponding author phone: (81)298-61-8262; fax: (81)29861-8258; e-mail:
[email protected]. † National Institute of Advanced Industrial Science and Technology. ‡ Kuwait Institute for Scientific Research. § Universite ´ de Bordeaux I. 10.1021/es001606q CCC: $20.00 Published on Web 06/21/2001
2001 American Chemical Society
of atmospheric particulate matter (1). Raining accelerates the deposition of fine particles (1, 11, 12). After deposition, PAHs contained in the particles are subject to the effects of sunlight and microorganisms. Sunlight degrades PAHs on soil (photodegradation), whereas microorganisms degrade PAHs in soil (biodegradation). Biodegradation of PAHs in soil has been investigated by many researchers (e.g., refs 13-15). On the other hand, photodegradation of PAHs in particulate matter deposited on soil has been investigated less. Although data on the photochemical behavior of PAHs in fly ash, atmospheric particles, wood soot, and DPM have been reported (16-23), most studies have been carried out for reactions that occur in the gas phase. For photodegradation of PAHs in DPM, Kamens et al. (18, 19) reported some results from their work on the nitration reaction of PAHs. They used a reaction chamber to simulate photochemical transformations of particulate-phase PAHs in the gas phase. Although these results are partly applicable to the prediction of the photolytic behavior of PAHs in DPM deposited on the ground, more data are needed. After deposition, DPM is either mixed with soil and irradiated by sunlight, leached into the soil by rainwater, or washed from road surfaces into rivers, lakes, and oceans. However, little is known about the photolytic behavior of PAHs in DPM deposited on the ground. Here we report some experimental results for the photochemical degradation of PAHs in DPM deposited on the ground. We determined the rate constants and half-lives for benzo[a]pyrene (BaPy), phenanthrene (Phe), fluoranthene (Flrt), pyrene (Py), and chrysene (Ch) in air for three probable cases: (1) DPM is placed on an inert surface, (2) DPM is mixed with soil, and (3) PAHs are leached from DPM and adsorbed to soil.
Experimental Section Photodegradation of PAHs. To mimic the photochemical degradation of particulate-phase PAHs by sunlight, we photoirradiated our samples under atmospheric conditions using a xenon lamp. We mainly used a 900-W Photo-Irradiator (Applied Photophysics, London, Model 4960) as a light source. Light from the lamp was passed through a glass filter (Toshiba UV-29) to eliminate light of shorter wavelengths (
