Preliminary Study On Regional Geochemistry Of Polycyclic Aromatic Hydrocarbons In The Pearl River Delta

Persistent organic pollutants (POPs) have been of great concern due to their persistence in the environment, their bioaccumulation potential in the tissues of animals and humans through the food chain, and their toxic properties for human and wildlife. Polycyclic aromatic hydrocarbons (PAHs) are widespread contaminants in the environment; some of the PAHs proved to be mutagenic, carcinogenic and teratogenic, and are listed as priority pollutants in the U.S. EPA and the European Community environmental regulations. This study focuses on the regional geochemistry of PAHs in the Pearl River Delta (PRD). The results acquired in this study will complement existing data on the distribution and fate of POPs in the sub-tropical environments.1. Spatial and seasonal distribution of gaseous PAHs in the PRD: Passive air sampler semipermeable membrane devices (SPMDs) were deployed at twelve sites in the PRD during 2001-2002 to study the distributions of atmospheric PAHs in this area. PAHs concentrations in SPMDs were found to be higher in winter than in summer, and significant differences in atmospheric PAHs concentration between sites were found, which match well with the assumed degree of traffic pollution and local industrialization/urbanization. Using the HiVol PAH data, SPMD sampling rates were calculated for some dominant gas-phase PAHs, to determine the atmospheric PAH concentrations at other sites. Results indicated that the SPMD sampling rates were higher in winter than in summer, and good agreements were found between SPMD-based air concentrations and the actual HiVol results. Also, good agreements were found between SPMD and pine needle for PAHs air sampling.2. Air-soil diffusive exchange of PAHs in the PRD: PAHs values in 72 soil samples in the Peal River Delta were determined. The distributions of PAHs in the soil largely follow in this gradient: urban sites > rural sites > remote sites and paddy soil > crop soil > primary soil. PAHs diagnostic ratios indicated that the PAHs in thesoil were mainly derived from vehicular (gasoline) exhaust. Soil-air fugacity quotients were calculated using the measured air and soil PAHs concentrations. The calculated soil/air fugacity quotients indicate that the soil may now be a source of some lighter PAHs (fluorene and phenanthrene) to the atmosphere, whereas acting as a sink for the heavier PAHs (fluoranthene and pyrene) for all combinations of temperature and soil OC content. It is found that the soil and air are closer to equilibrium for PAHs in remote sites than in urban sites, the PAHs in remote sites may have experienced adsorption process onto particle matter in the air during atmospheric transport.3. Sediment Records studies of atmospheric deposition PAHs: As persistent semivolatile compounds, many POPs have the unique potential of long-range atmospheric transport and contaminate regions far from the places of their production and application. High mountain lakes are interesting study sites since they accumulate allochthonous materials through atmospheric transport. Based on this foundation, sediment records of atmospheric deposition PAHs were investigated in a core from the Nanling mountain lake. From 1960 to 2003, there are nearly 1000 kg of PAHs deposited to Doushui lake through atmospheric transport. The PAHs fluxes displayed sharp increase since 2000, reflecting the rapid economic development undergoing in inland China. PAHs fractionation was observed during atmospheric transport process; the deposited PAHs in the sediment contain more of low molecular PAHs, suggesting that the lighter PAHs can transport to farther regions than heavier PAHs.4. Over 100 year sedimentary record of PAHs in the Pearl River Estuary:PAHs in the environment are originated mainly from anthropogenic activities. In this study, over 100 year sedimentary records of PAHs were investigated in a core collected from the west shoal of the the Pearl River estuary. Using the regional socioeconomic data, the relationship between PAHs pollution and economic development were also elucidated. Sedimentary PAHs fluxes showed sharp increase since 1985, which correlate positively with the sharp increase of regional GrossDomestic Product (GDP), vehicle number and power generation, it is suggested that the emissions from vehicle exhausts and power generation (mainly by coal and heavy oil combustion) were the likely key sources of PAHs in the Delta. Atmospheric deposition and soil runoff may serve as the important pathways for PAHs input to the sediment.