Comparison of organic pollutants in urban deposits of Guangzhou and Hong Kong metropolitan areas

Abstract

Compound Specific Isotope Analysis (CSIA) is a newly developed method that is able to measure the isotopic composition of specific compounds in complex environmental matrices. It proves considerably potential for application in environmental sciences, (1) to allocate and distinguish sources of organic compounds, and (2) to identify and quantify transformation reactions, sometimes even at a mechanistic level. This study mainly focused on the preliminary application of CSIA in the selected persistent organic pollutants (POPs) source appointment and photolysis process identification. Firstly, it is to establish the pretreatment method for selected POPs-CSIA in environmental samples such as soil (sediment). A DMF-n-pentane biphasic system for sample purification got high recovery and reproducibility, and could achieve effective removal of interfering compounds required of CSIA. It was evaluated that the detection limit for selected POPs of the instrument ranges from 6x10 "6 to 30x10 "6 with the injection of 2 IlL volume. The standard deviation (SD) of the target compounds is less than 0.3%0. The established pretreatment method for POPs-CSIA was applied to source identification for PAHs contaminated soil samples near a coke oven plant in the suburb of Beijing. The isotope signature suggested that it mainly came from coal carbonization. Secondly, it was obviously found that carbon isotope fractionation occurred during photolysis process of typical POPs -hexachlorobenzene (HCB). Stable carbon isotope ratios (13C) of HCB and its dechlorination product pentachlorobenzene (penta-CB) increased from -27.39/00 to 18.8%0 and from -33.99/oo to -19.5%0, respectively. The isotope fractionation of the reactants and products were described with the Rayleigh model, and the following enrichment factors (e) were obtained: -14.8%0 13C value of HCB, and 22.7%0 for the penta-CB. With the initial enrichment the factor can be used to estimate the fraction (f) of HCB remaining. It also provides insight into the photo-reaction progress by measuring the 13C in HCB and values of HCB and penta-CB with time. Strong enrichment of penta-CB during photochemical dechlorination might serve as a powerful tool to monitor the photolysis process, such information may provide additional evidence to aid further understanding of the chemical processes these compounds are undergoing in the environment.