Particulate Organic Matter And Organic Pollutants In Water Body Of The Xijiang River

Polycyclic aromatic hydrocarbons (PAHs) and organochlorine pesticides (OCPs) are typical toxic pollutants in the environment, some of them listed as priority pollutants. Due to its hydrophobic character, organic pollutants are also called hydrophobic organic compounds (HOCs). Sorption is one of the key processes affecting transformation and transport for HOCs in the environment. Natural organic matter (NOM) is the most important composition in the soils/sediments and aquatic environment, tending to react with HOCs and affect its distribution, bioavailability, bioaccumulation, mass transfer, pollutants transport, and biodegradation in the environment. In order to understand the heterogenous and structures of NOM in the suspended particulate matter, we take humic acid (HA), kerogen (KB), black carbon (BC) as an example. It would be helpful to explain the distribution and fate and building up forecast model of organic pollutants in the environment. It would be very important significance to understand thegeochemistry behavior and the environment effect of toxic organic pollutants in the system of earth's surface.In this thesis, PAHs and OCPs in the Xinjiang River were selected as target contaminants. The chemicals in the dissolved phase and suspended particle matter (SPM) phase were determined as the change of depth of water column in different seasons. The sources, composition characteristics, distribution between the dissolved phase and SPM phase and controlling factors were furthermore discussed. In order to understand the interaction between target chemicals and natural organic matter, a wet-chemical—oxidation method was used for the isolation of different NOM fractions such as humic acid, kerogen and black carbon. Elemental analyses, organic petrographic examination, and scanning electron microscopy were conducted for characterizing major physical and chemical properties of NOM fractions. The impact of NOM heterogeneity on the fate of environmental PAHs and OCPs are discussed thereby. In this study, several results were summarized as following:The characteristics of PAHs in the Xijiang River The PAH concentrations in the dissolved phase and SPM phase ranged from 21.7-138 ng/L and 40.9-665 ng/g, respectively. The total PAH content was higher in the flooding seasons than that in the dry seasons. In dissolved phase, the concentrations of three-ring PAHs were the most abundant in each season, whereas both three- and four-ring PAHs dominated the patterns in SPM. Comparison with the reported results of Europe countries, the total concentrations of the PAHs in the Xijiang River were much higher than those of less polluted aquatic systems. However, they are lower than PAH concentrations in several major Chinese rivers such as Minjiang and Daya Bay rivers. According to the ratios of three pairs of isomeric PAH compounds, the possible source of the PAH contamination was mainly pyrolytic input derived from the combustion of fossil fuels and biomass. The PAH concentrations of the Xijiang River were lower than 50% lethal concentration (LC50 ) as low as 10 (a.g/Lfor various organisms, evaluated by risk assessment of PAHs. The single-point Koc values computed for the PAHs were correlated well with their A"ow values. Even though limited samples were examined in this thesis, a preliminary result of the annual loading of PAHs were calculated by ourdata. The estimated annual loadings of Ant, BaA, Bghi? and total PAHs were 1620, 330, 177 and 19400 kg, respectively.The characteristics of OCPs in the Xijiang River The OCP concentrations in the dissolved phase and SPM phase were 1.12-13.6 ng/L and 93.8-660 \i%l kg, respectively. The total OCP content was lower in the flooding seasons than that in the dry seasons. Compared with other reported results, the total concentrations of the OCPs in the Xijiang River were much lower. From the characteristics of HCHs and DDTs compositions, the main sources of HCHs were the mixture of technical HCH and y-HCH, and the use of dicofol might be the new source of DDT. The estimated annual loadings of HCHs, DDTs and total OCPs were 92.3, 71.1 and 489.6 kg/a, respectively.The characteristics of HA, KB and BC in the SPM from the Xijiang River The NOM are heterogenous in the SPM from the Xijiang River, including HA, KB, and a large amount of BC. HA and KB are both macromolecule polymers, derived from organism which through unseasing geochemical processes of biodegradation, oxidation-deoxidization, polymerization. HA is the product of forpart evolvement, while KB is more evolved by HA. Differing from HA and KB, BC is produced from incomplete combustion of biomass and fossil fuel. From HA, KB to BC, the structure is more condensed and tightly-knit;the characteristic is more stable;and the maturation is more greater.