Pollution Characteristics Of Representative Persistent Toxic Substances Of Tiaozi River, Siping City Section

Persistent toxic substances are trace pollutants with strong biological andecological toxicity, which are difficult to degrade in the environment. They can beaccumulated, enriched and amplified continuously in ecosystems through the foodchain. Persistent organic pollutants and heavy metal pollutants are typical persistenttoxic pollutants. Persistent toxic substances can be circulated throughout the solid,liquid and gas on earth and be transported into the water environment through largescale and long distance. The persistent toxic substances in the water environment candirectly act on the organisms through the overlying water, and also can migrate andtransform between overlying water and interstitial water and sediment under thephysical chemical and biological function in the water, resulting in a permanenteffect on water quality, thus affecting the aquatic ecosystem safety. The naturalrestoration of persistent toxic substances is quite difficult. The artificial measures toremove persistent toxic substance will lead to a high cost and are not mature.Therefore, persistent toxic substances in the environment are attached high attentionby domestic and international experts and scholars.Study on source apportionment of the pollutants was developed from theresearch of atmospheric particulates, and now the study has reached its maturity,however, the study on the source apportionment of pollutants in water is less. Fromthe point of the types of pollutants, PAHs has been attached more attention in thestudy of source apportionment of pollutants because of its more types and morecomplex sources. At the same time, it has been reported on OCPs, heavy metals,COD and other pollutants and pollution index. From the point of the methods ofresearch, there are special methods which are only suitable for a typical class ofpollutants, and also there are relatively common methods. Most of the sources ofresearch methods are used in analysis of pollutant source of atmospheric particles.The common qualitative analysis methods mainly include profile chart, compositionand ratio analysis, the characteristic compound and so on; the quantitative analysis methods mainly include cluster analysis, fugacity model, chemical mass balance,principal factor analysis,multivariate linear regression and so on. Although therehave been some researches about PAHs and OCPs source apportionment in Chineselocal water environment, but there are no researches about PAHs and OCPs sourceapportionment in the water environment of Tiaozi River.Ecological risk assessment is an assessment for the possibilities of adverseecological impact and its perniciousness after the ecosystem is affected byenvironmental pollution, human activities or natural disasters. Its goal is to studyecological hazards of environmental pollutants by the assessment method, to assessthe possibility of risks to the ecosystem and its components and the magnitude ofrisks and to provide the basic information and scientific basis for risk management.The ecological risk analysis of PAHs and OCPs are mostly qualitative and semiquantitative analysis at home and aboard. Although the existing research onecological risk evaluation of the PAHs and OCPs in China local water environmenthas been carried out, there is no study to evaluate the risk of PAHs and OCPs in thewater environment of Tiaozi River.Water and surface sediment samples were collected from the Tiaozi River andtributaries into the river to measure the contents of the16priority PAHs published byEnvironmental Protection Agency, two kinds of typical organochlorinepesticides(OCPs, four kinds of HCH isomers and4kinds of DDT homologues)andsix kinds of heavy metals(Pb、Cu、Ni、Mn、Cd and Zn). Based on the measure of thecontent of pollutants in river water and surface sediments in different water periods,persistent toxic substances spatial distribution, sources and ecological risk in thisriver will be studied in order to provide scientific evidence for effective pollutioncontrol of Tiaozi River. At the same time, the results of the study will providescientific reference to formulate reasonable scheme of the total amount control of thewater pollution, the standards of environmental quality and the regionalenvironmental planning for environmental protection department and the relevantgovernment departments.Results indicated that9kinds of priority PAHs were detected in water and10in sediments of Tiaozi River while the contents of PAHs with5~6benzene rings werebelow the detection limit. Overall, the contents of PAHs were at a low level inLiaohe River Basin. Temporospatial distributions of PAHs in the river water andsediments were similar: The PAHs levels decreased in the order of winter>autumn> spring> summer and decreased from the upstream to the downstream. Thepreliminary analysis reveals that PAHs in the river were mainly from the combustionof coal and transportation. Components of PAHs in water showed scarcely noecological risks and that in sediments showed low ecological risks. Potentialnegative ecological risks existed in only some individual monomers and there wereno obvious distinctions in different periods. α, β and γ-hexachlorocyclohexanes(HCHs) were detected in all the samples, and δ-hexachlorocyclohexanes (HCHs) andDichlorodiphenyl trichloroethanes (DDTs) in all the samples were below thedetection limit. In contrast, temporospatial distributions of HCHs in the river waterand sediments were opposite: HCHs levels in the water decreased in the order:summer> spring> autumn> winter and reduced from the downstream to theupstream; HCHs levels in the sediments decreased in the order: winter> autumn>spring> summer and decreased from the upstream to the downstream. In this studyarea, OCPs were from the past use of lindane. Basically, there were no ecologicalrisks for the OCPs in the water and surface sediments of Tiaozi River.Temporospatial distributions of heavy metals in the river water and sediments weresimilar: The heavy metal levels decreased in the order of winter> autumn> spring>summer and decreased from the upstream to the downstream. The analysis revealedthat heavy metals in the river were mainly from the surface runoff and discharge ofindustrial wastewater. Ecological risk of heavy metals in Tiaozi River is low. In thesurface sediments, ecological risk of Cd is moderate, and ecological risk of othermetallic elements is low. In general, the ecological risk of typical persistent toxicsubstances in Tiaozi River and surface sediments is at the low level.