重金属在胶州湾表层沉积物中的分布与富集

DISTRIBUTION AND ENRICHMENT OF HEAVY METALS IN SURFACE SEDIMENTS OF JIAOZHOU BAY

用原子吸收法测定了胶州湾表层沉积物中重金属的含量并运用平均富集因子(AEF)对其污染与富集状况进行了分析与评价,发现重金属在胶州湾表层沉积物中的分布极不均衡,高浓度值主要分布在河口区,与历史资料相比,平均含量都有所升高,Cu、Zn、Pb、Cd、Hg、Cr、As已有不同程度的污染富集。污染源主要来自工业和居民生活排污,沉积物中有机质的存在也对重金属的分布与富集起着重要的作用。

Marine sediments, the sinks for pollutants, are widely recognized as a potential source of pollution, not only because they are always toxic above a certain level, but also they linger at sea bottom for long period. The sediments may therefore be indicative of long and medium-term metal loads. Heavy metals can be natural components of sediments. They come from rock outcrops and soils due to their geochemical mobility. They can be also anthropogenie, as artificial pollutants coming from industrial or urban discharges. Jiaozhou Bay is a semi-enclosed bay in eastern part of Shandong Peninsula, China, 390 km2 and 7 m deep in average, surrounded by Qingdao City with 7 million population. A dozen of small rivers meet in the bay; the largest one is Dagu River, in annual average runoff of 6.61 × 108 m^3 . Most of these rivers have become discharge passages for industrial and household wastes. In this study, concentrations of heavy metals （Zn, Pb, Cd, Cu, As, Hg, Cr, Al, Fe, and Mn） in surface sediments of Jiaozhou Bay were determined and the average enrichment factors （ AEFs ） were used to assess the metal contamination. The contents of organic matter in samples in Jiaozhou Bay varied considerably, ranging between 27.72 % and 0.89%. High concentration occurred in Haipo River mouth and Loushan River mouth, while low concentration in outer bay. In inner bay, the levels of organic matter were in median level between 4.91 %-10.23% . The organic material in the sediment was positively related with Cu, Zn, Cd, and Hg. As a good binding substrate for these metals, organic matter can cause change of these metals in the sediments. Cd, Cr, Cu, Pb, and Hg had a similar distribution pattern with the one in 1989; however, all the mean values were higher in this study. Compared to other bays in China, the contents of Cd, Cr, Cu, Pb, Zn, and Hg were higher than those in Bohai Bay; the mean value of Pb （35.17 mg/kg） was very close to the mean value of Pb （38.9 mg/kg） in Honghai Bay （near Shanwei of Guangdong）, but the Zn content doubled for nearly 100 times in Jiaozhou Bay. As a whole, these metals distributed mainly in the eastern part of Jiaozhou Bay near river outfalls and the Qingdao Harbor. Moreover, a clear gradually declining in the concentration was shown from river mouths to outer sea. Anthropogenie inputs to inner bay were clearly indicated. But for As, there was an exception. High As values were observed at Dagu River mouth and near Qingdao Harbor, which may have resulted from run-off from agricultural areas using As-rich fertilizers or pesticides, or busy ocean shipping. In total metal concentration, Cu and Cr showed the closest positive correlation, indicating their similar origin and behavior. To estimate the possible hazard of heavy metal contamination in the bay, the average enrichment factors, an indicator of average concentration of a given metal, and the background value were calculated. Using the classification of Hhkanson （1980）, the metals in this bay can be divided into three groups： 1） negligible to low contamination, including Zn, Pb, Cr, Mn, and Fe; 2） moderate contamination including Cu and Cd; 3） severe contamination, in- cluding As and Hg. These findings are supported by the results of principal component analysis （PCA）. Three principal compo- nents were identified taking 86.48 % of the total variance. Factor 1, the general loading of the bottom sediment with heavy metals, accounted for 52.61% and characterized by high levels of Cu, Cd and Cr. Therefore, Factor 1 is closely related to the point sources of metal contamination. Factor 2 accounted for 17.37 % of the total variance. A high and positive loading occurred for LOI, corresponding closely to the concentration of organic matter in the bottom sediments, indicated the importance of the organic matter in banding metal ions in the sediments. The concentrations of elements examined were positively correlated with LOI. Thus, the degradation of organic matter and their concomitants would release metals and become secondary source of metal pollutant. Factor 3 was characterized by a high positive contribution of Fe and Mn. Fe and Mn are included in same geochemical matrix with other heavy metal elements; they could therefore be used as an indicator to heavy metal pollution. A large amount of untreated land-sourced metal-bearing discharges entering the bay without getting sufficient dilution in the bay or fast transportation to outer sea, have caused the heavy metal accumulation in sediment Besides, organic matters are important for the re-distribution and accumulation in the sediments.