AvailableAvailable online online at www.sciencedirect.com at www.sciencedirect.com Procedia Engineering ProcediaProcedia Engineering Engineering 00 (2011) 18 (2011)000–000 318 – 323 www.elsevier.com/locate/procedia

The Second SREE Conference on Chemical Engineering Speciation of Heavy Metals in the Sediments from Different Eutrophic Lakes of

LU Cheng-xiu, CHENG Jie-mina

College of Population Resources and Environment, Normal University, 250014, China

Abstract

The speciation and concentration of heavy metal Cu and Zn were examined by Tessier sequential extraction methods in sediments of Tai Lake, and Baiyangdian Lake. And the characteristics of overlying water were determined. The results showed three lakes all belong to eutrophic lakes, while Baiyangdian’s eutrophication is most serious, the concentration of TP is 0.48mg/L; in sediments Cu existed mainly in the form of residual and organic- bound fraction, these two forms accounted for more than 75% of the total content. Zn existed in the residual fraction, accounting for more than 50% of the total content, and the Fe/Mn oxide fraction ranked the second; the studies also showed the total “labile” fraction extracted from heavy metals was highest in the Tai Lake, which might bring ecological risk to the water ecological system again, and should be paid more attention to. The correlation between organic matter, Nutrients and heavy metals fractions were analyzed, the relevance is not remarkable. In this paper, the influence of eutrophication to fractions of heavy metal is scarcely.

© 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of Society for Resources, Environment and Engineering

Key words: eutrophication; sediment; heavy metals; speciation

1. Introduction

Being rich in natural organic matters, various living microorganisms, hydrous Fe-Mn oxides, minerals[1], lake sediments are easy to act with heavy metals by adsorption, complexion and precipitation, etc.which will affect the speciation of heavy metals[2,3]. Different forms of heavy metals vary with environmental conditions [4-5], and show different behaviors, bioavailability and toxicity. Therefore, speciation and distribution of heavy metals in the sediment has aroused widespread concern. Now relevant researches mostly focus on speciation of heavy metals in sediments of one lake, one river or one bay, assessment on its potential ecological risk [6-9]. While characteristics of speciation of

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1877-7058 © 2011 Published by Elsevier Ltd. doi:10.1016/j.proeng.2011.11.050 2 LU Cheng-xiuAuthor and CHENG name / ProcediaJie-min / ProcediaEngineering Engineering 00 (2011) 18 000–000 (2011) 318 – 323 319 heavy metals in sediments from lakes of different ecological types and different eutrophication degrees are rarely involved. However, there are different aquatic organisms in different algal lakes, hybrid lakes and macrophytic lakes, and the characteristics of water quality and pollution levels are diverse [10]. Naturally, the fractions of heavy metals are different. Comparison among speciation of heavy metals in the sediments from differently eutrophic lakes is of great significance in learning about transportation of heavy metals at sediment-water interface, and their toxic effects on aquatic organisms. In this research, the speciation of heavy metals Cu and Zn were examined by Tessier sequential extraction methods in sediments of the typical algal lake (Tai Lake), hybrid lake (Nansi Lake) and macrophytic lake (Baiyangdian Lake) with a view to assessing effects of eutrophication degrees on heavy metal behaviors and end results, which will provide a scientific basis for heavy metal pollution prevention and control.

2. Materials and Methods

2.1. Sample collection and processing

In this paper, the sampling point for Tai Lake is located in the portion of Huzhou, Zhejiang, the sampling point for Nansi Lake is located in the lower Weishan Lake area, and the sampling point for Baiyangdian Lake is near Duan Village, Baiyangdian. Respectively, in October 2009 (Tai Lake), May 2010 (Nansi Lake) and May 2009 ( Baiyangdian Lake), we used the self-made sampling devices to collect surface sediment samples at typical sewage outfalls in these three lakes, and at the same time collect samples of overlying water. Specific sample locations are shown in Table 1 and Figure 1.

Fig 1. Sites of sampling from different lake

Table 1. Location of Sampling sites and their geographic characters

Sample Point Longitude Latitude Approximate To Sample Point Description Tai Lake 120°06′10″ 30°57′28″ Xiaomeikou Sewage outfall, water quality deterioration, green Nansi Lake 117º08′46″ 34º43′17″ Aihu Village, Baiyangdian 115º56′33″ 38º50′43″ Weishan Lake Fisherman sewage outfall, water quality deterioration Lake Duan Village Village sewage outfall, smelly Various indicators of overlying water were entrusted to the local environment monitoring stations; sediment samples were taken back to the laboratory, and air dried at room temperature in a cool place, stones, weeds and other debris, etc. were removed. Air-dried samples were firstly coarsely ground 320 LU Cheng-xiuAuthor nameand CHENG / Procedia Jie-min Engineering / Procedia 00 Engineering(2011) 000–000 18 (2011) 318 – 323 3

through 20-mesh nylon sieve, then about 100 g were taken to be coarsely ground through 100-mesh sieve. The processed samples were sealed in polyethylene sample bags for test.

2.2. Analytical methods

Water quality analyses in various sampling locations were conducted in accordance with related contents in Water and Wastewater Monitoring Analysis Method[11];Analyses of the basic physical and chemical properties of sediments were conducted in accordance with regular soil analysis methods[12]; Analysis of forms of heavy metals was conducted with reference to Tessier method[2]; the total amount of heavy metals was digested with the digestion system of HCl-HNO3-HClO4, and determined by Model Z- 8000 flame atomic absorption spectrometry.

3. Results and Discussion

3.1. Main physical and chemical indicators of different lake sediments and overlying water

Water eutrophication is a result of combined action of many physical factors, chemical factors and biological variables, in which nitrogen and phosphorus nutrients are usually considered as the most important factor. Some studies have pointed out[13] that at total nitrogen of water (TN) > 0.2mg/L or total phosphorus (TP) > 0.02mg/L, it will lead to lake eutrophication. According to this, from Table 2, these three lake have all belong to eutrophic lakes, but at largely different levels of nutrition, in which the most serious eutrophication appeared in Baiyangdian Lake, and the lightest in Nansi Lake.

Table 2 characters of overlying water and sediment samples

Overlying Water (Unit: mg/L) Sediments (unit: mg/g) Sampling pH pH Point COD NH -N TN TP Organic Matter TN TP (dimensionless) cr 4 (dimensionless) Tai Lake 8.40 83.60 0.09 2.37 0.17 7.3 11.75 0.67 0.60 Nansi Lake 7.96 25.80 0.04 0.67 0.06 7.4 27.76 1.26 1.34 Baiyangdian 8.98 64.83 3.18 6.86 0.48 7.1 44.05 3.03 2.15 Lake With regards to sediments, the sequence for TP, TN and OM content is: Baiyangdian Lake > Nansi Lake > Tai Lake. It is generally believed that the nutrients contained in the bottom mud are resulted from sewage discharge, surface runoff and gradual accumulation of remains of dead aquatic organisms in lakes. Therefore, besides the relation to domestic sewage discharge, the high nutrient concentrations in sediments of Baiyangdian Lake were also connected to existence of a large number of aquatic plants. According to the survey, the plants in the sampling point of Baiyangdian Lake were mainly hornworts, and water terrapin, Spirodela, lotus, caltrop, etc., and remains of these hydrophytes would increase contents of TN and organic matters in the sediments. From table 2, we known that content of nutrients in sediments’ concentrations is not consistent with concentration trend of nitrogen and phosphorus in the overlying water. That is to say, total content of nitrogen and phosphorus in sediments cannot quantificationally reflect eutrophication of lakes.However, it might be noted that all the sampled lakes in this study are shallow lakes. Sediment-water interface of the shallow lake is often affected by external forces, resulting in suspension of a large number of sediments as well as continuous destruction on the interface [14]. In addition, content of organic matter in 4 LU Cheng-xiuAuthor and CHENG name / ProcediaJie-min / EngineeringProcedia Engineering 00 (2011) 18 000–000 (2011) 318 – 323 321 sediments has great impact on eutrophication. For example, organic matter consumes a large number of oxygen and releases nutrients such as C, N, P, S, etc. in mineralization, resulting in the accelerated eutrophication[15]. So after this study, special attention should be paid to eutrophication caused by increase in nutrients, which are brought about by resuspension of sediments, in Baiyangdian Lake and Nansi Lake.

3.2. Characteristics of total amount of heavy metals in various lake sediments

There are certain differences with the contents of Cu and Zn in different lake sediments (Table 3). The maximum values for contents of two types of heavy metals appear in Baiyangdian Lake, while the minimum is in Nansi Lake. Both types of metals have shown the characteristics of Zn ＞ Cu, indicating that the content of heavy metals in sediments is largely affected by the geochemical abundance.

Table 3. Contents of heavy metal in three sediment samples (unit: mg/kg)

Tai Lake Nansi Lake Baiyangdian Lake Local Local Local Item Measured Measure Measured Background Background Background Value ） d Value ） Value ） Value1 Value2 Value3 Cu 25.45 18.9 21.63 22.7 35.64 30.5 Zn 78.46 59.2 58.67 64.03 93.22 71.4

Note: 1) Background values of heavy metals Xiashu loess at Tai Lake Basin; 2) Background values of soil environment in Shandong; 3) Background values of soils in Hebei Plain. Of course, high total amount of heavy metals in lake sediments does not mean that the heavy metal pollution is serious, while the pollution degree of heavy metals in sediments is often closely related to the locally original background values. As can be seen from Table 3, the contents of Cu and Zn in sampling points of Baiyangdian Lake and Tai Lake were higher than the local background values, while the contents of two types of heavy metals in Nansi Lake were lower than the local background value. It indicated that the heavy metals in the sediments of Baiyangdian Lake and Tai Lake were subject to exogenous pollution.

3.3. Characteristics of fraction and distribution of heavy metals in various lake sediments

There is great difference in percentages of various forms of different heavy metals (Figure 2).

80 80 70 70 60 60

50 50

40 40 30 30

20 20 Percentages of Zn（%）

Percentages of Cu（%） of Percentages 10 10 0 0 Taihu Nansihu Baiyangdian Taihu Nansihu Baiyangdian

exc car Fe-Mn org res exc car Fe-Mn org res

Fig 2 percentages of the fractions of Cu, Zn in different sediments

Cu mainly takes on the forms of residual fraction and fraction bound to organic and sulfide, and the summation of two fractions takes 75 % -90% of the total amount, consistent to the analysis results of 322 LU Cheng-xiuAuthor nameand CHENG / Procedia Jie-min Engineering / Procedia 00 Engineering(2011) 000–000 18 (2011) 318 – 323 5

Ramos et al[16]. This is because that Cu has the property of easily forming organic complexes and sulfide copper and other minerals, which are difficult to break down. On the other side, Zn mainly exists in the residual fraction and the fraction bound to Fe-Mn oxides, indicating that Zn can easily be absorbed or co- precipitated by hydrated manganese oxides. It has been reported [17] that it is viewed that high stability constant occurs when Zn is combined with Fe- Mn oxides in sediments. In analysis on fractions of metal elements, what play an important role in effects on the environment are those in the “labile” fraction, which are exchangeable fraction and carbonate bound fraction, Fe/Mn oxides fraction and organic matter and sulfides fraction. Once there are changes on chemical or physical conditions such as pH, bioturbation, etc., those metal elements are likely to enter the overlying water, which may have great negative effects on the environment. So they can also be called as the effective fraction[18]. While the residual fraction, which is combined with the mineral lattice, is generally considered to have no bioavailability and no effects on the environment. With the development of economy, more and more heavy metals are discharged into the water by human beings. Most of them exist in are in the sediments in the mobile fraction so they are easily to be extracted and released. So, according to those in the “labile” fraction, not only the characteristics of man-made pollution of heavy metals can be determined but also the degree of difficulty of activating and releasing heavy metals and the possibility of secondary pollution in water–sediment exchange process can be represented. In these three lakes, as for the proportion of Cu in the form of “labile” fraction, the sequence is Tai Lake (56%) > Nansi Lake (30%) > Baiyangdian Lake (25%). the proportion of Zn in the form of “labile” fraction is Tai Lake (46%) > Baiyangdian Lake (36%) > Nansi Lake (24%). All the above show that human factors play an important role in pollution of heavy metals in sediments in Tai Lake. Moreover, we can also see that the potential risk of secondary release of Cu and Zn in sediments in Tai Lake is much higher than that in the other two lakes. It is generally believed that the content of organic carbon is an important controlling factor [19] that may affect the fraction and distribution of heavy metals. In this paper, we also made an analysis on correlation between the fractions of heavy metals and content of organic carbon, total nitrogen, and total phosphorus in sediments as well as the total amount of heavy metals. The results show that there is no significant correlation between content of organic carbon and Cu and Zn in various fractions, and fraction and distribution of heavy metals in lake sediments are commonly controlled by many factors. The organic carbon is not the main controlling factor while other characteristics of sediments such as mineral composition, particle composition, etc. may play a more important role. So, further studies are needed. Contents of TP and TN in sediments do not have significant correlation with fractions and total amount of Cu and Zn, which further shows that domestic sewage is not the major source of pollution of Cu and Zn and the degree of eutrophication has little impact on the fraction of heavy metals. This is only a preliminary result and relationship between fraction of heavy metals and eutrophication needs further studies.

4. Conclusion

(1) From the results of sampling this time, all the three lakes are eutrophic lakes. Degree of eutrophication of Baiyangdian Lake is the highest and that of Tai Lake is intermediate while that of Nansi Lake is the lowest. (2) In lake sediments, Cu mainly exists in the form of residual fraction, followed by the organic- bound fraction, while Zn mainly exists in forms of residual fraction and Fe/Mn oxide fraction. The total contents of both Cu and Zn in Baiyangdian Lake are the highest of all while content of the effective fraction in Tai Lake is the highest. The degree of difficulty of activating and releasing heavy metals in 6 LU Cheng-xiuAuthor and CHENG name / ProcediaJie-min / EngineeringProcedia Engineering 00 (2011) 18 000–000 (2011) 318 – 323 323 sediments in Tai Lake and the possibility of secondary pollution are much higher than those of the other two lakes. (3) In this study, the organic carbon, total nitrogen and total phosphorus in sediments do not have significant correlation with the fraction and the total amount of heavy metals. It can be considered that degree of eutrophication has little effect on the fraction of heavy metals, which may be mainly affected by mineral composition, particle size distribution, etc.

Acknowledgements

This study was supported by the National Basic Research Program:“Water environmental quality evolution and water quality criteria in lakes ”(2008CB418200).

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