Water-Sediment Partition of Polycyclic Aromatic Hydrocarbons ( PAHs ) in Nansi Lake

Based on field data of polycyclic aromatic hydrocarbons (PAHs) in water and sediment in Nansi Lake. The concentrations and the partitioning characteristic of PAHs in the water and sediment were studied. The lgKd of high molecular weight PAHs were higher than the low molecular weight PAHs. The most of PAHs Kd values were negligible correlated with TOC, soluble salt, clay and pH of the sediment in Nansi Lake.


Introduction
Polycyclic aromatic hydrocarbons (PAHs), containing two or more benzene rings, are widely distributed in the environment, for heir hydrophobicity, strong persistence and long-range transportation potential [1].PAHs usually exist in the form of free, DOM binding, SPM binding and sediment combination in the aquatic environment.Investigation of the distribution of PAHs in an aquatic environment is great significance for strategy designing of pollution control.Partitioning in the two phases plays an important role in their behavior in the environment.The distribution of PAHs was mainly influenced by the characters of sediment (organic carbon content, particle composition) and environmental conditions (pH value, soluble salt content and so on), besides the physicochemical characters of PAHs and environmental conditions (temperature, precipitation) [2].It is necessary to study the partitioning of PAHs in different aquatic environments, for the different partitioning behaviors of PAHs in different study areas.
Nansi Lake is the largest lake in Shandong province, the northern area of China, including Nanyang Lake, Dushan Lake, Zhaoyang Lake and Weishan Lake.It is an imporant buffer lake of the South-to-North Water Diversion Project (east route).Its water quality relates to the whole water quality conditions of South-to-North Water Diversion Project (east route) [3].Some studies [1,4,5] assessed the PAHs residues in water, sediment and aquatic organisms of Nansi Lake.However, there is little information on water-sediment Partition of Polycyclic Aromatic Hydrocarbons (PAHs) in Nasi lake.
The objectives of this research are to survey concentrations of PAHs in the water and sediment, to evaluate water-sediment partitioning coefficient (Kd) of PAHs, and to assess the relationship of characteristics in sediments with K d of PAHs in the Nansi Lake.

Site location and sample collection
The locations of the sampling sites are shown in the paper by Zhang [1].Water and surface sediment collected in May 2011.

Extraction procedure and chemical analysis
The Chemical reagents, extraction procedure, chemical analysis and Quality assurance are found in the literature [1].

The analysis of physicochemical character in surface sediment
The methods total organic carbon (TOC), mechanical analyses, soluble salt contents and pH of sediments were following the method of Zhang [3].Statistical analysis software Spss16.0 was used in this study.

Concentrations of PAHs in the water and sediment
The concentrations of PAHs in water and sediment samples are shown in Table 1.The results of PAHs in water and sediment samples came from the report by zhang [1].The concentrations of total PAHs ranged from 27.52 ng/L to 55. 06  water.
The concentrations of total PAHs ranged from 80.3 ng/g dw to 639.47 ng/g dw in sediment, with the average value of 225.18±206 ng/g dw.The high molecular weight (4-6 rings) PAHs were major compounds in sediment compared in water, accounting for approximately 56% of total PAHs in sediment.Those results were consistent with previous studies [6,7].nd not detected

Water-Sediment partitioning of PAHs in the Nansi Lake
The partitioning coefficient (K d ) of PAHs between sediment and water was calculated by the following formula: K d =C s /C w [8].where C s and C w represent PAHs concentration in sediment (ng/g dw) and water (ng/L) samples, respectively.The lgK d (L/kg) values at sediment-water interface from Nansi Lake are shown in table 2.
In this study, The Flu had higher lgK d value among the low molecular weight (2-3 rings) PAHs.The lgK d average values of the high molecular weight (4-6 rings) PAHs were in the range of 0.97-2.12except the not detected compounds.The lgK d values of InP, BaA, BaP, BbF were higher than the other high molecular weight PAHs.The InP, BaA, BaP and BbF were carcinogenic compounds, their average values of lgK d in this study were lower than those in report [9].
This result shows that the low molecular weight PAHs are main compounds in water and sediment, but, the lgK d values of high molecular weight PAHs were higher than the low molecular weight PAHs.This is mainly because the water solubility of PAHs is lower and the lipids are stronger with the number of benzene rings increasing.The higher octanol-water distribution coefficient of PAHs is stronger adsorbed in sediment.

The characteristics of surface sediment in the Nansi Lake
The results of characteristics of surface sediment are showed in Table 3.The value of TOC, soluble salt and pH ranged from 1.20 -6.06%, 1.40-4.66g/kg and 7.60-9.58,respectively.Concentrations of clay was lower than silt and sand concentrations.

The relationship of characteristics in sediments with Kd of PAHs
ng/L in water, with the average value of 34.38±10.34ng/L.The low molecular weight (2-3 rings) PAHs were dominant PAHs compounds, accounting for approximately 83% of total PAHs in

Table 1
The concentrations of PAHs in water and sediment samples

Table 2
Lg Kd (L/Kg) at sediment-water interface from Nansi Lake

Table 3
The characteristics of samples sites in the Nansi Lake.

Table 4
[10]s that the K d value of InP is positively correlated with TOC; the K d value of Ace is positively correlated with TOC, soluble salt and pH; the K d value of BghiP is positively correlated with soluble salt and Clay.Previous reports found that organic carbon, soluble salt, Clay, pH in sediment could affect the partitioning of PAHs between sediment and water.In the present study, the analysis results indicate that TOC, soluble salt, clay and pH of the sediment was negligible correlated with the Kd, which was consistent with Zhang[10].Further research is needed.

Table 4
Correlation of characteristics in sediments with Kd of PAHs in Nansi LakeThis study investigates the concentrations and the partitioning characteristic of PAHs in the water and sediment; evaluates the relationship of sediment characteristics with K d of PAHs in the water and sediment of Nansi Lake.The results indicate that only K d values of InP and Ace are positively correlated with TOC, the K d of most PAHs was negligible correlated with TOC, soluble salt, clay and pH of the sediment in Nansi Lake.