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重金属是环境中普遍存在的一类污染物,具有难降解性、生物富集性等特性[1]。重金属污染物经由“三废”即废渣、废水及废气等途径排放到周围环境中,并通过雨水冲刷、海陆间循环等汇聚于江河湖海中[2]。水体中的重金属通过吸附、络合和沉降等途径富集到沉积物中[3]。当水体理化性质发生改变时,吸附在河流沉积物中的重金属会向上水体中缓慢释放,造成水体的“二次污染”,沉积物已成为河流重金属污染的汇集地和重要内源[4]。因此,着手这方面的研究,有助于人们把握污染来源和改善城市水环境,具有实际意义和学术价值。
淮河位于中国东部,是中国七大江河之一。淮河江苏段作为淮河流域的重要组成部分,是南水北调东线的主线河流,在江苏省境内延伸至宿迁、淮安、盐城、扬州等8个省辖市。淮河江苏段主要包括洪泽湖和苏北灌溉总渠两大区域,水域面积为6.53万 km2,约占淮河流域的四分之一[5]。随着淮河两岸经济的发展,未处理的生活污水与工业废水的大量排放,致使淮河江苏段的重金属污染日趋严重[6]。余辉等在洪泽湖采集10个点位的表层沉积物并分析Cu、Zn、Pb、Cd、Cr、Hg和As等重金属的含量,发现洪泽湖中的Cd达到中污染水平,且存在较重的Cd生态风险[7]。最近的研究也发现,洪泽湖表层沉积物中重金属Cd的生态危害依然较大[8]。此外,陈孝杨等对淮河流域安徽段水系沉积物中的重金属开展调查,发现沉积物出现Cd和Mn重金属污染现象[9]。然而,关于淮河江苏段表层沉积物的重金属的研究相对较少。
本研究以江苏省内主要淮河江苏段为研究对象,调查表层沉积物8种重金属的含量,着重探讨沉积物中重金属空间分布特征及其来源,并对淮河江苏段主要污染现状作出评价,进一步完善淮河污染综合评价体系,以期为淮河水环境治理提供依据。
淮河江苏段沉积物重金属的分布特征、来源解析及其生态风险
Pollution characteristics, potential sources, and ecological risk assessment of heavy metals in surface sediments of Jiangsu section of Huaihe River
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摘要: 为了解淮河江苏段沉积物重金属的污染特征、空间分布及其生态风险,对其表层沉积物中重金属(Cd、Mn、Cu、Zn、As、Ni、Pb和Cr)的含量进行检测,利用相关性和主成分进行重金属来源分析,并采用富集系数与生物毒性不利影响对表层沉积物重金属进行污染评价。结果表明,除Cd与Cr外,Zn、Mn、As、Ni、Cu等重金属的含量均高于江苏土壤背景值。重金属含量空间分布差异明显,其中洪泽湖北部及围湖地区等地重金属污染状况最严重,来源可能来自城镇污水、工业废水等复合污染。富集水平排序为Zn >Mn >As >Ni>Cu >Pb >Cr>Cd,其中Mn、Zn富集程度最为明显。生物毒性不利影响评价总体处于中风险状态,主要贡献来源于Ni、Zn。除了Cu、Cd、Pb外,Ni、Zn、Cr、As重金属可能会对底栖动物产生危害作用。因此,淮河江苏段沉积物重金属整体表现为较重生态风险水平。Abstract: In order to understand the pollution characteristics, spatial distribution, potential sources, and ecological risk of heavy metals in the surface sediments of Huaihe river basin, the contents of heavy metals (Cd, Mn, Cu, Zn, As, Ni, Pb, and Cr) were analyzed. The potential sources of heavy metal were analyzed by correlation and principal component analysis. Using enrichment factor and mean Probable Effect Concentrations Quotients (mPEC-Q), the potential ecological risk degree of heavy metals in the sediments were evaluated. The results showed that except Cd, Cr, and As, the contents of Zn, Mn, As, Ni, and Cu were higher than their background values. The contents of heavy metals are higher in the north of Hongze, which may come from the combined pollution of domestic sewage and sewage discharge. The mPEC-Q are at medium risk level, and Ni, Zn, Cr, and As result in the damage to benthos. Thus, the heavy metals in surface sediments of Huaihe river basin showed a high ecological risk level.
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表 1 富集系数评价指标
Table 1. Enrichment factors of Evaluation index
等级
GradeEF值
Enrichment factors富集(污染)程度
Pollution gradeⅠ ≤1 无富集(无污染) Ⅱ 1—2 轻微富集(轻微污染) Ⅲ 2—5 中度富集(中度污染) Ⅳ 5 —20 显著富集(强污染) Ⅴ 20 —40 强烈富集(较强污染) Ⅵ >40 极强富集(极强污染) 表 2 各种重金属的 TEC、PEC 和
$ {T}_{\mathrm{r}}^{i} $ Table 2. TEC, PEC, and
of heavy metals$ {T}_{\mathrm{r}}^{i} $ Cr Cu Zn As Ni Cd Pb Mn TEC 43.4 121 31.6 9.79 22.7 0.99 35.8 — PEC 111 459 149 33 48.6 4.98 128 — $ {T}_{r}^{i} $ 2 5 1 10 5 30 5 — 表 3 mPEC-Q及RI风险等级划分
Table 3. Risk classification of mPEC-Q and RI
mPEC-Q及RI值 危害程度
Risk classificationmPEC-Q≤0.1或RI≤70 低风险或轻微生态风险 0.1<mPEC-Q≤1或70<RI≤140 中风险或中等生态风险 mPEC-Q>1或RI >140 高风险或强生态风险 表 4 重金属含量描述统计
Table 4. Descriptive statistics of each metal content
元素
Element含量变化范围
Content range平均值
Average value变异系数
Coefficient of variation江苏土壤背景值
Baseline values of elements
in soil of Jiangsu ProvinceCr 1.68—116.48 53.05 0.59 76.00 Mn 24.39—1438.74 786.42 0.50 629.00 Cu 0.81—52.85 27.83 0.54 26.00 Zn 23.12—199.04 109.17 0.43 73.00 As 0.05—18.00 10.55 0.51 9.40 Ni 0.19—80.86 36.60 0.58 32.90 Cd 0.04—0.27 0.07 2.74 0.15 Pb 0.97—48.58 26.80 0.54 26.80 -
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