Concentrations and chemical forms of potentially toxic metals in road-deposited sediments from different zones of Hangzhou, China

The 25 road-deposited sediments were collected from five different land-use zones （industrial, residential, commercial, park, and countryside） in Hangzhou, China. The concentrations of metals （Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, and Zn） in these samples were determined using ICP-AES after digestion with the mixture of HNO3-HF-HC1 （aqua regia）, and chemically fractionated according to the modified BCR （the European Community Bureau of Reference） sequential extraction procedure. The high metal concentration levels were detected in the sample from industrial zone and commercial zone having heavy traffic. While the low metal levels were noted in the street dust sample from residential zone, park, and countryside zone. The mobility sequence based on the sum of the BCR sequential extraction stages was： Zn （80.28%）, Pb （78.68%）, Cd （77.66%） 〉 Cu （73.34%） 〉 Mn （67.92%） 〉 Co （41.66%） 〉 Ni （30.36%） 〉 Cr （21.56%）, Fe （20.86%）. Correlation analysis and principal component analysis were applied to the data matrix to evaluate the analytical results and to identify the possible pollution sources of metals. Factor analysis showed that these areas were mainly contaminated by three sources, namely lithology, traffic, and industry.

Transferral of HMs pollution from road-deposited sediments to stormwater runoff during transport processes

Stormwater runoff derived from the wash-off of road-deposited sediments (RDS), contains elevated heavy metal (HM) concentrations and, thus, imposes an increasing threat to urban aquatic ecosystems. In-depth understanding of the variations of HMs pollution from RDS to stormwater during transport processes facilitates the development of effective RDS and stormwater control strategies. Toward this end, the distribution of HMs (Cu, Pb, Zn, Cr, and Ni) in RDS and stormwater were investigated simultaneously. The results show a preferential accumulation of Pb and Zn in the finer (< 38.5μm) RDS, and Cu, Cr and Ni in the coarser (38.5-150μm) RDS. For stormwater, n.d.~48.6% of HMs fractionated into the dissolved phase, and stormwater particles constitute the primary carriers of HMs. Furthennore, the accumulation of HMs in stormwater particles increased linearly with finer particle size distributions (PSD). Geoaccumulation index (Igeo) highlighted the predominant pollution of both RDS and stormwater particles by Cu, Pb and Zn. Nonetheless, Cu, Pb, and Ni mostly contributed the potential ecological risk of RDS, whereas Cu, Pb, and Zn mainly contributed that of stormwater particles. Moreover, contamination by Cu, Pb and Zn was significantly higher in stormwater particles than that in RDS. These differences are attributable to the solubility and size-dependent accumulation of HMs in RDS, as well as the PSD variations during transport processes. The study outcomes highlight the importance of very fine (nano- and submicron- scale) RDS in stormwater pollution and the necessity of control.

Particle size distribution and characteristics of heavy metals in road-deposited sediments from Beijing Olympic Park

Due to rapid urbanization and industrialization, heavy metals in road-deposited sediments（RDSs） of parks are emitted into the terrestrial, atmospheric, and water environment, and have a severe impact on residents＇ and tourists＇ health. To identify the distribution and characteristic of heavy metals in RDS and to assess the road environmental quality in Chinese parks, samples were collected from Beijing Olympic Park in the present study. The results indicated that particles with small grain size（〈150 μm） were the dominant fraction. The length of dry period was one of the main factors affecting the particle size distribution, as indicated by the variation of size fraction with the increase of dry days. The amount of heavy metal（i.e., Cu, Zn, Pb and Cd） content was the largest in particles with small size（〈150 μm） among all samples. Specifically, the percentage of Cu, Zn, Pb and Cd in these particles was 74.7%, 55.5%, 56.6% and 71.3%, respectively.Heavy metals adsorbed in sediments may mainly be contributed by road traffic emissions. The contamination levels of Pb and Cd were higher than Cu and Zn on the basis of the mean heavy metal contents. Specifically, the geoaccumulation index（I geo） decreased in the order：Cd〉Pb〉Cu〉Zn. This study analyzed the mobility of heavy metals in sediments using partial sequential extraction with the Tessier procedure. The results revealed that the apparent mobility and potential metal bioavailability of heavy metals in the sediments, based on the exchangeable and carbonate fractions, decreased in the order： Cd〉Zn≈Pb〉Cu.

Characterization of heavy metal desorption from road-deposited sediment under acid rain scenarios

Road-deposited sediments（RDS） on urban impervious surfaces are important carriers of heavy metals.Dissolved heavy metals that come from RDS influenced by acid rain,are more harmful to urban receiving water than particulate parts.RDS and its associated heavy metals were investigated at typical functional areas,including industrial,commercial and residential sites,in Guangdong,Southern China,which was an acid rain sensitive area.Total and dissolved heavy metals in five particle size fractions were analyzed using a shaking method under acid rain scenarios.Investigated heavy metals showed no difference in the proportion of dissolved fraction in the solution under different acid rain pHs above3.0,regardless of land use.Dissolved loading of heavy metals related to organic carbon content were different in runoff from main traffic roads of three land use types.Coarse particles（＆gt;150 μm） that could be efficiently removed by conventional street sweepers,accounted for 55.1%-47.1%of the total dissolved metal loading in runoff with pH 3.0-5.6.The obtained findings provided a significant scientific basis to understand heavy metal release and influence of RDS grain-size distribution and land use in dissolved heavy metal pollution affected by acid rain.

Heavy metals in road-deposited sediment and runoff in urban and intercity expressways

Road-deposited sediments(RDS)accumulated on road surfaces are an important environmental medium that often provides transport for heavy metals.In order to understand the characteristics of heavy metals in RDS,we investigated the size distribution and heavy metal(i.e.Cd,Cr,Cu,Ni,Pb and Zn)concentrations in RDS and road runoff in typical expressways of suburban and rural area in China.The results demonstrated that RDS particles from all impervious expressway surfaces were predominantly coarse particles(>250μm,58.4%±3.8%)and the RDS on all expressways contained more heavy metals than background soils.Furthermore,the concentrations of Cd,Cr,Cu,Ni,Pb and Zn increased with traffic volume,suggesting that these heavy metals are mainly derived from traffic activities.Moreover,it is found that although heavy metals were concentrated in fine grain fractions,the total loading is highest for the coarsest particles due to their large mass percentage.Additionally,it reveals that the heavy metal concentrations in road runoff of suburban expressway are higher than that in urban expressway.Our findings enhance the understanding of expressway pollution,and imply that for controlling runoff pollution from RDS,transportation agencies should be concerned with both fine and coarse particles and take cleaning methods into account.

镇江城市道路沉积物中重金属污染的来源分析

道路沉积物是一重要环境介质,其颗粒物积累的潜在毒性对于城市水体是一重要危害,因此,识别道路沉积物重金属的含量及来源就显得尤其重要.分析了采集于镇江市商业区、河滨公园、居民区和交通繁忙区的62个样品中的Zn、Pb、Cu、Cr和Ni 5种重金属,它们在交通繁荣区含量最大,Zn、Cu、Cr和Ni含量在商业区、河滨公园和居民区并无明显差异.通过主成分分析识别道路沉积物中重金属的来源,发现不同功能区的重金属来源有所差别,各功能区中第一主成分(贡献率70%以上)代表来自交通活动产生的污染源,或者是与工业污染源共同产生的混合污染源;第二主成分代表来自工业污染源或者是生活污染源,并且道路沉积物中重金属与有机质显著相关,最后计算了重金属浓度富集率(CER),以评价人类活动对于重金属污染的影响程度.结果表明,有机质是镇江城市道路沉积物中重金属的重要载体,人类活动对于该地区重金属污染影响达到中等或中等以上的程度.

城市道路暴雨径流重金属污染特征及其控制策略

城市街道暴雨径流中含有高浓度的重金属,被认为是影响城市受纳水体环境质量的非常重要的面源污染,但是我国目前对道路地表径流中重金属污染关注较少。文中综述了城市道路暴雨径流中重金属的主要来源、迁移途径及其对城市水体及土壤环境可能带来的潜在影响,重点对城市道路暴雨径流重金属污染负荷估算方法的研究进展和存在的不足进行了评述。同时,探讨了城市道路暴雨径流重金属污染控制技术的研究和发展重点,为今后相关研究提出明确的方向,也为市政设计单位开展城市道路暴雨径流污染控制基础工程设计和建设提供依据。

城市道路沉积物氮、磷溶出特性

国内外众多研究表明,城市不透水表面沉积物是雨水径流中污染物的重要来源。以北京市某道路沉积物为研究对象,对城市道路沉积物的粒径分布进行了分析,并通过批量实验,研究了不同粒径道路沉积物中氮、磷营养物及有机物(COD)的溶出特性。实验结果表明,粒径较大的沉积物中氮含量较高,而粒径较小的沉积物中磷含量较高;虽然TP、PO3-4、TN、NO-3、NH+4、COD的溶出浓度、溶出速率变化特征各不相同,但总体趋势是粒径越小氮、磷及COD溶出浓度和溶出速率越大,且最大溶出速率都出现在前5 min。因此,为实现对城市雨水径流污染的有效控制,应采用源头控制措施对小粒径道路沉积物和初期雨水进行有效控制。

雨水花园施工过程的场地污染特征研究

当前我国海绵城市建设中低影响开发(LID)施工场地污染普遍存在,但却没有引起足够的重视与正确的认识。为此,以镇江市雨水花园施工场地为例,分析了不同施工阶段地表沉积物的静态空间分布特征与动态径流污染特征,并与未施工场地进行对比。结果表明,开挖、铺砂、填土及种植阶段的地表沉积物单位面积质量分别为(478.7±14.57)、(261.74±37.79)、(76.18±17.22)、(31.83±9.44)g/m^2,均高于未施工场地[(17.71±2.81)g/m^2],且各施工阶段的地表沉积物均以粗粒径(149~1 000μm)为主;各施工阶段地表沉积物中的重金属含量均低于未施工场地,但重金属污染负荷均高于未施工场地,由高到低依次为开挖阶段、铺砂阶段、填土阶段、种植阶段;地表沉积物的扩散迁移距离约为120 m。施工道路径流中总悬浮固体与重金属浓度均高于未施工道路,施工道路径流中总悬浮固体的场次降雨径流平均浓度(EMC)约为未施工道路的2.8倍。基于上述结果,提出了适合我国海绵城市建设的LID场地径流污染控制措施。

基于地理探测器的城市要素对街尘累积和磷污染空间分异影响特征分析

量化分析城市要素对街尘及其负载磷素空间分异的影响特征可帮助指导大尺度空间城市非点源磷污染管控.本研究结合地理大数据(兴趣点等)与实地采样数据,利用地理探测器定量探究武汉市汉阳区城市要素对街尘累积量及街尘负载多形态磷素含量空间分异的解释能力.结果表明:①街尘累积量及街尘中磷素含量的空间分异程度随街尘粒径和磷形态变化.粒径<150μm街尘累积量的空间分异程度相对较高;铝结合态磷(Al-P)、闭蓄态磷(Oc-P)和有机态磷(Or-P)的空间分异程度整体较高,而碎屑态磷(De-P)和总磷(TP)的空间分异程度则相对较低;Oc-P和Or-P的空间分异程度随街尘粒径变化不大.②单因子条件下,车站类(POI I)、住宅学校类(POI II)和工厂汽修类(POI III)要素对街尘累积量和多种形态磷含量空间分异的解释力较强;路网(ROAD)主要对粒径<150μm街尘中部分磷素含量的空间分异有较强的解释力;餐饮商场类(POI IV)、娱乐休闲类(POI V)和医院类(POI VI)要素主要对>150μm街尘中磷素含量的空间分异有明显的解释力;景点类(POI VII)要素则对街尘累积量和磷素含量空间分异的解释力较弱.③城市要素交互往往增强其对街尘累积量和街尘磷素含量空间分异的解释力,但路网(ROAD)、车站类(POI I)和景点类(POI VII)要素与部分城市要素交互容易对其解释力产生非线性减弱或单因子非线性减弱作用.④基于城市要素布局对不同形态磷设置差异化的控制策略有利于街尘磷污染控制.