湖南水口山多金属矿区废石堆重金属污染评价及赋存形态分析

湖南水口山及周边是湖南省重金属污染较为严重的地区之一,龙王山金矿床是该区中部的一个重要金矿床.为调查该矿床废石堆污染状况、是否为周边环境的污染源、污染途径、重金属迁移能力和潜在的危害,对矿区FS17废石堆进行了自然淋滤水和24 m浅钻系统取样,开展重金属元素总量分析,利用单因子指数法和内梅罗综合污染指数法对其重金属污染程度进行污染评价,采用四步改良BCR提取法分析废石堆中8种重（类）金属元素（Pb、Zn、Cd、Cu、Cr、Ni、As和Fe）的赋存形态,并利用迁移指数量化废石堆重金属元素迁移能力;发现废石堆中Cd、Cu、Pb、As、Zn、Ni重金属元素严重超标,且在垂向上分布极不均匀;其自然淋滤水样中重金属元素Cd、Ni、Zn、Cu也严重超标;废石堆浅层重金属元素潜在迁移能力顺序为:Cd＞Ni≈Zn＞Cu＞Pb＞As＞Cr＞Fe,深层重金属元素迁移能力顺序为:Cd＞Zn＞Cu＞Ni＞Cr＞Pb＞As＞Fe,浅层重金属元素的迁移性大于深层;说明该废石堆重金属元素含量高,是周围环境重要污染源,酸性废水排放为其释放污染元素的主要途径;Cd、Cu、Zn、Ni迁移能力强,是周围环境的主要污染元素;Pb、Ni、As的迁移性在深层明显降低,可以通过埋深来削弱其迁移性,而Cr不会对周边环境产生污染.      

高邮湖底泥及出入湖河口表层沉积物重金属元素分布与潜在生态风险评价

为查清高邮湖底泥及出入湖河口表层沉积物重金属分布特征,评价其潜在生态风险,以湖区及周边25个底泥和沉积物样品为载体,重点研究8种重金属元素,选用单因子污染指数法、内梅罗综合指数法、地累积指数法和潜在生态风险指数法,相似比对重金属污染等级及评价潜在生态风险。测试数据表明,8种重金属元素中,仅Hg含量（平均值）未超过里下河浅洼平原表层土壤重金属元素背景值,As含量（最大值）超过农用地土壤污染风险筛选值。Pearson相关系数矩阵表明,重金属元素Ni与Cr、Pb、Zn、Cu之间具显著同源性;单因子污染指数法与内梅罗综合指数法评价结果显示,污染指数均值排序均为As＞Cd＞Pb＞Cu＞Zn＞Ni＞Cr＞Hg,但对As、Cd评价前者为轻度污染,后者为中度污染;地累积指数Igeo显示,仅As为轻度污染,其余元素均为无污染状态。沉积物单项潜在生态风险指数排序为Cd＞Hg＞As＞Pb＞Cu＞Ni＞Cr＞Zn,仅Cd属中风险,其余元素为低风险;研究区综合潜在生态风险指数RI均值为115.7,表明全区总体生态风险属于低风险状态,重金属有沿入湖河口向湖心区富集趋势。     

攀枝花钒钛磁铁矿区土壤重金属地球化学特征及污染评价

为了解攀枝花钒钛磁铁矿区土壤重金属的特征及污染程度,采集了矿区表层土壤样品和两个土壤剖面,用多种分析方法有针对性地分析了Cu、Pb、Zn、Ti、V、Co、Ni、As、Cd、Cr、Hg、Mn十二种元素。在分析分布特征基础上,对重金属进行了污染物负荷指数评价,结果发现:1)攀枝花钒钛磁铁矿矿区表层土壤大部分属于中等污染,少数属于强污染,个别达到了极强污染;2)Co、V、Cu、Cd、Ti几种元素的最高污染系数大,Zn、Mn、Ni、Cr四种元素的最高污染系数次之,Hg、Pb两种元素的最高污染系数较小,As的最高污染系数最小;3)从各区域的污染物负荷指数来看,排土场周围和朱矿采矿场下游附近污染程度较大,远离矿区以及矿区上游污染较小。     

广东大亚湾底质重金属分布特征与环境质量评价

大亚湾是粤东的大型海湾，毗邻深港，其环境质量现状及发展趋势颇受关注。对大亚湾海域45个表层站位、1口浅钻及2个柱状样重金属元素Hg、As、Cd、Cu、Pb、Cr、Zn进行分析，并对底质环境质量进行定量评价。其结果：①大亚湾海域Hg、As、Cu的污染指数Pi值均小于1．0，超标率为0，表明全区未受这些因子污染；②Cd、Zn、Pb、Cr的污染指数Pi值部分大于1．0，表明受到这些因子不同程度的污染，其中Pb的超标率最高，达93．3％，污染指数Pi值为0．83～2．25，为良好—中等污染，总体为轻微污染；Zn的超标率为76．9％，pf值为0．25～2．63，变化较大，总体为轻微污染；Cd的超标率为60．0％，Pi值为0．50～1．78，良好—轻微污染；Cr的超标率为17．8％，Pi值为0，49～1．90，良好—轻微污染；③综合污染指数为1．08～2．21，平均1．37，表明本区均不同程度地受重金属污染，总体属轻微污染，其中范和港污染最为严重，SQI值多在1．5以上，其次为中央列岛附近海域。湾口和澳头—霞涌近岸海域污染较轻。从钻孔及柱状样的重金属含量分布来看，在表层没有明显增多的趋势。     

北京市密云水库上游土壤重金属污染调查评价

2002年9月在密云水库周边及上游地区(北京境内)总共采集土样98个,以《土壤环境质量标准》GB15168-95Ⅰ级标准为评价标准,对密云水库上游地区土壤重金属Cd、Pb、As、Hg、Cr、Cu、Ni、Zn的污染状况作了初步评价。研究结果发现密云水库周边及上游地区重金属污染以Cr和Hg为主,牤牛河上游为污染最严重地区,清水河上游、潮河下游放马峪地区、德田沟--崎峰茶地区受Cr元素轻度污染。该地区土壤重金属污染,主要原因是金属矿山不合理排放的尾砂及废矿石等人为因素所致。     

大亚湾表层沉积物重金属元素形态特征、控制因素及风险评价分析

为了解大亚湾表层沉积物中重金属的污染状况,对大亚湾海域23个点位表层沉积物中7种重金属元素（Cr、Ni、Cu、Pb、Zn、Cd、As）的质量分数、形态特征、来源控制因素以及潜在生态风险进行了研究。采用优化BCR提取法分析重金属元素赋存形态,并依据各种重金属元素的形态特征与沉积物基质属性进行了相关因子分析,了解其分布的控制因素。结果表明：大亚湾沉积物重金属元素呈现环带状分布特征,从岸向湾内逐渐减小;重金属元素质量分数的高值区主要分布于大鹏澳、哑铃湾及范和港附近;重金属元素赋存形态中Cr、Ni、Cu、Zn、As主要以残渣态存在,Pb主要以可还原态存在,Cd主要以酸提取态存在;7种重金属元素各自非残渣态所占比率从大到小为Pb(78.83%)、Cd(78.65%)、Cu(48.54%)、Zn(48.10%)、Ni(38.31%)、Cr(28.43%)、As(27.76%),即Pb最高,As最低,表明Pb的迁移性最强;通过因子分析,大亚湾重金属主要为沿岸自然风化产物的输入,其次为工业废水及养殖污水。运用酸提取态风险评估法对重金属元素潜在生态风险进行评价,发现研究区所选重金属元素综合风险评价Cd为高风险,其余重金属为中-低风险等级。     

固体聚合膜电解浓集法测量天然水中低含量氚的化学淬灭效应研究

固体聚合膜电解浓集法是浓缩氚含量较低(1 Bq/m~3)的天然水样的常用方法,但因水样自身含有杂质离子或电解装置聚合膜带入杂质进入浓集液,使浓集液偏酸性,在测量过程中易产生化学淬灭效应,导致氚的测量值偏低。本文研究了水样自身存在的杂质离子和聚合膜上残留的杂质离子、样品溶液的pH值及其电导率所产生的化学淬灭效应的影响,实验表明,为减少化学淬灭效应,提高测量低含量氚的准确性,需保证水样溶液呈中性,电导率≤1μS/cm,同时避免杂质沉积在聚合膜上。如果水样溶液的pH值偏酸性、电导率大于1μS/cm,可采用酸碱混合型离子交换树脂去除水样中自身的杂质;对于聚合膜引入的杂质,可在电解后的水样中加入微量氨水将其pH值调节至中性。     

首钢地区表层土壤重金属的分布特征及污染评价

利用多元统计分析和空间分析相结合的方法,分析了首钢地区表层土壤中Fe、Cr、Ni、V、As、Cd、Pb、Cu、Zn、Hg 10种重金属元素的地球化学特征。研究结果表明,10种元素可以归结为4类:第一类Ni、V、As的含量低于自然背景值,主要受成土母质等自然因素的影响;第二类Cd、Cu、Pb、Zn的含量已经超出自然背景值,其中Cu、Pb、Zn属于轻度污染,Cd属于中度污染,这一类元素主要受到交通和冶炼等人为因素的影响,高值区主要分布于居民区;第三类为Fe、Cr,同时受到自然因素和人为因素的共同影响,高值区集中分布在厂区和部分居民区;第四类为Hg,Hg因其是一种非点源污染的元素而单独聚为一类,主要受到人为因素的影响且高值样点位于河流区。总体而言,首钢地区表层土壤已经受到部分污染,需密切关注其对环境的危害及人群的潜在健康风险。本研究对该区域土壤污染风险评价和土地利用规划等具有一定的借鉴意义。     

某城市规划新区表层土壤重金属潜在生态风险评价

为评价某城市规划新区表层土壤质量,利用网格法采集表层土样1000件,分析8种重金属(Cd、 Cu、 Zn、 Ni、Cr、Pb、Hg、As)元素的含量,并分别运用污染负荷指数(PLI)和潜在生态危害指数(RI)评价研究区表层土壤中重金属的污染程度和危害等级。利用克里金插值法研究土壤PLI和RI的空间分布特征。结果表明:研究区内表层土壤重金属平均值均大于中国土壤背景值,Cd、Cu、Ni较为富集。研究区Cd和Cu元素为重度污染,Cd的生态危害性较强,87.90%的土样为重金属轻微污染,60.83%的土样为中等生态危害。污染较为严重和风险较强的地区主要位于研究区西南部河流两岸,Cu和Cd可能受到了人类活动的影响而偏高。     

湘中桃江锰矿废矿堆环境地球化学分析

对湘中桃江锰矿废矿堆的废石进行了主量元素、稀土元素、微量元素和重金属元素的地球化学分析。野外观察及分析结果表明:组成废矿堆的岩石主要是赋矿围岩中奥陶统黑色页岩和原生碳酸锰矿石。这些废石富含Cu、Pb、Zn、Cr、Tl、Sb、U等重金属元素。废石暴露地表而遭受风化分解,导致Sc、V、Cr、U、Cd、Th等重金属元素淋滤释出,在废石样品中均表现出不同程度的迁移特征,且以V、Cd、U的迁移性最为强烈。此外,黑色页岩中Ni、Cu、Zn、Pb、Tl、Sb也明显发生淋失。这些重金属元素如Cd、Tl等毒性极强,进入矿区周围不断积聚,便可能对环境造成严重的影响。故对区内分布的废矿堆作为重金属污染源应高度重视。     

Heavy metal distribution in karst soils from Croatia and Slovakia

With the use of the optimised three-step BCR sequential-extraction procedure it was possible to assess the mobility of selected elements in soil profiles from Croatian and Slovakian karst terrains. The soils in the Croatian karst were enriched in Cr, Ni, V, Mn, Cu, Cd and Mo, while soils from the Slovak Karst had high Pb and Zn concentrations. It was determined that the elements were most readily mobilised from the topsoil and the degree of mobility decreased with depth. Cr and Ni were mainly bound to the residual fraction, and Pb in the oxidisable fraction. Cu mobility was high in samples treated with agrochemicals throughout the soil profile.     

Distribution and immobilization of heavy metals in Pliocene aquifer sediments in Wadi El Natrun depression, Western Desert

The Pliocene aquifer receives inflow of Miocene and Pleistocene aquifer waters in Wadi El Natrun depression. The aquifer also receives inflow from the agricultural activity and septic tanks. Nine sediment samples were collected from the Pliocene aquifer in Wadi E1 Natrun. Heavy metal (Cu, Sr, Zn, Mn, Fe, Al, Ba, Cr, Ni, V, Cd, Co, Mo, and Pb) concentrations of Pliocene aquifer sediments were investigated in bulk, sand, and mud fractions. The determination of extractable trace metals (Cu, Zn, Fe, Mn, and Pb) in Pliocene aquifer sediments using sequential extraction procedure (four steps) has been performed in order to study environmental pathways (e.g., mobility of metals, bounding states). These employ a series of successively stronger chemical leaching reagents which nominally target the different compositional fractions. By analyzing the liquid leachates and the residual solid components, it is possible to determine not only the type and concentration of metals retained in each phase but also their potential ecological significance. Cu, Sr, Zn, Mn, Fe, and Al concentrations are higher in finer sediments than in coarser sediments, while Ba, Cr, Ni, V, Cd, Co, Mo, and Pb are enriched in the coarser fraction. The differences in relative concentrations are attributed to intense anthropogenic inputs from different sources. Heavy metal concentrations are higher than global average concentrations in sandstone, USEPA guidelines, and other local and international aquifer sediments. The order of trace elements in the bulk Pliocene aquifer sediments, from high to low concentrations, is Fe?>?Al?>?Mn?>?Cr?>?Zn?>?Cu?>?Ni?>?V?>?Sr?>?Ba?>?Pb?>?Mo?>?Cd?>?Co. The Pliocene aquifer sediments are highly contaminated for most toxic metals, except Pb and Co which have moderate contamination. The active soluble (F0) and exchangeable (F1) phases are represented by high concentrations of Cu, Zn, Fe, and Mn and relatively higher concentrations of Pb and Cd. This may be due to the increase of silt and clay fractions (mud) in sediments, which act as an adsorbent, retaining metals through ion exchange and other processes. The order of mobility of heavy metals in this phase is found to be Pb?>?Cd?>?Zn?>?Cu?>?Fe?>?Mn. The values of the active phase of most heavy metals are relatively high, indicating that Pliocene sediments are potentially a major sink for heavy metals characterized by high mobility and bioavailability. Fe–Mn oxyhydroxide phase is the most important fraction among labile fractions and represents 22% for Cd, 20% for Fe, 11% for Zn, 8% for Cu, 5% for Pb, and 3% for Mn. The organic matter-bound fraction contains 80% of Mn, 72% of Cu, 68% of Zn, 60% of Fe, 35% of Pb, and 30% of Cd (as mean). Summarizing the sequential extraction, a very good immobilization of the heavy metals by the organic matter-bound fraction is followed by the carbonate-exchangeable-bound fraction. The mobility of the Cd metal in the active and Fe–Mn oxyhydroxide phases is the highest, while the Mn metal had the lowest mobility.     

雄安新区某金属冶炼区土壤重金属污染程度及风险评价

为支撑雄安新区土地资源科学管理,完善中国土壤污染评价体系,文章以雄安新区某废旧金属冶炼区为研究区开展地质调查,采集541件表层土壤样品,测定了土壤中的Cd、Hg、Pb、As、Cu、Zn、Cr、Ni八种重金属元素的含量和pH,采用主成分分析法研究重金属元素的组合及分布特征,通过单因子指数法、内梅罗综合指数法、地质累积指数法、潜在生态风险评价法和人体健康风险评价法对土壤重金属的污染程度及风险进行评价。结果显示：研究区土壤中Cu、Zn、Cd、Pb元素超标主要受冶炼活动影响,As、Hg元素高值异常主要由受唐河污染的地下水灌溉引起;单因子污染指数超标比例大小顺序为Cd>As>Cu>Zn>Pb>Hg>Cr=Ni;内梅罗综合指数评价结果显示54%的样品达到了污染水平;地质累积指数超标比例大小为Cd>Cu>Pb>As>Zn>Hg>Ni>Cr,Cu、Cd、Zn、Pb、As极重污染比例分别为13.5%、10.2%、9.1%、10.9%、17.2%;Cd和Hg是主要的生态危害元素,Cd中等-强生态危害比例为65.2%,Hg中等-强生态危害比例为71.3%;非致癌风险因子主要为As、Cr、Pb,95.2%样品对儿童的非致癌风险超过了1,29件样品中As对儿童的致癌风险超过10^-4,研究区土壤重金属对儿童具有较高的健康风险。     

Nitric-acid soluble fractions of 21 elements in Norwegian podzols: Factors affecting regional differences in vertical distribution

Distributions of 21 major and trace elements in HNO₃ extracts of different horizons were studied in 13 podzol profiles from the boreal forest in different parts of Norway using ICP–MS. On the basis of ratios between the HNO₃-extractable fractions in the various horizons some general trends were elucidated. Two different groups of elements concentrated in the humus layer relative to the mineral horizons were identified, one mainly associated with contributions from air pollution (As, Cd, Sb, Pb), another one with plant nutrient circulation (K, Ca, Mn and to a lesser extent Mg, Co, Ni, Rb) and some with both mechanisms (Cu, Zn, Tl). The elements most clearly enriched along with Fe in the B horizon were V, Pb, Al, and Cr in that order, Pb partly because of leaching from the polluted organic surface soil. Four soils in the far south showed a behaviour distinctly different from the rest and were treated as a separate group. Relative to the more northerly sites the surface horizons of these soils were strongly depleted in lithogenic elements (Mg, Al, K, Ca, Sc, V, Cr, Mn, Fe, Co, La) and enriched in elements typical of long-range transport of pollutants (As, Cd, Sb, Tl, Pb). Also the B horizon in the southern soils was strongly depleted in the lithogenic group elements, including Fe and the associated metals. The main reason for this difference is assumed to be the greater influence of transboundary air pollution and associated metals and stronger soil acidification in the far south of the country.     

Multivariate statistical techniques for evaluating and identifying the environmental significance of heavy metal contamination in sediments of the Yangtze River, China

The concentrations of heavy metals (Cr, Co, Ni, Cu, Zn, Pb, Cd, As, Hg, and Fe) in sediments of the Yangtze River, China, were investigated to evaluate levels of contamination and their potential sources. The lowest heavy metal concentrations were found in the source regions of the river basin. Relatively high concentrations of metals, except Cr, were found in the Sichuan Basin, and the highest concentrations were in the Xiangjiang and Shun’anhe rivers. All concentrations, except Ni, were higher than global averages. Principal component analysis and hierarchical cluster analysis showed that Zn, Pb, As, Hg, and Cd were derived mainly from the exploitation of various multi-metal minerals, industrial wastewater, and domestic sewage. Cu, Co, and Fe were derived mainly from natural weathering (erosion). Cr and Ni were derived mainly from agricultural activities, municipal and industrial wastewater. Sediment pollution was assessed using the geoaccumulation index (I _geo) and enrichment factor (EF). Among the ten heavy metals assessed, Cd and Pb had the highest I _geo values, followed by Cu, As, Zn, and Hg. The I _geo values of Fe, Cr, Co, and Ni were <0 in all sediments. EF provided similar information to I _geo: no enrichment was found for Cr, Co, and Ni. Cu, Zn, As, and Hg were relatively enriched at some sites while Cd and Pb showed significant enrichment.     

Fractionation and risk assessment of heavy metals in soil samples collected along Zerqa River,Jordan

The objectives of the current study were to determine the chemical partitioning of Pb, Ni, Zn, Co, Cr, Mn, Fe and Cd using sequential extraction procedure and to assess the environmental risk associated with these metals in the farming soils along Zerqa River. Metal concentrations were measured by atomic absorption spectrophotometer. The study area demonstrated a wide range for pH, organic matter, carbonate contents, and cation exchange capacity, and is polluted with Pb, Cd, Mn, and Cu. The extensive use of fertilizers and pesticides in the agricultural activities, and discharge of treated and untreated wastewater are the major sources of pollution in the study area. Principal component analysis coupled with Pearson’s correlation analysis between the heavy metals revealed strong and positive correlation between these metals in the study area. According to the Risk Assessment Code (RAC), major portions of Cd and Mn are contained in exchangeable and carbonates fractions and therefore can easily enter the food chain. These metals pose a high to very high risk to the environment. Cu, Ni, Pb, and Zn pose medium risk, while Cr poses a low environment risk.     

包头市典型工业区表层土壤中重金属污染状况及其潜在生态风险研究

为了解包头市典型工业企业对其所在地土壤中重金属含量的影响及污染现状,利用相关性系数对其表层土壤中7种重金属(Cu、Zn、Pb、Cr、Cd、Mn、Ni)来源进行研究,并采用内梅罗综合污染指数法和潜在生态危害指数对其污染状况进行评价。结果表明,7种重金属含量平均值均高于内蒙古土壤背景值,其中Cd、Mn、Ni超标率已达100%,而Cu、Pb、Zn的超标率分别为97%、93%和93%,只有Cr超标率较低(53%),污染程度依次为CdPbCuNiZnMnCr,其中Pb和Cd为重度污染,Cu、Zn、Ni为中度污染,Cr、Mn为轻度污染;Cu、Zn、Cr、Mn、Ni可能同时来自工业生产和交通运输两个源,而Pb和Cd除上述来源外,燃煤烟气的排放有较大贡献。潜在生态危害依次为CdPbCuNiCrZnMn,其中Cd的潜在生态风险最大,应予以高度重视,其他金属的风险均为轻微。     

Distribution and sequential extraction of some heavy metals in urban soils of Guiyang City,China

Sixty-two soil samples collected from different functional zones of Guiyang were analyzed for total concentrations and sequential extraction of Cr, Cu, Pb, Zn and Cd by ICP spectrometry. The average total concentrations ofCr, Cu, Pb, Zn and Cd in the soils of Guiyang were 92.9, 51.6, 44.1,139.3 and 0.28 mg/kg, respectively. The soils have been polluted by Cr, Cu, Pb, Zn and Cd to some extent in comparison with the background values of Guiyang. Significant differences were recognized in the concentrations of Cr, Cu, Pb, Zn and Cd in different functional zones. As for the sequential extraction, Cr, Cu and Zn were present mainly in the residual fraction, and Pb was present mainly in the oxidizable fraction. The reducible fraction of Cd accounts for 47.5%, and the residual fraction is lowest. The mobility and bioavailability of heavy metals follow the order of Cd〉Pb〉Cu〉Cr〉Zn.     

Heavy metal history from cores in Wellington Harbour,New Zealand

Analysis of ten heavy metals (Ag, Cd, Cr, Cu, Fe, Mn, Ni, Pb, Sb, Zn) in six sediment cores from Wellington Harbour show both anthropogenic enrichments and diagenetic modifications. Absolute concentrations determined by two methods, x-ray fluorescence and acid leaching for bioavailability, are not comparable. However, vertical trends in concentrations of the cored sediment are comparable. To assess levels of anthropogenic pollution, enrichment factors (enriched concentrations in upper core divided by background levels in lower core) are preferred over index of accumulation (I _geo) values because preindustrial or background levels of heavy metals are well constrained. The ten metals are placed into three groups: (1) Cu, Pb, and Zn, which show the most anthropogenic enrichment; (2) As, Cd, Cr, Ni, and Sb, which are often associated with anthropogenic pollution but show only minor enrichment; and (3) Fe and Mn, which are diagenetically enriched. Assuming harbor waters are well mixed, anthropogenic enrichments of Cu, Pb, and Zn, are time correlative, but the degree of enrichment depends on the method of analysis and core location. Levels of As, Cd, Pb, and Zn show small variations in preindustrial sediments that are not related to changes in grain size and probably result from changes in the oxidation-reduction potential of the sediments and salinity of the pore waters.     

近50年来抚仙湖重金属污染的沉积记录*

文章以抚仙湖污染严重的北部和基本未受人类活动影响的中部为研究对象,分别采集了沉积岩芯FB和FZ,通过对岩芯的¹³⁷ Cs测年和重金属元素(Cu,Ni,Ti,Cr,V,Pb,Cd和Zn)的含量分析,研究了湖泊重金属来源和污染历史,并利用地质累积指数法评价了湖泊重金属污染程度。结果表明:抚仙湖北部的平均沉积速率约为2.0~2.8mm/a;20世纪80年代以前,湖泊北部和中部的重金属元素(Cu,Ni,Ti,V,Pb,Cd,Zn)以自然来源为主;80年代以后,抚仙湖受到人类活动的影响,但湖泊中部Cu,Ni,Ti,V,Pb,Zn以及湖泊北部Cu,Ni,Ti,V仍以自然来源为主;湖泊北部Pb和Zn地质累积指数值小于1,属无污染到中度污染;北部Cd地质累积指数为3~4,达强度污染;中部Cd地质累积指数为2~3,属中强度污染;且Pb,Zn和Cd污染程度有加速增大的趋势。