粤北典型工矿区土壤重金属富集特征、来源解析及风险评价

为了解粤北典型工矿区土壤重金属污染状况,以研究区的表层土壤(0～20 cm)为研究对象,在测定209个样点土壤重金属(As、 Cd、 Cr、 Cu、 Hg、 Ni、 Pb和Zn)含量的基础上,运用GIS和主成分分析法解析8种土壤重金属来源和空间分布特征,并采用地累积指数法和潜在生态危害指数法系统评估其污染状况和生态风险.结果表明：(1)除Ni以外,其余7种元素均超过全国土壤背景值,但低于污染风险筛选值,土壤环境整体较为清洁.(2)土壤重金属空间分布各异,As和Pb含量呈现西北-东南向条带状分布,Cd、 Cu、 Hg和Zn含量在研究区总体上呈中部向四周同心圆状递减分布,与工矿企业位置基本吻合,而Cr和Ni含量的空间分布与工业企业等污染源的位置没有直接关系.(3)8种元素可辨识为3个主成分,PC1(Cd、 Cu、 Pb和Zn)主要受铅锌矿选冶、交通排放和农业生产等人类活动影响;PC2(Cr和Ni)属自然来源,主要受成土母质影响;PC3(As和Hg)主要受有色金属冶炼和火力发电等工业活动影响.(4)通过地累积指数法发现,8种重金属风险程度依次为：Cd>As>Zn>Hg>...     

泉州市街道灰尘中重金属来源分析

用ICP-MS测定了泉州市不同功能区街道灰尘中11种重金属元素(Cr、Fe、Mn、Ni、Cu、Zn、Cd、Sb、Pb、Bi、Co)的含量。结果表明,上述元素的平均含量均高于当地土壤背景值,尤以Zn、Cd、Sb、Pb富集较严重。多元统计分析(相关分析、因子分析、聚类分析)结果显示,泉州市街道灰尘中上述重金属来源可分为三大类:Cu、Pb、Sb、Cd、Bi主要来自机械加工和交通污染;Mn、Zn主要来自农药喷洒和生活污染;Fe、Cr、Ni、Co则主要来自钢铁工业污染和自然源。     

新疆和硕绿洲农田土壤重金属污染及生态风险

新疆和硕绿洲采集82个耕地土壤样品,测定其中As、Cd、Cr、Cu、Mn、Ni、Pb和Zn等8种重金属元素的含量。采用地统计法、污染负荷指数(PLI)和潜在生态风险指数(RI)评估农田土壤重金属污染和潜在生态风险,并讨论重金属主要来源。结果表明:(1)和硕绿洲农田土壤所有重金属元素含量平均值均未超出国家二级标准的限值,Cd、Cr、Ni、Pb和Zn含量的平均值分别超出新疆灌耕土背景值的2.0、1.51、1.18、2.13和8.47倍。(2)农田土壤Cd与Zn呈现中度污染,Cr、Cu、Ni和Pb轻度污染,Mn轻微污染,As无污染。研究区PLI平均值呈现轻度污染。(3)各重金属元素单项生态风险指数从大到小依次为:Cd、Ni、As、Cu、Cr、Zn与Pb。农田RI平均值属于轻微生态风险。重金属元素含量、污染与生态风险空间分布格局各不相同。(4)和硕绿洲农田土壤As、Pb和Zn主要受到人为因素的影响,Cr、Cu、Mn和Ni主要受到土壤地球化学作用的影响,Cd受人为污染和自然因素共同影响。Cd是研究区农田土壤主要的污染因子之一,对农田土壤污染及潜在生态风险的贡献较大,农田土壤Cd污染值得关注。     

环巢湖典型农业区土壤重金属来源解析

重金属来源解析是防止或减少土壤重金属污染的必要前提。为此,采集并分析了环巢湖典型农业区408个表层土壤样品中As、Cd、Cr、Cu、Ni、Pb、Zn等7种重金属元素含量。地积累指数评价结果表明土壤重金属污染总体处于0~1级。综合相关性分析、主成分分析和聚类分析结果可知:(1)Cd、Cu、Pb、Zn主要来源于大气沉降、畜禽粪肥和化肥等人类活动;(2)成土母质是Cr和Ni的主要来源;(3)As有人类活动和成土母质双重来源。用绝对主成分得分-多元线性回归模型(APCS-MLR)对土壤中重金属来源进行了定量解析,解析结果与主成分分析和聚类分析结果相符。可见,多元统计分析结合APCS-MLR模型能很好地应用于土壤重金属来源解析。     

苏州古城区域河道底泥的重金属污染分布及生态风险评价

本文分析了苏州古城区域20个代表性断面中8种重金属（Cd、Cu、Cr、As、Mn、Ni、Pb和Zn）的含量,评价了重金属的污染程度和潜在生态风险并甄别了污染来源.结果表明,苏州古城区域河道底泥中Cd、Cu、Cr、As、Mn、Ni、Pb和Zn的平均含量分别为1.1、142.6、90.2、17.2、800.1、63.3、199.1和384.2 mg·kg^-1,超过江苏省土壤背景值的采样点比例分别为100%、100%、65%、95%、70%、100%、95%和100%.利用地累积指数评价发现,8种重金属元素污染程度依次为Pb > Cd > Cu > Zn > Cr > Ni > As > Mn,总体上Pb处于强度污染水平,Cd、Cu、Zn和Cr处于中强度污染水平,Ni和As处于轻度污染水平,Mn处于无污染水平.潜在生态风险指数评价显示,8种重元素的潜在生态风险依次为Cd > Pb > Cu > As > Ni > Zn > Cr > Mn,总体上Cd、Pb和Cu处于中风险水平,其余5种重金属处于低风险水平.古城区域内北部河道和南部河道底泥重金属的平均含量、地累积指数值和潜在生态风险指数值均大于干将河和环城河,水环境重金属治理应重点关注古城区域内部.相关性分析和主成分分析表明,Cd、Cu、Cr、As、Ni、Pb和Zn元素可能源于化肥、路面老化、轮胎磨损和尾气排放等人为因素,Mn则主要源于自然因素.     

承德市滦河流域土壤重金属地球化学基线厘定及其累积特征

选择承德市滦河流域为研究区,系统采集了351个表层土壤样品(0～20cm),测定了Cu、Ni、Cd、Cr、Pb、Zn、Hg、V、Ti、Mn、As和Co共12种重金属的含量,运用基于参比元素的标准化方法和累积频率曲线法确定了12种重金属元素的地球化学基线值,结合主成分分析法与地统计方法统计结果,分析了重金属的空间结构和分布特征,利用地累积指数法对不同土壤类型和土地利用方式表层土壤重金属累积程度进行了分类评价.结果表明,滦河流域表层土壤V、Ti、Cd、Pb、Mn和Co元素地球化学基线值高于河北省背景值,As、Zn、Cr、Cu、Ni和Hg元素地球化学基线值低于河北省背景值.表层土壤重金属总体累积程度由强至弱为:Cd Pb Cu Ti Mn Zn Cr Ni Co V Hg As,80%以上的土壤样品中Pb、Ti、V、As和Co元素属无累积-中度累积水平,70%以上土壤样品中Hg、Mn、Ni、Cu、As、Cd和Cr元素属无累积-中度累积水平.土壤重金属总体累积程度在棕壤、褐土和潮土中依次增大;在工矿用地、灌木林地中较高,林地、草地中相对最低.农用地表层土壤中Pb、Cd元素累积程度相对较高,分别有27. 69%和25. 38%的样品属中等以上累积水平.滦河流域表层土壤Ti、V、Co、Ni和Cr元素同源性较高,与原生高地质背景相关; Cd、Pb、Zn,Mn、Cu和As元素污染累积受成土母岩和人为因素共同作用影响,Hg元素累积则主要来源于人为活动.     

阳宗海沉积物重金属污染评价及来源解析

对沉积物中重金属进行污染评价及来源分析有助于为重金属污染治理提供决策依据。该研究以阳宗海不同湖岸湖滨湿地沉积物为研究对象,运用沉积物富集系数法和内梅罗指数法评价沉积物中9种重金属污染程度,并运用聚类分析和因子分析法对重金属污染来源进行识别。结果表明:(1)阳宗海湖滨湿地沉积物中重金属在不同湖岸呈现不同分布特征,As、Cd、Cr、Zn、Mn在东部含量较高,Co、Cu、Ni最高值出现在北部;Pb最高值出现在南部;(2)在研究区域Cd属于重度污染,As、Zn、Cu、Cr、Ni、Pb和Co均属于中等污染水平,且EF值均大于1,表明该研究区的重金属污染物除了来自地壳和自然风化过程,还受到于人类活动、工业生产等外源污染影响;(3)阳宗海不同湖岸重金属Mn和Cd累积效应最为显著,在东部湖滨湿地As和Cu的累积效应也较显著,其余重金属在不同湖滨湿地表现出不同程度的污染累积;(4)因子分析可将9种重金属归为第一主成分(Zn、Cu、Cd、Ni、Pb、Co、Mn),贡献率为72.16%,为工业因子,第二主成分(As、Cd)为能源因子,通过聚类表明,该研究区域在污染程度上可分为3大类,主要受西南季风、铝厂、火电厂等影响。基于该研究结果,在今后环境治理时应该加强污染源控制,保护阳宗海生态环境。     

锰矿区周边农田土壤重金属污染特征、来源解析及风险评价

为了解锰矿周边农田土壤重金属污染和生态风险情况,采集某矿区周边174份农田土壤样品,分析了土壤中8种重金属(Cu、 Zn、 Pb、 Cr、 Ni、 Mn、 As和Hg)的含量,采用主成分分析(PCA)和正定矩阵因子分解模型(PMF)分析土壤重金属的来源,通过单因子污染指数法、地累积指数法、潜在生态风险指数法和人体健康风险评价模型评价土壤重金属生态环境风险.结果表明,研究区农田土壤Cu、 Zn、 Cr、 Ni、 Mn和Hg含量的均值均高于贵州省土壤背景值,100%样本Zn和38.86%样本Cu均超过农用地土壤污染风险筛选值.源解析显示农田土壤重金属的主要来源为矿业开采排放源,其次为农业活动和交通运输混合源、自然源和农业活动源.风险评价结果表明,土壤中Ni、 Cr、 Pb和As属于清洁水平,Hg和Cu属于轻度污染水平,Zn属于偏中度污染水平,Mn属于偏重污染水平.Cu、 Zn、 Pb、 Cr、 Ni、 Mn和As存在轻微潜在生态风险,Hg存在强潜在生态风险.研究区整体存在强潜在生态风险,8种重金属存在致癌风险和0～5岁儿童非致癌风险,主要贡献因子分别是Cr和Mn.     

北京北部水系沉积物中重金属的研究

主要研究了北京市北部水系沉积物中重金属(As、Hg、Cd、Cr、Cu、Mn、Ni、Pb、Ti和Zn)含量和来源.在潮白河及密云水库流域采集了17个沉积物样品,温榆河流域采集了5个样品,重金属含量As和Hg采用原子荧光光谱法测定,Cd、Cr、Cu、Mn、Ni、Pb、Ti和Zn含量用电感耦合等离子发射光谱法测定.研究结果表明,沉积物中重金属元素没有出现明显的富集状况,只有Hg、Cd、Cr和Zn在一些采样点有较高的富集.相关性分析表明Hg、Cd、Zn和Cu互相之间呈显著正相关(r0.06;p0.01),而Hg与Cr、Mn、Ni、Pb和Ti没有明显的相关性.通过主成分分析研究重金属的来源,发现前3个主成分贡献率分别为38%、23%和17%.因此,Hg、Cd、Zn和Cu作为第一主成分被认为与人类活动的工矿业开采有关,第二主成分As和Mn与人类活动的农业生产和生活污水排放有关,第三主成分Cr、Ni和Ti与岩石风化和土壤侵蚀有关.     

青藏高原表土重金属污染评价与来源解析

为了解青藏高原表层土壤重金属的污染特征、空间分布及污染来源,沿东北-西南方向对青藏高原表土(0～20 cm)样品进行了采集,对土壤中的Ba、Cd、Co、Cr、Cu、Fe、Mn、Mo、Ni、Pb、Sb、Sc和Zn等13种重金属总量进行了分析,并利用主成分分析-绝对主成分分数-多元线性回归(PCA-APCS-MLR)受体模型初步定量解析了重金属的潜在来源.结果表明Cd和Sb均显著超标,分别是20世纪70年代青藏高原土壤背景值的2. 13与1. 52倍.富集因子(EF)、地累积指数(I_(geo))和Nemero综合指数(PN)分析同样表明青藏高原表土主要以Cd和Sb污染为主,但污染程度普遍不高.在空间分布方面,青藏高原中部、东南部及东北部均呈不同程度污染,但中部及东南部污染相对较重. PCA-APCS-MLR分析表明,青藏高原土壤重金属主要有3个来源,分别为自然、交通和采矿等综合因素. Co、Cr、Cu、Fe、Mn、Ni和Sc主要受自然因素影响,Ba、Cd、Mo和Pb主要受交通因素影响,Zn主要受自然和交通因素共同影响,Sb主要受采矿、自然和交通等综合因素影响.青藏高原土壤重金属污染防治过程中应着重考虑受交通、采矿等综合因素影响下的Cd和Sb污染.     

Effects of two sludge application on fractionation and phytotoxicity of zinc and copper in the soil

The potential harm of heavy metals is a primary concern in application of sludge to the agricultural land. A pot experiment was conducted to evaluate the effect of two sludges on fractionation of Zn and Cu in soil and their phytotoxicity to pakchoi. The loamy soil was mixed with 0%, 20%, 40%, 60% and 80% (by weight) of digested sewage sludge (SS) and composted sludge (SC). The additions of both sludges caused a significant raise in all fractions, resulting in that exchangeable (EXCH) and organic bound (OM) became predominance of Zn and organic bound Cu occupied the largest portion. There was more available amount of Zn and Cu in SS treatments than SC treatments. During the pot experiment, the concentration of Zn in EXCH, carbonate (CAR) and OM and Cu in EXCH and OM fractions decreased in all treatments, so their bioavailability reduced. Germination rate and plant biomass decreased when the addition rate was high and the best yield appeared in 20% mixtures at the harvest of pakchoi. The two sludges increased tissue contents of Zn and Cu especially in the SS treatments. Zn in pakchoi was not only in relationship to ΔEXCH and ΔCAR forms but also in ΔOM forms in the sludge-soil mixtures. Tissue content of Cu in pakchoi grown on SC-soils could not be predicted by ΔEXCH. These correlation rates between Zn and Cu accumulation in pakchoi and variation of different fractions increased with time, which might indicate that sludges represented stronger impacts on the plant in long-term land application.     

Intraspecific differences in effects of co-contamination of cadmium and

A hydroponic experiment was carried out to study intraspecific differences in the effects of different concentrations of cadmium (Cd)(0-10 mg/L) and arsenate (As(V)) (0-8 mg/L) on the growth parameters and accumulation of Cd and As in six wheat varieties Jing-9428, Duokang-1, Jingdong-11, Jing-411, Jingdong-8 and Zhongmai-8. The endpoints of wheat seedlings, including seed germination,biomass, root length and shoot height, decreased with increasing the Cd and As concentrations. Significant differences in seed germination, biomass, root length, shoot height and the accumulation of Cd and As were observed between the treatments and among the varieties (p ＜ 0.05). The lethal dosage 50% were about 20, 80, 60, 60, 80 and 20 mg As/L for Jing-9428, Duokang-1, Jingdong-11,Jing-411, Jingdong-8 and Zhongmai-8, respectively, and the corresponding values for Cd were about 30, 80, 20, 40, 60 and 10 mg Cd/L, respectively. Among the six varieties, Duokang-1 was found to be the most resistant to Cd and As toxicity, and Zhongmai-8 was the most sensitive to Cd and As co-contamination. The resistance of the six varieties was found dependant on the seedling uptake of Cd and As. Duokang-1 was the most suitable for cultivation in Cd and As co-contaminated soils.     

EDTA-enhanced phytoremediation of lead contaminated soil by Bidens maximowicziana

Phytoremediation is a potential cleanup technology for the removal of heavy metals from contaminated soils.Bidens maximowicziana is a new Pb hyperaccumulator,which not only has remarkable tolerance to Pb but also extraordinary accumulation capacity for Pb.The maximum Pb concentration was 1509.3 mg/kg in roots and 2164.7 mg/kg in overground tissues.The Pb distribution order in the B. maximowicziana was:leaf>stem>root.The effect of amendments on phytoremediation was also studied.The mobility of soil Pb and the Pb concentrations in plants were both increased by EDTA application.Compared with CK(control check),EDTA application promoted translocation of Pb to overground parts of the plant.The Pb concentrations in overground parts of plants was increased from 24.23-680.56 mg/kg to 29.07-1905.57 mg/kg.This research demonstrated that B.maximowicziana appeared to be suitable for phytoremediation of Pb contaminated soil,especially,combination with EDTA.     

Distribution and ecological effect of mercury in Laogang landfill, Shanghai, China

Laogang landfill near Shanghai is the largest landfill in China, and receives about 10000 t of daily garbage per day, Samples of topsoil and plants were analyzed to evaluate mercury pollution from the landfill. For topsoil samples, there were significant correlations among total mercury （HgT）, combinative mercury （Hgc） and gaseous mercury （HgG）, and content of total organic carbon （TOC）, but, no significantly relationship was found between Hg content and filling time. Hg content changes in vertical profiles with time showed that the average Hgv of profiles 1992, 1996, and 2000 was similar, but their average HgG was quite different. HgT was significantly correlated with Hgc in profile 1992 and 2000, and Hgv was significantly correlated with Hg6 in profile 1996. HgG/Hgv ratio in profile samples decreased in the order of （HgG,/HgT）1992〉（HgG/HgT）1996〉〉（HgG/HgT）2000. A simple outline of Hg release in landfill could be drawn： with increasing of filling time, degradation undergoes different biodegradation, accordingly, gaseous mercury goes through small, more, and small proportion to total mercury. Distribution of Hg in plants was inhomogeneous, following the order of leaf〉root〉stem. The highest value of leaf may be associated with higher atmospheric Hg from landfill. Ligneous plants （e.g. Phyllostachys glanca, Prunus salicina and Ligustrum lucidum） are capable of enriching more Hg than herbaceous plants.     

Toxic effects of acetochlor, methamidophos and their combination on nifH gene in soil

Toxic effects of two agrochemicals on nifH gene in agricultural black soil were investigated using denaturing gradient gel electrophoresis （DGGE） and sequencing approaches in a microcosm experiment. Changes of soil nifH gene diversity and composition were examined following the application of acetochlor, methamidophos and their combination. Acetochlor reduced the nifH gene diversity （both in gene richness and diversity index values） and caused changes in the nifH gene composition. The effects of acetochlor on nifH gene were strengthened as the concentration of acetochlor increased. Cluster analysis of DGGE banding patterns showed that nifH gene composition which had been affected by low concentration of acetochlor （50 mg/kg） recovered firstly. Methamidophos reduced nifH gene richness that except at 4 weeks. The medium concentration of methamidophos （150 mg/kg） caused the most apparent changes in nifH gene diversity at the first week while the high concentration of methamidophos （250 mg/kg） produced prominent effects on nifH gene diversity in the following weeks. Cluster analysis showed that minimal changes of nifH gene composition were found at 1 week and maximal changes at 4 weeks. Toxic effects of acetochlor and methamidophos combination on nifH gene were also apparent. Different nifH genes （bands） responded differently to the impact of agrochemicals： four individual bands were eliminated by the application of the agrochemicals, five bands became predominant by the stimulation of the agrochemicals, and four bands showed strong resistance to the influence of the agrochemicals. Fifteen prominent bands were partially sequenced, yielding 15 different nifH sequences, which were used for phylogenetic reconstructions. All sequences were affiliated with the alpha- and beta-proteobacteria, showing higher similarity to eight different diazotrophic genera.     

Enzymatic oxidation of aqueous pentachlorophenol

The influence of the nonionic surfactant Tween 80 on pentachlorophenol （PCP） oxidation catalyzed by horseradish peroxidase was studied. The surfactant was tested at concentrations below and above its critical micelle concentration （CMC）. Enhancement of PCP removal was observed at sub-CMCs. The presence of Tween 80 in the reaction mixture reduced enzyme inactivation which occurred through a combination of free radical attack and sorption by precipitated products. A simple first-order model was able to simulate time profiles for enzyme inactivation in the presence or absence of Tween 80. At supra-CMCs, the surfactant caused noticeable reductions in PCP removal, presumably through micelle partitioning of PCP which precluded the hydrophobic PCP molecule from interacting with the enzyme.     

Decomposition of alachlor by ozonation and its mechanism

Decomposition and corresponding mechanism of alachlor, an endocrine disruptor in water by ozonation were investigated. Results showed that alachlor could not be completely mineralized by ozone alone. Many intermediates and final products were formed during the process, including aromatic compounds, aliphatic carboxylic acids, and inorganic ions. In evoluting these products, some of them with weak polarity were qualitatively identified by GC-MS. The information of inorganic ions suggested that the dechlorination was the first and the fastest step in the ozonation of alachlor.     

Arsenic uptake by arbuscular mycorrhizal maize （Zea mays L.） grown in an arsenic-contaminated soil with added phosphorus

The effects of arbuscular mycorrhizal (AM) fungus (Glomus mosseae) and phosphorus (P) addition (100 mg/kg soil) on arsenic (As) uptake by maize plants (Zea mays L.) from an As-contaminated soil were examined in a glasshouse experiment.Non-mycorrhizal and zero-P addition controls were included.Plant biomass and concentrations and uptake of As,P,and other nutrients,AM colonization,root lengths,and hyphal length densities were determined.The results indicated that addition of P significantly inhibited root colonization and development of extraradical mycelium.Root length and dry weight both increased markedly with mycorrhizal colonization under the zero-P treatments,but shoot and root biomass of AM plants was depressed by P application.AM fungal inoculation decreased shoot As concentrations when no P was added,and shoot and root As concentrations of AM plants increased 2.6 and 1.4 times with P addition,respectively.Shoot and root uptake of P,Mn,Cu,and Zn increased,but shoot Fe uptake decreased by 44.6%,with inoculation, when P was added.P addition reduced shoot P,Fe,Mn,Cu,and Zn uptake of AM plants,but increased root Fe and Mn uptake of the nonmycorrhizal ones.AM colonization therefore appeared to enhance plant tolerance to As in low P soil,and have some potential for the phytostabilization of As-contaminated soil,however,P application may introduce additional environmental risk by increasing soil As mobility.     

Degradation of metabolites accumulated of benzo[a]pyrene by coupling Penicillium Chrysogenum with KMnO4

Several main metabolites of benzo[a]pyrene （BaP） formed by Penicillium chrysogenum, Benzo[a]pyrene-1,6-quinone （BP 1,6- quinone）, trans-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene （BP 7,8-diol）, 3-hydroxybenzo[a]pyrene （3-OHBP）, were identified by high-performance liquid chromatography （HPLC）. The three metabolites were liable to be accumulated and were hardly further metabolized because of their toxicity to microorganisms. However, their further degradation was essential for the complete degradation of BaP. To enhance their degradation, two methods, degradation by coupling Penicillium chrysogenum with KMnO4 and degradation only by Penicillium chrysogenum, were compared; Meanwhile, the parameters of degradation in the superior method were optimized. The results showed that （1） the method of coupling Penicillium chrysogenum with KMnO4 was better and was the first method to be used in the degradation of BaP and its metabolites; （2） the metabolite, BP 1,6-quinone was the most liable to be accumulated in pure cultures; （3） the effect of degradation was the best when the concentration of KMnO4 in the cultures was 0.01% （w/v）, concentration of the three compounds was 5 mg/L and pH was 6.2. Based on the experimental results, a novel concept with regard to the bioremediation of BaP-contaminated environment was discussed, considering the influence on environmental toxicity of the accumulated metabolites.     

Impact of atrazine and nitrogen fertilizers on the sorption of chlorotoluron in soil and model sorbents

Sorption of chlorotoluron in ammonium sulfate, urea and atrazine multi-solutes system was investigated by batch experiments. The results showed application of nitrogen fertilizers to the soil could affect the behavior of chlorotoluron. At the same concentration of N, sorption of chlorotoluron decreased as the concentration of atrazine increased on the day 0 and 6 in soil, respectively. The sorption of chlorotoluron increased from 0 to 6 d when soils were preincubated with deionized water, ammonium sulfate and urea solution for 6 d. That indicated incubation time was one of the most important factors for the sorption of chlorotoluron in nitrogen fertilizers treatments. The individual sorption isotherms of chlorotoluron in rubbery polymer and silica were strictly linear in single solute system, but there were competition sorption between pesticides or between pesticides and nitrogen fertilizers. That indicated the sorption taken place by concurrent solid-phase dissolution mechanism and sorption on the interface of water-organic matter or water-mineral matter.