Changes in chemical forms of lead in temperate and semiarid soils in sterile and unsterile conditions

Sequential extraction has been used as a suitable method for fractionation of chemical forms of trace elements and study of their plant availability. Surface soils were sampled from Guilan and Hamadan provinces in north and northwest of Iran with temperate and semiarid climates. The chemical forms of Pb in the Pb(NO₃)₂-treated (400 μg Pb g⁻¹) soils have been studied in solid state incubation (FC) at 27°C in sterile and unsterile conditions. After 20 min and 3600 h a sequential extraction scheme was also used to fractionate Pb of incubated samples into soluble-exchangeable (Sol-Exch), carbonates associated (ACar), organic matter associated (AOM), Mn oxide associated (AMnOx), Fe oxide associated (AFeOx), and residual (Res) forms. Temperate soil samples had higher clay content, cation exchange capacity (CEC), dichromate oxidable organic carbon (OC), total Kjeldahl-nitrogen (TN), biological activity, amorphous and crystalline Fe and Al, but semiarid soil samples had higher sand content, pH, equivalent calcium carbonate (ECC), available P and K. Soil lead fractionation revealed that in both groups of soils Pb largely changed to exchangeable, carbonates associated and organic associated forms after 20 min. The chemical forms of Pb differed widely among soils after 3600-h incubation. The conversion rate of Pb from more available forms to less available forms was higher in temperate soils with higher Fe–Mn oxides and OM contents compared to semiarid soils. In temperate soils after 3600-h incubation, greater content of Pb was observed in Res (68%), AOM (14%), ACar (7%), and AMnOx (5%) fractions. However, in semiarid soils greater content of Pb was observed in Res (61%), ACar (16%), Sol-Exch (8%), and AOM (8%) fractions. The sum of AMnOx and AFeOx chemical forms for Pb in semiarid soils compared to temperate soils was lower. It was only 7% against 9% in temperate soils. Soil microorganisms in unsterile soils had significant effect on AOM, AFeOx and Res fractions of Pb. They not only increased AOM and AFeOx fractions of Pb in soils but also decreased Res fraction of Pb significantly.     

Experimental warming shows that decomposition temperature sensitivity increases with soil organic matter recalcitrance

Soil C decomposition is sensitive to changes in temperature, and even small increases in temperature may prompt large releases of C from soils. But much of what we know about soil C responses to global change is based on short-term incubation data and model output that implicitly assumes soil C pools are composed of organic matter fractions with uniform temperature sensitivities. In contrast, kinetic theory based on chemical reactions suggests that older, more-resistant C fractions may be more temperature sensitive. Recent research on the subject is inconclusive, indicating that the temperature sensitivity of labile soil organic matter (OM) decomposition could either be greater than, less than, or equivalent to that of resistant soil OM. We incubated soils at constant temperature to deplete them of labile soil OM and then successively assessed the CO2-C efflux in response to warming. We found that the decomposition response to experimental warming early during soil incubation (when more labile C remained) was less than that later when labile C was depleted. These results suggest that the temperature sensitivity of resistant soil OM pools is greater than that for labile soil OM and that global change-driven soil C losses may be greater than previously estimated.     

外源铅铜镉在长三角和珠三角农业土壤中的转化

选择了我国经济发达地区的长江三角洲和珠江三角洲10个代表性农业土壤，采用室内培养和化学分级方法研究了加入外源铅、铜、镉在土壤中的动态变化及转化趋势，探讨了碳酸钙、粉煤灰、猪粪和钢渣等土壤改良剂对土壤重金属形态的影响。结果表明，随着土壤重金属负荷的提高，土壤中交换态重金属的比例增大，残余态比例下降，有效性提高，对环境威胁增大。当重金属加入最较低时，重金属优先向氧化物结合态、有机质结合态转化；而当加入最较高时，向交换态和碳酸盐结合态转化的比例明皿增加。pH和土壤组分对重金属在土壤中的转化有显著的影响，土壤pH下降可使交换态Cd、Cu、Pb的比例递增。加入碳酸钙、粉煤灰、猪粪和钢渣等改良剂可显著地降低土壤中交换态重金属比例，增加其它形态的重金属比例。     

The importance of different forms of Pb on diminishing biological activities in a calcareous soil

In this experimental study, we evaluated the effect of different lead (Pb) fractions on biological properties in soil spiked with 0, 600, 1200 and 1800 mg kg^?1 Pb, during a 90-day incubation period at 25?28°C. Different Pb fractions were measured by sequential extraction at days 1 and 90 after soil treatment. Diethylenetriaminepentaacetic acid (DTPA)-extractable Pb and soil biological properties at days 1, 5, 15, 45 and 90 were measured. The concentration of Pb in soluble and exchangeable fractions was very high at day 1, but it showed remarkable transfer into carbonate and residual fractions by day 90. Substrate-induced respiration, basal respiration, acid and alkaline phosphatases, microbial populations (bacterial, fungal and actinomycetes) and biomass carbon decreased significantly with soil contamination compared with the control. With Pb ageing, these biological properties increased. Metabolic quotient (qCO₂) increased significantly compared with the control with increasing Pb concentration. The toxicity of various forms of Pb for the biological status of the soil was in the following order: KNO₃ extractable>NaOH extractable>EDTA extractable>HNO ₃ extractable>total content Pb. Thus, the bioavailable fractions are better indicators of Pb pollution in soils.     

Seasonal Variations and Chemical Forms of Heavy Metals in Soils and Dusts from the Satellite Cities of Seoul, Korea

This research investigated heavy metal pollution of soils and dusts in two representative satellite cities of Seoul, Korea and studied the seasonal variations in metal concentrations through the rainy season and the chemical forms of metals using a sequential extraction analysis. The metal dispersion pattern was illustrated to match with urban structure. Soil and dust samples were collected from the cities of Uijeongbu and Koyang, which are the northern and northwestern satellite cities of Seoul (the capital), before and after rainy season. Concentrations of Cu, Pb and Zn were higher than those of the world averages for soils, and their levels decreased after rain, particularly in highly contaminated samples. Relatively high pH values were found in roadside soils, but no seasonal variation was found after the rainy season. The three metals (Cu, Pb and Zn) in soils and dusts were associated with various chemical fractions of soils and dusts as distinguished by the sequential extraction scheme, and a strong similarity of metal association between soils and dusts was found, which indicates that airborne dust may be a principle source of soil contamination. Copper is uniformly distributed, and Pb is largely associated with the reducible phase. There is an appreciable proportion of total Zn in the exchangeable/water-acid soluble fraction. After the rainy season, the most soluble fractions in soils and dusts were leached away. In terms of mobility and bioavailability of metals in soils and dusts, the order Zn >> Cu > Pb is suggested. Geographical variations of total metals corresponded well with urbanised areas of cities, especially the industrial complex and major motorways.     

Lead availability in soils from Portugal’s Centre Region with special reference to bioaccessibility

Previous environmental biomonitoring studies indicated higher environmental lead (Pb) pollution levels at the districts of Aveiro and Leiria (Portugal). In evaluating the risk for human health, which is associated with contaminated soils after oral uptake, total soil concentrations have generally been held against criteria established from toxicological studies based upon the assumption that the uptake of the contaminant is similar in the toxicological studies and from the soils assessed. This assumption is not always valid, as most toxicological studies are carried out with soluble forms of the contaminants, whereas many soil contaminants are or become embedded in the soil matrix and thus exhibit limited availability. This study intends to estimate the soluble fraction of Pb in the soils from central Portugal, and to assess the bioaccessibility of Pb and, hence, infer exposure and risk for human health. Yet, as the physical–chemical properties of the soil exert some control over the solubility of Pb in the surface environment, the relation between such soil properties and the estimated soluble and/or bioaccessible fractions of Pb is also investigated. Other objective, with a more practical nature, was to give some contribution to find a suitable in vitro mimetic of the gastrointestinal tract environment. The results indicate relatively low total metal concentrations in the soils, even if differences between regions were observed. The Aveiro district has the higher total Pb concentration and the metal is in more soluble forms, that is, geoavailable. Soils with higher concentrations of soluble Pb show higher estimates of bioaccessible Pb. Soil pH seems to influence human bioaccessibility of Pb.     

The effects of soil properties and temperature on the adsorption isotherms of lead on some temperate and semiarid surface soils of Iran

Sorption of metal ions by soil and clay minerals is a complex process involving different mechanisms, and controlled by different variables that can interact. The aim of this work was to study the retention mechanisms of Pb ions on different soil samples. Surface soils were sampled from Guilan and Hamadan provinces in north and northwest of Iran with temperate and semiarid climates. The adsorption isotherms of Pb on the soils have been studied at 15, 27 and 37°C. The adsorption data for different soils were fitted into Langmuir and Freundlich models. Temperate soil samples had higher clay content, cation exchange capacity, dichromate (oxidable) organic carbon, total Kjeldahl-nitrogen, biological activity, amorphous and crystalline Fe and Al, but semiarid soil samples had higher sand content, pH, equivalent calcium carbonate, available P and K. Lead adsorption data obtained from semiarid soils against those obtained from temperate soils were better fitted in both Langmuir and Freundlich models. Langmuir constants Q ₀ for Pb adsorption in semiarid soils were considerably lower than those for Pb adsorption in temperate soils. However, the binding energy (K _L) of Pb and Freundlich constant n were higher for data of semiarid soils. The effect of temperature on the Pb adsorption was positive especially in temperate soils; however, soil properties had higher effects on Pb adsorption.     

污染土壤中有机质结合态重金属的研究

用物理与化学相结合的方法研究了2个污染土壤剖面中有机质结合重金属（Cd、Cu、Pb和Zn）的分布，把有机质相结合态重金属分为颗粒状有机质（POM）结合的重金属和与细土腐殖质结合的重金属。结果表明，土壤POM对重金属有明品的富集作用，其中〉2mmPOM重金属Cd、Cu、Pb和Zn的富集系数分别在1．4～3．2、2．5～2．6、2．8—3．9和3．0～3．9之间；而0．05～2mmPOM重金属Cd、Cu、Pb和Zn的富集系数分别在2．7～7．8、3．2～6．4、3．2～9．3和3．2～5．6之间，0．05～2mmPOM组分中重金属的平均富集高于〉2mmPOM组分。POM中重金属的富集程度与土壤重金属的积累呈正相关。有机质结合态重金属占土壤重金属总最的比例随土壤有机质积累而增高，表土层约40％以上的重金属以有机质结合态存在。     

中国典型土壤中铅的生物可给性的影响因素分析与健康风险评估

土壤铅污染及其危害备受关注。作为评估其对人体健康风险的科学指标之一,土壤铅的生物可给性的影响因素仍不甚明确。采集中国5种典型土壤(红壤、褐土、黑土、棕壤和黄壤),根据国标中一类建设用地的管制值制备成800 mg·kg^-1的铅污染土壤样品,利用先进的基于生理学的体外试验方法(改进的PBET模型)研究经口部摄入的土壤铅的生物可给性及其对人体的健康风险,进而从土壤理化性质和铅的赋存形态角度,全面综合地探讨土壤铅的生物可给性的影响因素,并分析不同土壤间差异的原因。结果表明,土壤铅在胃阶段的生物可给性为72.7%—82.6%,各类型土壤间差异极显著,其中红壤较高而黑土较低;进入小肠阶段后,土壤铅的生物可给性极显著降低至22.8%—27.7%,各类型土壤间无显著差异。土壤铅对人体的健康风险评估结果与之相同。对儿童而言,土壤铅在胃阶段的非致癌风险达到可接受限值的2.1倍;且整体而言,土壤铅对儿童的非致癌风险平均达到成人的7.6倍,必须加以重视。此外,土壤铅的生物可给性与土壤pH、有机质质量分数和迁移系数均存在高度显著相关性,其中,土壤pH是影响土壤铅在胃肠道的生物可给性的主导因子。通过体外试验可直接、简便而准确地获取土壤铅的生物可给性信息,建议在今后实地的污染土壤健康风险评估工作中引入该方法。该研究成果将为铅污染土壤健康风险评估工作提供准确的科学依据与有价值的参考。     

施用石灰对Pb、Cd、Zn在土壤中的形态及大白菜中累积的影响

重金属的不同形态对于作物吸收重金属及受害具有十分密切的关系,通过施用石灰改变重金属的形态、毒性以及对作物的影响具有重要的意义。以大白菜(Brassica pekinensis)为研究对象,通过盆栽试验,探讨了在铅、镉和锌污染土壤上,施用石灰对土壤中不同形态镉、铅和锌含量及在大白菜中累积的影响。结果表明,施用石灰后,土壤中碳酸盐结合态Pb、Cd和Zn含量明显减少,铁、锰氧化物结合态和有机物结合态Pb、Cd和Zn含量明显增加;对大白菜吸收Pb、Cd和Zn均起到较好的抑制作用,石灰用量为5g·kg-1土时,对大白菜吸收Pb、Cd和Zn的抑制效果最好。     

Heavy metals in soils and crops in Southeast Asia

In a reconnaissance soil geochemical and plant survey undertaken to study the heavy metal uptake by major food crops in Malaysia, 241 soils were analysed for cation exchange capacity (CEC), organic carbon (C), pH, electrical conductivity (EC) and available phosphorus (P) using appropriate procedures. These soils were also analysed for arsenic (As), cadmium (Cd), cobalt (Co), chromium (Cr), copper (Cu), mercury (Hg), nickel (Ni), lead (Pb) and zinc (Zn) using aqua regia digestion, together with 180 plant samples using nitric acid digestion. Regression analysis between the edible plant part and aqua regia soluble soil As, Cd, Cr, Cu, Hg, Ni, Pb and Zn concentrations sampled throughout Peninsular Malaysia, indicated a positive relationship for Pb in all the plants sampled in the survey (R ² = 0.195, p < 0.001), for Ni in corn (R ² = 0.649, p < 0.005), for Cu in chilli (R ² = 0.344, p < 0.010) and for Zn in chilli (R ² = 0.501, p < 0.001). Principal component analysis of the soil data suggested that concentrations of Co, Ni, Pb and Zn were strongly correlated with concentrations of Al and Fe, which is suggestive of evidence of background variations due to changes in soil mineralogy. Thus the evidence for widespread contamination of soils by these elements through agricultural activities is not strong. Chromium was correlated with soil pH and EC, Na, S, and Ca while Hg was not correlated with any of these components, suggesting diffuse pollution by aerial deposition. However As, Cd, Cu were strongly associated with organic matter and available and aqua regia soluble soil P, which we attribute to inputs in agricultural fertilisers and soil organic amendments (e.g. manures, composts).     

The influence of physicochemical parameters on bioaccessibility-adjusted hazard quotients for copper,lead and zinc in different grain size fractions of urban street dusts and soils

When the hazard quotient for ingestion (HQI) of a trace element in soil and dust particles is adjusted for the element’s bioaccessibility, the HQI is typically reduced as compared to its calculation using pseudo-total element concentration. However, those studies have mostly used bulk particles (<2 mm or <250 µm), and the reduction in HQI when expressed as bioaccessible metal may not be similar among particle size fractions, the possibility probed by the present study of street dusts and soils collected in Tehran. The highest Cu, Pb and Zn near-total concentrations occurred in the finest particles of dusts and soils. Bioaccessible concentrations of Cu, Pb and Zn in the particles (mg kg^?1) were obtained using simple bioaccessibility extraction test (SBET). The bioaccessibility (%) did not vary much among near-total concentrations. In the bulk (<250 µm) sample, the bioaccessible concentration of Cu and Pb increased as the pH of sample increased, while Zn bioaccessibility (%) in the bulk particles was influenced by organic matter and cation exchange capacity. X-ray diffraction identified sulfide and sulfate minerals in all of the size-fractionated particles, which are insoluble to slightly soluble in acidic conditions and included most of the Cu and Pb in the samples. The only Zn-bearing mineral identified was hemimorphite, which would be highly soluble in the SBET conditions. The calculated HQI suggested potential non-carcinogenic health risk to children and adults from ingestions of soils and dusts regardless of particle size consideration, in the order of Zn > Pb ≥ Cu. The HQI calculated from near-total metal was not much different for particle size classes relative to bulk particles; however, the bioaccessibility percent-adjusted HQI for Pb was higher for the smaller particles than the bulk. This work is novel in its approach to compare HQI for a bulk sample of particles with its composite particle size fractions.     

Preliminary assessment of surface soil lead concentrations in Melbourne,Australia

Urban soils in many cities have been found to be contaminated with lead from past usage of leaded petrol, deteriorating lead-based exterior paints and industrial sources. Currently, the spatial distribution of soil lead concentrations in the Melbourne metropolitan area is unknown. The objective of this study was to perform a preliminary assessment of the spatial distributions of the surface soil lead (Pb) concentrations in the Melbourne metropolitan area, Australia. Fifty-eight surface soil samples were collected at a depth of 0–2 cm along three linear transects oriented across the Melbourne metropolitan area. Surface soil samples were also collected at a higher density in five Melbourne suburbs. Soil cores (0–50 cm) were collected in four locations, soil transects were collected at intervals with distance away from the roadway (0–50 m) in two inner city parks, and one control soil sample was collected in a rural setting. The median soil Pb concentration of the soil transect samples was 173 mg/kg (range 32–710 mg/kg), and the median soil Pb concentration of the five suburbs was 69 mg/kg (range 9–1750 mg/kg). The suburb of Footscray had the highest soil Pb concentration with a median soil Pb concentration of 192 mg/kg (range 40–1750 mg/kg). Soil Pb concentrations were generally higher nearest the centre of the Melbourne metropolitan area and in the west of Melbourne and lower in the outer suburbs to the east and north of the city centre. Soil Pb concentrations decreased with distance from roadways in the two transects taken from urban parks, and soil lead decreased with depth in the four soil cores. The soil Pb concentrations in the Melbourne metropolitan area appear to be lower than soil lead concentrations observed in inner city areas of Sydney New South Wales (NSW) and Newcastle NSW. The spatial extent of the soil Pb hazard remains undefined in portions of the Melbourne metropolitan area.     

岩溶山区不同土地利用方式对土壤活性有机碳动态的影响

对贵州茂兰自然保护区内三种典型土地利用方式(林地、草地和耕地)下土壤活性有机碳组分(土壤溶解有机碳和土壤微生物量碳)的月变化及其对环境因子的响应进行了研究,结果表明在不同的土地利用方式下上覆植被类型不同,其凋落物数量、质量及分解行为不同,有机质的输入量及质量也不相同,从而形成不同的土壤溶解有机碳含量差异,土壤有机碳的大小也存在较大差别。研究结果显示:从全年平均值来看,林地土壤溶解有机碳分别比草地和耕地高25%、48%;从3月到8月,三者均随气温的上升呈增加的趋势,林地和耕地在8月均达到最大值,而草地则在10月达到最大值;林地和草地土壤微生物量碳分别高于耕地81%和45%,林地和草地在10月达到最大值。不同的土地利用方式导致土壤活性有机碳的差异较大,这说明岩溶生态系统中土地利用方式对土壤碳库的大小有较大影响。不同土地利用方式下土壤活性有机碳对环境因子的响应也各不相同,这表明土壤活性碳受众多因素的制约而呈现出一种动态平衡关系,进一步的机理仍需要进行深入研究。     

Effect of acid rain on the fractionation of heavy metals and major elements in contaminated soils

Acid rain is a serious environmental problem worldwide. In the present study, we investigated the effect of acid rain (1:1 equivalent basis H₂SO₄:HNO₃) at pH values of 2.0, 4.0 and 7.0 on the fractionation of heavy metals (Cd, Cu, Fe, Mn, Ni, Pb and Zn) and major elements (K, Na, Ca, and Mg) in contaminated calcareous soils over a 2084 h period. Heavy metals and major elements in soil samples were fractionated before and after 2084 h kinetic release using a sequential extraction procedure. Before kinetic studies the predominant fractions of K, Na, Ca, Mg, Cd and Ni were mainly associated with carbonate fraction (CARB), whereas Fe, Mn and Zn were associated with the Fe–Mn oxide fraction (Fe–Mn oxide). The highest percentage of Pb and Cu were found in the exchangeable (EXC) and organic matter (OM) fractions, respectively. After kinetic study using different simulated acid rain solutions, the major fractions of heavy metals (expect of Cu) and Na was the same as before release. Upon the application of different acid rain solutions, K and Mg were found dominantly in Fe–Mn oxide fraction, whereas Ca was in the EXC fraction. The results provide valuable information regarding metal mobility and indicated that speciation of metals (Cu and Zn) and major elements in contaminated calcareous soils can be affected by acid rain.     

Distribution and mobility of metals in agricultural soils near a copper smelter in South China

The distribution and mobility of heavy metals in the paddy soils surrounding a copper smelting plant in south China was investigated. We assessed the degree of metal contamination using an index of geoaccumulation. The metals were divided into two groups: (1) Cu, Zn, Pb and Cd, whose concentrations were heavily affected by anthropogenic inputs, and (2) Ni, Co and Cr, which were mainly of geochemical origin. Concentrations of Cu, Cd, Zn, and Pb in the polluted soils were higher than the Chinese soil quality criteria. The chemical partitioning patterns of Pb, Zn and Cu indicated that Pb was largely associated with the residual and NH₂OH HCl extractable fractions. In contrast, Cd was predominantly associated with the MgCl₂ extractable fraction. A large proportion of Cu was bound to the acidic H₂O₂ extractable fractions, while Zn was predominantly found in the residual phase. The fraction of mobile species, which potentially is the most harmful to the environment, was found to be elevated compared to unpolluted soils in which heavy metals are more strongly bound to the matrix. The mobility of the metals was studied by water extraction using a modification of Tessier’s procedure, and the order of mobility was Zn > Cd > Cu  > Pb.     

Natural and synthesised iron-rich amendments for As and Pb immobilisation in agricultural soil

The immobilisation of heavy metals in contaminated soils is a promising alternative to conventional remediation techniques. Very few studies have focused on the use of iron-rich nanomaterials and natural materials for the adsorption of toxic metals in soils. Synthesised iron-rich nanomaterials (Fe and Zr–Fe oxides) and natural iron-rich materials (natural red earth; NRE) were used to immobilise As and Pb in contaminated agricultural soil. Total concentrations of As and Pb in the initial soil (as control) were 170.76 and 1945.11 mg kg^?1, respectively. Amendments were applied into the soil at 1, 2.5 and 5% (w/w) in triplicate and incubated for 150 days. Except for the NRE-amended soil, soil pH decreased from 5.6 to 4.9 with increasing application rates of Fe and Zr–Fe oxides. With addition of Fe and Zr–Fe oxides at 5%, the ammonium acetate (NHO₄Ac)-extractable Pb was greatly decreased by 83 and 65% compared with NRE addition (43%). All subjected amendments also led to a decrease in NHO₄Ac-extractable As in the soils, indicating the high capacity of As immobilisation. Soil amended with NRE showed a lower ratio of cy19:0 to 18:1ω7c, indicating decreased microbial stress. The toxicity characteristic leaching procedure produced results similar to the NHO₄Ac extraction for As and Pb. The NRE addition is recommended for immobilising heavy metals and maintaining biological soil properties.     

不同类型土壤中外源镍对赤子爱胜蚓的急性毒性

按照国际标准化组织(ISO)颁布的蚯蚓毒性试验方法,研究了镍离子在我国13种典型土壤中对赤子爱胜蚓(Eisenia fetida)的急性毒性,发现镍离子在不同类型土壤中对蚯蚓的半数致死浓度(LC50)变化范围为243.8-1970.6 mg·kg-1,镍离子在不同土壤中的毒性大小顺序为:湖南红壤＞重庆紫壤＞江西红壤＞河...     

红壤有机无机复合状况及氮素形态分布与肥力的关系

不同肥力红壤有机无机复合状况及氮素形态分布的研究结果表明，土壤肥力水平提高，有机无机复合量增大．复合量与土壤有机质、全氮、碱解氮、速效磷和ＣＥＣ呈显著或极显著正相关，与速效钾、缓效钾的相关性不显著；复合度与上述肥力性状的相关性均不显著．因此，可以用复合量来评价肥力状况．红壤酸解性氮占全氮７７％－８６％；在酸解性氮中，各组分氮所占比例为氨基酸态氮＞酸解氨态氮＞酸解未鉴别态氮＞氨基糖态氮．氨基酸态氮占酸解性氮的比率为高肥力红壤大于低肥力红壤，且与土壤有机质、全氮、碱解氮、速效磷里显著正相关，也可作为衡量土壤肥力状况的指标之一．     

Chemical fractionation of metals in core sediments of Orogodo River,southern Nigeria

Sequential chemical extraction of metals (Cu, Ni, Mn, Fe, Pb, Cr, and Zn) from core sediments of the Orogodo River was carried out with a view of providing information on the phase distribution of these metals with respect to depths and seasons. The results indicate that copper was speciated into organic matter/sulfide, Fe–Mn oxides, and residual forms at 0–5?cm depth while at deeper sections copper was predominantly in the residual form. Nickel was speciated mainly into Fe–Mn oxides and residual forms. The average of lead in various particulate phases of the sediment are 0–100% for residual; 0–8% for carbonate; 0–16.2% for exchangeable; 0–10% for organic matter/sulfide form and 22–56% for Fe–Mn oxides bound metals. Manganese was speciated into exchangeable (10–36%) and Fe–Mn oxides bound (10–48%) at the surface layers of 0–20?cm depths and predominantly in the residual form in deeper sections implying partitioning into trioctahydral clay and/or well-defined crystalline oxides. Iron was predominantly in the Fe–Mn oxides and residual fractions, less than 8% in the organic fraction, and 24.4–37.3% in the exchangeable and carbonates fractions at the surface. The percentage contributions of iron in the exchangeable and carbonate fractions decreased to 3.2% at 55–60?cm depth. The amount of chromium in the exchangeable fraction ranged from 0% to 7% for exchangeable; 0–26.5% for organic matter/sulfide bound; 3.8–17.9% for Fe–Mn oxides; and 46.8–100% for residual fraction. The mobility factors of the metals indicated that these metals were relatively mobile at top sections as compared with deeper sections. The overall picture of metal mobility and availability indicates potential contamination risk by Fe, Zn, Mn, and Pb in the Orogodo River sediment system.