Radiation hazard assessment in Egyptian painting oxides. A comparative study

Building materials are potential sources of radiation, which represents a risk factor for human disease including cancer. In this work, the natural radioactivity due to the presence of ²³⁸U, ²²⁶Ra, ²³²Th and ⁴⁰K in different painting oxides has been measured using gamma spectrometry with a Hyper Pure germanium detector. The concentrations of the heavy metals (Cd, Co, Mn, Pb, Ni, Sr, Rb, Cr, Cu and Zn) were determined by atomic absorption spectrometry in order to investigate their possible correlation with radioactive elements. The activity concentrations of ²³⁸U, ²²⁶Ra, ²³²Th and ⁴⁰K ranged from 15 ± 0.75 to 126 ± 14, 2.35 ± 0.09 to 72.96 ± 1.96, 1.76 ± 0.31 to 12.88 ± 0.7 and 2.26 ± 0.09 to 200 ± 3.34 Bq kg⁻¹, respectively. The calculated radium-equivalents were lower than values recommended for construction materials (370 Bq kg⁻¹). The absorbed dose rates due to the natural radioactivity of the investigated samples ranged from 8.11 ± 0.24 to 68.46 ± 4.20 nGy/h. Also, the results revealed that some heavy metals (Cd, Co, Mn and Rb) were correlated with ²³⁸U, ²²⁶Ra, ²³²Th or ⁴⁰K.     

华东某铀矿区周边河流表层沉积物的天然放射性评价

利用高纯锗γ能谱分析仪测量中国华东某铀矿区附近河流沉积物的放射性核素比活度,计算γ辐射吸收剂量率(D)、有效镭浓度(Ra_(eq))、外照射指数(H_(ex))、内照射指数(H_(in))、年有效剂量当量(AEDE(室内和室外))和年性腺剂量当量(AGDE)等放射性参数,并开展沉积物的放射性危害评估,最后通过Pearson线性系数确定放射性核素比活度之间的相关性。结果表明,河流沉积物中放射性核素~(238)U、~(226)Ra、~(232)Th和40K的平均比活度分别为51.55、37.32、57.63和756.86 Bq·kg~(-1),除~(226)Ra外,其他放射性核素的比活度均高于中国平均值;距离污染区较远或存在河流稀释作用的区域,沉积物的天然放射性核素处于正常水平,作为建筑材料使用时比活度不存在超标;放射性核素~(238)U、~(226)Ra和~(232)Th之间存在显著相关性。     

Natural radioactivity and trace metals in crude oils: implication for health

Crude oil samples were collected from six different fields in the central Niger Delta in order to determine their natural radioactivity and trace element contents, with the aim of assessing the radiological health implications and environmental health hazard of the metals, and also to provide natural radioactivity baseline data that could be used for more comprehensive future study in this respect. The activity concentrations of the radionuclides were measured using a well, accurately calibrated and shielded vertical cryostat, Canberra coaxial high-purity germanium (HPGe) detector system, and the derived doses were evaluated. The metal concentrations were determined by the graphite furnace atomic absorption spectroscopic (GFAAS) method. The radionuclides identified with reliable regularity belong to the decay series of naturally occurring radionuclides headed by ²³⁸U and ²³²Th along with the non-decay series radionuclide, ⁴⁰K. The averaged activity concentrations obtained were 10.52 ± 0.03 Bq kg⁻¹, 0.80 ± 0.37 Bq kg⁻¹ and 0.17 ± 0.09 Bq kg⁻¹ for ⁴⁰K, ²³⁸U and ²³²Th, respectively. The equivalent doses were very low, ranging from 0.0028 to 0.012 mSv year⁻¹ with a mean value of 0.0070 mSv year⁻¹. The results obtained were low, and hence, the radioactivity content from the crude oils in the Niger delta oil province of Nigeria do not constitute any health hazard to occupationally exposed workers, the public and the end user. The concentrations of the elements (As, Cd, Co, Fe, Mn, Ni, Se and V) determined ranged from 0.73 to 202.90 ppb with an average of 74.35 ppb for the oil samples analysed. The pattern of occurrence of each element agreed with the earlier studies from other parts of the Niger Delta. It was obvious from this study and previous ones that the Niger Delta oils have low metal contents. However, despite the low concentrations, they could still pose an intrinsic health hazard considering their cumulative effects in the environment. Also, various studies on the impact of oil spillage and activities of oil exploration and production on organisms in the immediate environment suggest this.     

Radionuclide concentrations in raw and purified phosphoric acids from Brazil and their processing wastes: implications for radiation exposures

Radionuclides from the U and Th natural series are present in alkaline rocks, which are used as feedstock in Brazil for the production of raw phosphoric acid, which can be considered as a NORM (naturally occurring radioactive material). As a result of the purification of raw phosphoric acid to food-grade phosphoric acid, two by-products are generated, i.e., solid and liquid wastes. Taking this into account, the main aim of this study was to evaluate the fluxes of natural radionuclide in the production of food-grade phosphoric acids in Brazil, to determine the radiological impact caused by ingestion of food-grade phosphoric acid, and to evaluate the solid waste environmental hazards caused by its application in crop soils. Radiological characterization of raw phosphoric acid, food-grade phosphoric acid, solid waste, and liquid waste was performed by alpha and gamma spectrometry. The ²³⁸U, ²³⁴U, ²²⁶Ra, and ²³²Th activity concentrations varied depending on the source of raw phosphoric acid. Decreasing radionuclides activity concentrations in raw phosphoric acids used by the producer of the purified phosphoric acid were observed as follows: Tapira (raw phosphoric acid D) > Catal?o (raw phosphoric acids B and C) > Cajati (raw phosphoric acid A). The industrial purification process produces a reduction in radionuclide activity concentrations in food-grade phosphoric acid in relation to raw phosphoric acid produced in plant D and single raw phosphoric acid used in recent years. The most common use of food-grade phosphoric acid is in cola soft drinks, with an average consumption in Brazil of 72 l per person per year. Each liter of cola soft drink contains 0.5 ml of food-grade phosphoric acid, which gives an annual average intake of 36 ml of food-grade phosphoric acid per person. Under these conditions, radionuclide intake through consumption of food-grade phosphoric acid per year per person via cola soft drinks is not hazardous to human health in Brazil. Considering these annual additions of ²³⁸U, ²²⁶Ra, ²³²Th and ⁴⁰K, and since these radionuclide should be homogeneously distributed in the upper 10 cm of soils with an assumed apparent density of 1.5 g/cm³, a maximum increase of 0.19 ± 0.03 Bq kg⁻¹ of soil is expected for ²³⁸U and ²³⁴U. Thus, the addition of solid waste as phosphate fertilizers to Brazilian agricultural soils does not represent a hazard to the ecosystem or to human health.     

滨海滩涂不同围垦年代垦区农作物重金属累积特征及其与氮、磷的关系

为探明滨海滩涂围垦区农作物重金属累积特征及其与围垦年代、作物氮磷含量及化学计量比的关系,采集盐城地区不同围垦年代(围垦20、30、40、60年)农田4种主要作物(大麦、小麦、油菜、蚕豆)样品63个,测定了其根、茎叶和籽粒中Cd、Cu、Zn、Pb、Hg、As及全氮(N)、全磷(P)和粗蛋白(CP)含量,分析了重金属累积特征及与围垦年代、N、P、CP及N/P比的关系,并采用单因子污染指数法和内梅罗综合污染指数法对重金属污染程度和安全水平进行了评价。结果表明,1)围垦农田作物整株各指标含量分别为Cd (0.52±0.94)、Cu (12.98±16.00)、Zn (34.93±27.91)、Pb (3.50±5.88)、Hg (0.0063±0.0063)、As (1.94±3.72) mg·kg~(-1)及N(13.69±8.27)、P (5.98±2.24)、CP (79.55±49.54) g·kg~(-1);籽粒中则分别为(0.0059±0.020)、(1.83±1.48)、(11.13±4.45)、(0.09±0.30)、(0.0023±0.0036)、(0.0021±0.0048) mg·kg~(-1)及(19.21±7.68)、(6.04±1.64)、(111.78±47.81) g·kg~(-1); 2)作物重金属均表现为根茎叶籽粒,N和CP与之相反,表现为根茎叶籽粒,而P则表现为根籽粒茎叶; 3)不同围垦年代之间作物重金属、N、P、CP含量、N/P比及综合污染指数(Pz)均没有显著差异(P0.05); 4)各作物籽粒6种重金属单因子污染指数均值均小于1,除个别样品Pb超标(超标率11%)外,其他重金属均未超标; 5)作物籽粒重金属Pz均值为0.38,表明该地区作物重金属总体处于安全级,但大麦、小麦、油菜籽粒均有样品Pb含量超过警戒线,个别样品甚至达到重度污染水平; 6)作物整株各重金属之间、重金属与P之间均存在显著正相关(P0.01),而重金属与N、CP、N/P存在显著负相关(P0.01),在籽粒中则相关性均不显著(P0.05)。以上结果显示,盐城滨海滩涂围垦区作物重金属累积与围垦时间关系不大,其含量目前尚处于可接受范围内,但Pb污染值得关注,作物重金属与P之间存在一定的相互促进作用,而与N存在一定的拮抗作用,高氮低磷的机体养分状况有助于降低重金属含量。     

重金属积累对土壤酶活性的影响

研究了华北平原某铅冶炼厂附近农田33个土壤样品中重金属积累对土壤酶活性的影响。结果表明,样品中Pb和Cd全量的平均值分别为144和5.59mg·kg-1,DTPA态Pb和Cd含量平均值分别为54.1和0.964mg·kg-1,均超过了未污染农田潮土的正常范围,而Cu、Ni和Zn的有效性和全量与未污染土壤接近;土壤过氧化氢酶活性与DTPA态Pb和Cd含量、全Pb含量均呈显著的负线性关系(P<0.01);与磷酸酶和脲酶相比,土壤脱氢酶活性更易受到土壤中Pb和Cd积累的影响;随DTPA-Ni含量增加,土壤蛋白酶和碱性磷酸酶活性增加(P<0.1);土壤脲酶活性与重金属全量或有效态重金属含量无显著相关性(P>0.1)。以上结果说明,利用土壤过氧化氢酶和脱氢酶活性能够表征基本性质较为一致的土壤中重金属污染程度;与重金属全量相比,有效态重金属对土壤酶活性影响更大。     

Effect of air-borne heavy metals on the biochemical signature of tree species in an industrial region,with an emphasis on anticipated performance index

The present study demonstrates elevated concentrations of air-borne heavy metals (Fe, 4.791; Cr, 3.142; Pb, 1.718; Cd, 0.069 μg·m^?3) in an industrial region and their subsequent accumulation in tree species grown in that area. Lagerstomia speciosa showed the highest leaf metal concentrations, whereas the lowest metal concentration was observed in Acacia moniliformis. Air accumulation factors (AAF) for heavy metals were in the sequence Cd>Cr>Pb>Fe. Plants exposed to air-borne heavy metals showed a significant (p<0.01, p<0.05) decrease in total chlorophyll and soluble sugars content, with higher synthesis of cellular antioxidants compared with ascorbic acids, proline and thiols (NP-SH). Plants with higher air-borne metal accumulation factors (AAF) generally have a high air pollution tolerance index (APTI) value. Assessment of the anticipated performance index (API) gave Alstonia scholaris as the ‘best variety’ and A. moniliformis and Shorea robusta as ‘very good’ for plantation and greenbelt development in an industrial region.     

Concentrations of Heavy Metals in Muscle with Relation to the Growth of Two Marine Fish Species

Heavy metal concentrations in muscle and their relation to thegrowth of two marine fish species,including tonguefish( Cynoglossus arel) and mullet( Mugil cephalus),were studied. The samples were collected in Bach Dang estuary andconcentrations of heavy metals( As,Cd,Co,Mn,Cu,Zn,Pb,and V) in muscle of the fisheswere determined. The result showed that the accumulated trend of heavy metal is different between fish species. The concentration of As,Zn,Mn,V,Cu,Pb,Co and Cd in tonguefish were 73. 7 ± 30. 6,22. 82 ± 4.87,3. 44 ± 2. 13,1. 61 ± 0. 15,0. 71 ± 0. 13,0. 45 ± 0. 24,0. 03 ± 0. 02 and 0. 02 ± 0. 02 mg·g-1,respectively. Meanwhile the concentration of Zn,As,V,Mn,Cu,Pb,Co and Cd in mullet were 83. 41 ±19. 68,9. 78 ± 1. 92,1. 36 ± 0. 54,1. 29 ± 0. 51,0. 65 ± 0. 12,0. 42 ± 0. 20,0. 06 ± 0. 03 and0. 03 ± 0. 01mg·g-1,respectively. Comparison of metal levels among thesespecies indicated that the concentrations of As and Mn in tonguefish were significantly higher than those in mullet,whereas Zn levels in mullet were found to be higher than that in tonguefish. There is no significant differences of Cd,Co,Cu,Pb and V levels in muscle between two species. Significant inversed relationshipsbetween concentration levels of metals and lengths of tonguefish were found for Mn,Cu and Zn,butnot for As,Cd,Pb,and V. There were no significant relationships between the heavy metal concentrations and the length of mullet. In general,decreasesof the heavy metal concentrations corresponded to the increases of fish body lengths,particularly for As,Co,Cu,Mn and V and the exception for Cd. Terefore reduced risks were associated with consuming biggermullet fish,and increased risks of As and Cd were associated with consuming bigger tonguefish in Bach Dang river mouth.     

Characteristics,sources and health risk assessment of toxic heavy metals in PM<Subscript>2.5</Subscript> at a megacity of southwest China

Twenty trace elements in fine particulate matters (i.e., PM_2.5) at urban Chengdu, a southwest megacity of China, were determined to study the characteristics, sources and human health risk of particulate toxic heavy metals. This work mainly focused on eight toxic heavy metal elements (As, Cd, Cr, Cu, Mn, Ni, Pb and Zn). The average concentration of PM_2.5 was 165.1 ± 84.7 µg m^?3 during the study period, significantly exceeding the National Ambient Air Quality Standard (35 µg m^?3 in annual average). The particulate heavy metal pollution was very serious in which Cd and As concentrations in PM_2.5 significantly surpassed the WHO standard. The enrichment factor values of heavy metals were typically higher than 10, suggesting that they were mainly influenced by anthropogenic sources. More specifically, the Cr, Mn and Ni were slightly enriched, Cu was highly enriched, while As, Cd, Pb and Zn were severely enriched. The results of correlation analysis showed that Cd may come from metallurgy and mechanical manufacturing emissions, and the other metals were predominately influenced by traffic emissions and coal combustion. The results of health risk assessment indicated that As, Mn and Cd would pose a significant non-carcinogenic health risk to both children and adults, while Cr would cause carcinogenic risk. Other toxic heavy metals were within a safe level.     

环草隆对城市绿地重金属污染土壤有机氮矿化、基础呼吸及相关酶活性的影响

城市土壤重金属和有机污染物复合污染广泛存在,而城市草坪除草剂的应用使城市绿地土壤的农药污染问题成为了新的关注点。为了准确评价城市绿地重金属污染土壤的农药污染生态风险,选择不同重金属污染程度的土壤为研究对象,以土壤有机氮矿化量、基础呼吸以及土壤酶活性为指标,采用室内模拟试验方法,探讨了草坪除草剂环草隆污染对土壤微生物的生态毒理效应。结果表明:(1)土壤有机氮矿化、基础呼吸、芳基硫酸酯酶和碱性磷酸酶对重金属和环草隆污染响应较为敏感,脲酶和蔗糖酶对重金属和环草隆污染不敏感。(2)环草隆浓度为0~1 000 mg·kg~(-1)范围内,和污染较轻的样点N土壤的碱性磷酸酶活性抑制(激活)率的线性相关关系显著,和污染较为严重的样点D和G土壤的芳基硫酸酯酶活性抑制(激活)率的线性关系显著。(3)土壤中环草隆对样点D和G土壤芳香硫酸酯酶活性、对样点N土壤碱性磷酸酶活性抑制(激活)率的EC10分别为568 mg·kg~(-1)、1 306 mg·kg~(-1)(抑制值)和56 mg·kg~(-1)(激活值)、99 mg·kg~(-1),EC50分别为1 901 mg·kg~(-1)、3 806 mg·kg~(-1)、2 321 mg·kg~(-1)。以上研究结果能够为城市土壤重金属和农药复合污染生态风险评价提供基础数据和技术方法。     

Radionuclides,trace elements,and radium residence in phosphogypsum of Jordan

Voluminous stockpiles of phosphogypsum (PG) generated during the wet process production of phosphoric acid are stored at many sites around the world and pose problems for their safe storage, disposal, or utilization. A major concern is the elevated concentration of long-lived ²²⁶Ra (half-life = 1,600 years) inherited from the processed phosphate rock. Knowledge of the abundance and mode-of-occurrence of radium (Ra) in PG is critical for accurate prediction of Ra leachability and radon (Rn) emanation, and for prediction of radiation-exposure pathways to workers and to the public. The mean (±SD) of ²²⁶Ra concentrations in ten samples of Jordan PG is 601 ± 98 Bq/kg, which falls near the midrange of values reported for PG samples collected worldwide. Jordan PG generally shows no analytically significant enrichment (<10%) of ²²⁶Ra in the finer (<53 μm) grain size fraction. Phosphogypsum samples collected from two industrial sites with different sources of phosphate rock feedstock show consistent differences in concentration of ²²⁶Ra and rare earth elements, and also consistent trends of enrichment in these elements with increasing age of PG. Water-insoluble residues from Jordan PG constitute <10% of PG mass but contain 30–65% of the ²²⁶Ra. ²²⁶Ra correlates closely with Ba in the water-insoluble residues. Uniformly tiny (<10 μm) grains of barite (barium sulfate) observed with scanning electron microscopy have crystal morphologies that indicate their formation during the wet process. Barite is a well-documented and efficient scavenger of Ra from solution and is also very insoluble in water and mineral acids. Radium-bearing barite in PG influences the environmental mobility of radium and the radiation-exposure pathways near PG stockpiles.     

Anthropogenic metal pollution in surface sediments of the Tambaraparni River Estuary

Estuarine sediments in the<63 μm size fraction were collected from 15 stations within the Tambaraparni River Estuary, located on the east coast of India. The distribution of the heavy metals Cd, Co, Cr, Cu, Ni, Pb and Zn was recorded. Our analysis distinguished two groups of elements. First, Cd, Pb and Zn, which occurred in higher than expected concentrations indicative of pollution, and second, Co, Cr, Cu and Ni, which occurred at background levels. The highest metal concentration found in the study area was for Zn (1200 μ g·g^?1), and the lowest was for Cd (0.42 μ g·g^?1). It is presumed that river run-off, industrial waters and untreated domestic waters are major contributors to heavy metal pollution in the Tambaraparni River Estuary. The concentrations of heavy metal species in surface sediments (<2 m water depth) of the Tambaraparni Estuary were studied to determine the extent of anthropogenic inputs from catchment areas and to understand anthropogenic effects on geochemical process in this tropical estuarine system.     

Assessment of toxicity of heavy metal contaminated soils by the toxicity characteristic leaching procedure

The concentrations of Cu, Zn, Pb and Cd in soils near a lead–zinc mine located in Shangyu, Zhejiang Province, China, were determined and their toxicity was assessed using the toxicity characteristic leaching procedure (TCLP) developed by the United States Environmental Protection Agency. The TCLP method is a currently recognized international method for evaluation of heavy metal pollution in soils. The available levels of Cu, Zn, Pb and Cd were 8.2–36, 23–143, 6.4–1367 and 0.41–2.2 mg kg⁻¹, respectively, while the international standards were 15, 25, 5 and 0.5 mg kg⁻¹, respectively. Soils around the mine were more polluted with Zn and Pb, followed by Cd and Cu. Moreover, the levels of heavy metals in the soils extracted by TCLP indicated that extraction fluid 2 was more effective than extraction fluid 1 in extracting the heavy metals from the polluted soils and there was a positive correlation between fluids 1 and 2. Available heavy metal contents determined by TCLP were correlated with soil total heavy metal contents.     

Chemical speciation and potential ecological risk assessment of heavy metals in volcanic rocks of Southern Qinghai,China

ABSTRACT

Seven volcanic rocks samples were collected from Southern Qinghai to analyze chemical speciation and migration behavior of heavy metals by sequential chemical extraction procedure and column leaching test. The geo-accumulation index, ecological risk index and the risk assessment code were applied to assess the heavy metal pollution and potential environmental effects in this area. Results revealed that the total concentrations of heavy metals did not exceed the background values in soil of this area. Most of the samples produced acid rock drainage. The order of heavy metal migration and transformation sequence in the volcanic rocks of Zhiduo region was Cd?>?Pb?>?As?=?Cu?=?Zn?=?Mn based on the geo-accumulation index and Cd caused heavy pollution, which was also confirmed by the leaching test. Moderate potential ecological risk posed by heavy metals occurred in the study area based on the potential ecological risk index. Cd contributed to most of ecological risk while the remaining heavy metals (except As) exerted medium to high risks to the environment according to the risk assessment code evaluation results. In summary, volcanic rocks possessed potential risks to the surroundings due to potential release of heavy metals. Cd that caused the pollution should be paid special attention.     

松花江鱼体中重金属的富集及污染评价

为研究松花江鱼类重金属的污染现状,采用原子吸收分光光度法测定了松花江鱼体中Cu、Zn、Pb、Cd含量,利用F732-V型测汞仪测定了Hg含量,并采用均值型综合污染指数法对重金属污染进行评价。结果表明,松花江鱼体中重金属含量从高到低依次为Zn、Pb、Cu、Hg、Cd,其中,Cu、Zn含量在第二松花江和干流江段的差异不大,Pb和Hg含量在第二松花江江段明显高于干流江段,而Cd含量在干流江段相对较高。不同鱼类体内重金属含量差异较大,除Zn以外,其他4种重金属在肉食性鱼类体内的含量均高于杂食性和植食性鱼类。2006年监测结果表明,松花江鱼体中Cu、Zn、Hg、Cd含量均较低,其污染状况较20世纪90年代已明显好转,但Pb污染程度却在不断加剧,并且受Pb污染的影响,松花江鱼类重金属的综合污染程度较高,特别是第二松花江江段已达到重污染水平。     

贵阳市中心城区土壤重金属污染现状及其评价

以贵阳市中心城区五大功能区(工业区、商业区、行政区、文教区、居民区)的土壤为对象,研究土壤中重金属(Hg、As、Cu、Cr和Zn)污染的特征,采用单因子污染指数和内梅罗(N.L.Neiow)综合污染指数法对土壤重金属污染现状进行了检测与初步评价,Hakanson潜在生态危害指数评价法评价了土壤重金属的潜在生态危害,其结...     

广州市区植物叶片重金属元素含量及其大气污染评价

文章通过对广州市区植物叶片中重金属元素含量的分析，研究了植物大气环境污染指数，探讨了植物叶片重金属元素含量与城市大气环境污染之间的关系。结果表明，植物叶片中Cu,Pb,Cd,Cr元素污染都较严重，在重污染区这些元素的含量明显高于清洁对照区；用植物污染指数可以综合评价大气环境质量状况；利用植物叶片内的重金属含量变化，为大气污染生物监测和环境质量评价提供了科学依据。     

Determination of metals in printed wiring boards of waste mobile phones

Metal contents of waste mobile phones represent a major environmental risk, especially considering the adoption of inappropriate management options in developing countries including open burning and disposal into surface water bodies. In this study the metal contents of mobile phone printed wiring board (PWB) samples were assessed. Sixty-two waste mobile phones of 15 brands were collected, dismantled, and their PWB samples were analyzed for Cu, Pb, Ag and Cd. The metal concentrations in the samples varied widely between and within brands. Among these metals, Cu and Pb were found to be at very high concentrations. The range (mean?±?SD) of Cu and Pb concentrations were 94.1–532?g?kg^?1 (250?±?92.3?g?kg^?1) and 7.0–46.2?g?kg^?1 (20.1?±?8.4?g?kg^?1), respectively. All Cu and Pb concentrations exceeded toxicity threshold limit concentration (TTLC) regulatory limits used in characterizing wastes as hazardous in the state of California, USA. The mean Cu and Pb concentrations exceeded the corresponding TTLC limits by factors of 100 and 20, respectively. The Ag and Cd concentrations were in the range 59.4–759?mg?kg^?1 (mean 227?±?104?mg?kg^?1) and ND – 15.6?mg?kg^?1 (2.1?±?3.3?mg?kg^?1), respectively.     

The accumulation levels of heavy metals (Ni,Cr, Sr, & Ag) in marine algae from southwest coast of India

In the context of use of marine algae as biological indicators of heavy metal pollution in coastal waters, six species of marine algae collected from the southwest coast of India were analysed for the levels of heavy metals (Ni, Cr, Sr, and Ag). Interspecies and interclass variations were determined on a spatial and temporal scale. The metal contents varied in the ranges, Ni: 0.20–21.06?µg?g^?1 (mean?=?10.13?µg?g^?1), Cr: non-detectable level (ND)–37.18?µg?g^?1 (mean?=?13.86?µg?g^?1), Sr: 2.19–103.90?µg?g^?1 (mean =?29.40?µg?g^?1), and Ag: ND–6.39?µg?g^?1 (mean?=?1.80?µg?g^?1). Ni and Cr contents were of similar magnitude to those reported for algae from polluted areas.     

Heavy metals and soil microbes

Heavy metal pollution is a global issue due to health risks associated with metal contamination. Although many metals are essential for life, they can be harmful to man, animal, plant and microorganisms at toxic levels. Occurrence of heavy metals in soil is mainly attributed to natural weathering of metal-rich parent material and anthropogenic activities such as industrial, mining, agricultural activities. Here we review the effect of soil microbes on the biosorption and bioavailability of heavy metals; the mechanisms of heavy metals sequestration by plant and microbes; and the effects of pollution on soil microbial diversity and activities. The major points are: anthropogenic activities constitute the major source of heavy metals in the environment. Soil chemistry is the major determinant of metal solubility, movement and availability in the soil. High levels of heavy metals in living tissues cause severe organ impairment, neurological disorders and eventual death. Elevated levels of heavy metals in soils decrease microbial population, diversity and activities. Nonetheless, certain soil microbes tolerate and use heavy metals in their systems; as such they are used for bioremediation of polluted soils. Soil microbes can be used for remediation of contaminated soils either directly or by making heavy metals bioavailable in the rhizosphere of plants. Such plants can accumulate 100 mg g^?1 Cd and As; 1000 mg g^?1 Co, Cu, Cr, Ni and 10,000 mg g^?1 Pb, Mn and Ni; and translocate metals to harvestable parts. Microbial activity changes soil physical properties such as soil structure and biochemical properties such as pH, soil redox state, soil enzymes that influence the solubility and bioavailability of heavy metals. The concept of ecological dose (ED₅₀) and lethal concentration (LC₅₀) was developed in response to the need to easily quantify the influence of pollutants on microbial-mediated ecological processes in various ecosystems.