Soil chromium bioremediation: Synergic activity of actinobacteria and plants

The aim of this work was to evaluate a strategy to reduce the bioavailable chromium fraction in soil, using a Cr(VI) resistant microorganism, Streptomyces sp. MC1, under non sterile conditions, with maize plants as bioindicator and/or bioremediator.Soil samples were contaminated with 100, 200 and 400 mg kg⁻¹ of Cr(VI) or Cr(III). Bioavailable chromium (35%) was only detected in samples with Cr(VI). Soil samples with Cr(VI) 200 mg kg⁻¹ were inoculated with Streptomyces sp. MC1, and bioavailable chromium decreased up to 73%.Zea mays seedlings were planted in soil samples contaminated with chromium. Plantlets accumulated chromium mainly as Cr(III), and biomass decreased up to 88%. Streptomyces sp. MC1 was inoculated in soil samples contaminated with 200 mg kg⁻¹ of Cr(VI) and Z.mays seedlings were planted.Streptomyces sp. MC1 caused Z.mays biomass increase (57%), chromium accumulation and bioavailable chromium decreased up to 46% and 96%, respectively.This work constitutes the first contribution of cooperative action between actinobacteria and Z.mays in the bioremediation of Cr(VI) contaminated soil. The large removal capacity of bioavailable chromium by Streptomyces sp. MC1 and Z.mays infers that they could be successfully applied together in bioremediation of soils contaminated with Cr(VI).     

Phytoremediation as a prospective method for rehabilitation of areas contaminated by long-term sewage sludge storage: A Ukrainian–Greek case study

Soil contamination by heavy metals could be caused by long-term storage of sewage sludge on the territory of most municipal wastewater treatment plants (WWTPs) worldwide. Different methods to deal with heavy metal pollution and rehabilitation can be applied, but they are costly. Phytoremediation is a method using plants in order to extract, sequester and/or detoxify pollutants such as heavy metals. Phytotechnologies are more advantageous economically, than other in situ and ex situ remedial approaches (they estimated to be at least 40% less costly) (ITRC, 2001).In this work the suitability of several plant species for phytoremediation under natural conditions was studied. Brassica napus, Medicago sativa, Zea mays, Triticum aestivum and Hordeum vulgare were grown in pots with sewage sludge from “Bezludivka” WWTP in Kharkiv, Ukraine and from Sindos WWTP in Thessaloniki, Greece.Plants in the experimental series were compared to those in the control samples (the same species grown in compost). In experimental series, shoot growth was less reduced in T. aestivum and H. vulgare than in the other plant species studied. M. sativa had the lowest germination rate. Generally B. napus and M. sativa, giving less biomass production than Z. mays and T. aestivum, were characterized by higher ability to accumulate heavy metals (Cd, Cu, Ni, Pb, Zn, Cr, As and Hg).     

Effect of domestic sewage wastewater irrigation on nutritional and nutraceutical perspectives of Eleusine coracana and Zea mays (raw and processed) from selected semi-urban and rural areas of Coimbatore,Tamil Nadu

Abstract

Rapid growth of the urban population, particularly in developing countries, places an enormous pressure on water. Sewage farming is common in all urban areas in India. This study is an attempt to evaluate the effect of diluted sewage wastewater irrigation on cultivation of Eleusine coracana and Zea mays from selected semi-urban and rural areas of Coimbatore, Tamil Nadu. For this, parameters analyzed were water/soil quality, crop quality, and mineral analysis including heavy metal composition and in vitro antioxidant potential. From the results, the physicochemical parameters of both rural and semi-urban wastewater samples are within the permissible limits according to the WHO. In mineral analysis, the heavy metals such as Pb, Fe, and Zn are high in all samples and Ni, Cr, and Cu are within the permissible limits in rural samples but slightly high in semi-urban samples. The proximate composition provides general overview of the nutritional value of a food. E. coracana and Z. mays samples collected from rural area show adequate mineral profile required for growth and nutrition. Both the samples show significant antioxidant values significant at p < 0.05. The results demonstrated that the diluted sewage wastewater has physicochemical properties for safe irrigation. Micronutrient and heavy metal contents in the plant samples were not extremely high and were within the range of FAO/WHO standards.     

The role of bacteria on heavy-metal extraction and uptake by plants growing on multi-metal-contaminated soils

Four bacterial isolates were examined for their ability to increase the availability of water soluble Cu, Cr, Pb and Zn in soils and for their effect on metals uptake by Zea mays and Sorghum bicolor. Random Amplified Polymorphic DNA (RAPD) analysis was used to show that the bacterial cultures were genetically diverse. Bacterial isolates S3, S28, S22 and S29 had 16S rRNA gene sequences that were most similar to Bacillus subtilis, Bacillus pumilus, Pseudomonas pseudoalcaligenes and Brevibacterium halotolerans based on 100% similarity in their 16S rDNA gene sequence, respectively. Filtrate liquid media that had supported B. pumilus and B. subtilis growth significantly increased Cr and Cu extraction from soil polluted with tannery effluent and from Cu-rich soil, respectively, compared to axenic media. The highest concentrations of Pb (0.2 g kg⁻¹), Zn (4 g kg⁻¹) and Cu (2 g kg⁻¹) were accumulated in shoots of Z. mays grown on Cu-rich soil inoculated with Br. halotolerans. The highest concentration of Cr (5 g kg⁻¹) was accumulated in S. bicolor roots grown in tannery-effluent-polluted soil inoculated with a mixed inoculum of bacterial strains. These results show that bacteria play an important role in increasing metal availability in soil, thus enhancing Cr, Pb, Zn and Cu accumulation by Z. mays and S. bicolor.     

金毛狗对重金属的富集特性的研究

为探讨金毛狗[Cibotium barometz(L.) J. Sm.]对重金属的富集能力,在广东省选取6个样点(南岭、南昆山、白云山、大岭山、梧桐山、西樵山)采集金毛狗的叶片、根状茎和根际土壤,采用ICP-MS测定9种重金属元素(Cr、Mn、Ni、Cu、Zn、As、Cd、Hg、Pb)的含量。结果表明,样地土壤已受到不同程度的重金属污染,土壤中Cd和Hg含量均高于广东省土壤背景值,分别为背景值的1.61~4.82倍和4.74~11.79倍。西樵山土壤中Cd含量最大,南岭土壤中Hg含量最大。在9种元素中,金毛狗对Hg的转运系数最高,达4.8,对Cd的富集系数最高,达2.2,Cu和Cd元素的转运系数和富集系数均大于1。这说明金毛狗对重金属元素的富集能力较弱而转运能力较强。     

Growth and bioaccumulation characteristics of watercress (Nasturtium officinale R. BR.) exposed to cadmium,cobalt and chromium

Abstract

The aim of this study is to determine the effects of Cd, Co and Cr on the growth of watercress (Nasturtium officinale) and to determine the bioaccumulation properties of these heavy metals by the plant. N. officinale individuals were exposed to different concentrations of Cd, Co and Cr for 72 h. Relative growth rates (RGR) and bioconcentration factor (BCF) ratios were calculated for each metal concentration. RGR values of plants exposed to Co slightly increased in lower concentrations, but then decreased again. In contrast, RGR values of plants exposed to Cd and Cr decreased linearly. Significant positive relationships were observed among the concentrations of Cd, Co and Cr in N. officinale and in the culture solution. BCF ratios were highest for plants exposed to Co, and lowest for plants exposed to Cr. The most efficient uptake of Cd, Co and Cr occurred at the external solution concentrations at 0.5, 0.5 and 10 mM, respectively.     

Phytoremediation of Landfill Leachate with Colocasia esculenta,Gynerum sagittatum and Heliconia psittacorum in Constructed Wetlands

This study assessed the accumulation of Cd (II), Hg (II), Cr (VI) and Pb (II) in Gynerium sagittatum (Gs), Colocasia esculenta (Ce) and Heliconia psittacorum (He) planted in constructed wetlands treating synthetic landfill leachate. Sixteen bioreactors were operated in two experimental blocks. Metal concentrations in the influent and effluent; root, stem, branch and leaves of plants were analysed, as well as COD, N-NH₄⁺, TKN, T, pH, ORP, DO, and EC. Average removal efficiencies of COD, TKN and NH₄⁺-N were 66, 67 and 72%, respectively and heavy metal removal ranged from 92 to 98% in all units. Cr (VI) was not detected in any effluent sample. The bioconcentration factors (BCF) were 10⁰ -10². The BCF of Cr (VI) was the lowest: 0.59 and 2.5 (L kg^?1) for Gs and He respectively; whilst Cd (II) had the highest (130–135 L kg^?1) for Gs. Roots showed a higher metal content than shoots. Translocation factors (TF) were lower, He was the plant exhibiting TFs >1 for Pb (II), Cr (T) and Hg (II) and 0.4–0.9 for Cd (II) and Cr (VI). The evaluated plants demonstrate their suitability for phytoremediation of landfill leachate and all of them can be categorized as metals accumulators.     

The role of organic vs. inorganic fertilizers in reducing phytoavailability of heavy metals in a wastewater-irrigated area

Long-term use of industrial and domestic wastewater for irrigation leads to accumulation of heavy metals in the soil and consequently in the edible portion of the plants. This study examined the role of fertilizers in reducing the heavy metal availability in the soil, and subsequent uptake in Beta vulgaris L. (var. All green). The effects of organic fertilizer as farmyard manure (FYM), commercial inorganic nitrogen, phosphorus and potassium (NPK) and a combination of FYM + N were compared with control having no fertilization on physico-chemical properties of the soil and heavy metal concentrations in the soil and plants. Soil treatments led to changes in the physico-chemical properties of the soil, modifying the phytoavailability of heavy metals. Phytoavailabilty of Cd, Cu, Pb, Zn, Mn, Ni and Cr was lowest in FYM- and highest in NPK- treated soil, compared to the untreated control. The yield of B. vulgaris was also highest in FYM-treated soil. As the application of FYM alone and in combination with N resulted in reduced heavy metal uptake and better yield, it may be considered an easy and cost-effective technique for reducing the levels of contamination in food crops.     

Bioaccumulation and rhizofiltration potential of Pistia stratiotes L. for mitigating water pollution in the Egyptian wetlands

The bioaccumulation and rhizofiltration potential of P. stratiotes for heavy metals were investigated to mitigate water pollution in the Egyptian wetlands. Plant and water samples were collected monthly through nine quadrats equally distributed along three sites at Al-Sero drain in Giza Province. The annual mean of the shoot biomass was 10 times that of the root. The concentrations of shoot heavy metals fell in the order: Fe < Mn < Cr < Pb < Cu < Zn < Ni < Co < Cd, while that of the roots were: Fe < Mn < Cr < Pb < Zn < Ni < Co < Cu < Cd. The bio-concentration factor (BCF) of most investigated heavy metals, except Cr and Pb, was greater than 1000, while the translocation factor (TF) of most investigated metals, except Pb and Cu, did not exceed one. The rhizofiltration potential (RP) of heavy metals was higher than 1000 for Fe, and 100 for Cr, Pb and Cu. Significant positive correlations between Fe and Cu in water with those in plant roots and leaves, respectively were recorded, which, in addition to the high BCF and RP, indicate the potential use of P. stratiotes in mitigating these toxic metals.     

Pollution characteristics and risk assessment of heavy metals in the soil of a construction waste landfill site

Heavy metals found in construction waste can enter soil and water bodies through surface runoff and leachate, where they represent an environmental hazard. In this study, we investigate the pollution characteristics and ecological risks of eight heavy metals (Cd, Cr, Cu, Mn, Ni, Pb, Zn, and As) in the soils of an unofficial construction waste landfill site in Beijing, China. The results indicate that long-term disposal of construction waste in the dry riverbed can reduce the pH value of the soil, increase the soil organic carbon content, and affect the total amount and distribution of heavy metals. Moreover, the landfill site pollutes the external soil environment, with Cd, Zn, Pb, and Cu as the characteristic pollutants. According to the Nemerow comprehensive pollution index and potential ecological risk assessment, heavy metal pollution decreases in the following order: internal soil > bottom soil > boundary soil. Cd, Zn, Pb, and Cu pollution is higher in the internal region, with single heavy-metal pollution indexes (Pi) of 1.41, 1.65, 1.26, and 1.28, respectively. Conversely, the Pi for Cr is higher in boundary and bottom soils (1.91 and 1.94, respectively). Risk assessment codes indicate that Cd and Mn pose the greatest environmental risk (31.9% and 17.8%, respectively) as they have the highest effective content, bioavailability, and mobility. Thus, environmental monitoring is a necessity for these metals.     

Phytoavailability of Heavy Metals and Metalloids in Soils Irrigated with Wastewater,Akaki, Ethiopia: A Greenhouse Study

Irrigation with untreated wastewater from several industrial, commercial, and domestic discharges for decades caused accumulation of various heavy metals and metalloids in soils along the Akaki River in Ethiopia. Assessment of environmental threats and the potential phytoremediation of the soils require understanding of the toxic elements’ uptake and distribution in plant parts. Hence, a greenhouse study was performed to examine the phytoavailability and distribution of Cr, Ni, Co, Cu, Zn, Cd, Pb, Hg, Se, V, and As in forage grasses: Oat (Avena sativa), Rhodes grass (Chloris gayana), Setaria (Setaria sphacelata), and the legumes Alfalfa (Medicago sativa) and Desmodium (Desmodium unicinatum). The average contents of Cr, Ni, Co, Cu, Zn, Pb, Hg, Se, and V in the plants were generally higher than the background levels for forage grasses/legumes, and some of these elements were in the phytotoxic range. Root bioconcentration factor (BCF = root to soil concentration ratio) > 1 was observed for Cu (Oat, Rhodes, Desmodium, and Setaria: Fluvisol), Zn (Setaria: Fluvisol), Cd (Rhodes: Fluvisol; Setaria from both soils) and Hg (Oat and Alfalfa: Fluvisol). Alfalfa and Desmodium displayed translocation factor > 1 (TF = shoot to root concentration ratio) for most heavy metals. Most heavy metals/metalloids may pose a health threat to humans and stock via introduction to the food chain. The plant factors (species and plant part), soil factors (soil type, soil fractions, pH, and CEC), and their interactions significantly (p < 0.05) influenced plant heavy metal and metalloid levels. However, the role of plant part and species emerged as the most important on heavy metal uptake, translocation, sequestration, and ultimately transfer to the food chain. Accordingly, the uptake and distribution of heavy metals/metalloids in the plants reflect the potential environmental and health hazards attributable to the use of fodder grasses, legumes, and cultivation of vegetables in soils with polymetallic and metalloid contamination.     

Growth,metal accumulation and yield performance of Brassica campestris L. (cv. Pusa Jaikisan) grown on soil amended with tannery sludge/fly ash mixture

Application of sewage sludge and fly ash (FA) to soil is gaining practice and has become an alternative to chemical fertilizers in many countries. The present study aimed to assess the potential of fly ash–tannery sludge (TS) mixture in two ratios {4 (TS):1 (FA), denoted as A and 4 (TS):2 (FA) denoted as B} and different amendments were made with soil to study the yield and metal availability and their uptake by Brassica campestris L. (cv. Pusa Jaikisan). Experimental data showed that increase in dry matter yield and oil content of B. campestris was noted in lower amendments of soil with mixture A. However, total chlorophyll content of the leaf increased significantly, whereas carotenoid content showed non-significant increase in all the amendments with mixtures A and B as compared to control. The translocation of most of the tested metals (Pb, Mn, Cd, Ni, and Fe) in the shoot of the plant was found higher except Cr, Cu, and Co. Overall, experimental results showed that mixture A (≥10%) was found to be suitable due to better yield and less accumulation of metal in the seed of B. campestris.     

成都平原北部水稻土重金属含量状况及其潜在生态风险评价

为了解成都平原水稻土重金属含量状况和潜在的生态风险,选取成都平原北部水稻土典型区域为研究对象,采集了158个表层土壤样品,分析了土壤中pH值和Cd、Cu、As、Hg、Pb、Cr、Ni 7种重金属元素含量,以20世纪80年代测定的成都平原土壤重金属元素背景值为评价标准,采用Hakanson潜在生态危害指数法对研究区域的重金属潜在生态风险进行了评价。结果表明:研究区域水稻土Cd、Hg、Ni、Cu、Pb、Cr和As平均含量分别为0.709、0.187、32.08、34.12、31.52、82.13 mg/kg和7.25 mg/kg;Cd、Ni、Cu和Hg 4种重金属超过《土壤环境质量标准》(GB15618-1995) Ⅱ级标准值样本比例分别为87.34%、8.23%、3.80%和3.80%,Cd含量超标严重。7种重金属元素变异系数幅度为18.35%-49.03%,由大到小依次为Cd、Hg、Cu、As、Ni、Cr、Pb。75.32%的样本达到中度或较强重金属潜在生态风险,区域整体表现为中度潜在生态风险(RI平均值为198.65),Cd和Hg为高生态风险元素,对潜在生态风险贡献率分别为62.27%和20.78%,As、Pb、Cu、Ni、Cr为低生态风险元素;风险概率图显示城区周边和绵远河沿线的潜在生态风险等级较高。因此,成都平原水稻土农业生产中应采取一定的措施防控农产品Cd和Hg污染。     

黄河口盐地碱蓬湿地土壤-植物系统重金属污染评价

以黄河口盐地碱蓬湿地为例,评价了淹水和非淹水区湿地表层土壤As、Cd、Cu、Cr、Pb和Zn 6种重金属的污染程度及其在土壤-植物系统中的迁移、富集特征,分析了不同积水深度和土壤理化性质对研究区土壤重金属含量的影响.研究结果表明,与土壤或沉积物质量标准相比,黄河口盐地碱蓬湿地土壤受As和Cd污染最严重,而其它重金属污染较轻;非淹水土壤Cd、Cr和Zn含量高于淹水湿地,而As、Cu和Pb则较低;而且淹水土壤As含量随积水深度增加而呈下降趋势,但积水深度对其他重金属含量的影响不明显.相关性分析结果表明,按照受土壤关键影响因子的不同重金属(除As外)可以分为两类:第一类为Cd、Cr和Zn,这些重金属含量受土壤pH值和盐分影响较大,且相互间存在显著正相关关系,表明它们可能有相同的来源;第二类为Pb和Cu,它们受土壤pH值、盐分和有机质的影响,且Pb和Cu之间存在显著正相关关系.除Cr、Cu和Zn外,重金属在盐地碱蓬的根系内一般不发生显著富集,但绝大多数重金属都表现出地上部分的含量比根系更高的现象.     

Heavy metal accumulation in rice (Oryza sativa) near electronic waste dumps and related human health risk assessment

This research was conducted to assess heavy metal contamination in the environment and within Oryza sativa. The translocation factors (TFs) and bioaccumulation factors (BAFs) for heavy metals in O. sativa and estimated daily intake (EDI) and health risk index (HRI) were measured. The samples were analyzed for heavy metals using inductively coupled plasma optical emission spectrometry (ICP-OES). Pb and Cr concentrations in water samples within and near the electronic-waste dumping area exceeded water quality standards for surface water sources from the Pollution Control Department in the Ministry of Natural Resources and Environment of Thailand (PCD). The Pb concentration in soil samples within the area also exceeded soil quality standards for habitat and agriculture from PCD. Most of the metals were highly concentrated in roots, except for Mn which has the highest concentration in leaves. Pb concentrations in rice grains exceeded the FAO/WHO standard (0.2 mg/kg). The average TF values for heavy metals from the soil to roots, roots to stems, stems to leaves, and stems to grains were Mn > Pb > Ni > Cr, Mn > Cr > Ni > Pb, Ni > Pb > Mn > Cr, and Pb > Ni > Cr > Mn, respectively. The average BAF values in O. sativa were Mn > Ni > Pb > Cr. The EDI for Cr, Pb, Mn, and Ni via O. sativa consumption were 6.19, 6.02, 370.57, and 3.80 µg/kg/day, respectively. The HRI for Cr, Pb, Mn, and Ni via O. sativa consumption were 0.30, 1.50, 2.60, and 0.002, respectively.     

Evaluation of bioconcentration factors of metals and non-metals in crops and soil from abandoned mines in Korea

Hazard evaluation of different heavy metal exposure on the crops cultivated around two abandoned metal mine sites was conducted. Bioconcentration Factor (BCF) of nine heavy metals including Cu, Cd, Hg, As, Cr, Zn, Pb, Mn, and Al in the samples of brown rice cultivated at exposed soil were measured. Soil-plant BCF was measured and compared with Korean and US EPA standards. BCF values of analyzed heavy metals except Hg and As were below the limits. BCF of Hg was over 5 times higher than the standard limit. Excess cancer risk (ECR) and hazard quotient (HQ) values of As was higher than the limit and suggested to have carcinogenic as well as non-carcinogenic threat to the public exposed to the sites. The data presented could be utilized in prioritizing abandoned metal mine sites for health effect survey.     

新疆焉耆盆地辣椒地土壤重金属污染及生态风险预警

从新疆加工辣椒主产地(焉耆盆地)采集105个辣椒地典型土壤样品,测定其中As、Cd、Cr、Cu、Mn、Ni、Pb和Zn等8种重金属元素的含量。采用污染负荷指数(Pollution load index,PLI)、潜在生态风险指数(Potential ecological risk index,RI)和生态风险预警指数(Ecological risk warning index,I_(ER))对辣椒地土壤重金属污染及生态风险进行评价。结果表明:(1)焉耆盆地辣椒地土壤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1.65、1.40、1.32、3.21、6.42倍。辣椒地土壤Pb和Zn呈现重度污染,Cd、Cr和Ni轻度污染,As、Mn和Cu无污染。(2)土壤PLI平均值为1.40,呈现轻度污染。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、Pb、Cr、Zn。土壤RI平均值为18.40,属于轻微生态风险态势,IER平均值为-4.78,属于无警态势;博湖县辣椒地污染水平、潜在生态风险程度与生态风险预警等级最高,焉耆县污染水平、潜在生态风险程度与生态风险预警等级最低。(3)辣椒地土壤As、Cd、Pb与Zn主要受到人类活动的影响,Cr、Cu、Mn和Ni主要受到土壤地球化学作用的控制。Cd是焉耆盆地辣椒地生态风险等级最高的重金属元素,研究区农业生产过程中要防范Cd的污染风险。     

三峡库区消落带典型植物根际土壤磷形态特征

三峡库区消落带生态系统演变对水库安全具有重要影响,其中植物群落演变与土壤氮磷形态转化及释放等广受关注。然而,消落带植物根际效应与土壤磷形态关系及潜在影响并不清楚。选择三峡库区澎溪河消落带为研究对象,分别在冲积潮土、紫色土和水稻土分布的消落区采集典型草本植物(狗牙根、香附子、苍耳)和农作物(玉米)根际、非根际土壤,分析无机磷和有机磷的形态特征,探讨了消落带典型植物生长对土壤磷形态的根际效应及潜在影响。结果表明,土壤类型对土壤磷含量及磷赋存形态具有显著影响,紫色土磷含量最高,且活性磷含量低于冲积潮土和水稻土,表现出磷库稳定性较高;4种植物根际土壤全磷、有效磷及不同形态无机、有机磷(弱吸附态磷WA-P、潜在活性磷PA-P、铁铝结合态磷Fe/Al-P、钙结合态磷Ca-P、残渣态磷R-P)含量均高于非根际,表现出明显的根际富集效应;不同植物根际土壤全磷和有效磷表现为狗牙根苍耳香附子玉米,但磷形态在不同植物根际富集水平不同:活性较高的WA-P、PA-P含量在玉米和苍耳覆盖区均高于狗牙根和香附子,而较稳定Ca-P_i、R-P_i、Fe/Al-P_o、Ca-P_o含量在狗牙根和香附子覆盖区更高,表明玉米和苍耳生长有利于稳定性磷的活化,提高消落带土壤磷流失风险。不同植物根际对不同形态磷富集率差异明显,且玉米根际对活性磷形态的富集率最高,表明农业活动可能加速土壤稳定性磷的活化。pH、土壤有机质、土壤容重与无机磷的赋存形态关系密切,而有机磷赋存形态受pH影响显著,植物根际有机质积累和有机酸分泌等是影响土壤磷形态变化的主要因素。消落带植物群落演变及恢复对土壤磷形态转化具有重要影响。     

Heavy metal removal from a multi-metal solution and wastewater by Salvinia natans

Salvinia showed capacity to accumulate and hence remove more than one heavy metal from multi-metal solutions, though efficiency for heavy metal uptake varied for each metal present in different combinations. The pattern of heavy metal accumulation was confirmed by energy-dispersive X-ray fluorescence (EDXRF) analysis. There was a gradual decrease in heavy metal content in the wastewater samples when fresh biomass was replenished at definite time intervals of treatment. Zn, Cu, Ni and Cr removal to the extent of 84.8%, 73.8%, 56.8%, and 41.4%, respectively, was noted after four samplings of fresh biomass replenishment. Salvinia therefore can be recommended as a species for cleaning water contaminated with heavy metals.     

Effectiveness of naturally occurring Aphis gossypii on tomato plants as a bio-indicator for heavy metals in Riyadh and Hafar Al-Batin,Saudi Arabia

Although certain pollutants can be biologically degraded by microorganisms, rendering their impact short-term, others can not be impaired, such that their effect persists. The present study evaluates the effectiveness of using a field-collected aphid, Aphis gossypii, as a bio-indicator for heavy metals in tomato farms in Riyadh and Hafar Al-Batin, Saudi Arabia. Heavy metals were selected (Cd, Cu, Zn, and Pb) and measured for comparative screening in field-collected plants, soil, and aphids using inductively coupled plasma-mass spectrometry (ICP-MS). Field-collected aphids from both studied regions were identified as Aphis gossypii. In Riyadh, there was no significant difference observed for Cd, Cu, and Zn for all experimental samples, while, Pb was showed differences among samples especially tomato leaves None of the studied samples in Hafar Al-Batin were showed statistically significant differences in Cd, in reverse to significant differences in the other heavy metals. Comparing concentrations of selected heavy metals between the two studied regions was showed that neither region showed a significant difference in heavy metals except for Cu. This study demonstrates that tomato leaf samples showed the highest concentrations of most studied heavy metals, followed by soil, then aphids. Aphids were utilized as a bio-indicator of heavy metals in the studied regions.