Fate of heavy metals in vertical subsurface flow constructed wetlands treating secondary treated petroleum refinery wastewater in Kaduna,Nigeria

This study examined the performance of pilot-scale vertical subsurface flow constructed wetlands (VSF–CWs) planted with three indigenous plants, i.e. Typha latifolia, Cyperus alternifolius, and Cynodon dactylon, in removing heavy metals from secondary treated refinery wastewater under tropical conditions. The T. latifolia-planted VSF–CW had the best heavy metal removal performance, followed by the Cyperus alternifolius-planted VSF–CW and then the Cynodon dactylon-planted VSF–CW. The data indicated that Cu, Cr, Zn, Pb, Cd, and Fe were accumulated in the plants at all the three VSF–CWs. However, the accumulation of the heavy metals in the plants accounted for only a rather small fraction (0.09–16%) of the overall heavy metal removal by the wetlands. The plant roots accumulated the highest amount of heavy metals, followed by the leaves, and then the stem. Cr and Fe were mainly retained in the roots of T. latifolia, Cyperus alternifolius, and Cynodon dactylon (TF < 1), meaning that Cr and Fe were only partially transported to the leaves of these plants. This study showed that VSF–CWs planted with T. latifolia, Cyperus Alternifolius, and Cynodon dactylon can be used for the large-scale removal of heavy metals from secondary refinery wastewater.     

Effects of Municipal Sewage Sludge Doses on the Chlorophyll Contents and Heavy Metal Concentration of Sugar Beet (Beta vulgaris var. saccharifera)

The present study was conducted to assess the suitability of sewage sludge amendment (SSA) in soil for Beta vulgaris var. saccharifera (sugar beet) by evaluating the heavy metal accumulation and physiological responses of plants grown at a 10%, 25%, and 50% sewage sludge amendment rate. The sewage sludge amendment was modified by the physicochemical properties of soil, thus increasing the availability of heavy metals in the soil and consequently increasing accumulation in plant parts. Cd, Pb, Ni, and Cu concentrations in roots were significantly higher in plants grown at 25% as compared to 50% SSA; however, Cr and Zn concentration was higher at 50% than 25% SSA. The concentrations of heavy metal showed a trend of Zn > Ni > Cu > Cr > Pb > Cd in roots and Zn > Cu > Ni > Cr > Pb > Cd in leaves. The only instance in which the chlorophyll content did not increase after the sewage sludge treatments was 50%. There were approximately 1.12-fold differences between the control and 50% sewage sludge application for chlorophyll content. The sewage sludge amendment led to a significant increase in Pb, Cr, Cd, Cu, Zn, and Ni concentrations of the soil. The heavy metal accumulation in the soil after the treatments did not exceed the limits for the land application of sewage sludge recommended by the US Environmental Protection Agency (US EPA). The increased concentration of heavy metals in the soil due to the sewage sludge amendment led to increases in heavy metal uptake and the leaf and root concentrations of Ni, Zn, Cd, Cu, Cr, Pb, and Zn in plants as compared to those grown on unamended soil. More accumulation occurred in roots and leaves than in shoots for most of the heavy metals. The concentrations of Cd, Cr, and Pb were more than the permissible limits of national standards in the edible portion of sugar beet grown on different sewage sludge amendment ratios. The study concludes that the sewage sludge amendment in the soil for growing sugar beet may not be a good option due to risk of contamination of Cr, Pb, and Cd.     

Heavy metals potential health risk assessment through consumption of wastewater irrigated wild plants: A case study

This study investigates the potential health risk assessment of heavy metals consumption through wild plants (WPs) irrigated with wastewater and fresh water in the Bannu district, Pakistan. Therefore, soil and WP samples were collected and analyzed for heavy metals by atomic absorption spectrophotometer (Varian FAAS-240). Wastewater irrigated soil showed an elevated level for Cd (5.05–14.50 mg/Kg) and Ni (99.35–104.85 mg/Kg), while Cd (3.35–4.84 mg/Kg) concentration in the fresh water irrigated soil also surpassed the maximum allowable limits (MAL) set by the World Health Organization. Similarly, selected wastewater irrigated plants and fresh water irrigated plants also exceeded the MAL set by the Food and Agriculture Organization for Cd, Pb, and Cr (except for Cr in Vicia sativa). Heavy metal concentrations through WPs consumption were evaluated for the health risk index (HRI). The HRI value for each selected WPs was <1. However, total HRI values through WPs consumption was >1. Therefore, WPs consumption of the study area may pose a potential threat to the local community.     

Baseline water quality of municipal ponds and metal removal ability of Typha latifolia L. from sewage and industrial wastewaters

Municipal effluent of three rural settings of Islamabad was assessed for physicochemical and microbiological parameters by collecting wastewater from inlet and center of ponds. Results showed that water quality was comparatively better at the center as Typha latifolia plants were growing toward the center of ponds. In another study, the wastewater treatment ability of T. latifolia was investigated by growing them in industrial and municipal effluent under greenhouse conditions. Water and plant samples were collected periodically (3rd, 10th, 17th, 24th, and 31st day after transplanting) for the measurement of Pb, Cu, and Cd concentrations. A decrease in heavy metal concentration of both effluents was observed as the experiment progressed and metal removal percentages ranged between 81% and 96%. Complementary the increase in metal concentration in plant tissues was observed over experimental period. Among plant tissues, metal concentration of Pb was highest i.e. 362 mg kg^?1 in roots and 313 mg kg^?1 in shoots at end of experiment. Pb, Cu, and Cd concentrations were higher in roots than shoots and hence translocation factors were less than 1.0. Metal removal efficiency was better from industrial wastewater and was in order of Pb > Cu > Cd. T. latifolia can be used for remediation of heavy metal-polluted wastewater.     

Accumulation and distribution of heavy metals in a simulated mangrove system treated with sewage

Constructed tide tanks were used to examine the accumulation and distribution of heavy metals in various components of a simulated mangrove ecosystem. Young Kandelia candel plants grown in mangrove soils were irrigated with wastewater of various strengths twice a week for a period of one year. The amounts of heavy metals released via tidal water and leaf litter were monitored at regular time intervals. The quantities of heavy metals retained in mangrove soil and various plant parts were also determined. Results show that most heavy metals from wastewater were retained in soils with little being uptake by plants or released into tidal seawater. However, the amounts of metals retained in plants on a per unit dry weight base were higher than those in soils as the biomass production from the young mangrove plants was much smaller when compared to the vast quantity of soils used in this study. A significantly higher heavy metal content was found in roots than in the aerial parts of the mangrove plant,indicating that the roots act as a barrier for metal translocation and protect the sensitive parts of the plant from metal contamination. In both soil and plant, concentrations of Zn, Cd, Pb and Ni increased with the strengths of wastewater, although the bioaccumulation factors for these metals decreased when wastewater strengths increased. These results suggest that the mangrove soil component has a large capacity to retain heavy metals, and the role of mangrove plants in retaining metals will depend on plant age and their biomass production. This revised version was published online in August 2006 with corrections to the Cover Date.     

Factors affecting the distribution of cadmium,copper and lead and their effect upon yield and zinc content in bush beans (Phaseolus vulgaris L.)

Summary Concentrations of Cd, Pb and Cu in the roots, stems and leaves of bulgarian bush beans (Phaseolus vulgaris L.) were determined for plants grown in various soils of increasing levels of contamination of these metals. Most of each heavy metal absorbed by plants was retained in roots. Concentrations of Cd, Pb and Cu in roots increased in response to soil concentrations, whereas, in stems, only Cd and Pb concentrations increased and Cu concentration was relatively constant. It is thought that Cu transport to the stele was metabolically controlled, whereas Cd and Pb reached the stem by leakage across non suberised areas of the endodermis. Uptake of heavy metals was associated with a decrease in zinc content in plants and a decrease in yield. By regression analysis decrease in both zinc content and plant yield could be best related to Cd content in stems. Possible reasons for these effects are discussed.     

Effects of Cadmium and Mixed Heavy Metals on Rice Growth in Liaoning,China

Joint effects of Cd and other heavy metals (Pb, Cu, Zn and As) on the growth and development of rice plants and the uptake of these heavy metals by rice were studied using the pot-culture method combined with chemical and statistical analyses. The results showed that the growth and development of rice plants were strongly influenced by the double-element combined pollution. There was an average decrease in the height of rice plants of 4.0–5.0 cm, and grain yield was decreased by 20.0–30.0%, compared with the control. The uptake of Cd by rice plants was promoted due to the interactions between Cd and the other heavy metals added to the soil. The Cd concentration in roots, stems/leaves and seeds increased 31.6–47.7, 16.7–61.5 and 19.6–78.6%, respectively. Due to interactions, uptake of Pb, Cu and Zn by roots and stems/leaves was inhibited, accumulation of Pb, Cu and Zn in seeds was increased, uptake of As by roots was promoted and uptake of As by stems/leaves was inhibited. In particular, the upward transporting ability of the heavy metals absorbed by rice plants was significantly increased.     

菰和菖蒲对重金属的胁迫反应及其富集能力

通过盆栽实验研究了Cu—Zn—Ph-Cd复合污染条件下,菰和菖蒲的生长状况、生理特性及吸收和富集重金属的能力。结果表明,高浓度污染下菰和菖蒲不能存活;低、中浓度中菖蒲的生长受到抑制,菰各生长指标与对照相比差异不显著,表明菰对低、中浓度重金属的耐性强于菖蒲。随着污染浓度的增加,菰和菖蒲叶片叶绿索含量显著降低;菰叶绿素a／b值略有降低,菖蒲叶绿素a／b值显著降低;菰和菖蒲叶片脯氨酸含量、相对电导率显著升高,超氧化物歧化酶（SOD）、过氧化物酶（POD）活性在低浓度时升高,中浓度时降低。菰体内重金属含量为Zn〉Cu〉Pb〉Cd,菖蒲体内的含量为Cu〉Zn〉Pb〉Cd,且二者体内的重金属含量都随着污染浓度的增加而升高。菰和菖蒲对Cd的富集系数较大,地上部分（茎与叶）和地下部分（根与根状茎）均大于1;对Pb的富集系数较小,地上部分和地下部分均小于1。菰和菖蒲地下部分重金属含量均高于地上部分含量,二者根系对4种重金属都有较强的滞留效应,平均滞留率均大于50％。各处理中菰对重金属的吸收量均高于菖蒲。综合分析菰和菖蒲的生长、生理及富集重金属的能力,菰比菖蒲更适用于低、中浓度重金属污染水体的生态修复。     

Performance of rose scented geranium (Pelargonium graveolens) in heavy metal polluted soil vis-à-vis phytoaccumulation of metals

An investigation was carried out to evaluate the effect of heavy metal toxicity on growth, herb, oil yield and quality and metal accumulation in rose scented geranium (Pelargonium graveolens) grown in heavy metal enriched soils. Four heavy metals (Cd, Ni, Cr, and Pb) each at two levels (10 and 20 mg kg–1 soil) were tested on geranium. Results indicated that Cr concentration in soil at 20 mg kg–1 reduced leaves, stem and root yield by 70, 83, and 45%, respectively, over control. Root growth was significantly affected in Cr stressed soil. Nickel, Cr, and Cd concentration and accumulation in plant increased with higher application of these metals. Chromium, nickel and cadmium uptake was observed to be higher in leaves than in stem and roots. Essential oil constituents were generally not significantly affected by heavy metals except Pb at 10 and 20 ppm, which significantly increased the content of citronellol and Ni at 20 ppm increased the content of geraniol. Looking in to the higher accumulation of toxic metals by geranium and the minimal impact of heavy metals on quality of essential oil, geranium can be commercially cultivated in heavy metal polluted soil for production of high value essential oil.     

Human health risks from consuming cabbage (Brassica oleracea L. var. capitata) grown on wastewater irrigated soil

The present study investigated the impact of cumulative irrigation with wastewater on the soil properties and, its health hazards on the consumers of cabbage plants at south Cairo Province, Egypt. Irrigation water, soil and cabbage plants were sample d from two polluted and other two unpolluted farms. The physicochemical properties of water and soil were analyzed and the growth parameters, as well as nutrients and heavy metals concentration in cabbage were investigated. In addition, the daily intake of metals (DIM) and health risk index (HRI) were estimated. Wastewater posed a decrease in the availability of N, P and K, but increases heavy metals in the soil solution. Cabbage stem and root lengths as well as the number of leaves and biomass were greatly reduced in the polluted farms. In addition, the photosynthetic pigments, carbohydrates and proteins were decreased under pollution stress. The concentration of most investigated metals in the leaves and roots were increased with translocation factor greater than one for Pb, Cd, As, Cr, Ni, Fe, and Co. The study revealed that the HRI exceeded one for Pb and Cd in polluted and unpolluted plants; and Fe in polluted ones. Irrigation with wastewater is not suitable for cabbage as it has health risks on humans due to accumulation of heavy metals. It worth noting that, the high ability of cabbage plants to accumulate Pb and Cd from both polluted and unpolluted soils should be taken into consideration when consuming this plant.     

Phytoaccumulation of Heavy Metals in Natural Vegetation at the Municipal Wastewater Site in Abbottabad,Pakistan

Heavy metal accumulation in crops and soils from wastewater irrigation poses a significant threat to the human health. A study was carried out to investigate the removal potential of heavy metals (HM) by native plant species, namely Cannabis sativa L., Chenopodium album L., Datura stramonium L., Sonchus asper L., Amaranthus viridus L., Oenothera rosea (LHer), Xanthium stramonium L., Polygonum macalosa L., Nasturtium officinale L. and Conyza canadensis L. growing at the municipal wastewater site in Abbottabad city, Pakistan. The HM concentrations varied among plants depending on the species. Metal concentrations across species varied in the order iron (Fe) > zinc (Zn) > chromium (Cr) > nickel (Ni) > cadmium (Cd). Majority of the species accumulated more HM in roots than shoots. Among species, the concentrations (both in roots and shoots) were in the order C. sativa > C. album > X. stramonium > C. canadensis > A. viridus > N. officinale > P. macalosa > D. stramonium > S. asper > O. rosea. No species was identified as a hyperaccumulator. All species exhibited a translocation factor (TF) less than 1. Species like C. sativa, C. album and X. stramonium gave higher (> 1) biological concentration factor (BCF) and biological accumulation coefficient (BAC) especially for Fe, Cr and Cd than other species. Higher accumulation of heavy metals in these plant species signifies the general application of these species for phytostabilization and phytoextraction of HM from polluted soils.     

Bioremediation of Heavy Metals in Liquid Media Through Fungi Isolated from Contaminated Sources

Wastewater particularly from electroplating, paint, leather, metal and tanning industries contain enormous amount of heavy metals. Microorganisms including fungi have been reported to exclude heavy metals from wastewater through bioaccumulation and biosorption at low cost and in eco-friendly way. An attempt was, therefore, made to isolate fungi from sites contaminated with heavy metals for higher tolerance and removal of heavy metals from wastewater. Seventy-six fungal isolates tolerant to heavy metals like Pb, Cd, Cr and Ni were isolated from sewage, sludge and industrial effluents containing heavy metals. Four fungi (Phanerochaete chrysosporium, Aspegillus awamori, Aspergillus flavus, Trichoderma viride) also were included in this study. The majority of the fungal isolates were able to tolerate up to 400 ppm concentration of Pb, Cd, Cr and Ni. The most heavy metal tolerant fungi were studied for removal of heavy metals from liquid media at 50 ppm concentration. Results indicated removal of substantial amount of heavy metals by some of the fungi. With respect to Pb, Cd, Cr and Ni, maximum uptake of 59.67, 16.25, 0.55, and 0.55 mg/g was observed by fungi Pb3 (Aspergillus terreus), Trichoderma viride, Cr8 (Trichoderma longibrachiatum), and isolate Ni27 (A. niger) respectively. This indicated the potential of these fungi as biosorbent for removal of heavy metals from wastewater and industrial effluents containing higher concentration of heavy metals.     

STABILITY OF ENHANCED YIELD AND METAL UPTAKE BY SUNFLOWER MUTANTS FOR IMPROVED PHYTOREMEDIATION

Plant biomass and metal shoot accumulation are key factors for efficient phytoextraction. In a previous study, chemical mutagenesis has been used to improve the phytoextraction potential of sunflowers. The main goal of the present study was to assess the stability of sunflower mutants with improved biomass and metal accumulation properties in the 3^rd and 4th generations. As compared to control plants, the best M₃ mutants showed the following improvement of metal extraction: Cd 3–5-fold, Zn 4–5-fold, and Pb 3–5-fold. The best M₄ sunflowers also showed enhanced metal extraction: Cd 3–4- fold, Zn 5–7-fold, Pb 6–8-fold and Cr 5–7-fold. The control sunflower inbred line IBL 04, grown directly on the field, accumulated metals in individual organs in the following decreasing order: Cd and Zn: leaves > stem > roots > flower > seeds; Cr: roots > flower > seeds > leaves > stem. The best sunflower mutants showed either higher metal accumulation in shoots or enhanced metal accumulation in roots, suggesting to improved phytoextraction or rhizofiltration efficiency, respectively.     

公路绿化植物油松(Pinus tabulaeformis)和小叶杨(Populus simonii)对重金属元素的吸收与积累

对内蒙古西部公路绿化植物油松（Pinus tabulaeformis）、小叶杨（Populus simonii）及其根际土壤中重金属元素（Cd、Hg、Pb、Cu、Zn、Ni、Cr）和类金属元素（As和Se）含量以及根际土壤重金属（Cu、Zn、Pb、Ni和Cr）形态、土壤pH值进行了测定。对比分析了公路沿线不同绿化植物及其不同器官对重金属元素的吸收与积累特征。结果表明：绿化植物根际土壤对重金属元素的吸附及污染程度以Cd为最高。随原子序数的递增,小叶杨和油松两种植物的根部和茎叶两种营养器官中重金属的含量均表现出“N”字形变动趋势。而且重金属元素在不同植物不同器官中的含量具有Zn〉Cu〉Ni,Cr,As,Pb〉Cd〉Hg的基本规律。小叶杨茎叶对重金属元素Cr、Ni和Pb的富集能力较根部为强,油松茎叶对重金属元素Cr、Ni、Cu和Pb的富集能力较根部为强。绿化植物根际土壤重金属元素有效态占总量百分比的大小序列为Zn〉Pb〉Ni、Cr〉Cu,与重金属元素在不同植物不同器官中的含量大小序列Zn〉Cu〉Ni、Cr、As、Pb〉Cd〉Hg并非趋于一致。公路绿化植物对根际土壤中重金属元素的吸收和积累与重金属元素有效态所占的比例有关。     

Phytoaccumulation of Heavy Metals in Natural Plants Thriving on Wastewater Effluent at Hattar Industrial Estate,Pakistan

The objective of this research was to compare the potential of native plants for the phytoaccumulation of heavy metals (HM). Thirteen predominant plant species (including trees, bushes and grasses) namely Ricinus communis, Ipomoea carnea, Cannabis sativa, Parthenium hysterophorus, Acacia nilotica, Dalbergia sissoo, Acacia modesta, Solanum nigrum, Xanthium stromarium, Chenopodium album, Cynodon dactylon, Eleusine indica, and Dactyloctenium aegyptium were collected from the wastewater originated from Hattar industrial estate of Pakistan, Plants shoots and roots were analyzed for heavy metals / metalloid: Pb, Cr, Cd, Zn, Fe, Ni, and As. Among plant species, the accumulation potential for HM varied depending on the type of element. Regardless of the plant species, HM concentrations varied in the order of Fe > Zn > Cr > Pb > Ni > Cd > As. Tree species of R. communis, A. nilotica, A. modesta, and D. sissoo exhibited an enhanced concentrations of metals. Accumulation pattern of Fe, Pb, Cd, and As in plants could be related to the HM composition of soil and wastewater. Most of the species exhibited higher HM composition in the root as compared to shoot. The species that found with greater ability to absorb HM in the root, got higher HM concentrations in its shoot. Shoot tissue concentrations of HM were attained by the species as D. sissoo > A. modesta > A. nilotica > R. communis > I. carnea > C. album > E. indica > P. hysterophorus > S. nigrum > C. sativa > D. aegyptium > X. strumarium > C. dactylon. Based on results, tree plants were noticed as higher accumulators of HM in polluted soils.     

Heavy metal bioaccumulation by the organs of Phragmites australis (common reed) and their potential use as contamination indicators

The concentrations of heavy metals in the roots, rhizomes, stems and leaves of the aquatic macrophyte Phragmites australis (common reed), and in the corresponding water and sediment samples from the mouth area of the Imera Meridionale River (Sicily, Italy), were investigated to ascertain whether plant organs are characterized by differential accumulation, and to test the suitability of the various organs for heavy metal biomonitoring of water and soil. Heavy metals considered were Cd, Cr, Cu, Hg, Mn, Ni, Pb, Zn. Results showed that belowground organs were the primary areas of metal accumulation. In particular, metal concentrations in plant organs decreased in the order of root > rhizome ≥ leaf > stem. All four organs showed significant differences in concentration for Cr, Hg, Mn, Zn, thus suggesting low mobility from roots to rhizomes and to aboveground organs. Although the organs followed different decreasing trends of metal concentration, the trend Mn > Zn > Pb > Cu was found in each plant organ. Mn showed the highest concentrations in all organs whereas the lowest concentrations regarded Cd and Cr in the belowground and aboveground organs, respectively. The toxic threshold was exceeded by Cr in roots, rhizomes and leaves, Mn in roots and leaves, Ni in roots. The highest average concentrations were found as follows: Cd, Hg, Pb, Zn in root, Cr, Mn, Ni in sediment, Cu in water. Positive linear relationships were found between heavy metal concentrations in all plant organs and those in water and sediment, thus indicating the potential use of such organs for pollution monitoring of water and sediment. Advantages of using plant species as biomonitors, especially Phragmites australis, were also discussed.     

Accumulation and translocation of heavy metals in the canola (Brassica napus L.)—soil system in Yangtze River Delta, China

Aims and methods

Concentrations of heavy metals such as Cd, As, Hg, Pb, Cr, Cu, Zn and Ni in different tissues (seeds, roots and shoots) of the mature canola (Brassica napus L.) plants and in the associated rhizosphere soils from Yangtze River Delta (YRD) region of China, were determined to evaluate the heavy metals’ pollution in the soils and the canola seeds, and to discuss their accumulation and translocation characteristics in canola plants. At the same time, the phytoextraction potential of the canola plant for the above heavy metals was theoretically calculated and discussed on the basis of above measured data.

Results

The results showed that the concentration ranges of Cd, As, Hg, Pb, Cr, Cu, Zn and Ni in the rhizosphere soils were 0.115–0.481, 3.40–20.5, 0.069–0.682, 9.92–27.4, 46.8–86.6, 17.7–253.3, 65.2–511.7 and 16.0–37.8?mg?kg^?1, respectively. The concentrations of Cu, Zn and Hg at some sampling sites exceeded the 2nd grade threshods of Chinese national environmental quality standard for soils. The potential ecological risk of heavy metals in the canola rhizosphere soils decreased in the order of Zhejiang > Shanghai > Jiangsu provinces. The concentration ranges of above heavy metals in the canola seeds were 0.032–0.067, 0.002–0.005, 0.001–0.005, 0.053–0.165, 0.191–0.855, 3.01–13.20, 34.82–96.95 and 0.343–2.86?mg?kg^?1, respectively, with Cu and Zn at some sampling sites exceeding the permissible concentrations in foods of China. Heavy metals’ concentrations in canola seeds didn’t increase with their increasing concentrations in the rhizosphere soils. The bioconcentration factors (BCFs) of most heavy metals in the canola seeds decreased with their increasing concentrations in the associated rhizosphere soils. The average BCFs of heavy metals decreased in the order of Zn (0.488)>Cd (0.241)>Cu (0.145)>Ni (0.038)>Hg (0.021)>Pb (0.005)=Cr (0.005)>As (0.000) in the canola seeds, Cd (1.550)>Cu (0.595)>Zn (0.422)>Hg (0.138)>Ni (0.085)>Pb (0.080)>As (0.035)>Cr (0.031) in the roots, and Cd (0.846)>Zn (0.242)>Cu (0.205)>Hg (0.159)>Ni (0.031)>Pb (0.025)>As (0.012)>Cr (0.007) in the shoots, respectively. The accumulation capacity for most of the above heavy metals in the mature canola tissues was root > shoot > seed, with the exceptions of seed > root > shoot for Zn and shoot > root > seed for Hg. Except Hg from root to shoot and Zn from root to seed, translocation factors (TFs) of above heavy metals were lower than 1.0.

Conclusions

The concentrations, BCFs and TFs of above heavy metals in the canola tissues indicated that the investigated canola plants did not meet the criteria of hyperaccumulators for the above heavy metals. The phytoextracton potential of the studied canola plants for the above heavy metals from the polluted soils was very limited. It would take 920, 3,170 and 3,762?years (assuming two crops per year) to reduce the initial soil Zn, Cu and Hg concentrations, respectively, from the most polluted soil concentrations to the 2nd grade thresholds of Chinese national environmental quality standard for soils.     

Assessment of heavy metal induced stress responses in pea (Pisum sativum L.)

Exposure of plants to heavy metals severely affects their growth and physiological processes. Nevertheless, different plants show variable responses to different heavy metals, generally in a concentration-dependent manner. In this study, phytotoxic effects of cadmium (Cd), cobalt (Co) and lead (Pb) applied as chlorides at concentration 500, 750, 1000 and 1250 ppm were evaluated on seed germination, early seedling growth and dry biomass of pea (Pisum sativum L.). A lower concentration (500 ppm) of Pb promoted seed germination but declined other growth parameters. Higher concentration had a phytotoxic influence on the pea. Cd and Co severely affected germination and seedling growth of pea resulting in complete failure of germination and seedling growth at higher metal concentration. Tolerance index (TI) calculated for seed germination and dry biomass indicated that tested plant had zero tolerance to 1250 ppm of Cd as well as 750 ppm and higher concentrations of Co. The order of heavy metals for their phytotoxic effects was Co > Cd > Pb. The study suggests that P. sativum is relatively tolerant to Pb but highly sensitive to Co and Cd.     

Comparison of heavy metal phytoremediation in monoculture and intercropping systems of Phyllostachys praecox and Sedum plumbizincicola in polluted soil

A bamboo species (Phyllostachys praecox) and a Cd/Zn hyperaccumulator (Sedum plumbizincicola) were tested under different planting systems to compare their heavy metal phytoremediation ability. P. praecox (MP), S. plumbizincicola (MS) and P. praecox × S. plumbizincicola (IPS) plantations were established in Cu, Zn, and Cd-contaminated soil. Soil properties and heavy metal contents in plants were determined and compared after four years of plantation establishment. The rankings of available and total metal contents in soil layers were MP > MS > IPS (0–20 cm) and MP > IPS > MS (20–40 cm, except for Cu), respectively. The Cu and Zn contents in mature bamboo tissues were significantly lower, but the Cd contents in bamboo tissues (except for leaves) higher, in the IPS than in the MP. The bioconcentration and the translocation factors in most of bamboo tissues showed an increasing trend from the MP to the IPS. Heavy metal distribution in plants is greatly affected by the planting patterns. The tested intercropping system of two plant species showed higher biomass productivity, implying more heavy metals can be removed from the soil through the harvesting of plants. Therefore, the IPS leads to significant improvement of soil phytoremediation.     

Heavy metal accumulation in plants grown in heavily polluted soils

In a polluted area, samples of soils and plants were collected and analyzed in order to assess the mobility and accumulation of Cd, Pb and Zn in plants as influenced by the of different metal forms in soil. Metals were accumulated in roots. Metal mobility in plants decreased in the order Zn>Cd>Pb; it was generally lower in heavily polluted areas. The content of all the three metals in plant roots correlated with topsoil concentration of their 2 mol/L HNO₃-extractable forms. Besides, Cd and Zn correlated with exchangeable and Zn also with the organic form content. The concentration factor as a measure of metal mobility from soil to plants decreased with increasing level of contamination. Presented at the 4th Mini-Symposium on Biosorption and Microbial Degradation, Prague, Czech Republic, November 26–29, 1996.