Volume 1 Number 1 & 2 2007

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CONTENTS AND ABSTRACTS

Number 1

Po-Hsu Kao, Cheng-Chieh Huang, Zeng-Yei Hseu (Taiwan) Chemical Speciation and Phytotoxicity of Heavy Metals in Sewage Sludge for the Germination of Chinese Cabbage Seeds (pp 1-6)

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Original Research Paper: Single extractions with distilled water and diethylene-triamine-pentaacetic acid (DTPA), and a sequential extraction procedure were conducted in this study to determine the chemical speciation of Cd, Cr, Cu, Ni, Pb and Zn in four municipal sewage sludges and subsequently evaluate the phytotoxicity of the metals by a seed germination test of Chinese cabbage (Brassica chinensis L.). Analytical results indicated that a high percentage of organic carbon was found in all the sludges, and thus beneficial to application on agricultural land. Total concentrations of the heavy metals were much lower than the pollutant concentration limits for land application of sewage sludge in the USA and Europe. However, Cu and Zn were the most abundant elements in the sewage sludges in this study. In most cases, the water extractable contents of the heavy metals in the sludges were undetectable. However, the heavy metal contents with DTPA extraction were much higher than those with water extraction, respectively. Additionally, the Fe-Mn oxide fraction of Zn was the dominant solid phase, but Zn was the most mobile metal in all the sludges. Lead and Cr were concentrated in residual fractions, while Cu showed the organic fraction as being dominant. The seed germination test of Chinese cabbage showed no significant (p<0.05) inhibition by the sludge extracts with different dilution ratios, but the original sludge extracts inhibited the root growth of Chinese cabbage. Copper, Ni and Zn might cause toxicity to plant growth, as demonstrated in this study.

Reda A. Abou-Shanab, Hanan A. Ghozlan, Khaled M. Ghanem, Hassan A. Moawad (Egypt) Heavy Metals in Soils and Plants from Various Metal-Contaminated Sites in Egypt (pp 7-12)

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Original Research Paper: A field-survey of higher plants growing in metal-contaminated sites in Egypt was conducted to examine the scope and magnitude of metal/soil contamination in Egypt, and to determine the existence of Egyptian plant flora that accumulate large concentrations of metals in their shoots which might be useful in phytoremediation. Eight sites were investigated in northwestern Egypt, the Nile Delta region, and southeastern parts of the country. Soil samples and 61 plant species were collected from these sites and were analysed for Cd, Cr, Co, Cu, Fe, Ni, Pb, and Zn. Each soil exhibited a high concentration of one or more metals. Maximum Cr and Ni contents were observed in Diplachne fusca (674 mg Cr kg^-1 and 253 mg Ni kg^-1 DM). The highest Cu concentration (174 mg kg^-1) was observed in Urtica urens. The concentration of Pb in Conyza discoridies (508 mg kg^-1) was 11 times greater than the total Pb concentration in soil. Cichorium endivia contained 938 mg Zn kg^-1 that was approximately two-fold the maximum value of Zn in the uncontaminated plant samples.

Number 2

S.B. Agrawal, Anita Singh, R.K. Sharma, M. Agrawal (India) Bioaccumulation of Heavy Metals in Vegetables: A Threat to Human Health (pp 13-23)

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Invited Review: Rapid growth in urbanization and industrialization has increased the levels of heavy metals in the environment and consequently in the food chain. Consumption of contaminated food by human beings and other animals may pose a serious threat to their health. Vegetables are a major portion of the human diet, providing micro- and macronutrients, fibers, antioxidants, vitamins, etc. Vegetables are often grown in suburban areas commonly contaminated with heavy metals. Depending on the nature of vegetables, some of them have a great potential to accumulate higher concentrations of heavy metals than others. The present review describes the uptake and accumulation of heavy metals in vegetables, their role in remediation of heavy metals from contaminated areas and the negative impact of heavy metals on vegetables and human health through their consumption.

Fabio Alexandre Chinalia (Ireland), Mirna Helena Regali-Seleghin, Elisete Marcia Correa (Brazil) 2,4-D Toxicity: Cause, Effect and Control (pp 24-33)

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Invited Review: The herbicide 2,4-Dichlorophenoxyacetic acid (2,4-D) is one of the many different man-made agrochemicals in use today. This herbicide has a deleterious hormonal effect increasing DNA, RNA and protein synthesis in plants, especially in meristematic tissues of broad-leaved weeds, which are the commonly targeted organisms. This compound can also be used in water reservoirs for the control of algae and it can be toxic for several trophic levels. The mechanism of action for non-targeted organisms is not fully elucidated but the herbicide alters cellular membrane integrity and acts by inhibiting enzymatic complexes involved in electron transfer, stress response to reactive oxygen compounds and oxidative phosphorylation. The herbicide has low to moderate acute toxicity towards humans and animals, but some results suggest a chronicle and/or genotoxic metabolic disturbances. Once applied to the soil the risks of being transported to and by aquatic systems are complex and case-specific, but often associated with several other controlling variables apart from the presence of microorganisms capable of carrying out biodegradation. 2,4-D is commonly degraded by several strains in weeks or in a few months and phylogenetic analyses indicate independent recruitment of the 2,4-D catabolic pathway. However, this gene transference is rarely discussed in the context of biosafety and/or its influence on the microbial ecology of natural communities. Several bioremediation strategies are reported to control 2,4-D contamination and toxicity by commonly altering the indigenous microbial communities’ structure and/or metabolism. Policies related to pesticides might also affect the environmental contamination by 2,4-D once this compound can be used as an alternative to replace more toxic ones.

Susana Rodríguez Couto, José L. Toca Herrera (Spain) Laccases in Pollution Control (pp 34-45)

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Invited Review: Environmental pollution with hazardous wastes containing recalcitrant synthetic chemicals (xenobiotics) has become one of the major ecological problems. Unlike the naturally-occurring organic compounds that are readily degraded upon introduction into the environment, xenobiotics are extremely resistant to biodegradation by native microorganisms. Additionally, the implementation of more and more stringent environmental regulations on hazardous wastes has impelled the search for innovative and environmentally-friendly treatment technologies to complement or substitute the conventional ones. Thus, a great deal of research has recently been focused on investigating the potential arising from the use of enzymes that have been isolated from their parent organisms to catalyse the transformation of targeted pollutants. Among such enzymes, laccases (benzenediol: oxygen oxidoreductases; EC 1.10.3.2) are outstanding, since they have the following properties: low substrate specificity, they do not need the addition or synthesis of a cofactor, as their cosubstrate - oxygen - is usually present in their environment, most laccases are extracellular which facilitates the purification procedures, they generally exhibit a considerable level of stability in the extracellular environment and the inducible expression of laccases in most fungal species also contributes to their easy applicability in biotechnological processes. All this makes laccase enzymes very useful for their application in bioremediation of polluted sites. The present paper reviews the potential application of laccases in pollution control.

Michael W.H. Evangelou, Mathias Ebel, Andreas Schaeffer (Germany) Tobacco (Nicotiana Tabacum) a Potent Phytoremediator (pp 46-53)

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Invited Mini-Review: The low-cost, plant-based phytoremediation technique has often been described as a promising technique to remediate agricultural land contaminated with organic and inorganic pollutants. The plants used, have to meet certain requirements, which are fulfilled by tobacco (Nicotiana tabacum). It is a fast growing plant with a high biomass, which is easily harvested. Its propagation is simple, as each plant generates thousands of seeds. It can prosper everywhere between the 50^th latitude north and the 40^th latitude south and has no demanding requirements on temperature, humidity and soil conditions. Tobacco has also revealed a high tolerance for various organic and inorganic pollutants. It can accumulate heavy metals in relatively high-levels, especially Cd, in comparison to other species and has also shown not be susceptible to various organic pollutants, such as polychlorinated biphenyls (PCB) and trinitrotoluene (TNT). Its rapid growth, high leave biomass and its high disposition for transformation has made tobacco an optimal plant for genetic engineering. It has not only been applied in the field of medicine, e.g. production of antibodies, but also in the area of phytoremediation. Metal chelator, metal transporter, metallothionein (MT), and phytochelatin (PC) genes have been transferred to plants for improved metal uptake and sequestration. Also the expression of bacterial enzymes has enabled the reduction of phytotoxicty or the concentration reduction of various organic pollutants.

Uchechukwu E. Ezeji, Sylvia O. Anyadoh, Vincent I. Ibekwe (Nigeria) Clean up of Crude Oil-Contaminated Soil (pp 54-59)

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Invited Mini-Review: Crude oil contamination of the environment has been an age-long phenomenon and a serious subject of concern. The effect of oil on soil depends on the size, quantity and grade of oil spilled. Crude oil contamination does not damage the soil permanently but has some adverse effects on crops and other vegetation. Over the years attempts have been made to find the cheapest, most efficient and environmentally-friendly method for the clean-up crude oil contaminated soil. This review is aimed at analysing the different methods used in the clean-up of contaminated soil. Crude oil contaminated soil can be cleaned up using physico-chemical, thermal and biological treatments. The first two methods have been found to be grossly inadequate and ineffective, and may result in further contamination. Biological methods (bioremediation and phytoremediation) have received considerable attention during the last few years as the most promising and environmentally benign technique for effective clean-up of crude oil contaminated soil. A wide range of bioremediation strategies is being developed to treat contaminated soil.

J.C. Igwe (Nigeria) A Review of Potentially Low Cost Sorbents for Heavy Metal Removal and Recovery (pp 60-69)

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Invited Review: The incidence of toxic substances in the environment has increased as a result of industrialization. These toxic substances are mostly found in wastewater effluents. Heavy metals are one group of these toxic substances, whose toxicity to both man and the environment has been on the increase. The environmentally adverse effects of heavy metal toxicity are so much that their removal and recovery have become very important. Many conventional methods of heavy metal removal from aqueous streams have been used, including: precipitation, ion exchange, coagulation, reverse osmosis, adsorption, among others. These conventional methods are very expensive and sometimes generate effluent sludge, which causes more disposal problems. Bioremediation of these heavy metals using low cost biosorbents have been in focus recently. These consist of a group of applications, which involve the detoxification of hazardous substances by means of microbes and plants, instead of transferring them from one medium to another. This process is characterized as less disruptive and can often be carried out on site, eliminating the need to transport the toxic materials to treatment sites. Biosorbents are prepared from naturally abundant and/or waste biomass. Due to the high uptake capacity and cost effective source of the raw materials, biosorption is a progression towards a perspective method. Therefore, this paper reviews the toxicity of heavy metals and the use of potentially low cost sorbents for their removal. The removal efficiency of these heavy metals using biosorbents compares favourably with conventional adsorbents based on certain sorption parameters, hence making biosorbents a viable alternative for metal removal and recovery.

K.S. Sagyndyk, S.S. Aidossova (Kazakhstan), M.N.V. Prasad (India) Grasses Tolerant to Radionuclides Growing in Kazakhstan Nuclear Test Sites Exhibit Structural and Ultrastructural Changes - Implications for Phytoremediation and Involved Risks (pp 70-77)

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Original Research Paper: The vegetation of the study area in Kazakhstan represents steppes predominated by xerophytic grasses such as Stipa capillata, Festuca valesiaca and Agropyron cristatum. This region is contaminated by radionuclides, products of 357 underground nuclear explosions and tests carried out during 1949 to 1989. This area is being used as grazing land and partly for mining (coal and gold). Focussed radioecological and radiophytoremediation investigations on the migration of radionuclides from underground water into soils, translocation to plant aerial parts, the transfer factor and concomitant effects on the food chain viz., underground water-soils-plants-animals are rather scanty. This paper details the anatomical structural changes in the stems and leaves of the abundant grasses viz. S. capillata, F. valesiaca and A. cristatum due to radionuclides and the implications for radiophytoremedition and involved risks.

J.C. Schulenburg, P.J. Dillon, K.M. Somers, J.G. Winter (Canada) The Impact of Golf Course Construction on Benthic Macroinvertebrate Communities: An Evaluation of Bioassessment Techniques (pp 78-90)

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Original Research Paper: There are numerous methods for assessing Benthic Macroinvertebrate (BMI) community heath using the Reference Condition Approach (RCA); however, no standard method of BMI analysis has been established. This study attempted to evaluate four distance measures and determined the most robust method for producing benthic indices that can be used in a multivariate approach. In Muskoka, BMI stream communities were collected from test sites located on golf courses that were at various stages of construction to being fully operational. BMI communities were also collected at references sites from streams that were considered to be relatively pristine. With this study design each site was classified according to one of four land-use categories. The classified BMI data were then used to calculate the four distance measures. These were Jaccard (presence and absence), Chi-square, Bray-Curtis based on BMI taxonomic group abundances, and Bray-Curtis on benthic indices. Criteria used to evaluate the distance measures were strength of correlations with NMDS axes; average Euclidean distance among land-use group means; temporal variability; number of Mantel tests that were significant between BMI and land-use matrices; and number of Mantel tests that were not significant between BMI and physical-geographic matrices. Each measure had different strengths, but Bray-Curtis based on benthic indices scored the best according to the criteria. In conclusion the first three axes from this distance measure are recommended to be used as BMI indices in bioassessment. Testing and compensating for temporal and spatial variation were found to be necessary when using any distance measure to calculate BMI indices.

Q. Sun (China), Z.L. He (China/USA), X.E. Yang, X.N. Guo (China) Effects of Copper Contamination on Enzyme Activities in Paddy Soils (pp 91-95)

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Original Research Paper: Soil contamination by heavy metals has rapidly increased in Southern China in the last decade due to rapid development of industries. One of the concerns regarding heavy metal pollution is the impact on soil functions. Enzyme activity, one of the important biochemical properties that is related to soil functions, has been reported to quickly respond to external heavy metal input. Laboratory and incubation studies were conducted to investigate the effects of anthropogenic loading of copper (Cu) on the activities of catalase, urease, invertase, and acid phosphatase in three paddy soils. The results indicate that external Cu²⁺ loading caused a significant reduction in the activities of all the four enzymes and the reduction (18-87%) was positively related to the increase in Cu²⁺ input from 0 to 1600 mg kg^-1 soil. However, the pattern of response varied between soil types and among the different Cu²⁺ loading rates. The activities of invertase in purplish clayey soil (PCS) and catalase in PCS and yellowish red soil (YRS) were stimulated at low Cu²⁺ loadings (<200 mg.kg^-1) although external Cu²⁺ loading generally resulted in inhibition of activities for all the four enzymes, especially at higher loading rates (>200 mg kg^-1). Urease was the most sensitive whereas catalase was the most tolerant to Cu²⁺ contamination. The mean ED₅₀ (ecological dose) of Cu²⁺ across the three soils was 652 mg.kg^-1 for phophatase, 431 mg.kg^-1 for invertase, and 269 mg.kg^-1 for urease. These critical values varied with soil type, likely due to differences in soil properties and the nature of the enzyme. Based on the ED₅₀ values of Cu for urease, the upper limits of Cu²⁺ contamination were 316 mg.kg^-1, 312 mg.kg^-1, and 180 mg.kg^-1, respectively, for the PCS, YRS, and silt loam soil (SLS).