Sewage Sludge-amended Soil Research Articles

The effect of PCB-contaminated sewage sludge and sediment on metabolism of cucumber plants (Cucumis sativus L.)

Increasing amounts of sewage sludge are produced nowadays, which need to be disposed of in a safe and responsible manner. Likewise, bottom sediments from small urban water bodies undergo periodical dredging and need to be utilized. These deposits often contain Persistant Organic Pollutants (POPs) and other toxic substances. Plants can be used to reduce these pollutants during or before disposal to land (phytoremediation). Cucurbitaceae are known to accumulate high levels of POPs, including polychlorinated biphenyls (PCB), compared with other plant species but such accumulation may lead to secondary oxidative stress that may limit their value. This study examined the impact of sewage sludge and urban lake sediment on soil toxicity, measured as PCB concentration, and changes in the antioxidative system of cucumber plants grown in the soils.There was an average reduction of PCB by 38.63% and 27.38% in soil amended with sewage sludge and sediment, respectively after 5 weeks of cucumber plant cultivation. In the case of plants grown with sewage sludge, guaiacol peroxidase (POx) activity significantly decreased to 49% of the control at the highest dose given, while that of glutathione S-transferase (GST) increased to 172% of the control value in the same treatment. α-Tocopherol concentration was higher in the plants grown in the sewage sludge amended soil.

Copper desorption kinetics in wheat (Triticum aestivum L.) rhizosphere in some sewage sludge amended soils

Rhizosphere has different chemical and biological properties from bulk soils. Information about copper (Cu) desorption characteristics in the rhizosphere soils is limited. The objectives of this study were to determine Cu desorption characteristics and the correlation of its parameters with Cu extracted by DTPA-TEA, AB-DTPA and Mehlich 3 in bulk and rhizosphere amended soils with sewage sludge (10 g of sewage sludge was added to 1 kg soil) under greenhouse conditions in a rhizobox. The kinetics of Cu desorption in the rhizosphere and bulk was determined by successive extraction with DTPA-TEA in a period of 1 to 504 h at 25 ± 1 °C. The results showed that Cu extracted using several chemical extractants in the rhizosphere were significantly (P < 0.05) lower than in the bulk amended soils. In addition, Cu extracted using successive extraction in the rhizosphere were significantly (P < 0.01) lower than in the bulk soils. The best model for describing extraction data for the bulk and rhizosphere soils was the parabolic diffusion equation. Desorption kinetics of Cu conformed fairly well to first order and power function models. The results indicated that Cu diffusion rate in the wheat rhizosphere soils lower than in the bulk soils. Cu desorption rate in parabolic diffusion ranged from 0.326 to 0.580 mg kg−1 h−1/2 in the bulk soils, while it ranged from 0.282 to 0.490 mg kg−1 h−1/2 in the rhizosphere soils. Significant correlation (P < 0.05) between determine R values of parabolic diffusion and Cu desorption during 504 h with extracted Cu using DTPA-TEA, AB-DTPA and Mehlich 3 were found in the bulk and the rhizosphere soils. The results of this research revealed that Cu desorption characteristics in the wheat rhizosphere soils are quite different from bulk soils amended with sewage sludge.

Nitrogen metabolism is related to improved water‐use efficiency of nodulated alfalfa grown with sewage sludge under drought

AbstractLeguminous plants grown in sewage sludge–amended soils can acquire nitrogen by assimilation of nitrate and ammonium from the soil solution or from atmospheric‐dinitrogen (N2) fixation through association with N2‐fixing bacteria. We proposed that operation of both metabolic processes could contribute to alleviate the impact of drought in sludge‐treated plants. A greenhouse experiment was conducted to evaluate the involvement of nodule metabolism in the use efficiency of water and N in sludge‐treated plants. Treatments comprised (1) plants inoculated with rhizobia and amended with sewage sludge; (2) plants inoculated with rhizobia without any amendment; and (3) noninoculated plants supplied with ammonium nitrate, each under well‐watered and drought conditions. Under drought, sludge‐treated plants had increased plant growth and higher photosynthetic and water‐use efficiencies than untreated plants. Drought stimulated nitrate reductase and GS/GOGAT activities but did not affect the activities of phosphoenolpyruvate carboxylase and malate dehydrogenase or the leghemoglobin concentration. The results suggest that under drought conditions, both N2 fixation and nitrate assimilation in nodules of sludge‐treated plants contributed to improve plant N supply and to increase the drought tolerance of alfalfa.

Effect of wheat (Triticum aestivumL.) rhizosphere on fractionations of copper in some sewage sludge amended soils

Our purpose was to quantify the effect of rhizosphere processes on the fractions of Copper (Cu) in 10 soils amended with sewage sludge under greenhouse conditions by using a rhizobox. For amended soils, 1% (w/w) of sewage sludge was added to soil samples and then amended soils were incubated at field capacity, for 1 month. After incubation, soils were put in rhizobox and seeds of wheat were planted. Plants were harvested after 8 weeks and rhizosphere and bulk soils were separated. Fractions of Cu in the rhizosphere and bulk soils were determined. The results showed that Cu extracted using several extractants in rhizospheric soils were significantly (P<0.01) lower than in bulk soils. In the rhizosphere of amended soils the average of residual Cu, Cu associated with iron-manganese oxides, Cu associated with organic matter, Cu associated with carbonates and exchangeable Cu were 18.8, 2.10, 1.00, 0.37 and 0.24 mg kg -1 respectively, whereas above fractions in the bulk soils were 18.1, 2.43, 0.80, 0.42 and 0.30 mg kg -1 respectively. This study illustrated that Cu-fractions in the wheat rhizosphere were different compare to bulk soils in sewage sludge amended soils.

Bioremediation of Hydrocarbon Contaminated Soil Using Selected Organic Wastes

Traditionally soil remediation has been known to be among the most expensive treatments in the world. Thus, various strategies have been opted to investigate the most cost-effective solution to deal with contaminated sites. Among the highly potential approach is bioremediation since many studies have reported of its effectiveness in removing numerous pollutants from many contaminated sites. It mainly involved biostimulation where organic or inorganic components were introduced to enhance indigenous microbial growth that directly degrades the contaminants. This paper aims to identify potential organic wastes in enhancing the biodegradation of used lubricating oil in contaminated soil. To achieve the objective, sewage sludge and cow dung were selected as the organic components to be added individually into the 10% (w/w) used lubricant oil-contaminated soil. Each set up with 1.5kg of used lubricant oil-contaminated soil were added with 10% of the organic matter (sewage sludge or cow dung) and left for degradation for 98 days in plastic vessels. Periodic sampling of soil from each vessel was carried out at 14 days interval for total petroleum hydrocarbon analysis, and isolation and enumeration of bacteria. Results indicated that after 98 days of exposure to the organic matters, biodegradation of used lubricant in the soil were much higher than that of the control set-ups. Cow dung amended set-ups showed 94% biodegradation while sewage sludge amendment gave 82%, as compared to the control set-up (56%). This probably was due to the presence of additional nutrient in the organic matter amended soil which enhanced the indigenous microbes’ degradation capabilities. As for the performance, the biodegradation rate of the two organic matters differed due to the differences in the nutrient content, particularly of available N and P. In addition, cow dung amended-soil was found to have improved soil physiochemical characteristics that enabled speedy adaption by the microbes to the contaminated soil. Statistical analysis indicated a significant difference at P<0.05. Based on the first order kinetics model, cow dung amended soil gave the highest biodegradation rate of 0.2086/day with used-lubricant half-life of 3.32 day. On the other hand, sewage sludge amended soil has a biodegradation rate of 0.149/day with used-lubricant half-life of 4.65 days. These biodegradation rates were significantly higher than that of the control soil (0.0915/day) and autoclaved soil (0.0309/day). As for the microbial counts, cow dung amended soil recorded (69–122) ×107 CFU/g while sewage sludge amended soil recorded (63–96) × 107 CFU/g. On the other hand the control soil recorded (52–73) ×107 CFU/g. Again, the presence of available nutrients required by the microbes could be the contributing factor to the high distribution of microbes in the organic matter amended soil as compared to the control soil. In conclusion, cow dung and sewage sludge can be an effective organic amendment for the biodegradation of used lubricant contaminated soil. Both organic matters proved to enhance the multiplication of indigenous microbes thus enabling rapid biodegradation of the contaminant in the soil.

Zinc desorption kinetics in wheat (Triticum Aestivum L.) rhizosphere in some sewage sludge amended soils

Abstract The objectives of this study were to determine Zn desorption characteristics and the correlation of these parameters with Zn extracted by DTPA-TEA method in bulk and rhizosphere amended soils with sewage sludge under greenhouse conditions by using a rhizobox. For amended soils 10 g of sewage sludge was added to 1 kg of 10 soil samples. The kinetics of Zn desorption in bulk and rhizosphere was determined by successive extraction with DTPA-TEA in a period of 1 to 504 h at 25±1 0 C. The results showed that Zn extracted using successive extraction in the rhizosphere were significantly ( p <0.01) higher than in the bulk amended soils. The best model for describing extraction data for bulk and rhizosphere soils was the power function equation. The results indicated that Zn desorption rate in the wheat rhizosphere soils more than bulk soils. The results showed that significant correlation ( p <0.05) between Zn desorption characteristics and DTPA-TEA-Zn were found in the bulk and rhizosphere soils. The results of this research revealed that Zn desorption characteristics that are help to estimate the Zn supplying power of soils in the wheat rhizosphere, are quite different than bulk amended with sewage sludge.

Distribution and Mobility of Zn, Pb and Cd in a Sewage Sludge-Amended Soil

The distribution of the metallic trace elements (MTE) Zn, Pb and Cd in a sludge-amended soil and their partitioning in specific soil microystems are studied by comparing their contents in amended and control soils. This comparison is achieved at the metric scale of the bulk soil horizons and at the micrometric scale of the weathering microsites (weathering rock-forming minerals and their specific weathered products). The chemical analyses of the MTE in the bulk samples do not show any anthropic contamination of the amended soil with repeated sewage sludge spreading. The chemical analyses of the bulk

Application of a battery of biotests for the determination of leachate toxicity to bacteria and invertebrates from sewage sludge-amended soil

The objective of the study was to determine the leachates toxicity from sewage sludge-amended soils (sandy and loamy). Samples originated from a plot experiment realized over a period of 29 months. Two types of soil were fertilized with sewage sludges at the dose of 3 % (90 t/ha). Soil samples were taken after 0, 7, 17, and 29 months from the application of sewage sludges. Leachates were obtained according to the EN 12457–2 protocol. The following commercial tests were applied for the estimation of the toxicity: Microtox (Vibrio fischeri), Microbial assay for toxic risk assessment (ten bacteria and one yeast), Protoxkit F™ (Tetrahymena thermophila), Rotoxkit F™ (Brachionus calyciflorus), and Daphtoxkit F™ (Daphnia magna). The test organisms displayed varied toxicity with relation to the soils amended with sewage sludges. The toxicity of the leachates depended both on the soil type and on the kind of sewage sludge applied. Notable differences were also observed in the sensitivity of the test organisms to the presence of sewage sludge in the soil. The highest sensitivity was a characteristic of B. calyciflorus, while the lowest sensitivity to the presence of the sludges was revealed by the protozoa T. thermophila. Throughout the periods of the study, constant variations of toxicity were observed for most of the test organisms. The intensity as well as the range of those variations depended both on the kind of test organism and on the kind of sludge and soil type. In most cases, an increase of the toxicity of soils amended with the sewage sludges was observed after 29 months of the experiment.Electronic supplementary materialThe online version of this article (doi:10.1007/s11356-012-1268-3) contains supplementary material, which is available to authorized users.

The Phytotoxicity Changes of Sewage Sludge-Amended Soils

The aim of the present study was the estimation of changes in the phytotoxicity of soils amended with sewage sludge with relation to Lepidium sativum, Sinapis alba and Sorghum saccharatum. The study was realised in the system of a plot experiment for a period of 29 months. Samples for analyses were taken at the beginning of the experiment, and then after 5, 17 and 29 months. Two kinds of sewage sludge, with varying properties, were added to a sandy soil (soil S) or a loamy soil (soil L) at the dose of 90 t/ha. The addition of sewage sludge to the soils at the start of the experiment caused a significant reduction of both seed germination capacity and root length of the test plants, the toxic effect being distinctly related to the test plant species. With the passage of time the negative effect of sewage sludge weakened, the extent of its reduction depending both of the kind of sewage sludge applied and on the type of soil. Phytotoxicity of the soils amended with the sewage sludges was significantly lower at the end of the experiment than at the beginning. The species of the plants grown on the soils also had a significant effect on their phytotoxicity. The greatest reduction of toxicity was observed in the soil on which no plants were grown (sandy soil) and in the soil under a culture of willow (loamy soil). Solid phase of sewage sludge-amended soils was characterised by higher toxicity than their extracts.Electronic supplementary materialThe online version of this article (doi:10.1007/s11270-012-1248-8) contains supplementary material, which is available to authorized users.

Long-term amendment of Spanish soils with sewage sludge: Effects on soil functioning

Wastewater treatment processes generate highly biodegradable solid wastes. As their fate is an environmental issue of great concern, public administrations promote a sustainable management of urban wastes. The objective of the present study was to analyze the systematic and periodical use, for 16 years, of anaerobically digested sewage sludge as an agricultural fertilizer by assessing the effects on some soil physical–chemical, functional, and ecotoxicological properties. The results showed that the input of sludge enhances soil properties proportionally to the application doses and/or frequency. The organic amendments increased the organic matter content (and its aromaticity), the soil nitrogen, and the microbial activity, improving carbon and nitrogen mineralization processes and some enzymatic functions. However, a maximum dose was identified (40Mgha−1year−1), beyond which soil properties do not improve, and may even worsen. Regarding environmental risks, although the bioluminescent bacteria test showed no toxicity on soil extracts, potential adverse effects such as some potentially toxic elements accumulation, phytotoxicity and the likelihood of groundwater pollution by nitrates or dissolved organic matter should be taken into account. The complementarity of studying soil functioning parameters and ecotoxicological effects, together with the analysis of pollutant content, must be enhanced. This assures a more realistic assessment of long-term effects of sewage sludge-amended soils.

Characteristics of heavy metal accumulation on fly ash- and sewage sludge-amended calcific soil

Land disposal of fly ash (FA) and sewage sludge (SS) is a major problem due largely to their potentially harmful constituents. In this paper, a potting experiment was performed to evaluate the effects on the plant growth and to discuss in particular the potential hazard to soils and plants according to the characteristics of heavy metal accumulation and migration when FA and SS are used as the amendments of calcific soil in a limestone mining area. The results showed that the application of FA-SS mixture is capable of accelerating the growth of plants and improving the biomass production at either 1:1 or 1:2 FA-SS mixture: soil (w/w). The highest yields were obtained at 1:1 (w/w) mixing ratio. When compared with the Element Background Values of Soils in China, the analysis on heavy metals indicated that the contents of Pb, Cr, Hg, Cd, As, Ni, Cu and Zn in the amended soils came up to the second-class environmental quality standards, only Hg and Cd showed significant accumulation. At the same time, though the metal concentrations in roots were higher than those for the control, the concentrations except Cu, Zn in shoots were lower. And all the heavy metal contents in the plants were substantially lower than the toxicity limits. The results indicated that the combined use of FA and SS at a rational rate of application should pose no danger to both soil and food chain based on the characteristics of the FS and SS, heavy metals and calcific soil.

Mudanças químicas e fitodisponibilidade de zinco estimada por método isotópico, em solo tratado com lodo de esgoto

Zn availability in Red Latossol (Rhodic Ferralsol) of different pH amended with different rates of sewage sludge was studied by the isotopic 65Zn L value method. Soil chemical properties were found to be altered by SS addition. Zn concentration and Zn derived from SS (ZnpfSS) in plant, and Zn phytoavailability (L value), were increased with increasing SS rates. The linear correlation coefficient of plant Zn with SS rates and with L value was significant at 1% probability. The L value proved an efficient method for predicting Zn phytoavailability in sewage sludge-amended soil with different pH under the soil conditions studied.

Modification to degradation of hexazinone in forest soils amended with sewage sludge

Influences of one sewage sludge on degradation of hexazinone and formation of its major metabolites were investigated in four forest soils (A, B, C and D), collected in Zhejiang Province, China. In non-amended forest soils, the degradation half-life of hexazinone was 21.4, 30.4, 19.4 and 32.8 days in forest soil A, B, C and D, respectively. Degradation could start in soil A and C without lag period because the two soils had been contaminated by this herbicide for a long time, possibly leading to completion of acclimation period of hexazinone-degrading bacteria. In forest soils amended with sewage sludge, the degradation rate constant increased by 17.3% in soil A, 48.2% in soil B, 8.1% in soil C and 51.6% in soil D, respectively. The higher degradation rates (soil A and C) in non-amended soils accord with the lower rate increase in sewage sludge-amended soils. Under non-sterile conditions, biological mechanism accounted for 51.8–62.4% of hexazinone degradation in four soils. Under sterile conditions, the four soils had the similar chemical degradation capacity for hexazinone. In non-amended soil B, only one metabolite (B) was detected, while two metabolites (B and C) were found in sewage sludge-amended soil B. Similarly situated in agricultural soils, N-demethylation at 6-position of triazine ring, hydroxylation at the 4-positon of cyclohexyl group, and removal of the dimethylamino group with formation of a carbonyl group at 6-position of triazine ring appear to be the principal mechanism involved in hexazinone degradation in sewage sludge-amended forest soils. These data will improve understanding of the actual pollution risk as a result of forest soil fertilization with sewage sludge.

Improving substrate fertility to enhance growth and reproductive ability of a Pinus halepensis Mill. afforestation in a restored limestone quarry

We have evaluated the effects of improving substrate fertility on the growth and reproduction of a P. halepensis plantation in a restored limestone quarry on a stony calcareous regolith (R plots). The natural substrate was supplemented by adding a 0.2 m layer of a fine textured soil (RS plots) or a sewage sludge amended soil (RSS plots). The treatments were performed when the pines were 7 years old, and tree growth (height and trunk and canopy diameter) was monitored over the subsequent 12 years. The reproductive status of the trees was also measured when the pines were 20 years old. Tree growth was proportional to the amount of soil nutrients: 12 years after treatment the mean height of the R, RS and RSS trees was 1.5, 3.1 and 6.2 m respectively and growth increases over the baseline were 76, 264 and 632%. The treatment also affected the age of onset of reproduction (15, 11 and 9 years, respectively), the average number of cones per tree (12, 43 and 61), and the amount of seeds per cone (37, 52 and 72), but did not modify the germination percentage of pine seeds (ca 71.5%). Soil organic carbon increased proportionally to the vegetation development, contributing to carbon sequestration. These results suggest that improving the nutritional status of the soil not only improves the growth of trees, but it also ameliorates their reproductive ability (earlier reproduction onset and larger seed crop size). Implications for soil restoration through afforestation are also discussed.

Impacts of anthropogenic activity on the ecology of class 1 integrons and integron-associated genes in the environment.

The impact of human activity on the selection for antibiotic resistance in the environment is largely unknown, although considerable amounts of antibiotics are introduced through domestic wastewater and farm animal waste. Selection for resistance may occur by exposure to antibiotic residues or by co-selection for mobile genetic elements (MGEs) which carry genes of varying activity. Class 1 integrons are genetic elements that carry antibiotic and quaternary ammonium compound (QAC) resistance genes that confer resistance to detergents and biocides. This study aimed to investigate the prevalence and diversity of class 1 integron and integron-associated QAC resistance genes in bacteria associated with industrial waste, sewage sludge and pig slurry. We show that prevalence of class 1 integrons is higher in bacteria exposed to detergents and/or antibiotic residues, specifically in sewage sludge and pig slurry compared with agricultural soils to which these waste products are amended. We also show that QAC resistance genes are more prevalent in the presence of detergents. Studies of class 1 integron prevalence in sewage sludge amended soil showed measurable differences compared with controls. Insertion sequence elements were discovered in integrons from QAC contaminated sediment, acting as powerful promoters likely to upregulate cassette gene expression. On the basis of this data, >1 × 10(19) bacteria carrying class 1 integrons enter the United Kingdom environment by disposal of sewage sludge each year.

Effect of silver nanoparticle surface coating on bioaccumulation and reproductive toxicity in earthworms (Eisenia fetida)

The purpose of this study was to investigate the effect of surface coating on the toxicity of silver nanoparticles (Ag NPs) soil. Earthworms (Eisenia fetida) were exposed to AgNO3 and Ag NPs with similar size ranges coated with either polyvinylpyrrolidone (hydrophilic) or oleic acid (amphiphilic) during a standard sub-chronic reproduction toxicity test. No significant effects on growth or mortality were observed within any of the test treatments. Significant decreases in reproduction were seen in earthworms exposed to AgNO3, (94.21 mg kg-1) as well as earthworms exposed to Ag NPs with either coating (727.6 mg kg-1 for oleic acid and 773.3 mg kg-1 for polyvinylpyrrolidone). The concentrations of Ag NPs at which effects were observed are much higher than predicted concentrations of Ag NPs in sewage sludge amended soils; however, the concentrations at which adverse effects of AgNO3 were observed are similar to the highest concentrations of Ag presently observed in sewage sludge in the United States. Earthworms accumulated Ag in a concentration-dependent manner from all Ag sources, with more Ag accumulating in tissues from AgNO3 compared to earthorms exposed to equivalent concentrations of Ag NPs. No differences were observed in Ag accumulation or toxicity between earthworms exposed to Ag NPs with polyvinylpyrrolidone or oleic acid coatings.

Biomass production and nutrient concentration of kenaf grown on sewage sludge-amended soil

Due to increasingly strict control of wastewater treatment, the production of sewage sludge is surging and the problem of its disposal is therefore also growing. Recycling this waste as a fertilizer is an economically and environmentally attractive option. Determining the availability of macro- and micronutrients in these sludges is important if such wastes are to provide sufficient nutrients to crops while causing minimal environmental damage. A greenhouse study with two kenaf cultivars (‘Everglades 41’ and ‘Tainung 2’) was designed to evaluate the effects of sewage sludge processing mode on plant development, biomass yield, and nutrient availability. Two different processing modes of sludges (digested dewatered and pelletized-heat dried) applied at two rates, 10 and 20 Mg ha-1 were compared with inorganic N and a zero-N control. Plant height, basal stems diameter and biomass production increased slightly with the sewage sludge treatments but in different manners depending on the kenaf cultivar in question. Both sludges were similar in their ability to supply N to the plants. Apparent N recovery and N fertilizer equivalent value were greater in the low dosage treatments. Of the two cultivars, ‘Everglades 41’ showed greater mean values for all the variables studied. No differences were found in leaf P, K, Ca, Mg contents among treatments. The Zn and Cu concentrations were the only trace elements that increased in the leaf tissues with sludge application, although the values recorded were well below critical environmental thresholds.

Transport of zinc, copper, and lead in a sewage sludge amended calcareous soil

The application of sewage sludge on farmland is practised in many countries since sludge is rich in macro- and micro- nutrients. However, increasing use of sewage sludge on farmland has raised concerns about the potential transport of heavy metals into food chains and groundwater. This study determined for a calcareous soil the effects of sludge application on soil physical properties and transport of zinc (Zn), copper (Cu), and lead (Pb). Secondary anaerobic digested sewage sludge was applied at rates of 0, 25, 50, and 100 t/ha (on a dried weight basis) for four consecutive years and mixed in the top 20-cm of soil. Corn (Zea mays L.) was planted as a spring crop, followed by wheat (Triticum aestivum) as a winter crop. Sludge application increased the dissolved organic matter content and modified the soil structure, increased the soil infiltration rate, saturated hydraulic conductivity, and aggregate stability, and decreased the bulk density. Sludge application greatly increased DTPA (diethylenetriamine pentaacetic acid)-extractable soil metal concentrations to 50 cm depth and significantly to 1 m. In the plots that received four application of 100 t/ha sewage sludge, the mean concentrations of Zn, Cu, and Pb in subsoil increased by 1600, 7, and 4.5 times, respectively, compared with the control. The results indicate that a combination of enhanced soil physical properties, heavy and inefficient irrigation and high organic matter content with heavy metals cause significant metal mobility. High sludge applications pose risks of groundwater and food chain contamination and rates are best restricted to those reflecting the nutrient demand of crops (20 t/ha every 4 to 5 yr or an average of 4 to 5 t/ha/yr).

Application of chemometric methods in the evaluation of chemical and spectroscopic data on organic matter from Oxisols in sewage sludge applications

Chemometric methods can contribute to soil research by permitting the extraction of more information from the data. The aim of this work was to use Principal Component Analysis to evaluate data obtained through chemical and spectroscopic methods on the changes in the humification process of soil organic matter from two tropical soils after sewage sludge application. In this case, humic acids extracted from Typic Eutrorthox and Typic Haplorthox soils with and without sewage sludge application for 7 consecutive years were studied. The results obtained for all of the samples and methods showed two clusters: samples extracted from the two soil types. These expected results indicated the textural difference between the two soils was more significant than the differences between treatments (control and sewage sludge application) or between depths. In this case, an individual chemometric treatment was made for each type of soil. It was noted that the characterization of the humic acids extracted from soils with and without sewage sludge application after 7 consecutive years using several methods supplies important results about changes in the humification degree of soil organic matter. These important result obtained by Principal Component Analysis justify further research using these methods to characterize the changes in the humic acids extracted from sewage sludge-amended soils.

Heavy metals extractability in a soil amended with sewage sludge

Few investigations have been carried out about the comparison of desorption rate and amount of heavy metals extracted successively by organic acid mixtures mimicking the rhizosphere and routine extractants in sewage sludge-amended soils. Extractions of Zn, Cd, Ni, Cr, and Cu were performed in samples of a sewage sludge-amended soil using seven extractants: four organic acid mixtures and three routine extractants (DTPA, Mehlich-I, and ammonium acetate). Results from single pass extractions, in which the extractable metal contents were determined by simply extracting the soil a single time, as well as from 15 successive extractions, in which the solid residues of the first extraction was successively extracted 14 additional times, of heavy metals were analyzed. The extractability of heavy metals in a single pass extraction was, in general, as follows: Mehlich-I &gt; DTPA &gt; organic acids &gt; NH4OAc. The highest rates of extraction followed the general order: DTPA &gt; Mehlich-I &gt; organic acids &gt; NH4OAc. While Mehlich-I presented the highest extractability of heavy metals among studied extractants, DTPA showed a high extractability of Zn, Cd, Ni, and Cu in a single extraction as well as the highest rates of extraction among the studied extractants. The transfer of heavy metals from soil to organic acid solutions is slower than to DTPA and Mehlich-I extractants.