Soil Conditioner In Agriculture Research Articles

Effect of particle size and application rate of steel (Linz-Donawitz, LD) slag on heavy metal built-up in soil and their transfer dynamics in spinach (Spinacia oleracea L.)

Linz-Donawitz (LD) slag is a solid industrial waste generated during the production of steel. In general, the amount of LD slag produced varies from 300 to 400 kg ton-1 of steel. Presently only 25 % of the steel slag, which is also rich in various macro and micro-nutrients, is being reused in India compared to 70–100 % in other countries. The present study deals with the possibility of utilizing LD slagas a nutrient rich low-cost soil conditioner in agriculture. An experiment was thus conducted to determine the effect of LD slag application at rates 0.25, 0.50 and 1 t ha-1 in two particle sizes i.e., <50 and <100 microns (µ) on spinach (Spinacia oleracea L.). Physico-chemical, biological characteristics and heavy metals in soil and latter’s transfer from soil to the foliage was also determined. The results showed that an application of LD slag @1 tha-1 and 100 µ particle size significantly improved the soil microbial count and activity of enzymes such as dehydrogenase and phosphatase while at a smaller particle size of LD slag (50 µ) @ 1 tha-1, a significant increase in the foliage yield of spinach was observed. The risk due to heavy metals present in the steel slag as evidence by indicator of heavy metal content in plants i.e. transfer factor (TF), hazard quotient (HQ) and hazard index (HI) was within the permissible range. However long-term effect of steel slag application on ecotoxicity and phytotoxicity levels must be deciphered. In conclusion the application of LD slag in spinach does not negatively impact the soil health and in fact causes an increase in the economic yield of spinach.

Development and Substantiation of Approaches to the Management of Sewage Sludge of Different Storage Periods

A widespread method of sewage sludge disposal is still simple storage in sludge lagoons. Subsequent thermal utilization is hardly possible because sludge properties change over time and energy content is reduced. Use as a soil conditioner in agriculture or landscaping is usually not possible due to high heavy metal contents. This paper describes a method in which a 10-year-old accumulated sewage sludge can be utilized as technical soil by mixing it with pyrolized fresh sewage sludge. For this purpose, physicochemical and toxicological characteristics of sewage sludge of different storage periods were identified, processes of thermal destruction of sewage sludge analyzed, toxicological characteristics of solid products of thermal sludge treatment determined, and the possibility of using the sewage sludge–pyrolysate mixture as technical soil was assessed. Results show that the gross calorific value of fresh and one-year stored sewage sludge is with approx. 15,000 kJ/kg dry basis sufficient to produce pyrolysate autothermally. It is also shown that when the pyrolysis residue is mixed with fresh or 1-year old sewage sludge, heavy metals can be immobilized and thus the leaching of heavy metals significantly reduced by up to 75%. The method described can thus be a possible option for recycling accumulated sewage sludge.

Production and Production-Increasing Factors of Biochar

In the article, we deal with biochar-related research and our own developments. Studies in the literature show that biochar can be used as a soil conditioner in agriculture and horticulture. It improves many physical, chemical, and biological properties of the soil and substrate. It increases the water retention capacity while reducing the leaching of nutrients. Through these, you can improve the profit of producers, the sustainability of production, and the efficiency of fertiliser use. By increasing water retention, biochar can reduce irrigation needs and enable production on limited water resources. The developed and presented equipment was called the resting bed (fixed bed) version. Drying and carbonization are also carried out by direct heat transfer. The material, with a temperature equalised by moving drying and a homogeneous composition, enters the reactor. The high-temperature gas and air mixture is introduced into the dryer by a gas jet pump. The energy obtained by burning the pyrolysis gases produced during carbonization ensures the heating of the system, so there is no need for significant external energy input. Due to the structure of the system, the PAH content of the final product is low.

Modeling of thermo-chemical pretreatment of yam peel substrate for biogas energy production: RSM, ANN, and ANFIS comparative approach

The modeling and optimization of the substrate treatment process in biogas energy production from yam peel substrates via anaerobic digestion was the purpose of this work. Thermo-chemical pretreatment method was used in the substrate treatment. The instrumental analysis of the substrate was investigated using FTIR and SEM. Central composite design was used in the design of experiment and intelligent modeling of the substrate treatment in the biogas production via adaptive neuro-fuzzy inference systems (ANFIS), artificial neural network (ANN), and response surface methodology (RSM). The kinetics of the anaerobic digestion process was studied using five kinetic models. The result indicated that among the three process parameters investigated, temperature has the most significant effect on the substrate pretreatment. The instrumental analysis showed that the thermo-chemical modification of the substrate resulted in the transformation of its bond structure and the solubilization of the hemicelluloses molecules. ANFIS, ANN, and RSM models were efficient in modeling the anaerobic digestion process with correlation coefficient of 0.9997, 0.9997 and 0.9887, respectively showing good agreement between the experimental and predicted biogas yield. Further statistical error indices involving HYBRID (ANFIS=0.3180, ANN=0.3207, and RSM=11.157), RMSE (ANFIS=0.3359, ANN=0.8235, and RSM=4.969), and ARE (ANFIS=0.3068, ANN=0.3075, and RSM=1.5756) depicted the ANFIS as being marginally better than the ANN in simulating and modeling the anaerobic digestion. Optimization of the ANFIS model yielded a biogas volume of 356.24 ml at concentration, time, and temperature of 0.04 N, 60 s and 80 °C, respectively. The kinetics of the cumulative biogas production was described by the Modified Logistics, Transference and the Logistics models. The purification of the biogas by scrubbing gave about 92% methane gas. The sediments from the digestion with low C/N ratio could be used as manure and soil conditioner in agriculture.

Recent advances in developing innovative sorbents for phosphorus removal-perspective and opportunities.

Phosphorus is an essential mineral for the growth of plants which is supplied in the form of fertilizers. Phosphorus remains an inseparable part of developing agrarian economics. Phosphorus enters waterways through three different sources: domestic, agricultural, and industrial sources. Rainfall is the main cause for washing away a large amount of phosphates from farm soils into nearby waterways. The surplus of phosphorus in the water sources cause eutrophication and degradation of the habitat with an adverse effect on aquatic life and plants. Phosphate elimination is necessary to control eutrophication in water sources. Among the different methods reported for the removal and recovery of phosphorus: ion exchange, precipitation, crystallization, and others, adsorption standout as a sustainable solution. The current review offers a comparative assessment of the literature on novel materials and techniques for the removal of phosphorus. Herein, different adsorbents, their behaviors, mechanisms, and capacity of materials are discussed in detail. The adsorbents are categorized under different heads: iron-based, silica-alumina-based, calcium-based, biochar-based wherein the metal and metal oxides are employed in phosphorus removal. The ideal attribute of adsorbent will be the utilization of spent adsorbents as a phosphate plant food and a soil conditioner in agriculture. The review provides the perspective on the current research with potential challenges and directives for possible research in the field.

Mitigating N2O emissions from agricultural soils with fungivorous mites.

Nitrous oxide (N2O) is an important greenhouse gas and an ozone-depleting substance. Due to the long persistence of N2O in the atmosphere, the mitigation of anthropogenic N2O emissions, which are mainly derived from microbial N2O-producing processes, including nitrification and denitrification by bacteria, archaea, and fungi, in agricultural soils, is urgently necessary. Members of mesofauna affect microbial processes by consuming microbial biomass in soil. However, how microbial consumption affects N2O emissions is largely unknown. Here, we report the significant role of fungivorous mites, the major mesofaunal group in agricultural soils, in regulating N2O production by fungi, and the results can be applied to the mitigation of N2O emissions. We found that the application of coconut husks, which is the low-value part of coconut and is commonly employed as a soil conditioner in agriculture, to soil can supply a favorable habitat for fungivorous mites due to its porous structure and thereby increase the mite abundance in agricultural fields. Because mites rapidly consume fungal N2O producers in soil, the increase in mite abundance substantially decreases the N2O emissions from soil. Our findings might provide new insight into the mechanisms of soil N2O emissions and broaden the options for the mitigation of N2O emissions.

Extraction of Rare Earth Elements from Phospho-Gypsum: Concentrate Digestion, Leaching, and Purification

Rare earth-bearing gypsum tailings from the fertilizer industry are a potential source for an economically viable and sustainable production of rare earth elements. Large quantities are generated inter alia in Catalão, Brazil, as a by-product in a fertilizer production plant. Hitherto, the gypsum has been used as soil conditioner in agriculture or was dumped. The cooperative project, “Catalão Monazite: Economical exploitation of rare earth elements from monazite-bearing secondary raw materials,” intends to extract rare earth elements from these gypsum tailings. In this paper, a chemical process route to obtain a mixed rare earth carbonate from a monazite concentrate, was investigated. The results of the digestion, leaching, and precipitation experiments are presented and discussed herein. This includes reagent choice, process parameter optimization through experimental design, mineralogical characterization of the feed material and residues, purification of the leach solution, and precipitation of the rare earth as carbonates. The results showed that a rare earth extraction of about 90% without the mobilization of key impurities is possible during a sulfuric acid digestion with two heating stages and subsequent leaching with water. In the following purification step, the remaining impurities were precipitated with ammonium solution and the rare earth elements were successfully recovered as carbonates with a mixture of ammonium solution and ammonium bicarbonate.

Solid-Liquid Extraction with Low Temperature Purification Coupled with Gas Chromatography and Mass Spectrometry for Determination of Polychlorinated Biphenyls in Sewage Sludge

Sewage sludge is the residue produced by the wastewater treatment plants, which can be used as soil conditioner in agriculture. However, the current legislation recommends monitoring chemical contaminants such as polychlorinated biphenyls (PCBs). In this study, solid-liquid extraction with low temperature purification (SLE-LTP) was optimized and validated for monitoring six PCBs. The analyses were performed by gas chromatography and mass spectrometry. Sulfur interference was removed by 1.5 g of copper metal. The extraction was carried out using 6.50 mL isopropanol, 1.50 mL ethyl acetate, 0.1 g NaCl, 0.8 mL water and 15 min into ultrasound. Extraction percentages were between 82 and 94% and relative standard deviation ≤ 16% for low concentrations. Detection and quantification limits were 3.3 and 10 µg kg-1, respectively. The method was applied to sludge samples collected monthly in the wastewater treatment plant and PCB 52 was detected in six samples.

Slow pyrolysis of different Brazilian waste biomasses as sources of soil conditioners and energy, and for environmental protection

This paper explores the viability of producing energy and agricultural soil conditioners with biochars and bio-oils from the pyrolysis of biomasses that in some cases are potential environmental pollutants. This approach addresses the need to develop sustainable production systems that minimize pollution and soil degradation, and meet the demand for renewable fuels. Large volumes of biomass from different sources are available in Brazil, including Eucalyptus crop residues (CE), castor meal (CM), coconut pericarp (CP), sugarcane bagasse (SB), and water hyacinth (WH). CM char and SB bio-oil are good prospects for energy generation. Characterization using DRIFT, 13C NMR, and van Krevelen diagrams indicated that after carbonization, aromatic structures were predominant in the biochars produced from the CP, CE, and SB biomasses, while aliphatic groups were abundant in the biochars from CM and WH. Analysis using EPR showed that unpaired electrons were preferentially located on carbon atoms in the case of the CP, CE, and SB biochars, with EPR g values around 2.0030, while the CM and WH biochars presented g values around 2.0035, indicating that the unpaired electrons were closer to oxygen atoms. In terms of bio-oil chemical composition, the most abundant compounds were 3-pyridinol and furans (WH), phenols (CP), and hexadecanoic, octadecanoic, 9,12-octadecenoic (z,z), 3-docosenoic, and 5-docosenoic acids (present only in the CM bio-oil). The bio-oils from SB and CE were quite similar and the main compound was 1,2,6-hexanetriol. The biomass sources studied produced reasonable amounts of bio-oil, and could compete as suitable raw materials for biofuel production.

Effects of biochar on earthworms in arable soil: avoidance test and field trial in boreal loamy sand

Biochar is widely studied as a combined soil conditioner in agriculture and a potential carbon sink. The knowledge of the effects of field application of biochar on soil fauna remains limited. Earthworms are a globally common and important faunal group in arable soils and the purpose of our study was to determine the effects of biochar on earthworms under both laboratory and field conditions in a boreal loamy sand. An avoidance test using the earthworm Aporrectodea caliginosa Sav. was conducted for periods of 2 and 14 days with 16gkg−1 spruce chip biochar. The same biochar was mixed into the top 10cm of soil at 0 or 30tha−1 and its effect on earthworm density and biomass was studied over four and half months in a field experiment where wheat was grown with or without inorganic fertilizer application. In the avoidance test, biochar application did not affect the habitat choice of earthworms in the first 2d, but after 14d, they tended to avoid it. The avoidance was possibly the avoidance was possibly caused by a slight decline in soil water potential. Under field conditions the highest earthworm densities and biomasses were measured in biochar amended soils. None of the differences among the treatments studied were, however, statistically significant (p>0.05). The time scale of the study was sufficient for reliably demonstrating the lack of strong toxic effects and immediate avoidance reactions caused by biochar application

Sewage sludge processing determines its impact on soil microbial community structure and function

Composting and thermal drying are amongst the most commonly used post-digestion processes for allowing sanitation and biological stabilization of sewage sludge from municipal treatment plants, and making it suitable as soil conditioner for use in agriculture. To assess the impact of sludge-derived materials on soil microbial properties, fresh (LAF), composted (LAC) and thermally dried (LAT) sludge fractions, each resulting from a different post-treatment process of a same aerobically digested sewage sludge, were added at 1% (w/w) application rate on two contrasting (a loam and a loamy sand) soils and incubated under laboratory conditions for 28 days. Soil respiration, microbial ATP content, hydrolytic activities and arginine ammonification rate were monitored throughout the incubation period. Results showed that soil biochemical variables, including the metabolic quotient (qCO2), were markedly stimulated after sludge application, and the magnitude of this stimulatory effect was dependent on sludge type (precisely LAT>LAF>LAC), but not on soil type. This effect was related to the content of stable organic matter, which was lower in LAT. Genetic fingerprinting by PCR–DGGE revealed that compositional shifts of soil bacterial and, at greater extent, actinobacterial communities were responsive to the amendment with a differing sludge fraction. The observed time-dependent changes in the DGGE profiles of amended soils reflected the microbial turnover dependent on the sludge nutrient input, whereas no indications of adverse effects of sludge-borne contaminants were noted. Our findings indicate that composting rather thermal drying can represent a more appropriate post-digestion process to make sewage sludge suitable for use as soil conditioner in agriculture.

Separation of some rice straw components and studying their effect on some hydro-physical properties of two different soils

Recycling the rice straw (RS) have been carried out using a simple laboratory procedure for different application purposes mainly the soil conditioning. Cellulose, Silica and Lignin could be extracted in a single process in almost pure form that is suitable for many environmental and industrial purposes. The raw RS, straw carbonized ash (RA), extracted Cellulose, Silica and Lignin were characterized by thermo-gravimetric analysis (TGA), FT-IR and elemental analysis. The mentioned materials were studied as agricultural soil conditioners. They were added in different concentrations to two soil samples different in their properties. Bulk density (BD), total porosity (TP), water holding capacity (WHC), field capacity (FC) and hydraulic conductivity (Ksat) were estimated as examples of the studied soil physical properties. An enhancement in the studied properties for the sandy non-calcareous soil sample has been observed. For the more saline calcareous soil sample, the additives nearly have no effect on most of the studied properties. Some interaction between the soil particles, the additive particles and/or the absorbed water and may be present. The studied material may be promising as sandy soil conditioners.

Simultaneous and Sequential Extraction Protocols as Tools for Determination of Zinc Bioavailability in Dried Anaerobic Sludge

Abstract Production of unsettleable sewage sludge with high water content is one of the problems of intensification of industrial activities and environmental protection. Sewage sludge with low toxic metals concentrations can be utilized as fertilizer and soil conditioner in agriculture. For determination of metal bioavailability, a wide range of extraction protocols and fractionation analyses can be used. We studied the distribution and quantified the leaching and bioavailability of zinc from dried anaerobic sludge by simultaneous, multi-step and three different sequential extraction protocols. For determination of zinc, the galvanostatic stripping chronopotentiometry (SCP) and electrothermal atomic absorption spectrometry (ETAAS) were used. The distribution of Zn in sequential extraction protocols was determined using a fivestep chemical fractionation procedures (BCR, Tessier and Van Hullebusch protocols). The potential bioavailability (0.9% NaCl, 0.1 mol/dm3 HCl, 0.1 mol/dm3 HNO3, 0.1 mol/dm3 CH3COOH, 0.1 mol/dm3 Na2EDTA, 0.1 mol/dm3 CaCl2, 0.1 mol/dm3 MgCl2, 0.1 mol/dm3 (NH4)2C2O4.H2O extraction) and pseudo total (aqua regia extraction and ETAAS analyses) content of Zn in sludge was determined. The amount of aqua regia extractable zinc in sludge samples was 650 ± 12 mg/kg (d.w.). We found out that the zinc was extractable from anaerobic sludge in first hour of contact time for all tested agents. Zinc was extracted with highest efficiency by 0.1 mol/dm3 (NH4)2C2O4.H2O, 0.1 mol/dm3 HCl and 0.1 mol/dm3 Na2EDTA. Sequential extraction protocols showed that the maximum extractable amount of zinc 126.3 ± 2.6 mg Zn / kg d.w. was bound to organic matter and sulfides. High concentrations of zinc in residual fractions were leachable under extraction conditions of strong acids only.

Characterization of Brazilian oil shale byproducts planned for use as soil conditioners for food and agro-energy production

The Brazilian oil shale byproducts resulting from the Petrosix pyrolysis (retortage) process were submitted to a set of analytical techniques to evaluate their possible use as agricultural soil conditioners. Liquid dichloromethane extracts from the solid samples were analyzed using capillary column gas chromatography–mass spectrometry. The results showed that of the 16 PAHs designated by the U.S. EPA as priority pollutants, only phenanthrene, fluorene and naphthalene, present in the retorted oil shale sample taken from inside storage piles; benzo[k]fluoranthene, present in the dolomite limestone layer between the two layers of oil shale in the mine structure; and naphthalene, present in powdered raw oil shale, were above the limits established by the EPA. The solid Brazilian oil shale byproduct samples were also analyzed by X-ray diffractometry (XRD), diffuse reflectance ultraviolet–visible spectroscopy (DRUV–VIS), X-ray fluorescence spectroscopy (XRF) and electron paramagnetic resonance (EPR) spectroscopy. The XRD analysis showed that the pyrolysis process produces a “weathering” transformation, for example with the appearance of kaolinite diffraction lines in the retorted samples. The DRUV–VIS and XRF spectroscopy results indicated iron oxide goethite interactions with the PAHs present in the solid samples studied. The EPR spectroscopy showed that the samples row oil shale (g=2.0044) and the powder oil shale (g=2.0035), before the dichloromethane extraction, presented organic free radical signals associated with oxygen atoms. The other Brazilian oil shale byproduct samples, before and after the dichloromethane extraction, showed organic free radical signals associated with carbon atoms (g=2.0022–2.0031).

The value of compost

Sub-department Environmental Technology, Wageningen University, P.O.B 8129, 6700 EV, Wageningen, TheNetherlands (* author for correspondence, e-mail: aad.termorshuizan@wur.nl)1. IntroductionComposting is the controlled decomposition oforganic matter resulting in stabilized and sanitizedorganic matter that can be used as soil conditionerin agriculture. There exist multiple compostingmethods, varying from the small, home-madereactors used by individual households, to therelatively simple, on-site reactors used by farmers,to the large, simple to complex reactors used byprofessional composters to which the biowaste hasto be transported.If organic matter is targeted for agriculturaluse, the major reason for composting is sanitation(i.e. the inactivation of pathogens) of the material.In addition, apart from the presence of pathogensin fresh organic matter, returning great amounts ofuncomposted, fresh organic matter to agriculturalfields may have a stimulatory effect on plantpathogens already present in soil. The value ofcompost is difficult to summarize in one sentence,as its amendment to soil essentially has multiplepositive effects, which in turn also affect eachother. For example, an increase of soil organicmatter content improves the water holdingcapacity, which makes plants less prone to condi-tions of dry weather. As a result of that, they maybecome more resistant against pathogens thatspecifically affect plants under stress.Thisreviewaimstosummarizethemainwaysinwhich compost affects the functioning of the soil.Wefocusmainly oncompostedbiowaste,which weuse in its broad sense, including organic householdwaste, green waste and crop residues, but manyaspects also apply to composted manures.2. SanitationA major goal of composting is the removal ofpathogens. Although much emphasis is often puton the potential survival of some plant, human oranimal pathogens during compositing, it must berealized that the majority of pathogens is promptlyand completely killed during the heat phase ofcomposting (e.g. Bollen et al. 1989). Moreover,many pathogens that are known to have some po-tential to survive normal composting conditionsoccuronlyrarely,whichresultsinaverylowchanceofoccurrenceinbiowaste.TobaccoMosaicVirusisanexampleofsuchapathogen.Thisviruscancauselargecroplosseswhenintroducedintoacrop,butitis virtually absent in Dutch agriculture. The com-mon presence of this virus in tobacco of cigarettessmoked in the Netherlands (pers. comm. D. Peters,Virology, Wageningen University) is most likely ofsubstantial greater risk for agriculture than itspresence in compost. So, not only the fate ofpathogens during composting needs to be includedin a risk assessment, but also the probability ofpathogen incidence in biowaste and the probabilitythat presence in compost leads to phytosanitaryproblems.The scale of composting is an issue that af-fects phytosanitary aspects: large compostingfacilities collect organic matter from a multitudeof sources and one compost heap may thereforecontain various pathogens. Moreover, such largefacilities also distribute the compost to a largearea. So, the need for inactivating the pathogensin such large facilities is therefore great, asotherwise there would be uncontrolled spread ofpathogens. At the other extreme, on-farm com-posting facilities do not introduce pathogensfrom elsewhere, but reduced ability to controlthe composting process (relative to large com-posting facilities) may lead to limited survival ofsome plant pathogens. Although such a survivalis unwanted, the consequences for farm man-agement may be limited as these pathogens useto be all soil-borne, and their possible presence

Removal of heavy metals from sewage sludge by extraction with organic acids

Waste water treatment in activated sludge plants results in the production of large amounts of surplus sludge. After composting the sludge can be reused as fertiliser and soil conditioner in agriculture. Compared to landfilling and incineration, utilisation of sludge-compost is a more sustainable treatment because it recycles both nutrients and organic matter. However the high levels of heavy metals in sludge frequently prevent the reuse of sludge compost in agriculture. The extraction of heavy metals from the sludge before composting is therefore a necessary step to achieve a more sustainable sludge treatment. Extraction of heavy metals by inorganic acids and complexing agents has severe drawbacks. Organic acids could be an attractive extracting agent because the extraction can be performed at mildly acidic conditions (pH 3-5) and they are biologically degradable. The extraction was studied for heavy metals Cu and Zn and for competing metals Ca and Fe. The rate of extraction increases for increasing temperature and citric acid concentration. Cu can be extracted for 60-70% and Zn for 90-100% by citric acid at pH 3-4. A first economic valuation of the extraction and subsequent composting process showed that the total costs of the treatment process are below the costs of incineration.

Removal of heavy metals from sewage sludge by extraction with organic acids

Waste water treatment in activated sludge plants results in the production of large amounts of surplus sludge. After composting the sludge can be reused as fertiliser and soil conditioner in agriculture. Compared to landfilling and incineration, utilisation of sludge-compost is a more sustainable treatment because it recycles both nutrients and organic matter. However the high levels of heavy metals in sludge frequently prevent the reuse of sludge compost in agriculture. The extraction of heavy metals from the sludge before composting is therefore a necessary step to achieve a more sustainable sludge treatment. Extraction of heavy metals by inorganic acids and complexing agents has severe drawbacks. Organic acids could be an attractive extracting agent because the extraction can be performed at mildly acidic conditions (pH 3-5) and they are biologically degradable. The extraction was studied for heavy metals Cu and Zn and for competing metals Ca and Fe. The rate of extraction increases for increasing temperature and citric acid concentration. Cu can be extracted for 60-70% and Zn for 90-100% by citric acid at pH 3-4. A first economic valuation of the extraction and subsequent composting process showed that the total costs of the treatment process are below the costs of incineration.

Control of metal application rates from sewage sludge utilization in agriculture

During the treatment of sewage, a sludge is produced, which must be disposed. For many treatment works, agricultural use of the sludge is the most cost‐effective disposal option. In using sludge as a fertilizer replacement or soil conditioner in agriculture, the environment must not be endangered. In this objective, toxic metal accumulation is of special interest because excessive concentrations in sludged soil can reduce crop yields or result in unacceptable accumulations of toxic metals in crops with consequent hazard to the food chain. Although sewage sludge contains certain quantities of metals from natural sources, there are significant amounts derived from industrial effluents discharged to sewers. The paper will review all of these aspects and will examine critically the various policies of controlling metal accumulation in sludged soil with particular reference to the soil quality criteria (maximum permissible concentrations) which have been adopted.