Sewage Sludge-treated Soils Research Articles

Heavy metals accumulation in wheat (Triticum aestivum L.) roots and shoots grown in calcareous soils treated with non-spiked and spiked sewage sludge.

With growing urbanization and agriculture, the quantity of sewage sludge production increases every year. For the purpose of risk management, it is crucial to figure out how much heavy metals are transported to different parts of plants when sewage sludge is used. A greenhouse experiment was carried out to investigate the accumulation of heavy metals in wheat (Triticum aestivum L.) grown in 30 calcareous soils. The soils in this study were subjected to three different treatments: soils treated with sewage sludge at a rate of 2.5%, soils treated with sewage sludge at a rate of 2.5% and enriched with heavy metals, and control soils that received neither sewage sludge nor heavy metals. Wheat grown in sewage sludge-treated soils had the highest mean dry matter, and was 2.11 and 1.25 times greater than wheat grown in control and spiked-sewage sludge-treated soils, respectively. In all treatments, wheat roots had greater heavy metal levels than wheat shoots. Among all the heavy metals examined, Pb and Cu had the highest bioconcentration factors for roots and shoots (BCFRoots and BCFShoots) in control and sewage sludge-treated soils, followed by Cd in spiked-sewage sludge-treated soils, and Co and Ni had the lowest BCFRoots and BCFShoots across all treatments. In spiked-sewage sludge-treated soils, the root restriction for heavy metals translocation was more important for Co, Cu, and Ni than for Pb and Zn, indicating that wheat can be grown safely in a variety of calcareous soils amended with sewage sludge with high content of Cd, Co, Cu, and Ni. Reducing the transfer of Pb and Zn from soils to wheat in soils treated with sewage sludge yet having high concentrations of these heavy metals should be considered as a top priority strategy for preserving wheat products. Since a wide range of calcareous soils was used in this study and because calcareous soils make up the majority of soils in the Middle East, the findings are relevant for all of the countries in this region.

Quarry restoration treatments from recycled waste modify the physicochemical soil properties, composition and activity of bacterial communities and priming effect in semi-arid areas

The selection of a suitable organic amendment for recovery of semi-arid soils degraded by mining is key to the success of an ecological restoration. The aim of this research is to study the short-term responses of physicochemical, biochemical and biological properties, as well as the changes of a soil bacterial community at the genus level after application of five types of organic amendments in a limestone quarry in Almería (SE, Spain). The relationship among bacterial taxa with biochemical and physicochemical properties and priming effect from restored soils was also analysed. Six months after the application of organic amendments, the values of different soil status, such as total organic carbon, total nitrogen, assimilable phosphorus and labile organic matter forms (carbohydrates and polyphenols), basal respiration (BR) and enzymatic activities increased significantly with respect to unrestored soils. Similarly, a positive priming effect of soil organic matter mineralisation was produced by all organic amendments, being significantly higher (p < 0.05) in sewage sludge-treated soils. Bacterial diversity was higher in restored than in control soils. The restoration caused changes in soil bacterial communities' composition at the phylum and genus levels. It was observed that soil bacterial communities were significantly related to several physical, chemical and biochemical soil properties, establishing two different co-occurrence patterns between restored and unrestored soils. A first bacterial co-occurrence pattern showed significant positive correlations to pH and C/N ratio and negativity with the rest of the soil properties. The second bacterial pattern was positively correlated with carbohydrates, μg of C, priming effect, BR, β-glucosidase and phosphatase and negatively with pH and C/N ratio. It was concluded that soil bacterial communities are clearly influenced by the types of organic amendments applied. Bacterial taxa such as Taibaiella or Pseudomonas could perform key functions in the carbon cycle in restored soils.

Interactive Effects of Biochar and Sewage Sludge on Bioavailability and Plant Uptake of Cu, Fe, and Zn, and Spinach (Spinacia oleracea L.) Yields under Wastewater Irrigation

Biochar can influence bioavailability of micronutrients and crop yields in sewage sludge-treated soils, but the mechanisms of its effects remain poorly understood. Therefore, this field experiment was conducted on a Luvisol and Cambisol to investigate the bioavailability and uptake of some micronutrients and spinach (Spinacia oleracea L.) yields grown in soil amended with biochar and sewage sludge. Ten treatments arranged in randomized complete block design with three levels of biochar (0, 2.5, 5 t/ha) and sewage sludge (0, 6, 12 t/ha) and combinations thereof were applied. High rate of sole sewage sludge, and its combination with biochar significantly (p &lt; 0.05) increased yield on the Luvisol. On the Cambisol, only marginal yield increase resulted from high rates of sole organic amendments and chemical fertilizer, while co-applications decreased yields. Co-amendments generally increased bioavailability of micronutrients relative to sole amendments in the order Fe &gt; Cu = Zn, with greater increase on the Cambisol, but uptake of micronutrients decreased with co-application rates of amendments. Contents of micronutrients in plant leaves were within the normal range, except for a combination of highest dosage of co-amendments on the Cambisol (Fe; 560 mg/kg), which resulted in leaf necrosis and 7% yield depression. The results showed greater yield response of spinach to co-application of amendments on the Luvisol.

Long-term effects of residual sewage sludge application in tropical soils under Eucalyptus plantations

Studies regarding the residual effects of sewage sludge in soil several years after the first and only application are still scarce, especially for tropical areas under forestry management. In these soils, the residual effects can represent a neglected phenomenon, since silvicultural management experiences a longer crop rotation cycle compared to most common agricultural cycles. Consequently, under forestry management, sewage sludge applications can represent an event occurring just once over cycles of several years. This study aimed to evaluate the long-term effects of residual sewage sludge application in infertile tropical soils under Eucalyptus plantations in terms of both the main chemical features (pH, soil organic matter, N, P, S, K, Ca, Mg, and cation-exchange capacity) and the potentially toxic elements (As, Ba, Cd, Co, Cr, Cu, Mo, Ni, Pb, Se, and Zn) concentrations/behaviors of soil. Residual effects were evaluated in four areas (São Paulo State, Brazil) after 10.0, 12.2, 12.4, and 17.2 years from the first and only application, respectively. Differences in terms of treatments were evaluated by analysis of variance; correlations and similarity analyzed by principal component and cluster analysis, respectively. The results showed that soil organic matter, main macronutrients (N and P), and cation-exchange capacity contents were generally higher in sewage sludge-treated soils while potentially toxic element contents tended to increase at increasing sewage sludge doses. In most of the investigated treatments, the potentially toxic element concentrations were usually below both the soil natural background concentrations and quality reference values. Principal component and cluster analysis revealed that differences among areas were primary due to differences in applied sewage sludge type and amount. The effects of residual sewage sludge application on soil, in terms of both the pros and cons, can be detected even many years after the first and only application. Studies on the long-term effects of sewage sludge should be mandatory for both monitoring the pedoenvironment and for guiding policymakers and producers on the best practices for their reuse and management.

Selected persistent organic pollutants (POPs) in the rhizosphere of sewage sludge-treated soil: implications for the biodegradability of POPs

ABSTRACTThe impact of regular application of sewage sludge or farmyard manure on the organic contaminant loads in soil was assessed in a model rhizobox experiment. Two soils originating from a long-term field crop rotation and fertilizer experiment running since 1996 were used. The total polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), organochlorinated pesticides (OCPs), polybrominated diphenyl ethers (PBDEs), perfluorooctanoic acid (PFOA), and perfluorooctane sulfonate (PFOS) contents were determined in the rhizosphere and bulk soil. The results showed low but still detectable contents of PCBs and OCPs in the soil, substances which were banned a few decades ago. Among the OCPs, dichlorodiphenyltrichloroethane (DDT) and its metabolites reaching up to 18.2 µg kg−1 of the soil even exceeded the preventive levels for these compounds in agricultural soils, i.e. 7.5 µg kg−1 of soil. For PBDEs, PFOA, and PFOS, their contents in the soil significantly increased with sewage sludge application. The enhancement of the potential biodegradability of the POPs in the rhizosphere was confirmed only for hexachlorocyclohexane (γ-HCH), where, the level of γ-HCH increased significantly in the rhizosphere soil compared to bulk soil. Thus, natural attenuation of POPs in the soil-plant system seems to be insufficient for most of the investigated compounds.

Collembola Reproduction Decreases with Aging of Silver Nanoparticles in a Sewage Sludge-Treated Soil

Silver nanoparticles (AgNP) are integrated into various products due to their antimicrobial characteristics and hence, the application of AgNP is increasing. During production, use and disposal AgNP are emitted and enter the environment via several pathways. Soils are considered a major sink of AgNP. The aim of the present study was to determine the toxic effect of AgNP on Folsomia candida reproduction to illustrate potential impact on terrestrial ecosystems. The AgNP-dependent reduction of F. candida reproduction was studied in RefeSol 01-A, LUFA 2.2 and OECD soil at 0.3 µg – 50 mg Ag kg-1. To simulate realistic exposure pathways, effects on F. candida reproduction after the application of AgNP via sewage sludge and after aging this treatment in the soil for up to 140 days were studied using environmentally relevant concentrations. The OECD representative AgNP, NM-300K, and AgNO3, as a metal salt reference, were used in all experiments. The generated data demonstrate that the presence of AgNP in the soil in the low mg Ag kg-1 concentration range results in significant, but concentration independent inhibition of F. candida reproduction in RefeSol 01-A and LUFA 2.2. Significant inhibition of F. candida reproduction due to AgNP was also observed for soil amended with AgNP treated sludge. An increase in inhibition with aging of the AgNP in the soil was evident. In conclusion, our results demonstrate that, at environmentally relevant concentrations, AgNP adsorption to sludge and subsequent aging in soil lead to a toxic effect on soil invertebrates.

Soil microbial community structure affected by 53 years of nitrogen fertilisation and different organic amendments

The Ultuna long-term soil organic matter experiment in Sweden (59′82° N, 17′65° E) was started in 1956 to study the effects of different N fertilisers and organic amendments on soil properties. In this study, samples were taken from 11 of the treatments, including unfertilised bare fallow and cropped fallow, straw with and without N addition, green manure, peat, farmyard manure, sawdust, sewage sludge, calcium nitrate and ammonium sulphate, with n = 4 for each treatment. Samples were taken from topsoil (0–20 cm) and subsoil (27–40 cm depth) and analysed for concentrations of phospholipid fatty acids (PLFAs), organic C, total N and pH. The results showed that the subsoil samples reflected the total PLFA content of the topsoil, but not the microbial community structure. Total PLFA content was well correlated with total organic C and total N in both topsoil and subsoil. Total PLFA content in topsoil samples was highest in the sewage sludge treatment (89 ± 22 nmol PLFA g dw−1). This contradicts earlier findings on microbial biomass in this sewage sludge-treated soil, which indicated inhibition of microorganisms, probably by heavy metals added with sludge. A switch towards microbial growth and faster decomposition of organic matter occurred around 2000, coinciding with lowered heavy metal content in the sludge. According to the PLFA data, the microbial community in the sewage sludge treatment is now dominated by Gram-positive bacteria. A lack of Gram-negative bacteria was also observed for the ammonium sulphate treatment, obviously caused by a drop in pH to 4.2.

Plant availability of trace elements in sewage sludge-treated soils: methodology¹

Synthetic root exudates were formulated based on the organic acid composition of root exudates derived from the rhizosphere of aseptically grown corn plants, pH of the rhizosphere, and the background chemical matrices of the soil solutions. The synthetic root exudates, which mimic the chemical conditions of the rhizosphere environment where soil-borne metals are dissolved and absorbed by plants, were used to extract metals from sewage-sludge treated soils 16 successive times. The concentrations of Zn, Cd, Ni, Cr, and Cu of the sludge-treated soil were 71.74, 0.21, 15.90, 58.12, and 37.44 mg kg-1, respectively. The composition of synthetic root exudates consisted of acetic, butyric, glutaric, lactic, maleic, propionic, pyruvic, succinic, tartaric, and valeric acids. The organic acid mixtures had concentrations of 0.05 and 0.1 mol L-1 -COOH. The trace elements removed by successive extractions may be considered representative for the availability of these metals to plants in these soils. The chemical speciation of the metals in the liquid phase was calculated; results showed that metals in sludge-treated soils were dissolved and formed soluble complexes with the different organic acid-based root exudates. The most reactive organic acid ligands were lactate, maleate, tartarate, and acetate. The inorganic ligands of chloride and sulfate played insignificant roles in metal dissolution. Except for Cd, free ions did not represent an important chemical species of the metals in the soil rhizosphere. As different metals formed soluble complexes with different ligands in the rhizosphere, no extractor, based on a single reagent would be able to recover all of the potentially plant-available metals from soils; the root exudate-derived organic acid mixtures tested in this study may be better suited to recover potentially plant-available metals from soils than the conventional extractors.

Extratores químicos empregados na determinação de P como indicadores ambientais em solos tratados com lodo de esgoto

A aplicação de lodo de esgoto pode contribuir para elevar os teores de alguns nutrientes no solo de forma inadequada, como, por exemplo, o P. Na prática, as doses de lodo de esgoto são calculadas com base na necessidade de N das culturas, não levando em conta a necessidade de P ou o destino do P aplicado com o resíduo. O P é um nutriente frequentemente associado com a aceleração da eutrofização nos corpos hídricos, em virtude do seu transporte por meio da enxurrada. O presente trabalho teve por objetivo avaliar se três extratores químicos empregados na determinação de P em solos para fins de fertilidade (CaCl2 0,01 mol L-1; Mehlich-1 e RTA) e um índice ambiental (GSP) poderiam ser utilizados na avaliação de impactos ambientais negativos, promovidos pelo deslocamento de P adicionado ao solo por lodo de esgoto em direção a corpos de água. A resposta desses extratores na determinação de P dos solos tratados com lodo de esgoto foi avaliada nas condições convencionais de uso e variando o tempo de extração do método original em busca da maior extração de P. Além disso, os extratores também foram avaliados após a alteração do pH das amostras de solo originais para modificar a disponibilidade de P. Os resultados obtidos com os extratores químicos foram comparados com os do fracionamento do P nas amostras. O fracionamento de P mostrou que a aplicação de lodo aumentou não apenas as concentrações totais de P no solo, mas também sua disponibilidade. Esse efeito foi mais pronunciado no solo de Jaguariúna (argiloso) do que no de Itatinga (arenoso). Houve aumento nas frações de P orgânico e inorgânico lábil e de P ligado a Al e Fe, em decorrência da aplicação do resíduo. Contudo, as frações de P solúvel e P ligado a Ca não foram encontradas em teores significativos nas amostras estudadas. Considerando que a alteração da disponibilidade de P induzida pela alteração do pH original das amostras não alterou as classes de teores do nutriente no solo empregadas usualmente nas recomendações de adubação, os extratores químicos e o indicador ambiental estudados são muito razoáveis para prever também riscos ambientais

Cinética de solubilização de metais pesados por ácidos orgânicos em solos tratados com lodo de esgoto

A presença de ligantes orgânicos na rizosfera tem importante papel no processo de solubilização de metais pesados em solos tratados com lodo de esgoto. Ácidos orgânicos de baixo peso molecular exsudados por raízes e, ou, liberados por microrganismos são considerados agentes mobilizadores desses metais. No presente estudo, determinou-se a cinética de solubilização de Cu, Cr, Ni e Zn em solos tratados com lodo de esgoto, utilizando solução com mistura de quatro ácidos orgânicos (acético, cítrico, lático e oxálico) preparada para obter concentração final de 0,05 e 0,10 mol L-1. A extração foi feita segundo o método de "batch". A solução 0,10 mol L-1 de ácidos orgânicos extraiu maiores quantidades de Cu, Cr, Ni e Zn do que a solução 0,05 mol L¹. A cinética de solubilização apresentou duas fases: uma inicial, com rápida liberação dos metais, seguida de outra mais lenta, tendendo ao equilíbrio. As constantes de velocidade de solubilização mais altas foram observadas para Ni e Zn, seguidos de Cu e Cr. Os valores para o reservatório lábil variaram entre 2 e 15 % do total de cada metal pesado estudado. A porcentagem que este reservatório representou, em relação ao total, obedeceu à ordem: Zn &gt; Cu &lt;FONT FACE=Symbol&gt;@&lt;/FONT&gt; Ni &gt; Cr.

The use of bioassays for evaluating the toxicity of sewage sludge and sewage sludge-amended soil

In soils, the most commonly mentioned hazardous substances are metals. One of the sources of its accumulation is the application of sewage sludge. However, little information is available regarding the estimation of the toxicity of sewage sludge or soil treated with sewage sludge, even by means of a battery of bioassays. In this study an evaluation of a battery of bioassays was carried out for toxicity assessment of sewage sludge and sewage sludge-treated soil. The objectives of this study were a) to compare the sensitivity of the different bioassays for the toxicity determination of sewage sludge contaminated with metals and soil treated with this sewage sludge, b) to elaborate a procedure for the attribution of sewage sludge samples to hazard classes based on the ecotoxicological data, and c) to evaluate the suitability of elutriate bioassays and microbial toxicity tests for the assessment of sewage sludge-treated soil. Experiments were carried out on grey forest soil (Haplic Greyzem) treated with existent sewage sludge obtained from the Municipal Wastewater Treatment Plant of the city of Kazan, Tatarstan, Russia. Portions of sludge were preliminary spiked by adding water-soluble chlorides or nitrates containing the following metals/metalloids: As, Cd, Cr, Cu, Hg, Mn, Ni, Pb, Zn. The test battery included four organisms —bacteriumPseudomonas putida, protozoanParamecium caudatum, water fleaDaphnia magna and higher plantRaphanus sativus. In addition, the toxicity of the soils treated with sludge was measured using microbial bioassays based on the estimation of microbial respiration, microbial biomass, N2-fixation activity and calculation of the metabolic quotient. The comparison of the toxicity values (expressed as the lowest dilution factor which exhibits 10% inhibition of an estimated parameter) of three model samples of sewage sludge prepared by us showed different sensitivities for all test organisms. The most sensitive was observed in theDaphnia test, while a similar sensitivity was noted for theParamecium test. The other two tests proved to be less sensitive to the components of the sludge. The analysis of the soils treated with the sewage sludge samples, using the previously mentioned tests, showed that all metal-contaminated sludge treatments as well as the control soil were not significantly inhibitory to all elutriate tests except for that withDaphnia. The microbial toxicity studies including estimation of the microbial biomass C, respiration and N2-fixating activity appear to be more sensitive than the elutriate tests for toxicity in the case of soil treated with metal-contaminated sewage sludge. An integrated ecotoxicological approach to classify the sewage sludge into hazard classes is proposed based on toxicological analyses. The test battery including four bioassays is elaborated to establish the toxicity status of the sewage sludge. The proposed procedure is easy to apply, cost effective and relatively fast. The application of microbial toxicity tests can be very useful for risk assessment in the case of soil treated with metal-contaminated sewage sludge. The application of the bioassays appears to be very promising mainly for the risk identification of highly contaminated matrices with hardly identified composition such as sewage sludge or soil-associated contaminants. However, the future success in elaborating reliable toxicity tests can be achieved only by the progress in standardizing, national legislators and efforts of researchers.

Phosphorus sorption and availability in soils amended with animal manures and sewage sludge.

Soils that receive large applications of animal wastes and sewage sludge are vulnerable to releasing environmentally significant concentrations of dissolved P available to subsurface flow owing to the gradual saturation of the soil's P sorption capacity. This study evaluated P sorption (calculated from Langmuir isotherms) and availability of P (as CaCl2-P and resin P) in soils incubated for 20 d with poultry litter, poultry manure, cattle slurry, municipal sewage sludge, or KH2PO4, added on a P-equivalent basis (100 mg P kg(-1)). All the P sources had a marked negative effect on P sorption and a positive effect on P availability in all soils. In the cattle slurry- and KH2PO4-treated soils, the decreases in P sorption maximum (19-66%) and binding energy (25-89%) were consistently larger than the corresponding decreases (7-41% and 11-30%) in poultry litter-, poultry manure-, and sewage sludge-treated soils. The effects of cattle slurry and KH2PO4 on P availability were, in most cases, larger than those of the other P sources. In the poultry litter, poultry manure, and sewage sludge treatments, the increase in soil solution P was inversely related (R2 = 0.75) to the input of Ca from these relatively high Ca (13.5-42 g kg(-1)) sources. Correlation analyses implied that the magnitude of the changes in P sorption and availability was not related to the water-extractable P content of the P sources. Future research on the sustainable application of organic wastes to agricultural soils needs to consider the non-P- as well as P-containing components of the waste.

Availability and fractionation of phosphorus in sewage sludge-amended soils1

A laboratory incubation study was conducted with the objective of determining the effects of time, temperature, and soil properties on availability and chemical fractions of phosphorus (P) in sewage sludge-amended soils. Anaerobically digested sewage sludge was mixed with three soils (Crofton silty clay loam, Moody silty clay loam, and Thurman sandy loam) at a rate equivalent to 80 Mg sludge ha−1. The mixtures were incubated at 25 and 37°C for up to 120 days. Phosphorus in sewage sludge-treated soils was extracted with iron-oxide impregnated filter paper strips (strip-P). Phosphorus also was fractionated chemically into four components by sequential extraction. Phosphorus concentration in all fractions increased with sludge application. Strip-P concentration was higher at 25°C in all soils than at 37°C over the entire period of incubation. Soluble-P was greatest in sandy Thurman soil at both temperatures over all incubation times. A sharp increase in non-occluded P (NOC-P) concentration occurred in all soils with time at both temperatures. Occluded P (OC-P) in all soils decreased more rapidly with time at 37°C than at 25°C. Calcium-P (Ca-P) concentration was unaffected by time and was highest in calcareous Crofton soil. Soil texture and the presence of carbonates strongly influence the fate of P from applied sewage sludge. It was concluded, based on time trends that sludge as a P source on a P-limited soil should be applied well before the period of maximum plant demand. Elevated temperature (37°C) typical of mid-summer, promotes depletion of more available (strip-P and soluble P) fractions compared with lower temperature (25°C). *Contribution of the University of Nebraska Agric. Res. Div., Lincoln, NE as paper no. 13093.

Chemical properties and enzyme activity in a sewage sludge-treated soil

A soil sample was taken from the top 0–20 cm at Jaboticabal county, São Paulo State, Brazil, air dried, sieved to 5 mm, and placed into pots (2700 g per pot). Sewage sludge was air-dried, ground to 2 mm, and thoroughly mixed to the top 0–10 cm soil of each pot, which were irrigated with distilled water in a total volume equivalent to the last 30 years average rainfall in the region. Sorghum was sowed 120 days after sewage sludge incorporation and then the irrigation was made according to the plants' requirement. When the plants were about 10 cm high, they were thinned to two per pot. Soil samples (0–10, 10–20, and 20–30 cm depth) were obtained immediately after the incorporation of sewage sludge and at 30, 60, 120, and 170 days after, air dried, sieved to 2 mm and analyzed for organic matter (OM), pH (0,01 mol L−1 CaCl2), extractable P (resin), potassium (K), calcium (Ca), and magnesium (Mg), amylase and cellulase activity. Sewage sludge increased soil OM, pH, extractable phosphorus (P), K, Ca, amylase and cellulase activity, especially at the rate 16 t ha−1. Organic matter, extractable P, K, Ca, Mg, and amylase activity were higher in the top 0–10 cm, while pH was higher in the 20–30 cm layer. Amylase activity was not affected by sampling depth. Organic matter, pH, extractable P, K, Ca, and Mg decreased during the experimental period. Amylase activity decreased until sorghum was sowed and increased afterwards. Cellulase activity increased until 90 days after sewage sludge application and then decreased. Sewage sludge used in the experiment should already contain some amylase activity or a substance that was a soil enzyme activator and also a substance that was an inhibitor of soil cellulase inhibitor. Some of the plant nutrients contained in sewage sludge, mainly P, did not migrate down the soil column, an indication that sewage sludge should be incorporated into the soil to improve nutrient bioavailability. Sorghum roots increased amylase activity but did not affect cellulase activity.

Leaching of cadmium, nickel, and zinc down the profile of sewage sludge-treated soil

The leachability of cadmium (Cd), nickel (Ni), and zinc (Zn) was studied in repacked 40 cm-soil columns. The hypotheses tested were that DOC (Dissolved Organic Carbon) will influence the metal movement, and that this will be increased with the water application rates. Sludge was placed on the top of the columns at rates of 0, 10, and 50 t ha− 1 and two water regimes were applied, equivalent to 450 mm and 900 mm per year. It was found that at 50 t ha− 1, the total concentrations of Cd and Zn were significantly higher than the control down to a depth of 8 cm, while Ni moved to 10 cm. In the leachates collected underneath the columns, soluble forms of Ni and Zn were found in significantly higher concentrations at 50 t ha− 1 than in the control. DOC was also found in the leachates at elevated concentrations in the high sludge treatment. This indicated that sludge-evolved DOC might have played a significant role in facilitating soluble Ni and Zn transport down the soil profile. Calculations of the budget of metals (metals entering the soil columns compared to the amounts lost from columns) indicated that the elution of Ni, Zn and DOC was enhanced at 900 mm, compared to 450 mm. The results suggest the adverse environmental implications that may exist in conditions that include high precipitation, sandy soils and elevated sewage sludge application rates.

Heavy Metal Uptake by Willow Clones from Sewage Sludge-Treated Soil: The Potential for Phytoremediation

ABSTRACT Willow (Salix spp.) has shown potential for use in the phytoremediation of soil contaminated with heavy metals. In particular, it can be grown in short rotation coppice systems to produce biomass that can be used for energy production. Twenty different species or varieties of willow, grown over 2 years (1995 to 1997) on a soil that was highly contaminated with heavy metals due to long-term sewage sludge disposal, showed considerable variation in survival, biomass production and metal uptake. The willows could be divided into two groups after the first harvest. One group had relatively low Ni and Cu in the bark and high Cd and Zn in the wood, with a good survival rate and biomass production. This group partitioned Cu, Cd, and Zn into the wood tissue from the bark, whereas Ni was excluded. The second group had relatively high Ni and Cu in the bark and low Cd and Zn in the wood and performed poorly in terms of survival and biomass production. Of the 20 types of willow used, 11 showed potential for use in phytoremediation, combining good survival and biomass production with high metal uptake. Of the others, 2 failed to survive until the second harvest and the other 7 had very poor survival rates.

Availability of Cd, Ni and Zn to Ryegrass in Sewage Sludge-Treated Soils at Different Temperatures

A pot experiment to compare the availability of Cd, Ni and Znto ryegrass (Lolium perenne L.) was conducted at 15 and 25 °C. For this purpose, three ratesof sewage sludge (0, 10 and 50 t ha-1) were applied in aloamy sand (LS) and a clay loam (CL). Heavy metal availabilityassessed by soil extractions with 0.05 M CaCl2 and the organic matter content were monitored during a period of twoyears, while uptake by ryegrass was monitored over one year after addition of the sludge. The concentrations of Cd and Ni in both the ryegrass and the soil extracts increased significantly, during the first year, especially at 50 t ha-1. However, in the second year metal availability reached a plateau. During the first year, in the ryegrass Znconcentrations did not show an increase, but in the soil CaCl2-extracted Zn increased. During the same period,the organic matter content decreased rapidly, especially at25 °C, in the first year and much more slowly in thesecond, giving a total decrease of 16%. Temperature had a marked effect on metal availability; both soil extracts andplant samples from the 25 °C treatment had greater concentrations of Cd, Ni and Zn than those at 15 °C. This may be attributed to the organic matter, which decomposedmore rapidly at 25 °C. Moreover, soil-plant transfercoefficients (Tc) of the metals were significantly higher at 25 °C than at 15 °C, with Cd showing the greatest difference, followed in decreasing order by Zn and Ni.

Essential Oil Quality and Heavy Metal Concentrations of Peppermint Grown on a Municipal Sludge‐Amended Soil

Potentially hazardous heavy metals accumulated in soil may present a long-term problem for plant growth and human health. If non-food crops are grown on heavy metal-contaminated soils, the potential for food chain transfer of hazardous heavy metal elements from contaminated soils to consumers may be reduced. In a pot experiment, peppermint (Mentha X piperita L.) was grown on sewage sludge-treated soils that had metal concentrations 3 to 60 times higher than those of the control soil. The plants were harvested before anthesis, approximately 100 d after transplanting. The metal contents of plant tissue and essential oil extracted from leaves were determined; organic chemical compositions of the extracted oils were also analyzed. The results of the experiment indicated that the biomass production was not affected by the presence of metals up to 6.1, 256, 182, 86, 173, and 601 mg kg -1 dry weight for Cd, Cr, Cu, Ni, Pb, and Zn, respectively. The concentrations of Cd, Cr, Cu, Ni, and Pb in peppermint grown on sewage sludge-treated soils were not significantly different from those grown on control soil. Plant tissue Zn concentrations were significantly higher when the Zn concentration of the soils exceeded 260 mg kg -1 dry weight. The metal concentrations of the extracted oils of the control and the sewage sludge treatments were not significantly different and were always <1 mg L -1 . The chemical composition of oil was not affected by the presence of metals in sludge-treated soils.

Effect of soil pH on availability to crops of metals in sewage sludge-treated soils. I. Nickel, copper and zinc uptake and toxicity to ryegrass

The effect of soil pH value on concentrations of Ni, Cu and Zn in ryegrass grown on two sludge-treated soils was examined under field conditions and the maximum permissible soil limit values for these elements were determined which prevent phytotoxicity in crops where sewage sludge is applied to agricultural soils with pH <6.0. Concentrations of all the elements in ryegrass decreased as simple linear functions of increasing soil pH and this response was consistent across the range of pH values measured (pH 4.2–7.0). The response of individual elements tended to differ though, with Cu being less sensitive to changing pH conditions compared with Zn and Ni which responded in a similar mammer. The yield of ryegrass also increased with increasing soil pH value probably due to the effects on Zn uptake as the crop content of Zn exceeded known upper critical tissue concentrations for this element at both sites. The proportional change in metal content of ryegrass at pH 5.0, 5.5 and 7.0 from tissue concentrations at pH 6.0 was calculated to determine the permissible soil concentration values on the basis of current maximum limits set by the Sludge Regulations in the UK for sludge-treated agricultural land at pH 6.0–7.0. The estimated permissible concentrations of Ni and Zn in soil corresponded with the regulatory values at the low pH ranges, but were substantially above the current soil limits at pH 7.0 indicating larger quantities of these elements could be safely applied under alkaline soil conditions. The estimated soil limits for Cu implied that the current Regulations were highly precautionary for this element.

Effect of soil pH on availability to crops of metals in sewage sludge-treated soils. II. Cadmium uptake by crops and implications for human dietary intake

Appropriate pH-related permissible soil-limit concentrations for cadmium in sewage sludge-treated agricultural soils were estimated from the proportional changes in concentrations of cadmium in potatoes, oats and ryegrass grown on two sludge-amended soils and at different pH values. Implications for potential human dietary intake of cadmium were also assessed. Yields of crops increased with increasing soil pH, probably in response to decreasing uptake of zinc as soil pH value was raised. In general, cadmium concentrations in peeled potato tubers, potato peelings, oat straw and ryegrass decreased as simple linear functions of increasing soil pH over the range of pH values measured (pH 3·9·7·6). Cadmium concentrations in potato peel were particularly sensitive to changing pH conditions, whereas cadmium levels in oat grain were independent of soil pH. On the basis that a highly precautionary approach is adopted in setting soil standards for heavy metals, appropriate permissible concentrations of cadmium in sludge-treated agricultural soil which protect the human food chain were determined as 2·0 and 2·5 mg Cd Kg −1 for banded pH ranges of 5·0–5·5 and 5·5–6·0, respectively.