Plant availability of heavy metals in a soil amended with a high dose of sewage sludge under drought conditions

The objective of this research was to study the effect of water deficit on soil heavy metal availability and metal uptake by ryegrass (Lolium multiflorum Lam.) plants grown in a soil amended with a high dose of rural sewage sludge. Three fertility treatments were applied: sewage sludge (SS), mineral fertilizer (M), and control (C); unamended). The levels of irrigation were: well-watered (W) and water deficit (D). Microbial respiration decreased the total organic C (TOC) in sludge-treated soils, but this did not enhance soil DTPA-extractable heavy metal concentrations. Indeed, Zn, Cu, Mn and Ni availability decreased during the experiment. C- and M-treated soils showed either no changes or increases of some trace element concentrations during the incubation. In the plant experiment, ryegrass dry matter (DM) yield, relative water content (RWC) and leaf water potential (_w) decreased in drought conditions. Sludge addition increased metal concentrations in plants. However, in some instances, SS-treated plants showed either similar or lower transfer coefficient (Tc) values than did plants in the C and M treatments. Water deficit decreased the concentration and the Tc of some metals in roots of M and SS plants. Results indicate that sludge-borne heavy metals were maintained in chemical forms of low availability. The lower metal uptake by SS and M plants under dry conditions cannot be attributed to a lower availability of these elements in soil.     

The change of heavy metals fractions during hydrochar decomposition in soils amended with different municipal sewage sludge hydrochars

Purpose

This study was to investigate the changes of heavy metals in the soils amended with different municipal sewage sludge hydrochars.

Materials and methods

Sewage sludge hydrochars prepared at either 190 or 260 °C, for 1, 6, 12, 18, or 24 h, respectively, were added to soil samples and then incubated for 60 days. Water-extractable organic carbon (WEOC) and CO₂ evolution were determined during the incubation. The total quantities of heavy metals and their different fractions were analyzed by inductively coupled plasma spectrometry (ICP).

Results and discussion

Hydrochar-amended soils had much higher water-extractable carbon and more CO₂ evolution than control soil, indicating that the added hydrochars contained a significant amount of WEOC and could be decomposed during the incubation. Hydrochar addition immediately and significantly increased the total heavy metals of the soil. Moreover, both oxidizable and residual fractions of all heavy metals were significantly higher in all the hydrochar-added soils than those in control soil. Both oxidable and residual fractions of heavy metals decreased in the hydrochar-amended soils during 60-day incubation. In contrary, both acid soluble and reducible fractions of heavy metals increased in the hydrochar-amended soils during incubation. It is thus obvious that the heavy metals in both oxidable and residual fractions may be released during hydrochar decomposition and then be adsorbed by soil matrix such as carbonates, iron oxides, and clays.

Conclusions

Municipal sewage sludge can be readily carbonized into hydrochar. However, it is watchful of applying the hydrochar into soil since hydrochar addition increases in both total and bioavailable heavy metals in soil. More work is particularly required to investigate the long-term impacts on soil and environment.

     

Wheat grown on volcanic ash with slow releasing nitrogen fertilizer and amended with sewage sludge compost

Abstract

The volcanic ash of the Mount Pinatubo in Philippines is used in this study. The major drawbacks of this volcanic ash for growing agricultural crops are nitrogen (N) and iron (Fe) deficiencies with low organic matter contents. The objective of this study is to investigate the effect of sewage sludge compost on wheat through shoot and root development as well as dry matter production by pot culture. Either oxamide or polyolefinresin‐coated urea (PORCU) along with potash and phosphate fertilizers is applied to each pot containing volcanic ash. Application of sewage sludge compost in oxamide treatment yield a better plant height with an extended root length and high dry matter production compared to PORCU. However, statistical analysis of the data on plant height shows significant level (p<0.001, n=36), while those on root growth and dry matter production show no significant difference (p<0.335 and 0.564, n=36). Thus it is concluded that the coupling effect of oxamide and sewage sludge compost has a greater impact on plants, while growing on this ash.     

Impact of heavy metal amended sewage sludge on forest soils as assessed by bacterial and fungal biosensors

Bacterial and fungal bioluminescence-based biosensors were used as indicators of potential heavy metal toxicity to microorganisms in the needle litter of a mature Pinus radiata forest under heavy metal contaminated sewage sludge. Sewage sludge was amended with increasing concentrations of Cu, Ni and Zn and applied to the surface of a mature P. radiata forest. The response of the bacterial and fungal biosensors to soluble Cu, Ni and Zn in needle litter extracts was investigated. The bioluminescence response of the bacterial biosensor Escherichia coli HB101 pUCD607 declined as water-soluble Zn concentrations increased. The effective concentrations that gave a 50% reduction in bioluminescence (EC₅₀ values) for water-soluble Zn and total litter Zn were 1.3 mg l⁻¹ and 3700 mg kg⁻¹, respectively. The bioluminescence response of the fungal biosensor Armillaria mellea declined as soluble Cu concentrations increased. The EC₅₀ values for water-soluble Cu and total litter Cu were 0.12 mg l⁻¹ and 540 mg kg⁻¹, respectively. No decline in bioluminescence was noted for either the bacterial or fungal biosensor on exposure to increasing concentrations of water-soluble Ni. The use of a combination of bacterial and fungal biosensors offers a rapid and sensitive tool for assessing toxicity of heavy metals to microorganisms and, thus, elucidating the environmental impact of contaminants in sewage sludge on litter dwelling microorganisms.     

Heavy metal uptake by blue grama growing in a degraded semiarid soil amended with sewage sludge

Sewage sludge application to semiarid grassland may represent a beneficial means of utilizing this waste product for restoration of degraded sites. Consequently, dried municipal sewage sludge was applied at three rates (22.5, 45, and 90 Mg ha^–1) to a degraded semiarid grassland soil in order to determine the effects of sludge amendments on forage productivity, soil heavy metal content, and metal uptake by blue grama (Bouteloua gracilis).Soil and plant properties in control and amended plots were measured after 1, 2, and 5 growing seasons.Soil nutrients increased linearly with increased sludge application in the first two growing seasons. Consequently, forage quality and total production of blue grama improved significantly over the unamended control as the tissue levels of N, P, K, and crude protein increased. Cadmium and Pb in the sludge-treated plots did not increase significantly over the control after 1 and 2 growing seasons. Levels of DTPA-extractable soil micronutrients (Cu, Fe, Mn, Zn) increased linearly with increased sludge application rate to soil concentrations recommended for adequate plant growth. Soil N, P, and K concentrations remained higher in the sludge-amended soils after 5 growing seasons, while Cu and Cd increased to slightly above desireable limits as the soil pH decreased to 7.4 and 7.0 in the 45 and 90 Mg ha^–1 treatments, respectively. However, with the exception of Mn which remained within desirable limits, metal concentrations (including Cu and Cd) in blue grama tissue were not significantly different from the control treatment after five growing seasons. Based on soil and plant tissue metal concentrations, it appears that sludge applied at rates between 22.5 and 45 Mg ha^–1 will maintain the most favorable nutrient levels coupled with significant improvements in forage production in this semiarid grassland environment.     

Residual metal reactivity of humic acids extracted,from soil amended with sewage sludge

Copper, Fe, and Mn were used as probes to investigate residual metal reactivity for humic acid (HA) samples extracted from a loam soil, either non-amended or amended with anaerobically digested sewage sludge for 4, 5, 6, or 7 yr at 90 t ha^?1. yr^?1. Irrespective of their origin, the HA complexes significant amounts of metal, in forms stable against intense water-leaching, in the order Fe > Cl > Mn. Sludge-amended soil HA adsorbed and retained Fe in amounts greater than HA extracted fron non-amended soil. Metal adsorption occurred mainly by cation-exchange replacement of metals previousl: bound to HA. Water-stable Fe³⁺-HA complexes prepared in the laboratory were partially stable agains H⁺ and metal ion exchange reactions, whereas Cu²⁺ and Mn²⁺ in laboratory-prepared, water-stabl HA complexes were desorbed almost completely by these two reactions. Electron spin resonance spectra indicated that the laboratory-prepared metal-HA complexes had a chemical composition and molecula structure similar to that of indigenous metal-HA complexes, which were stable against all leachin, and cation-exchange treatments. Although the HA samples showed a maximal metal binding (i.e. saturation) as metal loading of the sludge-amended soil increased, they still exhibited a high residua binding capacity for the three metals used as probes.     

Renovation of a pear orchard site with sludge compost

Abstract

A lime‐stabilized sewage sludge compost was used as a surface amendment to improve the soil and nutritional status of a number of established pear cultivars grown on an acidic, low ferility soil site. Leaf Ca status was significantly increased while trace metals were not elevated and in most cases decreased by sludge compost over the course of the study. Soil chemical properties were modified in a manner similar to liming. Addition of sludge composts, particularly low metal containing materials, appears to represent an acceptable aid in renovating established pear orchards located on poor soil sites. Leaf, fruit flesh or peel Cd were not significantly effected by the compost addition. The compost added twice the recommended level of available N the first year and sub‐optimum N the following two years. Leaf N, although significantly increased in the composted versus non‐composted controls, was below sufficiency levels by the third year after addition. This indicates that compost cannot fully supply required N from a one time application even over the short term.     

Effects of municipal solid waste compost and sewage sludge on mineralization of soil organic matter

This work sets out to verify whether the application of municipal solid waste compost (MSWC) or treated urban sewage sludge (USS) organic amendments efficiently promote organic matter (OM) increases in a Haplic Podzol (PZha) and in a Calcic Vertisol (VRcc). For that purpose, carbon (C) mineralization and C kinetic parameters were studied, using a laboratory experimental incubation setup. The results showed that the addition of the amendments to the soils increased their mineralization capacities, and that the highest C mineralization rate was reached at the end of the first 2 d of incubation. The different characteristics of the soils seem to have influenced the C mineralization rates during the 28-d incubation. The USS induced higher C mineralization than the MSWC, and the PZha soil gave rise to higher C mineralization than VRcc. For all treatments, C mineralization adjusted well to an exponential plus linear kinetic model, suggesting that the organic C of the amendments was made up of two organic pools of differing degrees of stability. With the exception of the application of USS 60 t ha⁻¹, all the treatments increased the OM content on both soils, or at least the OM remained constant throughout the incubation.     

Enzyme activity and microbial biomass in a field soil amended with municipal refuse

Summary Changes in enzyme activity levels, in biomass-C content, and in the rate of fluorescein diacetate hydrolysis were measured in a loamy soil to which solid municipal refuse had been applied as compost over a 3-year period at two different rates. Addition of the compost caused significant increases in the activity of all enzymes tested. The increases were much higher at 90 t ha^-1 year^-1 than at 30 t ha^-1 year^-1. Significant increases were also observed in the biomass-C content and in the rate of fluorescein diacetate hydrolysis. Significant correlations among changes in biomass-C content and the rate of fluorescein diacetate hydrolysis and the changes in all enzymes tested were found.Two activity indices were calculated; a biological index of fertility and an enzyme activity number. No correlations were found between the biological index of fertility and the changes in the various enzyme activities. However, significant correlations were found either between enzyme activity number and most of the changes in enzyme activity, or between the enzyme activity number index and the biomass-C content (r=0.850). The use of a new activity index, the hydrolysis coefficient, is proposed. This coefficient was significantly correlated with biomass-C content (r=0.925) and with the enzyme activity number index (r=0.780).     

Heavy metals in mine soils amended with sewage sludge

In order to reclaim a clay quarry, a topsoil material was mixed with gravelly spoil at different ratios and with various rates of sewage sludge. The influence of three spoil/topsoil ratios (1:1, 2:1 and 3:1) and three sludge rates (40, 80 and 120 t ha⁻¹) on chemical properties of the resulting material was investigated, with emphasis on heavy metal (Fe, Cu, Mn, Ni and Zn) contents. The mixtures topsoil/spoil/sludge were water saturated and incubated for 15 or 30 days in a chamber under controlled conditions. The incubated samples were analysed for pH, total carbon and nitrogen, and total, available, exchangeable and soluble heavy metals. The addition of spoil to the topsoil increased the volume of material available, by utilizing an inert material unsuitable by itself to grow plants. The addition of sewage sludge repaired the disadvantages of the spoil, increasing the pH and the organic matter contents. The total heavy metal contents in the mixtures followed the sequence Fe>>Mn>>Zn, Cu>Ni. All except Cu were within the ranges allowed for agricultural lands. The available heavy metals constituted a small fraction of total contents and decrease with time due to complexation and immobilization processes. The exchangeable and soluble fractions were almost negligible; only small amounts of Mn, Zn and Cu were detected. Therefore, the risk of contamination by heavy metals is insignificant in the conditions investigated. Copyright © 1999 John Wiley & Sons, Ltd.     

Carbon and trace element mobility in an urban soil amended with green waste compost

Background, aim and scope  

The amendment of degraded urban soils using recycled organic wastes offers potential improvements to physicochemical status and functionality, but there is a paucity of knowledge on the potential impact on residual contaminants in soil. The aim of this study was to evaluate the mobility of trace metals and arsenic (As) through an urban soil following amendment with green waste compost over an annual cycle.     

Determination of mobile heavy metal fraction in soil: Results of a pot experiment with sewage sludge

Abstract

The development of a method using a chelating resin to assess heavy metal mobility in soil and the first results obtained from a pot experiment with sewage sludge additions were studied. The resin was Chelex 100 with the calcium (Ca)‐form of the resin proving to be best suited for the extraction. The efficiency of recovery of the heavy metals from an aqueous solution ranged from 81.2% for cadmium (Cd) to 102% for copper (Cu) within 24 hours. For heavy metal extractions from a soil sample, a 96 hour extraction period was found to be optimum. The extracted heavy metal portion was comparable with the results obtained with an ammonium acetate (NH₄AOc) extraction. Total heavy metal contents in the substrate of the pot experiment did not show a significant influence due to the sewage sludge treatments, although considerable amounts of heavy metals were added by the sewage sludge. This effect can be both due to the incomplete recovery of heavy metals by an aqua regia extraction and leaching losses of these elements from the pots. Rape (Raphanus sativus L.) plants did not have any heavy metal contents which might indicate a high availability in soil, with the Cd and Cr contents in the rape biomass being partly lower in the sewage sludge‐treated pots than in the control plants; however, zinc (Zn) uptake slightly increased with increasing sewage sludge treatments. The Chelex 100 extraction procedure was correlated with Cd plant uptake, while the NH₄AOc extraction procedure was better related to the Zn uptake by rape plants.     

Phosphorus fractions and phosphorus delivery potential of a luvisol derived from loess amended with organic materials

In a long-term field experiment, started in 1962, the fate of P applied with different organic materials [farmyard manure (FYM), compost and sewage sludge] in comparison to mineral fertilizer was investigated. Soil samples were collected after 38 years' continuous addition of these amendments to a luvisol derived from loess and cultivated to a cereal-root crop sequence. The total P (P_t) content of all treatments increased compared with the original soil; NaOH-inorganic P (NaOH-P_i) representing Fe- and Al-bound P was the dominant inorganic fraction. At the beginning of the experiment the various P pools could be quantitatively ranked in the following order: NaOH-P_i>residual P~NaHCO₃-P_i>H₂O-P>HCl-P. The order changed as follows: NaOH-P_i>NaHCO₃-P_i>residual P~H₂O-P>HCl-P, with transformations of non-labile residual P to the labile NaHCO₃-P_i pool with continued P fertilization and cropping. In addition, the content of organic P (P_o) forms (NaOH-P_o and NaHCO₃-P_o) increased. P_t delivery potential (desorbable P pool) increased between 35% and 185% compared to the P delivery potential in 1962. Compared to mineral fertilizer application, the application of organics resulted in a significantly higher, and FYM in a lower, P adsorption capacity of soils. The calcium lactate-extractable P (plant-available P) increased from 43.1 mg kg^-1 soil in 1962 to 175.9 mg kg^-1 soil in the treatment with 49 t compost ha^-1. The increase in the citrate-dithionate Fe-O ranged between 44% and 154% in the different treatments compared to the Fe-O content in 1962. In a pot experiment with soil from the field experiment, P removal by ryegrass was in the following sequence: FYM>compost=sewage sludge>mineral fertilizer.     

Carbon and nitrogen mineralization of sewage sludge compost in soils with a different initial pH

Soil properties may affect the decomposition of added organic materials and inorganic nitrogen (N) production in agricultural soils. Three soils, Potu (Pu), Sankengtzu (Sk) and Erhlin (Eh) soils, mixed with sewage sludge compost (SSC) at application rates of 0 (control), 25, 75 and 150 Mg ha⁻¹ were selected from Taiwan for incubation for 112 days. The aim of the present study was to examine the effects of SSC application rates on the carbon decomposition rate, N transformation and pH changes in three soils with different initial soil pH values (4.8–7.7). The results indicated that the highest peaks of the CO₂ evolution rate occurred after 3 days of incubation, for all treatments. The Pu soil (pH 4.8) had a relatively low rate of CO₂ evolution, total amounts of CO₂ evolution and percentage of added organic C loss, all of which resulted from inhibition of microbial activity under low pH. For the Pu and Sk soils, the concentration of NH₄⁺-N reached its peak after 7–14 days of incubation, which indicated that ammonification might have occurred in the two soils with low initial pH values. NO₃⁻-N rapidly accumulated in the first 7 days of incubation in the Eh soil (pH 7.7). The direction and extent of the soil pH changes were influenced by the N in the SSC and the initial soil pH. Ammonification of organic N in the SSC caused the soil pH to increase, whereas nitrification of mineralized N caused the soil pH to decline. Consequently, the initial soil pH greatly affected the rate of carbon decomposition, ammonification and nitrification of SSC.     

The influence of compost addition on heavy metal distribution between operationally defined geochemical fractions and on metal accumulation in plant

Purpose

Metal distribution patterns among geochemical fractions are informative for metal phytoavailability. Compost added to polluted soils may adsorb metals on the less phytoavailable fractions. A bioassay experiment was conducted to establish possible correlations between metal concentrations in different soil fractions and metal contents in edible plant parts and to investigate the influence of different compost loads on heavy metal availability to plants.

Materials and methods

Chinese cabbage plants were grown in pots with sandy and clayey soils and soils mixed with different doses of biosolid compost spiked with soluble heavy metal salts (Cd, Cu, and Pb). The metals’ distribution pattern in the soil and mixed samples was determined by sequential extraction procedure (modified BCR protocol). The studied fractions, from most to least bioavailable, were water-extractable (WE), exchangeable-adsorbed (EXC), associated with carbonates and acetic acid-soluble forms (CARB), occluded by reducible (hydro)oxides of Fe and Mn (RO), and associated with organic matter (OM) and a residual fraction (RES). Metal concentrations in soil extracts and in the digested plant tissue were measured by ICP-AES.

Results and discussion

The highest compost doses (72 and 115 Mg ha^?1) enhanced cabbage yield significantly. No excessive phytoaccumulation of metals was observed in plants grown in the clayey soil or its mixtures with compost. The compost dose of 72 Mg ha^?1 was optimal in decreasing Cu accumulation by plants grown in sandy soil, and 28.8 Mg ha^?1 was found to be effective in reducing Cd and Pb uptake. Metals were accumulated in plants primarily from the WE, EXC, and CARB fractions, whereas other fractions decreased phytoaccumulation. Compost addition suppressed heavy metal mobility, but different fractions were active in pollutant sorption, depending on soil type and metal.

Conclusions

Compost addition increased metal proportions in the RO and OM fractions, reducing metal phytoavailability. This is especially important for sandy soils with low adsorption ability and higher vulnerability to metal pollution than clayey soils. A compost dose of 20% v/v (or 28.8 Mg ha^?1) effectively reduced plant accumulation of Cd and Pb. We propose using the first three steps of the modified BCR protocol as a three-step sequential-extraction procedure for the most phytoavailable fractions of heavy metal: WE, EXC, and CARB.     

Microbiological processes in gray forest soil treated with sewage sludge compost

The effect of compost made of sewage sludge and applied in dose up to 90 t/ha on the microbial biomass, soil respiration, nitrogen-fixing activity, and on the organic matter content and concentrations of toxic metals in the gray forest soil of a nursery forest garden was studied in a field experiment. It was found that the adverse effects of the compost components on the studied parameters of the microbial communities were not observed two years after the compost application; this fact suggested that the soil microbial community overcame the stress caused by this anthropogenic impact.     

Plant colonization and biomass production in a xeric torriorthent amended with urban solid refuse

A long-term field experiment was conducted in a semiarid Mediterranean site to determine the effect of the application of several doses (6·5, 13, 19·5 and 26 kg m⁻²) of urban solid refuse (USR) on the plant colonization, plant cover and biomass production. The plant species richness did not increase in all the treated plots with respect to the control except immediately after the treatment was applied. This increase was only maintained after three years in the lowest dose of USR and the control. The addition of USR slowed floristic change and the lowest percentages of change corresponded to those plots receiving the highest doses. The plot receiving the lowest doses behaved in a similar way to the control plot. Plant cover increased substantially in the plots treated with USR compared with the control plot, even the lowest doses increasing the cover by 500 per cent. Plant biomass also significantly increased in all the amended plots compared with the control, although such increases were not directly proportional to the doses of USR added. USR can be considered an effective organic amendment to regenerate the plant cover of degraded soils. © 1997 John Wiley & Sons, Ltd.     

Magnesium deficiency in Douglas-fir and Grand fir growing on a sandy outwash soil amended with sewage sludge

Soil and plant samples were collected from chlorotic plantations of Grand fir (Abies grandis) and Douglas-fir (Pseudotsuga menziesii) in Winter, 1989. The soils had been amended in 1981 with an average of 300 dry Mg ha^?1 of municipal sewage sludge. The sludge amendment resulted in an N application rate of approximately 8000 kg ha^?1. Foliage analysis indicated a severe Mg deficiency (0.25 g kg^?1 in sludge-treated vs. 0.93 g kg^?1 in untreated area) might be the cause of chlorosis. No other nutrient showed concentrations in the deficient or toxic ranges. Trace metal levels in foliage were elevated significantly for Ni, Cd and Cr in sludge-treated sites, but not toxic levels. Soil samples taken to a depth of 1.4 m indicated the potential for soil acidification (up to 0.9 pH unit) in soil surface horizons. In addition, exchangeable Ca, Mg and K may have been depleted in surface horizons. Exchangeable Al and Fe were greater in the surface of sludge-treated sites. These observations and the loss of much of the nitrogen added during the sludge amendment indicated that nitrification and cation leaching was likely the mechanism for acidification and depletion of exchangeable cations. Fertilization of the plantation with MgSO₄ or dolomitic limestone was carried out in Spring 1990. New foliage collected in June, 1990 was non-chlorotic and significantly higher in Mg concentration than unfertilized foliage (1.1. vs. 0.7 g kg^?1, respectively). Results of this study indicate that it is important to assess the potential for initiating a nutrient deficiency due to secondary effects of sludge application in forest systems.     

Restoration of giant cardon cacti in barren desert soil amended with common compost and inoculated with Azospirillum brasilense

Barren desert soil that otherwise could not support perennial plant growth was amended with six levels of common agricultural compost. Seedlings of the giant cardon cactus, one of the primary plant species responsible for soil stabilization in the southern Sonoran Desert, were inoculated with the plant-growth-promoting bacterium Azospirillum brasilense Cd, planted, and grown for 18 months under nursery conditions typical for slow-growth cacti. Control plants were grown without compost amendment, without inoculation (negative control), or in fertile, rare “resource island” soil preferred by cardon seedlings (positive control). During the prolonged growth period, the decisive factor in seedling growth in barren soil was the addition of small amounts of common compost; 6 to 25% of the growth substrate volume gave the best growth response and, to a lesser extent, so did inoculation with A. brasilense Cd. Although the bacteria significantly affects plant growth when amended with “resource island” soil and added to barren soil, its effect on plant growth was far smaller than when compost alone was added. Compost added to barren soil significantly increased the dry weight parameters of the plant to almost similar levels obtained by the “resource island” soil; however, the compost amendment supports a more voluminous and greener plant with elevated pigment levels. This study shows that barren soil supplemented with compost can replace the rare “resource island” soil for cardon nurseries destined to abate soil erosion in the desert.