Cadmium availability to wheat grain in soils treated with sewage sludge or metal salts

Grain Cd concentrations were determined in wheat (Triticum aestivum L.) grown in 1999, 2001 and 2003, at six sludge cake field experiments. Three of these sites also had comparisons with Cd availability from metal amended liquid sludge and metal salts. Grain Cd concentrations in all years and at all sites were significantly linearly correlated with NH4NO3 extractable Cd and soil total Cd (P<0.001). Soil extractability was greater in the liquid sludge and metal salt experiments than in the cake experiments, as were grain Cd concentrations. Across all the sites, NH4NO3 extractable soil Cd was no better at predicting grain Cd than soil total Cd. Stepwise multiple linear regression analysis showed that soil total Cd, pH and organic carbon were the only significant (P<0.001) variables influencing wheat grain Cd concentrations, explaining 78% of the variance across all field experiments (1408 plots). This regression predicted that the current UK soil total Cd limit of 3 mg kg(-1) was not sufficiently protective against producing grain above the European Union (EU) grain Cd Maximum Permissible Concentration (MPC) of 0.235 mg Cd kg(-1) dry weight, unless the soil pH was > 6.8. Our predictions show that grain would be below the MPC with > 95% confidence with the proposed new EU draft regulations permitting maximum total Cd concentrations in soils receiving sludge of 0.5 mg kg(-1) for soils of pH 5-6, 1 mg kg(-1) for soils of pH 6-7, and 1.5 mg kg(-1) for soils of pH > or = 7.     

The persistence of polynuclear aromatic hydrocarbons (PAHs) in sewage sludge amended agricultural soils

In 1968, five metal enriched sewage sludges containing different concentrations of polynuclear aromatic hydrocarbons (PAHs) were applied to different plots on field soils at two experimental sites, Luddington and Lee Valley, in the UK. This resulted in substantial increases in the total PAH soil concentrations in all plots. Since application, losses have occurred, with the high molecular weight PAHs being more persistent. Calculated half-lives range from under 2 years for naphthalene to over 9 years for benzo[ghi]perylene and coronene. The losses of PAH compounds in these field experiments can be related, in part, to their physico-chemical properties, notably the octanol: water partition coefficient.     

Plant accumulation of potentially toxic elements in sewage sludge as affected by soil organic matter level and mycorrhizal fungi.

Leek (Allium ameloprasum) was grown in pot trials in two clay loams of contrasting organic contents, with and without indigenous mycorrhizal propagules. Sewage sludges containing varying levels of Cd, Cu and Zn were added. Extractable soil metals, plant growth, major nutrient content and accumulation of metals, and soil microbial indices were investigated. The aim was to establish whether soil organic content and mycorrhizal status affected plant and microbial exposure to these metals. Extractable metals were higher and responses to inputs more pronounced in the arable, lower organic matter soil, although only Cd showed a soil difference in the CaCl2 fraction. There were no metal toxic effects on plants and some evidence to suggest that they promoted growth. Uptake of each metal was higher in the larger plants of the grassland, higher organic matter soil. Inoculation with arbuscular mycorrhizal fungi increased root Cd and Zn concentrations. With the exception of Cd (roots) and Zn (shoots), higher inputs of sludge metals did not increase plant metals. Zn and Cu, but not Cd, concentrations were higher in roots than in shoots.     

The use of model compounds to elucidate metal forms in sewage sludge

Model phases of metal precipitates and organically bound metal were used to corroborate the nature of metal species found in sewage sludge by a sequential chemical extraction scheme. Model phase extractions supported the identification of the major species of Cd and Ni as carbonate (EDTA-extractable), Zn as organically-bound (Na(4)P(2)O(7)-extractable) and Pb as organically-bound or carbonate, although considerable overlap of fractions was apparent. Identification of the major species of Cu as sulphide (HNO(3)-extractable) could not be confirmed. The selectivity and efficiency of certain reagents was found to differ when used in sequence with other reagents, as opposed to being applied individually to model metal phases. Sample preparation was found to influence metal fractionation profiles in a model organic phase.     

Comparison of sewage sludge toxicity to plants and invertebrates in three different soils

Understanding the effect of soil type on the overall toxicity of sewage sludge is one of the most important issues concerning environmental risks associated with the sewage sludge land application. The aim of the study was to determine the influence of different soils (sandy, loamy and OECD soil) on sewage sludges toxicity in relation to plants (Lepidium sativum, Sorghum saccharatum, Sinapis alba) and an invertebrate species (Heterocypris incongruens). The most evident negative influence of sewage sludges on root growth was observed in the case of OECD soil. The EC(50) values determined on the basis of the root growth inhibition of all tested plants were in the range 0.1-6.4%, 0.03-9.4% and 6.6-22.1% (% of sewage sludgekg(-1) soil) for OECD, sandy and loamy soil, respectively. Soil type also affects the sewage sludge toxicity in relation to H. incongruens. The LC(50) (mortality) values ranged from 0.26% to 11.5% depending on the sludge tested. For EC(50) (growth inhibition) values ranged from 10.7% to 36.2%.     

Bioavailability and plant accumulation of heavy metals and phosphorus in agricultural soils amended by long-term application of sewage sludge

Amendment of agricultural soils with municipal sewage sludges provides a valuable source of plant nutrients and organic matter. Nevertheless, addition of heavy metals and risks of eutrophication continue to be of concern. Metal behaviour in soils and plant uptake are dependent on the nature of the metal, sludge/soil physico-chemical properties and plant species. A pot experiment was carried out to evaluate plant production and heavy metal uptake, soil heavy metal pools and bioavailability, and soil P pools and possible leaching losses, in agricultural soils amended with sewage sludge for at least 10 years (F20) compared to non-amended soils (control). Sewage sludge application increased soil pH, N, Olsen-extractable-P, DOC and exchangeable Ca, Mg and K concentrations. Total and EDTA-extractable soil concentrations of Cu and Zn were also significantly greater in F20, and soil metal (Cu, Mn and Zn) and P fractionation altered. Compared to the control, in F20 relative amounts of acid-extractable (Mn, Zn), reducible (Mn, Zn) and oxidisable (Cu, Zn) metal fractions were greater, and a dominance of inorganic P forms was observed. Analyses of F20 soil solutions highlighted risks of PO4 and Cu leaching. However, despite the observed increases in metal bioavailability sewage sludge applications did not lead to an increase in plant shoot concentrations (in wild plants or crop species). On the contrary, depending on the plant species, Mn and Zn tissue concentrations were within the deficiency level for most plants.     

Distribution coefficients of potentially toxic elements in soils from the eastern Amazon

The solid-solution distribution or partition coefficient (Kd) is a measure of affinity of potentially toxic elements (PTE) for soil colloids. Kd plays a key role in several models for defining PTE guideline values in soils and for assessing environmental risks, and its value depends on edaphic and climatic conditions of the sites where the soils occur. This study quantified Kd values for Cd, Co, Cr, Cu, Hg, Ni, Pb, and Zn from representative soil samples from Brazil’s eastern Amazon region, which measures 1.2 million km². The Kd values obtained were lower than those set by both international and Brazilian environmental agencies and were correlated with the pH, Fe and Mn oxide content, and cationic exchange capacity of the soils. The following order of decreasing affinity was observed: Pb?>?Cu?>?Hg?>?Cr?>?Cd?≈?Co?>?Ni?>?Zn.     

Effects of past sewage sludge additions on heavy metal availability in light textured soils: implications for crop yields and metal uptakes

The effect of heavy metal additions in past sewage sludge applications on soil metal availability and the growth and yield of crops was evaluated at two sites in the UK. At Gleadthorpe, sewage sludges enriched with salts of zinc (Zn), copper (Cu) and nickel (Ni) had been applied to a loamy sand in 1982 and additionally naturally contaminated Zn and Cu sludge cakes in 1986. At Rosemaund, sewage sludges naturally contaminated with Zn, Cu, Ni and chromium (Cr) had been applied in 1968-1971 to a sandy loam. From 1994 to 1997, the yields of both cereals and legumes at Gleadthorpe were up to 3 t/ha lower than the no-sludge control where total topsoil Zn and Cu concentrations exceeded 200 and 120 mg/kg, respectively, but only when topsoil ammonium nitrate extractable metal levels also exceeded 40 mg/kg Zn and 0.9 mg/kg Cu. At Rosemaund, yields were only decreased where total topsoil Cu concentrations exceeded 220 mg/kg or 0.7 mg/kg ammonium nitrate extractable Cu. These results demonstrate the importance of measuring extractable as well as total heavy metal concentrations in topsoils when assessing likely effects on plant yields and metal uptakes, and setting soil quality criteria.     

From agricultural use of sewage sludge to nutrient extraction: A soil science outlook

The composition of municipal wastewater and sewage sludge reflects the use and proliferation of elements and contaminants within society. In Sweden, official statistics show that concentrations of toxic metals in municipal sewage sludge have steadily decreased, by up to 90 %, since the 1970s, due to environmental programmes and statutory limits on metals in sludge and soil. Results from long-term field experiments show that reduced metal pollution during repeated sewage sludge application has reversed negative trends in soil biology. Despite this Swedish success story, organic waste recycling from Swedish towns and cities to arable land is still limited to only about 20 % of the total amount produced. Resistance among industries and consumers to products grown on land treated with sewage sludge may not always be scientifically grounded; however, there are rational obstacles to application of sewage sludge to land based on its inherent properties rather than its content of pollutants. We argue that application of urban organic wastes to soil is an efficient form of recycling for small municipalities, but that organic waste treatment from large cities requires other solutions. The large volumes of sewage sludge collected in towns and cities are not equitably distributed back to arable land because of the following: (i) The high water and low nutrient content in sewage sludge make long-distance transportation too expensive; and (ii) the low plant availability of nutrients in sewage sludge results in small yield increases even after many years of repeated sludge addition. Therefore, nutrient extraction from urban wastes instead of direct organic waste recycling is a possible way forward. The trend for increased combustion of urban wastes will make ash a key waste type in future. Combustion not only concentrates the nutrients in the ash but also leads to metal enrichment; hence, direct application of the ash to land is most often not possible. However, inorganic fertiliser (e.g. mono-ammonium phosphate fertiliser, MAP) can be produced from metal-contaminated sewage sludge ash in a process whereby the metals are removed. We argue that the view on organic waste recycling needs to be diversified in order to improve the urban–rural nutrient cycle, since only recycling urban organic wastes directly is not a viable option to close the urban–rural nutrient cycle. Recovery and recycling of nutrients from organic wastes are a possible solution. When organic waste recycling is complemented by nutrient extraction, some nutrient loops within society can be closed, enabling more sustainable agricultural production in future.     

Distribution of metals in grassland soils following surface applications of sewage sludge

In order to decide on a suitable sampling depth for grassland soil treated with sewage sludge and to assess implications for grazing animals, a field trial on two soils was designed to estimate the distribution of metals in grassland soil profiles following surface applications of sludge. Thus the sites represented permanent grassland where no form of cultivation had taken place. Soil cores were taken using specialised equipment to 30 cm depth and divided into seven sections. Movement from the soil surface to a depth of 10 cm was observed for all of the seven metals, Cd, Cr, Cu, Mo, Ni, Pb and Zn, but most of the metal (60%-100%, mean 87%) remained in the upper 5 cm of soil. It was concluded that sampling to a depth of 5 or 7.5 cm would be most suitable for monitoring long-term grassland treated with surface applications of sludge.     

The use of sewage sludge as remediation for imidacloprid toxicity in soils

Environmental Science and Pollution Research - This study investigated the influence of the sewage sludge (SS) soil amendment on the chronic toxicity of imidacloprid (through the seed dressing...     

Degradation of organic pollutants in Mediterranean forest soils amended with sewage sludge

The degradation of two groups of organic pollutants in three different Mediterranean forest soils amended with sewage sludge was studied for nine months. The sewage sludge produced by a domestic water treatment plant was applied to soils developed from limestone, marl and sandstone, showing contrasting alkalinity and texture. The compounds analysed were: linear alkylbenzene sulphonates (LAS) with a 10–13 carbon alkylic chain, and nonylphenolic compounds, including nonylphenol (NP) and nonylphenol ethoxylates with one and two ethoxy groups (NP1EO + NP2EO). These compounds were studied because they frequently exceed the limits proposed for sludge application to land in Europe. After nine months, LAS decomposition was 86–96%, and NP + NP1EO + NP2EO decomposition was 61–84%, which can be considered high. Temporal trends in LAS and NP + NP1EO + NP2EO decomposition were similar, and the concentrations of both types of compounds were highly correlated. The decomposition rates were higher in the period of 6–9 months (summer period) than in the period 0–6 months (winter + spring period) for total LAS and NP + NP1EO + NP2EO. Differences in decay rates with regard to soil type were not significant. The average values of decay rates found are similar to those observed in agricultural soils.     

Laboratory evaluations of the thermal degradation properties of toxic organic materials in sewage sludge

Laboratory thermal decomposition studies were performed to evaluate potential emissions from sewage sludge incinerators. Precisely controlled thermal decomposition experiments were conducted on sludge spiked with mixtures of hazardous organic compounds, on mixtures of pure compounds without sludge, and on unspiked sludge. Experiments were conducted in nitrogen and air atmospheres with gas phase reaction times of 2.0 seconds over the temperature range 300 degrees C-1000 degrees C. It was found that sludge inhibited the decomposition of moderately stable spiked contaminants but accelerated the decomposition of the most stable components. This effect was attributed to radical scavengers produced by the sludge matrix at lower temperatures which then decomposed at higher temperatures. A multiple hearth simulation study suggested that most of the organic material present in the sludge matrix is vaporized within the upper hearths that are held at lower temperatures and may consequently escape from such incinerators undestroyed. A number of stable byproducts resulted from the sludge decomposition that may be of environmental concern.     

Influence of cadmium on carbon and nitrogen mineralization in sewage sludge amended soils

The effect of cadmium on C and N mineralization in sewage sludge amended and unamended sandy loam, loam and clay loam soils was studied during 2 months incubation at 30+/-1 degrees C. The sludge amendment caused 15-39% increase in microbial respiration, with the maximum C mineralization in sandy loam and the minimum in loam soil. The addition of 10 microg Cd g(-1) soil had no remarkable effect on C and N mineralization and microbial biomass; whereas significant decreases in the above parameters were observed at 25 and 50 microg Cd g(-1) soil, irrespective of the sludge addition. Less NO3(-)-N accumulated at higher Cd concentration. Cd recovery was high in sandy loam and low in clay loam soil. DTPA extractable Cd exhibited a significant negative correlation with microbial biomass (r=-0.58* to -0.86*; p < 0.05).     

Effect of sewage sludges contaminated with polybrominated diphenylethers on agricultural soils

The fate of polybrominated diphenyl ethers (PBDEs) in sewage sludge after agricultural application was analysed. This study was based on the analysis of sewage sludge and sludge amended soil samples collected during 2005. PBDE concentrations in sewage sludge ranged from 197 to 1185ng/g dry weight (dw), being deca-BDE-209 the predominant congener. PBDE levels in soils ranged between 21 and 690ng/g dw, being BDE-209 also the predominant congener in all soil samples. Sewage-sludge amendment at the research stations increased concentrations of all BDE congeners 1.2- to 45-fold, with the highest increases for BDE-209. Results obtained evidenced the cumulative effect of the sludge application rates. Moreover, high levels found at soils four years after the last sludge application indicate persistence of PBDEs in soils, including deca-BDE-209.     

Anaerobic formation and degradation of toxic aromatic compounds in agricultural and communal sewage deposits

Relatively high concentrations of phenol, p-cresol, phenylacetic acid and other aromatic compounds were found in agricultural and communal sewage deposits. These toxic aromatic compounds are products of the bacterial degradation of aromatic amino acids under anaerobic conditions. In laboratory experiments at 26 degrees C and under N2-atmosphere, the same aromatics were formed from the amino acid tyrosine and from gelatine in assays inoculated with sewage sludge. After exhaustion of tyrosine and gelatine, respectively, concentrations of the accumulated phenol and other aromatics remained stable for months, i.e., phenol, p-cresol, phenylacetic acid etc. are dead-end products of the bacterial metabolism under these conditions. After addition of sodium nitrate the aromatic compounds are metabolically decomposed by denitrification within weeks.     

污泥中氧化硫硫杆菌的分离及其应用效果

以硫粉为能源物质,采用Waksman液体培养基培养,然后以Waksman固体培养基平板接种法直接从污泥中分离出1株高度嗜酸的氧化硫硫杆菌(Thiobacillus thiooxidan).该菌株适应环境速度快,易于驯化.序批式试验法研究表明,接种该菌株进行污泥生物淋滤可有效溶出污泥中的重金属.经过14 d的生物淋滤,Zn、Cu、Pb、Cr的最高去除率分别达到97%、96%、43%、44%.     

曝气强度对城市污泥重金属生物沥滤过程的影响研究

以氧化亚铁作为底物,氧化亚铁硫杆菌（Thiobacillusferrooxidans）为主要沥滤微生物,在底物投配比为10 g/L,温度为25℃,污泥浓度为123g/L的条件下,采用5种不同曝气强度对桂林城市污泥中重金属进行生物沥滤试验。结果表明,生物沥滤的经济曝气强度宜控制在每升污泥0.4L/（min·L）,沥滤3 d后,污泥中超标元素Cu、Zn和Cd的去除率分别达到62.53%、67.80%和54.63%,沥滤处理后污泥中残余重金属含量符合污泥农用的国家标准。     

Investigation of potentially bioavailable and sequestrated forms of polycyclic aromatic hydrocarbons during sewage sludge composting

The present study focuses on the influence of the composting process on the formation of potentially bioavailable and sequestrated PAH fractions. The potentially bioavailable fraction was determined by means of a mild-solvent extraction (with n-butanol). The total and potentially bioavailable PAH content was evaluated in the consecutive composting stages, i.e. at the onset of the experiment, after the stabilization phase (on the 35th day), and after the maturation phase (on the 76th day). Four municipal sewage sludges with differentiated PAH content were selected for the present experiment. Eleven PAHs from the US EPA list (with exception of naphthalene, acenaphthylene, acenaphtene, fluorene and benz[ah]anthracene) were determined for the purpose of this experiment. The content of the total PAHs ranged from 3052 to 10352microg kg(-1). The share of the potentially bioavailable fraction was at a similar level in the sludge samples tested and ranged from 75% to 81%. Greater differences were noted in the share of the bioavailable fraction in the case of individual PAH groups. The influence of the composting process on the contribution of the potentially bioavailable fraction of the PAH clearly depended on the stage of the experiment and sewage sludge type. However, in the case of all sludges, a lowering of the bioavailable fraction by 19-52% as compared to the level at the outset of the experiment was observed. During the first phase (stabilization) of the sewage sludge composting process, a reduction of the PAH content took place mainly at the expense of potentially bioavailable fraction, whereas in the second phase (maturation), sequestration processes predominated. The above phenomenon was most clearly visible for the 6-rings PAHs.     

Effects of sewage sludge biochar on plant metal availability after application to a Mediterranean soil

Pyrolytic conversion of sewage sludge into biochar could be a sustainable management option for Mediterranean agricultural soils. The aim of this work is to evaluate the effects of biochar from sewage sludge pyrolysis on soil properties; heavy metals solubility and bioavailability in a Mediterranean agricultural soil and compared with those of raw sewage sludge. Biochar (B) was prepared by pyrolysis of selected sewage sludge (SL) at 500 °C. The pyrolysis process decreased the plant-available of Cu, Ni, Zn and Pb, the mobile forms of Cu, Ni, Zn, Cd and Pb and also the risk of leaching of Cu, Ni, Zn and Cd. A selected Mediterranean soil was amended with SL and B at two different rates in mass: 4% and 8%. The incubation experiment (200 d) was conducted in order to study carbon mineralization and trace metal solubility and bioavailability of these treatments. Both types of amendments increased soil respiration with respect to the control soil. The increase was lower in the case of B than when SL was directly added. Metals mobility was studied in soil after the incubation and it can be established that the risk of leaching of Cu, Ni and Zn were lower in the soil treated with biochar that in sewage sludge treatment. Biochar amended samples also reduced plant availability of Ni, Zn, Cd and Pb when compared to sewage sludge amended samples.