Sludge-amended Soil Research Articles

Modification of natural radionuclide uptake by wheat using a NORM by-product as soil amendment.

Drinking Water Treatment Plants (DWTPs) can be optimised for removal of natural radionuclides, thus meeting EU legislation. Removed radionuclides (234,238U, 226Ra and 210Po) go into sludges. What would happen if these sludges were used in agriculture? Wheat plantlets were cultivated in original and sludge-amended soils under laboratory controlled conditions. Soil-to plant transfer was significantly increased in factors ranging 1.2–3.7, 2.0–5.6, and 1.6–2.4 for 234,238U, 226Ra and 210Po, respectively. The additional input was preferentially accumulated in roots.

Evaluation of forage yield and nutritional quality of triticale grown in sewage sludge–amended soil

Application of sewage sludge provides not only a means for its disposal, but also refers to as an agricultural practice to improve soil fertility and to increase crop yields. This research was initiated to examine the impact of sewage sludge on the growth, yield, and nutritional quality of triticale “X Triticosecale Wittmack” crop used as a diet of the milking Sicilo-Sarde ewes. Treatments were a zero-N-control (C), 6 t DM ha−1 of sewage sludge (SS) equivalent to 92 kg N ha−1, and 100 kg N ha−1 of mineral fertilizer (MF). The results showed an increase in forage dry matter production, by an average value of 62% at heading stage, when compared with control. Heavy metal contents in different parts of triticale did not vary in the presence of SS, remaining approximately similar to those recorded in C and MF treatments. Sewage sludge had no harmful effect on sheep performance, especially its milk production and quality.

Evaluating the effects of sewage sludge compost applications on the microbial activity, the nutrient and heavy metal content of a Chernozem soil in a field survey

Sewage sludge contains organic matter and micro and macronutrients which are potentially useful for agricultural usage. However, it can be harmful when containing undesirable amounts of organic pollutants, heavy metals, or pathogens. Our study focused on examining the changes in the extractable nutrient, organic matter and heavy metal contents of a Chernozem soil and the alteration of the soil biological activity as a consequence of low-dose municipal sewage sludge compost applications (0.5 t/ha). Sampling campaigns were done in 2018 near Újkígyós (SE Hungary) during which composite soil samples (0–30 cm and 30–60 cm) and groundwater samples were collected for assessing changes in the nutrient and heavy metal concentrations as a result of compost amendments’ use. Additionally, upper soil (0–50 cm) and subsoil (50–80 cm) were sampled for assessing biological parameters, considered to be aerobic and anaerobic soil layers, respectively. Soil samples were analyzed for the basic pedological parameters (pH, organic matter, carbonates and texture), nutrients (K2O, P2O5, N-forms and organic matter) and heavy metal concentrations following standard extraction procedures. The microbial properties were characterized by colony-forming units (CFUs) and enzyme activity measurements. The results of the nutrient analyses show significantly increased soil-bound K2O, P2O5 and NO2− + NO3− contents linked to the sewage sludge treatments. However, neither the organic matter nor the heavy metal content varied significantly in the sludge-amended soil compared with a control site. The microbiological analyses revealed that the sewage sludge treatments tended to increase the aerobic CFUs, but not that of the anaerobic microbes. The average catalase enzyme activity in both the aerobic and anaerobic samples and the average dehydrogenase activity only in the aerobic layers showed a slight but not significant increase in the compost-amended soils. Overall, these results convincingly demonstrated that amending soils with low doses of municipal sewage sludge composts (lacking any industrial sources) can be a sustainable fertilizing practice taking advantage of their high N, P and K contents that are slowly converted to their bioavailable forms thus preventing their excessive leaching in the groundwater.

Study of Evolution of Microbiological Properties in Sewage Sludge-Amended Soils: A Pilot Experience.

Large amounts of sewage sludge are generated in urban wastewater treatment plants and used as fertilizer in agriculture due to its characteristics. They can contain contaminants such as heavy metals and pathogenic microorganisms. The objective of this research work is to study, in real conditions, the evolution of microbial concentration in agricultural soils fertilized by biologically treated sewage sludge. The sludge (6.25 tons Ha−1) was applied in two agricultural soils with different textures and crops. A microbiological (total coliforms, Escherichia coli, Staphylococcus aureus, Enterococcus sp., Pseudomonas sp., Salmonella sp. and total mesophylls) and physical-chemical characterization of the sludge, soils and irrigation water were carried out. The evolution of these parameters during sowing, growth and harvesting of crops was studied. Initially, sewage sludge had a higher concentration of microorganisms than soils. Irrigation water also contained microorganisms, fewer than sewage sludge amendment but not negligible. After amendment, there were no differences in the microbiological evolution in the two types of soil. In general, bacterial concentrations after crop harvest were lower than bacterial concentrations detected before sewage sludge amendment. Consequently, the application of sludge from water treatment processes did not worsen the microbiological quality of agricultural soil in this study at real conditions.

Dose effect of Zn and Cu in sludge-amended soils on vegetable uptake of trace elements, antibiotics, and antibiotic resistance genes: Human health implications

The application of sewage sludge to agricultural fields reduces the need for mineral fertilizers by increasing soil organic matter, but may also increase soil pollution. Previous studies indicate that zinc and copper, as the most abundant elements in sewage sludge, affect plant uptake of other contaminants. This paper aims to investigate and compare the effect of increasing amounts of Zn and Cu in sludge-amended soils on the accumulation of trace elements (TEs), antibiotics (ABs), and antibiotic resistance genes (ARGs) in lettuce and radish. The vegetables were grown under controlled conditions, and the influence on plant physiology and human health were also evaluated. The results show that the addition of Zn and Cu significantly increased the concentration of TEs in the edible tissue of both vegetables. According to the hazard quotient (HQ) of the TEs, the human health risk increased 2 to 3 times and was 3–4 times greater in lettuce than in radish. In contrast to the TEs, the occurrence of ABs and most of the ARGs was higher in radish roots than lettuce leaves. ABs were not detected in lettuce leaves, and the amount of all ARGs except blaTEM was 10 times lower than in radish roots. On the other hand, the addition of Zn and Cu had no significant effect on the occurrence of ABs and ARGs in the edible part of the vegetables, and no damage was found to plant productivity or physiology. The results show that the consumption of lettuce and radish grown in sewage-sludge-amended soils under tested doses of Cu and Zn does not pose an adverse human health effect, as the total HQ value was always less than 1, and the presence of ABs and ARGs was not found to have any potential impact. Nevertheless, further studies are needed to estimate the long-term effect on human health of crops grown under frequent application of biosolids in arable soil.

Sludge Amendment Affect the Persistence, Carbon Mineralization and Enzyme Activity of Atrazine and Bifenthrin.

Atrazine and bifenthrin persistence study was carried out in three sludge amended soil under laboratory condition. Atrazine persisted shorter in sludge amended soil sludge-3 (half-life 23.4days) followed by sludge-2 (half-life 30.1days) and sludge-1 (half-life 37.1days) than unamended control (half-life 150.5days). Bifenthrin followed the similar pattern with sludge-3 (half-life 43.1days) which increased to 50.3, 60.2 and 75.2days, respectively in sludge-2, sludge-1 and unamended control representing an immense influence of sludges on degradation. Duncan's Multiple Range Test revealed that carbon mineralization process was significantly influenced by all the sludges (p < 0.0001). Sludge-3 indicated highest Cmin (initial 118.16 to final 133.64mg CO2-C/kg) in bifenthrin and 129.91mg CO2-C/kg in atrazine. The relatively high Cmin rate in sludge amended soil than unamended control suggested a lower persistency of both the pesticides and thus decreasing its potential ecological risk. Sludge-3 sludge amended soil increased the dehydrogenase enzyme activity as compared to sludge-1 and sludge-2 sludge in atrazine.

Impact of urban sewage sludge on soil physico-chemical properties and phytotoxicity as influenced by soil texture and reuse conditions.

Urban sewage sludge (USS) is increasingly applied to agricultural soils, but mixed results have been reported because of variations in reuse conditions. Most field trials have been conducted in cropping systems, which conceal intrinsic soil responses to sludge amendments due to the rhizosphere effect and farming practices. Therefore, the current field study highlights long-term changes in bare soil properties in strict relationship with soil texture and USS dose. Two agricultural soils (loamy sand [LS] and sandy [S]) were amended annually with increasing sludge rates up to 120 t ha-1 yr-1 for 5 yr under unvegetated conditions. Outcomes showed a USS dose-dependent variation of all studied parameters in topsoil samples. Soil salinization was the most significant risk related to excessive USS doses. Total dissolved salts (TDS) in saturated paste extracts reached the highest concentrations of 37.2 and 43.1 g L-1 in S soil and LS soil, respectively, treated with 120 t USS ha-1 yr-1 . This was also reflected by electrical conductivityof the saturated paste extract (ECe ) exceeding 4,000 µS cm-1 in both treatments. As observed for TDS, fertility indicators and bioavailable metals varied with soil texture due to the greater retention capacity of LS soil owing to higher fine fraction content. Soil phytotoxicity was estimated by the seed germination index (GI) calculated for lettuce, alfalfa, oat, and durum wheat. The GI was species dependent, indicating different degrees of sensitivity or tolerance to increasing USS rates. Lettuce germination was significantly affected by changes in soil conditions showing negative correlations with ECe and soluble metals. In contrast, treatment with USS enhanced the GI of wheat, reflecting higher salinity tolerance and a positive effect of sludge on abiotic conditions that control germination in soil. Therefore, the choice of adapted plant species is the key factor for successful cropping trials in sludge-amended soils.

Integration of sequential extraction, chemical analysis and statistical tools for the availability risk assessment of heavy metals in sludge amended soils

This work has been conducted as an integrated approach to study the behavior of soils to the metals from sludge amendment. Bureau Commun Reference (BCR) methodology was used as an appropriate tool to harvest precious information about heavy metals evolution versus depth before and after sludge treatments. This three-step extraction procedure (i.e., BCR) may clarify the leaching or retention of heavy metals from the amended soils, as well as their risk level. Our results indicated that sludge applications has shown an increasing flux of heavy metals towards amended soils, of which Pb was the most abundant. Heavy metals mobility in control and amended soils showed that main influencing factors are pH and total organic carbon, especially for copper mobility. Almost all of the metals decreased with soil depth, except for Ni. Speciation of heavy metals in sludges showed that about 45% of Pb, Cu and Ni were associated with residual fraction; Cd was mainly bound to reducible fraction. Speciation forms in the control soil indicated that short term application of sludge has remobilized a fraction of heavy metals into their most labile forms (i.e., exchangeable and reducible fraction). Multivariate statistical analysis suggested that Cd, Zn, Pb and Cu preferentially accumulated in organic-rich surface horizons and clay layers where adsorption played an important role as a determining mechanism. Nevertheless, adsorption did not appear to be directly controlled by high pH values (pH > 7). From Cluster Analysis (CA), one can easily recognize that Pb, Zn and Cu movement in soil profiles were significantly affected by pH, especially residual fraction, labile fraction and reducible fraction.

Engineered silver nanoparticle (Ag-NP) behaviour in domestic on-site wastewater treatment plants and in sewage sludge amended-soils

Untreated sludge from small-scale on-site domestic wastewater treatment systems (septic tanks) was spiked with 20, 60 and 100 nm silver nanoparticles (Ag-NPs) to investigate Ag-NP behaviour in these systems that are widely distributed in rural areas. In addition, the release of Ag-NPs from a previously spiked clay-rich loam reference soil (LUFA 2.4) was evaluated, in the presence and absence of untreated sludge, to simulate the common practice of sludge disposal by spreading on agricultural land. Single particle ICP-MS was used to determine Ag-NP size distribution and the results were compared with total Ag (Ag-NP and ionic) measured in acid digested samples. As documented previously for large municipal scale wastewater treatment plants, Ag-NPs are found to be overwhelmingly (~98%) retained in the sludge in these small-scale systems. The Ag-NP retention efficiency on the LUFA reference soil amended with sludge is approximately 10 times greater than that of LUFA soil alone (in the absence of sludge). For soil spiked with 60 nm Ag-NPs, the calculated average diameter of Ag-NPs in the supernatant, after 24 h was 45 ± 3 nm (dissolution rate 7.2E−06 mol/m2·h for 60 nm Ag-NP), smaller than that of supernatant from the combined sludge/soil system (52 ± 2 nm), indicating lower Ag-NP dissolution rates in the sludge-amended soil. This study provides new information about the leachability of Ag-NPs from septic tank sludge and suggests that the effluent and sludge from septic tanks are potential sources of both nano- and dissolved ionic-Ag to environmental waters.

Prediction models for monitoring heavy-metal accumulation by wheat (Triticum aestivum L.) plants grown in sewage sludge amended soil

Prediction of heavy-metal concentration in the edible parts of economic crops, based on their concentration in soil and other environmental factors, is urgently required for human risk assessment. The present investigation aimed to develop regression models for predicting heavy-metal concentration in wheat plants via their contents in sewage sludge amended soil, organic matter (OM) content and soil pH. The concentration of heavy metals in the plant tissues reflected its concentration in the soil with high Fe followed by Al, Mn, Cr, Zn, Ni, Co, Cu, and Pb. Soil OM content had a significant positive correlation with all investigated heavy-metal concentrations in the different tissues of wheat plants, while soil pH was negatively significant with most heavy metals except spike Pb and grain Cr. The bio-concentration factor of Al, Cu, and Zn from soil to wheat root was >1, while that of shoot, spikes, and grains was <1 for all heavy metals. Significantly valid regression models were developed with fluctuated coefficient of determination (R2), high model efficiency (ME) values and low mean normalized average error (MNAE). The significant positive correlations between the concentration of some heavy metals in the soil and the same in wheat tissues indicate the potential of this plant as a biomonitor for these metals in contaminated soils. The significant correlations between heavy-metal concentrations in soil and its properties (pH and OM) with metal concentrations in wheat plants support the prediction model as an appropriate option. This study recommends the use of models with R2 greater than 50% and recommend other researchers to use our models according to their own specific conditions.

Alteration of Crop Yield and Quality of Three Vegetables upon Exposure to Silver Nanoparticles in Sludge-Amended Soil

The impacts of land application of sludge contaminated with silver nanoparticles (Ag NPs) on crop yield and nutritional quality are relatively unknown. Chili (Capsicum annuum L.), lettuce (Lactuca ...

Brewery sludge quality, agronomic importance and its short-term residual effect on soil properties

Wastewater sludge generated from agro-industrial wastewater treatment plants is accepted as a good option for land application as a soil conditioner and substitute mineral fertilizers. However, the quality of the sludge sometimes posed a threat to the surroundings. The objective of the study is to evaluate the biochemical characteristics and fertilizer potential of brewery wastewater sludge for agricultural reuse. A field experiment was conducted in a randomized block design array with three replications using brewery wastewater sludge, and nitrogen, phosphorus and sulfur (NPS) containing commercial fertilizer along with control treatments. The result showed that sludge application significantly increased average above biomass production by 5.7% and 37.2% over the NPS and control plots, respectively. Also, the sludge-amended plot produced more grain yield of maize with 26.8% greater than the control. The brewery sludge temporary residual effect analysis revealed that the addition of the sludge led significant changes in soil pH reduction and soil electrical conductivity, total phosphorus, total nitrogen and total potassium increment as compared to others and background concentration. Similarly, lead and fecal coliform concentrations in the sludge-amended soil showed 150% and 24.4% increments, respectively, over the control. In general, the preliminary sludge temporary residual effect analysis showed an encouraging outcome on soil basic properties and maize crop productivity. Conversely, future long-term study is essential to monitor the effect of soil salinity, heavy metal and pathogen contaminations on soil and crop production.

REVIEW PAPER ON BEVERAGE AGRO-INDUSTRIAL WASTEWATER TREATMENT PLANT BIO-SLUDGE FOR FERTILIZER POTENTIAL IN ETHIOPA

Agro-industrial sectors in Ethiopia are highly expanding sector and offers substantial challenges for the environment and public health. The brewery industries use large quantities of water for their production processes and at the end, they discharged large amount of effluents that contains a high strength organic waste. The main objective of this review paper is to discuss and summarize the characteristics, treatment techniques, fertilizer potential and other available management options of breweries sludge generated from wastewater treatment plants. Recent (2015) research finding indicated that the brewery sludge contains a very high nitrogen and potassium content, i.e., 420.25 kg ha(-1) and 840 kg ha' respectively compared to the control. Scientific evidences indicated that brewery sludge amended soil they have the tendency to produce more yields (4081.6 kg ha(-1)). Brewery sludge has also other beneficial advantages in production of biogas and building materials with co-digestion with other organic solid residues. The probable drawbacks of the use of sludge on agricultural land application is its pollutant loads including heavy metals, organic compounds and pathogens. Therefore, more research investigation has to be done on the possible sludge treatment mechanisms and the feasibility of sludge generated from brewery industries for agricultural recycling.

Bioaccumulation of Trace Metals in Plants Grown in Sewage Sludge Amended Soil

A survey was established to study the mobility of metals (Cr, Mo, Cu, and Zn) from soils amended with municipal sewage sludge (SS) into plants grown at three locations in Kentucky and compare metal concentrations in plants to their permissible standard limits. The field experiments were established at Meade, Adair, and Franklin Counties in Kentucky areas where commercial growers use SS as alternative to inorganic fertilizers. Metals in soil and plant tissue were quantified using Inductively Coupled Plasma (ICP) spectrometer. Results revealed that different trace metals had different uptake pattern by different plants. Cr concentrations in beans has shown very little accumulation in bean seeds. Cr and Mo concentrations in plants grown at the three locations were below the permissible level of 1.3 µg g^-1 tissue. Other than onion bulbs, Cu concentrations were above the permissible level of 10 µg g^-1 tissue in plants grown at Meade site. At the Adair site, Cu was above the limit only in tobacco leaves. Whereas at Franklin site, Cu was above the limit in potato tubers, onion bulbs, and tomato fruits. Zn concentration in all plants tested never exceeded the permissible level of 0.6 µg g^-1 tissue.

Sewage sludge land application: Balancing act between agronomic benefits and environmental concerns

Land disposal of sewage sludge has become an attractive practice worldwide. However, ubiquitous presence of toxic metals raises environmental and public health concerns regarding subsequent plant uptake. This study was intended to determine the suitability of sewage sludge application under hot environmental condition using tomato crop. A greenhouse experiment was conducted to investigate various levels of heavy metals as well as potential health risks associated with the consumption of tomato fruit grown in sludge amended soil. Plant samples were collected on four different growth stages: beginning of the experiment before planting, twice during growing period, and at the end of the experiment (post-harvest). Samples were analyzed for commonly occurring heavy metal contaminants (Cd, Cr, Cu, Pb and Zn). In this study, we did not observe consistent relationship between metal concentrations in tomato plant and various sludge ratio. Heavy metal levels were consistently greater in roots than other parts of tomato plant, followed by stem. The most salient finding from our study was that Cd and Pb, two very important metals because of their solubility and subsequent mobility, were not detectable in tomato fruits under any of the sludge treatments, compared to other parts of tomato plants. The trend in transfer factors (TF) followed the sequence Zn > Cu > Cr > Cd for roots and Zn > Cu > Cr for fruits, suggesting the risk of heavy metal TF to tomato fruits is minimal. It can be inferred from these results that potential risk may be greater through consumption of leafy vegetables and tuber crops.

An ecohydrological approach to the river contamination by PCDDs, PCDFs and dl-PCBs \u2013 concentrations, distribution and removal using phytoremediation techniques

The levels of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and dioxin-like polychlorinated biphenyls (dl-PCBs) in the Pilica River and Sulejów Reservoir were found to be 46% higher during the flood season than during stable flow periods. In addition, PCDD/PCDF and dl-PCB mass loads increased by 5- to 12-fold and by 23- to 60-fold for toxic equivalency (TEQ) during flooding. The Sulejów Reservoir was found to play a positive role in reducing PCDD, PCDF and dl-PCB transport within the study period, with reductions ranging from 17 to 83% for total concentrations, and 33 to 79% for TEQ. Wastewater Treatment Plants (WTPs) were not efficient at mass concentration removal, with small displaying the least efficiency. WTPs discharge pollutants into the aquatic environment, they also produce sludge that requires disposal, similar to reservoir sediments. Sludge- or sediment-born PCDDs, PCDFs and dl-PCBs may be removed using phytoremediation. The cultivation of cucumber and zucchini, two efficient phytoremediators of organic pollutants, on polluted substrate resulted in a mean decrease in PCDD + PCDF + dl-PCB TEQ concentrations: 64% for cucumber and 69% for zucchini in sludge-amended soil, and by 52% for cucumber and 51% for zucchini in sediment-amended soil.

Occurrence, fate and environmental risk of anionic surfactants, bisphenol A, perfluorinated compounds and personal care products in sludge stabilization treatments

In this work, twenty-three endocrine disrupting compounds have been monitored in sludge from different stages of four sludge stabilization treatments (anaerobic digestion, aerobic digestion, composting and anaerobic stabilization ponds). Their occurrence and fate in sludge stabilization plants and their potential environmental risk in treated sludge and in treated sludge-amended soils have been evaluated. Monitored compounds were six perfluoroalkyl compounds (PFC), four anionic surfactants (sodium alkylsulfates), a plasticiser (bisphenol A (BPA)), four preservatives (parabens), six UV-filters (benzophenones) and two biocides (triclosan and triclocarban). Only two of the UV-filters were not detected in any of the 141 analysed samples. Anionic surfactants (mean concentrations up to 1673 ng/g dry matter (dm) for the sum of surfactants) were the compounds at the highest concentration levels followed by biocides (up to 512 ng/g dm) and UV-filters (up to 662 ng/g dm). The concentrations of anionic surfactants, preservatives and UV-filters decreased 78, 25 and 80%, respectively, after anaerobic digestion. The concentration of perfluorinated carboxylic acids only decreased after composting (80% reduction) whereas biocides and BPA were not affected by any of the studied treatments. Environmental risks (risk quotients > 1) were obtained for all compounds, except for triclocarban and sodium octadecylsulfate, in treated sludge. In treated sludge-amended soils, risk quotients were lower than 1 for all compounds except for triclosan.

Modelling maize grain yield and nitrate leaching from sludge-amended soils across agro-ecological zones: A case study from South Africa

When applying municipal sludge according to crop N requirements, the primary aim should be optimizing sludge application rates in order to maximize crop yield and minimize environmental impacts through nitrate leaching. Nitrate leaching and subsequent groundwater contamination is potentially one of the most important factors limiting the long-term viability of sludge application to agricultural soils. This study assessed maize grain yield and potential nitrate leaching from sludge-amended soils, using the SWB-Sci model, based on crop nitrogen requirements and inorganic fertilizer. The following hypotheses were tested using the SWB­-Sci model and 20 years of measured weather data for 4 of the 6 South African agro-ecological zones. Under dryland maize cropping, grain yield and nitrate leaching from sludge-amended soils compared to inorganic fertilizer: (1) will remain the same across agro-ecological zones and sites, (2) will not vary across seasons at a specific site, and (3) will not vary across soil textures. Model simulations showed that annual maize grain yield and nitrate leaching varied significantly (P &gt; 0.05) across the four agro-ecological zones, both for sludge-amended and inorganic fertilizer amended soils. The annual maize grain yield and nitrate leaching from sludge-amended soils were 12.6 t∙ha-1 and 32.7 kgNO3-N∙ha−1 compared to 10.2 t∙ha-1 and 43.2 kgNO3-N∙ha−1 for inorganic fertilizer in the super-humid zone. Similarly, maize grain yield and nitrate leaching varied significantly across seasons and soil textures for both sludge and inorganic fertilizer amended soils. However, nitrate losses were lower from sludge-amended soils (2.3–8.2%) compared to inorganic fertilizer (11.1–26.7%) across all zones in South Africa. Therefore, sludge applied according to crop N requirements has a lower environmental impact from nitrate leaching than commercial inorganic fertilizer. Further validation of these findings is recommended, using field studies, and monitoring potential P accumulation for soils that received sludge according to crop N requirements.

Novel clinically relevant antibiotic resistance genes associated with sewage sludge and industrial waste streams revealed by functional metagenomic screening

A growing body of evidence indicates that anthropogenic activities can result in increased prevalence of antimicrobial resistance genes (ARGs) in bacteria in natural environments. Many environmental studies have used next-generation sequencing methods to sequence the metagenome. However, this approach is limited as it does not identify divergent uncharacterized genes or demonstrate activity. Characterization of ARGs in environmental metagenomes is important for understanding the evolution and dissemination of resistance, as there are several examples of clinically important resistance genes originating in environmental species. The current study employed a functional metagenomic approach to detect genes encoding resistance to extended spectrum β-lactams (ESBLs) and carbapenems in sewage sludge, sludge amended soil, quaternary ammonium compound (QAC) impacted reed bed sediment and less impacted long term curated grassland soil. ESBL and carbapenemase genes were detected in sewage sludge, sludge amended soils and QAC impacted soil with varying degrees of homology to clinically important β-lactamase genes. The flanking regions were sequenced to identify potential host background and genetic context. Novel β-lactamase genes were found in Gram negative bacteria, with one gene adjacent to an insertion sequence ISPme1, suggesting a recent mobilization event and/ the potential for future transfer. Sewage sludge and quaternary ammonium compound (QAC) rich industrial effluent appear to disseminate and/or select for ESBL genes which were not detected in long term curated grassland soils. This work confirms the natural environment as a reservoir of novel and mobilizable resistance genes, which may pose a threat to human and animal health.

Effect of biochar addition to sewage sludge on cadmium, copper and lead speciation in sewage sludge-amended soil

The goal of the present work was to evaluate the speciation of cadmium (Cd), copper (Cu) and lead (Pb) in sewage sludge (SL) amended soil and SL-biochar (BC) amended soil in a long-term field experiment. SL or SL with biochar (at the dose of 2.5%, 5.0% or 10%) were applied to the soil. The dose of SL in the soil was 11 tdw/ha. At the beginning of the study, after 12 and 18 months the distribution of Cd, Cu and Pb was determined between the following fractions: (1) water soluble, exchangeable and bound to carbonates (F1), (2) bound to Fe–Mn oxides (F2), (3) bound to organic matter (F3) and (4) bound to quartz, feldspars, etc. (F4). The soil, SL and biochar were characterized by different distribution of Pb, Cu and Cd. The highest mobility of Cd and Cu was observed in the control soil, while Pb in SL. Addition of SL to the soil caused the increased of the mobility index of Cu and Pb, increasing the risk associated with the presence of these metals in the mobile soil fraction (F1). However, the addition of biochar to SL before application to the soil modified the distribution of studied elements. The most mobile and bioavailable fractions (F1) were transferred to less bioavailable (F2, F3) and potentially immobile fractions (F4).