SS-amended Soil Research Articles

Coupling Sewage Sludge Amendment with Cyanobacterial Inoculation to Enhance Stability and Carbon Gain in Dryland Degraded Soils

Sewage sludge (SS) is widely used as a soil conditioner in agricultural soil due to its high content of organic matter and nutrients. In addition, inoculants based on soil microorganisms, such as cyanobacteria, are being applied successfully in soil restoration to improve soil stability and fertility in agriculture. However, the combination of SS and cyanobacteria inoculation is an unexplored application that may be highly beneficial to soil. In this outdoor experiment, we studied the ability of cyanobacteria inoculum to grow on degraded soil amended with different concentrations of composted SS, and examined the effects of both SS concentration and cyanobacteria application on carbon gain and soil stability. We also explored the feasibility of using cyanobacteria for immobilizing salts in SS-amended soil. Our results showed that cyanobacteria growth increased in the soil amended with the lowest SS concentration tested (5 t ha−1, on soil 2 cm deep), as shown by its higher chlorophyll a content and associated deeper spectral absorption peak at 680 nm. At higher SS concentrations, inoculum growth decreased, which was attributed to competition of the inoculated cyanobacteria with the native SS bacterial community. However, SS significantly enhanced soil organic carbon gain and tightly-bound exopolysaccharide content. Cyanobacteria inoculation significantly improved soil stability and reduced soil’s wind erodibility. Moreover, it led to a decrease in the lixiviate electrical conductivity of salt-contaminated soils, indicating its potential for salt immobilization and soil bioremediation. Therefore, cyanobacteria inoculation, along with adequately dosed SS surface application, is an efficient strategy for improving carbon gain and surface stability in dryland agricultural soil.

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

This study investigated the influence of the sewage sludge (SS) soil amendment on the chronic toxicity of imidacloprid (through the seed dressing formulation MUCH 600 FS®-600g active ingredient L-1) to collembolans Folsomia candida. Individuals 10-12days old were exposed to two contrasting tropical soils (Oxisol and Entisol) amended with SS doses (0, 20, 40, 80, 160, and 320g SS kg-1 soil; the SS doses have low intrinsic toxicity, which was checked before its application) in a full factorial combination with five imidacloprid concentrations (varying from 0.25 to 4mgkg-1 in Oxisol and 0.03-0.5mgkg-1 in Entisol) plus a control. None of the SS doses (without imidacloprid) in both soils reduced the number of generated juvenile collembolans. The imidacloprid concentrations reducing the collembolan reproduction in 50% (EC50) in Oxisol and Entisol without SS were 0.49 and 0.08mgkg-1, respectively. However, the EC50 values generally increased with increasing SS doses in soils, varying from 1.03 to 1.41 in Oxisol and 0.07 to 0.21 in Entisol. The SS-amended soils showed 2.1- to 2.9-fold lower imidacloprid toxicity (EC50-based) in Oxisol and 1.8- to 2.7-fold lower toxicity in Entisol. Our results suggest the most effective SS doses alleviating the imidacloprid toxicity (EC50-based) to collembolans are 20gkg-1 in Oxisol and 80gkg-1 in Entisol. These results indicate that the tested SS has the potential to be employed as a soil amendment agent by reducing the toxicity of imidacloprid to the reproduction of F. candida.

Biochar alleviating heavy metals phytotoxicity in sludge-amended soil varies with plant adaptability

Recycling sewage sludge (SS) to soil potentially causes soil heavy metal (HM) pollution and plant phytotoxicity. Biochar plays an important role in alleviating HM phytotoxicity, and responses vary with the feedstocks and usage of biochar. However, the effect of plant adaptability on biochar-mediated alleviation is poorly understood. Here, SS-derived biochar (SB) and rice straw-derived biochar (RB) applied at rates of 1.5% and 3% (W/W, SB1.5, SB3, RB1.5, and RB3) were used to improve the properties of soil amended with SS at 50% (W/W). Alleviation of phytotoxicity by biochar was further analyzed with SS-sensitive plant Monstera deliciosa and SS-resistant plant Ruellia simplex. Results revealed that both SB and RB significantly decreased the soil's bulk density and increased water retention. They also changed soil organic matter content and HMs fractionation. The addition of SB or RB alleviated the SS phytotoxicity, and they significantly promoted the growth and the root morphology and physiological index of M. deliciosa. But for R. simplex, these significant changes only synchronously occurred in SB3 treatment. The alleviation in M. deliciosa was more prominent and more closely connected with soil property changes than in R. simplex. Also, more soil property predictors were observed to play an important role in M. deliciosa growth than in R. simplex growth. These results indicated that biochar alleviating HMs phytotoxicity in SS-amended soil is associated with the changes of soil property. Moreover, the alleviation varies more prominently with plant adaptability than with biochar feedstocks and usage.

Planned Application of Sewage Sludge Recirculates Nutrients to Agricultural Soil and Improves Growth of Okra (Abelmoschus esculentus (L.) Moench) Plants

The aim of this study was to investigate the feasibility of using sewage sludge (SS) biosolids as a low-cost soil fertilizer to improve soil characteristics and crop yields. Okra (Abelmoschus esculentus (L.) Moench) plants were grown in soil supplemented with different concentrations of SS (0, 10, 20, 30, 40, and 50 g/kg). The results showed that SS soil application led to improved soil quality with a 93% increase of organic matter (at SS dose of 10 g/kg), decreased pH (a reduction from 8.38 to 7.34), and enhanced macro- and micro- nutrient contents. The levels of all the investigated heavy metals (HMs; Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, and Zn) in the postharvest SS-amended soil were within the prescribed safe limits. The application of SS to soil considerably enhanced the growth parameters of okra plants. Total biomass increased 13-fold and absolute growth rate increased 10-fold compared to plants grown in nonamended (control) soils. Among the applied SS doses, the 10 g/kg SS dose led to the highest values of the measured growth parameters, compared to those of plants grown in control soils. The induced growth at 10 g/kg SS was accompanied by a substantial increase in metal content in roots, stems, leaves, and fruits; however, all levels remained within safe limits. Consequently, the data presented in this study suggest that SS could be used as a sustainable organic fertilizer, also serving as an ecofriendly method of SS recycling.

Evaluation of Land Potential for Use of Biosolids in the Coastal Mediterranean Karst Region

The aim of this study was to evaluate the potential of agricultural land in the coastal Adriatic Karst region (Šibenik region, Croatia) for biosolids application by integrating spatial data from different sources: digital maps and remote sensing, parcel identification system, GIS field observations and measurements focusing on specific land and soil properties. Due to the rapid development of the wastewater treatment industry, excessive accumulation of sewage sludge (SS) in wastewater treatment plants is a growing problem worldwide. Management options for land application of biosolids require a comprehensive characterization of both SS and SS-amended soils. The assessment of agricultural land in the study area for SS disposal was based on EU and national legislation. The evaluation revealed that agricultural land in the study area accounts for only 10% of the total area (25,736 ha), but only a quarter of the existing land (6065 ha) is suitable for biosolids application. Furthermore, the data indicate that the sewage sludge can be safely applied to the soil in terms of soil metals according to the Croatian legislation. The short-term potential of the soil to sustain this ecosystem service, namely soil improvement with biosolids, should be used to determine the inherent long-term potential based on resistance to soil degradation and resilience. However, caution is needed and the long-term effects should be investigated before biosolids are continuously used for soil application.

Pyrolysis Treatment Enables Safe Application of Sewage Sludge in Horticulture: Tracking Potentially Toxic Elements Through the Biochar-Soil–Plant System in Tomato

Biochar production via pyrolysis is a promising option for treating sewage sludge (SS). Here we investigated the uptake of potentially toxic elements (PTEs) from SS and its biochar (450 °C) into cherry tomato (Lycopersicon esculentum L.) plants and their fruits in pot experiments (2, 5 and 10%), to assess the health risks associated with fruit consumption. We further studied the ability of the PTE-rich amendments to immobilize PTEs already present in soil through spiking of soil (pH 7.4) with Cd, Cu and Zn. Our findings suggest that tomato consumption is not a human health risk when grown in soil amended with SS and its biochar; in most treatments PTE uptake into fruits was similar to the control. Vegetative plant growth was highest in SS-amended soils. Yet 5 and 10% biochar-amended soils significantly increased tomato fruit yield relative to untreated SS application (400–500% higher than 10% SS-amended soil) and significantly decreased fruit uptake of Cu and Zn. Importantly, biochar also significantly immobilized PTEs present in contaminated (spiked) soil. As expected, available (DTPA-extractable) PTE contents were typically lower in biochar-amended soil and sequential extraction indicated that the PTEs were predominantly bound in more recalcitrant soil fractions (organic matter associated and Fe–Mn oxides-bound). We conclude that pyrolysis can be a key technology for treatment of PTE-rich SS and subsequent use of the produced biochar in urban, and potentially even PTE-contaminated, horticultural sites.

Agricultural Soils Amended With Thermally-Dried Anaerobically-Digested Sewage Sludge Showed Increased Risk of Antibiotic Resistance Dissemination.

The application of sewage sludge (SS) to agricultural soil can help meet crop nutrient requirements and enhance soil properties, while reusing an organic by-product. However, SS can be a source of antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs), resulting in an increased risk of antibiotic resistance dissemination. We studied the effect of the application of thermally-dried anaerobically-digested SS on (i) soil physicochemical and microbial properties, and (ii) the relative abundance of 85 ARGs and 10 MGE-genes in soil. Soil samples were taken from a variety of SS-amended agricultural fields differing in three factors: dose of application, dosage of application, and elapsed time after the last application. The relative abundance of both ARGs and MGE-genes was higher in SS-amended soils, compared to non-amended soils, particularly in those with a more recent SS application. Some physicochemical parameters (i.e., cation exchange capacity, copper concentration, phosphorus content) were positively correlated with the relative abundance of ARGs and MGE-genes. Sewage sludge application was the key factor to explain the distribution pattern of ARGs and MGE-genes. The 30 most abundant families within the soil prokaryotic community accounted for 66% of the total variation of ARG and MGE-gene relative abundances. Soil prokaryotic α-diversity was negatively correlated with the relative abundance of ARGs and MGE-genes. We concluded that agricultural soils amended with thermally-dried anaerobically-digested sewage sludge showed increased risk of antibiotic resistance dissemination.

Diversified effects of co-planting landscape plants on heavy metals pollution remediation in urban soil amended with sewage sludge

Recycling sewage sludge (SS) as a soil amendment potentially causes soil heavy metals (HMs) contamination. This study investigated the potential roles of landscape plants co-planting in SS-amended soil remediation. Three landscape trees Mangifera persiciforma, Bischofia javanica, and Neolamarckia cadamba (NC), and three ground cover plants Dianella ensifolia, Syngonium podophyllum, and Schefflera odorata (SO) were selected for the tree-ground cover co-planting. Species in different co-planting treatments exhibited diversified effects on the growth, root morphology, HMs uptake, and HMs accumulation. Five plant characteristics including total root length, total surface of roots (diameter <2 mm), specific root length, shoot dry weight and root dry weight played crucial roles in plant HMs uptake. Structural equation modeling analysis revealed that different co-planting treatments drive species to develop an active, passive, or avoidance strategy to accumulate HMs, resulting in a diversity of HMs removal efficiency. Co-planting of NC with SO promoted NC and SO HMs accumulation and resulted in the greatest HMs contents decline (48.0% for Cd, 24.9% for Cu, 33.8% for Zn, and 27.2% for Ni) and the lowest potential ecological risk. Co-planting of landscape tree and ground cover plants with an active strategy can be a potential candidate for HMs phytoremediation of SS-amended soil.

Survey of Listeria monocytogenes contamination of various environmental samples and associated health risks

Listeria monocytogenes is the causative agent of listeriosis, one of the most important foodborne infections. Pre-harvest contamination of ready to eat crops constitutes a potential source of Listeria infections. The aim of this study was to investigate the presence of Listeria spp. and L. monocytogenes via molecular methods in wastewater effluent, sewage sludge (SS) and livestock manure as potential sources of Listeria. The presence of L. monocytogenes in wastewater-irrigated soil and crops was also investigated. Quantitative microbial risk assessment (QMRA) was performed for analysis of Listeria infections for SS workers and farmers. The results of survey showed no presence of L. monocytogenes in wastewater effluent and wastewater-irrigated soil and crop samples, whereas L. monocytogenes was detected in SS (50%) and manure (8%) samples. QMRA analysis using exponential model showed that the likelihood of Listeria infections from direct ingestion of SS to be very low. In contrast, Beta-Poisson dose-response model showed an annual risk of Listeria infections higher than the proposed value of 10−4 per person per year (pppy) by EPA, with the highest risk (4.41 × 10−1 pppy) for SS workers. Based on our results, the agricultural use of wastewater doesn't seem to present risk of Listeria infections for consumers of wastewater-irrigated crops. However, direct ingestion of SS may pose a risk for exposed individuals. The estimated risk values could be further improved by obtaining accurate insights into the prevalence of Listeria infections especially at national or regional level. Further studies are also needed to determine inactivation rate of Listeria in SS-amended soils in arid and semi-arid areas.

The response of cucumber plants (Cucumis sativus L.) to the application of PCB-contaminated sewage sludge and urban sediment.

BackgroundThe increasing production of sewage sludge (SS) engenders the problem of its responsible utilization and disposal. Likewise, urban sediments (SED) are deposited at the bottom of urban reservoirs and sedimentation ponds, and these require periodical dredging and utilization. However, while the SS and SED deposits often contain nutrients such as nitrogen and phosphorus; however, they also contain a variety of hazardous compounds including heavy metals, Persistent Organic Pollutants (POPs) and microbial pollutants. Fortunately, some species of Cucurbitaceae can accumulate high levels of POPs, such as polychlorinated dibenzo-p-dioxins (PCDD), polychlorinated dibenzofurans (PCDF) and polychlorinated biphenyls (PCB), in their tissues.MethodsSS was collected from the Lodz Municipal Wastewater Treatment Plant and SED from the Sokołówka Sequential Biofiltration System. The SS and SED samples were added to soil in flower pots at three concentrations (1.8 g, 5.4 g and 10.8 g per flower pot), and one pot was left as an unamended control (C). Soil PCB concentrations were determined before cucumber planting, and after five weeks of growth. Also, total soluble protein, total chlorophyll content, chlorophyll a/b ratio and degree of lipid peroxidation (TBARS) were examined in the leaves of the cucumber plants (Cucumis sativus L.) cv. Cezar after five weeks. Antioxidative response was assessed by ascorbate peroxidase (APx) and catalase (CAT) assay.ResultsThe initial PCB concentration in soil after application of SS or SED was dependent on the applied dose. After five weeks, PCB concentration fell significantly for all samples and confirmed that the dose of SS/SED had a strong effect. Soil remediation was found to be more effective after SS application. Total soluble protein content in the cucumber leaf tissues was dependent on both the type and the dose of the applied amendments, and increased with greater SS doses in the soil. The total chlorophyll content remained unchanged, and the chlorophyll a/b ratio was slightly elevated only after the application of the highest SS and SED dose. The use of SS and SED did not significantly affect TBARS content. APx activity fell after SS or SED application; however, CAT activity tended to increase, but only in the leaves of plants grown in SS-amended soil.DiscussionThe cultivation of cucumber plants reduces PCB concentration in soil amended with SS or SED; however, this effect is more evident in the case of SS. SS application also induced more intensive changes in the activity of enzymes engaged in antioxidative response and oxidative stress markers in plant tissues than SED. The levels of PCB in the SS may have triggered a more severe imbalance between pro- and antioxidative reactions in plants. Cucumber plants appear to be resistant to the presence of toxic substances in SS and SED, and the addition of SS and SED not only acts as a fertilizer, but also protects against accelerated aging.

Geo- and nano-materials affect the mono-metal and competitive sorption of Cd, Cu, Ni, and Zn in a sewage sludge-treated alkaline soil.

We evaluated the effect of geomaterials (modified zeolite and bentonite using CaCl2) and nanoparticles (ZnO and MgO) on the mono-metal and competitive sorption of cadmium (Cd), copper (Cu), nickel (Ni), and zinc (Zn) in an alkaline soil treated with three sewage sludges (SSs) collected from Isfahan, Rasht and Shiraz, Iran. The three SSs increased Cu sorption compared to the control. Sorption of Cd and Zn increased by the addition of Isfahan SS, but decreased by that of Rasht SS. Isfahan SS increased significantly the distribution coefficient of Cd, Cu, and Zn by 1.9, 1.2 and 1.5 times, respectively, compared to the control. The geomaterials and nanoparticles increased metal sorption in the SS-amended soil. Zeolite and MgO were the best sorbents for Cu in Rasht and Shiraz SS-treated soil, while ZnO and MgO were better in Isfahan SS-treated soil. Bentonite showed the highest Cd sorption capacity in Isfahan SS-treated soil, and MgO in the Shiraz SS-treated soil. ZnO showed the highest sorption capacity for Ni among the three SSs treatments. The nanoparticles showed higher sorption capacity for Zn than the geomaterials. We conclude that zeolite, bentonite, ZnO and MgO could be suitable immobilizing agents for Cd, Cu, Ni, and Zn in SS-amended alkaline soils.

Aminocyclopyrachlor and mesotrione sorption–desorption in municipal sewage sludge-amended soil

ABSTRACT The application of sewage sludge (SS) in agriculture is a practice used worldwide, and it is commonly applied in sugarcane to supply nutrients, with beneficial effects on crop productivity and soil; but SS can increase sorption and decrease desorption of herbicides. However, in tropical soils such as in Brazil, there are no studies regarding the behavior of pre-emergent herbicides, mainly aminocyclopyrachlor and mesotrione, in SS-amended soil. The aim of the present study was to determine the effect of municipal SS applied in agriculture on the sorption–desorption of aminocyclopyrachlor and mesotrione in clay soil. Aminocyclopyrachlor (pyrimidine-2-14C-aminocyclopyrachlor) and mesotrione (cyclohexane-2-14C-mesotrione) sorption–desorption was evaluated using a batch equilibrium method. Soil was amended at 0% (control – unamended), 0.1%, 1%, and 10% (w∙w–1) of air-dried SS corresponding to 1.2, 12, and 120 t∙ha–1. The Freundlich Kf sorption values of aminocyclopyrachlor and mesotrione were similar for all treatments, ranging from 1.07 to 1.45 and 3.48 to 4.25 µmol (1–1/n) L1/n∙kg–1, respectively. Overall, the lowest Kd sorption value of these herbicides was reported for SS-amended soil (1%), while in the SS-amended soil (10%) it was higher than unamended soil. The H value for aminocyclopyrachlor was ~1 (no hysteresis) and for mesotrione was on average 0.4 (hysteresis occurring). In conclusion, the present study indicates that SS applied in any crop to supply nutrients can slightly affect the sorption–desorption of aminocyclopyrachlor and mesotrione, but this small difference does not affect the bioavailability of these herbicides for weed control.

Comparison of N Mineralization Rate and Pattern in Different Manure- and Sewage Sludge-Amended Calcareous Soil

ABSTRACTA 12-week incubation experiment was conducted to determine the pattern and rate of N mineralized from organic materials. Treatments consisted of sheep manure (SM), cattle manure (CM), poultry manure (PM), sewage sludge (SS) at 1% (W/W) level, and unfertilized treatment with three replications. The concentrations of nitrate (NO3)- nitrogen (N) and ammonium (NH4)-N were determined in day 1 and 1, 2, 4, 8, and 12 weeks after the beginning of incubation. Results indicated that the magnitude of N mineralized during the incubation time periods was in the order of CM (134 mg kg−1) > PM (83 mg kg−1) > SS (56 mg kg−1) > SM (55 mg kg−1), and different management is required for obtaining optimum N-use efficiency. In conclusion, improving N-uptake efficiency in manure- and SS-amended soils depends on the pattern and rate of N mineralization to synchronize N released with crop N demand periods.

Long-term, low technicality sewage sludge amendment and irrigation with treated wastewater under Mediterranean climate: impact on agronomical soil quality.

We evaluated the agronomic quality of loam to clay-loam soils from a Mediterranean area, which have been submitted for more than 10years to irregular and poorly controlled treated wastewater (TWW) irrigation and sewage sludge (SS) amendment, both TWW and SS issuing from a domestic effluent treatment plant. A soil was submitted to SS amendment only, another to TWW irrigation only, another to both treatments, and another was not submitted to any of these treatments. We found that the agronomic quality of the treated soils has not decreased. In treated soils, it was observed a slight increase of pH, an increase of the cation exchange capacity, and no change of either salinity or electrical conductivity. Sodium adsorption ratio and exchangeable sodium percentage remained satisfactory, below 13 and 15, respectively, and no infiltration problems were observed, indicating that rainwater percolation was sufficient to leach the salt brought by SS or TWW. The soil organic matter (SOM) increased in all SS-amended and/or TWW-irrigated soils, the increase being higher in SS-amended soils. The SOM kept a satisfactory C/N ratio, lower than 15; the SUVA (Specific UV Absorbance)and E2/E3 index showed normal characteristics of the water-extracted organic matter (WEOC). Both SS amendment and TWW irrigation brought high amounts of nutrients in the considered soils and increased the nutrients disponibility, especially regarding K and P, as shown by the nutrient concentrations in the soil water extracts. The pH increase does not seem to be a problem for the bioavailability of trace elements, at least regarding Cu, Zn, Co, and Fe. Complementary studies should be undertaken for Ni. These observations highlight the potential agronomical benefits of application of wastewater and sewage sludge, even without great technicality, the better results being obtained using both SS amendment and TWW irrigation.

Effects of nanoparticles and modified clays on Cd, Cu, Ni and Zn release from sewage sludge-amended soil assessed through a kinetic study

The objectives of this study were to evaluate the kinetic release (0.5–88 h extraction) and fractionation of cadmium (Cd), copper (Cu), nickel (Ni) and zinc (Zn) in a soil amended with sewage sludge (SS) from Arak (SA), Rasht (SR) and Shiraz (SSh), in presence of zeolite and bentonite modified clays (MCs) and ZnO and MgO nanoparticles (NPs). The initial release of potentially toxic elements (PTEs) occurred rapidly during 1 to 4 h followed by a slower rate. The amount of Cd released in the soil + SA, soil + SR and soil + SSh was 2.44, 2.61 and 2.53 mg kg−1, respectively while when the adsorbents were added to this mixtures it was in the range of 1.33–2.07, 1.52–2.49 and 1.50–2.08 mg kg−1, respectively. The amount of Cu released decreased from 5.07, 6.06 and 5.11 mg kg−1 in the soil + SA, soil + SR and soil + SSh to the ranges of 2.72–2.07, 3.51–5.06, 2.68–3.24 mg kg−1 in presence of adsorbents. Also, the release of Ni and Zn was significantly affected by the presence of MCs and NPs. The release kinetics of Cd, Cu and Ni were described well by pseudo-second-order equation. Also, the exchangeable fraction of the PTEs in the SS-amended soil was reduced in presence of NPs and MCs as the MgO NP had the greatest effect. According to the results, using all the MCs and NPs for keeping the mobility of Cd, Cu, Ni and Zn low in soil amended with SS is suggested.

Nanoparticles and modified clays influenced distribution of heavy metals fractions in a light-textured soil amended with sewage sludges

We comparatively assessed the effect of modified clays (MCs) (zeolite and bentonite) and nanoparticles (NPs) (ZnO and MgO) on the distribution of cadmium (Cd), copper (Cu), nickel (Ni) and zinc (Zn) fractions in a light-textured soil amended with five sewage sludges (SSs) differed in chemical properties during a 92-day incubation experiment in the laboratory. Results indicated that presence of adsorbents and incubation time were critical parameters in stabilizing metals in SS-amended soil. The adsorbents that significantly decreased the easily soluble and exchangeable of metals in SS-amended soil (rate 2%) were bentonite, ZnO and MgO for Cd and Cu, ZnO and MgO for Ni, and bentonite and MgO for Zn. The calculated mobility factor of the metals at five incubation times (5, 15, 29, 57 and 92days) was found in the range of 34.7–51.8 for Cd, 16.7–20.0 for Cu, 15.0–27.7 for Ni, and 35.3–40.7 for Zn indicating a higher mobility of Cd. The addition of MCs and NPs decreased the available fraction of metals, and among them, we suggest bentonite and MgO as novel, promising and feasible adsorbents with the unique characteristics in ameliorating the toxic effects of metals by converting their form from labile to non-labile phases in the SS-amended soil.

Application of mesotrione at different doses in an amended soil: Dissipation and effect on the soil microbial biomass and activity

The aim of this work was to estimate the dissipation of mesotrione applied at three doses (2, 10 and 50mgkg−1 dw) in an unamended agricultural soil, and this same soil amended with two organic residues (green compost (C) and sewage sludge (SS)). The effects of herbicide and organic residue on the abundance and activity of soil microbial communities were also assessed by determining soil microbial parameters such as biomass, dehydrogenase activity (DHA), and respiration. Lower dissipation rates were observed for a higher herbicide dose. The highest half-life (DT50) values were observed in the SS-amended soil for the three herbicide doses applied. Biomass values increased in the amended soils compared to the unamended one in all the cases studied, and increased over the incubation period in the SS-amended soil. DHA mean values significantly decreased in the SS-amended soil, and increased in the C-amended soil compared to the unamended ones, under all conditions. At time 0days, respiration values were significantly higher in SS-amended soils (untreated and treated with mesotrione) than in the unamended and C-amended soils. The effect of mesotrione on soil biomass, DHA and respiration was different depending on incubation time and soil amendment and herbicide dose applied. The results support the need to consider the possible non-target effects of pesticides and organic amendments simultaneously applied on soil microbial communities to prevent negative impacts on soil quality.

Mineralisation of organic fertilisers used by urban farmers in Harare and their effects on maize (Zea mays L.) biomass production and uptake of nutrients and heavy metals

Nutrient release patterns and heavy metal contamination risks associated with animal manure and organic municipal wastes used as basal fertilisers are largely unknown in Zimbabwe. Carbon, nitrogen and phosphorus mineralisation patterns were determined in a 56-day incubation experiment of domestic sewage sludge (SS), pig (PG), poultry (PM) and cattle manures (CM). Maize biomass production, and nutrient and heavy metal (cadmium, copper, nickel and zinc) uptake were determined in a greenhouse experiment. Inorganic fertiliser, PG, PM, SS and CM were applied to the first maize crop and a second maize crop grown without addition of fertilisers. Aboveground biomass was harvested at four weeks after emergence. Fertiliser treatments had significant (p < 0.01) effects on mineralisation. Carbon, nitrogen and phosphorus mineralisation followed the order PG > PM > CM > SS. Maize grown in PM- and PG-amended soils had significantly (p < 0.01) higher biomass, nitrogen and phosphorus uptake than inorganic fertiliser-amended soil in the first crop. The second crop grown in organic fertiliser-amended soils had significantly (p < 0.01) higher biomass and nutrient uptake than inorganic fertiliser-amended soil. Heavy metal uptake was highest in SS-amended soils. Poultry and PG manures mineralised faster than SS and CM. Organic fertilisers had more residual fertility. Nickel toxicity is likely when SS is used as a fertiliser.

Phytoextractability of Cd from Soil by Some Oilseed Species as Affected by Sewage Sludge and Farmyard Manure

A pot experiment was conducted on cadmium (Cd)–enriched (0, 40, 80, 120, 160 mg Cd kg−1 soil, using CdCl2), untreated (Unamended), 3% sewage sludge–treated (SS-amended), and 3% farmyard manure–treated (FYM-amended) soils to evaluate the phytoextractibility of Cd by three oilseed crop species (viz., Brassica juncea, Brassica napus, and Eruca sativa). Visual observation showed that at or above 40 ppm Cd, some light chlorotic symptoms, resembling iron (Fe) chlorosis, appeared after 2 to 3 weeks of germination. The extent of chlorosis followed the order Eruca sativa > Brassica napus > Brassica juncea, and for amendment treatments Unamended > SS-amended > FYM-amended soils. Both the amendments resulted in an increased biomass production in comparison to the Unamended soil, with the effect being more pronounced for FYM. The dry-matter yield of different plant parts followed the order FYM-amended > SS-amended > Unamended soils. For plant species, it followed the order Brassica juncea > Brassica napus > Eruca sativa. The Cd concentration in different plant parts followed the order leaf > stem > seed in all the three species. Amongst the species, the concentration followed the order Brassica napus > Brassica juncea > Eruca sativa, and for amendment treatments SS-amended > Unamended > FYM-amended soils. The mean Cd uptake by different plant species followed the order Brassica juncea > Brassica napus > Eruca sativa, and for amendment treatments SS-amended soil > Unamended soil > FYM-amended soil. The amounts of exchangeable, carbonate bound, Fe-Mn oxide bound, and organic-matter-bound fractions of Cd in the postharvest soil samples increased with the addition of Cd in soil. However, the residual fraction did not change much. At comparable levels of Cd additions, application of sewage sludge as well as FYM resulted in decreases in the exchangeable and Fe-Mn oxide–bound fractions and an increase in the organic-matter-bound fraction. The beneficial effect of sewage sludge and FYM on biomass production was attributed to (i) improvement in the physicochemical and biological environment of the growth medium, (ii) additional supply of essential nutrients, and (iii) possible decrease in toxic effect of added Cd through organo-metallic complexation reactions.

National inventory of alkylphenol ethoxylate compounds in U.S. sewage sludges and chemical fate in outdoor soil mesocosms

We determined the first nationwide inventories of alkylphenol surfactants in U.S. sewage sludges (SS) using samples from the U.S. Environmental Protection Agency's 2001 national SS survey. Additionally, analysis of archived 3-year outdoor mesocosm samples served to determine chemical fates in SS-amended soil. Nonylphenol (NP) was the most abundant analyte (534 ± 192 mg/kg) in SS composites, followed by its mono- and di-ethoxylates (62.1 ± 28 and 59.5 ± 52 mg/kg, respectively). The mean annual load of NP and its ethoxylates in SS was estimated at 2408–7149 metric tonnes, of which 1204–4289 is applied on U.S. land. NP compounds showed observable loss from SS/soil mixtures (1:2), with mean half-lives ranging from 301 to 495 days. Surfactant levels in U.S. SS ten-times in excess of European regulations, substantial releases to U.S. soils, and prolonged half-lives found under field conditions, all argue for the U.S. to follow Europe's move from 20 years ago to regulate these chemicals.