Biosolids compost amendment for reducing soil lead hazards: a pilot study of Orgro amendment and grass seeding in urban yards

In situ inactivation of soil Pb is an alternative to soil removal and replacement that has been demonstrated in recent years at industrial sites with hazardous soil Pb concentrations. Most children exposed to elevated soil Pb, however, reside in urban areas, and no government programs exist to remediate such soils unless an industrial source caused the contamination. Modern regulated biosolids composts have low Pb concentrations and low bioaccessible Pb fractions and can improve grass growth on urban soils. High Fe and P biosolids composts can reduce the bioavailability and bioaccessibility of soil Pb and can aid in establishing vegetation that would reduce soil transfer into homes. For these reasons, we conducted a field test of their use to reduce Pb bioaccessibility in urban soils in Baltimore, MD USA. We chose biosolids compost for its expected reduction in the bioaccessible Pb fraction of urban soils, ease of use by urban residents, and ability to beautify urban areas. Nine urban yards with mean soil Pb concentrations >800 mg Pb kg(-1) were selected and sampled at several distances from the house foundation before soil treatment. The soils were rototilled to 20 cm depth to prepare the sites, and resampled. The yards were then amended with 6-8 cm depth of Orgro biosolids compost (110-180 dry t/ha) rich in Fe and P, mixed well by rototilling, and resampled. Kentucky bluegrass (Poa pratensis) was seeded and became well established. Soils were resampled 1 year later. At each sampling time, total soil Pb was measured using a modified U.S. EPA nitric acid hotplate digestion method (SW 846 Method 3050) and bioaccessible Pb fraction was measured using the Solubility/Bioaccesibility Research Consortium standard operating procedure with modifications, including the use of glycine-buffered HCl at pH 2.2. Samples of untreated soils were collected from each yard and mixed well to serve as controls for the Pb bioaccessibility of field treated soils over time independent of positional variance within yards. At 1-year post-treatment, grass cover was healthy and reductions in bioaccessible Pb concentrations compared to pre-tillage were 64% (from 1655 to 595 mg kg(-1)) and 67% (from 1381 to 453 mg kg(-1)) at the sampling lines closest to the houses. Little or no reduction in bioaccessible Pb concentration was observed at sampling lines more remote from the house that also had the lowest bioaccessible Pb concentrations at pre-tillage (620 and 436 mg kg(-1), respectively). For the control soils, changes over time in total Pb and bioaccessible Pb concentrations and the bioaccessible Pb fraction were insignificant. This study confirms the viability of in situ remediation of soils in urban areas where children are at risk of high Pb exposure from lead in paint, dust and soil.     

Metal contamination at a wood preservation site: characterisation and experimental studies on remediation

The aim of this investigation was to determine the occurrence of As, Cu, Cr and Zn in the soil at an abandoned wood preservation unit and to examine some possible extractants for the contaminants in the soil. The mean As content of the contaminated surface soils (0-10 cm) was 186 mg kg(-1), where as the mean concentrations of Cu, Cr and Zn in soils from the contaminated area were 26, 29 and 91 mg kg(-1), respectively. The elevated As content in the mineral soils is related to adsorption of inorganic As phases in the fine grained fractions, which are characterised by large surface area and high positive surface charge under the current acidic conditions. Cu and Cr were found to be rather mobile, which is reflected in their lower abundance in soils and significant accumulation in sediments in the drainage leaving the area. The fine fraction of the soil (<0.125 mm) has an average metal content increased by nearly 34% as compared to the <2-mm fraction conventionally used for the analysis and assessment of soil contamination. The <2-mm fraction constitutes approximately 65% of the total weight while the fine fraction (<0.125 mm) constitutes approximately 10%. These facts, taken together, are essential for the choice of remediation measures. Oxalate solutions have been tested as extractants for soil remediation. Dark acid oxalate extraction dissolves the amorphous Al- and Fe-oxides and hydroxides and mobilises the adsorbed inorganic As species. Oxalate also acts as a ligand for the cationic heavy metals, releasing them from exchangeable sites. With a three-step sequential leaching, up to 98-99% of the metals could be removed. At lower concentrations and higher pH, the leaching decreased to approximately 70%.     

Biochar for the mitigation of nitrate leaching from soil amended with biosolids

Countries with sewage treatment plants produce on average 27 kg of dried biosolids/person/yr. Concerns about nitrate leaching limit the rate at which biosolids are added to soil. We sought to determine whether biochar, a form of charcoal that is added to soil, could reduce nitrate leaching from biosolids amended soil. We set up 24 (0.5 m × 0.75 m) lysimeters, filled with two soil types (Templeton Silt Loam and Ashley Dene silt loam) and amended with combinations of biochar (102 t/ha equivalent) and biosolids (600 and 1200 kg N/ha equivalent). Pasture and leachates were sampled over 5 months. Nitrate leaching from biochar plus biosolids amended soils were reduced to levels at or below the control treatments. Pasture N concentrations were similarly affected by biochar addition. Future research should focus on unravelling the mechanism responsible for the change in the nitrogen cycle in soils amended with biosolids and biochar.     

Metal extraction by Alyssum serpyllifolium ssp. lusitanicum on mine-spoil soils from Spain

The efficiency of Alyssum serpyllifolium ssp. lusitanicum (Brassicaceae) for use in phytoextraction of polymetallic contaminated soils was evaluated. A. serpyllifolium was grown on two mine-spoil soils (MS1 and MS2): MS1 is contaminated with Cr (283 mg kg(-1)) and MS2 is moderately contaminated with Cr (263 mg kg(-1)), Cu (264 mg kg(-1)), Pb (1433 mg kg(-1)) and Zn (377 mg kg(-1)). Soils were limed to about pH 6.0 (MS1/Ca and MS2/Ca) or limed and amended with NPK fertilisers (MS1/NPK and MS2/NPK). Biomass was reduced on MS2/Ca due to Cu phytotoxicity. Fertilisation increased biomass by 10-fold on MS1/NPK, but root growth was reduced by 7-fold compared with MS1/Ca. Plants accumulated Mn, Ni and Zn in shoots, and both metal content and transportation were generally greater in MS2 than in MS1. Zinc bioaccumulation factors (BF, shoot([metal])/soil([metal])) were significantly greater in MS2 than in MS1. However, metal yields were greatest in plants grown on MS1/NPK. Concentrations of EDTA-, NH(4)Cl- and Mehlich 3 (M3)-extractable Mn and Zn were greater after plant growth. Concentrations of M3-extractable Cr, Ni, Pb and Zn were increased at the rhizosphere. Sequential extractions showed changes in the metal distribution among different soil fractions after growth. This could reflect the buffering capacity of these soils or the plants' ability to mobilise metals from less plant-available soil pools. Results suggest that A. serpyllifolium could be suitable for phytoextraction uses in polymetallic-contaminated soils, provided Cu concentrations were not phytotoxic. However, further optimisation of growth and metal extraction are required.     

Extractability of metals and ecotoxicity of soils from two old wood impregnation sites in Finland

Four metal-contaminated soil samples were classified using physical methods, extracted by selective extraction procedures and analyzed for chemical concentrations. De-ionized water, 0.01 mol/l barium chloride, 1 mol/l ammonium acetate and concentrated nitric acid were used as extraction solutions. Ecotoxicity of water extracts and soil samples was analyzed in order to describe the bioavailability of the contaminants. Samples from old wood impregnation plants contained high amounts of As, Cu, Cr and Zn, which originated from chromated copper arsenate, ammoniacal copper-zinc arsenate, and ammoniacal copper quaternary compound. Total As concentrations of the heavily contaminated samples varied from 752 to 4340 mg/kg, Cu concentrations from 339 to 2330 mg/kg, Cr concentrations from 367 to 2,140 mg/kg and Zn concentrations from 79 to 966 mg/kg. The extractabilities of metals differed according to soil type, extractant and element. Cu and Zn were proposed to cause the highest toxicity in the water extracts of the soils. Ecotoxicity tests displayed rather high differences in sensitivity both for water extracts and for solid soil samples. Reproduction of Enchytraeus sp. was the most sensitive and seed germination of Lactuca sativa the least sensitive and the other tests were in decreasing order of sensitivity: Folsomia candida>reverse electron transport>MetPLATE>Toxichromotest>Allium cepa root growth>Lemna sp. growth. As a conclusion, polluted soils rich in sand retain heavy metals with less firm bindings, particularly in the case of Cu and Zn, than soils rich in clay, indicating that chemical methods for measuring the bioavailability of metals need to be optimized taking into account the soil type, acidity, redox state and the individual contaminants.     

Alkaline biosolids and EDTA for phytoremediation of an acidic loamy soil spiked with cadmium

A greenhouse experiment was conducted to investigate the growth of Brassica juncea and Cd phytoextraction in a mimicked Cd contaminated acidic loamy soil amended with alkaline biosolids, prepared from sewage sludge and coal fly ash, in the presence and absence of EDTA at 2 mmol kg(-1). The acidic loamy soil was spiked with 0, 5, 20, 50 and 100 mg Cd kg(-1) in the form of CdCO(3) and then amended with 4% alkaline biosolids (w/w). Alkaline biosolids and 0.12% CaCO(3) amendments resulted in a higher biomass than unamended soil spiked with 20 mg kg(-1) Cd where plants did not survive and of the two amendments, alkaline biosolids amendment had higher plant dry weight yield and phytoextraction of Cd. Adding 2 mmol kg(-1) EDTA to alkaline biosolids amended soil significantly increased the solubility of Cd ions by 9- to 29-fold, but plant Cd accumulation decreased by a factor of 24-48%. The results indicate that alkaline biosolids amendment is an effective approach for assisting growth of B. juncea and phytoextraction of Cd from the contaminated acidic loamy soil, but further application of chelating agents did not enhance the phytoextraction efficiency of Cd.     

Glomalin-related soil protein in a Mediterranean ecosystem affected by a copper smelter and its contribution to Cu and Zn sequestration

The amount of glomalin-related soil protein (GRSP), a glycoprotein produced by arbuscular mycorrhizal fungi (AMF), its contribution to the sequestering of Cu and Zn in the soil, and the microsite variation of other soil traits (pH, water-stable aggregates--[WSA], soil organic carbon--[SOC]) was studied in a semi-arid Mediterranean ecosystem near a copper smelter and affected by deposit of metal-rich particles since 1964. Rhizospheric (R) and non-rhizospheric (NR) soil of four representative plants (Argemone subfusiformis, Baccharis linearis, Oenothera affinis and Polypogon viridis) was analyzed. The results showed a strong variability in GRSP (6.6-36.8 mg g(-1)), Cu content (62-831 mg kg(-1) for the total Cu and 5.8-326 mg kg(-1) for the available Cu) and pH (4.2-5.5) in the different plant and rhizospheric zones analyzed. A strong relationship between the GRSP with the soil Cu and Zn contents was found (r=0.89 and 0.76 for Cu and Zn respectively, p<0.001). The GRSP-bound Cu ranged from 3.76 to 89.0 mg g(-1) soil and represents 1.44-27.5% of the total Cu content in soil. Moreover, the WSA reached 89% in P. viridis R. For this plant, the C contained in GRSP represented up to 89% of SOC, and this coincided with the most extreme conditions of soil degradation within the ecosystem (the highest content of heavy metals and low pH values). This study provides evidence on the role of the GRSP in Cu and Zn sequestration and suggests a highly efficient mechanism of AMF to mitigate stress leading to stabilization of soils highly polluted by mining activities.     

Detection of the antimicrobials triclocarban and triclosan in agricultural soils following land application of municipal biosolids

The occurrence of the antimicrobials triclocarban (TCC) and triclosan (TCS) was investigated in agricultural soils following land application of biosolids using liquid chromatography-tandem mass spectrometry (LC-MS-MS) with negative ion multimode ionization. The method detection limits were 0.58 ng TCC/g soil, 3.08 ng TCC/g biosolids, 0.05 ng TCS/g soil and 0.11 ng TCS/g biosolids and the average recovery from all of the sample matrices was >95%. Antimicrobial concentrations in biosolids from three Michigan wastewater treatment plants (WWTPs) ranged from 4890 to 9280 ng/g, and from 90 to 7060 ng/g, for TCC and TCS respectively. Antimicrobial analysis of soil samples, collected over two years, from ten agricultural sites previously amended with biosolids, indicated TCC was present at higher concentrations (1.24-7.01 ng/g and 1.20-65.10 ng/g in 2007 and 2008) compared to TCS (0.16-1.02 ng/g and from the method detection limit, <0.05-0.28 ng/g in 2007 and 2008). Soil antimicrobial concentrations could not be correlated to any soil characteristic, or to the time of last biosolids application, which occurred in either 2003, 2004 or 2007. To our knowledge, our data represent the first report of TCC, and the first comparison of TCC and TCS concentrations, in biosolids-amended agricultural soils. Such information is important because approximately 50% of US biosolids are land applied, therefore, any downstream effects of either antimicrobial are likely to be widespread.     

Remediation measures and displacement of pollutants in soils affected by the spill of a pyrite mine

The soils affected by the spill of a pyrite mine were analysed in 100 sampling points at three depths (0-10, 10-30, and 30-50 cm) in 1998 (after the tailings were removed), 1999 (after the cleaning of the highly contaminated areas), and 2004 (after the tilling of the upper 20-25 cm). The comparative study reveals that the removal of the tailings left a heterogeneous distribution pattern of the contaminants, with highly polluted spots alternating with less contaminated areas. The cleanup did not substantially lower the concentration in the highly polluted soils, and the spread of the pollutants increased the concentration in As and Pb in the uppermost 10 cm of 60% of the soils, while the Zn and Cd concentrations increased in only 30% of the soils. Given the high concentration of pollutants in the topsoil (especially As), the tilling of the upper 20-25 cm, despite reducing the average concentration of pollutants in the uppermost 10 cm, did not substantially lower the percentage of soils that exceeded the concentration of 40 mg As kg^− 1 dry soil and almost doubled the percentage of soils that surpassed this concentration between 10 and 30 cm. Meanwhile, the displacement of Zn and Cd within the soil supported the reduction in the percentage of soils that in the upper 10 cm exceeded the reference concentrations of these elements (900 mg Zn kg^− 1 dry soil and 2 mg Cd kg^− 1 dry soil), and the percentage of soils exceeding these concentrations between 10 and 50 cm in depth did not increase. Six years after the spill and at the end of all remediation measures, the intervention levels defined by the Environmental Agency of the Regional Government of Andalusia for natural parks were exceeded in the uppermost 10 cm in 35% of the soils.     

Mercury and other trace elements in soils affected by the mine tailing spill in Aznalcóllar (SW Spain)

The Aznalcóllar accident (28th April 1998) occurred because the collapse of the tailing-dam dike of the Aznalcóllar-Los Frailes mines. Soils were affected by a slurry of acidic water loaded with trace elements, finely divided metal sulphides, and materials used in the refining /floating process. Studies carried out before and after the soil restoration activities (sludge removal, amending, tilling, and afforestation) showed severe trace-element contamination (mainly As, Cd, Cu, Pb, Tl and Zn) in the superficial layer of the sludge-affected soils. Despite Hg being an important component of the Los Frailes ore and therefore of the contaminant sludge, data on Hg content of sludge-affected soils are scarce and sometimes controversial. The aim of this study was to determine the effect of the spill and of restoration measures on the Hg content of soils and how this related to other elements. Concentration of Hg immediately after the spill was 8-fold above background (0.061+/-0.012 mg kg(-1); mean+/-SD) at the surface (0-5 cm) and 3-4-fold greater in deeper layers (0-20; 0-50 cm). After the remediation measures, mean values of Hg and other elements (As, Cd, Cu, Pb and Zn) were very variable and remained above background values. These anomalies are due to the sludge left on the soil surface or buried during restoration operations, resulting in an irregular distribution of trace elements. The highest values for the less mobile elements (up to 176 mg kg(-1) As, 2.36 mg kg(-1) Hg and 1556 mg kg(-1) Pb) were observed in the area 1 km downstream of the tailings dam.     

Short-term effects of biosolid and municipal solid waste applications on heavy metals distribution in a degraded soil under a semi-arid environment

Digested biosolid (SS) and municipal solid waste (MSW) were surface-applied to a degraded carbonated soil, under semi-arid environment, at rates of 0 and 80 Mg/ha, to determine the changes in organic matter and in the distribution of heavy metals in the topsoil, 1 year after its application. Waste application slightly increased the organic matter content and improved the composition of humic fractions in the treated soils, mainly in the MSW amended plots. A sequential extraction method (Tessier et al., 1979) was used to determine the distribution of Cd, Cr, Cu, Ni, Pb and Zn in both the waste and the amended.soils. Waste application had little effect on the total concentration of Ni and Cr in the treated soils as a consequence of the low availability of these metals in the wastes. A considerable increase of Cd, Cu, Pb and Zn was observed as a consequence of the high content and/or high availability of these metals in the wastes. The more labile fraction (exchangeable fraction) of all metals studied increased slightly (< 1.5 mg/kg) when SS and MSW were added. However, a remarkable increase in the Fe/Mn oxide fraction of Cd, Cu and Pb and in the organic fraction of Zn were noted in treated plots, this increase being higher in the MSW treated soils.     

Influence of copper fungicide residues on occurrence of earthworms in avocado orchard soils

The compost worm Eisenia fetida was used to demonstrate the avoidance by worms of Cu contaminated soil. Soils were collected from two avocado orchards in north eastern New South Wales, Australia. In avoidance trials, worms preferred non-contaminated control soils, sourced from adjacent to the orchard or an OECD control soil, when Cu residues in the orchard soils reached 4-34 mg Cu kg(-1). At levels of 553 mg Cu kg(-1), 90% avoidance of orchard soil was observed. The worms showed preference for the soils in the order; uncontaminated field derived soil >OECD standard soil >Cu contaminated orchard soil. It was demonstrated that OECD standard soil was less favoured by worms than control soil derived from the test sites. While Cu was found to be the primary influence on worm avoidance in orchard soil, other factors, such as elevated soil Zn concentrations, could not be discounted. In a corresponding field study, it was shown that earthworms occurred at lower density in orchard soils with a history of Cu fungicide use. In one such orchard, soil Cu concentrations of up to 270 mg kg(-1) were determined and no earthworms were found, while nearby control sites and less contaminated sites within the orchard had up to 40.7 g m(-2) earthworm biomass. Considering the potential for Cu to accumulate in these soils and the subsequent impacts on soil biota, our results highlight the importance of limiting future application of Cu based fungicides.     

Quantifying heavy metal inputs to agricultural soils in England and Wales

Heavy metal inputs to agricultural soils in England and Wales were estimated from major sources, including atmospheric deposition, biosolids, livestock manures, inorganic fertilisers and lime, industrial by‐product ‘wastes’ and composts (year 2000). Across the whole agricultural land area, atmospheric deposition was the main source of most metals ranging from 25 to 85% of total inputs. Livestock manures and biosolids were also important sources representing 37 and 8% of total zinc (Zn) inputs, 40 and 17% for copper (Cu), and 10 and 4% for cadmium, respectively. The highest heavy metal input rates on a field basis were generally from biosolids, although Zn and Cu inputs from pig manures were equivalent to 46–52% of biosolids inputs (both applied at a rate of 250 kg/ha total N). The study provided baseline information to develop and focus policies limiting heavy metal inputs to and accumulation in topsoils.     

Exposure assessment of a burning ground for chemical ammunition on the Great War battlefields of Verdun

The destruction of arsenical shells from the 1914/18 war in the vicinity of Verdun (France) during the 1920s resulted in a locally limited but severe soil contamination by arsenic and heavy metals. At the study site, the main part of the contaminant inventory occurs in the upper 20 cm of the topsoil which is essentially composed of combustion residues. Besides, some Cu (cmax.=16,877 mg/kg) and Pb (cmax.=26,398 mg/kg) in this layer, As (cmax.=175,907 mg/kg) and Zn (cmax.=133,237 mg/kg) were detected in very high concentrations. The mobilities of Cu, Mn, Pb and Zn in the soil system were derived from ammonium nitrate eluates. They are strongly influenced by the soil pH and can be described by quadratic regression curves from which threshold pH values were calculated. Below these values more than 10% of the element content was available as mobile species. Within the examined pH range, this method could not be adopted for arsenic, because the mobility of As was only slightly controlled by the soil pH. In the heavily contaminated topsoil, Cu and Pb were fixed by the moderately acidic soil pH which varied from 4.8 to 5.8. No migration to the underlying horizons occurred. A different behavior was observed for As and Zn. The calculated threshold pH of Zn was 5.5, so certain amount of this element was transferred to the subsoil and the leachate (cmax.=350 microg/l). However, a major dispersion of Zn was prevented by a rise of the soil pH in the carbonate-containing subsoil. Elevated concentrations of As were found in all soil horizons up to a depth of 2 m and also in the leachate (cmax.=2377 microg/l). Contrary to Cu, Pb and Zn the mobility of As evidently was less affected by the subsoil. Regarding organic contaminants, nitroaromatic explosives were detected only in minor concentrations in the soil (cmax.=14.7 mg/kg) and the leachate (cmax.=13.5 microg/l). No aromatic organoarsenicals were detected in the soil and the leachate samples. The main hazard of the site is the severe arsenic contamination and the transfer of this carcinogen by leachate, surface runoff and probably by wind. Nevertheless, some studies on the effects of the contaminant inventory on the local vegetation revealed that ammonium nitrate elutable zinc is responsible for the spatial distribution of some tolerant plant species and not arsenic. Previously undetected buried munitions from the former delaboration facility can be an other source of environmental contaminants. This is supported by elevated concentrations of chlorate (cmax.=71 mg/l) and perchlorate (cmax.=0.8 mg/l) detected in the leachate samples. This is the second report about environmental contamination related to post-war ammunition destruction activities along the 1914/18 Western Front.     

Mapping the total phosphorus concentration of biosolid amended surface soils using LANDSAT TM data

Conventional methods for soil sampling and analysis for soil variability in chemical characteristics are too time-consuming and expensive for multi-seasonal monitoring over large-scale areas. Hence, the objectives of this study are: 1) to determine changes in chemical concentrations of soils that are amended with treated sewage sludge; and 2) to determine if LANDSAT TM data can be used to map surface chemical characteristics of such amended soils. For this study, we selected two fields in NW Ohio, designated as F34 and F11, that had been applied with 34 and 11 ton acre^− 1 of biosolids, respectively. Soil samples from a total of 70 sampling locations across the two fields were collected one day prior to LANDSAT 5 overpass and were analyzed for several elemental concentrations. The accumulation of Ba, Cd, Cu, S and P were found to be significantly higher in the surface soils of field F34, compared to field F11. Regression equations were established to search for algorithms that could map these five elemental concentrations in the surface soils using six, dark-object-subtracted (DOS) LANDSAT TM bands and the 15 non-reciprocal spectral ratios derived from these six bands for the May 20, 2005, LANDSAT 5 TM image. Phosphorus (P) had the highest R² adjusted value (67.9%) among all five elements considered, and the resulting algorithm employed only spectral ratios. This model was successfully tested for robustness by applying it to another LANDSAT TM image obtained on June 5, 2005. Our results enabled us to conclude that LANDSAT TM imagery of bare-soil fields can be used to quantify and map the spatial variation of total phosphorous concentration in surface soils. This research has significant implications for identification and mapping of areas with high P, which is important for implementing and monitoring the best phosphorous management practices across the region.     

Impact of biosolids on the persistence and dissipation pathways of triclosan and triclocarban in an agricultural soil

The broad spectrum antimicrobial agents triclosan (TCS) and triclocarban (TCC) are widely used in many personal care products. Knowledge concerning the fate of these two compounds in different environmental matrices is scarce. In this study, the fate of TCS and TCC in soil following direct addition, or when residues were applied via either liquid municipal biosolids (LMB) or dewatered municipal biosolids (DMB) was investigated in laboratory dissipation experiments and under outdoor conditions using radioisotope methods. In laboratory incubations, ¹⁴C-TCC or ¹⁴C-TCS was added to microcosms containing a loam soil and the rate of ¹⁴CO₂ accumulation and loss of solvent-extractable ¹⁴C were determined during incubation at 30 °C. Compared to when TCC or TCS was added directly to soil, both chemicals were mineralized more rapidly when applied in LMB, and both were mineralized more slowly when applied in DMB. The application matrix had no effect on the rate of removal of extractable residues. In field experiments, parent compounds were incorporated directly in soil, incorporated via LMB, or a single aggregate of amended DMB was applied to the soil surface. During the experiment soil temperatures ranged from 20 °C to 10 °C. Dissipation was much slower in the field than in the laboratory experiments. Removal of non-extractable residues was faster in the presence of LMB than the other treatments. Recovery of extractable and non-extractable residues suggested that there was little atmospheric loss of ¹⁴C. Triclocarban readily formed non-extractable residues with DMB whereas TCS did not. Overall, this study has identified that both the pathways and the kinetics of TCS and TCC dissipation in soil are different when the chemicals are carried in biosolids compared to when these chemicals are added directly to the soil.     

Comparative value of phosphate sources on the immobilization of lead, and leaching of lead and phosphorus in lead contaminated soils

The mobility and bioavailability of lead (Pb) in soils can be mitigated by its immobilization using both soluble and insoluble phosphate (P) compounds. The effectiveness of insoluble P sources on Pb immobilization depends on their rate of dissolution which can be enhanced by phosphate solubilizing bacteria (PSB). In this study, the effect of soluble (potassium dihydrogen phosphate) and insoluble (rock phosphate in the presence and absence of PSB) P compounds on the immobilization of Pb, and leaching of Pb and P was examined using both naturally contaminated (SR soil: NH₄NO₃ extractable Pb: 28.7 mg/kg, pH: 5.88, organic matter: 0.7%) and Pb spiked (AH soil: NH₄NO₃ extractable Pb: 42.7 mg/kg, pH: 5.23, organic matter: 10.9%) soils. Phosphate compounds were added at the rate of 200 mg P/kg and 800 mg P/kg for SR and AH soils, respectively. Soluble P treatment immobilized 80% and 57% of Pb in SR and AH soils, respectively. Insoluble rock phosphate immobilized 40% and 9% of Pb without PSB, and 60% and 17% with PSB in SR and AH soils, respectively. Lead leaching was the lowest when soils were amended with rock phosphate in the presence of PSB, which reduced Pb leaching by 36% for SR soil and 18% for AH soil compared to the control. The leaching of Pb increased when the soils were amended with soluble P because soluble P treatment increased dissolved organic carbon (DOC) concentration of soil, thereby increasing Pb mobility. Soluble P treatment significantly increased P leaching and 9% of total added P was leached from low P retaining AH soil. The optimum level of P amendment is a critical issue when soluble P is used as a Pb immobilizing agent because of eutrophication resulting from excessive P leaching to surface and ground water. While the soluble P compound was effective in the immobilization of Pb, it resulted in P leaching which increased with increasing levels of P addition. However, rock phosphate amendment with PSB achieved the immobilization of Pb with a minimum effect on both Pb and P leaching.     

Evaluation of metal concentrations in edible vegetables grown in compost amended soil

Agricultural uses of compost usually have a positive effect on the yield of vegetable crops for human consumption. However, compost that contains heavy metals can transfer these components to soils and plants. To evaluate the contamination levels of metals in soil, compost, and edible vegetables, the Mn, Zn, Pb, Cd, Cu, and Ni total contents were measured. Metal availability in soils, as well as other variables – the pH, CEC (cation exchange capacity), total nitrogen, organic carbon, particle size distribution and mineralogy of the clay fraction – were examined in the soil samples. The analysed compost samples were produced from urban solid waste, cattle manure, and edible vegetable and tree pruning residues. The values of pH, CEC, total nitrogen, organic matter, exchangeable hydrogen and carboxylic groups were measured in the compost samples. Of the six metals examined in the soils, in general, Mn and Zn attained the highest concentrations, followed by Cu. Relatively high Mn, Zn, Cu, Cd and Pb concentrations were found in the soils. Metal concentrations extracted with DTPA were below the critical levels in soils, i.e. the levels above which toxicity is likely. In general, Zn, Pb, Cd, Cu and Ni concentrations in compost were lower than those reported by other workers, while Mn levels were within the range for this metal in compost. The results showed that there was an effect of the vegetable type (p < 0.01) for all the parameters examined. High Pb concentrations were found in lettuce and chive as compared with the tolerance limit for this metal in fresh vegetables in Brazil. Cadmium concentrations were also enhanced in the fresh vegetables compared with the typical concentrations of metals in plants. Zinc, Cu, Cd, and Ni concentrations were lower than the tolerance limits established for foods by the Brazilian legislation.     

The non-steroidal anti-inflammatory drug diclofenac is readily biodegradable in agricultural soils

Diclofenac, 2-[2-[(2,6-dichlorophenyl)amino]phenyl]acetic acid, is an important non-steroidal anti-inflammatory drug widely used for human and animals to reduce inflammation and pain. Diclofenac could potentially reach agricultural lands through the application of municipal biosolids or wastewater, and in the absence of any environmental fate data, we evaluated its persistence in agricultural soils incubated in the laboratory. ¹⁴C-Diclofenac was rapidly mineralized without a lag when added to soils varying widely in texture (sandy loam, loam, clay loam). Over a range of temperature and moisture conditions extractable ¹⁴C-diclofenac residues decreased with half lives < 5 days. No extractable transformation products were detectable by HPLC. Diclofenac mineralization in the loam soil was abolished by heat sterilization. Addition of biosolids to sterile or non-sterile soil did not accelerate the dissipation of diclofenac. These findings indicate that diclofenac is readily biodegradable in agricultural soils.     

Fate of the antiretroviral drug tenofovir in agricultural soil

Tenofovir (9-(R)-(2-phosphonylmethoxypropyl)-adenine) is an antiretroviral drug widely used for the treatment of human immunodeficiency virus (HIV-1) and Hepatitis B virus (HBV) infections. Tenofovir is extensively and rapidly excreted unchanged in the urine. In the expectation that tenofovir could potentially reach agricultural lands through the application of municipal biosolids or wastewater, and in the absence of any environmental fate data, we evaluated its persistence in selected agricultural soils. Less than 10% of [adenine-8-¹⁴C]-tenofovir added to soils varying widely in texture (sand, loam, clay loam) was mineralized in a 2-month incubation under laboratory conditions. Tenofovir was less readily extractable from clay soils than from a loam or a sandy loam soil. Radioactive residues of tenofovir were removed from the soil extractable fraction with DT₅₀s ranging from 24 ± 2 to 67 + 22 days (first order kinetic model) or 44 + 9 to 127 + 55 days (zero order model). No extractable transformation products were detectable by HPLC. Tenofovir mineralization in the loam soil increased with temperature (range 4 °C to 30 °C), and did not occur in autoclaved soil, suggesting a microbial basis. Mineralization rates increased with soil moisture content, ranging from air-dried to saturated. In summary, tenofovir was relatively persistent in soils, there were no extractable transformation products detected, and the response of [adenine-8-¹⁴C]-tenofovir mineralization to soil temperature and heat sterilization indicated that the molecule was biodegraded by aerobic microorganisms. Sorption isotherms with dewatered biosolids suggested that tenofovir residues could potentially partition into the particulate fraction during sewage treatment.