Fernando Madrid

Molecular alterations of organic fractions from urban waste in the course of composting and their further transformation in amended soil

Abstract The evolution of various analytical characteristics (including the concentrations of water-soluble fractions, free and esterified lipids, and humic-like substances) of solid urban waste in the course of a 7-week composting process have been monitored in two independent piles composted during different seasons (Spring/Autumn). Whereas the concentration of water-soluble and mineral fractions tended to increase during composting, the opposite was observed for total organic matter and free lipid. Unmatured compost showed comparatively high amounts of esterified lipid. The absence of monotonic trends shown by this fraction, and by total humic-like substances indicate two successive stages of compost microbial reworking. Gas chromatography-mass spectrometry (GC-MS) analysis of the lipid fractions progressively removed by step-wise chemolysis allows the appraisal of different lipid species, which differ in their resistance to biodegradation. Extended composting does not contribute to the accumulation of progressively aromatised humic-type materials similar to those present in soil. Both pyrolysis (Py)-GC-MS and spectroscopic techniques (Fourier transform infrared spectroscopy, FT-IR, and 13 C nuclear magnetic resonance spectroscopy, NMR) confirm that compost-derived humic acid-like substances are not structurally comparable to soil humic acids. Finally, the fate of the compost organic fractions has been investigated in two soils amended with different doses of the final compost. In general, the most conspicuous compost-induced effects were reflected by the differences in the qualitative and quantitative composition of the soil lipid. The results indicate that compost application cannot be considered to contribute to the mid-term accumulation of stable forms of organic matter in soil.

Cadmium availability in soil and retention in oak roots: potential for phytostabilization

Afforestation of contaminated land by trees is considered as a feasible strategy for the extensive stabilization of contaminants. In this work, we studied the patterns of metal availability (Cd, Cu, Pb and Zn) in a contaminated and afforested area. Specifically, we observed the response of Holm oak (Quercus ilex subsp. ballota) leaves to changes in the availability of metals under field conditions, focusing on Cd. Under controlled conditions we studied the performance of oak seedlings exposed to high levels of Cd, with the aim of analyzing the patterns of translocation and tolerance of the seedlings. Cadmium was the most available metal, in relative terms; 15% of the total Cd in the soil was extracted with NH4NO3. The availabilities of Cd, Cu and Zn showed exponential relationships with soil pH (pH values ranged from 2.4 to 8.4). Cadmium accumulation in the leaves was not related to the changes in Cd availability. Greenhouse studies showed that seedlings had a high Cd retention capacity in fine roots (up to 7 gkg(-1)) and low rates of Cd translocation to the leaves (transfer coefficients below 0.03). Root biomass and thickness was altered by exposure to Cd. In spite of this, the chlorophyll fluorescence measurements (an indicator of plant stress) only differed slightly from the control treatment at a Cd dose of 200 mgL(-1). Due to the relatively high tolerance to Cd and the capacity of roots to retain this metal, Holm oak may be useful for the phytostabilization of soils contaminated by Cd.

Metal content of surface soils in parks and allotments from three European cities: initial pilot study results

A pilot study of metal content and basic soil properties was undertaken in a number of parks and allotments in the cities of Glasgow, UK, Torino, Italy, and Sevilla, Spain. Between 40 and 60 samples were collected from each city, with soil from two depths. The maximum metal contents (aqua regia) found were 698 mg/kg Cu; 1004 mg/kg Zn; 300 mg/kg Ni; 356 mg/kg Cr and 7051 mg/kg Pb. Variability of metal content showed similar patterns across all cities, with a number of outlier data points. Surface and subsurface samples were comparable within sites. Cu, Zn and Pb levels appeared to contain most variability and extreme data points, while Ni and Cr were more homogeneous. The data support previously published observations of anthropogenic association (Cu, Zn and Pb) and natural sources (Ni and Cr), found in urban environments influenced by diffuse pollution. Within the Glasgow data, differences in the variability of metal content in park and allotment soil are not dramatic, but do reflect the influence of different agronomic activities. The study has provided baseline information for ongoing pan-European urban soil research funded through the EU.

Effect of contact time and the use of hydroxypropyl-β-cyclodextrin in the removal of fluorene and fluoranthene from contaminated soils

Sorption-desorption experiments of fluorene (FLU) and fluoranthene (FLT) in soils were carried out and correlated to their removal from aged contaminated soils using aqueous solutions in the absence and in the presence of hydroxypropyl-β-cyclodextrin (HPBCD) as the extraction agent. FLU became more resistant to extraction in aged contaminated soils due to its initial adsorption onto the mineral and amorphous soil organic matter (SOM) domains, sites of lower binding energy from which, due to its small size, it could spread towards the condensed SOM as the contact time increased. Therefore, FLU will not be easily desorbed from aged contaminated soils due to physical entrapment mechanisms, even when using HPBCD as extractant, presenting FLU low risks to the environment. On the contrary, FLT was extracted from aged soils in the presence of HPBCD in solutions to a much greater extent than in its absence. Due to its more hydrophobic character FLT sorption in soils was relatively quicker, remaining more or less fixed on hydrophobic sites of the organic matter (OM) with different energies, and therefore the amount of FLT extracted was almost constant for different ageing times. During extraction experiments, the influence of the OM quality of the soils was also highlighted because an inverse proportionality between OM content of soil and extractability of sorbed FLT was observed. It was concluded that soils with lower OM content that had more diagenetically processed OM could block the extraction of FLT more effectively than soils with higher OM content that are less humified. This indicates the need to use not only adsorption-desorption data in contaminant fate and transport models, but also extraction studies in aged contaminated soils and other complementary analytical approaches when assessing soil contamination-related risks.

Effect of an organic amendment on availability and bio-accessibility of some metals in soils of urban recreational areas.

A composted biosolid from wastewater treatment was added to soils of two public parks of Sevilla, and successive samples were taken during one year. In one of the parks, a second addition of biosolid was carried out after the first year. The soil contents in metals (pseudo-total) and their plant-available and oral bio-accessible fractions were significantly altered when the soils were amended with biosolid. Increase of the bio-accessible metal contents represents a deterioration of the environmental quality of recreational areas, where hand-to-mouth transfer of pollutants to children is likely to occur, although part of the metals added might be leached by rainfall or irrigation. The limits established in several countries for metal contents of soils in recreational areas are often exceeded after application of the biosolid. A careful study of the metal contents of recycled wastes is thus recommended before being used for green area maintenance.

Effects of the presence of a composted biosolid on the metal immobilizing action of an urban soil

The influence of a composted biosolid from urban wastewater treatment on the retention and solubility of Cu, Pb or Zn added to a soil was studied by batch adsorption/desorption experiments, equilibrating both materials and their mixtures with solutions containing various metal concentrations. The composted biosolid adsorbed less Cu or Pb and slightly more Zn than the soil, and thus caused a noticeable decrease in the retention of Cu or Pb and an increase in Zn adsorption by soil-biosolid mixtures, but these effects in the mixtures were not additive for any metal. The pH effects were studied by means of (log metal concentration)/pH diagrams. It was shown that Cu behaviour was different from that of the other metals: the relation between pH and Cu concentrations suggested similar solubilities in the presence of the biosolid and the mixtures, whereas the biosolid-free soil gave data located on a region of the diagram corresponding to slightly lower solubility. In the case of Pb or Zn, the data for the biosolid were located in a region of the diagram corresponding to clearly lower solubilities than those for the biosolid/soil mixtures. It was concluded that the biosolid has little effect on metal solubility when it is mixed with the soil in the proportions used here.

Assisted attenuation of a soil contaminated by diuron using hydroxypropyl-β-cyclodextrin and organic amendments

Diuron desorption and mineralisation were studied on an amended and artificially contaminated soil. The amendments used comprised two different composted organic residues i.e., sewage sludge (SS) mixed with pruning wastes, and urban solid residues (USR), and two different solutions (with inorganic salts as the micronutrients and hydroxypropyl-β-cyclodextrin (HPBCD)). After applying micronutrients to activate the soil flora, 15.5% mineralisation could be reached after 150 days, indicating that the soil has a potential capacity to mineralise the herbicide through biostimulation-assisted attenuation. Diuron mineralisation was also improved when HPBCD solutions were applied. Indeed, the extent of herbicide mineralisation reached 29.7% with this application. Moreover, both the lag phase and the half-life time (DT50) were reduced to 33 and 1,778 days, respectively, relative to the application of just micronutrients (i.e., 39 and 6297 days, respectively). Organic amendments were also applied (i.e., USR and SS) on the contaminated soil: it was found that the diuron mineralisation rate was improved as the amendment concentration increased. The joint application of all treatments investigated at the best conditions tested was conducted to obtain the best diuron mineralisation results. The micronutrient amendment plus 4% USR or SS amendment plus HPBCD solution (10-fold diuron initially spiked) caused an extent of diuron mineralisation 33.2 or 46.5%, respectively.

Use of urea to correct immature urban composts for agricultural purposes

Abstract Municipal solid waste composts are often inadequately stabilized for agricultural purposes. In addition, compost quality may be even more reduced by loss of nitrogen (N) during the composting process. We have utilized a compost with a high content of soluble sugars (11 mg g‐1, DM, indicating immaturity) and a low ? concentration (0.95%, DM). The compost had a low level of heavy metals. Results obtained in a germination bioassay conducted with cress, ryegrass and sunflower in a compost‐sand mixture reflected the immaturity of the compost. Such composts should be fortified with ? (in a complete fertilizer, when possible), at the same time avoiding an intimate contact with the soil (e.g., plowing down). When the compost (and raw wastes and wastes at the 4th week of composting) was mixed with a soil at a heavy rate (2.5 % w:w), ryegrass seedling emergence in pots was not affected, but the plantlets’ fresh weight in the compost treatment was significantly lower than that in the control (soil) and lower than that in the raw wastes, probably due to the lower ? concentration. As expected, plantlet fresh weight was notably increased by the combination of compost and wastes with a complete fertilizer. The application of compost in combination with a complete fertilizer or urea did not affect either dry matter production or nutrient uptake of ryegrass, despite the combinations being applied just at sowing (in pots). Results obtained in these experiments indicate that combining immature composts with urea [supplemented with phosphorus (P) and potassium (K), when possible] at a ratio of about 50:1 (about 200 kg urea per 101 compost) could be sufficient to prevent negative results in crop establishment. Such practices could contribute to overcoming the limited fertilizing capacity of the composts.

Effect of controlled release formulations of diuron and alachlor herbicides on the biochemical activity of agricultural soils

The use of pesticides in agriculture is essential because it reduces the economic losses caused by pests, improving crop yields. In spite of the growing number of studies concerning the development and application of controlled release formulations (CRFs) of pesticides in agricultural soils, there are no studies about the effects of such formulations on the biochemical properties. In this paper the dissipation of diuron and alachlor in three agricultural soils for 127days, applied either as commercial or CRFs, was determined as well as their concomitant effects on soil biochemical properties. Dehydrogenase, urease, β-glucosidase and phosphatase activities were measured thought the experimental period. The application of alachlor as CRF increases its half-life time in soils, whereas no differences were noticed between diuron formulations due to its slower degradation, which takes longer than its release from the CRF. At the end of the incubation period, the enzymatic activities were the same after the use of diuron either as commercial or CRF, recovering the soil previous status. For alachlor formulations, no differences in enzymatic activities were again observed between both formulations, but their levels in soils were enhanced. Therefore, the use of these CRFs does not adversely affect the soil biochemical properties.

Quality and comparability of measurement of potentially toxic elements in urban soils by a group of european laboratories

A study has been conducted to assess the quality and comparability of measurement of aqua-regia-soluble cadmium, chromium, copper, iron, manganese, nickel, lead, and zinc in urban soils within a small cohort of European research laboratories specializing in soil science or environmental analytical chemistry. An initial survey indicated that highly variable levels of analytical quality control (e.g. use of certified reference materials) were routinely implemented in participant laboratories. When a set of soil samples—differing in metal contents and in characteristics such as pH and organic-matter content—were exchanged and analysed, approximately 20% of results differed from target values by more than 25%. A principal-component analysis was applied to data for chromium, copper, nickel, lead, and zinc, and proved successful in assessing overall laboratory performance. The study indicates that greater prominence needs to be given to quality assurance and control if comparable data are to be generated in international, collaborative research projects.