Jose M. Alvarez

Influence of thermal treatment on sequential extraction and leaching behaviour of trace metals in a contaminated sewage sludge

The losses of weight and organic matter of a sludge caused by thermal treatments at 180 degrees C, 300 degrees C and 400 degrees C were determined in order to assess how the possibilities of sludge use were influenced. The sludge heated at 180 degrees C lost small amounts of weight and organic matter (9.8%) but the losses from the two other treatments were large enough (92.2% and 99.9% in organic matter) to preclude the use of the sludges as organic amendments. The concentration and potential lability and leachability of Cr, Cu, Fe, Mn, Ni, Pb and Zn in the native sludge and in the thermal-treated sludge samples were studied by means of a five-step chemical fractionation method and a column experiment. As a consequence of heating, the trace metals were more strongly fixed in the treated sludges, as could be seen by the decrease with temperature of the ratio between the sum of the first two sequential-extracted fractions and the residual fraction. The leaching results showed that, for the native sludge, the quantities of studied metals leached were larger than for the sludge heated to 180 degrees C. The order of leachability of metals was the same in both cases, and the same equation could be used to calculate the quantities of metals leached. The amounts of metals leached correlated significantly with the first extracted fraction (exchangeable metals) and an equation could be used to calculate the quantities leached, as a function of that fraction.

Metal mobility and potential bioavailability in organic matter-rich soil-sludge mixtures: effect of soil type and contact time

The potential bioavailability of metals in two 2:1 (w:w) soil:sludge mixtures prepared by adding sludge to two different soils was studied. The samples were incubated for 1 year at ambient temperature and humidity close to field capacity. The distribution of Cr, Cu, Mn, Pb and Zn in sequential extractions was periodically determined using a five-step chemical fractionation procedure (MgCl2, NaOAc/HOAc, (NH4)2C2O4+H2C2O4, Na4P2O7, HF+HNO3). The potential availability (DTPA extraction) of Cu, Mn, and Zn, organic matter content, and the pH were also determined. The pH of the soils was 5.9 and 8.5 but the pH of both mixtures was similar to the sludge pH (6.3) due to the buffering capacity of sludge organic matter. A decrease in the amount of the organic matter with time and a modification in its composition was observed in the mixtures. The ratio between the quantities of humic and fulvic acids (IA/SA) varied from start to end of the experiment from 0.17 to 0.49 for Soil I-sludge mixture and from 0.22 to 0.42 for Soil II-sludge mixture. All metals, except Mn, became more easily extractable after 1 year of incubation. A positive significant correlation between the metal amounts extracted with DTPA and the sum of the first two sequential extracted fractions (F1+F2) was found. With the sludge rate used the behaviour of cations in the mixtures was fundamentally controlled by the sludge, but the type of soil still had an influence for Cr, Mn and Pb. In spite of the increase of the potential mobility of metals with time, the size of the available amounts declined at the end of the experiment.

Manganese and zinc in acidic agricultural soils from Central Spain: distribution and phytoavailability prediction with chemical extraction tests.

The extractability and distribution of manganese (Mn) and zinc (Zn) were evaluated in acidic agricultural soils from Central Spain. Both single (0.1 M hydrochloride [HCl] and 0.05 M ethylenediaminetetraacetate [EDTA]) and sequential extraction procedures (SEP) (modified Tessier procedure and Community Bureau of Reference [BCR] protocol) were applied to 29 representative soils that belong to the Alfisol, Inceptisol, and Entisol orders. Average relative Mn extractabilities with respect to the total content (16.6% for HCl and 31.9% for EDTA) were higher than those of Zn (7.7% for HCl and 6.5% for EDTA). Manganese was mainly released in the oxide-bound phase of both SEP (33.1% for modified Tessier and 48.9% for BCR), whereas Zn was predominantly found in the residual fraction (49.1% for modified Tessier and 31.4% for BCR). Significant correlations were only found between the amounts of extractable Zn and the oxide-bound fraction in both SEP. Few relationships were established between Zn fractions extracted by the BCR procedure and those obtained with the Tessier method. Both metal concentrations in spring barley (Hordeum vulgare L., cv Beka) grown in 11 selected soils and the calculated soil/plant transfer coefficients (soil/plant concentration factor (CF), mean values of 31.2 for Mn and 196 for Zn) were poorly (or not at all) correlated with the different extracted soil fractions (single and sequential). A number of empirical equations have been obtained by regression analyses to predict the Mn and Zn uptake by barley, with soil metal forms and some soil characteristics as components (pH for Mn and organic matter for Zn). Values of R2 in the equations were relatively low (<68%). Single-extraction techniques produced worse results than SEP for the evaluation of Mn phytoavailability. The modified Tessier procedure provided better predictions of Zn uptake by plants than BCR, but not better than those obtained with the HCl extraction method.

Effects of chelated zinc, soluble and coated fertilizers, on soil zinc status and zinc nutrition of maize

Abstract Maize (Zea mays L.) was greenhouse cultivated with doses of 5, 10, and 15 ppm of zinc (Zn) in order to test the effectiveness of laboratory‐prepared coated and uncoated Zn fertilizers with commercial Zn‐EDTA and Zn‐ligno‐sulphonate (LS). Large increases were achieved both in crop yield and in Zn uptake in all cases while a large part of the Zn applied remained in the soil in easily plant‐available forms. Positive significant correlations were obtained between available Zn and the first three sequentially extracted fractions (water soluble plus exchangeable, organically complexed and that associated to amorphous sesquioxides) and also between the variables, yield, Zn concentration, and plant Zn uptake. Zinc uptake by the maize plants can be fairly accurately predicted from its sequential fractioning in the soil using an equation obtained by multiple regression analysis. Consideration of the amounts of Zn remaining as available (DTPA extractable) in the soil and results of a plant analysis let us c...

Evaluation of composition and performance of composts derived from guacamole production residues

The utilization of organic wastes to improve soils or for growth media components in local farms and nurseries can reduce the environmental pollution linked to waste disposal while increasing the sustainability of crop production. This approach could be applied to waste products generated from the production of guacamole (an emerging activity in the avocado production areas in mainland Spain), where appropriate treatment of this oily and doughy waste product has not been previously reported. The aim of this work is to study the feasibility of co-composting guacamole production residues (GR) with garden pruning waste (PW) as bulking agent, and the possible use of the compost produced depending on its quality. A windrow composting trial using three GR:PW ratios, 2:1, 1:2, and 1:7 was carried out. Temperature, moisture, organic matter, and C/N ratio were used to follow the evolution of the composting process during 7 months. After an additional 3-month curing period, composts were sieved to less than 10 mm and a set of European quality criteria was used to assess compost quality and intended use. In general, the 3 composting mixtures followed the classical process evolution, with minor differences among them. The 1:2 GR:PW ratio appeared most adequate for combining better process evolution and maximum GR ratio. Except for their high pH that limits their use as growing media component in some particular cases, the obtained composts fulfilled the more stringent European standards for commercial composts. Self-heating tests confirmed the high stability of the composts produced. The germination of cress by the direct contact method was satisfactory for composts GR:PW 1:2 and 1:7, showing no signs of toxicity. Avocado seedlings planted in substrates containing 67% of the GR:PW composts exhibited greater plant growth than those in the control treatment, and with no signs of phytotoxicity. The results open an interesting opportunity for the sustainable treatment of avocado fruit by-products derived from guacamole and avocado oil processing.

Changes with time of zinc forms in an acid, a neutral, and a calcareous soil amended with three organic zinc complexes

Three zinc (Zn) fertilisers were added as soluble organic salts (Zn-ethylenediaminetetraacetate plus fulvic and humic acids, Zn-lignosulfonate plus ethylenediaminetetraacetate, and Zn-2-hydroxy-1,2,3-propanetricarboxilate) at several levels, to 3 representative types of soils, to study the behaviour of Zn applied. Samples of treated and untreated soils were incubated for 15, 30, and 60 days at 22rC and field capacity. A selective sequential dissolution procedure and DTPA extraction were employed to determine the changes in Zn distribution. The distribution and the percentage conversion into different forms of the added metal were dependent on soil type, Zn sources, and Zn loading level. After an initial increase in all forms of Zn in the treated soils, Zn concentration in the water-soluble plus exchangeable fraction and the amounts extracted with DTPA began to decrease. At the end of the experiment, Zn in the most labile fraction was detected in the calcareous soil (pHw 8.3) only when the mixture of fulvic and humic acids with Zn-EDTA chelate was applied (e.g. 1.59 mgskg of Zn in the 20 mgskg treatment). The highest conversion values of Zn applied in this calcareous soil occurred in the amorphous Fe-oxide bound and residual fractions of all fertilisation treatments and a low conversion value occurred in the carbonate-bound fraction. fulvic acid, humic acid, Zn-EDTA, Zn-lignosulfonate, Zn-2-hydroxy-1,2,3-propanetricarboxilate, Zn extractability.

Mobility and distribution of zinc forms in columns of an acid, a neutral, and a calcareous soil treated with three organic zinc complexes under laboratory conditions

Three liquid zinc (Zn) fertilisers were mixed with the upper 1.5 cm of columns representing 3 different soil profiles: Aquic Haploxeralf, of an acid nature and with hydromorphic problems; Calcic Haploxeralf, of a neutral nature; and Typic Xerorthents, of a calcareous nature. They were periodically irrigated for 60 days. Most of the applied Zn remained in the top of the soil when it was added as Zn-lignosulfonate plus EDTA or Zn-2-hydroxy-1,2,3-propanotricarboxilate. When Zn-EDTA plus fulvic and humic acid fertiliser was applied, Zn migrated and distributed throughout the soil resulting in losses of Zn by leaching of 2.29% in acidic soil, 27.36% in neutral soil, and 10.5% in calcareous soil of the Zn applied. The 3 fertilisers produce sufficient concentrations of the bioavailable Zn forms in the Ap horizons (DTPA and Mehlich-3 extractable Zn) for the cultivation of different plants. In the calcareous soil, which contained free CaCO3, the amount of Zn extracted by Mehlich-3 was higher than in soils with no free CaCO3. Distribution of Zn in the soil was studied at the beginning and end of the experiment by means of one sequential fractionation and showed that added Zn remained in more labile fractions for uptake by plants in the acid and neutral soils when compared with the control. When Zn was added to calcareous soil, no amount of Zn was detected in the water-soluble plus exchangeable fraction at the end of experiment for any Zn fertiliser source.

Effect of inorganic and organic copper fertilizers on copper nutrition in Spinacia oleracea and on labile copper in soil.

To ensure an optimal concentration of Cu in food crops, the effectiveness of eight liquid Cu fertilizers was studied in a spinach ( Spinacia oleracea L.) crop grown on Cu-deficient soil under greenhouse conditions. Plant dry matter yields, Cu concentrations in spinach plants (total and morpholino acid (MES)- and ethylenediaminedisuccinic acid (EDDS)-extractable), and Cu uptakes were studied. The behavior of Cu in soil was evaluated by both single and sequential extraction procedures. The highest quantities of Cu in labile forms in the soil, total uptakes, and Cu concentrations in the plants were associated with the application of the two sources that contained Cu chelated by EDTA and/or DTPA. The fertilizers containing these Cu chelates represent a promising approach to achieve high levels of agronomic biofortification. The stronger correlations obtained between low-molecular-weight organic acid-extractable Cu in soil and the Cu concentrations and Cu uptakes by the plants show the suitability of this soil extraction method for predicting Cu available to spinach plants.

Mobility and extractability of zinc in soil columns amended with micronutrient formulations

Abstract The behaviour of zinc (Zn) was studied by adding a slow‐release fertilizer (Micromax) which contains zinc sulfate (ZnSO4) to soil columns of two types of soil of distinct characteristics, but both soils with critical levels of Zn available to plants (extractable with DTPA). By sequential extraction, the residual amount of Zn in the soils was found to be the major fraction which explained the deficiency of this micronutrient in the two soils. After three months in the soil columns subjected to systematic irrigation, the added Zn evolved throughout the soil columns, modifying the percentage distribution of Zn at the various depths. The most labile fraction, and thus the most available to plants was increased. In the soil with the highest pH, and active calcium carbonate (CaCO3) and clay contents, Zn migrated less, moving only a short distance; while in the acid soil, Zn evolved throughout the whole column. The DTPA‐extractable Zn content increased considerably in the zone where the fertilizer was a...

The influence of moisture on the residual effects of natural zinc chelates applied to two different soils

The aim of this study was to compare the behavior of residual Zn from three natural chelates (Zn-aminolignosulfonate (Zn-AML),Zn-polyhydroxyphenylcarboxylate (Zn-PHP) and Zn-ethylenediamine disuccinate (Zn-EDDS)) applied at different rates (0, 5 and 10 mg Zn/kg soil) to a flax crop grown during the previous year. This incubation experiment was carried out over 75 days under two different moisture conditions (60% field capacity and waterlogged) in two different soils (acidic (Soil acid )and calcareous (Soil calc )). The potential available Zn concentration and short- term available Zn were estimated under both moisture conditions using the diethylenetriaminepentaacetic acid - triethanolamine (DTPA-TEA) and low-molecular-weight organic acids (LMWOAs) methods, respectively. Water- soluble Zn was estimated in both soils under 60% field capacity conditions. Immediately available Zn (the Zn concentration in the soil solution) was estimated under waterlogged conditions. The pH and Eh were also determined in both soils. Incubation of both soils under both moisture conditions led to decreases in the potential available Zn and short-term available Zn concentrations. Water-soluble Zn concentrations in soils under 60% field conditions, immediately available Zn in soils and the Eh parameter under waterlogged conditions also decreased with time. The residual effect of Zn-AML applied at a rate of 10 mg Zn/kg in Soil acid produced the highest available and short-term Zn concentrations, and the residual effect of Zn-EDDS produced the highest short-term Zn concentration in Soil calc .