Copper and zinc retention by an organically amended soil

Changes in chemical fractionation of copper and zinc in soil as a function of incubation moisture content and organic matter amendments

Copper and zinc are essential micronutrients that are potentially toxic when present in excess in soils. Their bioavailability depends on their speciation in soil, but this may vary with environmental conditions. Aeration and hence redox conditions, and organic matter amendments are among the factors likely to cause variation on metal fractionation. We have monitored the chemical fractionation of both native and added copper and zinc in a clay loam top soil during a 5-month laboratory incubation. The effects of aeration (moist soil or flooded) and addition of two organic matter amendments, alfalfa straw or leaf compost, were studied. Metal spike was more labile than legacy metal, and was slowly redistributed over the incubation period. Organic matter caused short-lived flushes of metals, attributed to metal chelation with soluble organic matter. This effect was greater for straw than for more stable compost. There was no evidence that added organic matter increased the capacity of soil organic matter to immobilise metal. Flooding solubilized soil metal (hydr)oxides, releasing legacy Cu and Zn, but with less effect on the capacity to immobilise metal spike. Effects of flooding and organic matter addition were not additive. Both metals appear to be precipitated as sulphides under reducing conditions, and accounted for in the acid soluble phase. Monitoring the dynamics of metal distribution gives a more comprehensive understanding of underlying processes than would a single measurement, and is closer to in campo conditions than slurry microcosms.

Environmentally safe release of plant available potassium and micronutrients from organically amended rock mineral powder

The staggering production of rock dusts and quarry by-products of mining activities poses an immense environmental burden that warrants research for value-added recycling of these rock mineral powders (RMP). In this study, an incubation experiment was conducted to determine potassium (K) and micronutrients (Zn, Cu, Fe and Mn) release from a quarry RMP to support plant nutrition. Four different size fractions of the RMP were incubated with organic amendments (cow dung and legume straw) under controlled conditions for 90 days. Samples were collected at different intervals (7, 15, 30, 45, 60 and 90 days) for the analysis of available K and micronutrients in the mineral-OM mixtures and leachates. There was a significant (p <0.05) increase in pH of leachates from the mineral-OM mixtures. The K release was significantly higher from the finer size fraction of RMP. About 18.7% Zn added as RMP was released during the incubation period. Zn release increased from 4.7 to 23.2% as the particle size of RMP decreased. Similarly, Cu release from RMP increased from 2.9 to 21.6%, with a decrease in the particle size. Fe and Mn recovery from RMP recorded 11.2 and 6.6%, respectively. Combined application of OM and RMP showed significantly higher nutrient release than other treatments. This study indicates that effective blending of RMP with organic amendments could be a potential source of K and micronutrients in agriculture without posing a risk of toxic element contamination to the soil.

Mechanisms governing the leaching of soil metals as a result of disposal of olive mill wastewater on agricultural soils

Olive mill wastewater (OMWW) is an acidic, saline, and organic matter-rich aqueous byproduct of olive oil production that is usually disposed of by spreading on agricultural soils. This study tested whether spreading OMWW can release indigenous soil metals (Fe, Mn, Cu and Zn) through pH, redox, and DOM complexation-related mechanisms, using three agricultural soils having different textures and chemical properties, and controlled pH and redox conditions (pH5.6 or 8.4; ORP from -200 to +250mV). Comparison treatments included a solution having the same salt content and composition as OMWW but lacking OM, and deionized water (DW). In all three soils and under all pH and redox conditions, the model salt solution and DW treatments solubilized considerably fewer metal cations than did OMWW. Overall, the primary factor in metals release from the soils by OMWW was the DOM fraction. pH, redox and soil type played secondary but important roles in solubilization of the various metals. pH had a major impact on Mn leaching but no impact on Fe and Cu leaching. Conversely, redox did not affect Mn leaching, but lower redox conditions contributed to elevated release of both Fe and Cu. For the most part, released metals were sourced from water soluble, exchangeable, easily reducible, and moderately reducible soil metals pools. Fe, Mn and Cu released from the soils by OMWW featured mainly as metal-organic complexes, and OMWW generally caused Zn precipitation in the soils. Soils rich in clay and organic matter under reduced pH and low redox conditions released substantially more metal cations than did a sand-rich soil. Spreading OMWW may result in sequestration of essential micronutrients like Zn, and increased availability of other micronutrients such as Fe, Mn and Cu.

Vermicompost dose and mycorrhization determine the efficiency of copper phytoremediation by Canavalia ensiformis

The phytoremediation of copper (Cu)-contaminated sandy soils can be influenced by the addition of vermicompost to the soil and the mycorrhization of plants. The objective of this study was to evaluate the effects of inoculation with the mycorrhizal fungus Rhizophagus clarus and the addition of different doses of bovine manure vermicompost on the phytoremediation of a sandy soil with a high Cu content using Canavalia ensiformis. Soil contaminated with 100 mg kg^-1 Cu received five doses of vermicompost and was cultivated with C. ensiformis, with and without inoculation with mycorrhizal fungus, and the Cu and nutrients in the soil and soil solution were evaluated. The concentrations of Cu and other nutrients and the biomass and Cu phytotoxicity in the plants were quantified by gauging the photochemical efficiency, concentration of photosynthetic pigments and activity of oxidative stress enzymes. The vermicompost increased the soil pH and nutrient concentrations and reduced the Cu content of the solution. When the vermicompost was applied at a dose equivalent to 80 mg phosphorus (P) kg^-1, the phytoextraction efficiency was higher, but the phytostabilization efficiency was higher for vermicompost doses of 10 and 20 mg P kg^-1. The presence of mycorrhizal fungi increased Cu phytostabilization, especially at vermicompost doses of 10 and 20 mg P kg^-1. The use of vermicompost at low doses and inoculation with mycorrhizal fungi increase the phytostabilization potential of C. ensiformis in sandy soil contaminated by Cu.

Critical review on the environmental fate of quaternary ammonium herbicides in soils devoted to vineyards

Quaternary Ammonium Herbicides (QUATs) are nonselective contact herbicides, widely used at weed emergence to protect a wide range of crops. The benefits achieved by the use of these herbicides are indisputable. In soils devoted to vineyards, their uses increase the yield and the quality of the grapes for winemaking. However, several environmental dangers have emerged from the overuse of these compounds. Therefore, there has been a great interest in the presence of these compounds in soils, water, and food. Once in the soil, the mobility of these agrochemicals plays an important role in their fate and transport in the environment. This is why we mainly focused our review on (a) their physical and chemical properties and their activity, (b) the factors affecting their mobility in soils, (c) the quality of surrounding waters, and (d) the measures to reduce their contamination, especially in the case of agricultural soils devoted to vineyards.

Heavy metal retention in copper mine soil treated with mussel shells: batch and column experiments

Batch and column experiments are used to study the effects of ground mussel shell amendment on the retention of heavy metals in acidic mine soil. The soil pH increases proportionally with the mussel shell concentration employed. Mussel shell amendment increases Cu, Cd, Ni and Zn retention in mine soil when compared with unamended soil. In fact, Cu retention was 6480μmolkg(-1) (43% of the total added) when the maximum metal concentration (1570μM) was added to the unamended soil, whereas retention reached 15,039μmolkg(-1) (99.9% of the total Cu added) when soil was amended with 24gkg(-1) mussel shell; in the case of Cd, adsorption increases from 3257μmolkg(-1) (15% of the total added) for the unamended soil, to 13,200μmolkg(-1) (87% of the total added) for the shell-amended soil; Ni retention increased from 3767μmolkg(-1) (25% of the total added) corresponding to unamended soil, to 11,854μmolkg(-1) (77% of the total added) for the shell-amended soil; and finally, Zn retention increased from 4684μmolkg(-1) (31% of the total added), for unamended soil, to 14,952μmolkg(-1) (98% of the total added) for shell-amended soil. The results of the constant flow transport experiments show that the addition of the 24gkg(-1) mussel shells can retain Cu, Cd, Ni and Zn within the first few centimetres of the column length, indicating the usefulness of ground mussel shells to drastically decrease the mobility and availability of these pollutants and to facilitate soil remediation.

Long-term variability of metals from fungicides applied in amended young vineyard fields of La Rioja (Spain)

The long-term variability of total Cu content from fungicides applied in a certified wine region of Spain (La Rioja) and of other metals (Cd, Cr, Ni, Pb, and Zn) was evaluated in three young vineyard soils and subsoils unamended and amended with spent mushroom substrates (SMS) over a 3-year period (2006-2008). SMS is a promising agricultural residue as an amendment to increase the soil organic matter content but may modify the behaviour of metals from pesticide utilisation in vineyards. Fresh and composted SMS was applied each year at a rate of 25 t ha(-1) (dry-weight). Copper concentrations in the three unamended soils were 21.2-88.5, 25.5-77.1, and 29.4-78.4 mg kg(-1). They exceeded natural Cu concentrations of the region and reference sub-lethal hazardous concentration for soil organism. The concentrations of Cd, Ni, Pb, and Zn were largely below the sub-lethal limits. Thus, although Cu levels were lower than those of established vineyards, vine performance, and productivity might be affected. The variation in behaviour between different amendments for each soil was high, so a generic conclusion could not be drawn. The amendment practice seemed to have caused temporarily Cu mobilization respect to untreated soils. Total zinc concentrations fall within the range of the natural soil of La Rioja and were significantly affected (p < 0.05) especially by fresh state SMS addition, with increasing up to 75% respect to untreated specimen. The results indicated a build-up of fresh sites for metal retention at both surface and subsurface level, although no accumulation of metals was observed in the short-term period. However, the benefit for soils and the negative effects need to be monitored in the long run.

Application of manure and compost to contaminated soils and its effect on zinc accumulation by Solanum nigrum inoculated with arbuscular mycorrhizal fungi

Zn accumulation in Solanum nigrum grown in naturally contaminated soil in the presence of different types of organic amendments was assessed. Under the same conditions, the response of the plant to inoculation with two different isolates of arbuscular mycorrhizal fungi (AMF) (Glomus claroideum and Glomus intraradices) was also evaluated. S. nigrum grown in the non-amended soil always presented higher Zn accumulation in the tissues, with the addition of amendments inducing reductions of up to 80 and 40%, for manure and compost, respectively, and enhancing plant biomass yields. The establishment of S. nigrum in the Zn contaminated soil combined with the application of amendments led to a 70-80% reduction in the amount of Zn leached through the soil. The use of S. nigrum in combination with manure appeared as an effective method for reducing the effects of soil contamination, diminishing Zn transfer to other environmental compartments via percolation.

Effects of two sludge application on fractionation and phytotoxicity of zinc and copper in soil

The potential harm of heavy metals is a primary concern in application of sludge to the agricultural land. A pot experiment was conducted to evaluate the effect of two sludges on fractionation of Zn and Cu in soil and their phytotoxicity to pakchoi. The loamy soil was mixed with 0%, 20%, 40%, 60% and 80% (by weight) of digested sewage sludge (SS) and composted sludge (SC). The additions of the both sludges caused a significant raise in all fractions, resulting in that exchangeable (EXCH) and organic matter (OM) became predominance for Zn and organic bound Cu occupied the largest portion. There was more available amount for Zn and Cu in SS treatments than SC treatments. During the pot experiment, the concentration of Zn in EXCH, carbonate (CAR) and OM and Cu in EXCH and OM fractions decreased in all treatments, so their bioavailability reduced. Germination rate and plant biomass decreased when the addition rate was high and the best yield appeared in 20% mixtures at the harvest of pakchoi. The two sludges increased tissue contents of Zn and Cu especially in the SS treatments. Zn in pakchoi was not only in relationship to deltaEXCH and deltaCAR forms but also in deltaOM forms in the sludge-soil mixtures. Tissue content of Cu in pakchoi grown on SC-soils could not be predicted by deltaEXCH. These correlation rates between Zn and Cu accumulation in pakchoi and variation of different fractions increased with time, which might indicate that sludges represented stronger impacts on the plant in long-term land application.

Sorption of As, Cd and Tl as influenced by industrial by-products applied to an acidic soil: equilibrium and kinetic experiments

In situ stabilization of toxic elements in contaminated soils by the addition of amendments is being considered as an effective technique for remediation. In this paper, we performed both kinetics and equilibrium-based sorption experiments of three toxic elements (As, Cd and Tl) in soils amended with two by-products (phosphogypsum and sugar foam, rich in gypsum and calcium carbonate, respectively) to ascertain the feasibility of their application for improving the sorption capacity of As, Cd and Tl from the soil at 25, 35 and 50 degrees C. Kinetic studies indicated that the sorption follows a pseudo-second-order (PSO) kinetics and the sorption is a two-step diffusion process where both film and intraparticle diffusion played important roles in the sorption mechanisms of the elements. The Langmuir isotherms applied for sorption studies showed that the estimated maximum sorption capacity of the elements in control and amended soils decreased in the order of Cd>As>Tl. Using the thermodynamic equilibrium parameters obtained at different temperatures, the thermodynamic constants of sorption (DeltaG, DeltaH and DeltaS) were also evaluated, indicating spontaneous and endothermic nature of the process, except Tl which was exothermic. An optimal scaling procedure was undertaken to determine the relationships between the kinetic and equilibrium sorption parameters. By means of statistical analysis it was seen that these inter-parametric relationships are dependent on the element nature.

Copper bioavailability in the rhizosphere of maize (Zea mays L.) grown in two Italian soils

In this study, potentially bioavailable copper was estimated in two soils (a fungicide polluted and a natural soil) using a passive sampling technique, DGT. As plants can alter copper mobility and bioavailability in the soil, the rhizosphere properties of Zea mays L. were investigated using rhizoboxes. Compared to the total concentration, the soluble and the potentially bioavailable copper concentration in the bulk soils were generally low (less than 0.20% and 0.06% respectively), with a sixfold increase in the rhizosphere of the polluted soil. Our results suggest that maize cultivation in a polluted vineyard soil could increase the potentially available fraction of copper. DGTs showed a good sensitivity to soil properties and to root-induced changes in the rhizosphere, but the potentially bioavailable copper could not be related to the copper concentration in the above ground parts of maize. The results suggest that DGT may be used to predict some effects of the cultivation of polluted soils, for example, metal mobility and increased availability, but they cannot mimic the uptake of a tolerant plant. For both soils, dissolved organic carbon (DOC) concentrations were threefold higher in the rhizosphere than in the bulk soil, whilst bioaccumulation in leaves and roots was not significant. DOC production, usually effective in ion mobilization and assimilation, may help also in the reduction of Cu uptake at toxic concentrations. The sequestration of available Cu in soil and soil solution by DOC seems to contribute to maize tolerance.

Reactions of compost-derived humic substances with lead, copper, cadmium, and zinc

Thermodynamic stability constants of the formation of complexes from the reactions of humic substances with various metals are usually used as parameters to judge the reactivities of both humic substances and metals. However, in calculating the thermodynamic stability constants, complicated processes for the acquisition of activities of components in reactions are absolutely inevitable. In this study, we investigated the average conditional concentration quotients of the complexes formed from the reaction of metals with humic substances and the relations of these quotients to thermodynamic stability constants. The characterized humic substances including HA (MW>1,000), FA (MW>1,000), and FA (MW<1,000) extracted from a swine compost were prepared to react with Pb, Cu, Cd, and Zn at 25 degrees C and at pH 4.00 and 6.50. Reactions of HA (MW>1,000), FA (MW>1,000), and FA (MW<1,000) with the four metals were carried out at 1:0.1, 1:0.5, 1:1, 1:5, and 1:10 ligand:metal stoichiometry. The concentrations of the free ions of Pb, Cu, Cd, and Zn in the reaction systems of metal-HA suspensions and metal-FA solutions were measured by anodic stripping voltammetry (ASV). The sequence of the average conditional concentration quotients of the formed complexes from the reaction of humic substances with metals was FA(MW<1,000)>FA(MW>1,000)>HA(MW>1,000), showing the relative reactivities of the fractions of swine compost-derived humic substances. The sequence of reacting metals with humic substances was Pb>Cu>Cd>Zn, which is in good agreement with the sequence reported by judging the thermodynamic stability constants. The average conditional concentration quotients of the formed complexes from the reaction of humic substances with metals were thus useful parameters that can be directly related to thermodynamic stability constants and other parameters.

Variation of metals in bed sediments of Qaraaoun Reservoir, Lebanon

The Qaraaoun Reservoir (impoundment of the River Litani) is the only artificial surface water body in the country, Lebanon. Earlier study on the water quality of the Qaraaoun Reservoir identified three water quality zoning with a central distinct zone suitable for multipurpose water usage. The objective of this study was to extend the earlier work by considering the total metal content of reservoir bed sediments and hence to evaluate factors that control metal deposition or capture. Water samples were collected from 15 sampling sites and sediment samples were simultaneously collected from 9 sites. Water parameters analyzed were pH, Eh, DO and temperature. Sediment samples were dried and sieved and sediment < 75 microm was retained for analysis. Sediments were subjected to a stepwise heating process with aqua regia to extract the metals, and their content in sediments determined by ICP-MS. The sediment data revealed higher metal contents where the river entered the reservoir which matched higher concentrations of water parameters at the influx site. Regression analysis of total metals in sediments with distance from the river Litani influx point to the dam revealed a log trend for Fe, Cr and Ni, whereas, the concentrations of Cu, Zn, Cd, Pb were better described by a polynomial regression. Three sediment zones were identified: entrance, oxidation (central) and reducing (near dam) zones. Sediment contents of Zn, Cu and Pb correlated with organic content, whereas sediment Cr and Ni were associated with iron. It was concluded that sediments act as a sink for metals and the deposition of metals is primarily related to sediment organic content and the level of dissolved oxygen in water.

Copper and Zn uptake by radish and pakchoi as affected by application of livestock and poultry manures

Environmental safety of agricultural utilization of livestock and poultry manures from intensive farming is attracting great attention because the manures often contain high concentrations of heavy metals and organic pollutants. Pot experiments, in which a pig manure (PM), a chicken manure (CM) and a commercial organic manure (OM) with different concentrations of Cu and Zn to simulate soil metal accumulation by manure application for different times were utilized in a garden soil at a rate of 2% (W/W), were conducted to study the effect of application of these livestock and poultry manures on growth of radish (Raphanus sativus L.) and pakchoi (Brassica chinensis L.) as well as their Cu and Zn uptake. The results exhibit that the manures except the PM improved the growth of radish and pakchoi. The difference of biomass among the same manure treatments containing different concentrations of Cu and Zn, however, was insignificant. In addition, application of the livestock and poultry manures significantly increased soil pHs and electric conductivities (EC) compared with the control, which is ascribed that these manures had high pH and contained large amounts of inorganic ions. The available soil Zn concentrations in the PM were higher than that in the CM and OM, and the extractable soil Cu concentrations in the three manures were almost the same after radish growth in the garden soil but were different after pakchoi growth. Zinc and Cu concentrations in the radish and pakchoi tissues increased when the soil Zn and Cu concentrations increased by manures application, but were still within a safe value. An except is the treatment PM4 in which the Zn concentration of the above-ground part of radish was 28.7 mg kg-1, exceeding the Chinese Food Hygiene Standard of 20 mg kg-1 based on fresh weight. Good correlation was obtained between the extractable soil Zn (or Cu) concentrations extracted by 1.0 mol l-1 NH4NO3 and the Zn (or Cu) concentrations in radish and pakchoi tissues, which was expected to be effective in forecasting Cu and Zn availability to radish and pakchoi in manure agronomic utilization.

Solubility of phosphorus and heavy metals in potting media amended with yard waste-biosolids compost

The potential risk of surface and ground water contamination by phosphorus (P) and heavy metals leached from compost-based containerized media has become an environmental concern. Solubility and fractionation of P and heavy metals were evaluated in media containing 0, 25, 50, 75, or 100% compost derived from biosolids and yard trimmings for potential impacts on the environment. As compost proportion in peat-based media increased from 0 to 100%, concentrations of total P, Cd, Cu, Ni, Pb, Zn, and Mn in the media increased whereas concentrations of total Co and Cr decreased. Except for Cu, all heavy metals in the water-soluble fraction decreased with increasing compost proportion in the media, because of higher Fe, Al, and Ca concentrations and pH values of the composts than the peat. When the media pH is controlled and maintained at normal range of plant growth (5.5-6.5), leaching of the heavy metals is minimal. Incorporation of compost to the peat-based media also decreased the proportion of total P that was water-soluble. However, concentrations of bioavailable inorganic phosphorus (NaHCO3-IP), readily mineralizable organic phosphorus (NaHCO3-OP), potentially bioavailable inorganic phosphorus (NaOH-IP), and potentially bioavailable organic phosphorus (NaOH-OP) were still higher in the media amended with compost because of higher total P concentration in the compost. Further study is needed to verify if less or no topdressing of chemical P fertilizer should be applied to the compost-amended media to minimize P effect on the environment when compost-amended potting media are used for nursery or greenhouse crop production systems.