Domy C. Adriano

Immobilization and phytoavailability of cadmium in variable charge soils. II. Effect of lime addition

We examined the effect of biosolid compost on the adsorption and complexation of cadmium (Cd) in two soils (Egmont and Manawatu) which varied in their organic matter content. The effect of biosolid compost on the uptake of Cd from the Manawatu soil, treated with various levels of Cd (0–10 mg Cd kg−1 soil), was also examined using mustard (Brassica juncea L.) plants. The transformation of Cd in soil was evaluated by a chemical fractionation scheme. Addition of biosolid compost increased negative charge in soil. The effect of biosolid compost on Cd adsorption varied between the soils, with a large portion of the sorbed Cd remaining in solution as an organic complex. Increasing addition of Cd increased Cd concentration in plants, resulting in decreased plant growth at high levels of Cd (i.e., phytotoxicity). Addition of biosolid compost was effective in reducing the phytotoxicity of Cd as indicated by the decrease in the concentration of NH4OAc extractable-Cd and soil solution-Cd. The solid-phase fractionation study indicated that the addition of biosolid compost decreased the concentration of the soluble and exchangeable Cd fraction but increased the concentration of organic-bound Cd fraction in soil. Alleviation of Cd phytotoxicity by biosolid compost can be attributed primarily to complexation of Cd by the organic matter in the biosolid compost.

Soil acidification and liming interactions with nutrientand heavy metal transformationand bioavailability

Abstract “ No other single chemical soil characteristic is more important in determining the chemical environment of higher plants and soil microbes than the pH. There are few reactions involving any component of the soil or of its biological inhabitants that are not sensitive to soil pH. This sensitivity must be recognized in any soil-management system.” “ Lime is truly a foundation for much of modern humid-region agriculture. Knowing how pH is controlled, how it influences the supply and availability of essential plant nutrients as well as toxic elements, how it affects higher plants and human beings, and how it can be ameliorated is essential for the conservation and sustainable management of soils throughout the world.” (Brady and Weil, 1999) Under areas where rainfall exceeds evapotranspiration, soil acidification is an ongoing natural process, which can either be accelerated by the activity of plants, animals and humans or can be impeded by careful management practices. In areas affected by industrial activities, soil acidification is caused by acid drainage from pyrite oxidation and also from acid precipitation. In areas that remain unaffected by industrial pollution, soil acidification in managed ecosystems is mainly caused by the release of protons (H + ) during the transformation and cycling of carbon (C), nitrogen (N) and sulfur (S). Just like in managed ecosystems, soil acidification in natural ecosystems caused by acid drainage and acid precipitation can have adverse impacts where soils have low pH buffering capacity. Liming is the most common management practice aimed at neutralizing the acid produced, thereby overcoming the adverse impacts of soil acidification. This review brings together fundamental aspects of soil acidification and recent developments on the implications of liming in relation to soil processes, particularly nutrient and heavy metal transformation and bioavailability in soils. The article first outlines the various soil, plant and microbial processes that generate acid (protons; H + ions) both under natural and managed ecosystems. It then discusses the effects of soil acidity on soil chemical and biological properties. The effect of liming to overcome the problems associated with soil acidity is examined in relation to the transformation of nutrient ions and heavy metals. The practical implications of liming to overcome heavy metal toxicity have been discussed in relation to the adsorption, leaching and phytoavailability of these metal ions. Future research should aim to focus on the development of methods to quantify lime-enhanced (im)mobilization of nutrient ions and heavy metals in soils and to explore further the role of liming in remediating contaminated soils.

Chapter One – Dissolved Organic Matter: Biogeochemistry, Dynamics, and Environmental Significance in Soils

Abstract Dissolved organic matter (DOM) is defined as the organic matter fraction in solution that passes through a 0.45 μm filter. Although DOM is ubiquitous in terrestrial and aquatic ecosystems, it represents only a small proportion of the total organic matter in soil. However, DOM, being the most mobile and actively cycling organic matter fraction, influences a spectrum of biogeochemical processes in the aquatic and terrestrial environments. Biological fixation of atmospheric CO 2 during photosynthesis by higher plants is the primary driver of global carbon cycle. A major portion of the carbon in organic matter in the aquatic environment is derived from the transport of carbon produced in the terrestrial environment. However, much of the terrestrially produced DOM is consumed by microbes, photo degraded, or adsorbed in soils and sediments as it passes to the ocean. The majority of DOM in terrestrial and aquatic environments is ultimately returned to atmosphere as CO 2 through microbial respiration, thereby renewing the atmospheric CO 2 reserve for photosynthesis. Dissolved organic matter plays a significant role in influencing the dynamics and interactions of nutrients and contaminants in soils and microbial functions, thereby serving as a sensitive indicator of shifts in ecological processes. This chapter aims to highlight knowledge on the production of DOM in soils under different management regimes, identify its sources and sinks, and integrate its dynamics with various soil processes. Understanding the significance of DOM in soil processes can enhance development of strategies to mitigate DOM-induced environmental impacts. This review encourages greater interactions between terrestrial and aquatic biogeochemists and ecologists, which is essential for unraveling the fundamental biogeochemical processes involved in the synthesis of DOM in terrestrial ecosystem, its subsequent transport to aquatic ecosystem, and its role in environmental sustainability, buffering of nutrients and pollutants (metal(loid)s and organics), and the net effect on the global carbon cycle.

Selected bioavailability assays to test the efficacy of amendment-induced immobilization of lead in soils

Lead immobilization in 10 soils contaminated with Pb from different origin was examined using lime (CaCO3), a mix of cyclonic ash and steelshots (CA+ST), and a North Carolina phosphate rock. The immobilization efficacy of the three amendments was evaluated using single (CaCl2solution) and sequential (BCR method) chemical extractions in tandem with a microbiological Pb biosensor (BIOMET), a Pb phytotoxicity test, Pb plant uptake, and a Physiologically Based Extraction Test (PBET) mimicking Pb bioavailability in the human gastro-intestinal tract. The results demonstrated the necessity of using a diverse suite of bioavailability methodology when in situ metal immobilization is assessed. Sequential (BCR) extractions and PBET analysis indicated that PR was the most effective amendment. PR however, proved ineffective in totally preventing Pb phytotoxicity and Pb uptake on all soils tested. On the contrary, CA+ST and lime decreased BIOMET Pb, Pb phytotoxicity, and Pb uptake to a far greater extent than did PR. BIOMET detectable Pb and Pb uptake, however, were strongly related to Pb in soluble or exchangeable soil fractions (i.e., CaCl2 extractable). By combining these fractions with the acid-extractable Pb, accomplished by using acetic acid extractant, the recently developed BCR sequential extraction scheme appeared to have lost some valuable information on judging Pb bioavailability. The data show that different amendments do not behave consistently across different soils with different sources of contamination. Different indices for measuring Pb bioavailability are also not necessarily consistent within particular soil and amendment combinations.

Background concentrations of elements in soils of China

Mean concentrations of 62 elements, pH, organic matter and grain size have been computed for soil samples from 4,095 locations throughout mainland China The compositions of geochemical data between mainland China and the conterminous United States and between Tibet and Alaska show a close correspondence for most elements determined. These geochemical data may reveal evidence of regional variations in the abundance of elements in soils. In general, the sequence for metal content in samples of soil orders was: Lithosol>Cold-highland soils>Inceptisol> Aridisol = Mollisol>Ultisol>Alfisol>Oxisol. This trend was apparently a result of climatic influence on soil genesis, with the Oxisols (high rainfall areas with highly weathered and highly leached soils) yielding the lowest elemental mean values. However, the highest mean values of most trace elements in the Lithosols were a result of its relatively high indigenous elemental contents as well as chemical properties of the bedrock from which the soils were formed.

Role of phosphorus in (Im)mobilization and bioavailability of heavy metals in the soil-plant system.

A large number of studies have provided conclusive evidence for the potential value of both water-soluble (e.g.. DAP) and water-insoluble (e.g., apatite, also known as PRs) P compounds to immobilize metals in soils, thereby reducing their bioavailability for plant uptake. It is, however, important to recognize that, depending on the nature of P compounds and the heavy metal species, application of these materials can cause either mobilization or immobilization of the metals. Furthermore, some of these materials contain high levels of metals and can act as an agent of metal introduction to soils. Accordingly. these materials should be scrutinized before their large-scale use as immobilizing agent in contaminated sites. Although mobilization by certain P compounds enhances the bioavailability of metals, immobilization inhibits their plant uptake and reduces their transport in soils and subsequent groundwater contamination. Whenever phytoremediation of contaminated sites is practicable, appropriate P compounds can be used to enhance the bioavailability of metals for plant uptake. Removal of metals through phytoremediation techniques and the subsequent recovery of the metals or their safe disposal are attracting research and commercial interests. Phosphate compounds can be used to enhance the solubilization of metals, leading to their increased uptake by plants. However, when it is not possible to remove the metals from the contaminated sites by phytoremediation, other viable options such as in situ immobilization should be considered as an integral part of risk management. One way to facilitate such immobilization is by altering the physicochemical properties of the metal-soil complex by introducing a multipurpose anion, such as phosphate, that enhances metal adsorption via anion-induced negative charge (i.e., CEC) and metal precipitation. It is important to recognize that large-scale use of P compounds can lead to surface and groundwater contamination of this element. It is therefore, important that future research should aim to focus on the role of P compounds on in situ remediation and natural attenuation in metal-contaminated sites, with minimum impact of P on quality of water sources.

Influence of zeolite, apatite and Fe-oxide on Cd and Pb uptake by crops

Natural zeolite (clinoptilolite), hydroxyapatite and an iron-oxide waste by-product (Fe-rich, a trademark name of E.I. du Pont de Nemours) were added to an artificially contaminated Appling soil to immobilize and limit the uptake of metals by crops. A greenhouse pot study employed spiking the soil with Cd and Pb from metal flue dust. Maize (Zea mays) and barley (Hordeum vulgare) were planted in 7-kg potted soil to determine the effects of Cd and Pb on plant growth and uptake. Sequential extraction of soil indicates the substantial influence of soil pH and type of ameliorant on the chemical form and bioavailability of the metals. Data indicates that a dose of 50 g/kg of soil of iron-oxide appears to be very effective, based on the yields, metal contents of plant tissues and available forms of Cd and Pb in the soil. Lower doses of zeolite and apatite (15 g/kg and 4 g/kg soil, respectively) in most cases also reduced significantly the uptake of Cd and Pb by crops.

Phytoremediation of soil contaminated with low concentrations of radionuclides

Ecosystems throughout the world have been contaminated with radionuclides by above-ground nuclear testing, nuclear reactor accidents and nuclear power generation. Radioisotopes characteristic of nuclear fission, such as 137Cs and 90Sr, that are released into the environment can become more concentrated as they move up the food chain often becoming human health hazards. Natural environmental processes will redistribute long lived radionuclides that are released into the environment among soil, plants and wildlife. Numerous studies have shown that 137 Cs and 90Sr are not removed from the top 0.4 meters of soil even under high rainfall, and migration rate from the top few centimeters of soil is slow. The top 0.4 meters of the soil is where plant roots actively accumulate elements. Since plants are known to take up and accumulate 137 Cs and 90Sr removal of these radionuclides from contaminated soils by plants could provide a reliable and economical method of remediation. One approach is to use fast growing plants inoculated with mycorrhizal fungi combined with soil organic amendments to maximize the plant accumulation and removal of radionuclides from contaminated soils, followed by harvest of above-ground portion of the plants. High temperature combustion would be used to oxidize plant material concentrating 137 Cs and 90Sr, in ash for disposal. When areas of land have been contaminated with radionuclides are large, using energy intensive engineering solutions to remediate huge volumes of soil is not feasible or economical. Plants are proposed as a viable and cost effective method to remove radionuclides from the soils that have been contaminated by nuclear testing and nuclear reactor accidents.

Mechanisms and Pathways of Trace Element Mobility in Soils

Publisher Summary The importance of trace elements (TEs) in soils depends largely on their fraction that has immediate biological function, that is, the fraction of the total soil burden that is soluble, mobile, and bio-available. The nature and extent of mobility and bioavailability underlines the integrity and sustainability of a particular environment and in particular, the role of TEs in the functioning and wellbeing of an ecological endpoint. The chapter discusses the basic mechanisms in the solubility and mobility of the TEs in the soil, including their movement in the soil profile, the entire vadose zone and the eventual leaching to the ground water. The mechanism leads to the several transport pathways in soil responsible for disseminating TEs in the form of gaseous, aqueous, colloids, and particulate matter. The chapter discusses the most pertinent factors influencing the partitioning and movement of TEs, and finally illustrates transport modeling of the most environmentally important TEs and their applications typified by field case studies, with an emphasis on transport modeling in the vadose zone. TE transport pathways include diffusion and dispersion, preferential flow, colloidal transport, soluble metal complexes, leaching and runoff, and volatilization. There are basic physical, chemical, and biological processes that control mobility of TEs in soils. The processes that sequester TEs can be grossly termed sorption, which to a large extent, determines the partitioning between the solid and solution phase. Factors like soil pH, chemical speciation, soil organic matter, fertilizers and soil amendments, redox potential, and clay content and soil structure affecting trace element mobility and transport are discussed.

Effects of selected trace metals on germinating seeds of six plant species

Seeds of cabbage, lettuce, millet, radish, turnip, and wheat were treated with solutions containing Be, Ni, Tl, or V, and subsequent effects on seed germination and radicle elongation were measured after three days. Treatment with low concentrations of Be, Ni, or V stimulated root elongation in most species. Higher concentrations of these elements and all treatment with Tl caused reductions in root elongation. In general, turnip and lettuce were the most sensitive of the plants studied to the metals tested, while wheat and millet were the least sensitive.