Competitive sorption of heavy metal by soils. Isotherms and fractional factorial experiments

Competing ions strongly affect heavy metal sorption onto the solid surfaces of soil. This study evaluated competitive sorption of Cd, Cu, Ni, Pb and Zn on three soils: Calcixerollic Xerochrept, Paralithic Xerorthent and Lithic Haplumbrept. Monometal and competitive sorption isotherms were obtained at 25 degrees C. The individual effect of ions on retention of the others was ascertained by a fractional factorial analysis design. Most of the sorption isotherms belonged to type L subtype 2 in the classification of Giles. In competitive sorption the initial linear part was shorter and the knee sharper when compared with monometal sorption isotherms. Parameters related to sorptive capacity, such as Point B, Langmuir monolayer and Freundlich distribution coefficient, were higher in monometal than in competitive sorption, and in basic soils than in acidic soil. Calcium desorbed at different points of the sorption isotherms indicated that cationic exchange with Ca was the main retention mechanism in calcareous soils. For Pb, the ratio Ca desorbed/Pb sorbed was close to one; for Cu, Ni and Zn the ratio ranged from 1.20 to 1.37, probably due to partial dissolution of calcium carbonates by hydrolytic processes during retention. On the other hand, Cd had a ratio around 0.6 reflecting another additional retention mechanism, probably surface complexation. Fractional factorial design confirmed that the presence of the cations investigated reduced the amount of the five metals retained, but the presence of Cu and Pb in the system depressed Ni, Cd and Zn sorption more than the inverse. Cation mobility was enhanced when equilibrium concentration increased and the effect was higher in Ca-saturated soils.     

Integrated assessment of heavy metal (Pb, Zn, Cd) highway pollution: bioaccumulation in soil, Graminaceae and land snails

To assess the contamination induced by traffic at the vicinity of a highway (A31, France), several complementary studies were carried out on two sites, with different profiles and traffic intensity. Concentrations of zinc, lead and cadmium were measured by atomic absorption spectrophotometry in deposits, roadside soil and autochthonous plants (Graminaceae) gathered at the vicinity of the highway (1-320 m), and in the viscera of snails Helix aspersa, transferred as sentinel in the sites. According to the results obtained for different compartments, the highway induces a contamination on the surrounding environment, up to 320 m, but with the maximum contamination observed between 5 and 20 m: the concentrations measured in plants at the vicinity of the highway were 2.1 mg Pb kg(-1) DW, 0.06 mg Cd kg(-1) DW, 62 mg Zn kg(-1) DW and the concentrations measured in snails were 21.3 mg Pb kg(-1) DW, 5.7 mg Cd kg(-1) DW, 510.8 mg Zn kg(-1) DW. The levels measured decreased with increasing distance from the highway. Results of the three metals studied indicated that lead seems to be the best metal to evaluate road transport contamination.     

Isotherms and sequential extraction procedures for evaluating sorption and distribution of heavy metals in soils

Heavy metals are potentially toxic to human life and the environment. Their contaminating effect in soils depends on chemical associations. Hence, determining the chemical form of a metal in soils is important to evaluate its mobility and bioavailability. We utilized a sequential extraction procedure and sorption isotherms (monometal and competitive) to evaluate the mobility and distribution of Cd, Cu, Ni, Pb, and Zn in four soils differing in their physicochemical properties: Calcixerollic Xerochrepts (Cx1 and Cx2), Paralithic Xerorthent (Px) and Lithic Haplumbrept (Lh). Most of the metals retained under point B conditions of sorption isotherms were extracted from the more mobile fractions: exchangeable and carbonates, in contrast with the profiles of the original soils where metals were preferently associated with the residual fraction. In soils having carbonate concentration under 6% (Cx1 and Lh), the exchangeable fraction was predominant, whereas in calcareous soils (Cx2 and Px) metals extracted from carbonates predominated. Partitioning profiles were in accordance with the affinity sequences deduced from the initial slope of isotherms and showed that the soils had a greater number of surface sites and higher affinity for Pb and Cu than for Cd, Ni, or Zn. In general, the simultaneous presence of the cations under study increased the percentages of metals released in the exchangeable fraction. The tendency towards less specific forms was more noticeable in Cx2 and Px soils and for Ni, Zn, and Cd. The affinity of inorganic surfaces was larger for Zn than for Cd or Ni, but the affinity of organic surfaces was larger for Cd or Ni than for Zn.     

Eutrophication: impacts of excess nutrient inputs on freshwater, marine, and terrestrial ecosystems

In the mid-1800s, the agricultural chemist Justus von Liebig demonstrated strong positive relationships between soil nutrient supplies and the growth yields of terrestrial plants, and it has since been found that freshwater and marine plants are equally responsive to nutrient inputs. Anthropogenic inputs of nutrients to the Earth's surface and atmosphere have increased greatly during the past two centuries. This nutrient enrichment, or eutrophication, can lead to highly undesirable changes in ecosystem structure and function, however. In this paper we briefly review the process, the impacts, and the potential management of cultural eutrophication in freshwater, marine, and terrestrial ecosystems. We present two brief case studies (one freshwater and one marine) demonstrating that nutrient loading restriction is the essential cornerstone of aquatic eutrophication control. In addition, we present results of a preliminary statistical analysis that is consistent with the hypothesis that anthropogenic emissions of oxidized nitrogen could be influencing atmospheric levels of carbon dioxide via nitrogen stimulation of global primary production.     

Role of organic acids in enhancing the desorption and uptake of weathered p,p'-DDE by Cucurbita pepo

Experiments were conducted to assess the effect of seven organic acids [succinic, tartaric, malic, malonic, oxalic, citric, ethylene-diaminetetraacetic (EDTA)] over a concentration range of two orders of magnitude (0.001-0.10 M) on the abiotic desorption of weathered p,p'-DDE and the extraction of polyvalent inorganic ions from soil. At 0.05 M all organic acids significantly increased contaminant desorption by 19-80%. Organic acids also increased the aqueous concentration of eight inorganic constituents extracted from soil, with at least a six-fold increase in the release of Al, Fe, Mn, and P at 0.001 M. Zucchini seedlings grown for 28 d in soil containing weathered p,p'-DDE (300 ng/g, dry weight) were periodically amended with distilled water, citric or oxalic acids (0.01 M). Plants receiving water removed 1.7% of the p,p'-DDE from the soil. Seedlings amended with citric or oxalic acids removed 2.1 and 1.9% of the contaminant, respectively, and contained up to 66% more contaminant in the shoot system than unamended vegetation. A second crop of untreated (distilled water) zucchini in the same soil removed more contaminant than the first crop (2.5%), although the addition of organic acids did not further enhance contaminant uptake. The data indicate that the addition of low molecular weight organic acids causes the partial dissolution of the soil structure through the chelation of inorganic structural ions, potentially enhancing bioavailability and having implications for the phytoremediation of persistent organic pollutants in soil.     

Determination of metal partitioning in porewater extracted from the Seine River Estuary sediment (France)

Total dissolved trace and major metals and their partitioning in porewater sediment have been investigated at two sites in the Seine River estuary (France). For this purpose, solid phase extraction (SPE) has been employed using specific chelating resins for the separation and preconcentration of organic and inorganic forms of studied metals under controlled (N2) inert atmosphere. In fact, the study is focused on the development of a method for sample collection and handling under inert atmosphere in order to avoid some potential artefacts of the extracted porewater, to preserve the samples from possible chemical oxidation changes and to determine metals partitioning between organic and inorganic forms. For this point, a separation and preconcentration method using two columns in series (chelamine and C18 columns) was used. The trace and major metals fixed on the two resins for all determinations were stripped by nitric acid (2 M) and analyzed by Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES) and Zeeman Graphite Furnace Atomic Absorption Spectroscopy (ZGF-AAS). The relationship between the distribution of metals and physico-chemical parameters such as pH and Eh (redox potential) as a function of depth was discussed. Some tendency in the distributions and seasonal variability of these traces and major metals are improved. The concentrations for all studied metals decreased as a function of depth where iron and manganese were found at mg L(-1) levels and other metals were found at [micro sign]g L(-1) levels, as well as there were significant fractions of all metals (except of manganese) which were complexed by organic matter. The comparison of data for the major elements (Fe and Mn), obtained by direct determination (without preconcentration) and preconcentration, show a very good recovery.     

Design principles and common pool resource management: an institutional approach to evaluating community management in semi-arid Tanzania

This paper analyses the role of institutions in the management of common pool resources (CPRs) in semi-arid Tanzania. Common property regimes have often been considered inadequate for the management of CPRs because of the problems of excludability, but they are becoming more widely supported as the way forward to overcome the problems of resource use and degradation in developing countries. A series of design principles for long enduring common property institutions have been proposed by Ostrom, but there is concern that they are not applicable to a wide range of real life situations or that they may be specific to certain types of CPR. Here, we compare these principles to the situation prevailing in 12 villages in six districts in semi-arid Tanzania. Data on management institutions were collected through semi-structured interviews and meetings at district and village level. The combined information was used to make a qualitative assessment of the strength with which each design principle appeared to operate in the management of forest, pasture and water resources. Boundaries, conflict and negotiation in CPR management are of key importance in semi-arid regions. However, the need for flexibility in order to deal with ecological uncertainty means that many management institutions would be considered weak or absent according to the design principle approach. This supports the view that the design principles should not be used as a 'blueprint to be imposed on resource management regimes' rather that they provide a framework for investigating common property regimes with the proviso that, certainly for semi-arid regions, they may highlight where management cannot be explained by institutional theory alone.     

Short-term exposure to ozone altered the relative feed value of an alfalfa cultivar

Biomonitors are organisms that provide quantitative information on environmental quality. There are some constraints and limitations for the use of plants as biomonitors of soil pollution, as pointed out recently by some authors in this journal. However, we defend the use of plants as biomonitors, and argue that they have important advantages over soil analyses as indicators of soil quality, particularly when investigations are made on a large scale.