Distribution of cadmium among geochemical fractions in floodplain soils of progressing development

Soil and plant contamination by potentially toxic and emerging elements and the associated human health risk in some Egyptian environments

The aim of this work was to assess the origins, mobility, bioavailability and potential health risks of V, Cr, Co, As, Se, Mo, Cd, Sn and Sb, which are not sufficiently studied in the terrestrial environment of Egypt. This has been carried out by employing a combination of chemical fractionation, plants uptake, mathematical modeling and risk assessment approaches on a wide range of soils and plants sampled from industrial, urban and agricultural locations across Egypt. The contents of As, Cd, Sn and Sb were elevated in the soils of some urban and industrial locations within Cairo, although their soil geo-accumulation (I_geo) indices remained ≤ 2, indicating only moderate contamination. Selenium showed moderate to heavy contamination levels (I_geo up to 4.7) in all sampling locations, and Sb was highly elevated (I_geo = 7.1; extreme contamination) in one industrial location. Therefore, Se was the most important contributor to the pollution load followed by Sb and Cd. Both principle component analysis (of total content) and geochemical fractionation (by sequential extraction) suggested that V, Cr and Co are mostly of geogenic origin, while Se and Sb contents appear to be highly influenced by anthropogenic inputs. The most mobile and bioavailable element was Cd with a large non-residual fraction in all soils (76% of total Cd). The bio-concentration factors of Cd in leafy and fruiting plants were 50 times larger than other elements (except Mo) indicating preferential systematic plant uptake of Cd. Risk assessment models showed an overall low noncarcinogenic and carcinogenic risks to the population of Egypt due to the studied elements with only a few anomalies.

Health risk assessment of potentially toxic elements in soils along the Central Elbe River, Germany

Floodplain soils across Central Elbe River (CER), Germany, vary considerably in potentially toxic element (PTE) content. However, there has never been a comprehensive study that links PTE levels with human health risk for children and adults. Our objective was to determine the contamination of 13 PTEs in 94 soil profiles along CER and assess the associated health risk via diverse indices for adults and children. Of 94 soil profiles, we measured soil properties and total content of arsenic, barium, chromium, copper, nickel, lead, rubidium, tin, strontium, vanadium, zinc, and zirconium using x-ray fluorescence spectrometer (XRF). We calculated the Contamination Factor and the Pollution Load Index (PLI), and assessed the health risk for male and female adults as well as for children. Topsoil median contents of Cr (84 mg kg^-1), Cu (42), Ni (33), and Zn (195) exceeded the Precautionary Values for sandy soils according to the German Federal Soil Protection and Contaminated Sites Ordinance, while As, Pb, and V were 32, 73, and 77 mg kg^-1, respectively. Median topsoil PLI was 1.73, indicating elevated multi-element contamination, with 90th percentile and maximum values being 3.20 and 4.31, respectively. All PTE concentrations were higher in top- compared to subsoils. Also at the 50th percentile the most enriched elements were Sn and As, followed by Zr and Rb, while in the 90th percentile Sn and As were followed by Zn, Pb and Cu. Median children's hazard index (HI) was higher than unity (HI = 2.27) and the 90th percentile was 5.53, indicating elevated health risk. Adult median HIs were 0.18 for male and 0.21 for female persons. Arsenic was found to be the primary contributor to total risk, accounting of 57.4% of HI in all three-person groupings, with Cr (17.3%) being the second, and V (10.2%) the third. Children's health is at dramatically higher risk than that of adults; also As, Cr, Pb, and V have a predominant role in contamination-related health risks. The presence of V, a less-expected element, among those of major risk contribution, reveals the necessity of monitoring areas at large scale. Our results demonstrate that our study may serve as a model for similar works studying multi-element-contaminated areas in future.

Compost and sulfur affect the mobilization and phyto-availability of Cd and Ni to sorghum and barnyard grass in a spiked fluvial soil

Soil reclamation via additives can cause contradictory effects on the mobilization of toxic elements in soils under dry and wet conditions. Therefore, our aim was to investigate the impact of compost and sulfur in two rates (1.25 and 2.5%) on fractionation, mobilization, and phyto-availability of cadmium (Cd) and nickel (Ni) to sorghum (dry soil) and barnyard grass (wet soil) in a fluvial soil spiked with 25 mg Cd or 200 mg Ni/kg soil. Compost decreased the solubility and mobilization of Cd (especially in dry soil) and Ni (in both soils). Sulfur increased the solubility of Cd (31% in dry soil-49% in wet soil) and Ni (4.6% in wet soil-8.7% in dry soil). Sulfur altered the carbonate fraction of Cd to the soluble fraction and the residual fraction of Cd and Ni to the non-residual fraction. Compost decreased Cd and increased Ni in sorghum, but enhanced Cd and degraded Ni in grass. Sulfur increased Cd and Ni in both plants, and the increasing rate of Cd was higher in grass than in sorghum, while Ni was higher in sorghum than in grass. These results suggest that compost can be used as an immobilizing agent for Cd in the dry soil and Ni in the wet soil; however, it might be used as mobilizing agent for Cd in the wet soil and Ni in the dry soil. Sulfur (with rate 2.5%) can be used for enhancing the phyto-extraction of Cd and Ni (especially Cd) from contaminated alkaline soils.

Geochemical source, deposition, and environmental risk assessment of cadmium in surface and core sediments from the Bohai Sea, China

Geochemical sources, spatio-temporal distribution, and associated environmental risk of Cd in the Bohai Sea were investigated using data from 405 surface sediment samples and two sediment cores. Local point Cd sources, TOC content, and currents are the main controlling factors of Cd distribution. The contribution of Cd from river discharge surpasses that from atmospheric deposition. Sediment-quality guidelines, enrichment factors, and chemical fraction analysis were used to assess metal toxicity in the collected sediments. Results show that Bohai Sea sediments have a moderate Cd enrichment level. This enrichment poses a high risk due to the relatively high mobility and bioavailability of Cd despite measured levels below sediment-quality guidelines at most stations. Vertical profiles of Cd concentrations, Al-normalized enrichment factors, and excess burial fluxes combined with ²¹⁰Pb dating reveal the history of Cd pollution in the Bohai Sea over the last century. Data show Cd unvaried before the 1800s, a slight increase from the 1800s to the late 1950s, a decrease from the late 1960s to the 1970s, and an increase from the 1980s to 2001, including a relatively high value in 1998. Historic variation in Cd is closely associated with both natural and anthropogenic activities.

Chemical speciation and bioavailability of cadmium in the temperate and semiarid soils treated with wheat residue

Heavy metal bioavailability depends on metal fractions in soil. The impacts of mild wheat residue (<2 mm) and incubation time on fractions of Cd were studied in two different spiked soils sampled from Hamadan and Lahijan, Iran with semiarid and temperate climates, respectively. Two factorial experiments were done in two soils polluted with 10 μg Cd g(-1) soil separately. Organic matter (0 and 5 % wheat straw) and soil incubation time (24 and 3600 h) were factors examined in three replicates. The transformation of Cd from KNO3 extractable form to less available fractions was higher in semiarid soils with lower clay and OM contents and higher pH and carbonate contents compared to temperate soils. In polluted semiarid soils after 24 h incubation, greater content of Cd was observed in residual (HNO3 extractable) (45 %), carbonates associated (EDTA extractable) (34 %), organic matter associated (NaOH extractable) (11 %), and KNO3 extractable (10 %) fractions, but in temperate soils, greater content of Cd was observed in KNO3 extractable (61 %), HNO3 extractable (14 %), EDTA extractable (13 %), and NaOH extractable (12 %) fractions. KNO3 extractable form of Cd was decreased, and NaOH extractable and HNO3 extractable forms of Cd were increased by addition of wheat residue to both soils. The initial decrease of added Cd from KNO3 extractable form to less mobile fractions in Hamadan soil was very interesting. But this change was not observed in Lahijan soil. Since contamination factor was significantly high in temperate soils compared to semiarid soils in all treatments, the risk of Cd environmental pollution in temperate region is considerably high.

Bioaccumulation of potentially toxic trace elements in benthic organisms of Admiralty Bay (King George Island, Antarctica)

Data about the concentration, accumulation and transfer of potentially toxic elements in Antarctic marine food webs are essential for understanding the impacts of these elements, and for monitoring the pollution contribution of scientific stations, mainly in Admiralty Bay due to the 2012 fire in the Brazilian scientific station. Accordingly, the concentration of As, Cd, Cu, Ni, Pb and Zn was measured in eight benthic species collected in the 2005/2006 austral summer and the relationship between concentration and trophic position (indicated by δ(15)N values) was tested. A wide variation in metal content was observed depending on the species and the element. In the studied trophic positions, it was observed bioaccumulation for As, Cd and Pb, which are toxic elements with no biological function. In addition, Cd showed a positive relationship between concentration and trophic level suggesting the possible biomagnification of this element.

Bioremediation of Cd-DDT co-contaminated soil using the Cd-hyperaccumulator Sedum alfredii and DDT-degrading microbes

The development of an integrated strategy for the remediation of soil co-contaminated by heavy metals and persistent organic pollutants is a major research priority for the decontamination of soil slated for use in agricultural production. The objective of this study was to develop a bioremediation strategy for fields co-contaminated with cadmium (Cd), dichlorodiphenyltrichloroethane (DDT), and its metabolites 1, 1-dichloro-2, 2-bis (4-chlorophenyl) ethylene (DDE) and 1, 1-dichloro-2, 2-bis (4-chlorophenyl) ethane (DDD) (DDT, DDE, and DDD are collectively called DDs) using an identified Cd-hyperaccumulator plant Sedum alfredii (SA) and DDT-degrading microbes (DDT-1). Initially, inoculation with DDT-1 was shown to increase SA root biomass in a pot experiment. When SA was applied together with DDT-1, the levels of Cd and DDs in the co-contaminated soil decreased by 32.1-40.3% and 33.9-37.6%, respectively, in a pot experiment over 18 months compared to 3.25% and 3.76% decreases in soil Cd and DDs, respectively, in unplanted, untreated controls. A subsequent field study (18-month duration) in which the levels of Cd and DDs decreased by 31.1% and 53.6%, respectively, confirmed the beneficial results of this approach. This study demonstrates that the integrated bioremediation strategy is effective for the remediation of Cd-DDs co-contaminated soils.

Distribution and bioavailability of cadmium in ornithogenic coral-sand sediments of the Xisha archipelago, South China Sea

Total cadmium (Cd) concentrations in four ornithogenic coral-sand sedimentary profiles displayed a strong positive correlation with guano-derived phosphorus, but had no correlation with plant-originated organic matter in the top sediments. These results indicate that the total Cd distributions were predominantly controlled by guano input. Bioavailable Cd and zinc (Zn) had a greater input rate in the top sediments with respect to total Cd and total Zn, and a positive correlation with total organic carbon (TOC) derived from plant humus. Multi-regression analysis showed that the total Cd and TOC explained over 80% of the variation of bioavailable Cd, suggesting that both guano and plant inputs could significantly influence the distribution of bioavailable Cd, and that plant biocycling processes contribute more to the recent increase of bioavailable Cd. A pollution assessment indicates that the Yongle archipelago is moderately to strongly polluted with guano-derived Cd.

Reproduction and biochemical responses in Enchytraeus albidus (Oligochaeta) to zinc or cadmium exposures

To better understand chemical modes of action, emphasis has been given to stress responses at lower levels of biological organization. Cholinesterases and antioxidant defenses are among the most used biomarkers due to their crucial role in the neurocholinergic transmission and in cell homeostasis preventing DNA damage, enzymatic inactivation and lipid peroxidation. The main goal of this study was to investigate the effects of zinc and cadmium on survival and reproduction of E. albidus and to assess metals oxidative stress potential and neurotoxic effects at concentrations that affected reproduction. Both metals affected the enchytraeids' survival and reproduction and induced significant changes in the antioxidant defenses as well as increased lipid peroxidation, indicating oxidative damage. This study demonstrates that determining effects at different levels of biological organization can give better information on the physiological responses of enchytraeids in metal contamination events and further unravel the mechanistic processes dealing with metal stress.

A simulation experiment as a method for the investigation of the mobility of heavy metals from inundated land

A simulation experiment was used to study the interaction of river water with different soils (arable land, orchards, meadows, pastures and forestland). The results obtained by sequential extraction before and after the simulation experiment were compared in order to determine the substrates of the heavy metals in inundated land and to evaluate their mobility. Samples of various soils were collected from the region of the future accumulation Lake Bogovina (Serbia) and analyzed for ten elements using AAS, GFAAS and ICP. Investigation of the nature of the association of heavy metals and the identification of their substrates were provided by a five-step sequential extraction. Correlation analysis was used as a method for the determination of the substrates for heavy metals. The good correlation among the microelements and certain macroelements indicated the substrates of the microelements. Manganese and iron had a good correlation with most of the microelements. Calcium had only a few correlations with some microelements. Some elements, such as nickel and cadmium, had one substrate before and another after the simulation experiment.

How do long-term development and periodical changes of river-floodplain systems affect the fate of contaminants? Results from European rivers

In many densely populated areas, riverine floodplains have been strongly impacted and degraded by river channelization and flood protection dikes. Floodplains act as buffers for flood water and as filters for nutrients and pollutants carried with river water and sediment from upstream source areas. Based on results of the EU-funded "AquaTerra" project (2004-2009), we analyze changes in the dynamics of European river-floodplain systems over different temporal scales and assess their effects on contaminant behaviour and ecosystem functioning. We find that human-induced changes in the hydrologic regime of rivers have direct and severe consequences on nutrient cycling and contaminant retention in adjacent floodplains. We point out the complex interactions of contaminants with nutrient availability and other physico-chemical characteristics (pH, organic matter) in determining ecotoxicity and habitat quality, and draw conclusions for improved floodplain management.

The hormetic effect of cadmium on the activity of antioxidant enzymes in the earthworm Eisenia fetida

The hormetic dose-response relationships induced by environmental toxic agents are often characterized by low-dose stimulation and high-dose inhibition. Confirmation of the general phenomenon of hormesis may have significant implications for ecological risk assessment, although the mechanisms that underlie hormesis remain an enigma. In this study, a model-based approach for describing a dose-response relationship incorporating the hormetic effect was applied to the detection and estimation of the hormetic effect of cadmium (Cd) on the activity of antioxidant enzymes in the earthworm Eisenia fetida. The results showed that Cd at low concentrations induced an increase in the activity of catalase and superoxide dismutase (SOD), but high concentrations inhibited the enzymes, and this was reflected in an inverted U-shaped curve. The maximum hormetic magnitude of SOD activity was higher than that of catalase. The presence of hormesis induced by cadmium in the earthworm may be related to activation of adaptive pathways.

Sequential extractions and isotope analysis for discriminating the chemical forms and origins of Pb in sediment from Liaodong Bay, China

Sequential extraction integrated with isotope analysis was carried out on a sediment core from Liaodong Bay, northeast China, for characterizing Pb in various extraction phases and its possible sources. Results show that in all extracted fractions Pb concentrations increased abruptly in the top part of the sediments that deposited after 1980, but remained lower and rather constant before 1980. Consistent with the variation pattern of Pb concentration, the 206Pb/207Pb ratio displays a dramatic decrease around 1980. These findings strongly suggest serious Pb pollution since then. The Pb concentration and the isotopic ratios of 206Pb/207Pb and 208Pb/207Pb in the residual fraction show rather small changes through the entire core, and are similar to those of uncontaminated Chinese loess, possibly representing the characteristics of the regional geogenic background. The isotopic ratios of the sediments before 1980 varied in different extracted fractions with a linear pattern, from the residual at the highest toward the average signature of automobile exhausts and Pb-Zn deposits, implying a prominent two-end member mixing style of the Pb origin; one is the regional geologic background and the other is anthropogenic sources. The difference in isotopic ratios between the extractions might be indicative of varied proportions of the two sources. For sediments after 1980, however, the isotope ratios in nonresidual fractions are all relatively low and show little differentiation, which may suggest that polluted Pb dominates all the extracted fractions for the top part of the core.

Trace metal dynamics in floodplain soils of the river Elbe: a review

This paper reviews trace metal dynamics in floodplain soils using the Elbe floodplains in Germany as an example of extraordinary importance because of the pollution level of its sediments and soils. Trace metal dynamics are determined by processes of retention and release, which are influenced by a number of soil properties including pH value, redox potential, organic matter, type and amount of clay minerals, iron-, manganese- and aluminum-oxides. Today floodplains act as important sinks for contaminants but under changing hydraulic and geochemical conditions they may also act as sources for pollutants. In floodplains such changes may be extremes in flooding or dry periods that particularly lead to altered redox potentials and that in turn influence the pH value, the mineralization of organic matter as well as the charge of the pedogenic oxides. Such reactions may affect the bioavailability of trace metals in soils and it can be clearly seen that the bioavailability of metals is an important factor for estimating trace metal remobilization in floodplain soils. However as bioavailability is not a constant factor, there is still a lack of quantification of metal mobilization particularly on the basis of changing geochemical conditions. Moreover, mobile amounts of metals in the soil solution do not indicate to which extent remobilized metals will be transported to water bodies or plants and therefore potentially have toxicological effects. Consequently, floodplain areas still need to be taken into consideration when studying the role and behavior of sediments and soils for transporting pollutants within river systems, particularly concerning the Water Framework Directive.

Bioaccumulation assessment via an adapted multi-species soil system (MS.3) and its application using cadmium

This paper presents an experimental design for quantifying the transfer of chemicals at low trophic levels of terrestrial ecosystems. The soil microcosms, MS.3(foodchain) (food chain multi-specie soil system) covered the transfer from soil to earthworms (Eisenia fetida) and from soil to plant (Triticum aestivum), then to phytophagus (Rhopalosiphum padi) and finally predator (Chrysoperla carnea) species. Cadmium was used as model pollutant. Cadmium accumulation in foliar invertebrates was related to the species biology. A significant transfer of this metal through the minimized food chain was found for all species, but not a biomagnification in the predator species. Results pointed out the relevance of foliar invertebrates and their trophic relationships as additional exposure routes for assessing secondary poisoning in predators. Hence, MS.3(foodchain), could be applied for terrestrial environmental risk assessment when potential bioaccumulation could be expected.