Chemical Fractions Of Sediments Research Articles

Cadmium chemical fractions in sediments: effect of grain size, pH, organic acids, and inorganic ions

Cadmium chemical fractions in sediments: effect of grain size, pH, organic acids, and inorganic ions

Connecting sources, fractions and algal availability of sediment phosphorus in shallow lakes: An approach to the criteria for sediment phosphorus concentrations

Although point and nonpoint sources contribute roughly equal nutrient loads to lakes, their relative role in supporting algae growth has not been clarified. In this research, we have established a quantitative relationship between algae-available phosphorus (P) and P chemical fractions in sediments; the latter indicates the relative contribution of point versus nonpoint sources. Surface sediments from three large shallow lakes in eastern China, namely, the Chaohu, Taihu and Hongzehu Lakes, were sampled to assess their algae-available P and chemically extracted P fractions. The algae-available P primarily comes from iron/aluminium (hydr)oxide-bound P (Fe/Al-bound P), 45% of which is algae-available P. The ratio of Fe/Al-bound P to calcium compound-bound P (Ca-bound P) indicated the relative contribution of point to nonpoint sources, with the point sources contributing the majority of increased Fe/Al-bound P in sediments. Therefore, the reduction of point sources from urbanized areas, rather than nonpoint sources from agricultural areas that primarily contribute to the Ca-bound P fraction, should be prioritized to alleviate cyanobacterial algal blooms (CyanoHABs) in shallow lakes with sediment P as a potential source to support algae growth. With these important results, we proposed a conceptual model for “P-pumping suction” from sediments to algae to aid in the development of the criteria for sediment P concentrations in shallow lakes.

Titanium and zinc-containing nanoparticles in estuarine sediments: Occurrence and their environmental implications

Understanding the behavior and risk of nanoparticles (NPs) in the aquatic environment is currently limited by the lack of quantitative characterization of NPs in the environmental matrices, such as sediments. In this study, based on the single particle (SP)-ICP-MS technique, metal-containing NPs, including Ti- and Zn-containing NPs, were analyzed in sediments taken along the Yangtze Estuary. Combined with the traditional sequential extraction method that has been widely used for metal risk assessment, different single extraction methods were used to understand the association of NPs with different chemical fractions in sediments and their potential environmental implications. Ti-containing NPs, with an average size of 81 nm, ranged from 3.02 × 107 parts/mg to 9.61 × 107 parts/mg, and Zn-containing NPs, with an average size of 41 nm, ranged from 2.47 × 106 parts/mg to 1.21 × 107 parts/mg. Both correlation and redundancy analyses showed that particle concentrations of Ti-containing NPs in sediment were significantly correlated to the Ti-containing NPs in the residual fraction and salinity, indicating that Ti-containing NPs in sediments may be dominated by Ti-containing NPs in the residue fractions of sediments. Large amounts of these NPs may be released from the residual fraction that has been considered to be not bioavailable and “environmentally safe” in the traditional environmental risk assessment of metals in sediments. Zn-containing NPs, mostly associated with carbonates, were positively correlated to all the bioavailable fractions of Zn in sediments, suggesting that these NPs may be largely presented in the bioavailable fraction. This study showed that, vast numbers of NPs with minute sizes were present in estuarine sediments, and that they were associated with different chemical fractions with different potential environmental risks. The study findings call for further research to update the traditional risk assessment method.

Spectroscopic Study of Sediments from Chapala Lake in Western Mexico

The first 10 cm of sediment from Lake Chapala, Western Mexico are in constant activity related to the exchange and speciation of metal cations. Samples of this sediment were analyzed in electron paramagnetic resonance (EPR) equipment to study the paramagnetic metals. Assays indicated that only Fe3+ was present in a detectable amount. This cation, along with chemical fractions of sediment obtained by sequential extraction, was analyzed by EPR. The analysis supported by infrared data revealed that Fe3+ was present in diluted and concentrated domains. Easily exchangeable iron was retained by carbonyl groups in organic matter. The carbonate fraction and oxides contained iron in concentrated domains. The alumina-silicate fraction (that resisted the sequential extraction digestions) presented diluted domains of iron in the octahedral alumina sheet along with occlusions of concentrated domains. This last inference was obtained by comparing EPR results against the spectrum of iron in synthetic model clay.

The characteristic of Pb isotopic compositions in different chemical fractions in sediments from Three Gorges Reservoir, China

To explore the distribution and sources of Pb within the Three Gorges Reservoir (TGR), Pb concentrations and isotope ratios were measured in sediment cores collected from one mainstream and three tributaries. The results showed that sediments contained an average of 43.54 mg kg−1 of Pb, roughly 1.6 times higher than the geochemical background concentration. Mainstream sediments showed higher average Pb concentrations but slightly less 206Pb/207Pb and more radiogenic 207Pb/208Pb ratios than all tributaries. Most Pb occurred in reducible phases, with much less in exchangeable and oxidizable fractions; thus, Fe–Mn oxides may be the major sink of anthropogenic Pb. Bi-plots of 206Pb/207Pb versus Pb content, and of 206Pb/207Pb versus 207Pb/208Pb, indicated that coal combustion was the predominant anthropogenic Pb source for exchangeable, reducible, and oxidizable fractions, while residual Pb mainly occurred naturally. The average percentage of coal consumption contribution was 61.1% for the Pb contamination in sediments in the lower reaches in the TGR region.

Radionuclide speciation in sediments of the Yenisei River

The examination of sediment samples collected from the Yenisei River revealed the presence of artificial radionuclides characteristic of radioactive discharges from the MCC facility: isotopes of europium (152Eu, 154Eu, and 155Eu), cesium (137Cs and 134Cs), 60Co,90Sr, and transuranium elements. Radionuclide concentrations in sediment layers remained high as far as 240 km downstream of the MCC. The vertical distribution of radionuclides in sediment cores was very complex, and down-core variations were due to different amounts of radionuclides released by the MCC and due to variations in the hydrologic conditions in the river. Sequential extraction performed on samples of the upper layers of the sediment core showed different degrees of potential environmental availability of artificial radionuclides: the amounts of extracted 90Sr, 152Eu and 241Am were the largest (60–80% of initial activity), then followed 60Co (30%), 238,239,240Pu (15–30%), and, last, 137Cs (5–15%). The distribution of 238U among chemical fractions of sediments was similar to that of 60Co and 238,239,240Pu: 30–40% of 238U initial activity was extracted. In a few samples, 241Am was present in the unextractable form, which may be accounted for by the presence of microparticles of the reactor fuel.

Heavy Metals Fractionation in Ganga River Sediments, India

The Ganga River is the largest river in India which, originates in the Himalayas and along with the Brahmaputra River, another Himalayan river, transports enormous amounts of sediments from the Indian sub-continent to the Bay of Bengal. Because of the important role of river sediments in the biogeochemical cycling of elements, the Ganga river sediments, collected from its origin to the down stretches, were studied in the present context, to assess the heavy metals associated with different chemical fractions of sediments. The fractionation of metals were studied in the sediments using SM&T protocol for the extraction of heavy metals and geo-accumulation index (GAI) (Muller, Schwermetalle in den sedimenten des rheins - Veranderungen seit. Umschau, 79, 778-783, 1979) and Metal Enrichment Factor (MEF) in different fractions were calculated. As with many river systems, residual fractions constitute more than 60% of total metals, except Zn, Cu and Cr. However, the reducible and organic and sulfide components also act as major sinks for metals in the down stretches of the river, which is supported by the high GAI and MEF values. The GAI values range between 4 and 5 and MEF exceed more than 20 for almost all the locations in the downstream locations indicating to the addition of metals through urban and industrial effluents, as compared to the low metals concentrations with less GAI and MEF in the pristine river sediments from the rivers in Himalayas.

Evaluating the role of desorption in bioavailability of sediment-associated contaminants using oligochaetes, semipermeable membrane devices and Tenax extraction

The success of the rapidly desorbing fraction as an available fraction was challenged by using sediment ingesting and non-ingesting oligochaetes ( Lumbriculus variegatus) together with passive samplers (semipermeable membrane devices, SPMDs) in accumulation and kinetic modelling exercises for carbon-14 labelled model compounds (pyrene, benzo[ a]pyrene and 3,4,3′,4′-tetrachlorobiphenyl). Passive samplers clearly produced lower uptake rate constants and steady state factors than either of the oligochaete treatments when residue concentrations were based on animal lipid or total SPMD weight. The rapidly desorbing chemical fractions in sediments did not show a significant relationship with the biota sediment accumulation factors or SPMD accumulation factors. A distinctly better relationship was observed between the accumulation factors and the desorption rate constants. The results support the assumption that desorption plays an important role in bioavailability, although animal behaviour and the diffusional limitations of hydrophobic contaminants in sediment together probably affect the actual available pool.

Study of Fractionation and Potential Mobility of Metal from the Guadalquivir Estuary: Changes in Mobility with Time and Influence of the Aznalcollar Mining Spill

This study analyzed the evolution of metal levels in surface sediments from the Guadalquivir estuary between 1997 and 2002 and assessed the impact of the April 1998 Aznalcollar tailings dam failure and subsequent cleanup on metal concentrations in surface sediments. We also analyzed metal distribution with time in five chemical fractions of the surface sediments: exchangable, carbonate, reducible, oxidizable, and residual. This work showed that the April 1998 Aznalcollar tailings dam failure caused a considerable increase in the concentrations of Cd, Zn, Cu, and Pb in the surface sediments of the Guadalquivir estuary. It was also found there was a change in the distribution of Cd, Zn, Cu, and Pb between the chemical fractions of the sediment after the failure of the dam. There were increases in the percentages of Cd in the carbonate fraction, of Zn and Pb in the reducible fraction, and of Cu in the oxidizable fraction, whereas the percentages of these elements associated with the residual fraction decreased. In 1999, there was a decrease in the metal concentrations in the surface sediments from the Guadalquivir estuary, and by 2000 the chemical distribution and metal levels had returned to levels similar those before the dam failure.

Trace metal distribution in different chemical fractions of marine sediments along the eastern Aegean shelf

The major objective of this study was to carry out sequential chemical extraction for the partitioning of particulate trace metals in sediment samples, collected along the eastern Aegean shelf during cruises July‐August 1994, in the framework of a National Marine Measurement and Monitoring Programme for the Aegean Sea. Five metals, Cd, Pb, Cu, Zn and Cr were examined in each of sediment samples. Three chemical fractions of the sediments were separated and concentrations of the trace metals were determined by AAS techniques. The three different leaches used were hydroxylamine hydrochloride‐acetic acid, hydrogen peroxide and nitric‐perchloric acids. Metals were concentrated mainly in the fraction extracted by nitric‐perchloric acids. Lead in the first fraction were found in the sediments of Northern part of Aegean, where the concentration of organic material was high. The total concentrations of Cd, Cu, Zn, Cr were higher in Izmir Bay than the other sampling points. The distribution of Pb concentrations was the highest in Edremit Bay and Izmir Bay.

U and Th speciation in river sediments

A study of the distribution of some natural radionuclides in different chemical fractions of river bottom sediments has been carried out. The study has shown that the majority of the total U in sediments is located in the non-residual fractions, while Th is more likely to be present in the residual ones. This difference between U and Th reflects largely a much higher mobility of U relative to Th in surface and near-surface environments. Coprecipitation with amorphous ferromanganese oxyhydroxides is the main process of U and Th incorporation from the water column into the soil particles. Moreover, the distribution of the radionuclides and the analysis of the Th/U mass ratios in different chemical fractions of sediments has made an unequivocal connection between the enhanced U content in river sediments and the wastes discharged into the rivers by the operation of fertilizer industries.

Ultra-Small Carbon Samples and the Dating of Sediments

Radiocarbon dates from sediment core samples are usually obtained on the whole organic carbon portion in order to use as little of the valuable sediment as possible. Such measurements may not result in an accurate chronology of the sediment because the material may include carbon from different reservoirs at the time of deposition. The development of AMS techniques for dating ultra-small (20–500μg) carbon samples permits dating various components of cored sediments. We give examples of physical and chemical fractions of sediments which illustrate the large differences in ages obtainable from materials at the same sediment depth. The dating of all or several of these fractions demands more complex interpretations than just the derivation of a sedimentation rate from whole organic carbon dates.

Partitioning of heavy metals into selective chemical fractions in sediments from rivers in northern Greece

A five-step sequential extraction technique was used to determine the chemical association of heavy metals (Pb, Cd, Cu, Fe, Mn, Zn, Cr) with major sedimentary phases (exchangeable cations, easily reducible compounds, organic sulfidic phases, carbonates and residual components) in samples from rivers in northern Greece (Axios and Aliakmon). From the obtained data it can be seen that the surplus of metal contaminants introduced into the aquatic system from anthropogenic sources usually exists in relatively unstable chemical forms. A high proportion of the elements studied remains in the residual fraction for the Axios river and in the organic fraction for the Aliakmon. Most of the non-residual portion is bound to ferromanganese oxides and to organic matter.

Trace metal distribution in different chemical fractions of nearshore marine sediments

The major objective of this study was to carry out sequential chemical extractions for the partitioning of particulate trace metals in sediment samples, collected from False Bay. Eight metals, Cd, Cu, Cr, Fe, Mn, Ni, Pb and Zn, were examined in each of 65 samples. Three chemical fractions of the sediments were separated and the concentrations of the trace metals were determined in each, by atomic absorption techniques. The three different leaches used were hydroxylamine hydrochloride-acetic acid, hydrogen peroxide, and nitricperchloric acids. Fe and Pb were concentrated mainly in the fraction extracted by nitric-perchloric acid, while Cu, Zn and Ni were found mainly in the peroxide fraction. Most of the metals in the peroxide phase were found in the finer sediments in the central area of the bay, where the concentration of organic meterial was high. The metal concentrations (except for Pb) correlated well with the organic content of the sediments.