Leaching Of Sediments Research Articles

Radiogenic isotope record of Arctic Ocean circulation and weathering inputs of the past 15 million years

Lead (Pb), neodymium (Nd), and strontium (Sr) isotopic analyses were carried out on sediment leachates (reflecting the isotope composition of past seawater) and digests of the bulk residues (reflecting detrital continental inputs) of Integrated Ocean Drilling Program (IODP) Leg 302 and core PS2185 from the Lomonosov Ridge (Arctic Ocean). Our records are interpreted to reflect changes in continental erosion and oceanic circulation, driven predominantly by tectonic forcing on million‐year timescales in the older (pre‐2 Ma) part of the record and by climatic forcing of weathering and erosion of the Eurasian continental margin on thousand‐year timescales in the younger (post‐2 Ma) part. These data, covering the past ∼15 Ma, show that continental inputs to the central Arctic Ocean have been more closely linked to glacial and hydrological processes occurring on the Eurasian margin than on continental North America and Greenland. The constancy of the detrital input signatures supports the early existence of an Arctic sea ice cover, whereas the major initiation of Northern Hemisphere glaciation at 2.7 Ma appears to have had little impact on the weathering regime of the Eurasian continental margin.

Estimating the contribution of the authigenic mineral component to the long-term reactive silica accumulation on the western shelf of the Mississippi River Delta

Previous studies have shown how biogenic silica particles undergo conversion to aluminosilicate phases in large tropical deltaic systems, thus affecting the world ocean budget of major seawater cations. This study tackles the important question of the silica budget in the coastal zone of the Mississippi River Delta, providing evidence for the role of biogenic silica diagenesis in this subtropical system from direct examination of individual diatom particles, sediment leachates and pore-water composition. The estimated reactive silica stored in the study area (5990 km 2) is based on operational leaches that account for altered biogenic silica particles and other authigenic aluminosilicate phases in addition to fresh biogenic silica. Early diagenesis of silica in the delta front occurs mainly where more siliceous material is deposited. An inner-shelf area, where hypoxic conditions are found, significantly contributes to the formation of authigenic products of Si alteration. Data suggest that the limiting factor of silica alteration processes is the availability of detrital phases such as Al and Fe. The estimated total reactive silica accumulation in the study area is 1.45×10 10 mol Si year −1, representing ∼2.2% of the long-term bulk sediment accumulation. On the basis of a conservative appraisal, the authigenic mineral components account for ∼40% of the long-term reactive silica storage. This study shows that non-tropical deltaic systems are significantly more important sinks of silica than previously thought and that, where conditions are favourable, a consistent portion of reactive silica not leaving the shelf is stored within the delta in the form of authigenic components.

雨水浸透桝堆積物による重金属の吸脱着特性

To investigate the behavior of heavy metals in infiltration facilities receiving urban road runoff, we performed batch tests, which mimicked the sorption of heavy-metal species in road runoff by soakaway sediments. In soakaway sediment leachates, Ni and Cu were dominantly present as stable complexes, whereas most Zn existed as free ions and labile complexes. Ni and Cu in road runoff were adsorbed by all the soakaway sediments, whereas Zn was released from some soakaway sediments. Instead of the total Zn content in the soakaway sediments, the soluble fraction of Zn (i.e., the concentration of Zn released from sediments by deionized water) was a governing factor for the sorption from soakaways receiving road runoff; however, the behavior of Ni and Cu was not well explained by the total metal content, soluble fraction, and organic content. Desorption tests are useful in identifying soakaway sediments with limited adsorption capacities for Zn. The control and management of sediments based on desorption tests would be effective in minimizing groundwater contamination by heavy metals through infiltration facilities.

The sorption of heavy metal species by sediments in soakaways receiving urban road runoff

Infiltration facilities are designed for both the retention of non-point pollutants and the replenishment of groundwater in urban areas. In this study, sorption tests were conducted to evaluate the speciation of heavy metals and their behaviour in infiltration facilities receiving urban road runoff containing high DOC concentrations and stable heavy metal organic complexes. Road dust and three soakaway sediments were collected from heavy traffic areas and a residential area with an infiltration-type sewerage system in Tokyo, Japan. Sequential multiple batch tests were conducted by adding prepared road dust leachate (artificial road runoff) or deionised water to soakaway sediment to obtain soakaway sediment leachate (artificial percolating water from soakaway sediment), which mimicked the sorption by sediments in soakaways receiving urban road runoff. Heavy metal speciation was assessed by means of a combination of anion-exchange resin measurements and MINTEQA2 model calculations, and further validated by chelating resin measurements. In road dust leachates and soakaway sediment leachates, Cu predominantly existed as organic complexes and carbonates, whereas most Mn, Zn and Cd were found to exist in the form of free ions and carbonate complexes. Stable organic complexes of Cu in road dust leachates were strongly adsorbed by soakaway sediments despite the limited adsorption of DOC. On the other hand, desorption of free Mn, Zn and Cd ions from the sediment receiving road dust leachates was observed, indicating that heavy metals such as Mn, Zn and Cd may ultimately reach groundwater as free ions.

Chemical characterization of landfill leachates – 400 parameters and compounds

A large number of hazardous compounds can be expected to be present in landfill leachates, many of which have not yet been identified. Thus this study screened samples from 12 Swedish municipal landfill sites for 400 parameters and compounds. More than 90 organic and metal organic compounds and 50 inorganic elements were detected, some of which seem to have not been detected before. Compounds detected include halogenated aliphatic compounds, benzene and alkylated benzenes, phenol and alkylated phenols, ethoxylates, polycyclic aromatic compounds, phthalic esters, chlorinated benzenes, chlorinated phenols, PCB, chlorinated dioxins and chlorinated furans, bromated flame-retardants, pesticides, organic tin, methyl mercury and heavy metals. The presence of this large number of hazardous compounds in landfill leachates should have a significant impact on future landfill risk assessments and the development of leachate treatment methods. We propose that future research should pay more attention to the metal-organic and organic compounds detected in this study. We also suggest using leachate sediments as a matrix for detecting hydrophobic compounds, and reflecting on the degradation phase when evaluating results from monitoring studies. The extensive compilation of compounds in this paper can be used to select compounds to search for in future studies.

Trace element exposure in the environment from MSW landfill leachate sediments measured by a sequential extraction technique

Dredged leachate sediments from eight MSW landfills were dried and homogenized, and metals sequentially extracted. The concentrations of cadmium (Cd), copper (Cu), chromium (Cr), iron (Fe), lead (Pb), manganese (Mn), nickel (Ni) and zinc (Zn) were found to be similar to those reported for sewage sludge, and generally below the EU limits for use of sludge on agricultural land. Sequential extraction of the samples showed that the largest fractions of the heavy metals were associated with Fe- or Mn-oxides. Cr and Cu were the only metals investigated that were associated with the organic matter in the sediments to any significant extent (2–10% of Cr and 10–28% of Cu). Since the largest fractions of the metals studied were bound to Fe-oxides, and thus had a low mobility, these metals will generally have a low bioavailability under aerobic conditions when present in leachate sediments. This is most likely also valid for particulate matter suspended in MSW landfill leachate and released to the environment, since this is the source of the sediments.

English

The demand for natural gas is increasing due to the global energy crisis. Due to the demand for natural gas there have been major explorations in the Rocky Mountain States. One of the largest areas for natural gas extraction is the Powder River Basin, Wyoming. The process of extracting natural gas involves pumping water from coal seam aquifers that is mixed with the natural gas. Once the water and gas reach the surface they are separated and product water is disposed into a nearby disposal pond. The objectives of this study were to monitor water quality components, model the components in a water quality model, and monitor trace metals in the sediments of the disposal ponds. Samples were collected and analyzed for major cations, anions, and trace metals. Results from one year of sampling suggest wide ranges in pH, oxidation reduction potential, electrical conductivity, temperature, and dissolved oxygen. Concentrations for sodium were high when compared with the concentrations of the other major cations. Practical sodium adsorption ratios calculated from the concentrations of sodium, magnesium, and calcium ranged from 6.3 to 51.86. True sodium adsorption ration calculated from the activities of sodium, magnesium and calcium ranged from 7.07 to 88.05. The highest concentration of trace metals in both wells and disposal ponds were barium and boron. Sediment samples were also collected and a Toxic Characteristic Leaching Procedure was preformed to determine leachability and toxicity of trace metals. The two trace metals detected in sediment leachates were barium and manganese. When compared to groundwater drinking water standards both barium and boron concentrations in sediment leachates were above the limits.

The Late Eocene 187Os/188Os excursion: Chemostratigraphy, cosmic dust flux and the Early Oligocene glaciation

High resolution records (ca. 100 kyr) of Os isotope composition (187Os / 188Os) in bulk sediments from two tropical Pacific sites (ODP Sites 1218 and 1219) capture the complete Late Eocene 187Os / 188Os excursion and confirm that the Late Eocene 187Os / 188Os minimum, earlier reported by Ravizza and Peucker-Ehrenbrink [Earth Planet. Sci. Lett. 210 (2003) 151–165], is a global feature. Using the astronomically tuned age models available for these sites, it is suggested that the Late Eocene 187Os / 188Os minimum can be placed at 34.5 ± 0.1 Ma in the marine records. In addition, two other distinct features of the 187Os / 188Os excursion that are correlatable among sections are proposed as chemostratigraphic markers which can serve as age control points with a precision of ca. ± 0.1 Myr. We propose a speculative hypothesis that higher cosmic dust flux in the Late Eocene may have contributed to global cooling and Early Oligocene glaciation (Oi-1) by supplying bio-essential trace elements to the oceans and thereby resulting in higher ocean productivity, enhanced burial of organic carbon and draw down of atmospheric CO2. To determine if the hypothesis that enhanced cosmic dust flux in the Late Eocene was a cause for the 187Os / 188Os excursion can be tested by using the paired bulk sediment and leachate Os isotope composition; 187Os / 188Os were also measured in sediment leachates. Results of analyses of leachates are inconsistent between the south Atlantic and the Pacific sites, and therefore do not yield a robust test of this hypothesis. Comparison of 187Os / 188Os records with high resolution benthic foraminiferal δ18O records across the Eocene–Oligocene transition suggests that 187Os flux to the oceans decreased during cooling and ice growth leading to the Oi-1 glaciation, whereas subsequent decay of ice-sheets and deglacial weathering drove seawater 187Os / 188Os to higher values. Although the precise timing and magnitude of these changes in weathering fluxes and their effects on the marine 187Os / 188Os records are obscured by recovery from the Late Eocene 187Os / 188Os excursion, evidence of the global influence of glaciation on supply of Os to the ocean is robust as it has now been documented in both Pacific and Atlantic records.

Anaerobic Degradation of cis-1,2-Dichloroethylene and Vinyl Chloride by Clostridium sp. Strain DC1 Isolated from Landfill Leachate Sediment

The bacterial community structure of anaerobic enrichment cultures that are capable of degrading both cis -1,2-dichloroethylene ( cis -DCE) and vinyl chloride (VC) and isolation of the organism responsible for the degradation were investigated. Denaturing gradient gel electrophoresis (DGGE) of a PCR-amplified 16S rRNA gene from the cultures showed the possible predominance of Clostridium species. One isolate, designated strain DC1, was closely related to members of Clostridiaceae, based on 16S rRNA gene analysis, and the highest sequence similarity (98.9%) was obtained for Clostridium saccarobutylicum . In culture experiments, strain DC1 was shown to degrade cis -DCE and VC during the stationary phase of growth without accumulation of VC and/or ethene. The bacterial growth was not linked to the degradation of cis -DCE and VC. Stoichiometric analysis revealed that two moles of chloride ions as released from one mole of cis -DCE during the incubation period, indicating that cis -DCE was fully dechlorinated. The results appear consistent with the presence of a mechanism of oxidative dechlorination rather than respiratory reductive dechlorination; the latter is accompanied by transient formation of dechlorinated ethenes from cis -DCE and VC.

Effect of nutrient amendments on indigenous hydrocarbon biodegradation in oil-contaminated beach sediments.

Nutrient amendment to oil-contaminated beach sediments is a critical factor for the enhancement of indigenous microbial activity and biodegradation of petroleum hydrocarbons in the intertidal marine environment. In this study, we investigated the stimulatory effect of the slow-release fertilizers Osmocote (Os; Scotts, Marysville, OH) and Inipol EAP-22 (Ip; ATOFINA Chemicals, Philadelphia, PA) combined with inorganic nutrients on the bioremediation of oil-spiked beach sediments using an open irrigation system with artificial seawater over a 45-d period. Osmocote is comprised of a semipermeable membrane surrounding water-soluble inorganic N, P, and K. Inipol, which contains organic N and P, has been used for oil cleanup on beach substrate. Nutrient concentrations and microbial activity in sediments were monitored by analyzing sediment leachates and metabolic dehydrogenase activity of the microbial biomass, respectively. Loss of aliphatics (n-C12 to n-C33, pristane, and phytane) was significantly greater (total loss between 95 and 97%) in oil-spiked sediments treated with Os alone or in combination with other nutrient amendments, compared with an unamended oil-spiked control (26% loss) or sediments treated with the other nutrient amendments (28-65% loss). A combination of Os and soluble nutrients (SN) was favorable for the rapid metabolic stimulation of the indigenous microbial biomass, the sustained release of nutrients, and the enhanced biodegradation of petroleum hydrocarbons in leached, oil-contaminated sediments.

Biodegradation of cis-1,2-dichloroethylene and vinyl chloride in anaerobic cultures enriched from landfill leachate sediment under Fe(III)-reducing conditions.

An anaerobic, Fe(III)-reducing enrichment culture, which originated from a sediment sample collected at a landfill in Nanji-do, Seoul, Korea, was capable of degrading cis-1,2-dichloroethylene (cis-DCE) and vinyl chloride (VC). Although it exhibited the ability under Fe(III)-reducing conditions, the chlorinated ethenes degradation was not linked to the Fe(III) reduction. During cis-DCE degradation, no VC, ethene, or ethane was detected through the experimental period. Also, this culture did not accumulate ethene and ethane during the VC degradation. It was unlikely that cis-DCE was reductively dechlorinated to VC and then the VC formed was dechlorinated fast enough. Because the kinetic data showed that the rate of cis-DCE degradation was 3.5 times higher than that of VC. Whereas glucose supported the culture growth and the degradation, formate, acetate, butyrate, propionate, lactate, pyruvate, and yeast extract did not. The results appeared consistent with the involvement of oxidative degradation mechanism rather than reductive dechlorination mechanism. The traits of the culture described here are unusual in the anaerobic degradation of chlorinated ethenes and may be useful for searching an effective organism and mechanism regarding anaerobic cis-DCE and VC degradation.

Sample preparation for the determination of 241Am in sediments utilizing γ-spectroscopy

This paper describes a procedure developed to separate americium-241 from the bulk of a sample by coprecipitation followed by high sensitivity gamma-counting of the concentrate in a well-type detector. It enables the measurement of 241Am at low concentrations, e.g. fallout levels in soils and sediments, or where large sample sizes are not available. The method is much faster and more reliable than those involving separation from other alpha-emitters, electroplating and alpha-spectrometry. A number of tracer experiments was performed in order to optimize the conditions for coprecipitation of 241Am from sediment leachates. The general outline of the determination of americium is also given.

Gypsum Precipitation – A Medium to Control Sulphate Pollution of Freshwater Sediment Leachates

To treat sulphate pollution resulting from freshwater sediments,an experimental study was done. This experimental study was carried out to determine the effects of pH values and calcium supplements (as CaCl2) on the formation of gypsum in a representative wetland sediment that was aerated. It was foundthat the differences between dissolved sulphate in untreatedcontrol and the other treatments with CaCl2 amendments canbe attributed to the precipitation of gypsum. At the same time, the system was highly affected by Ca adsorption/desorption thatwas controlled by pH values. ECOSAT equilibrium simulations showed that CaCl2 additions (0.2–0.3 mol L-1) to aerated freshwater sediment resulted in removal of 78–98% ofsulphate (from its total content) from the solution. It wascaused by favourable conditions for gypsum formation i.e. acidicpH values were not increased due to the neutral character of CaCl2. On the contrary to CaCl2 amendments, CaCO3supplements (in the same Ca doses as applied in CaCl2) caused the removal of only 5–25% of sulphate. The significantincrease of pH values after the application of CaCO3 limitedgypsum formation due to high saturation of the system with CO3 -2 and HCO3 -. It resulted in the prevalence of CaCO3 formation in this system. However, theaddition of Cl- can facilitate the mobilisation of cationicmetals like Cd and Pb in the form of Cl--complexes. Therefore, CaCl2 treatment should be used in the sites thatdo not contain elevated amounts of these metals.

Chemistry of metal sulfides in anoxic sediments

Using sequential extraction of solid sulfides, the determination of acid volatile sulfides (AVS) and chromium reducible sulfurs (CRS) in anoxic sediments from the Authie Bay (in northern France) has been undertaken because of the importance of the sediments as sinks for iron, sulfur and trace metals and as possible sources of pollution when reduced sediments are mixed with oxic waters (as a result of a sediment remobilization induced by physical disturbances such as tidal currents and dredgings), and subsequently oxidized. Chemical analysis of solutions recovered after sequential leaching of sediments with 1 M HCl, 1 M HF and concentrated HNO3 has enabled us to obtain profiles, s. sediment depth, of trace metals associated with pyrite. Porewater concentration profiles s. depth have been determined for several cations (Ca2+, Cd2+, Cu2+, Fe2+, Mg2+, Mn2+, Na+, Pb2+, Sr2+ and Zn2+) and anions (CO32−, PO43−, SO42− and S2−). Using the chemical equilibrium modeling program MINEQL+ with these analytical data, thermodynamic calculations have given information about the possibility of precipitation of discrete metal sulfide phases (FeS as greigite and amorphous FeS; ZnS, PbS, CuS and CdS), and coprecipitation with adsorption on solid FeS to produce solid solutions with iron sulfides. The degree of trace metal pyritization, DTMP, has been determined for these metals and compared to the degree of pyritization, DOP. The findings suggest that in Authie-bay sediments Mn is well pyritized; whereas Zn, Cu, Ni and above all Cd are weakly pyritized (MnZn≃Cu>NiCd). These observations seem to be intimately related to the existence of the discrete/separate solid phases CuS, CdS and ZnS, as predicted by thermodynamic calculations. Finally, analysis of crude sediments, heavy minerals and pyrite extracted by a heavy liquid density separation method, has been performed with a Raman microprobe to gain information about the geochemical and mineralogical characteristics of these sediments. The efficiency of sequential leachings of sediments (which were used for sedimentary pyrite recovery/attack and analysis of pyritic Fe and trace metal) has also been evaluated by these techniques.

Os isotopic compositions of leachates and bulk sediments from the Bengal Fan

Os isotopic compositions and Os and Re concentrations were measured in H 2O 2—H 2SO 4 leachates and bulk sediment samples from Holes 717C and 718C of ODP Leg 116 in the Bengal Fan. Os isotopic results indicate that, at the sediment surface, the leachable Os fraction is derived from seawater. In contrast, leachable Os from Ganges River sediments has 187Os/ 188Os ratios [1] much higher than the marine value. This difference suggests that the leachable radiogenic Os carried by the river sediments is completely released to the oceans prior to sediment deposition in the Fan. A simple calculation, assuming these sediments to be typical of those delivered by the Ganges-Brahmaputra river system, suggests that this process can account for a substantial part of the rise in the seawater Os isotopic ratio observed over the past 16 m.y. Bengal Fan leachate 187Os/ 188Os ratios increase with increasing depositional age, in contrast to the seawater Os isotopic ratio, which decreases with increasing age. Several lines of evidence suggest that, at the time of sediment burial, the leachate Os compositions most likely reflected the seawater values. Thus, the current divergence is probably the result of post-depositional processes. One such process, in situ radiogenic ingrowth of 187Os, can be excluded because the measured Re concentrations of these sediments are too low. Similarly, since most of the bulk rock Os isotopic ratios were lower than those of the associated leachates, the high leachate 187Os/ 188Os values cannot be explained by in situ sediment alteration. Instead, it is proposed that the increase with age results from radiogenic Os brought in by thermoconvective circulation from further upslope in the Fan. The ultimate source of this 187Os would then be alteration of radiogenic sediments or post-depositional radioactive decay of Re in sediments rich in organic carbon. Finally, the divergence between the results obtained on Bengal Fan sediments and those obtained in the open ocean [2] by the same leaching technique suggest that Os sediment leachate data must be interpreted with caution.

The 36C1 ages of the brines in the Magadi-Natron basin, East Africa

The depression in the East African Rift which includes both Lake Magadi and Lake Natron forms a closed basin within which almost all the dissolved chloride originates in precipitation, since there is no important source of very ancient sedimentary chloride. This provides an ideal setting for the evaluation of the 36Cl methodology as a geochemical and hydrological tracer. The main source of recent water, as represented by the most dilute samples measured, is characterized by a 36C1/C1 ratio of 2.5 × 10 −14, in agreement with the calculated value expected in precipitation. Surface evaporation increases the chlorinity of the local freshwater inflow by about a factor of 110 without changing the isotopic ratio, indicating that little chloride enters the system in the form of sediment leachate. A second type of brine found in the basin occurs in a hot deep groundwater reservoir and is characterized by lower 36C1/C1 ratios (<1.2 × 10 -14). By comparing this value with the2.5× 10 −14 in recent recharge, one obtains an approximate salt accumulation age of 760 Ka which is consistent with the time of the first appearance of the lake. These older brines also have lower 18O and 2H values which indicate that they were recharged during a climatically different era. The 36C1/C1 ratios in the inflowing waters and in the accumulated brine, together with the known age of the Lake Magadi basin, may be used to estimate the importance of the hypogene and epigene, as opposed to the meteoric, mode of 36C1 production. Such a calculation shows that the hypogene and epigene processes together contribute less than 6% of the total 36C1 present in the lake.

A quantitative method for determination of trace metal concentrations in sedimentary pyrite

Trace metals commonly undergo chemical diagenesis in anoxic sediments from association with metal oxides, organic matter, and other reactive components to coprecipitates with authigenic pyrite. Whereas this process has long been recognized as a major aspect of trace metal diagenesis, no satisfactory method for quantifying trace metal concentrations in sedimentary pyrite has been available. We present a new method, derived from the Lord technique (as described in C.J. Lord, J. Sediment. Petrol., 52: 664–666), for the quantitative extraction of trace metals from sedimentary pyrite. The new method involves the sequential leaching of sediments using 1 M HCl (reactive fraction), 10 M HF (silicate fraction) and concentrated HNO 3 (pyrite fraction). Examples are presented of the application of this new method to trace metal diagenesis in two different sedimentary marine environments: Baffin Bay, TX, and the Mississippi Delta. To establish the relation between the transfer of Fe and the trace metal of interest to the pyrite phase, the degree of pyritization (DOP) was compared with the newly introduced degree of trace metal pyritization (DTMP). Results obtained by combining these two operationally defined parameters indicate that transition metals exhibit a trend of increasing DTMP with increasing DOP, whereas DTMP values for class B metals remain essentially constant with increasing DOP levels.

Artifacts associated with the chemical leaching of sediments for rare-earth elements

Using radioactive Eu as a tracer for rare-earth elements (REE), simple experiments were carried out to determine if an re-adsorption artifact occurs during the chemical leaching of marine sediments. Fourteen commonly used chemical leaching solutions were used with and without (controls) the presence of Buzzards Bay (Massachusetts, U.S.A.) sediment. All controls show 100% recovery of soluble 152Eu, indicating no adsorption or precipitation during handling. In contrast, almost all chemical leaching solutions show poor recoveries even at low (2–4) pH. Even for HCl and HNO 3, recoveries ranged from 25% to 85% at ≤ 0.2 M. Hydroxylamine hydrochloride in acetic acid, for example, shows only 33% and 57% recoveries for 0.02 M and 0.04 M concentrations, respectively. The results show that large-scale re-adsorption of REE onto sediments occurs even at low pH associated with mineral acids, organic chelators and reductive solutions. Given their large hydrolysis constants, a case is made that one would expect that REE, like Pb and Th, to exhibit significant re-adsorption onto sediments following their dissolution from specific phases. This result reinforces concerns in the literature that chemical leaching techniques have major artifacts associated with non-selectivity and re-adsorption of trace metals. Interpretations of REE diagenesis and authigenesis, based on chemical leaching data, should be viewed with caution.

Transport and release of transition elements during early diagenesis: Sequential leaching of sediments from MANOP Sites M and H. Part I. pH 5 acetic acid leach

Sediments from MANOP sites M and H in the eastern tropical Pacific Ocean can be partitioned into operationally defined phases by means of a sequential leach procedure. This paper reports the results of the first leach in the sequence, an acetic acid solution buffered as p H 5 with sodium acetate. This leach is designed to remove carbonate-bound and sorbed cations. The only cation bound in a consistent ratio to calcium in the carbonate is strontium. The molar ratio is 2 × 10 −3. In contrast, transition metals are sorbed onto the surfaces of other sedimentary particles. The proportions sorbed range from 2 to 10% of the total manganese, about 10% of the total nickel and copper, and less than 1% of the total iron. The pool of sorbed metals in surface sediments is sufficiently large and the rate of biological stirring is sufficiently rapid for this metal reservoir potentially to dominate the porewater reservoir in supplying metals to ferromanganese nodules. A simple model for nodule growth based upon transfer of metals through this reservoir suggests that only 1% of the sedimentary sorbed metals within a radius of 2 to 9 cm is required to support typical nodule growth rates.

Compressibility of distilled water and seawater

Dredged leachate sediments from eight MSW landfills were dried and homogenized, and metals sequentially extracted. The concentrations of cadmium (Cd), copper (Cu), chromium (Cr), iron (Fe), lead (Pb), manganese (Mn), nickel (Ni) and zinc (Zn) were found to be similar to those reported for sewage sludge, and generally below the EU limits for use of sludge on agricultural land. Sequential extraction of the samples showed that the largest fractions of the heavy metals were associated with Fe- or Mn-oxides. Cr and Cu were the only metals investigated that were associated with the organic matter in the sediments to any significant extent (2–10% of Cr and 10–28% of Cu). Since the largest fractions of the metals studied were bound to Fe-oxides, and thus had a low mobility, these metals will generally have a low bioavailability under aerobic conditions when present in leachate sediments. This is most likely also valid for particulate matter suspended in MSW landfill leachate and released to the environment, since this is the source of the sediments.