Large amounts of 137Cs have been accidentally released to the subsurface from the Hanford nuclear site in the state of Washington, USA. The cesium-containing liquids varied in ionic strengths, and often had high electrolyte contents, mainly in the form of NaNO3 and NaOH, reaching concentrations up to several moles per liter. In this study, we investigated the effect of ionic strengths on Cs migration through two types of porous media: silica sand and Hanford sediments. Cesium sorption and transport was studied in 1, 10, 100, and 1000 mM NaCl electrolyte solutions at pH 10. Sorption isotherms were constructed from batch equilibrium experiments and the batch-derived sorption parameters were compared with column breakthrough curves. Column transport experiments were analyzed with a two-site equilibrium-nonequilibrium model. Cesium sorption to the silica sand in batch experiments showed a linear sorption isotherm for all ionic strengths, which matched well with the results from the column experiments at 100 and 1000 mM ionic strength; however, the column experiments at 1 and 10 mM ionic strength indicated a nonlinear sorption behavior of Cs to the silica sand. Transport through silica sand occurred under one-site sorption and equilibrium conditions. Cesium sorption to Hanford sediments in both batch and column experiments was best described with a nonlinear Freundlich isotherm. The column experiments indicated that Cs transport in Hanford sediments occurred under two-site equilibrium and nonequilibrium sorption. The effect of ionic strength on Cs transport was much more pronounced in Hanford sediments than in silica sands. Effective retardation factors of Cs during transport through Hanford sediments were reduced by a factor of 10 when the ionic strength increased from 100 to 1000 mM; for silica sand, the effective retardation was reduced by a factor of 10 when ionic strength increased from 1 to 1000 mM. A two order of magnitude change in ionic strength was needed in the silica sand to observe the same change in Cs retardation as in Hanford sediments. 相似文献
Lake and brook bottom sediments were analyzed for chlorophenols to provide historical data of exposure assessment, after the water intake plant of a Finnish village had been found to be contaminated in 1987, and subsequently elevated non-Hodgkin lymphoma risk was detected. Highly elevated 2,3,4,6-tetrachlorophenol and pentachlorophenol levels were found in all four lake sediment cores investigated. The distribution was uneven with much higher concentrations in the estuary, in contrast to PCB compounds which were more evenly distributed within the basin. The inlet origin of the chlorophenols in the sediments was further supported by the regional distribution pattern of these compounds in the sediment and water along transects of the inlet and its tributaries. The composition of chlorophenol congeners in the sediments was similar to that in a commercial fungicide used by a local sawmill, but different from other sediment analyses reported in Finland, also implying a local source. Dating of three cores by Pb-210 and soot ball chronology indicated that the contamination of the watercourse started in the early 1970s at the latest but possibly earlier. This would provide the latency time required for tumour appearance in the 1970s and 1980s. 相似文献
Open-focused microwave-assisted extraction and ICP-OES determination of As, Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn from surface sediments of the estuary of Bilbao (Basque Country, North of Spain) was carried out. All the samples were collected at three different tributaries of the estuary (Asua, Galindo and Nerbioi-Ibaizabal) every two months during 1999. The digestion procedure was proposed from the conclusions of a fractionated factorial design, and the precision and accuracy of the method was verified using a certified reference sediment (RTC008-050). The results of the analysis were statistically treated by means of principal component analysis and correlation analysis. The principal component analysis of sediment data (32 samples × 9 metals) indicated different patterns of contamination regarding the tributary and sampling station. The two main patterns observed were a steady increment of the metal concentration along all the campaigns in the samples collected in the Galindo River and a seasonal variation in the Nerbioi-Ibaizabal River, with higher metallic content during summertime and lower content during wintertime. 相似文献
The desorption kinetics of in situ chlorobenzenes (dichlorobenzenes, pentachlorobenzene and hexachlorobenzene) and 2,4,4′-trichlorobiphenyl (PCB-28) were measured with a gas-purge technique for river Rhine suspended matter sampled in Lobith, The Netherlands. This suspended matter is the main source of sediment accumulation in lake Ketelmeer. In lake Ketelmeer sediment earlier observations showed that slow and very slow fractions dominate the desorption profile.
For the river Rhine suspended matter, only for PCB-28 a fast desorbing fraction of around 1.6% could be detected. The observed rate constants were on the average 0.2 h−1 for fast desorption, 0.004 h−1 for slow desorption, and 0.00022 h−1 for very slow desorption. These values are in agreement with previous findings for the sediment from lake Ketelmeer and with available literature data on fast, slow, and very slow desorption kinetics.
The results from this study show the similarity of desorption profiles between river Rhine suspended matter, and the top layer sediment from lake Ketelmeer. This indicates that slow and very slow fractions are already present in material forming the top layer of lake Ketelmeer, and were not formed after deposition of this material in the lake. The absence of detectable fast fractions for most compounds could be caused by the absence of recent pollution of the suspended matter. But, the observations may also be explained by a rapid disappearance of compounds from the fast fraction due to a combination of a high affinity of very slow sites for these compounds, and their relatively high volatility. 相似文献
Background Worldwide, large amounts of sediments have to be dredged annually from waterways and harbours. These sediments are sometimes
polluted with a variety of toxic compounds. In some countries, including Belgium, the load with the biocide tributyltin (TBT)
from ship coatings prohibits the dumping of harbour sludge into the sea. Land-based dumping is a commonly used alternative.
Objective This research investigated the feasibility to use land-deposited harbour sludge for plant production. In a field trial, the
growth of 38 more or less salt-tolerant plant species on low and high TBT-contaminated sediments was studied. The elimination
of TBT from sludge with and without vegetation was compared. The uptake of TBT and its degradation products di- and monobutyltin
(DBT and MBT) into harvest products under field conditions was determined.
- Experimental Set-up. Sediments dredged in May 2003 from the brackish waters of the port of Antwerp were analysed in the laboratory
for soil texture, pH, electroconductivity, sodium, magnesium, potassium, calcium, ammonium, nitrate, total nitrogen, chloride,
sulphur and the organotins TBT, DBT and MBT. The sediments were lagooned for one year to dewater, desalinate and improve their
structure. Salt-tolerant domestic and wild plants were selected and sown in May 2004. In August 2004, plants were harvested
and the produced biomass was determined. Samples were taken from vegetated and non-vegetated top and bottom sediments and
from plants growing above soil and analysed for TBT, DBT and MBT.
Results The fresh sediments showed a good supply with nutrients and a neutral pH, but were rather saline (EC 14 mS cm-1 of the saturated
paste extract). The salinity decreased to 3.7 mS cm-1 during lagoonation. The high and the low contaminated sediment had initially
43 and 1.6 mg TBT kg-1 dry weight, respectively. Besides TBT, several other contaminants were present in the sediments at
critical levels. The biomass production of the plant species from the field trial ranged from 0.2 to 13 tons dry mass per
hectare. Plants performing excellently were barley, sorghum, rape seed, a clover/grass mix and reed. If at all, a positive
influence of TBT on plant growth was seen. TBT was degraded significantly faster (>40%) below barley. The uptake of TBT, DBT
and MBT into stem and leaves of reed, grass and clover was very low, but measurable and not related to concentrations in soil.
No uptake of TBT or its metabolites into corn of barley was found.
Discussion This study confirmed former results: the toxicity of TBT to higher plants is low, and even high levels in soils would not
be a hindrance for crop production. The removal of TBT seemed to be increased by both lagooning and plant growth, although
the target values for sea dumping in use in certain European countries were not reached. A plausible explanation for the faster
degradation of TBT under vegetation is that oxygen is a limiting factor, and plants dewater the soil, thus aerating it. The
uptake of the organotins TBT, DBT and MBT into harvest products is probably due to attached soil particles.
Conclusions To summarize, barley was the optimal species: it grew very well despite the salinity of the dredged sediments, it had a significantly
positive effect on TBT removal; it showed no measurable uptake of TBT or the other butyltins into the harvested product; and
it is a cash crop well established in European agriculture.
Outlook The amounts of dredged sediments are high, and good soils are becoming increasingly rare. The feasibility of using dredged
sediments for non-food production, such as energy crops, should be investigated by a critical risk assessment. 相似文献