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After exposure for 21 d to sediment spiked with Cd, Pb, Cu, or Zn, oligochaetes (Lumbriculus variegatus) held in clean water depurated metal rapidly over the first few hours but much more slowly from 8 h up to 32 h. Results are consistent with previous work suggesting a 6-h depuration period as generally appropriate for sediment bioaccumulation studies with L. variegatus.
Estuarine sediments are frequently polluted with hydrocarbons from fuel spills and industrial wastes. Polycyclic aromatic hydrocarbons (PAHs) are components of these contaminants that tend to accumulate in the sediment due to their low aqueous solubility, low volatility, and high affinity for particulate matter. The toxic, recalcitrant, mutagenic, and carcinogenic nature of these compounds may require aggressive treatment to remediate polluted sites effectively. In petroleum-contaminated sediments near a petrochemical industry in Gwangyang Bay, Korea, in situ PAH concentrations ranged from 10 to 2,900 microg/kg dry sediment. To enhance the biodegradation rate of PAHs under anaerobic conditions, sediment samples were amended with biostimulating agents alone or in combination: nitrogen and phosphorus in the form of slow-release fertilizer (SRF), lactate, yeast extract (YE), and Tween 80. When added to the sediment individually, all tested agents enhanced the degradation of PAHs, including naphthalene, acenaphthene, anthracene, fluorene, phenanthrene, fluoranthene, pyrene, chrysene, and benzo[a]pyrene. Moreover, the combination of SRF, Tween 80, and lactate increased the PAH degradation rate 1.2-8.2 times above that of untreated sediment (0.01-10 microg PAH/kg dry sediment/day). Our results indicated that in situ contaminant PAHs in anoxic sediment, including high molecular weight PAHs, were degraded biologically and that the addition of stimulators increased the biodegradation potential of the intrinsic microbial populations. Our results will contribute to the development of new strategies for in situ treatment of PAH-contaminated anoxic sediments.
Based on the 1985 - 2003 fixed-position data in 9 runoff plots of Caijiachuan watershed in the Jixian county of Shanxi Province in loess area, this paper discussed the relationships between vegetation and runoff and sediment production on sloping lands of loess area. The results showed that natural-secondary forest had better function in soil and water conservation than artifical Robinia pseudoacacia forest, with runoff and sediment produced 65% - 82% and 23% - 92%, respectively. Multiple regression analysis indicated that runoff and sediment production had a significant correlation with rainfall and its intensity, but this relationship was decreased gradually with increasing canopy density. Different land-use type had different runoff and sediment production, e. g., Ostryopsis davidiana and natural-secondary forests had the least runoff and sediment production, artificial Robinia pseudoacacia and Pinus tabulaeformis forests had 5 folds of it as much as Ostryopsis davidiana forest, mixed apple trees and crops had 17.14 and 3.96 folds of it than Ostryopsis davidiana forest, respectively, while high-standard soil preparation could decrease the production obviously. Gray correlation analysis suggested that the stand canopy density and the biomass of herb and litter were the most important factors affecting the runoff and sediment production on sloping land, whose gray correlation degrees all exceeded 0.6. Mixed forest with multi-layer stand structure and shrub forest should be developed in vegetation re-construction of loess area, which could help to increase the coverage and litter thickness to dramatically decrease the runoff and sediment production on sloping land.
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The diffusive gradients in thin films technique (DGT) was used to measure depth profiles of mercury in river and marine sediments in situ to a spatial resolution of 0.5 cm. Agarose gel was used as the diffusive gel in the DGT probes. Two different selective resins-Chelex 100 with iminodiacetic groups and Spheron-Thiol with thiol groups incorporated in the polyacrylamide resin gel-were tested. The different capture efficiencies of the two adsorbents enabled the fractions of mercury bound in different species in sediment pore water to be estimated. Mercury concentrations obtained by DGT with Spheron-Thiol resin were very similar to those obtained after centrifugation. This indicates that DGT with Spheron-Thiol resin reports on total dissolved mercury levels. The concentration of mercury measured by DGT with Chelex-100 resin was much lower (by a factor of 5-20) for the same sediment samples. Chelex-100 does not have such a high affinity to mercury as Spheron-Thiol, and so it only reports on the content of labile mercury species, such as inorganic ions and weak complexes. The content of labile mercury species in the river sediment was approximately 20% of the total dissolved mercury in pore water, whereas in marine sediment only 7% of the mercury was present as labile species.
A wide range of estrogenic contaminants has been detected in the aquatic environment. Among these, natural and synthetic steroid estrogens, typically present in municipal sewage-treatment plant (STP) effluents, are the most potent. In this study a new GC-MS method has been developed for direct analysis of five major steroid estrogens (estrone, 17beta-estradiol, 17alpha-ethinylestradiol, dienestrol, and diethylstilbestrol) in river sediments. Four GC-MS systems used for analysis of underivatized analytes in purified extracts were compared. Relatively low detection limits (1.5-5 ng g(-1) dried sediment) and good repeatability of GC splitless injection (RSD 1-2%) were achieved by use of a system combining low-pressure gas chromatography with a single-quadrupole mass analyzer (LP-GC-MS). Use of orthogonal gas chromatography (GCxGC) hyphenated with high-speed time-of-flight mass spectrometry (HSTOF-MS) enabled not only significantly better resolution of target analytes, and their unequivocal identification, but also further improvement (decrease) of their detection limits. In addition to these outcomes, use of this unique GCxGC-TOF-MS system enabled identification of several other non-target chemicals, including pharmaceutical steroids, present in purified sediment extracts.
A method was developed for the simultaneous determination of 5 pyrethroid, 1 organophosphate, and 20 organochlorine pesticides in sediment. Pesticide residues were extracted using sonication with acetone-methylene chloride (1:1 vol/vol) and the extracts were subsequently cleaned with deactivated Florisil (magnesium silicate; U.S. Silica, Berkeley Springs, West Virginia). Gas chromatography with an electroncapture detector was used for analyte determination, and two columns were used for confirmation of the analytes. Four control sediments from different sources were spiked with a pesticide mix and analyzed for method validation. The method detection limits ranged from 0.22 to 0.85 microg/kg dry sediment. Recoveries for spiked samples at four concentrations (1, 5, 20, and 400 microg/kg dry sediment) were 71.9% to 129.8% with relative standard deviations (RSDs) < 11%. Taking the matrix effect into account, 1 microg/kg was chosen for the threshold of detection, but 0.5 microg/kg of spiked control sediment still provided good recoveries and RSDs. This method was validated using field-collected sediment taken from agricultural areas of Fresno County, California.