Concentration and annual accumulation values of heavy metals in lake sediments: Their significance in studies of the history of heavy metal pollution

The first part of the paper discusses the significance of using either concentration or accumulation values for expressing the results of investigations of lake sediment cores aimed at studying the history of heavy metal pollution. Neither the values for heavy metal concentration in the lake sediment, whether expressed per gram dry sediment or per gram soluble (organic) sediment, nor the values for their total annual accumulation per unit area of the lake bottom, can, on their own, provide an accurate picture of past pollution conditions, but when considered in combination they render a fairly reliable and detailed interpretation. The second part of the paper deals with Pb, Cd and Hg analyses of cores of varved sediments from several lakes in N. Sweden. Pb and Cd pollution increased during the second half of the 19th century. In most lakes, Hg pollution seems first to have started during the 20th century. Marked increases in both concentration and accumulation of heavy metals took place during the 20th century. For recent decades, the estimated accumulation rates of heavy metals from anthropogenic sources are: Pb 0.5–1.5 µg cm^–2 yr^–1, Cd 15–30 ng cm^–2 yr^–1 and Hg 1–2 ng cm^–2 yr^–1, Higher values were recorded in lakes affected by local emissions.     

Viable endospores of Thermoactinomyces vulgaris in lake sediments as indicators of agricultural history.

Bacteria of the genus Thermoactinomyces form endospores with an extreme longevity in natural habitats. We isolated Thermoactinomyces sacchari from 9,000-year-old varved (annually laminated) sediment; thus, T. sacchari is probably one of the oldest known living organisms. More importantly, we tested and verified the hypothesis that there is a relationship between concentrations of dormant, viable endospores of T. vulgaris in lake sediments and the extent of agriculture in the catchments of the lakes. In surface sediments, low concentrations were recorded in forest lakes and the concentrations increased with increasing areas of cultivated land around the lakes. In varved sediment cores from three lakes, we found a temporal relationship between records of T. vulgaris endospores and the pollen of plants indicating agriculture. Endospores were very rare in sediments deposited before agriculture, ca. 1100 A.D. From then to between 1300 and 1700 A.D., a period with restricted cultivation, low but more regular rates of accumulation of endospores were recorded. High endospore accumulation rates were found with the subsequent agricultural expansion. This investigation confirms suggestions that this bacterium could be used as a paleoindicator for agricultural activity and be complementary to pollen analyses. Viable bacteria in continuous records of lake sediments are also potential material for evolutionary studies.     

Photographic demonstration of the annual nature of a varve type common in N. Swedish lake sediments

Several lakes in northern Sweden have laminated sediments, of which many are interpreted as varved (annually laminated). In one of these lakes, a core of the recent sediment has been sampled annually since 1979 (except 1984). These cores verify that one varve, comprising of a thick summer layer (often colour-banded) and a thin winter layer, is formed each year. The cores also show, that, other than compaction, no change in visual appearance of the individual varves takes place after they have been overlain by new varves.     

Affibody protein capture microarrays: synthesis and evaluation of random and directed immobilization of affibody molecules

Affibody molecules, 58-amino acid three-helix bundle proteins directed to different targets by combinatorial engineering of staphylococcal protein A, were used as capture ligands on protein microarrays. An evaluation of slide types and immobilization strategies was performed to find suitable conditions for microarray production. Two affibody molecules, Z(Taq) and Z(IgA), binding Taq DNA polymerase and human IgA, respectively, were synthesized by solid phase peptide synthesis using an orthogonal protection scheme, allowing incorporation of selective immobilization handles. The resulting affibody variants were used for random surface immobilization (through amino groups) or oriented surface immobilization (through cysteine or biotin coupled to the side chain of Lys58). Evaluation of the immobilization techniques was carried out using both a real-time surface plasmon resonance biosensor system and a microarray system using fluorescent detection of Cy3-labeled target protein. The results from the biosensor analyses showed that directed immobilization strategies significantly improved the specific binding activity of affibody molecules. However, in the microarray system, random immobilization onto carboxymethyl dextran slides and oriented immobilization onto thiol dextran slides resulted in equally good signal intensities, whereas biotin-mediated immobilization onto streptavidin-coated slides produced slides with lower signal intensities and higher background staining. For the best slides, the limit of detection was 3 pM for IgA and 30 pM for Taq DNA polymerase.     

Fluorescence resonance energy transfer-based detection of analytes using antiidiotypic affinity protein pairs

A new method for specific detection of proteins based on fluorescence resonance energy transfer (FRET) using affinity proteins (affibodies) derived from combinatorial engineering of Staphylococcal protein A has been developed. Antiidiotypic affibody pairs were used in a homogeneous competitive binding assay, where the idiotypic, target-specific affibody was labeled with fluorescein and the antiidiotypic affibody was labeled with tetramethylrhodamine. Intermolecular FRET between the two fluorescent probes was observed in the antiidiotypic affibody complex, but upon addition of target protein the antiidiotypic affibody was displaced, which was monitored by a shift in the relative emission of the donor and acceptor fluorophores. The feasibility of the system was demonstrated by the detection of IgA and Taq DNA polymerase with high specificity, using two different antiidiotypic affibody pairs. Detection of Taq DNA polymerase in 25% human plasma was successfully carried out, demonstrating that the method can be used for analysis of proteins in samples of complex composition.     

Sedimentary records of carbonaceous particles from fossil fuel combustion

Carbonaceous particles produced by fossil fuel combustion can be found in considerable amounts in recent lake sediments. As these particles contain elemental carbon they are resistant to chemical decomposition and therefore both well preserved in sediments and possible to quantify. Sediment samples can be oxidized with H₂O₂ and digested with HF without the particles being destroyed. The pioneers in studying carbonaceous particles in lake sediments in relation to fossil fuel combustion were J. J. Griffin and E. D. Goldberg. They measured elemental carbon concentrations in Lake Michigan sediments, mainly by infrared assay. On the basis of these analyses, size distribution measurements and also morphological studies of single particles they concluded that the carbonaceous particle record reflected the onset of industrial activity and the increased intensities of fossil fuel combustion during the twentieth century. Similar results have been obtained from another lake in the USA by B. K. Kothari and M. Wahlen. We have counted spherical carbonaceous particles (larger than 5–10 µm), which are characteristic for oil and coal burning, in several lake sediments. In Swedish lakes, the annual accumulation of coarse carbonaceous spheres in varved sediments and the concentration stratigraphy in non-varved sediments, follow the same main pattern as statistical data for the Swedish coal and oil combustion over the last two centuries. Coarse carbonaceous spheres in two sediment profiles from Scottish lakes have also been counted. As for the USA and Sweden the sedimentary record was found to reflect the history of fossil fuel combustion.     

Chlorinated phenoxyacetic acids and chlorophenols in the modified Allium test

The chlorinated phenoxyacetic acids 2-methyl-4-chlorophenoxyacetic acid (MCPA), 2,4-dichlorophenoxyacetic acid (2,4-D), 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) and 2,4,5-T butoxyethyl ester and the chlorophenols 2,4-dichlorophenol and 2,4,5-trichlorophenol were tested for genotoxicity in the modified Allium test, which is based on exposure to the test chemicals of growing onions. The mean length of growing roots were measured and chromosome damage was recorded. Of the substances tested, MCPA was the most toxic and the chlorophenoxyacetic acids were more toxic than the chlorophenols. The lower threshold values for growth retardation were below 0.1 ppm for the acids, approx. at 0.1 ppm for the ester and less than 5 ppm for the phenols. Though a monocotyledon, Allium cepa was sensitive enough to respond to even low concentrations of these dicotyledon-selecting pesticides.     

Viable endospores of Thermoactinomyces vulgaris in lake sediments as indicators of agricultural history

Bacteria of the genus Thermoactinomyces form endospores with an extreme longevity in natural habitats. We isolated Thermoactinomyces sacchari from 9,000-year-old varved (annually laminated) sediment; thus, T. sacchari is probably one of the oldest known living organisms. More importantly, we tested and verified the hypothesis that there is a relationship between concentrations of dormant, viable endospores of T. vulgaris in lake sediments and the extent of agriculture in the catchments of the lakes. In surface sediments, low concentrations were recorded in forest lakes and the concentrations increased with increasing areas of cultivated land around the lakes. In varved sediment cores from three lakes, we found a temporal relationship between records of T. vulgaris endospores and the pollen of plants indicating agriculture. Endospores were very rare in sediments deposited before agriculture, ca. 1100 A.D. From then to between 1300 and 1700 A.D., a period with restricted cultivation, low but more regular rates of accumulation of endospores were recorded. High endospore accumulation rates were found with the subsequent agricultural expansion. This investigation confirms suggestions that this bacterium could be used as a paleoindicator for agricultural activity and be complementary to pollen analyses. Viable bacteria in continuous records of lake sediments are also potential material for evolutionary studies.