Temporal and spatial trends in heavy metal concentrations in the marine mussel Mytilus edulis from the Western Scheldt estuary (The Netherlands)

Since the first North Sea Conference (1984, Bremen), all countries bordering the North Sea made commitments to reduce discharge of hazardous substances into the North Sea. From Belgium and The Netherlands, large reductions (upto 90) in heavy metal emissions from land-based sources have been reported between 1985 and 2000. Recently, some studies in the Western Scheldt estuary (WS) have shown that total metal concentration in the water, sediments and suspended particles have decreased compared to levels in the 70s. However, data on aquatic organisms is still very limited and it is therefore difficult to confirm whether the reductions in pollution input and generally improving water quality in the WS have a corresponding impact on the levels of heavy metals in aquatic organisms. The current study measured metal concentrations in the soft tissues of mussels, Mytilus edulis (known to be good indicators of environmental metal pollution) during the period 1996–2002. Spatial (salinity and pollution gradients), temporal and seasonal variations were also studied. Results showed a down-stream decreasing trend for the metals studied (Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn) during all sampling campaigns. There was also a significant seasonal effect on tissue metal concentrations, with a peak observed around spring in both WS and the nearby less polluted Eastern Scheldt (ES). On temporal trends, a clear drop of metals in mussels was observed in the early 80s coinciding with the start of the efforts to reduce chemical pollution input into the North Sea. Since those early reductions, metal concentrations in mussels generally remained unchanged upto mid 90s. However, in recent times metal concentration in mussels have increased significantly, for example Cd in 2002 was almost 10 times the values in 1983 and similar to levels seen during the peak in the 70s. Other metals also increased in the 90s also reaching levels seen in the 70s. As there is no indication of recent increase in metal input into the estuary, we suggest that increased metal concentrations observed in mussels in recent years especially in the upper estuary are most likely a result of changes in physical and chemical speciation and metal bioavailability. Such changes may be caused by changes in some water quality parameters in the estuary (i.e. increased dissolved oxygen, concentration of organic matter), resulting in conditions that favour releases of sediment-bound metals into the water column. The relationship between metal content and season showed very similar annual profiles in the polluted WS and less polluted ES. Thus, seasonal variations in metal concentrations appear to be largely controlled by biological processes, while total body burdens are dependent on environmental levels and bioavailability.     

Establishment of the introduced kelp Undaria pinnatifida in Tasmania depends on disturbance to native algal assemblages

Despite recent rapid increases in the occurrence of nonindigenous marine organisms in the marine environment, few studies have critically examined the invasion process for a marine species. Here we use manipulative experiments to examine processes of invasion for the Asian kelp Undaria pinnatifida (Harvey) Suringar at two sites on the east coast of Tasmania. Disturbance to reduce cover of the native algal canopy was found to be critical in the establishment of U. pinnatifida, while the presence of a stable native algal canopy inhibited invasion. In the first sporophyte growth season following disturbance of the canopy, U. pinnatifida recruited in high densities (up to 19 plants m⁻²) while remaining rare or absent in un-manipulated plots. The timing of disturbance was also important. U. pinnatifida recruited in higher densities in plots where the native canopy was removed immediately prior to the sporophyte growth season (winter 2000), compared with plots where the canopy was removed 6 months earlier during the period of spore release (spring 1999). Removal of the native canopy also resulted in a significant increase in cover of sediment on the substratum. In the second year following canopy removal, U. pinnatifida abundance declined significantly, associated with a substantial recovery of native canopy-forming species. A feature of the recovery of the native algal canopy was a significant shift in species composition. Species dominant prior to canopy removal showed little if any signs of recovery. The recovery was instead dominated by canopy-forming species that were either rare or absent in the study areas prior to manipulation of the canopy.     

Presence of single-stranded DNA in PCR products of slow electrophoretic mobility.

PCR products were characterized by electrophoresis, blotting and hybridization. In addition to the bands of expected size, bands of slower electrophoretic mobility were often detected. The slower bands completely disappeared when the PCR products were subjected to slow cooling, treated with S1 nuclease or run on an alkaline gel, whereas the bands of expected size were unaffected. The slower bands are therefore likely to contain single-stranded DNA.     

Characteristics of a pyrimidine-specific 5'-nucleotidase in human erythrocytes.

A 5'-nucleotidase with unique specificity has been identified in the soluble fraction of normal human erythrocytes. It mediates the hydrolytic dephosphorylation of pyrimidine 5'-ribosemonophosphates but is catalytically ineffective with purine nucleotides or with the 2'-, 3'-, or cyclic isomers of pyrimidine nucleotides. Activities at 37 degrees in dialyzed hemolysates of nromal human erythrocytes averaged 7.3 and 6.2 mumol of Pi liberated per hour per g of hemoglobin for the substrates UMP and CMP, respectively. Activity with TMP as substrate was approximately one-half as much as with UMP or CMP. Apparent Michaelis constants were 0.33 mM UMP, 0.15 mM CMP, and 1.0 mM TMP. Magnesium was required for optimal activity, and this cation could not be replaced by Mn2+. Maximum activity was obtained between pH 7.0 and 7.5 with rapid decreases in more alkaline media and moderate decreases with acidification. The enzyme was quite sensitive to heat and was strongly inhibited by AMP, by some purine bases, and by both purine and pyrimidine nucleosides. Divalent cations of heavy metals were also strongly inhibitory, as were agents active against sulfhydryl groups. The presence of substrates and/or 2-mercaptoethanol provided considerable protection against some of these deleterious agents and conditions. Pyrimidine 5'-nucleotidase activity in hemolysates was clearly distinguishable from erythrocyte acid phosphatase and from leukocyte and serum alkaline phosphatases and nucleotidases.     

An empirical analysis of the factors contributing to 20-year decrease in soil pH in an old-field plantation of loblolly pine

The pH of weak-acid solutions is controlled by acid concentration (HA + A^–), the degree of acid dissociation (A^–/HA), and the strength of the acids present (pK_a). We developed an empirical approach that allows the relative importance of each of these factors to be estimated for soils. This empirical model was applied to soils collected from an old-field plantation of loblolly pine (Pinus taeda L.) at 5 and 25 years of age. During this period, soil pH dropped by 0.3 to 0.8 units, and extractable calcium, magnesium and potassium declined by 20 to 80%. The empirical model indicates that the decline in pH resulted largely from the reduction in base saturation of the exchange complex. However, the average acid strength of the exchange complex decreased during the 20 years, preventing a greater decline of perhaps 0.1 to 0.2 units in the observed pH. The rate of decrease in the acid neutralizing capacity to pH 3.5 was about 1.3 kmol_c/ha annually, while the increase in base neutralizing capacity was about 2.7 and 1.6 kmol_c/ha annually to pH 5.5 and 8.2, respectively. Extractable alkali and alkaline earth cations declined by about 2.2 kmol_c/ha annually, matched by the rate of increase in aluminium. These changes demonstrated the dynamic nature of poorly buffered soils, and indicated that changes in soil acidity may be expected over a period of decades (especially following changes in land-use).     

A second nonrandom translocation, der(16)t(1;16)(q21;q13), in Ewing sarcoma and peripheral neuroectodermal tumor

The majority of Ewing sarcomas and peripheral neuroectodermal tumors (PNET) that have been karyotyped contain a specific translocation, t(11;22)(q23;q11). We report here a second nonrandom translocation, der(16)t(1;16)(q21;q13), in 2 of 20 cases of Ewing sarcoma (seven previously unreported) and 2 of 7 cases of PNET (all previously unreported). All cases with this translocation also contained the t(11;22). Comparison of C-banding patterns in tumor and peripheral lymphocyte karyotypes in one case indicated that the likely breakpoints were 1q21 and 16q13. The presence of this translocation in cell lines will enable further investigation of the molecular events important in the pathogenesis of Ewing sarcoma and PNET.     

Genomic organization, chromosomal localization, and independent expression of human cyclin D genes.

Murine cDNA clones for three cyclin D genes that are normally expressed during the G1 phase of the cell cycle were used to clone the cognate human genes. Bacteriophage and cosmid clones encompassing five independent genomic loci were partially sequenced and chromosomally assigned by an analysis of somatic cell hybrids containing different human chromosomes and by fluorescence in situ hybridization to metaphase spreads from normal peripheral blood lymphocytes. The human cyclin D1 gene (approved gene symbol, CCND1) was assigned to chromosome band 11q13, cyclin D2 (CCND2) to chromosome band 12p13, and cyclin D3 (CCND3) to chromosome band 6p21. Pseudogenes containing sequences related to cyclin D2 and cyclin D3 mapped to chromosome bands 11q13 and 6p21, respectively. Partial nucleotide sequence analysis of exons within each gene revealed that the authentic human cyclin D genes are more related to their mouse counterparts than to each other. These genes are ubiquitously transcribed in human tumor cell lines derived from different cell lineages, but are independently and, in many cases, redundantly expressed. The complex patterns of expression of individual cyclin D genes and their evolutionary conservation across species suggest that each family member may play a distinct role in cell cycle progression.     

An interspecies comparison of normal levels of glycosylated hemoglobin and glycosylated albumin

Aminophenylboronic acid affinity chromatography was used to measure glycosylated hemoglobin and glycosylated albumin levels in a variety of species. The highest glycosylated hemoglobin levels were found in man, the lowest in the chicken and the pig. The highest glycosylated albumin levels were found in avian species, the lowest in the mouse and the rat. A simple kinetic model was used to analyze the rates of formation of glycosylated hemoglobin and albumin in the various species. Rates of glycosylated albumin formation were very similar across the species while rates of glycosylated hemoglobin formation were quite different, presumably reflecting wide differences in erythrocyte permeability to glucose among the species.