Application of differential pulse anodic stripping voltammetry to the determination of heavy metals in environmental samples.

A reliable procedure for the determination of the trace metals Cd, Cu, Ni, Pb and Zn in liquid and solid environmental samples by an advanced voltammetric method has been developed. A convenient method of sample pretreatment is wet digestion in a HNO3/HClO4 mixture. The simultaneous voltammetric determination of Cd, Cu, Pb and Zn is made at pH 2 by differential pulse anodic stripping voltammetry (DPASV); the simultaneous determination of Ni and Co at pH 9 after adsorptive accumulation of the respective complex with dimethylglyoxime at the electrode is made by adsorption differential pulse voltammetry (ADPV). The particular advantages of the voltametric approach in food control for heavy metals are high sensitivity, good precision and accuracy, the possibilities for the simultaneous determination of groups of metals and low cost instrumentation.

Levels of heavy metals in the tidal Elbe and its estuary and the heavy metal input into the sea.

Surface water samples were collected during missions in 1977, 1978, 1980 and 1983 at different sampling stations along the tidal Elbe, from river km 632 downstream from Hamburg to the outer end of the estuary. Special care was taken to minimize contamination during sampling, handling and analysis. Within the tidal Elbe five distinct zones of substantial anthropogenic heavy metal pollution inputs can be detected. An attempt is made to define anthropogenic background levels, which are extremely low for the dissolved trace metals Cd and Pb; 35 and 65 ng/kg, respectively. The level of dissolved Cu is 2200 ng/kg. Total baseline levels of Cd, Pb and Cu are, respectively, 120, 2500 and 4200 ng/kg. In the five river zones affected by anthropogenic trace metal inputs, distinctly larger maximum levels can occur. They decrease to the background values after mixing with the main water body. More elevated levels caused by re-suspension in the mixing zone with maximum turbidity can be assumed. Nickel and Co data are from one mission only. The order of magnitude of the trace metal input from the Elbe into the sea is evaluated.

Comparative studies on the distribution of heavy metals in the oceans and coastal waters.

Results of our investigations during the last five years are summarized. The concentrations of Cd, Pb and Cu have been determined in coastal areas of the Western Mediterranean and the North Sea, reflecting the influence of the pollution sources along the shore line. Deep sea water and surface water sample from the Pacific, Atlantic, Mediterranean and Arctic Sea have been analyzed for Cd, Pb, Cu and at some stations also additionally for Ni, Co. It is demonstrated that concentration levels of surface and deep sea waters may differ significantly in diverse oceans. The same is valid to a greater extent for coastal waters affected particularly by anthropogenic input that can be dispersed by tidal currents. Applying reliable sampling methods and the voltammetric determination procedure in particular suitable for heavy metals at the trace level, significant contributions to a consistent data basis for the distribution of heavy metals in the sea could be achieved.

Prenatal and early postnatal development of the glial cells in the median eminence of the rat.

The development of the glial cells of the rat median eminence (ME), including the supraependymal cells, was investigated from embryonic day (ED) 14 through postnatal day (PD) 7, and pituicyte development from ED 12 through ED 17. The anlage of the ME and neurohypophysis shows a neuroepithelial-like structure at ED 12. From ED 13 to 15, the cells of both regions start to differentiate. At the ultrastructural level, only one cell type appears. At the beginning of ED 16, glioblasts of the oligodendrocyte and astrocyte series migrate laterally (from the region of the arcuate nucleus) into the ME. Also at this time the first distinctive structural features appear in the neurohypophysial anlage, the cells of which later develop into pituicytes. Starting at ED 18, tanycytes and astrocytic tanycytes arise in the ME from local glial cells, and somewhat later oligodendroblasts and astroblasts are formed from immigrant glioblasts. Due to their common features, the pituicytes, tanycytes and astrocytic tanycytes apparently represent different forms of the same parent cell type. Microglial and supraependymal cells are first seen at ED 12. Initially, they resemble the prenatal phagocytic connective tissue cells and mature in fetus into typical electron-dense microglia and macrophage-like supraependymal cells. Both cell types are apparently of mesodermal origin. The microglial elements of the ME probably migrate from the mesenchyma through the basement into the nervous tissue. The intraventricular macrophages of the infundibular region may originate from microglia, epiplexal cells and subarachnoid macrophages.