Transfer, sources and sinks for major and trace elements in urban and rural areas


BERNHARD SCHNETGER(1), HARTMUT HEINRICHS(2) and HANS-JÜRGEN BRUMSACK(1)
(1)Institute for Chemistry and Biology of the Marine Environment, University of Oldenburg,
(2)Geochemical Institute, University of Göttingen.

Introduction

In recent years much attention has been given to the determination of sources in the atmospheric particulates. It has been observed that urban particulates contain several toxic elements in concentrations that may influence the geocycle. To obtain an information about the sources and sinks of these materials and the mechanism of their removal from the atmosphere, the magnitude of anthropogenic sources must be known. For this reason city dust was analyzed and the sources for various elements were determined by modeling. Under the German DFG project "Case Study Harz Mountains" sinks and sources for atmospheric pollution were investigated.

Sources

Spider webs representing natural particle traps and air filter samples, collected in 11 urban areas in Germany from 1988 to 1991, have been analyzed for 40 elements to characterize urban particulates. The enrichment factors (EF) compared with the study of Lantzy and Mackenzie (1979) are of the same order of magnitude (Fig. 1). The close correlation between the two data sets implicates a similarity in the average chemical composition of urban particulates. Also the high EF of the elements point to a comparatively high and chemically similar anthropogenic component.


Fig. 1: Enrichment factors (Al-normalized) for urban particulates (Lantzy and Mackenzie (1979) and city dust (this work)


Urban particulate matter comprises motor vehicle emissions, abrasion of tyres and brake linings, paved road dust, abrasion of building, fly ash from coal, lignite and oil combustion, refuse incineration, cement and steel production, dust from crustal weathering, sea spray, plant detritus and additional sulfur and chlorine compounds of gas-phase

For identification of sources and calculation of fractions (results in Fig. 3a,b) we used receptor models that are based on an element mass balance taking into account the relative proportions of each source to a mixed sample. Calculated mixtures that fit best with the measured concentrations or enrichment factors in the bulk sample were determined (see box ).



Fig. 3a,b: Natural and anthropogenic sources of mineral material in city dust
(from Heinrichs 1993).



Sinks

It was found that the top soils of forested areas and lake sediments were enriched in heavy metals when compared with the natural background in this area. The mountain site forests of high atmospheric input and rocks low in carbonates are seriously damaged or in some cases completely destroyed. Protected sites or areas with rocks of higher acid neutralizing capacity are less vulnerable.

Remobilisation

An acidification front was observed which move from the high mountains downwards. In the damaged forested area, acidification of the soil mobilizes heavy metals into springs, tributaries and final deposition takes place in the sediments of a drinking water reservoir (lake Söse).
Till today the mobilisation of toxic elements from sediments of the drinking water reservoir did not occur. Extraction experiments have shown that most trace metals are ion-exchangeable and thus may potentially be released by acidification of the dam water, e.g. during snow melting in spring or during times of heavy raining.
This poster has been presented at the International Workshop on "Improvement of Environmental Transfer Models and Parameters" Tokyo, Japan, Feb. 5-6, 1996.
A paper with the same title was published in the associated Proceedings of this workshop and is available from B.Schnetger.