Aspen Bibliography

Suitability and use of poplars as bioindicators


H.J. Ballach

Document Type

Contribution to Book


Environ. Sci. & Pollut. Res.



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The introduction of the 3-way catalytic converter is presently being acclaimed by different sources in Germany as the solu- tion to the ozone problem. This hypothesis is viewed with scep- ticism: studies conducted in the USA, where the 3-way cata- lytic converter was introduced as early as 1975, show that the ozone problem has not been resolved by any means in that country. Moreover, the employment of the catalytic converter is associated with the emission of various elements occurring otherwise at extremely low background concentrations, e.g. the elements in the platinum group (Pt, Pd and Rh). A brief review of the literature reveals, for example, that platinum exhibited an unexpectedly high rate of accumulation in upper soil layers near highways in Germany within a few years of the introduction of catalytic converters.

The focus of this paper is on impact research. My own studies have shown that water-soluble Pt4. accumulates at a high rate in poplar roots. A six-week exposure of poplar cuttings to 34.8 ppb Pt4" results in disturbances affecting the water bal- ance of the plants and, in conjunctionwith this, typical symp- toms of moderate water stress. Cerium (Ce), another element released by catalytic converters, also displays a high degree of accumulation in plant roots. Water-soluble Pt4§ accumulates to an even greater degree in soil, giving rise to the following series arranged in order of decreasing affinity to platinum:soil > fine roots > coarse roots. In long-term experiments, even the metallic platinum contained in the active layer of catalytic converters accumulated in plant roots; the resulting distribu- tion among soil, fine roots and coarse roots was comparable to that of water-soluble platinum. Possible uptake mechanisms are discussed. The first results of this study indicate that plati- num apparently belongs to the elements with a strong affinity to humic matter, a fact which could possibly explain its espe- cially heavy accumulation in upper soil layers.