D. H. Brown

Mineral Cycling and Lichens: The Physiological Basis

A number of physiological processes relevant to the role of lichens in mineral cycling are discussed. Consideration is given to the cellular location of positively-charged cations, showing (a) the benefits of quantifying intracellular elements for the interpretation of toxic metal stress, and (b) how distribution patterns of physiologically essential elements may be altered by desiccation and rehydration under field and laboratory conditions. The quantitative significance of these dynamic processes associated with metal uptake and loss requires verification under field conditions. A modified sequential elution procedure is proposed that enables quantification of insoluble paniculate mineral matter (acquired by wet and dry deposition) in addition to soluble elements in intercellular, extracellular-exchangeable and intracellular sites.

The Monitoring and Risk Assessment of Zn Deposition Around a Metal Smelter in Latvia

Heavy metal concentrations in Hylocomium splendens collected around a metal smelter in Latvia showed very high concentrations of Zn (>200 μg/g), and elevated concentrations of Pb (38.3 μg/g) and Cu (18.3 μg/g). In an attempt to better evaluate the potential toxicity of the high Zn concentrations, a serial elution method was used to determine the concentrations of zinc in intercellular, extracellular exchangeable cell wall, intracellular, and particle fractions. The intercellular Zn concentrations represent the water soluble component of the total concentrations, and were low with no clear trends. Zn concentrations in the extra- and intracellular and particle fractions decreased exponentially from the pollutant source. Intracellular Zn concentrations in moss close to the emission source are within the range considered to be potentially toxic, from other single element exposure studies. The proportion of Zn in the relatively insoluble particle fraction, which is least associated with environmental risk, was greater closer to the pollution source, reaching > 30% in the oldest Hylocomium splendens segments.