The potential of tree-ring analysis for monitoring heavy metal pollution patterns

Abstract

The precise measurement of heavy metal levels within successive annual growth rings of trees presents, at first sight, an attractive and straightforward means for producing a detailed history of heavy metal pollution. However, before serious consideration is given to such a technique, many processes relating to the uptake, transport and deposition of heavy metals within trees must be understood. A brief survey of the pathways of metal uptake into trees is made, and consideration given to the external and internal factors which may operate in regulating metal entry. As the transport of metals within the tree is important, both pathways of metal transport, and the forms taken by metals during transport, are described. The regulation and patterns of metal deposition are fully considered, and emphasis is placed on internal factors which may regulate the rate of deposition, and the quantity of metal deposited, in a particular annual growth ring. The problem of possible lateral movement of metals between growth rings is also considered. Finally, conclusions are drawn regarding the potential of tree-ring analyses for producing pollution histories.