Plants as Monitors of Soil Contamination

Abstract

Assessing the potential of plants for monitoring heavy metal contamination of the environment, whatever the source, includes a thorough understanding of the processes that are involved in metal uptake by plants from soil. This understanding is essential even when rooted plants are to be used as monitors of air pollution, since it is often difficult to distinguish between the relative proportions of a total plant metal content that are derived from either aerial or soil sources. The following main processes are involved in soil-plant relationships:

• (1) Mechanisms of metal movement within soil; including diffusion, mass-flow, chemical exchange and complexing.

• (2) The distribution of the metal within an individual soil profile in relation to its chemistry within soil.

• (3) Mechanisms of metal uptake by plant roots in relation to root distribution in soil; including root structure and physiology, passive versus metabolic uptake, involvement of other ions, water relations and micro-organisms.

• (4) Translocation of metals from roots to shoots in relation to plant growth and development.

• (5) Translocation of metals within above-ground parts of plants in relation to metabolism, growth and development.

• (6) Loss of metals from plants via senescence, leaf-fall, leaf-leaching, exudation and volatilisation.