AIR HYGIENE REPORT no. 10
Contents

I INTRODUCTION

1 Background

In 1986, the Monitoring and Assessment Research Centre, MARC, at King's College London - University of London, supported by United Nations Environment Programme, prepared and published a technical report on Biological Monitoring of Environmental Contaminants Using Plants (Burton, 1986). This report highlighted in detail the increasing awareness of the effects of pollutants on plants and their potential as biomonitors/bioindicators of air pollutants in the terrestrial environment.

Physico-chemical measurement of air pollution levels is an objective and accurate method. It is essential for the accumulation of air quality data for the analysis of standards, interrelating effects, source reductions and general air pollution control. This enables the formulation of policies and regulations necessary for the protection of humans, animals and plants.

The response of plants to elevated concentrations of air contaminants is modified by other environmental factors and by the physiological status of the plant. Monitoring the plants directly assesses the integrated effects of these factors and contamination. Tingey (1989) emphasised that "there is no better indicator of the status of a species or a system than the species or system itself". Physical and chemical methods do not provide sufficient information on the risk associated with an exposure.

In contrast, biological methods allow direct assessment of risk from an exposure. Biological data can be used to estimate the environmental impact and potential impact on other organisms including humans. Often biological data have not necessarily been collected continuously, instead this can be performed periodically. Biological monitoring is generally less expensive than other methods and is thus particularly suitable for long-term monitoring over large areas without deploying sophisticated and high maintenance equipment. Biological monitoring has been defined as "the systematic use of biological responses to evaluate changes in the environment with the intent to use this information in a quality control programme. These changes often are due to anthropogenic sources ..." (Matthews, 1982). Biological monitoring of air pollutants can be passive or active. Passive methods observe plants growing naturally within the area of interest. Active methods detect the presence of air pollutants by placing test plants of known response and genotype into the study area.

A distinction is increasingly being made between using organisms as bioindicators and biomonitors in air pollution studies. According to Tingey (1989) "a bioindicator is an organism or biological response that reveals the presence or absence of an air pollutant by the occurrence of typical symptoms or measurable responses. A biomonitor provides information on the presence of the pollutant and attempts to provide additional information about the amount and intensity of the exposure." Similar definitions were outlined by Market et al. (1997).

The concept of bioindicators is of central importance in biological monitoring. Certain plant species are highly sensitive to particular air pollutants and show specific responses to pollution effects (for example the formation of brown upper surface speckle by ozone). These indicator species can be used to detect, recognise and monitor the presence or absence of pollutants. Considerations in bioindicator selection are summarised by Tingey (1989) and are presented in Box 1.1.

Bioaccumulative indicators are frequently regarded as biomonitors. Plants can also act as bioaccumulative indicators by accumulating air pollutants from their surroundings without necessarily displaying an obvious response. Analysis of their tissues provides an estimate of environmental concentrations of the pollutants (for example mosses are frequently used to monitor heavy metal deposition).

The earliest and currently most recognised effects of atmospheric pollutants on plants was revealed by correlations between plant species distributions with particular pollutants. A common example was the discovery of 'lichen deserts' in parts of the UK.

2 Project scope

The current project builds on these aspects of biological monitoring and updates and reviews progress in this topic over the past ten years. Activity in this field has accelerated over the last decade with the development of internationally co-ordinated monitoring networks, unilateral long-term monitoring research programmes in addition to new legislation. In general, investigations, which examine effects, which are not suitable for monitoring purposes, have not been considered in this review. There is a growing awareness of the importance of particular plant groups and communities in their own right and a vast amount of literature is concerned with impact assessments of air pollution on plants. The significance of such studies is appreciated but the current review focuses on biological monitoring as a practical management tool in detecting and assessing air pollution.

The review divides each chapter by pollutant type since methods used are generally dependent on the type of pollution under investigation. For this purpose, air pollutants are categorised into metals, gaseous and organic compounds. Heavy metals are generally non-acidic particulates and include lead, zinc etc. Gaseous pollutants included nitrogen oxides, sulphur dioxide, ozone (volatile organic compounds and nitrogen oxides, once emitted, undergo chemical transformation in the atmosphere in the presence of sunlight to form ozone) and fluoride. Organic and synthetic chemicals include substances such as dioxins, polycyclic aromatic hydrocarbons and organochlorines. Radionuclides and the indirect impact of air pollution - acidification of soil and water, will not be considered in the current review.

Each chapter is subdivided into plant groups. The review includes all plant species, which are currently or have potential of being used as biomonitors/bioindicators of air pollution. These will primarily be lichens, bryophytes (i.e. mosses), higher plants (such as trees, shrubs and crops), algae and fungi. Where applicable, comments on monitoring design are included in each section.

The review focuses exclusively on terrestrial environments omitting freshwater or marine habitats.

3 References

Burton, M.A.S. 1986 Biological monitoring of environmental contaminants (plants). MARC Report Number 32. Monitoring and Assessment Research Centre, King's College London, University of London.

Matthews, R.A., Buikema, Jr. A.L., Cairns, Jr. J. and Rodgers, Jr. J.H. 1982 Biological monitoring. Part IIA. Receiving system functional methods, relationships and indices. Water Research, 16, 129-139.

Market, B., Oehlmann, J. and Roth, M. 1997 General aspects of heavy metal monitoring by plants and animals. In: Environmental monitoring: Exposure, assessment and specimen banking, Subramanian, K.S. and Lyengar, G.V. (eds.), ACS Symposium series 654. American Chemical Society.

Tingey, D.T. 1989 Bioindicators in air pollution research - applications and constraints. In: Biologic markers of air pollution stress and damage in forests, Committee on biological markers of air pollution damage in trees. National Research Council, National Academy Press, Washington D.C.

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