In the past two decades there has been an increasing public awareness of the hazards that exist from the contamination of the environment by toxic substances. 'Heavy metals' and the terrestrial environment are but one facet of the impact of toxic substances on the natural environment, and the use of biological materials for indicating the occurrence of, and continually monitoring the presence of, these materials is a specific topic which is of considerable interest to a diverse range of individuals, organisations and disciplines. It was our intention when we first en visaged this book that it should contain a description of a range of circumstances in which biological monitoring techniques have been employed in the terrestrial environment and that it should be seen as a practical text which dealt with the merits, shortcomings and suitability of biological monitoring materials. Monitoring is, however, a manifold process. It serves not only to provide information on past and present concentrations of toxic materials in various components of the environ ment, but also to provide information on the processes of environmental release, transport, accumulation and toxicity. Indeed, this may be one of the greatest virtues of biological monitoring over other forms of monitor ing. According to the skill of the staff employed in the monitoring procedure, the information that is accrued can have a vastly different value.

This companion volume to Biological Monitoring of Exposure to Chemicals: Organic Compounds presents recent results from both field and laboratory studies investigating the presence of metals and organometallic compounds in biological media. A distinguished list of contributors describe studies which assess the extent of human exposure to metals, and recount fundamental studies at the molecular level, such as investigation of immunotoxicological effects of the interaction of metals during absorption and biological transformation. There is also a study of the biological monitoring of environmental contamination that demonstrates how biological samples determine the transport and fate of metals in the environment.

This document is the result of a conference on "Biological Monitoring of Metals" held in Rochester, June 2-6, 1986, organized jointly by the Environmental Health Sciences Center of the School of Medicine and Dentistry of the University of Rochester, NY, and the Scientific Committee on the Toxicology of Metals within the International Commission on Occupational Health (ICOH) at the Karolinska Institute and the National (Swedish) Institute of Environmental Medicine and the University of Umea, Sweden. The aim of the Conference was to define and evaluate the scientific basis for the biological monitoring of metals. The conference was co-sponsored by the World Health Organization through its International Program on Chemical Safety and received substantial encouragement and support from the Swedish Work Environmental Fund and the United States Environmental Protection Agency. This was the second conference organized jointly by the Scientific Committee on the Toxicology of Metals and The Toxicology Division of the University of Rochester. The previous joint conference was held in 1982 on the Reproductive and Developmental Toxicity of Metals. In addition, conferences have been organized by each group (see Appendices A and B). Several of these conferences are specially relevant to the topic of the current conference. These include the joint conference mentioned above and the conferences on dose-effect and dose-response relationship held in Tokyo in 1974 and on accumulation of metals held in Buenos Aires in 1972.

A summary of data on heavy metal accumulation, biomonitoring, toxicity and tolerance, metal contamination and pollution in the environment, and the importance of biodiversity for environmental monitoring and cleanup of metal-contaminated and polluted ecosystems. It advocates the use of bacteria, mycorrhizae, freshwater algae, salt marshes, bryo- an

Trace metals occur as natural constituents of the earth's crust, and are ever present constituents of soils, natural waters and living matter. The biological significance of this disparate assemblage of elements has gradually been uncovered during the twentieth century; the resultant picture is one of ever-increasing complexity. Several of these elements have been demonstrated to be essential to the functions of living organisms, others appear to only interact with living matter in a toxic manner, whilst an ever-decreasing number do not fall conveniently into either category. When the interactions between trace metals and plants are considered, one must take full account of the known chemical properties of each element. Consideration must be given to differences in chemical reactivity, solubility and to interactions with other inorganic and organic molecules. A clear understanding of the basic chemical properties of an element of interest is an essential pre-requisite to any subsequent consideration of its biological significance. Due consideration to basic chemical considerations is a theme which runs through the collection of chapters in both volumes.