Revival: Biogeochemistry of Trace Metals (1992)

Advances In Trace Substances Research

Domy C. Adriano

• Publisher: CRC Press
• Year: 2017
• ISBN:
  9781351368056
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Geology & Earth Sciences

Biogeochemistry of Trace Metals is a compendium of the most recent information available on the effects of trace metals in soil quality and its potential threat on the transfer of these contaminants to consumers. Most of the chapters in the book were presented as papers during the First International Conference on the Biogeochemistry of Trace Elements (formerly Metals in Soils, Plants, Waters, and Animals) held in Orlando, Florida in May, 1990. Topics discussed include background levels of metals in soils and/or plants (covering western Europe; temperate, humid Europe; and the People's Republic of China); metal cycling and transfer in the food chain in agroecosystems; uptake and accumulation of metals by bacteria, fungi, and invertebrates; mechanistic aspects of metals; the microbial aspects of soil selenium losses; and manganese sorption on soil constituents.

1
Trace Metals in the Environment: Retrospect and Prospect*

Brian Ε. Davies

Department of Environmental Science, University of Bradford, Bradford, West Yorkshire, BD7 1DP, England

Abstract

Progress made in understanding trace metals in the environment is reviewed, especially over the last 30 years. The main focus is research in soils, plant uptake, and implications for human health. Until the 1960s the major concern was micronutrient research. Since then, the subject has broadened to encompass excess concentrations of both micronutrients and toxic trace metals. Despite a great increase in our understanding of these metals, there are still important questions unanswered. These include establishing a sound basis for sampling soils, sample treatment, and data handling. There is a need to establish background concentrations of trace metals locally, regionally, and nationally. Our understanding of the composition and dynamics of the soil solution is far from satisfactory, especially in terms of its role as a supplier of nutrient ions. Present models for predicting plant uptake from soils are too simple, and more complex models are needed. More generally, trace metal research is still dominated by fact-finding, and insufficient emphasis is given to hypothesis testing and to predictive modeling. There is a lack of agreement on a rigorous definition of technical terms in common use. Although much is now known of the health effects of environmental levels of cadmium and lead, the more general impact of environmental concentrations of trace metals on health has been neglected.

Introduction

Trace metals, or more generally, trace elements, are now extensively researched in the life, agricultural, and environmental sciences. But widespread interest in trace metals has emerged from academic obscurity only over the last 25 to 30 years; essentially it is a post-World War II (1939-1945) subject. This shift in emphasis can be exemplified by comparing the 7th edition of Russell's classic text, Soil Conditions and Plant Growth (1937)¹ with the current 11th edition.² The former described, in a few paragraphs, boron, manganese, iron, and other trace metals as only having "stimulative and prophylactic effects" on plant growth, whereas the latter devotes a whole chapter (34 pages) to "Micronutrients and Toxic Elements."

It is important to understand something of the historical development of any subject in order to identify its major research topics, to describe their development, and, hence, to suggest the priorities of the future. We are probably too close in time to many of the major developments in trace metal research for a balanced history to be written; nonetheless, by trying to understand where we have come from we can better plan where we might go. I am primarily concerned in this chapter with trace metals in soils and plants since this is my own subject. My knowledge of trace elements in aquatic ecosystems or in animal or human health is not sufficiently detailed to allow me to attempt a valid synopsis: for animals and people a useful review has been provided by Mertz.³ Furthermore, the account which follows is not intended as an exhaustive review of the literature. It is the personal (perhaps idiosyncratic) view of someone who has been active in this field of research for some 25 years and has had the privilege of meeting many of the workers whose papers are cited. It is intended as a contribution to debate.

Historical Retrospect

The 1920s and 1930s were the years when the essentiality of trace metals for higher plants was of great interest for physiologists. Indeed, the rules for designating an element as essential were drawn up by Arnon and Stout⁴ at the end of that period. In the same decades, agronomists were describing the plant diseases or growth defects which were seen when elements such as boron or zinc were in restricted supply in agricultural or horticultural soils. But it was probably the wartime demands for greatly increased crop production that led to more and more areas of soil being identified where low concentrations of trace elements were limiting yields. The first major text devoted to trace elements in plants and animals was that of Stiles.⁵ Writing in the early 1940s, he observed that no copper deficiency diseases of plants were known to occur in Britain, yet within a few years that was no longer so. Caldwell⁶ described how the first case of copper deficiency in English agricultural crops was encountered in cereals in 1946 and 1947 on a reclaimed deep peat. He wrote, "In subsequent years many areas of deficiency were found ... in all the fenland counties." Thus we see how the imperatives for much increased food production in the 1940s led to the reclamation of peat lands with inherently low copper contents, the more intensive use of other soils made heavy demands on the ability to provide nutrients, and the marginal supply situation for micronutrients became evident. Now, copper problems for both crops and animals are widely recognized throughout the British Isles, as are deficiencies of other micronutrients. Tinker⁷ suggested that trace element deficiencies were a considerable but not excessive problem for British agriculture, and his rough estimate of the total annual cost of micronutrient fertilizers and sprays was between 2.5 and 3 million pounds sterling, "which is appreciable, even if far less than that of the major elements."

There are nine trace elements which are commonly accepted as micronutrients for higher plants, namely, boron, chlorine, copper, iron, manganese, molybdenum, nickel, sodium, and zinc. The situation for cobalt, iodine, silicon, and vanadium is equivocal. The essentiality for six was established before 1940: Mn by McHargue,⁸ Β by Warrington,⁹ Zn by Sommer and Lipman,¹⁰ Cu by Lipman and MacKinney¹¹ and independently by Sommer,¹² and Mo by Arnon and Stout.⁴ In the postwar period, the essentiality for CI was demonstrated by Broyer et al.,¹³ for Na by Brownell and Wood,¹⁴ and for Ni by Eskew et al.¹⁵ It is curious that, despite the rapidly growing interest in trace metals in the environmental and life sciences, little effort is apparently being put into deciding the essentiality or otherwise of other elements. Moreover, although nearly 70 years have lapsed since boron was established as an essential micronutrient, we still have no clear understanding of its role in plant metabolism. For bacteria and fungi, micronutrient and trace metal research are still in their infancy. The situation for plants contrasts with that for animals, where 14 trace elements (Si, V, Cr, Μn, Fe, Co, Ni, Cu, Zn, As, Se, Mo, I, and F) are recognized as essential; 7 were identified in the period 1950 to 1980.^3,16

The postwar period has seen a growing concern with excess concentrations of a number of elements in the environment as a consequence of anthropogenic emissions. Many of these elements are conveniently grouped together as heavy metals, although the term is not precisely defined (often authors adopt a lower limiting metallic density of 6 g cm^-3; see Davies and Jones in Wild²) and the origin of its usage is obscure. Figure 1 is based on a simple citation count for the trace metals Cd, Co, Cu, Ni, Pb, and Zn for soils and plants, using the abstracting journal Soils and Fertilizers as a source. The graph should not be interpreted too rigorously, since no attempt was made to guard against multiple citations. It does, however, demonstrate how publication rates have risen markedly since 1950.

FIGURE 1. Trace metal publications.

A critical historical account has yet to be written for heavy metal research, but it is nonetheless possible to note some seminal papers of the 1960s which have stimulated major areas of work in many countries over the following 20 to 30 years. This is not to deny the importance of earlier papers. For example, Griffith¹⁷ wrote a comprehensive account of the adverse consequences of fluvial dispersal of lead-rich mine wastes in west Wales immediately after World War I. A decade later Bertrand and Okada¹⁸ described elevated concentrations of lead in French soils.

Several overlapping developments had to take place before trace element research in the agricultural and life sciences became more than a local or minor interest. One was possibly a change of attitude in health care. Prior to the discovery and wide provision of antibiotics in the 1940s to cure bacterial infections and the simultaneous introduction of the insecticide DDT, which controlled the insect vectors of diseases, medical attention was largely preoccupied with the infectious diseases; the importance of other influences on health was less clear and often discounted.

Rachel Carson's book Silent Spring, eutrophication of lakes following river pollution by phosphates and nitrates from detergents and fertilizers, or the problems of combating smog and photochemical smog all awakened the public conscience to environmental degradation. Minamata (methyl mercury poisoning) and Itai-itai (cadmium) diseases in Japan helped focus attention on pollution by toxic metals. These all created a climate of thought in which it was acceptable to consider a role for trace metals in human health. Now, an ill-defined environmental influence is recognized as important in the etiology of diseases such as cancer, and there is some evidence to support a role for environmental and dietary trace metals.

The influence of new analytical techniques should also be recognized since they have made relatively easy, the rapid, and reliable analysis of trace metals. For example, Bertrand and Okada¹⁸ obtained their lead data from a hydrochloric acid extract of calcined soil which was saturated with hydrogen sulfide gas and allowed to stand for 24 hr in a sealed flask. This was followed by filtration and the precipitate was washed with more H₂S-saturated acid. The soil was reextracted, retreated with H₂S and, ultimately, the precipitates were bulked. Purification steps followed to remove other metal sulphides and, eventually, the pure, dry lead sulfate yield was weighed. One can only admire the perseverance in obtaining data for an element in soil in which no one at that time was really interested.

In the postwar period, spectrophotometry and in particular the dithizone method, become widely available for lead and other trace metals. Warren and Delavault¹⁹ were active in Canada studying trace elements in relation to biogeochemical prospecting. They wrote, "Surprisingly little is known about the distribution of lead in soils." They went on to comment that extraneous contamination should be taken into account in biogeochemical prospecting for new metal ores, and they named two previously unrecognized sources. One was contamination by petrol exhaust fumes (from tetraethyl lead as an anti-knock agent in the fuel) and the other was orchard insecticide spray (lead arsenate). They concluded that "industrial salting" provided a more widespread and serious problem than was anticipated. Subsequently, Cannon and Bowles²⁰ published their classic paper on lead in roadside soils and plants in Colorado and thereby launched a myriad of investigations by others over the next 28 years. The wider problem of urban contamination has also been a prolific research area, and this can be traced to a short report by Purves²¹ concerning contamination of soils in Edinburgh and Dundee (Scotland) by copper and boron. In recent years the problem of sewage sludge has occupied many workers. This topic also originated in the 1960s when Le Riehe²² published a paper on metal contamination of soil and the appearance of zinc-induced chlorosis in crop plants in the Woburn (England) market-garden exp...

Table of contents

• Cover
• Title
• Copyright
• Contents
• CHAPTER 1 Trace Metals in the Environment: Retrospect and Prospect
• CHAPTER 2 Trace Element Concentrations in Soils and Plants of Western Europe
• CHAPTER 3 Background Levels and Environmental Influences on Trace Metals in Soils of the Temperate Humid Zone of Europe
• CHAPTER 4 Metal Contamination of Flooded Soils, Rice Plants, and Surface Waters
• CHAPTER 5 The Transfer of Cadmium from Agricultural Soils to the Human Food Chain
• CHAPTER 6 Long-Term Application of Sewage Sludge and Its Effect on Metal Uptake by Crops
• CHAPTER 7 Fate of Trace Metals in Sewage Sludge Compost
• CHAPTER 8 Long-Term Behavior of Heavy Metals in Agricultural Soils: A Simple Analytical Model
• CHAPTER 9 Atmospheric Deposition of Metals to Agricultural Surfaces
• CHAPTER 10 Uptake and Accumulation of Metals in Bacteria and Fungi
• CHAPTER 11 Metals in Invertebrate Animals of Forest Ecosystems
• CHAPTER 12 Metal Tolerance in Plants: Signal Transduction and Acclimation Mechanisms
• CHAPTER 13 Dissipation of Soil Selenium by Microbial Volatilization
• CHAPTER 14 Mechanism of Manganese Adsorption on Soil Constituents
• CHAPTER 15 Multi-Element Analysis in Plant Materials — Analytical Tools and Biological Questions
• CHAPTER 16 Metal-Humic Substance Complexes in the Environment. Molecular and Mechanistic Aspects by Multiple Spectroscopic Approach
• Index