Contaminants and the Soil Environment in the Australasia-Pacific Region

I am honoured to be asked to speak on this topic but am daunted by the huge amount of work that has been done over a very long period in a range of contexts and for many potentially toxic contaminants. Having a personal perspective as a term of reference simplifies the task to some extent because of the extensive literature on this topic. This has inevitably resulted in additional emphasis on my own work which in the earlier stages of my scientific career was related to problems connected to the soil chemistry of trace metals, their availability to plants and soil fertility. I will only briefly refer to organic contaminants. I believe that many of the principles and mechanisms being investigated then have continued relevance although modern-day research has focussed on problems of soil contamination in which different heavy metals may be of concern. Equally, some of the weaknesses of early research approaches are still evident in currently published papers. The only difference is that with the advance in knowledge and experience, deficiencies in experimentation cannot now so easily be justified. These will be discussed later.

A contaminant is defined as a substance that is not natural to the soil, or a naturally occurring substance which has undesirable effects if its concentration exceeds a certain threshold. A number of non-metals have the potential to be contaminants in soil and water. Because of their high ionic potential, non-metals of Groups IIIA to VIA of the Periodic Table in their normal oxidation states form oxyanions (Sposito, 1984). Examples of non-metal oxyanions commonly found in the soil solution are borate (B(OH)⁻ ₄), biocarbonate (HCO⁻ ₃), nitrate (NO⁻ ₃), silicate (H₃SiO⁻ ₄), sulphate (SO²⁻ ₄), phosphate (H₂PO⁻ ₄), arsenate (AsO³⁻ ₄) and selenate (SeO²⁻ ₄). Other nonmetals such as Cl and F occur as the monovalent anions Cl⁻ and F⁻ The ubiquitous ion Cl forms soluble salts with the common cations in soil and is only a potential problem when the salt concentration of the soil solution or groundwater is high and specific Cl⁻ toxicity effects in plants may occur. On the other hand, F⁻ forms insoluble complexes with cations such as Al³⁺ and Ca²⁺ and is rarely an active contaminant except in some underground waters of the Great Artesian Basin. Of the other anions, HCO⁻ ₃ derives naturally from the dissolution of CO₂ in soil water and dissociation of the weak carbonic acid formed. Silicate is formed from mineral weathering and dissociation of the very weak acid Si(OH)₄. Both are benign. Sulphate as SO²⁻ ₄ and less commonly HSO⁻ ₄ forms complexes with the hydroxyl surfaces of Fe and Al oxides, the edge faces of crystalline clay minerals, and Al³⁺ and hydroxy Al species adsorbed on charged surfaces.

The 90 chemical elements that occur naturally in soils have a very wide range of abundance. Ninety-nine percent of the mass of most soils is made up of only eight elements: H, C, O, Mg, Al, Si, Ca, Fe. The remaining elements exist in such small proportions in typical soils that in most situations they would be regarded as insignificant impurities. Yet nearly all of the elements are important to us in some way. Thirty elements are essential to life.

The transport and fate of contaminants in subsurface systems has become one of the major research areas in the environmental/hydrological/earth sciences. This interest has been instigated by concerns associated with the effects of human activities on the environment. Numerous examples may be cited that illustrate the adverse impact of human activities on the subsurface environment, such as contamination of soil and groundwater by chemicals associated with industrial and commercial operations, service stations, waste disposal facilities, and agricultural production. An overview of the impact of such activities on the quality of the soil environment in the Australasia-Pacific Region is presented in Chapters 14 to 25.

Modern agriculture has led to serious declines in soil and water quality as a result of practices which are not sustainable in the long-term. The greatest impact on soil quality has been in terms of soil loss, an irreversible process with 25, 8 and 12% of the crop-, pasture- and rangeland, respectively, in the United States of America (USA) eroding at rates faster than soil loss tolerance levels (National Research Council, 1993). Despite the ravages of erosion being known for a long time, only very small reductions in erosion rates have been recorded in these categories of land over the period 1982 to 1987. This possibly reflects the prediction that crop yields are only likely to decline by 10% over the next 100 years due to soil erosion at current high input levels (Putnam et al., 1988) which indicates that, to be effective in countering erosion, efforts should focus on offsite damage caused to rivers and lakes. In terms of water quality, agriculture has been the source of 64 and 57% of the non-point pollution of rivers and lakes in the US, respectively, with sediment and nutrients accounting for 60 and 81% of the pollution in affected rivers and lakes, respectively (Carey, 1991). Non-point source pollution from soil erosion impairs beneficial uses of water, fish spawning and rearing habitats and increases the cost of municipal water treatment, maintenance of navigational channels, irrigation systems and reservoir storage (Clark et al., 1985). In the USA, soil erosion costs $1.3 billion in lost productivity and $3 billion in off-site economic damage (Ribaudo, 1987).

In many countries, the problems associated with the disposal of wastes generated by population centres, both large and small, together with associated industrial activity, have become significant environmental issues. The realisation that both controlled and uncontrolled disposal of wastes can result in the contamination of soils, surface waters and groundwaters has led to the development of a considerable assortment of regulatory measures and guidelines aimed at reducing or eliminating waste-related pollution. However, waste disposal and the associated environmental contamination from urban-industrial centres is an ongoing major issue, with the list of potential pollutants increasing as new chemicals and processes are developed. In addition, many sites contaminated in the past by waste disposal operations, or contaminated by a particular industrial process carried out at the site, continue to pose a serious threat to the environment.

Mining is of economic importance to many countries in the Australasia-Pacific region because in addition to providing export income, it is also the source of fuel, construction materials and raw materials for many manufactured goods. However, this chapter is essentially based on Australian experiences, unless otherwise stated, and therefore may not truly represent conditions in all countries of the Australasia-Pacific region.

This observation, which was made by the Director of the Victorian Environment Protection Authority, suggests that there is a need for better responses to the problem of land contamination in Australia. Although the problem now is widely regarded as a matter of serious environmental concern, effective legal responses are still being developed. The Federal constitutional system in Australia, under which environmental management functions are performed primarily by State and Territory governments (Chapter 14), has produced a variety of approaches to the management of contaminated land. The role of the Commonwealth government has been limited to a contribution to the production of National Guidelines for the Assessment and Management of Contaminated Sites and a Position Paper on Financial Liability for Contaminated Site Remediation. Only three States (New South Wales, Victoria and Queensland) have developed legislation which is directed specifically at the subject of contaminated land. For the other States and Territories, the problem is addressed to varying degrees through their general environment protection legislation.

Chapters 1 to 8 emphasize the adverse effects of contaminants on the soil and water environment. In this chapter the health risk assessment and management of contaminated sites are discussed with particular emphasis on Australia. There has been increasing concern over the assessment and management of contaminated sites in the Australasia-Pacific region over the last 10 years. This arises from community concerns about potential health risks, increasing urban redevelopment where old industrial sites may be reused for residential developments, and an increasing need by administrative authorities to ensure effective and cost conscious remediation of considerable numbers of sites affected usually by anthropogenic activities.

As discussed in this book, there are thousands of contaminated sites in prime residential areas throughout the world. With the increased publicity on the negative impacts of contaminants on the soil environment and on human health, the social impacts of contaminated sites are becoming a serious issue within the community and regulatory bodies. Thus the management of a contaminated site can be challenging for organisations charged with the responsibility for dealing with it. There are often many diverse interests, particularly if the site is located close to a residential area. Frequently these interests may be at odds with each other but each position held may, in its own right, have some validity and the problems are never clear cut. People who discover that they are living on or near a contaminated area of land generally react strongly to such news. Their reactions vary, and to a large extent are controlled by their existing knowledge of the environmental and health impact of the particular contaminant(s) and their lack of knowledge or access to information and decision makers.

The need for increased food production and the desire to improve the economic conditions have led to rapid industrialisation in many Asian countries. At present the impact of industrialisation on the soil environment in many countries in the Australasia-Pacific region is not clear although reports discussed in this book (Chapters 14 to 25) suggest that increasing reliance on agrichemicals and industrial effluents for irrigation purposes has resulted in extensive contamination of agricultural land. The lack of industrial zoning legislation in these countries has led to expansion of industries into regions traditionally used for agricultural purposes. This expansion together with the disposal of industrial wastes, fallout from industrial atmospheric emissions, and the use of polluted waters for irrigation of crops have resulted in contamination of valuable agricultural land in many countries in the Asia-Pacific region.

In many industrialised countries, contamination of soils and groundwater from improper disposal of hazardous industrial wastes is an environmental issue of increasing public concern, regulatory activity, and scientific investigation. In the United States (USA) alone, there are estimated to be about 400000 waste disposal sites where soil and groundwater contamination is deemed to be of sufficient extent and magnitude, that some type of remedial action is warranted to protect public health or to minimise adverse environmental and ecological impacts. The costs of cleaning up such sites over the next 20–30 years may easily exceed one trillion USA dollars. Experiences of environmental scientists and engineers in the USA over the past decade have shown, however, that the required regulatory levels may not be achieved at most sites, even after several decades of clean-up efforts using the existing technologies.

As land previously occupied by industry comes under pressure for redevelopment, it becomes evident that a large number of these sites are contaminated. Such contamination is a concern if it has the potential to become a health hazard to site occupiers or a threat to overall environmental quality. Soil remediation is a young technology whose ultimate success will be dependent upon a combination of chemical, physical and biological knowledge. This knowledge must be built on a sound understanding of the basic science behind the mobility, reactivity and toxicity of pollutants in natural ecosystems. However, the economics of remediation and the end-use of the treated land will be major factors in the widespread adoption of clean-up technologies. Possibly the greatest single stimulus for soil remediation will be legislative pressures that define the limits of various contaminants in soil, water and the atmosphere. These standards are likely to become increasingly stringent as analytical techniques improve. Whilst there may be little justification for these levels from toxicological data, the overriding consideration will be to reduce inorganic and organic contaminant levels to ‘below detectable limits’. The implementation and policing of these regulations will be a political as well as a scientific issue and special pleading, focused on using the best available technology, risk assessment and economics, will be a common feature of the debate.

Contaminated land is an increasingly important environmental, health, economic and planning issue in Australia and a number of initiatives and approaches have been developed for dealing with these issues. As part of this process Government agencies are placing greater emphasis on the state of soils and the soil environment, recognising the soil’s role as a potential repository for pollutants, as a transmitter of undesirable materials to surface and groundwaters and as a potential source of contaminants in the food chain.

China is a large country with a territory covering 50° N in latitude and 60° in longitude. The area extends from cold temperate regions in the north to subtropical and tropical regions in the south. It has the highest mountains in the world — the Himalayas. The annual precipitation ranges from less than 50 mm in desert regions to over 2000 mm along seashores. Such a wide geographical range and huge area result in great diversity of geology, climate and related vegetation. As a consequence, nearly all the principal types of soils of the world, ranging from tundra soils to intensively weathered latosols (Oxisols) can be found in the country.

It is commonly known that urbanisation and industralisation adversely affect our environmental quality. This is further aggravated in developing countries where industrial development is progressing rapidly compared with developed countries.

Environmental pollution in India, as elsewhere in the world, is a major issue of public policy and research. Unprecedented economic growth during the last fifty years has led to extensive environmental degradation of all parts of the ecosystem. During the past couple of decades, major programmes of afforestation, water and air pollution control have been launched by the Government along with the enactment of a comprehensive Act known as ‘Environmental Protection Act 1986’. There have also been major programmes aimed at the reclamation of wastelands, especially large stretches of both alkaline and acidic soils.

The Republic of Korea (South Korea) occupying the southern portion of the Korean Peninsula in East Asia, covers an area of 99 000 km². It is about 965 km long and about 217 km wide; it is bordered on the north by North Korea, on the east by the East Sea (Sea of Japan), on the south by the Korean Strait, and on the west by the Yellow Sea. As one of the most densely populated countries of Asia, it had a population estimated in 1991 at 43.5 million.

Malaysia is at present undergoing rapid development and tremendous changes especially in its economic structure. Previously, agriculture has been the main thrust of the Malaysian economy, but in recent years the industrial sector has continuously achieved high growth rates and is now the dominant force. This has resulted in an increase in urban population and the creation of new urban centres. The rapid industrialisation process in Malaysia coupled with global concern about environmental issues has fuelled environmental awareness in the country. In recent years reports on the deterioration of environment quality, especially in urban areas, have increased. Environmental issues are now of important political and social considerations.

In the last decade or so there has been escalating concern worldwide regarding the quality of the environment as affected by human activity. For agriculture, this has meant that many of the modern cultural practices have come under ever-increasing scrutiny by the public at large. Issues of importance to the consumer include the nutrient value of foodstuffs as well as any contamination by toxic substances, principally those arising from the farm production system itself. There is widespread distrust, much of it ill-informed, regarding the use of modern agrichemicals such as pesticides, fertilisers and animal health remedies and the effect of their use on food quality. However, any soil contamination (because soil is fundamental to most land-based plant or animal production systems) is extremely serious because the contaminant or its breakdown products may accumulate in food products ultimately for human consumption. In New Zealand (NZ), there is currently much activity in determining the causes and effects of heavy metal additions and pesticide residues on the quality of the agricultural environment. Additionally, there is increasing pressure from the public, both domestic and international, concerning the impact of agriculture on the wider environment. For example, off-farm water quality may be adversely affected and the important soil-mediated and other processes which might be involved are the subject of several major studies in NZ.

Pakistan occupies the basin of the eastern-most of the three great rivers that traverse the steppe desert of the old world, the Nile, the Tigris-Euphrates and the Indus. That these basins were the cradles of early civilisation gives to the Indus a distinctiveness that is lacking in other river basins in South Asia (Johnson, 1979). It lies between latitudes 24 and 37° N and between 61 and 75° E longitudes. On its east lies India; to the north and north west is Afghanistan; to the west is Iran; and in the south is the Arabian Sea. It has a common frontier in the north with China on the border of Gilgit Agency. Tajikistan is separated from Pakistan by a narrow strip of Afghan territory called Wakhan.

Papua New Guinea (PNG) comprises the eastern half of the island of New Guinea and outlying islands, north of Australia (Fig. 1). Irian Jaya, a province of Indonesia, occupies the western half. The total land area of PNG is 462840 km² and includes North Solomons, New Britain, New Ireland, Manus and many other islands. Much of the interior of mainland PNG is mountainous and heavily populated, with a total population of 3.8 ×10⁶ in 1990 (National Statistical Office 1993), and a mean population growth rate of 2.3% yr⁻¹. The people are culturally and linguistically diverse, and many tribal groups live in relative isolation. More than 700 distinct languages are spoken.

The South Pacific region has a reputation for sun-drenched beaches, clear waters and lush green vegetation. The possibility that contamination of the environment exists is often not considered. While this scenario does still exist in places, the situation is changing quite rapidly with increasing populations and industrial development contributing to problems that now require serious attention. Contaminated soils have been identified, but this issue has received minimal attention, partly because of a lack of appreciation of the areal extent and potential severity and partly because of inadequate resources to address the situation. This chapter examines the causes of contamination, the extent of the situation, assesses potential problems and makes recommendations for future action.

Sri Lanka is a pear shaped island, separated from the Indian continent by the Palk Strait, which at its narrowest has a width of 29 km. The island covers an area of about 65610km² and is approximately 430km long and 225km wide at its maximum extremities. The estimated population is 17 million.

Taiwan is located in the subtropical and tropical regions with high precipitation (>2500mmyr⁻¹) and high temperature (>22°C). The total area for rice and upland crop production is 8800 km² which is about 25% of the total area of Taiwan. The main Soil Orders of rural soils in Taiwan are Inceptisols, Alfisols, Ultisols and Entisols, based on the Keys to Soil Taxonomy (Soil Survey Staff; 1994) (Table 1).