|CHAPTER 38: CHEMICAL RISK - THE PROBLEM|
In this present report it is shown that there are few environmental problems in Europe that cannot be traced back to some sort of excessive loading of chemicals. Economic development has been driven to a considerable extent by progress and innovation achieved by the chemical industry. This process has led to the marketing and use in different applications of ever-increasing numbers and quantities of chemical substances. More than 10 million chemical compounds (natural or man-made) have been identified. Of these, about 100 000 are produced commercially (200 to 300 new chemicals enter the market each year) and are potential subjects of concern. Estimates suggest that the current world production of chemicals is about 400 million tonnes (LÃ¶nngren, 1992). Many chemicals are applied directly to the environment or are discharged after use. Adequate toxicological and ecotoxicological data have been produced for only a very small fraction of the chemicals, and data on environmental pathways and ecotoxicological effects are even more sparse (see Chapter 17).
From being regarded mainly as a potential risk to humans, chemical impact on the environment became of increasing concern from the 1960s. Before then there was little appreciation of the atmosphere and hydrosphere having limited capacity to assimilate the ever-increasing releases of chemicals. The bioaccumulation of certain chemicals in the food-chain and its consequences for the normal function of ecosystems and for human welfare were not well understood either. Apart from a few early signs of chemical threats to the environment (eg, mercury pollution as evidenced by the Minamata disease in Japan, high levels of mercury in game and fish in Sweden, lake eutrophication, PCB and DDT pollution) it was only relatively recently recognised that chemicals which enter the environment can, in general, cause serious detrimental effects in all environmental compartments and to human health whether they be released through normal operation or as a result of accidents. Accidental discharges of chemicals and their environmental effects are treated in detail in Chapter 30.
The human-generated sources of dangerous chemicals which enter the air are widespread. The smokestacks of factories, power-generating stations, waste incinerators, motor vehicles and smelter discharge emit sulphur dioxide, nitrogen oxides, carbon monoxide, hydrocarbons and other combustion products often contaminated with substances such as heavy metals, dioxins, furans, etc.
In highly industrialised or populated areas, chemicals are often released into waterbodies in exceptionally large volumes through industrial discharge pipes and municipal sewage. Apart from large volumes of chemicals entering the environment in such areas, the environmental danger comes from the fact that these releases contain significant amounts of many types of chemicals which are commercially used.
The release of highly toxic chemicals (often as contaminants in high-volume production chemicals) also causes serious problems. Well known examples for these substances are chlorinated hydrocarbons, heavy metals and hydrocarbons (see Chapter 14). Once a chemical is emitted to the air it is usually deposited with rainwater and snow and eventually ends in runoff into rivers and seas. Another main source of chemicals in the environment is from the agricultural use of pesticides, which contain potentially dangerous chemicals that can leach into groundwater. Some non-degradable (heavy metals) and very slowly degradable substances (PCBs, dioxins) can be transformed into more toxic intermediate compounds (DDE from DDT or methylmercury from mercury). On the other hand, bioaccumulation may take place in the food-chain, which can result in concentrations toxic to biota, especially top predators.
Natural transport from one compartment to the next further accelerates the dispersion of a given substance through the ecosystem (Figure 38.1). This eventually leads to accumulation of a substance and harmful effects in another compartment than that to which it was originally released. Most of the chemical compounds released to the environment are subject to biotic and/or abiotic degradation but some are persistent and therefore accumulate in the environment, leading to long-term exposure of organisms. Depending on the toxicity and persistence of the substance, exposure can lead to disorders, genetic mutation, adverse effects on reproduction, cancer, mortality and adverse effects on the nervous and immune systems. It may also cause effects on ecosystems.
A great variety of environmental perturbations caused by chemicals are considered in this report. In particular, the concentrations, trends and effects of chemicals in three environmental compartments: air, water (fresh and marine) and soil are thoroughly treated in Chapters 4 to 7. The human activities which promote the release of chemicals are described in Chapters 19 to 26, and the resulting loads to air and water with problem chemicals are the subject of Chapter 14. The health aspects and environmental impacts of a selection of chemicals considered to be particularly harmful are treated in Chapters 11 and 17. The environmental problems considered in this chapter of the report which relate to human activities and the emission of chemicals include: climate change, stratospheric ozone depletion, loss of biodiversity, major accidents, tropospheric photochemical oxidants, acidification and eutrophication.
To overcome the specific environmental problems caused by an identified chemical, remedial, preventative or legislative measures are taken in many industrialised countries (for example, controls on heavy metals, CFCs, PCBs, DDT, pentachlorophenol, etc). In the last few years, however, it has been generally recognised that such an approach is not sufficient. There must be an integrated concept which addresses the impact of all chemicals that may cause detrimental effects in the environment. However, such an integrated and systematic risk assessment approach is faced with a number of inherent difficulties, the most important being:
- the large number of new and existing chemicals which have to be considered;
- frequent lack of data which are needed for comprehensive risk assessment;
- the possibility that initially innocuous chemicals may react in the environment and be converted to more toxic compounds and cause unforeseen secondary impacts;
- the potential danger of almost any chemical to any kind of organism or ecosystem;
- dangerous contaminants as by-products in synthesised chemicals produced in large quantities;
- frequent lack of regional and global coordinated control measures; and
- time delays between regulatory measures and beneficial effects.