Traffic noise barriers

Source: Michael St Maur Sheil


INTRODUCTION

Pressures on the environment may occur through chemical, physical and biological agents. The subject of this chapter is physical agents, where physical fields are examined. The term physical fields is used here to encompass acoustic fields (noise and vibrations) and radiation and electromagnetic fields (ionising and non-ionising). These are considered below under three headings: noise, non-ionising radiation and ionising radiation.

Physical fields are part of the natural environment. Depending upon their properties and the surrounding conditions, physical fields are transmitted through the spaces in which we live, potentially affecting human health and nature. Human activity can add to, modify, and enhance and reduce the intensity of these fields. Furthermore, changes in physical fields can be linked to global environmental problems such as stratospheric ozone depletion (causing a potential increase in ultraviolet-B radiation) and climate change.

NOISE

The ability to hear sounds is a sensory function vital for human survival and communication. However, not all sounds are wanted. 'Unwanted sounds', for which the term 'noise' is normally used, often have their origin in human activities (mainly transport, industry and households).

This chapter addresses environmental noise ­ also referred to in the scientific literature as community, or residential, noise. Environmental noise is the noise experienced by people generated outside households. Noise experienced by people in the workplace or occupational environment is not considered in this chapter.

The results of an acoustic quality survey in European cities is presented in Chapter 10. The current section first concentrates on the concepts involved with the measurement of noise and vibration. This is followed by an assessment of the effects of noise on human health and nature, and then by a review of noise sources in Europe.

The availability and comparability of data on noise pollution in Europe are generally poor (Box 16A). Available data published by the OECD show that exposure to noise, which was fairly stable at the beginning of the 1980s, had increased by the end of the decade in some Western European countries (eg, France, Germany, The Netherlands, Switzerland) (OECD, 1991a). For sound levels Leq greater than 65 dB(A) (see Box 16B for a definition of Leq), exposure appears to have stabilised in some cases and increased in others. However, within the range 55 to 65 dB(A), exposure has significantly increased, apparently as a result of the fast-growing volume of road traffic . In the highly industrialised European countries such as Belgium, France, Germany, Italy, The Netherlands and the UK, but also Austria, the Slovak Republic, Spain and Switzerland, more than 50 per cent of the population is exposed to noise levels from road transport which are above Leq 55 dB(A), which is the level at which people become seriously annoyed during the daytime (WHO, 1993a).

The effects of noise

The nuisance effects of noise are difficult to quantify, as people's tolerance to noise levels and different types of noise vary considerably. Distinct variations in noise intensity and noise levels can occur from place to place (even within the same general area), and from one moment to the next. Similarly there can be large variations during each day, week or year. The main effects on people from noise occur along roads in both cities and rural areas, around airports and in residential areas.

The impact of noise on sensitive groups deserves particular attention (eg, school children, the elderly, the sick). The reaction of these groups may be considered as warning signals as to what may happen to other groups on exposure at higher noise levels. This group could constitute as much as 30 per cent of the population (K Andersson, Swedish Environmental Protection Agency, personal communication, 1994).

Annoyance

This is perhaps the most common adverse effect of noise on people and many complaints are made every year about many different types of noise. The feeling of annoyance results not only from interference with communication and sleep disturbance, but also from less well-defined feelings of being disturbed and affected during all kinds of activities as well as during periods of rest. There is, for example, evidence of a clear relationship between degrees of individual annoyance and noise levels; for example, it has been demonstrated that less use is made of private gardens and public parks when there is too much noise (OECD, 1991b).

If the percentage of the population which feels 'considerably annoyed' by the noise is determined through sociological surveys, then a picture like that in Figure 16.1 emerges. It shows how the various classes of noise sources, namely road traffic, air traffic, rail traffic and industry, contribute significantly to annoyance.

Whether and to what extent such exposure is ultimately harmful to human health and well-being has not yet been fully and conclusively explored, except at very high sound levels, when it causes hearing loss and tinnitus (ringing in the ears). The present state of knowledge, however, clearly indicates that long-term health effects due to environmental noise exposure cannot be excluded. In addition, a number of well-defined harmful effects on the quality of sleep, communication and psycho-physiological behaviour can be identified. There is a lack of evidence to indicate that such reactions to noise diminish with time, although within certain limits tolerances may be built up. However, it seems that complete physiological habituation to sleep-disturbing noise does not occur, not even after several years of exposure (Suter, 1992, in WHO, in press).

Sleep disturbance

Sleep disturbance is probably the most apparent effect of environmental noise. It can also be interpreted as a reduced quality of sleep, and may even occur when the people affected are not aware of it (H Ising, BGA, Berlin, personal communication). To ensure undisturbed sleep, single noise events (such as a passing aeroplane) should not exceed a maximum sound pressure level of approximately 55 dB(A) (H M Müller, DG XI, CEC, personal communication).

Interference with communication

The degree of interference of noise with speech or music depends on the noise level in relation to the level that conveys the desired information. An increasing noise level requires speakers to raise their voice and/or to get closer to the listener in order to be understood. Noise levels from about 35 dB(A) and above are seen to interfere with speech communication until, at noise levels of about 70 dB(A), normal speech communication becomes virtually impossible (Verein Deutscher Ingenieure, 1988, in von Meier, 1993). In classrooms where teaching has to take place over long distances, noise levels should not exceed 25 dB(A) (K Andersson, Solna, personal communication).

Extra-auditory effects

A great number of psycho-physiological effects of noise have been reported in the literature (WHO, 1993a). The most common responses are physiological stress, and at higher noise levels, cardiovascular reactions. Mental health effects and influences on performance and productivity have also been observed and documented (von Meier, 1993).

Intensive research on these subjects is ongoing (eg, Miedema, 1993), but it can be generally concluded from the present state of knowledge that exposure to environmental noise acts as a stressor to health, as it leads to measurable changes in, for example, blood pressure and heart rate. But there is not sufficient evidence yet to relate the exposure to environmental noise levels directly to specific health effects, although such relationships can by no means be excluded. It is presumably the total load of stressors, of which environmental noise is only one, that has a harmful and lasting effect on physical and mental health, seen as a statistical entity that allows great individual variations (see WHO, in press, for more details).

Low frequency noise and vibrations

While noise is pressure variations in air, vibration is wave motion in solid bodies, normally of low frequency. Low frequency noise and vibration are hence closely related. Vibrations will intensify the noise annoyance. Both have been linked with causing disturbance in residential areas. Vibration has not been well analysed.

The effects of noise on wildlife

The effects of noise on the natural environment have not yet been fully explored. Research results available point to extra-auditory effects, mainly unspecific stress reactions, on animals with an acute sense of hearing, under extremely high noise exposures from low-flying aircraft (Umweltbundesamt, 1987). However, noise effects of major proportions or of lasting harmful consequences on nature have not been reported. The evidence available so far is too sketchy and inconclusive fully to exclude such effects.

Economic costs

Environmental noise also has implications for costs and benefits in the economy more generally. For example, cost effects are known to exist as a result of the general degradation of residential areas by exposure to environmental noise (eg, lowering of rents and property prices). Noise-induced illnesses, losses of productivity, and a higher rate of accidents caused by sleep disturbance have obvious cost effects, but these are extremely difficult to quantify. There are recent indications that certain producers of low-noise equipment may gain some economic advantage over their competitors as public awareness of environmental noise disturbances increases.

The sources of noise

All European countries have adopted similar classifications of the sources of environmental noise. This classification relates the sources to specific human activities, thus making them easily identifiable. The major sources are road traffic, air traffic, rail traffic, industry and recreational activities. As a matter of expediency sometimes one or two additional classes are also included, such as noise from construction sites and from traffic on waterways. In the following paragraphs a brief source-specific analysis of the noise exposure data for Europe is provided.

Road-traffic noise

Road traffic is responsible for the highest percentage of the European population exposed to noise levels greater than 55 dB(A) (Leq, 24-hour). In particular, the high proportions of Leq between 55 and 65 dB(A) can be attributed to the growth of traffic volume during recent years (Figure 16.3). This more than offsets any possible results of tightening noise limits from road vehicles through engine/exhaust noise controls as exercised for example by EC legislation. In addition, tyre/road noise is now the dominant source of road-traffic noise, particularly in free-flowing traffic at speeds above 40 to 50 km/hour (von Meier, 1992). Roughly speaking, each increase of vehicle numbers by 25 per cent will result in a noise level increase of 1 dB, whereby one heavy goods vehicle is equivalent to about eight passenger cars.

Airport and air-traffic noise

Noise levels around airports have been reported for 27 airports (for nine European countries) by the OECD (OECD, 1993). Most exposure data are site-specific, depending on geographic location. It is difficult to deduce trends with poor time-series data, and to make comparisons between countries, owing to different limit values, measurement techniques and the diversity of descriptors being used. Average data for all German airports indicates, however, the number of people exposed to outdoor noise levels of daytime Leq>67 dB(A) has increased from 500 000 to 610 000 between 1980 and 1990, and for outdoor noise levels of daytime Leq>75 dB(A) from 100 000 to 122 000 (OECD, 1993). If such trends exist in other countries (which seems likely, due to increased air traffic over the last decade) it is a cause for concern.

The OECD has presented data for air traffic for 11 European countries (OECD, 1993). With the exception of The Netherlands, the extent of noise exposure due to air traffic is seen to be considerably less than to road traffic. Two opposing trends determine the present state and future levels of environmental noise from air traffic in Europe: on the one hand the increasing use of quieter aeroplanes, and on the other the rapid growth of air traffic (commercial, general aviation ­ eg, from light propeller aircraft used for recreation, executive jets and helicopters ­ and military aircraft). This later trend is compounded by an increase in shifting freight transport from day- to night-time.

Rail-traffic noise

Nine European countries supplied railway noise data to the OECD survey (OECD, 1993). Somewhat surprising is the high percentage of exposed people in the Slovak Republic. Switzerland is known to have a railway noise problem because the topographical constraints dictate that railway lines run through the same valleys as those where human habitation is concentrated.

Trends in rail-traffic noise are not clearly detectable. Great efforts are being made in Western European countries to limit rail-traffic noise by curative measures, mainly by screens along railway lines, but the introduction of high-speed trains in France, Germany and Spain ­ and shortly also in The Netherlands, Belgium and the UK ­ and planned extensions of railway networks, will increase the number of people exposed to noise.

On the whole, however, rail-traffic noise appears to be of much less importance than road-traffic noise. In dose­effect studies, railway noise is generally judged to be less annoying to people than other noises, in particular during the night (von Meier, 1993).

Noise from industry

Noise originates from all sorts of industrial activities, ranging from small workshops to livestock activities (abattoirs), outdoor factories (eg, for stone crushing), and heavy industry. Because of this great variety of industrial noise sources and of the different characters of the noises they emit, with regard to frequency content and time history, it is very difficult to compile an inventory of people non-occupationally exposed to industrial noise which is both representative for a certain country and comparable with other countries.

Exposure levels of more than 75 dB(A) rarely exist for industrial noise in Europe. Indeed, most exposure is below 55 dB(A). This does not mean, however, that industrial noise is a negligible environmental problem. On the contrary, people exposed to it can be very seriously annoyed and affected in their well-being. This depends on the character of the noise and on the attitude people have towards the source (eg, whether or not it is seen as economically important).

Recreational activities

Few data are available for noise from recreational activities in Europe. There is often an overlap with industrial noise for certain activities, such as catering. Loud noise from recreation tends to be confined to locally concentrated sources such as sports arenas, theme and leisure parks, shooting ranges, discotheques and rock venues. There is also some evidence of an increase in complaints from street noise (eg, from dogs barking, radios and recorded music) (UK DoE, 1992). New forms of tourism and recreation, such as motor sports, off-road racing and use of speedboats and water scooters, create noise which disturbs other (less noisy) holiday-makers. On the other hand, some forms of recreation require almost complete silence, such as bird-watching.

Overall noise environment in Europe

From the still somewhat limited noise exposure data available (for example, for road traffic, see Figure 16.3) it can, with some caution, be concluded that, at least at the national level, there are no systematic differences between groups of countries in Europe (eg, north­south or east­west). This is not necessarily the case for individual cities where Central and Eastern European cities appear to be noisier than Western European cities (see Chapter 10). But the possibility of such differences existing between countries cannot be ruled out, as they could be brought to light as more accurate data with wider coverage become available. In particular the dearth of data for Central and Eastern European countries accounts for the still somewhat fragmentary character of this inventory. However, a tentative analysis relating to the exposure to noise of the total population of Europe can be attempted (given a total population of Europe of 680 million). The result is shown in Figure 16.4.

Attention should be paid to interpreting Figure 16.4, as it does not take account of possible overlap between exposures from different sources (ie, some of the exposure attributed to road traffic could be attributed to rail traffic and vice versa). Nevertheless, Figure 16.4 is very clear in identifying road traffic as the predominant source of noise pollution. By relating Figure 16.4 to a dose­effect relationship for road traffic (which after all accounts for most of the cumulative exposure of the European population), it is possible to conclude the following:

Policies and strategies for noise abatement

There is a general consensus in OECD countries that the outdoor level of noise should not exceed 65 dB (daytime Leq). In the case of new residential areas the outdoor levels should not exceed 55 dB (daytime Leq). These levels now frequently serve as the reference for defining noise 'black spots', where the levels of exposure to noise exceed 65 or 70 dB(A) (Leq from 6 am to 10 pm), and 'grey areas' where the noise level is between 55 and 65 dB(A) (OECD, 1991b).

The European Commission stated in its 5th Environmental Action Programme that, 'no person should be exposed to noise levels which endanger health and quality of life'. This translates into the following targets for night-time exposure:

Extrapolating the first goal for the whole of Europe would mean that the number of highly exposed people (above 65 dB(A) during night-time) would be reduced by 9.7 million. The other goals would not reduce the number of people disturbed by noise, but in any case their number should not be allowed to increase. Noise pollution impinges also on other policy areas (particularly transport).

There are three main options available to achieve these goals: engineering (including landuse planning), legal, and education and information. Both engineering and legal measures need constant feeding through research and can succeed only if supported by the public. Hence, education and information of the public is required. Such measures should be seen as complementary actions which cannot yield any substantial results without the help of others. Some examples of such measures are provided in Box 16C. Noise protection measures should always be introduced at a very early stage, in order to improve acoustical quality and increase cost-effectiveness.

At the same time as the CEC's 5th Environmental Action Programme, other initiatives have been taken by different countries and organisations. The WHO recently issued an external review draft on an Environmental Health Criteria Document aimed at community noise (WHO, 1993a). Sweden at the same time published an Action Plan against noise (Kihlman, 1993). Several other countries, inter alia, The Netherlands, Denmark and Switzerland, are already implementing comprehensive programmes for improving noise, emphasising urban areas.

Outlook and conclusions

The estimate of 113 million people, or 17 per cent of the total European population, exposed to environmental noise levels that have serious negative impacts is an important cause for concern. This situation has arisen out of a gradually deteriorating situation over about the past 10 years. If this is extrapolated into the future, then the outlook can only be of continuing and increasing concern. Economic development in Central and Eastern European countries is likely to exert additional pressures in the future, particularly as a result of growing road traffic, as the first data from the 'New Bundesländer' (East Germany) have indicated (Umweltbundesamt, 1992b). To meet the objectives of the CEC's 5th Environmental Action Programme this trend will have to be reversed, requiring that all available noise control options be applied, with road-traffic noise being identified as the top priority.

Environmental noise pollution is thus a European problem of growing extent and concern. Only concerted actions on a technological as well as on a political level are able to improve the present situation and to reverse existing trends. The elements required to set up a successful noise control strategy are known and, as far as technology is concerned, readily available, but great efforts still need to be made on both national and European levels to set up and enforce noise legislation and to support this by education and information programmes and by promoting research and development.

NON-IONISING RADIATION

Physical fields arising from non-ionising and ionising radiation are additional agents exerting pressure on organisms in the environment. Box 16D explains the concepts and terminology associated with such fields. Their effects on human health are examined briefly in Chapter 11. Some parts of the electromagnetic spectrum, such as gamma rays and X-rays from nuclear sources and electron beams, which have wavelengths less than 10-8 metres, are said to be ionising (ie, radiations and fields that have enough energy to produce ionisation of matter such as gases and biological matter). These are discussed below in the next section. Radiations with a wavelength longer than 10-8 metres are said to be non-ionising. These include electromagnetic fields and non-ionising ultraviolet (UV) radiation, which are discussed in this section. The effects of low-frequency electric and magnetic fields are included (especially below power transmission lines) as well as exposure to UV-B radiation. Microwaves are not covered in this overview.

Human-induced sources of electromagnetic fields are generally small when compared with natural sources. However, suspicion has been directed towards certain human-made frequencies and wavelengths which happen to be far greater than those occurring naturally, although evidence of health effects from EMF is insubstantial.

With respect to ultraviolet light, the evidence of biological damage from exposure is clear. Some epidemiological evidence suggests that certain frequencies and/or wavelengths may be associated with human health effects. However, much of this exposure for humans appears to be related more to choice of lifestyle (such as sunbathing) than to environmental factors. This may yet be exacerbated by the depletion of the stratospheric ozone layer, whose equilibrium has been disrupted by emissions of CFCs and halons (see Chapter 28).

There are a few other types of non-ionising radiation which have demonstrated human health effects, including high-frequency fields, ultrasound and laser light. Medical applications of all three of these have demonstrated clear diagnostic or therapeutic benefits. In human terms, exposure is presently significant only in the occupational context, which is beyond the general scope of this overview.

Electromagnetic Fields

Sources

Natural

Electromagnetic fields (EMFs) are present naturally. The Earth has a 'static' (steady) magnetic field strong enough to turn a compass needle. EMF of various strengths also occur in thunderstorms, in the static electricity associated sometimes with clothes and furnishings, and in the electrical activity of the human body itself. The Earth's core is thought to be responsible for massive electric currents inside the Earth, which in turn are thought to be the source of most of the Earth's static magnetic field. This field has a strength of about 40 A/m (50 µT). A natural electrical field is also normally present at the Earth's surface due to the electrical charges in the upper atmosphere and from solar activity. At ground level during good weather this field is about 100 V/m, but during severe weather it may rise to many thousands of volts per metre.

Artificial

EMF are produced by power transmission lines and by most equipment that uses a mains supply, including everyday home appliances. Table 16.3 provides a basis for comparison of the field strengths associated with various sources in the environment. It is clear from this that the human-induced sources of EMF generally occur at much higher intensities than the naturally occurring fields, especially at the power frequencies of home appliances (50 Hz). Some of the fields to which humans are occasionally subjected are extremely strong. There is a general but unproven feeling, however, that DC (also referred to as 'static') fields, such as the Earth's magnetic field and that involved in magnetic resonance imaging (MRI), are less hazardous or problematic than AC (or 'non-static') fields. Human exposure to non-static fields generally comes through electricity use.

Effects of EMF

EMF may have direct or indirect effects on living organisms. Direct effects arise when electric fields induce a surface charge on an exposed body. This results in a distribution of electric current in the body, depending on exposure conditions, size, shape and position of the exposed body in the field. Observable biological effects may include vibration of body hair, stimulation of sensory receptors and cellular interactions. Indirect effects of EMF are defined as those that may occur when an electric current passes completely through the body when in contact with a conducting object. Observable effects may include the occurrence of visible discharges, sometimes known as 'sparks', or interference with medical implants such as cardiac pacemakers.

EMF act in a very different manner from most other environmental agents. A straightforward measure of field strength, analogous to a measure of the concentration of a chemical in the air or water, may not provide an accurate measure of exposure or risk. The exposure to EMF can be characterised by several different parameters (field strength, field direction, field orientation in relation to the body exposed, field complexity, and so on), though it is not known which of these parameters are associated with risk to human health and the organisms.

The WHO recently summarised the results of research studies on the impact of EMF in the laboratory on animals, on humans, at the cellular level, and on the biological effects of Extremely Low Frequency (ELF) fields (WHO, 1993b). Evidence for thermal effects of exposure to EMF is identified. There are also some epidemiological studies which claim increased incidence of cancer in children and adults, as well as workers occupationally exposed to magnetic fields of 50 to 60 Hz over long time periods (see reviews in UK NRPB, 1992). The greatest concern relates to children reportedly exposed to field strengths of 0.1 to 0.4 µT living in proximity to power lines.

Most studies have been criticised as no biological mechanism has been suggested to explain these effects and because of the low statistical significance of the results due to the low case numbers and inadequate controls. Consequently, there is still great uncertainty surrounding the possible carcinogenic effects of magnetic fields. Two recently published studies, from Sweden and Finland, of children living close to power lines (Verkasalo et al, 1993; Feychting and Ahlbom, 1993) concluded that electric and magnetic fields of transmission lines do not constitute a major public health problem regarding childhood cancer. The increased risk of childhood leukaemia noted in the Swedish study (one extra case per year) was indicated to be insignificant from a public health point of view.

At its meeting in May 1993, the International Commission on Non-Ionising Radiation Protection (ICNIRP) reviewed all available data on the possible carcinogenicity of 50 to 60 Hz magnetic fields. They concluded that there is no firm evidence of the existence of a carcinogenic hazard from exposure to ELF fields, but that the findings justify the proposal of a specific programme for further research (WHO, in press).

Policy and research

Present public safety standards for electromagnetic fields are based primarily upon laboratory experiments and modelling studies. These focus on exposure conditions known to cause physiological or chemical effects associated with the development of cancerous cells.

Some international standards have been set by, for example, the European Committee for Standardisation (CEN) and its subsidiary the European Committee for Electrotechnical Standardisation (CENELEC). Limits for electric and magnetic fields at power frequencies of 50 to 60 Hz in some European countries are shown in Table 16.4, together with the guide limits of the International Radiation Protection Association. Some individual countries such as Belgium, the former Czechoslovakia and the former USSR have set limit values for overhead power lines in different settings (general purpose, road crossings, accessible or inhabited areas and edge of right of way). However, there are no internationally agreed limits for overhead power lines (Maddock, 1992). See WHO (1993b) for details on other frequency ranges.

There are currently no proposals to legislate on the exposure of the general public to EMF in the EU. Attention in the EU is currently centred on concerns about occupational exposure of workers to the risks arising from physical agents (CEC, 1993b) ­ in the case of EMF, this includes primarily the exposure of those working on high-tension lines ­ and is further restricted to the thermal effects of such exposure.

The majority of European countries have protection standards which regulate occupational exposure to EMF, but the standards differ from each other in the permitted exposure levels, coverage of EM spectrum, permitted exposure time, and technical standards for EMF sources. These differences arise from disparate research findings consequential from questions on what constitutes a health hazard, and methodological differences in collection, processing and interpretation of results. An international research project at European level, in the framework of the European Commission's COST programme (COST 244 ­ 'Biomedical Effects of Electromagnetic Fields') aims to coordinate European research in this field. Its objective is to ensure the scientific background for developing common European protection standards in the whole spectrum of EMF, oriented both to the general population and to occupationally exposed personnel. The project entered the research phase in 1994 and is planned to end in 1997.

Outlook and conclusions

Public concern about EMF continues. The WHO predicts increases in EMF exposure in coming years as increased electrification accompanies socio-economic development (WHO, in press). This general scenario might perhaps be tempered in some respects by the following considerations.

  1. There are differences between Western Europe and Central and Eastern Europe in the trends for electricity consumption, and in the use of electrical appliances in the home. While trends put forward in the WHO socio-economic development scenario may well apply to Central and Eastern Europe for the next two decades, it is doubtful that anything similar will apply in Western Europe.
  2. In Central and Eastern Europe, most future electricity expansion could be accompanied by more modern equipment and appliances and more efficient generation, distribution and consumption practices, which may reduce EMF exposure.
  3. The spread of information and concerns about EMF in Western Europe will lead to prudent avoidance of EMF where possible, particularly through burying cables, as well as appliance designs that seek to limit EMF, improved energy efficiency, and so on. Such activities place in doubt an expected increasing trend in EMF as witnessed in Western Europe over the past decades, and may result in exposures beginning to decrease overall.

The problem of understanding EMF effects on health might be more rapidly resolved through epidemiological studies of electrical workers than through studies of the general public, who generally have much lower exposure.

The existing situation in Europe could be considered adequate, if the measures and limits internationally agreed for the protection of workers are properly implemented. Until further research results suggest otherwise, the IRPA (International Radiation Protection Association) limit for continuous exposure of the general public of 5 kV/m for electrical field strength (or a magnetic flux density of 0.1 mT at 50/60 Hertz) may be considered to provide substantial protection from possible health effects.

Ultraviolet radiation

Sources

Natural

Ultraviolet (UV) radiation is emitted by the sun with wavelengths between 10-7 and 10-8 metres as well as by various human-induced sources. The UV radiation band can be divided into three smaller bands: UV-A (320 to 400 nm), UV-B (280 to 320 nm) and UV-C (<280 nm). About 5 per cent of the total solar radiation that reaches the Earth's surface is ultraviolet. The amount and intensity (of UV-B especially) varies with the angle of the sun (time of day, season and latitude), the weather (clouds, mist, fog, etc) and the altitude. At sea level, about 95 per cent of the UV radiation is UV-A, 5 per cent is UV-B.

Most solar UV radiation which would otherwise reach the Earth's surface is absorbed by the atmosphere. However, human activities have been recognised to be changing the composition of the atmosphere, including the ozone layer (see Chapter 28). Such a change could permit a small but significant increase in the amount of UV radiation reaching the Earth's surface, with repercussions for human health and ecosystems.

Although ozone layer measurements have indicated a decrease in levels of stratospheric ozone, there is little evidence of increases in UV flux at the Earth's surface, with the exception of a large increase recorded in the South Pole region (see Box 16E). It has been suggested that the most common monitors (Robertson-Berger (RB) meters), designed before there was a perceived need for detailed knowledge of the UV spectrum, are not sensitive enough to detect the changes, which are occurring most importantly in the shorter wavelengths recorded by the meter (CEC, 1993c).

A recent Canadian study (Kerr and McElroy, 1993, cited in WHO, in press) showed that levels of UV-B in Toronto during the winter have increased by more than 5 per cent per year from 1989 to 1993, as ozone levels have decreased. At the time it was produced, this study was the most reliable of its kind with regard to the situation in the northern hemisphere.

Artificial

Technology has also introduced new sources of UV radiation and visible light which can have deleterious effects on human health. Much of the working population, and more and more of the general population, of Europe is now exposed to the UV radiation emanating from fluorescent and high-intensity quartz tungsten-halogen lamps over long periods. Likewise, industrial and medical uses of UV radiation are widespread, including such diverse applications as photo-polymerisation, disinfection and sterilisation, welding, and the widespread use of lasers.

Changing fashion and human behaviour patterns have also led to increased exposure to the sun and UV radiation, which has already demonstrated profound effects on human health, in particular skin cancers. The use of sun-lamps and sun-beds, most frequently for cosmetic reasons, is a common source of additional UV exposure. Prior to the mid-1970s, mercury lamps were generally used as sun-lamps, sources of high levels of both UV-B and UV-C. While some of these devices are surely still around, since the late 1970s fluorescent lamps, generating almost exclusively UV-A (the most important for tanning) and visible light, have mostly been produced for this application. A clear link has not been proven between the use of sun-lamps or sun-beds and the incidence of skin cancer. However, the use of artificial tanning equipment is widespread and largely uncontrolled. In addition, it should be noted that a 'safe' level of exposure has not been defined. It is estimated that 10 per cent of people in the Western world use sun-lamps or sun-beds (WHO, in press).

There is also an increasing use of UV light in working environments (Moseley, 1988, and WHO, in press):

Effects

Effects on humans

UV light is sufficiently energetic to rupture chemical bonds or to energise molecules into excited states which can initiate a variety of chemical and biological processes. UV-C is especially lethal to many living organisms since it interacts particularly with proteins and DNA. However, UV-C is not an environmental problem from natural sources, because it is almost completely absorbed by oxygen and ozone (even at reduced levels) in the atmosphere before it reaches the Earth's surface (CEC, 1993c). Artificial sources, on the other hand, deserve attention. The longer wavelengths represented by UV-A are little absorbed by the ozone or the atmosphere, but, compared with UV-C and much of UV-B, they are also relatively harmless to most living things.

UV-B, by contrast, which is partially absorbed by ozone in the atmosphere, is of special concern because it may have damaging effects on the biosphere. Unfortunately, slight changes in the ozone layer, which is especially suited to blocking UV-B wavelengths around 300 nm, may have a significant effect on the amount of UV-B that reaches the surface of the Earth. In fact, a reduction in ozone permits a very specific increase in UV-B radiation between 290 and 315 nm ­ precisely that waveband where solar irradiance is normally reduced by 10 000 times due to absorption by ozone. Extensive studies on humans have demonstrated that UV-B wavelengths of 290 nm are 1000 to 10 000 times as effective in producing damage to DNA, killing cells, and causing skin erythema and skin cancer than are visible light wavelengths longer than 300 nm (Moan et al, 1989, and McKinley and Diffey, 1987).

Many biological reactions are particularly sensitive to the 290 to 315 nm waveband, which may result from evolutionary adaptation because of the protection provided by the Earth's ozone layer. An instantaneous (in geological terms) change in this protection will not permit time for a similar modification to take place. Even the low levels of UV-B radiation that normally reach the Earth's surface can damage DNA, and cause sunburn, eye cataracts and some skin cancers (IARC, 1992), not to mention suppressing the normal human immune responses (Morrison, 1989). It is possible, therefore, that if ozone depletion or any other mechanism leads to significant increases in UV-B fluxes at the Earth's surface, this could have an important effect on the human immune response to certain allergens or infectious agents, as well as on the development of some cancers. The 'International Programme on Health, Solar UV Radiation and Environmental Change' (ITERSUN), a joint IARC/UNEP/WHO study which involves measurement of UV radiation at the surface, cancer incidence, ocular cataracts and immune suppression, may help resolve some of these uncertainties.

Effects on non-human targets

UV radiation can penetrate sea water to a depth of up to 50 metres, which is sufficient to cause various ecological effects. UV-B damage to phytoplankton in the laboratory has been reported, which goes beyond DNA effects to include impairment of cellular metabolism and motility (Smith, 1989). Increased levels of UV-B may bring irreversible damage or death to zooplankton, which are an essential element of the food-chain for all higher marine life forms. Other marine organisms in the upper levels of the sea include the eggs and larvae of fish, which would certainly be susceptible to damage from raised levels of UV-B (Smith, 1989).

The effects of enhanced levels of UV-B on plants varies between species, as well as between different populations of the same species, indicating the additional influence of reflections from the soil or other local variables (Tevini and Teramura, 1989). Most plants respond to some extent through adaptation, including photo-repair, accumulation of UV-absorbing pigments and delay in growth. Various food crops such as soya beans and cereals are especially sensitive to UV radiation. The causes are not well understood, but have been shown to involve an impairment of the photosynthetic mechanism. In general, increased levels of UV radiation are expected to lead to an increase in the production of less economically valuable plants, and a decrease in the production of the more valuable plants.

Most animals have developed a certain coat or pigmentation which protects them from the harmful effects of UV radiation, but many (cattle and sheep are the most widely studied) seem susceptible to ocular cancers at a rate which is directly proportional to UV exposure (Kopecky, 1978). Any significant increase in UV-B is expected to have significant effects on food-producing animals, and these effects may be assumed to be greater at higher latitudes. A question which now arises, however, is what impact ozone depletion, through increasing levels of UV-B radiation, has already had on the welfare of the biosphere (SCOPE, 1993).

Policies and strategies

Policies for reducing UV exposure have been determined, until now, through strategies for protecting the ozone layer (see Chapter 28). These have focused on two areas: reduction and eventual elimination of emissions of ozone-depleting substances, and 'active adaptation' to an environment of greater exposure to UV radiation. The Montreal Protocol (concluded in September 1987) and the London and Copenhagen amendments (June 1990 and November 1992, respectively) address the first of these. In many cases, controls already in force or being considered within the EU and some other European countries are even stricter than those agreed at Copenhagen (CEC, 1993c). Even if all countries comply with these agreements, however, ozone depletion may exceed any natural variations in the ozone layer that humans have had to cope with until now.

Outlook and conclusions

There is clear evidence from research involving both animals and humans of a direct causal relationship between UV radiation exposure and skin cancers. The rapid increase in European skin cancer cases in recent years is undoubtedly connected to social and recreational behaviour ­ the key factors ­ as well as to other less clear causes. Increased public awareness of the hazards of UV exposure is necessary, especially for individuals with sensitive skin types and for young children.

To date, there is little direct evidence in Europe that depletion of the stratospheric ozone layer has led to increases in terrestrial UV-B levels. It is widely suspected, however, that the consequences of ozone depletion may be substantial, including a broad range of effects on human health. The need to counter further depletion of the ozone layer is clear.

Efforts are continuing to ensure that the Montreal Protocol and subsequent agreements are respected. Meanwhile, active adaptation would involve behavioural change to avoid excessive exposure to the sun. Over the medium to long term, active adaptation could imply, for example, that biotechnology might contribute to the development of food crops with greater resistance to UV radiation.

A broad range of measurements, programmes and research is already being carried out in Europe. This interest is motivated in large part by the scientific interest and broad policy implications of ozone layer depletion. However, this research requires increasing coordination, or at least harmonisation, so that definitions, measurements, procedures and data will be comparable between European countries.

IONISING RADIATION

The energy level of some types of radiation is high enough so that when they interact with matter they cause the formation of electrically charged particles or ion-pairs and break molecular bonds. These so-called ionising radiations are by their nature potentially harmful to life; at high doses they can be lethal and at lower doses can cause genetic damage. Ionising radiation occurs naturally, and life on Earth has always been exposed to it. Human activities can, however, enhance exposure, and new sources have been created. The toxicity of radionuclides derives almost exclusively from the effects of the radiation which emanates from them, although some radionuclides, such as the isotopes of plutonium, are also highly chemically toxic.

Sources

Doses can be received from external radiation (the radiation source is outside the body in air, soil, etc) and from internal radiation (from radionuclides which enter the body by food, by drinking water and through inhalation). Terrestrial radionuclides are almost entirely responsible for internal exposures.

Natural

Natural sources include: primary and secondary cosmic radiation; radon and thoron in the air; and diverse radionuclides in the soil which may enter water and food.

The worldwide average annual effective dose from ionising radiations from natural sources to the average person is calculated to be about 2.4 mSv (UNSCEAR, 1993) (Table 16.6 and Figure 16.5). Corresponding values for the countries of Western Europe show somewhat higher levels, ranging 2 to 7 mSv (Figure 16.6).

Cosmic rays originate both in outer space and from the sun. Those coming from space remain fairly constant, but those from the sun are produced in bursts during solar flares. The intensity and number of cosmic rays which enter the Earth's atmosphere are affected by the earth's magnetic field; more cosmic rays enter near the poles than near the equator, so exposure decreases with decreasing latitude. Exposure to cosmic radiation increases with altitude due to the shielding effect of the atmosphere. Furthermore, some differences in indoor exposure to cosmic radiation arise due to variations in the shielding factor of different building designs. Other naturally occurring radionuclides acting as sources of ionising radiation are those continuously being produced by the interaction of cosmic rays and the atmosphere, eg, tritium (H-3).

All materials in the Earth's crust contain trace amounts of uranium, thorium and other naturally radioactive elements (terrestrial radiation). These nuclides include the long-lived isotopes potassium-40, uranium-238 and thorium-232, and, by radioactive decay, the medium to short-lived radionuclides radium-226 and radon-222, as well as their short-lived decay products. The activity level depends on the type of rock or soil ­ there is relatively high activity in granites, low activity in some sedimentary rocks and intermediate activity in soils. The gamma rays produced by these materials irradiate the whole body more or less uniformly. Since most building materials are extracted from the earth, they also contain natural radioactivity (particularly potassium-40, uranium-238 and thorium-232). Exposure to terrestrial radiation is therefore experienced both indoors as well as outdoors as a function of geology and the structure and type of the buildings.

Apart from exposure of the lungs to radon, thoron and their daughter products discussed below, the human body is internally exposed from natural radionuclides such as beryllium-7, potassium-40 and members of the uranium-238 decay series (especially lead-210 and polonium-210) and the thorium-232 decay series. These radionuclides enter the body by air, food and water. Exposure due to potassium-40 is essentially constant over a given population, but lead-210 and polonium-210 exposure are more variable with diet. Overall doses from all of these sources together do not vary much between individuals, but of course the cumulative dose increases with age.

Radon-222 is a radioactive gas which emits alpha particles. It is the direct daughter product of radium-226 formed during the radioactive decay of naturally occurring uranium-238. As this occurs in the Earth, radon eventually escapes to the open air, where it is quickly dispersed. When the gas enters a dwelling, however, either through the floor or from the walls, dispersal is much slower and the concentration may become higher than outdoors. As the gaseous radon itself decays (half-life 3.8 days), alpha- and beta-emitting daughter radionuclides are formed. These normally attach themselves to small particles or aerosols in the air and, when inhaled, deposit in the respiratory tract and lungs, irradiating these internal tissues. Concentrations of radon may vary appreciably from one locality to the next (frequently by a factor of ten or more), and they may vary dramatically from one house to another (sometimes by a factor of 100), particularly in relation to the ventilation rate which may have been reduced to conserve energy. Thoron (another name for radon-220) is produced by the decay of thorium-232, but levels and doses are generally much lower than those of radon-222 (about 10 per cent). The relative magnitude of the most important natural sources of radiation exposure in Western European countries is illustrated in Figure 16.6. Comparable data are not currently available for Central and Eastern Europe.

Artificial

Humans have increased their exposure to radiation from the environment through a number of activities. These include industrial activities where raw materials containing naturally occurring radionuclides at low concentrations are processed on a large scale (eg, the production of phosphate fertilisers, the extraction of oil and gas and the burning of fossil fuels), mining, the extraction of water from deep wells, the testing of nuclear weapons, the generation of nuclear power, and the use of radiation or products with high radioactivity in medicine, other industry and research. Ionising radiations can be made artificially either by the generation of appropriate electromagnetic fields, as in X-ray apparatus, or by the creation of artificial radionuclides produced in accelerators or by nuclear fission (atomic weapons or nuclear reactors). The general population is exposed to these ionising radiations either directly (eg, from medical uses) or through their presence in the environment (eg, discharges from the nuclear industry). Table 16.7 compares doses resulting from such artificial human-induced sources to an equivalent period of exposure to natural radiation sources (UNSCEAR, 1993). This perspective indicates that the increased exposure from most of these activities is, on the whole, not a great cause for concern. However, artificial radiation may in fact contribute a significant fraction of the dose over which there is some control. Particular attention is best devoted therefore to such sources of exposure, some of the most important of which are discussed below.

Medical exposure

With respect to the various artificial sources of exposure to ionising radiation, medical exposure is by far the greatest for the average individual and probably represents the area in which reductions in exposure would be most cost-effective. In any given year, probably a third of the Western European population is exposed to X-rays, with a dose up to 42 mSv/year (Vaas et al, 1991). In 1986, close to 50 per cent of the Russian population received X-rays for medical reasons (Nikitin et al, 1991); the increased exposure compared with Western Europe was caused largely by technical problems.

Nuclear medicine (diagnostic examination with radio-pharmaceuticals) contributes additional exposure of an estimated 1 to 2 per cent of the Western European population, with doses up to some 100 mSv/year (Vaas et al, 1991). Comparable figures are not available for Central and Eastern Europe.

Radiation therapy gives rise to very high (though usually localised) exposure of patients, but in this case such high levels of exposure are necessary to attain the objective of destroying cancerous cells.

Radioactive emissions and waste disposal

Most radioactive wastes are, or are planned to be, disposed of by concentration and confinement in surface, near surface or deep underground licensed facilities (see Chapter 15). Disposal by discharge to and subsequent dilution and dispersion in the environment is severely regulated at national and international level; its use is limited to some low-active liquid or gaseous effluents resulting from the operation of nuclear facilities (electronuclear, medical, etc). The authorised and controlled releases and discharges to water (lakes, rivers, and seas) and atmosphere from such facilities contributes directly to the dispersion of the radionuclides to the environment. In Western Europe, the spent fuel reprocessing plants (Sellafield, UK, and La Hague, France, and, to a lesser degree, Marcoule, also in France) are the most significant points of controlled release of liquid and gaseous effluents, the contribution from electronuclear power plants being individually much less. As a result of improved working practices, the level of radiologically significant discharges to the Irish Sea from Sellafield is now about 1 per cent of peak levels in the 1970s, when they were by far the most important from any single site in Western Europe (CEC, in press, see also Chapter 18).

The practice of dumping radioactive waste at sea has been regulated since 1975 by the London Convention (more correctly referred to as the International Convention on the Prevention of Marine Pollution) by dumping of waste and other matter. Up to 1983 dumping of low-level radioactive waste packages complying with specific criteria has been authorised and practised by some Western Europe countries in the northeast Atlantic under the aegis of the Nuclear Energy Agency of the OECD. No environmental contamination has been detected up to now. This practice was suspended in 1983, following a voluntary moratorium. Since 1994 the prohibition of all sea dumping has been accepted by all signatories to the convention other than the Russian Federation, which has not as yet been able to implement alternative approaches. Potential unquantified threats of environmental contamination are found in the Barents and Kara seas around the Novaya Zemlya archipelago. They result from the dumping of radioactive objects, including highly radioactive material, by the former USSR (Yablokov et al, 1993). For further information see Chapters 6 and 18.

Also in the former USSR, emissions into the Techa river (near Chelyabinsk and Sverdlovsk in the southern Ural mountains) in the 1940s and 1950s and associated operations of the Mayak nuclear facility (also the site of the Kyshtym radiation accident ­ see below) has resulted in severe contamination of the area. Furthermore, a small lake (Lake Karachay) continues to be used to store high-activity waste material and is probably the worst site of radioactive waste accumulation on earth (Burkart and Kellerer, in press).

Radiation accidents

Uncontrolled release of radionuclides to the environment can occur as a result of accidents during the handling, transport, use and disposal of radioactive materials and during the operation of nuclear facilities. From an environmental point of view a distinction should be made between abnormal nuclear events having consequences limited to a nuclear plant or site, and abnormal nuclear events causing off-site radioactive pollution. According to the International Nuclear Events Scale (INES), first introduced on a trial basis by the IAEA in 1989 and now formally adopted with some revisions (IAEA, 1992), only these latter should be called accidents, the former being anomalies or incidents. Accidents have been few, the most prominent being the Windscale reactor fire accident (UK, 1957), and, considerably worse, the severe accidents at the Kyshtym military reprocessing plant (USSR, 1957) and the Chernobyl power plant (Ukraine, 1986). The Chernobyl accident had the most widespread effect in Europe for increasing exposure to ionising radiations (see Box 18E). No accident has been reported since 1987 in Western Europe. Even relatively minor abnormal nuclear events have to be reported to the national safety authorities according to the provisions of national law. A number of international reporting systems are also in use on a voluntary basis, such as that directly associated with INES under the aegis of the IAEA.

Further information on accidents at nuclear installations can be found in Chapter 18, where the origin and impact of radiation accidents are examined. Radiation accidents are treated as a problem of environmental concern for Europe in Chapter 30.

Weapons testing

Atmospheric testing of nuclear weapons has been a major source of artificial radioactivity in the environment. The extensive testing in the 1950s and 1960s released enormous quantities of radionuclides into the upper atmosphere which have now dispersed throughout the whole environment. In terms of radiation exposure, the most significant radionuclides from this source are strontium-90 and caesium-137 with half-lives of approximately 30 years. Since the signing of the Test Ban Treaty in 1963, atmospheric tests have almost been eliminated (the last atmospheric test was conducted by China on 16 October 1980). However, fall-out continues to provide a certain component of routine radiation exposure, although annual doses have become very small compared with the variations in natural background radiation.

Effects and risks

Whether natural or artificial, the effects of ionising radiation on matter are the same ­ transferring energy which can break and rearrange the bonds holding molecules together. In biological materials, such chemical changes can have various types of consequences: effects can be deterministic (with a threshold dose above which the effect can be anticipated) or stochastic (with a statistical probability of occurrence decreasing with the dose but with no lower limit). Radiation sickness or organ and skin damage are deterministic effects. They occur only at high radiation doses at dose rates above a threshold, and the severity is related to the dose. Cancer and hereditary disorders are stochastic effects. Their probability, but not their severity, is assumed to be proportional to the dose even at very low doses (see below; ICRP, 1991).

Different types of radiation vary in their ability to penetrate matter and thus in the efficiency with which they transfer energy and induce biological effects. The conversion of absorbed doses to a common 'effective dose' permits different types of radiation exposure to be aggregated on a common basis. This effective dose is expressed in sievert (Sv) or sub-units thereof.

Because of its high rate of energy transfer, alpha radiation is one of the most damaging types of radiation. Internal exposure, primarily through the inhalation or ingestion of alpha emitting radionuclides, is of most concern for alpha radiation. Gamma radiation looses its energy over greater distances, causing less biological damage but being more penetrating.

In 1977, the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) assessed the risk of a fatal cancer from ionising radiation at 2.5 per cent per dose of 1 Sv (UNSCEAR, 1977). Since then, with the availability of additional data from Japan and improved methods of risk evaluation, the estimated risk has been increased to 5 per cent per Sv for the general population, ie, a cumulative dose of 1Sv gives a one in twenty chance of a fatal cancer occurring (ICRP, 1991). To apply this coefficient to the ordinary circumstances of exposure in order to develop a risk factor for protection purposes, allowing for the overall potential detriment to health, the risks of non-fatal cancers and hereditary defects suitably weighted for lethality and severity are also taken into account. This results in an all-inclusive risk factor of about 7.3 per cent per Sv. Applied to the worldwide (somewhat higher in Europe) average annual dose rate of 2.4 mSv per year, this implies a theoretical lifetime risk to the average individual of premature death from natural radiation-induced malignancy of about 1 per cent. In order to put this risk in perspective, it can be compared to an overall probability of death by cancer. For the population of the USA it has been estimated that 30 per cent of fatal cancers are induced primarily by smoking, 35 per cent by substances ingested in food, and 3 per cent by alcohol consumption (Doll and Peto, 1981). These effects have meant that even large-scale epidemiological studies have not been able to identify an influence on the incidence of cancer attributable to natural radiation.

Policies and strategies

The main areas of action have been for occupational safety (particularly in the medical and nuclear industries) and exposure to the general public. The non-occupational standard of 1 mSv/year applies to populations which may be exposed to artificial ionising radiation. ICRP (1991) recommends lifetime dose for the public from planned activities should not exceed 70 mSv, with a maximum of 5 mSv in any one year. The dose averaged over 5 years should be less than 1 mSv/year. This does not apply to natural background or medical exposure.

Natural exposure

Little can be done to prevent exposure to terrestrial and cosmic radiation. With regard to radon exposure, however, some authorities, including the European Commission, have recommended that high exposure to radon in the home should be avoided. There are also legal requirements in some European countries to limit exposure to radon in the workplace (Green et al, 1993). Public understanding of radon risk must be improved, and home owners should be encouraged to undertake the necessary measures and remedies.

Medical exposure

Radiation exposure of patients is assumed to provide direct benefits to these patients which more than offset the associated risks, and hence it would be counter-productive to impose general limits, especially in radiation therapy applications. In diagnostic applications, however, there is certainly scope for using more efficient X-ray techniques giving a reduction in exposure without affecting the benefits.

Outlook and conclusions

Exposure to radiation in general, and especially the role of the nuclear industry, attracts a great deal of consideration in politics and society as a whole, disproportionate to scientific claims or evidence. Therefore, there is a significant challenge to weigh these considerations properly together with the valid scientific and socio-economic evidence.

Little can be done about the risks of exposure from natural sources of ionising radiation; indeed, humans have always had to cope with such risks. Therefore, much of the potential future problem lies in the proliferation of different kinds of artificial radiation sources, and in particular from medical applications and the nuclear industry.

In medical sciences in particular, changes in tissue weighting factors proposed by ICRP (Clarke, 1991) may make for important changes in exposure assessments, due to the proposed increase in specific values for abdominal organs. This would render average medical exposures nearly as significant as natural exposures for humans, and create even more pressure for appropriate monitoring and control of these exposures. New recommendations have also recently been published for radon (ICRP, 1993).

Finally, estimates of average exposure of humans cannot reflect accurately the wide-ranging exposure of individuals. A margin of safety must be incorporated to ensure that particular groups, such as miners, airline staff, and those living in high-radon areas, are not exposed beyond the recommended control levels (see also WHO, in press).