Emissions from steelworks, Gijon, Spain
Source: Simon Fraser/Science Photo Library
INTRODUCTION |
Many of the environmental problems currently facing Europe result from the discharge of pollutants into the environment. Information on the characteristics, quantities and locations of such emissions are therefore essential to the assessment, prediction and understanding of their fate and potential environmental impact. A systematic analysis of emissions into the various environmental media is also crucial for establishing quantitative and qualitative relationships between these problems and the pressures from specific sectors of activities, production processes and technologies. Strategies for controlling and reducing discharges will become more effective as the quality and quantity of information on these emissions develop.
The term 'emissions' can encompass a wide range of agents, from chemical susbstances to noise and radiation. In this report, 'emissions' refer specifically to substances which are of no further use for the purposes of production, transformation or consumption and which are released to the environment air, water or land rather than recycled or re-used. These are usually referred to as atmospheric emissions when directly released to air, as wastewater when discharged to waterbodies and as waste when dumped to land or handled further before final dumping. Wastes are a particular form of emissions; throughout their extended life, wastes may change nature and location as they are handled and processed before disposal to land, causing emissions to air, water and soil.
This chapter presents an overview of emissions to air and water in Europe their physico-chemical characteristics, magnitude, pathways and sinks in the different environmental media. Wastes are treated separately in Chapter 15. The impacts of emissions are examined in detail in Chapters 4 to 11 and further developed in Chapters 27 to 38 as part of the presentation of prominent European environmental problems. Emissions are treated by sources in Chapters 19 to 26. Radioactive emissions are addressed in Chapters 16 and 18.
EMISSION INVENTORIES |
Information on pollutant emissions is usually compiled in emission inventories. Direct measurements are still infrequent and therefore emissions are usually estimated with the help of emission factors applied to statistics on human activities. Emission inventory methodologies have evolved over the past 20 years and there is now general appreciation of methodologies and of the types of data to be included in an emission inventory to ensure its completeness, consistency and transparency and hence its quality and usefulness (Box 14A).
Emission inventories serve several purposes ­ they help:
A wide range of emission inventories already exists at the national level in several European countries. Attempts to produce international integrated inventories of emissions have been made more recently in response to increased concerns for their transboundary environmental impacts (see Box 14B). Nevertheless, most of the existing inventories cover only emissions to the atmosphere. Emissions of pollutants into the air have been quantified most systematically and in greatest detail in recent years because of the increasing evidence of their impact on the local, regional and global levels. Emissions into waterbodies have long been considered to have more restricted dispersion and hence more local (or regional) impacts. Consequently, these have not been quantified in such detail to date. Instead, more attention has been given to measuring concentrations of water pollutants and monitoring water quality. Releases into or onto land, including the various types of waste, have been addressed with different approaches in European countries and accordingly information is incomplete and fragmentary. As yet, no agreement has been reached on a consistent classification system for developing inventories of such releases.
In addition to the limited coverage of existing inventories, another major obstacle to a European-wide assessment of emissions is their limited comparability. Many of the national inventories which do exist differ fundamentally in their scope and structure as well as in their method of data collection, geographic scale and range of emissions considered. The harmonisation of emission inventory methodologies at the European level is increasingly recognised as a priority (Box 14C).
Furthermore, the real value of information on emissions occurs not when data are available as disparate estimates from different sources into different media, but rather when data can be readily compared and integrated (Box 14B). A study on the feasibility of a European integrated emissions inventory (Briggs, 1993), carried out for the European Commission, has identified the links between emissions to air, water and land from a range of human activities, and the major environmental problems and targets of the EU Fifth Environment Action Programme. Many substances are released into more than one medium (or potentially transferred from one medium to another), are relevant to more than one environmental problem and are dependent on the same types of activities.
Consequently, data collected on activities relevant to one substance, one medium or one problem are likely to be relevant to other substances, media and problems. However, to date, most national and international programmes to quantify emissions have addressed the various policy areas separately. As a result, these programmes have produced non-comparable information a major obstacle to a more integrated approach to emission control. This implies the need not only to extend existing emission inventories to other areas, sources and media, but also to make the data within them more consistent and comparable (Briggs, 1993).
ATMOSPHERIC EMISSIONS |
Emissions to air arise from human activities and from natural processes. The share between global anthropogenic and natural emissions for a selected number of atmospheric compounds is given in Chapter 4 (see Table 4.7). Anthropogenic emissions occur during the extraction, distribution and combustion of fossil fuels, from various industrial processes, from waste treatment and disposal, from agriculture, and from a range of consumer products. Natural sources such as volcanic eruptions, forests, grasslands and wild animals are not further considered in this chapter.
Atmospheric emission inventories have developed from rough estimates of national emissions of sulphur dioxide, derived from national energy statistics, to highly detailed databases containing spatial information on human activities and their resulting emissions of a wide range of pollutants. Most countries have developed their own systems for compiling inventories of atmospheric emissions and there have been several initiatives to produce multinational inventories. However, national inventories are often not comparable in terms of, inter alia, source category splits and pollutants covered. On the other hand, international inventories have been limited either in the number of countries covered or in their source category splits (in some cases differentiating only between mobile and stationary sources).
In many inventory systems, attempts are made to differentiate between anthropogenic (or man-made), biogenic and natural emissions. However, the boundaries between these categories are not always well defined or definable and hence differences arise between inventories. For example, emissions from forests, including those which have been developed by humans for logging or other purposes, tend to be categorised as natural, whereas domesticated animals tend not to be considered as natural. The discussion below will avoid these ambiguous terms and focus on the different categories of human activities relevant to emissions, including agriculture, domesticated animals and managed land. Where inconsistencies arise or natural emissions not dependent on human activity are known to be included, these will be noted.
It is difficult to give a complete and consistent overview of the contribution of different sources of the various pollutants for all European countries; the completion of the CORINAIR90 inventory (Box 14C) will facilitate this task. Nevertheless, using existing inventories, it is possible to put European emissions of a number of pollutants into a global context, and to determine the main contributors and some spatial and temporal trends. The European contribution to global emissions of SO2, NOx, N2O, CO, CO2, CH4, CFCs and VOCs is summarised in Table 14.1. Temporal trends and spatial patterns are analysed below for sulphur dioxide, nitrogen oxides, volatile organic compounds, ammonia, carbon monoxide, carbon dioxide and methane. Except for heavy metals and metalloids, emissions of the various components of aerosols (both primary and secondary) and particulate matter have not been addressed due to the lack of consistent data from the different countries of Europe. The data used to produce maps and graphs presented in the following sections can be found in the Statistical Compendium.
Sulphur dioxide |
Sulphur dioxide (SO2) is released during the combustion of sulphur-containing fossil fuels and from certain industrial processes. It has effects on human health (see Chapters 4 and 11) and as one of the principal contributors to acidification has an impact on ecosystems and buildings (see Chapters 5, 9 and 31). As such, SO2 emissions have been quantified in the greatest detail for the longest period of time.
Table 14.1 indicates that Europe accounts for about one quarter of global emissions. The distribution in national total SO2 emissions from human activities across Europe in 1990 (Map 14.2) shows that Germany, the Russian Federation and the UK were the main contributors to SO2 emissions ­ each accounting for over 10 per cent of the European total in 1990 (see also Map 4.1a).
In most countries, the production of electricity accounts for at least half of total SO2 emissions, although this sector is not always separated from other stationary combustion source emissions in national inventories. The contribution from public power, cogeneration and the district heating sector (of which public power is by far the main contributor) is available for 20 European countries (EU12, Austria, Finland, Norway, Sweden, Bulgaria, Czech Republic, Poland and Slovakia) in 1990 from the first results of CORINAIR90. This sector accounted for 58 per cent of the total of 25 million tonnes of SO2 (Figure 14.1). National contributions from this sector ranged from 1 per cent in Luxembourg and Norway to 72 per cent in the UK and Bulgaria.
The other major source sectors were industrial and non-industrial (stationary) fossil-fuel combustion accounting for 21 and 10 per cent respectively of total European emissions of SO2 in 1990 and 28 and 15 per cent respectively of the Central European total in 1988 (Austria, Croatia, former Czechoslovakia, Hungary, Italy, Poland and Slovenia). By contrast, transport (mainly diesel-powered) accounted for about 3 per cent of these SO2 emissions across Europe as a whole.
There have been reductions in SO2 emissions in most countries over the last ten years as countries have addressed the issues of air quality and acidification and the requirements of the SO2 Protocol of the LRTAP Convention and related legislation on emission reductions. Figure 14.2 shows the downward trend in national total emissions from a selection of countries in more detail between 1980 and 1990. While a flat rate cut of 30 per cent in national emissions was the basis of the first sulphur protocol, critical loads now form an integral part of the new 1994 protocol (see Chapter 31).
Nitrogen oxides |
Nitrogen oxides (NOx) consist of the two gases, nitrogen dioxide (NO2) and nitric oxide (NO), formed in combustion processes from both the nitrogen present in the fuel and from the oxidation of nitrogen in air. NOx can reduce plant growth and cause visible damage to plant crops, contribute to acidification and the formation of ground-level ozone. Acute exposure to high concentrations of NO2 can cause breathing problems in humans.
Europe accounts for just under one quarter of global human-made emissions (Table 14.1). The distribution in national total NOx emissions across Europe in 1990 (Map 14.3) shows that the UK, the Russian Federation and (Western) Germany were the main contributors, each accounting for more than 10 per cent of the total NOx emissions in 1990 (see also Map 4.1b).
In most countries, road transport and the production of electricity are the main sources of NOx emissions. These sectors accounted for 46 and 22 per cent of European (20 countries) NOx emissions respectively in 1990 (Figure 14.3).
In contrast with the trend in SO2, there has been little change in total NOx emissions across Europe between 1980 and 1990. Some countries show a downward trend produced by the introduction of emission controls, while others show an upward trend where increased fuel consumption, particularly in the mobile sector, has not been compensated for by emission controls. Figure 14.4 shows the trends in annual NOx emissions in a selection of countries in more detail between 1980 and 1990. The NOx Protocol under the LRTAP Convention committed parties to a freeze on national emissions at 1987 levels by 1994, together with a package of abatement measures.
Volatile organic compounds (VOCs) |
The term VOC potentially covers thousands of chemical species, some of which are toxic to health or are precursors of photochemical pollution, greenhouse gases or stratospheric ozone depletion. In contrast to SO2 and NOx, few sources have been measured in any detail. Furthermore, different measurement campaigns have quantified different subsets of VOC species. The LRTAP Convention VOC Protocol has defined VOC as 'unless otherwise specified, all organic compounds of anthropogenic nature other than methane that are capable of producing photochemical oxidants by reaction with nitrogen oxides in the presence of sunlight'. The current EMEP Guidelines for Estimation and Reporting of Emission Data, however, define non-methane VOC (NMVOC) as 'all hydrocarbons and hydrocarbons where hydrogen atoms are partly or fully replaced by other atoms (for example sulphur, nitrogen, oxygen or halogens) which are volatile under ambient conditions, excluding CO, CO2, CH4, CFCs and halons'.
In effect the VOC Protocol addresses NMVOC, and the two definitions cover the same species. Nevertheless, inconsistencies continue and care needs to be taken when using VOC inventories, including CORINAIR85, to confirm whether or not methane (CH4) and other species are included in any VOC (or even NMVOC) emission estimate. Methane is a greenhouse gas and should now be quantified separately from NMVOC.
Map 14.4 presents estimates of national total VOC emissions for 1990 as reported to the UNECE (see also Map 4.1d). Due to the above complications, data for VOCs are less complete and consistent than for SO2 and NOx. Hence, the spatial distribution in national total VOC emissions across Europe should be viewed with some caution.
The combustion of fossil fuels, responsible for almost all SO2 and NOx emissions, accounts for only one third of NMVOC emissions in the CORINAIR90 inventory. The use of solvents, extraction and distribution of fossil fuels (solid fuel and gas) and forests (both coniferous and deciduous) accounted for about 50 per cent of the 1990 NMVOC total (Figure 14.5).
It is not yet possible to detect clear trends in VOC (or NMVOC) emissions; some countries appear to have reduced their emissions while others appear to show some increase over the past ten years. It will be necessary to await the production of more detailed, consistent time series of VOC emissions before confirming whether these trends are real or simply a reflection of the uncertainties in past methodologies.
The VOC Protocol under the LRTAP Convention adopted in 1991 introduces a stepped approach to controlling VOC emissions. The first step, which Parties may opt for on signature of, or accession to, the Protocol (although alternative options are available), is to take effective measures to reduce national annual emissions of VOC by at least 30 per cent by the year 1999 using 1988 (or another specified year between 1984 and 1990) as the baseline.
Ammonia |
Interest in ammonia (NH3) developed in the late 1980s to explain its contribution to acidification. The distribution in emissions across Europe shows that the traditional farming countries made the largest contributions to European emissions (see eg, Map 4.1c). The main sources of atmospheric ammonia are animal manure and the use of fertiliser. Hence ammonia emissions are dependent on the numbers of farm animals and the intensity of land-cultivation. Preliminary estimates made in the UK (WSL, 1992) indicate that about two-thirds of UK emissions in 1990 were from animal manure (in particular from cattle) and 22 per cent from the use of fertiliser. These sources accounted for 98 per cent of ammonia emissions in both Norway in 1991 (CBS, 1993) and The Netherlands in 1988 (VROM, 1992).
Carbon monoxide |
Carbon monoxide (CO) is derived from incomplete combustion of fossil fuels. It is toxic at high concentrations and contributes indirectly to global warming as a precursor of ozone. Emissions arise mainly from road transport, and Europe emits about 125 Mtonnes, or 11 per cent of the world total.
Carbon dioxide |
Carbon dioxide (CO2) is a key natural component of the carbon cycle. It is also the main contributor to enhanced global warming. Emissions from human activities in Europe are almost exclusively dependent on the combustion of fossil fuels. The production of electricity, combustion in industry, road transport and other non-industrial combustion (in approximately that order) are the main source sectors. Europe is responsible for about 30 per cent of global CO2 emissions. The distribution in contributions from individual European countries in 1990 (Map 14.5) identifies Germany and the UK as the major emitters. Trends in emissions from France and the UK over the period 1980 to 1990 are presented in Figure 14.6.
A major project led by the scientific assessment working group (WGI) of IPCC and OECD (OECD, 1991) is under way to develop guidelines on emission inventory methodology for greenhouse gas sources (and sinks) and help countries across the world produce comparable greenhouse gas inventories for the Framework Convention on Climate Change (FCCC). This project is working closely with the CORINAIR90 project to ensure compatibility for submissions to the FCCC from European countries. The FCCC was adopted in Rio de Janeiro in 1992, and entered into force in March 1994. Several countries, including collectively the 12 EU Member States, have adopted the objective of stabilising CO2 emissions by 2000 at 1990 levels.
Methane |
Methane (CH4) is a greenhouse gas and plays an important role in the production of tropospheric ozone. It has been estimated that European emissions are about 55 Mt (Table 14.1). However, methane emissions have not yet been quantified widely or systematically for many individual countries of Europe. Estimates will become available through the CORINAIR90 and the IPCC/OECD projects. Global emissions of methane are estimated to range from 240 to 590 million tonnes per year, with rice production, enteric fermentation in animals and coal-mining making the largest contributions. In the UK, it has been estimated (WSL, 1992) that animals, landfill, offshore oil/gas production, coalmining and gas distribution contributed 26, 23, 21, 19 and 8 per cent respectively to the total of nearly 4.4 million tonnes of CH4 emitted.
Heavy metals and metalloids |
Heavy metals are released during fuel combustion or from a range of industrial processes. However, emission inventories for these pollutants are less well developed than for the above gaseous pollutants. The most systematic and comprehensive work carried out for Europe to date has produced an unofficial set of national emission estimates for arsenic (As), cadmium (Cd), mercury (Hg), lead (Pb) and zinc (Zn) for the year 1982 (Axenfeld et al, 1992, which also included emission estimates for lead in 1985, not presented here).
Axenfeld et al's study (1992) indicates that the non-ferrous metal industry was the main source of As, Cd and Zn in 1982, accounting for 74, 65 and 57 per cent respectively. Power plant and other fuel combustion each accounted for 38 per cent of mercury emissions.
Road traffic (that is, the combustion of leaded petrol) accounted for three quarters of lead emissions in 1982. These emissions from road traffic have decreased markedly since 1982 although this sector probably remains the main source of lead in the atmosphere. Downward trends in national lead emissions from road traffic over the period 1980 to 1990 were due initially to the introduction of low-leaded fuel, then subsequently to the introduction of unleaded fuel and, in the case of Germany, the early introduction of vehicles equipped with catalysts which could not use leaded fuel.
Increasing attention is being given to heavy metal emissions, and more detailed and officially produced up-to-date heavy metal inventories are likely to become available within the next few years. The Executive Body of the LRTAP Convention has established a Task Force on Heavy Metals which will elaborate a state-of-the-art report on these pollutants, including emission inventory, atmospheric dispersion and deposition, analytical problems, technologies for the control of heavy metals, and economic problems, to provide the basis for elements of a possible protocol. The Paris Convention for the Prevention of Marine Pollution from Land-Based Sources (which covers the North Atlantic including the North Sea) and the Helsinki Convention on Protection of the Marine Environment of the Baltic Sea Area are also preparing atmospheric emission inventories for several heavy metals and other pollutants.
EMISSIONS TO WATER |
Emissions to water consist of a multitude of substances having different adverse effects on the environment. They can occur either as point or non-point (diffuse) source pollution arising from a variety of human activities. The fate and effect of emissions of polluting substances in a particular waterbody will depend not only on the amount of substances emitted, but also upon the hydrological, physical, chemical and biological conditions characterising the receiving body. Major point sources are:
Major non-point sources are:
Over the last few decades, there has been an increasing tendency in several European countries to reduce point source emissions. Pollution control measures have been adopted in the domestic sector and industry. This has not been followed by a simultaneous action for non-point source pollution and, consequently, the relative importance of diffuse source emissions in total emissions has increased.
The origins of emissions are treated in Chapters 19 to 26 and the relationships between emission of important pollutants (eg, nutrients and organic matter) and their aquatic effects have been treated in detail in Chapter 5. Very little quantitative information on emissions to water is available from international data banks, and, where available, the scale (national or regional statistics) is of little relevance for an assessment of river and lake pollution. Emission data on the relevant scale for these waterbodies (the catchment) is almost completely lacking. An important exception is the River Rhine, for which the International Commission for the Protection of the Rhine against Pollution has produced an emissions inventory. Two approaches to improve estimates of emissions to water are presented in Box 14D. Data on emissions of important polluting substances for some of the major European seas (eg, nutrients and heavy metals) have been gathered and they are treated in Chapter 6 describing the state of the European seas.
The discussion below expands upon the information referred to above and establishes links between the human activities and the state of the European waterbodies. The almost complete lack of emission data on the catchment scale makes this analysis difficult and consequently the information presented here is given by way of illustration. Special focus has been given to emissions from agriculture and from wastewater, for which more information is available. In many parts of Europe, these emissions are known to seriously restrict usage of water resources. A few examples, to illustrate the contribution of industry as a source of emissions into the aquatic environment, are also given.
Sources of nutrient concentrations in rivers and lakes |
The concern attached to nutrients discharged to waterbodies arises from the problem of eutrophication which they cause (Chapters 5 and 33). Nutrients in rivers and lakes originate from numerous sources such as the natural runoff from soil and bedrock weathering, and the enhanced runoff related to various human activities in catchment areas such as deforestation and agricultural activities, fertiliser application and irrigation. Many rivers are used to remove human waste products as either sewage discharge, stormwater runoff, or industrial effluent. The increase in nutrient concentrations above the natural background level depends on the demographic, industrial and agricultural development in the catchment. In sparsely populated areas with a low proportion of farmland and industrial development, the increase is low, in contrast to densely populated areas with an intensive agricultural production and many industries. Another important factor is the wastewater treatment process: an efficient high technology sewage plant may reduce the phosphorus discharge by more than 90 per cent compared with low technology sewage plant discharges.
There is a positive relationship between annual mean phosphorus concentrations in the water and the population density in river catchments (Figure 14.7). In catchments with fewer than 15 inhabitants per square kilometre, the phosphorus concentration is generally lower than 20 µg P/l, and in catchments with more than 100 inhabitants per square kilometre, phosphorus concentrations are usually higher than 200 µg P/l.
In densely populated areas such as Denmark, Germany, Latvia, and the River Po catchment in which one third of the Italian population lives, 43 to 64 per cent of the phosphorus discharge to inland surface waters is related to sewage discharge from the various municipalities (Figure 14.8). Industrial effluent is in general less important and makes up only 3 to 12 per cent of the total discharge. In these areas 22 to 41 per cent of the phosphorus discharge stems from agricultural activities. If there was no pollution, phosphorus levels would be only 5 to 10 per cent of the present level.
Sweden is sparsely populated, with many major towns located along the coast. The country has one of the highest levels of sewage water treatment in Europe, and river phosphorus concentrations are consequently low (see Figure 5.19 and Map 5.16). About 27 per cent of the phosphorus discharge to inland surface waters in Swedish rivers can be related to sewage and industrial discharges (Figure 14.8) and about 10 per cent to agricultural activities, while the remaining discharges originate from diffuse runoff from land areas.
Elevated nitrate concentrations in European surface waters have been strongly connected with modern agricultural practices, particularly the usage of nitrogen fertiliser (Stibe and Fleischer, 1991; Wright et al, 1991; Edwards et al, 1990; Pierre and Prat, 1989; Neill, 1989). There is a significant relationship between nitrogen concentrations and the percentage of farmland in river catchments (Figure 14.9). In rivers located in catchments with less than 10 per cent agricultural land, nitrogen levels are generally below 0.3 mg N/l, whereas nitrogen levels lie between 0.5 and 2.5 mg N/l in rivers where agricultural land constitutes 10 to 50 per cent of the catchment, and in rivers with the highest proportion of cultivated land in the catchment area, the nitrate and total nitrogen levels are generally above 1.5 and 2 mg N/l, respectively.
In Denmark, where 65 per cent of the total land area is farmland, approximately 80 per cent of the nitrogen discharge to inland waters is a consequence of agricultural activities (Figure 14.10). In Latvia a high proportion of the nitrogen discharge (70 per cent) can be related to agricultural activities. In Germany and the River Po catchment, agriculture is the single most important nitrogen source, representing about 50 per cent of the total amount discharged. Here, point source nitrogen discharges play an important role, with about 45 per cent of the total discharge, three quarters being attributable to municipality wastewater and the remaining quarter to industrial effluents. If there was no pollution, nitrogen levels in the above-mentioned areas would be only 10 per cent of the present levels.
In Sweden, only 6 per cent of the land area is cultivated, and river nitrogen concentrations are usually low (see Figure 5.20 and Map 5.18). Here approximately 40 per cent of the nitrogen discharge into inland surface waters can be related to human activities, the remaining 60 per cent being diffuse discharge from forested and uncultivated areas (background in Figure 14.10). Agricultural activities are responsible for more than two thirds of the nitrogen discharge related to human activities, the remaining third being attributable to point sources. However, in southern Sweden, with its relatively higher proportion of farmland, nitrogen concentrations increase, and a higher percentage of nitrogen discharge originates from agricultural activities (Fleischer et al, 1987). Additional indication of the importance of European agriculture for the pollution of surface waters with nutrients is presented in Table 14.2.
The average agricultural contribution from eight countries/regions with intensive agriculture (excluding Norway, Sweden and Finland) amounts to 64 per cent of total nitrogen loads, ranging from 50 per cent in Germany to 81 per cent in Denmark. The average agricultural contribution to the total phosphorus load of the aquatic environment is 31 per cent, ranging from 21 per cent in The Netherlands up to 41 per cent in Latvia. These are considered below in further detail.
Although these estimates of the contributions of nitrogen and phosphorus from agriculture to the total load of the aquatic environment have been obtained using different, and not always comparable, methods, Table 14.2 clearly indicates that agriculture plays a substantial role in the pollution of the aquatic environment all across Europe, not only with nitrates, but maybe more surprisingly also with phosphorus.
Nitrogen emissions from agriculture |
Many studies have linked increasing nitrate concentrations in rivers to intensification of agriculture and associated changes in soil structure, the extent of land drainage and especially fertiliser use. A substantial surplus of nitrogen is yearly applied to European croplands as artificial fertilisers or as manure. For two Western European countries (The Netherlands and Denmark) with very intensive agriculture, the inputs of nitrogen to agricultural land greatly exceed the amount removed with harvested crops. In The Netherlands (RIVM, 1992) the total yearly input to agricultural land was 1.25 million tonnes N in 1986 compared with 0.46 million removed with crops, and in Denmark (National Agency of Environmental Protection, 1991) the figures in the late 1980s were 0.72 and 0.36 million tonnes N, respectively. This surplus nitrogen is potentially lost as nitrates dissolved in the water leaching out of the root zone, or as ammonia emissions, or denitrified to the atmosphere. Other nitrogen species, for example ammonia and organic nitrogen, can also leach, but compared with nitrate these leaching losses are normally much lower (Table 14.3).
The relationship between nitrate leaving the plant's root zone (leaching) and nitrogen applied as fertiliser is not straightforward. Leaching losses show large variations in space and time depending on several factors, of which climate, soil and crop type, quantity of nitrogen present in the soil (from either natural sources or fertiliser inputs) and the temporal and spatial distribution of nitrogen applications are among the most important. For a discussion of these relationships the reader is referred to Chapter 5.
Table 14.3 shows that nitrate leaching may be 10 to 50 times higher in areas with intensive agriculture compared with leaching from natural areas with similar soil type. However, in many places denitrification processes in the soil (eg, microbiological reduction of nitrate by ferrous sulphide, ferrous ions, methane or organic matter under anaerobic conditions) are able to transform considerable amounts (up to 100 per cent (Postma and Boesen, 1991)) of the nitrates leached either to harmless nitrogen gas (N2), or to nitrous oxide (N2O), a gas that contributes to greenhouse warming and to destruction of the ozone layer (see Chapters 27 and 28). The impact of denitrification on groundwater quality, however, is not always beneficial. For example, nitrate reduction by ferrous sulphide may lead to increased concentrations of sulphate and ferrous ions which, especially in areas with low buffer capacities, increase the risk of acidification of groundwater and surface waters fed by groundwater (see Chapter 31).
Areal estimates of nitrate leaching give an indication of the potential emission to the aquatic environment. The nitrate loads that actually reach surface waterbodies from agricultural land are carried to rivers and lakes by seeping groundwater, lateral subsurface flow in the soil or in drainage tiles, and these loads are in general considerably lower than the amount of nitrate leached. This is not only due to denitrification in the soil and subsoil: important denitrification also takes place in meadows and alluvial forests bordering rivers and lakes (Christensen et al, 1992). These waterlogged habitats (for a detailed description of the function of these riparian zones the reader is referred to Chapter 8) have unfortunately been drained in many places and turned into arable land with less capacity to remove nitrates. The re-establishment of riparian zones on the floodplains would almost certainly help solve the nitrate problem of surface waters. This would be especially beneficial along headwater tributaries of the river network, since it is within these zones that the background water quality of the main river is determined. These small streams also comprise a significant proportion of the total channel length in any basin.
Reliable estimates of the input of nitrogen to surface waters from agriculture (often referred to as area coefficients, as they represent an integrated estimate of nitrogen losses from a river catchment) can best be obtained using the catchment approaches described in Box 14D. The figures presented in Table 14.4 clearly indicate that such inputs are significant, but considerably lower than the leaching losses shown in Table 14.3 for the same type of soils and landuse. Many studies have been carried out across Europe with the aim of establishing area coefficients for nitrate and to establish the relationships between nitrate losses and the factors controlling it.
Table 14.5 summarises the results from selected studies for nitrate losses to surface waters from areas with and without agriculture in different parts of Europe. These data were taken from a variety of conventional surveys using different methodologies. Although not comprehensive, they are indicative of the increase of nitrogen loading of the environment as landuse progresses from forest through grassland to arable agriculture. Thus, for example, Neill (1989) estimated that the average area coefficient from land to rivers in the southeastern part of Ireland was 2.0 kg N/ha/year for unploughed land compared with 76 kg N/ha/year for ploughed land. In areas with intensive agriculture (eg, northwestern Europe) the great majority of area coefficients for nitrate falls between 15 and 25 kg N/ha/year compared with natural areas with nitrate losses of about one tenth of those found for agricultural soils. For Central and Eastern Europe (Czech Republic, Latvia, Lithuania and Poland) area coefficients are in general lower than in northwestern Europe. There are two major reasons for this: both runoff and application rates of nitrogen fertilisers are lower in these countries than in northwestern Europe (see Map 5.7).
Precipitation variability within and between years is another factor heavily influencing areal losses. The largest nitrate losses occur in wet periods during the autumn and winter as the nitrogen demand of the crops is reduced and mineralisation of soil organic matter increases the nitrate content of the soil water. Particularly high loss rates have been observed during the first significant rainfall following drought periods (Roberts, 1987; Burt et al, 1988) and storm events (Webb and Walling, 1985).
Phosphorus emissions from agriculture |
Agricultural phosphorus balances for seven Western European countries in the temperate zone (Sibbesen, 1989) clearly indicate that more phosphorus in fertiliser and manure is added to soils than removed with harvested crops. By far the greatest proportion of this surplus, ranging from 5 kg P/ha/year in the UK to 59 kg P/ha/year in The Netherlands is, however, accumulated in the soil. Losses of phosphorus from agricultural soils to the aquatic environment are very small compared with the amount of phosphorus fertiliser applied and, until recently, these have been considered to be insignificant in relation to other anthropogenic inputs contaminating the aquatic environment. The loss of phosphorus from agriculture can be divided into a point source contribution (farm contribution) and a non-point contribution (area coefficient) carried to the recipient by either water or wind, the latter being of minor importance.
If storage facilities for excreta and silage of feed lots are either too small or not suitably constructed, phosphorus will sometimes be lost from these sources and find its way to the aquatic environment via surface runoff and drainpipes. Such losses are very difficult to monitor, but following episodes of heavy rain they can locally be large and very harmful to the environment.
The phosphorus area coefficient (a measure of phosphorus input to freshwater via groundwater, drainage water and surface runoff, including particulates) varies in the Nordic countries between 0.2 and 0.4 kg P/ha/year in Denmark and 0.7 to 1.8 kg P/ha/year in Finland and Norway, due to differences in soil type, topography, climate, fertiliser application and tillage conditions (Nordic Council of Ministers, 1991). As shown in Table 14.6, similar loss rates have been found elsewhere in countries in the Northern temperate zone.
The majority of measured phosphorus losses from fields are fairly similar for the temperate part of Europe and fall between 0.3 and 1.0 kg P/ha/year. Although these values seem low, recent Danish research (National Agency of Environmental Protection, 1991) has shown that such agricultural losses result in river and lake concentrations too high to prevent or reverse eutrophication even if all point source contributions were stopped.
Phosphorus losses are lower from areas without agriculture. The majority of reported loss rates for catchments with natural vegetation (mostly forested catchments) in the Northern temperate zone range from 0.05 to 0.1 kg P/ha/year (Nordic Council of Ministers, 1991), which is 30 per cent or less of loss rates from agricultural areas.
Substantial amounts of soil and phosphorus can be lost due to wind erosion on susceptible soils. Particularly sensitive are fine sandy soils in open areas and without crop cover during springtime. The wind is able to carry soil particles smaller than 0.1 mm diameter far away, whereas larger soil particles (0.1 to 0.5 mm) tend to be deposited in ditches, in streams and by hedges. Losses of about 2 to 3 cm soil sometimes occur in Denmark from land with a large proportion of fine sand (Sibbesen, 1989). Two to three centimetres of soil is equivalent to about 200 to 300 kg P/ha. Actual measurements of phosphorus loss by wind erosion are sparse, but phosphorus losses up to 18 kg/ha have been recorded by Sdobnikova (1989) from Russian fields subject to severe wind erosion. For further details on the environmental effects of wind erosion the reader is referred to Chapter 7.
Emissions of pesticides and their residues |
Very little (if any) systematic and comparable information is available on emissions of pesticides and their residues to the aquatic environment. Based on model calculations, a European overview showing the extent of the problem has been presented in Chapter 5. A few countries, however (see Statistical Compendium), have published results of their surveys of groundwater concentrations of some of the most widespread pesticides, of which the herbicides atrazine and simazine are among the most common substances to breach the EU drinking water standard of 0.5 µg/l for total pesticides and 0.1 µg/l for individual pesticides. Although the acute toxicity of these substances to animals and humans is only slight (LD50 < 5g/kg (Swanson and Lloyd, 1992), high concentrations of atrazine (>1 µg/l) are commonly found in groundwater under fields where this herbicide has been applied to kill dicotyledonous weeds. For example, high atrazine concentrations, detected in groundwater and surface waters of the Po Valley, Italy, in the mid-1980s, raised public awareness mainly because the long-term carcinogenic effects of atrazine are uncertain. As a consequence, sale and use of atrazine was banned by the Italian government in 1990. At the same time Germany also banned atrazine.
Wastewater is an important source of emissions to waterbodies. Wastewater comprises mainly industrial effluents (with or without separate treatment), household connections and stormwater runoff. Agricultural waste, leachate, and contaminated groundwater may also occasionally contribute to wastewater when sources are connected to sewer systems. Infiltration water into sewers below the groundwater table also acts as a source, driven by hydraulic forces. National statistics on wastewater emissions by volume and weight of polluting substances (eg, BOD, N, P and heavy metals) exist for several European countries, but such national figures are, from an environmental point of view, of only marginal interest because the water quality of a particular recipient (river, lake or coastal area) reflects human activities taking place in the catchment draining to the waterbody regardless of national boundaries. In addition, these statistics are often difficult to compare due to different interpretations between countries of what to include in them. For example, to obtain a national figure for volume discharge of wastewater, some countries add up emissions of untreated and treated effluents; some countries include stormwater runoff while others do not. The need to extend the inventory approach to water emissions has been stressed in Box 14C. Due to the lack of comparable wastewater statistics the following section concentrates on a brief description of the most widespread sewage treatment technologies and summarises their distribution across Europe.
Sewer systems conduct wastewater to the treatment plant. Combined sewers are constructed for transport of both wastewater and stormwater runoff, whereas separate sewers have one network for wastewater (dry weather sources) and another for stormwater runoff (wet weather sources). There are numerous different designs of wastewater treatment plants, involving combinations of physical, chemical and biological processes for separation and degradation of the pollutants.
Primary or physical treatment is of limited value in sewage treatment (Table 14.7) and involves the screening of the wastewater to remove large solids and the production of sludge by settling of particles on the bottom of large sedimentation lagoons or tanks. Recognising the inadequacies of primary treatment alone, biological or secondary treatment was introduced in the 1950s primarily to treat sewage from large population centres. In addition to physical treatment of the sewage, secondary treatment involves efficient bacteria-mediated degradation of organic matter. In the 1970s and 1980s low-technology methods were introduced in Germany and the Scandinavian countries for treating domestic sewage from very small villages and individual houses or farms which could be connected to the sewerage system only with difficulty. These methods (biological sand-filters and constructed reedbeds) apply microbiological degradation of organic matter and are also able to remove parts of the nutrients from the effluent.
Although giving rise to substantial environmental improvements (eg, improving oxygen conditions and decreasing the ammonia content of the receiving waters) secondary treatment was only able to remove a minor proportion of the nutrients creating eutrophication problems (see Chapter 5). Despite introduction of secondary treatment at many treatment plants in the 1960s, eutrophication problems continued to grow, particularly due to increased use of phosphorus-containing detergents. Chemical treatment was introduced in some European countries in the late 1960s and 1970s as a third step in the sewage treatment process, mainly to overcome eutrophication problems. Very efficient removal of phosphorus (Table 14.7) can be achieved by adding a chemical most often lime, aluminium or iron salts to the biologically treated sewage. These chemicals react with phosphorus to form compounds which precipitate and can be removed from the treatment plant with the organic sewage sludge (see Chapter 15). Removal of nitrogen is a further biological process. First, ammonia and organic nitrogen in the wastewater are transformed to nitrate in the process of nitrification. This process requires oxygen whereas the subsequent transformation of nitrate to gaseous nitrogen (denitrification) occurs only under oxygen-free conditions. Treatment plants with nitrification/denitrification technologies may remove as much as 8595 per cent of wastewater nitrogen.
In 1990 about 60 per cent of the European population, in 24 countries for which data were available, was served by sewage treatment of some nature. This average figure covers large variations between countries (Map 14.6) and it is based on OECD statistics, supplemented by data from some Eastern countries obtained from national environment reports and other published sources. However, comparisons and interpretations of sewage treatment statistics should be carried out with caution because it is not always clear how countries define treatment technologies. For example, tertiary treatment may in some countries consist of phosphorus removal only, while other countries in their definition, in addition to phosphorus removal, require nitrification/ denitrification to be included as well. For this report, it has not been possible to obtain data from all Eastern countries and therefore the estimated percentage of population served by sewage treatment plants may be too high. In Albania there are no sewage treatment plants at all and untreated domestic and industrial sewage is discharged directly into rivers and the Mediterranean. Sewage treatment facilities are also poorly developed (with less than 50 per cent of population served) in several Western and Southern countries (eg, Iceland, Ireland, Portugal, Belgium and Greece). On the other hand, in The Netherlands, Luxembourg, Switzerland and the Scandinavian countries, more than 90 per cent of the population was served by some sort of wastewater treatment plants, with Denmark serving 98 per cent of its population.
As illustrated in Map 14.6, there is also large variability between European countries concerning the percentage of population connected to any of the three most widespread sewage treatment technologies. The importance of inefficient primary treatment decreased in most countries over the period 197090 during which time, the construction of treatment plants applying more efficient secondary treatment increased significantly in almost all countries. However, in 1990 only a small percentage of Europe's population was served by the most efficient technology, tertiary treatment. The highest percentages are found in the Scandinavian countries, ranging from 21 per cent in Denmark to 84 per cent in Sweden. Also in Germany (30 per cent of population served) this technology is relatively widespread. Although efficient wastewater treatment technologies are able to improve water quality of receiving waters considerably by reducing inputs of dissolved or suspended pollutants, this happens at the expense of the production of large volumes of sewage sludge. As environmental and health pressures intensify to reduce discharges of untreated sewage into surface waterbodies, a substantial increase in production of sewage sludge is likely to occur. The disposal and environmental impacts of sewage sludge is dealt with in Chapter 15.
For a part of Eastern Europe, the Danube basin, WASH (1992) showed that all of the older and larger cities in five countries Czech Republic, Slovak Republic, Hungary, Romania and Bulgaria have combined sewer systems serving a majority of the population. Interceptors and pump stations have been built to receive flows from sewer systems and carry wastewater to treatment sites, but rarely do the interceptors serve all of a city. Secondary wastewater treatment plants have generally been designed for the larger cities, and have been built to various stages of completion. However, effective operation and maintenance of wastewater treatment plants has been achieved in only a handful of cities in the five countries. Critical pieces of equipment in treatment plants are often defective or inefficient, and many municipal plants are overloaded. Sludge treatment and disposal is a major problem at essentially all the plants. None of the plants provided disinfection of the treated effluent, and none was designed or equipped for removal of the nutrients, nitrogen and phosphorus.
Industrial emissions |
Industry and mining are the principal sources of synthetic organic chemicals and heavy metals in freshwater (WRI/UNEP/UNDP, 1992). Other important emissions from industry include organic matter and nutrients. There are few industries which do not make use of water, either directly as raw material as part of the manufactured product or indirectly for cooling, steam source, cleaning and circulation. A recent study (Meybeck et al, 1989) suggested that most synthetic organic chemical pollution is from chemical and petrochemical refineries, pharmaceutical manufacturing, iron and steel plants, wood pulp and paper processing, and food processing. Industrial sources of heavy-metals include: discharge of heavy-metal solutions from smelting and metal processing; use of metals and metal compounds in manufacture of paints, plastics and batteries; and tanning. Many of these activities generate liquid effluents which may contain many different chemicals, as well as organic matter, depending on the nature of the industrial processes involved (see Table 20.2). These discharges are a source of water pollution and have, especially during the 1960s and 1970s, caused considerable concern worldwide.
Examples from Western Europe The Netherlands and the River Rhine indicate that aquatic metal pollution has declined since its peak in the 1970s, partly as a result of improved wastewater treatment and reduced emissions from industry. Similarly, in Sweden discharges from most iron and steel works have now been considerably reduced. However, the flux of metals from many mines is continuing as a result of seepage from tailings and other mining wastes and these discharges now account for the bulk of inputs of cadmium, copper, lead and zinc to inland waters in Sweden. In the Nordic countries producing pulp and paper, the industrial emissions of organic matter have been substantially reduced in recent years. In Sweden, for example, the yearly emission of organic matter (taken as BOD) has decreased from some 700 000 tonnes at the beginning of the 1960s to 130 000 tonnes despite a 50 per cent increase in production (Nordic Council of Ministers, 1993).
In addition to heavy-metal pollution, mining activities can also result in severe acidification and salinisation of surface water (and groundwater). Coal and potash mining in, for example, Poland, East Germany and Alsace are but a few examples where such problems still occur. Further details are given in Chapter 5.
St Petersburg, with its five million inhabitants, numerous factories and inadequate sewage treatment, is one of the biggest polluters of the Baltic (Lothigius, 1993). There are approximately 300 metal-finishing firms here discharging, for example, large quantities of metals into the city's sewers. Apart from polluting the Baltic, these discharges disturb treatment processes at municipal sewage works and contaminate the sludge produced there.
In a study of industrial emissions (WASH, 1992) from plants producing, among other things, chemicals, steel, processed food and automobiles or refining petroleum products in five Danube countries (Czech Republic, Slovak Republic, Hungary, Romania and Bulgaria), it was shown that industrial wastewater treatment or pre-treatment was primitive and operated ineffectively. In addition, large industrial complexes have been developed at locations where available water resources cannot dilute or assimilate the emissions.
Generally, only few data on discharge of wastewater and polluting substances by sectors of industry are available. Systems of wastewater management, emissions inventories and reporting differ from one country to another, which makes comparisons almost impossible. However, there are a few examples of environmental agencies in some countries measuring discharges to water by industrial sectors and the tonnage and concentration of inputs from industry to rivers some even publish lists of the most polluting 'companies'. Some data for Eastern European countries have been published in national reports. Countries which publish relevant information of this kind at the national level include: Belgium (Flanders), Bulgaria, France, The Netherlands, the Scandinavian countries and the UK.
TOWARDS INTEGRATED POLLUTION PREVENTION AND CONTROL |
During the past two decades, European countries have achieved important progress in reducing emissions of traditional pollutants to air and water as a result of a number of concurrent factors, including:
These factors have not been equally important for all pollutants, across all economic sectors or across all European countries. Reduction has been achieved primarily in the emissions of sulphur dioxide associated with high-sulphur-containing fossil fuels and certain industrial processes; sulphur dioxide emissions have been cut on average about 40 per cent in Western European countries, but remain a concern at the local and regional level particularly in Eastern European countries. Emissions of NOx and VOCs have not decreased, but have either remained stable or increased. This is a cause of increasing concern for both their local and global impacts. In the next few years, European countries, which are responsible for about 30 per cent of global CO2, will have to stabilise these emissions to comply with the global Framework Climate Change Convention adopted at the UN Conference on Environment and Development (Rio, 1992).
Concerning emissions to water, the reduction of point source emissions of traditional water pollutants has been achieved in most Western European countries as a result of implementing advanced treatment technologies and improved industrial processes. Nevertheless, increased use of hazardous substances in production processes and consumer products has changed the composition of wastewater. In addition, intensive agriculture and livestock farming have combined with increasing use of chemicals to add an enormous pressure on the aquatic environment from non-point source emissions.
As policies to reduce emissions have been implemented, some important lessons have been learned. Emerging air and water pollution problems in the last two decades have been addressed separately. Most severe local pollution problems have been successfully dealt with by national programmes and regulations focusing on specific media. However, this approach has proved inadequate to face the cross-media nature of environmental problems. Pollution control technologies have shifted pollution problems from the air and surface water to soil and groundwater. The most visible effect is the increasing amount of waste in the form of ashes or sludges with high concentrations of hazardous substances from pollution control processes and the treatment of emission flows.
Criticism of the single-medium approach to environmental regulations emerged during the 1970s and 1980s. With the recognition of complex environmental problems, such as acidification, soil contamination and climate change, the need to move towards an integrated approach has been more fully appreciated. Several Northern and Western European countries have now adopted new regulations aiming at integrated pollution control. Adopting this approach should help prevent pollution problems instead of transferring them from one part of the environment to another. Following this line is also expected to improve the ability to set priorities and choose more efficient solutions. The European Commission (CEC, 1993) has submitted to Council a proposal for a Directive on Integrated Pollution Prevention and Control with the aim 'to prevent, wherever practicable, or minimise emissions from installations within the Community so as to achieve a high level of protection for the environment as a whole'.