- Email: [email protected]
Biogeodynamics of contaminated sediments and soils: perspectives for future research
Journal of Geochemical Exploration 62 Ž1998. 37–40
Biogeodynamics of contaminated sediments and soils: perspectives for future research W. Salomons
)
GKSS, Research Institute Geesthacht, Max-Planck Straße, D-21501 Geesthacht, Germany Accepted 6 November 1997
Abstract Soils and sediments are part of the hydrological cycle in which particulate material is transported from continents to oceans. Sediments and soils have a high storage capacity for contaminants. In any part of the hydrological cycle far less than 0.1% are actually dissolved in the water, and more than 99.9% is stored in the sediments and soils. The dissolved fraction, however, is the most mobile and most bio-available. Various interactions determine the actual concentrations of dissolved contaminants and cause changes in concentrations during transport. q 1998 Elsevier Science B.V. All rights reserved. Keywords: biogeodynamics; contaminants
1. Introduction The pathway of contaminants in the hydrological cycle from soils to oceanic sediments is shown in Fig. 1 as three interlocking wheels. The inner one, the atmosphere, is fast running and has a short residence time, the water wheel is slower moving and has residence times ranging from weeks Žrivers and estuaries. to years Žlakes and coastal waters. and even longer for the oceans. The outer wheel is the very slow moving particulates wheel where the residence times exceed those of the water wheel by orders of magnitude. The ultimate storage of all materials on the continents, be it sediments or soils, is of course the ocean floor, but before the presentday pollutants will end up there and become part of
)
E-mail: [email protected]
the geological cycle may take millions of years ŽSalomons and Stigliani, 1995.. Fig. 1A shows the situation in Western Europe as it existed before about 1970 Žno or little pollution control. and as it still exists in EasternrCentral Europe and increasingly in newly industrialising countries. In this situation there is a flux of contaminants from the center to the soils and sediments where more than 99% of the contaminants will be stored. Even if we take into account the recycling of metals in modern society, it will only delay the time period over which the pollutants ultimately will end up in sediments and soils.
2. Stored contaminants Past environmental research, studying single compartments like soils, rivers or estuaries, has been quite successful in reducing the impact on the envi-
0375-6742r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 5 - 6 7 4 2 Ž 9 7 . 0 0 0 6 3 - 0
38
W. Salomonsr Journal of Geochemical Exploration 62 (1998) 37–40
Fig. 1. The ‘wheels’ transporting pollutants in the environment. ŽA. The situation in Western Europe before 1970 with discharge of pollutants and accumulation in sediments and soils. ŽB. The situation after 1970 with environmental regulations in force and the stored pollutants now becoming a source for the surface and ground waters.
ronment of industrial point sources. Industry has responded to the legislation through end-of-pipe line solutions and by better management of the flow of substances with reduced losses to the environment, although some losses will always be inevitable. However, we still have to deal with the stored contaminants Žindustrial heritage. in sediments and soils. Hot spots, like industrial sites or contaminated harbours, which cover relatively small areas, can be cleaned up quite efficiently and many techniques have been developed in order to do this. However, in the US, and Western and Central Europe there are many large-scale polluted sites. These sites are simply too large to be cleaned up with available technologies at reasonable costs. They are polluted by mining activities, smelters and other large industries, and the pollution extends not only to soils, but also to sediments in water ways and reservoirs. In addition, similar, new sites are being created with little or no concern for environmental protection in many parts of the world. Also waste dumps are abundant and their number will increase in the future.
3. Source strength The impact on the environment depends on the source strength of the pollutants at the dump site. To obtain information on the source strength, and in particular how it changes with time, it is necessary to assess the time-dependent processes. Furthermore, large areas exist with low to moderate levels of contamination with heavy metals, pesticides and nu-
trients. This is in particular the case for those areas in Europe where intensive agriculture is practised. A prime example is the Netherlands. In a number of cases impacts of these diffuse pollutants are already noticeable through pollution of groundwater resources. Other examples of low to moderately polluted areas are those affected by atmospheric deposition of pollutants. In all cases the areas affected are large and it is not economically sound to clean up with conventional methods. Common to all of these Žat a first glance. nonrelated pollution cases is the important role of long-term processes. It is likely that large-scale contaminated sites, waste dumps and the diffuse polluted soils and sediments will exist for many years to come. It is necessary to take a long-term view toward insuring that the capacity to retain the contaminates is not diminished. Likewise, it will be necessary to understand the potential for large-scale contaminant mobilization at these sites triggered by changing environmental conditions. Furthermore long-term risk assessment of the intended economical use of these sites has to be based on sound Žbio.geochemical knowledge.
4. Mobility The mobility of contaminants is often determined by the pH, redox conditions and the presence of complexing agents such as dissolved organic matter and inorganic anions. These parameters which control the balance between the retention and mobility of the contaminants are coined Capacity Controlling Parameters ŽCCPs. or master variables. For short-term risk assessment Ž5 to 10 years. it is sufficient to understand how the master variables determine contaminant mobility and hence their leaching and bio-availability. Much information is available in the literature on this subject already. Much less is known about the processes which regulate the dynamics of the master variables and CCPs themselves. This knowledge gap is not that important for short-term processes which determine the acute pollution status of sediments and soils and their immediate short-term impact on the environment. Over the long term, however, changes in the CCPs and master variables can cause mobilization of vast
W. Salomonsr Journal of Geochemical Exploration 62 (1998) 37–40
stores of pollutants manifested by behaviour that is time-delayed and non-linear, precisely the kind of response that catches policy makers, the public, and even the scientists by surprise. One example of this syndrome in recent decades is the advent of acid deposition as a new environmental stress. The broad-scale acidification of the environment has led to a correspondingly broad-scale leaching of aluminium and other heavy metals from acid-impacted areas that is continuing to this day. For example, in Scandinavia levels of mercury in freshwater fish are increasing even though emissions and deposition of mercury have been decreasing for several decades. The contamination of fish has been attributed to the remobilization of mercury locked in watershed soils decades ago, and now mobilized by soil acidification. Changes in the CCPs are of a long-term nature and are initiated by changes in the major element cycles in the soil–sediment system. The effect of these changes on concentrations of elements in the soil solution are in particular non-linear for inorganic pollutants and may cause strong increases in concentrations over a short time period, in comparison with the time needed to accumulate the concentrations of pollutants. This can result in increased leaching to
39
ground- and surface waters, impact on the ecosystem and the necessity to take control measures at a short notice. If one wants to control, for instance, diffuse pollution and prevent non-linear responses, it is necessary to assess and manipulate those factors which determine the capacity controlling parameters and master variables. This implies that it is necessary to study in detail the major biogeochemical cycles of sulphur, nitrogen, carbon and also of calcium, iron and manganese.
5. Multi-disciplinary approach The soil–sediment system with its stored pollutants has to be treated as a dynamic system in which changes take place over time frames on the order of years to decades to centuries. The soil–sediment system as a dynamic entity can be described as biogeodynamics, since a full understanding of longterm changes requires the combination of scientists from the ‘geo’ and ‘bio’ sciences. A mono-disciplinary approach will not lead to a better understanding of the long-term behaviour of stored chemicals in the environment. On one side we have the scientist who know ‘nearly everything’ about the intricate
Fig. 2. Schematic diagram of the interactions between biogeochemical cycles, capacity-controlling parameters and the mobility of contaminants including the methods for immobilization through conventional clean-up or through geochemical engineering.
40
W. Salomonsr Journal of Geochemical Exploration 62 (1998) 37–40
interactions of chemicals with organic matter, adsorbing surfaces in the soils etc. On the other side we have the geo- and biogeochemist who studies the cycles of the major elements like carbon, nitrogen and sulphur: element cycles which determine the capacity-controlling parameters. It is necessary to bring these disciplines together with their own pieces of the puzzle to solve potential problems with continuous diffuse build-up of pollutants in soils and sediments and changes in major element cycles.
6. Process manipulation Fig. 2 illustrates the various ways in which it is possible to manipulate the processes The capacitycontrolling parameters can be changed by additives. In the case of pH changes this may be carbonates or slowly weathering silicates. To increase the adsorption capacity for phosphorus the addition of iron chloride to promote the precipitation of hydroxides has been suggested and tested. Human activities can inadvertently change biogeochemical cycles and hence the mobility of contaminants. Examples are civil engineering works, drainage of land, changing land use due to agricultural policy, population pres-
sure and the emissions and demand for space caused by the expected global increase in traffic. All of them have the potential to disturb biogeochemical cycles and hence the equilibria between accumulated contaminants in sedimentsrsoils and groundwater or surface water and can result in a increase in the rate of supply to the fast moving ‘water wheel’. In this case we deal with regional issues with a strong socio-economic component. This will require a regional approach in which for instance catchment areas and coastal regions are treated as a continuum, as is already common practice in the ‘geo-sciences’, but not to that extent in the ‘environmental sciences’. 7. Conclusion If the geo-sciences show the flexibility to team up with the socio-economic sciences they will have a challenging and fruitful future research area. References Salomons, W., Stigliani, B. ŽEds.., 1995. Biogeodynamics of Pollutants in Soils and Sediments: Risk Assessment of Delayed and Non-Linear Responses. Environmental Science Series, Springer, Berlin.
Biogeodynamics of contaminated sediments and soils: perspectives for future research W. Salomons
)
GKSS, Research Institute Geesthacht, Max-Planck Straße, D-21501 Geesthacht, Germany Accepted 6 November 1997
Abstract Soils and sediments are part of the hydrological cycle in which particulate material is transported from continents to oceans. Sediments and soils have a high storage capacity for contaminants. In any part of the hydrological cycle far less than 0.1% are actually dissolved in the water, and more than 99.9% is stored in the sediments and soils. The dissolved fraction, however, is the most mobile and most bio-available. Various interactions determine the actual concentrations of dissolved contaminants and cause changes in concentrations during transport. q 1998 Elsevier Science B.V. All rights reserved. Keywords: biogeodynamics; contaminants
1. Introduction The pathway of contaminants in the hydrological cycle from soils to oceanic sediments is shown in Fig. 1 as three interlocking wheels. The inner one, the atmosphere, is fast running and has a short residence time, the water wheel is slower moving and has residence times ranging from weeks Žrivers and estuaries. to years Žlakes and coastal waters. and even longer for the oceans. The outer wheel is the very slow moving particulates wheel where the residence times exceed those of the water wheel by orders of magnitude. The ultimate storage of all materials on the continents, be it sediments or soils, is of course the ocean floor, but before the presentday pollutants will end up there and become part of
)
E-mail: [email protected]
the geological cycle may take millions of years ŽSalomons and Stigliani, 1995.. Fig. 1A shows the situation in Western Europe as it existed before about 1970 Žno or little pollution control. and as it still exists in EasternrCentral Europe and increasingly in newly industrialising countries. In this situation there is a flux of contaminants from the center to the soils and sediments where more than 99% of the contaminants will be stored. Even if we take into account the recycling of metals in modern society, it will only delay the time period over which the pollutants ultimately will end up in sediments and soils.
2. Stored contaminants Past environmental research, studying single compartments like soils, rivers or estuaries, has been quite successful in reducing the impact on the envi-
0375-6742r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 5 - 6 7 4 2 Ž 9 7 . 0 0 0 6 3 - 0
38
W. Salomonsr Journal of Geochemical Exploration 62 (1998) 37–40
Fig. 1. The ‘wheels’ transporting pollutants in the environment. ŽA. The situation in Western Europe before 1970 with discharge of pollutants and accumulation in sediments and soils. ŽB. The situation after 1970 with environmental regulations in force and the stored pollutants now becoming a source for the surface and ground waters.
ronment of industrial point sources. Industry has responded to the legislation through end-of-pipe line solutions and by better management of the flow of substances with reduced losses to the environment, although some losses will always be inevitable. However, we still have to deal with the stored contaminants Žindustrial heritage. in sediments and soils. Hot spots, like industrial sites or contaminated harbours, which cover relatively small areas, can be cleaned up quite efficiently and many techniques have been developed in order to do this. However, in the US, and Western and Central Europe there are many large-scale polluted sites. These sites are simply too large to be cleaned up with available technologies at reasonable costs. They are polluted by mining activities, smelters and other large industries, and the pollution extends not only to soils, but also to sediments in water ways and reservoirs. In addition, similar, new sites are being created with little or no concern for environmental protection in many parts of the world. Also waste dumps are abundant and their number will increase in the future.
3. Source strength The impact on the environment depends on the source strength of the pollutants at the dump site. To obtain information on the source strength, and in particular how it changes with time, it is necessary to assess the time-dependent processes. Furthermore, large areas exist with low to moderate levels of contamination with heavy metals, pesticides and nu-
trients. This is in particular the case for those areas in Europe where intensive agriculture is practised. A prime example is the Netherlands. In a number of cases impacts of these diffuse pollutants are already noticeable through pollution of groundwater resources. Other examples of low to moderately polluted areas are those affected by atmospheric deposition of pollutants. In all cases the areas affected are large and it is not economically sound to clean up with conventional methods. Common to all of these Žat a first glance. nonrelated pollution cases is the important role of long-term processes. It is likely that large-scale contaminated sites, waste dumps and the diffuse polluted soils and sediments will exist for many years to come. It is necessary to take a long-term view toward insuring that the capacity to retain the contaminates is not diminished. Likewise, it will be necessary to understand the potential for large-scale contaminant mobilization at these sites triggered by changing environmental conditions. Furthermore long-term risk assessment of the intended economical use of these sites has to be based on sound Žbio.geochemical knowledge.
4. Mobility The mobility of contaminants is often determined by the pH, redox conditions and the presence of complexing agents such as dissolved organic matter and inorganic anions. These parameters which control the balance between the retention and mobility of the contaminants are coined Capacity Controlling Parameters ŽCCPs. or master variables. For short-term risk assessment Ž5 to 10 years. it is sufficient to understand how the master variables determine contaminant mobility and hence their leaching and bio-availability. Much information is available in the literature on this subject already. Much less is known about the processes which regulate the dynamics of the master variables and CCPs themselves. This knowledge gap is not that important for short-term processes which determine the acute pollution status of sediments and soils and their immediate short-term impact on the environment. Over the long term, however, changes in the CCPs and master variables can cause mobilization of vast
W. Salomonsr Journal of Geochemical Exploration 62 (1998) 37–40
stores of pollutants manifested by behaviour that is time-delayed and non-linear, precisely the kind of response that catches policy makers, the public, and even the scientists by surprise. One example of this syndrome in recent decades is the advent of acid deposition as a new environmental stress. The broad-scale acidification of the environment has led to a correspondingly broad-scale leaching of aluminium and other heavy metals from acid-impacted areas that is continuing to this day. For example, in Scandinavia levels of mercury in freshwater fish are increasing even though emissions and deposition of mercury have been decreasing for several decades. The contamination of fish has been attributed to the remobilization of mercury locked in watershed soils decades ago, and now mobilized by soil acidification. Changes in the CCPs are of a long-term nature and are initiated by changes in the major element cycles in the soil–sediment system. The effect of these changes on concentrations of elements in the soil solution are in particular non-linear for inorganic pollutants and may cause strong increases in concentrations over a short time period, in comparison with the time needed to accumulate the concentrations of pollutants. This can result in increased leaching to
39
ground- and surface waters, impact on the ecosystem and the necessity to take control measures at a short notice. If one wants to control, for instance, diffuse pollution and prevent non-linear responses, it is necessary to assess and manipulate those factors which determine the capacity controlling parameters and master variables. This implies that it is necessary to study in detail the major biogeochemical cycles of sulphur, nitrogen, carbon and also of calcium, iron and manganese.
5. Multi-disciplinary approach The soil–sediment system with its stored pollutants has to be treated as a dynamic system in which changes take place over time frames on the order of years to decades to centuries. The soil–sediment system as a dynamic entity can be described as biogeodynamics, since a full understanding of longterm changes requires the combination of scientists from the ‘geo’ and ‘bio’ sciences. A mono-disciplinary approach will not lead to a better understanding of the long-term behaviour of stored chemicals in the environment. On one side we have the scientist who know ‘nearly everything’ about the intricate
Fig. 2. Schematic diagram of the interactions between biogeochemical cycles, capacity-controlling parameters and the mobility of contaminants including the methods for immobilization through conventional clean-up or through geochemical engineering.
40
W. Salomonsr Journal of Geochemical Exploration 62 (1998) 37–40
interactions of chemicals with organic matter, adsorbing surfaces in the soils etc. On the other side we have the geo- and biogeochemist who studies the cycles of the major elements like carbon, nitrogen and sulphur: element cycles which determine the capacity-controlling parameters. It is necessary to bring these disciplines together with their own pieces of the puzzle to solve potential problems with continuous diffuse build-up of pollutants in soils and sediments and changes in major element cycles.
6. Process manipulation Fig. 2 illustrates the various ways in which it is possible to manipulate the processes The capacitycontrolling parameters can be changed by additives. In the case of pH changes this may be carbonates or slowly weathering silicates. To increase the adsorption capacity for phosphorus the addition of iron chloride to promote the precipitation of hydroxides has been suggested and tested. Human activities can inadvertently change biogeochemical cycles and hence the mobility of contaminants. Examples are civil engineering works, drainage of land, changing land use due to agricultural policy, population pres-
sure and the emissions and demand for space caused by the expected global increase in traffic. All of them have the potential to disturb biogeochemical cycles and hence the equilibria between accumulated contaminants in sedimentsrsoils and groundwater or surface water and can result in a increase in the rate of supply to the fast moving ‘water wheel’. In this case we deal with regional issues with a strong socio-economic component. This will require a regional approach in which for instance catchment areas and coastal regions are treated as a continuum, as is already common practice in the ‘geo-sciences’, but not to that extent in the ‘environmental sciences’. 7. Conclusion If the geo-sciences show the flexibility to team up with the socio-economic sciences they will have a challenging and fruitful future research area. References Salomons, W., Stigliani, B. ŽEds.., 1995. Biogeodynamics of Pollutants in Soils and Sediments: Risk Assessment of Delayed and Non-Linear Responses. Environmental Science Series, Springer, Berlin.