Environmental specimen bank of the Federal Republic of Germany Significance of surfactants

J. D. Schladot (S) • H. W. Dürbeck E. Klumpp • M. J. Schwuger Institute of Applied Physical Chemistry, Research Centre Jülich (KFA), P.O. Box 1913, 52425 Jülich, FRG

Abstract Environmental contaminants in water, soil, and air, as well as changes in their concentration with respect to space and time may be quite effectively detected by the analysis of appropriate indicators (biomatrices from different levels of the food chain, sediments, sludges, dusts) which accumulate these chemicals by several orders of magnitude.

However, regular monitoring of the environment should not be restricted to presently known substances. The suitable storage of representative indicator specimens allows also the retrospective analysis of chemicals which are not detectable at present or which have not been regarded as environmental pollutants so far.

Therefore, the German Environmental Specimen Bank (ESB) of the Federal Government was established in 1985 with the purpose of storing representative samples from the terrestrial and aquatic environment as well as from human beings for future decades without any change in chemical composition.

In spite of its relatively limited time of operation, the ESB has already obtained a variety of promising results which support not only the success of legislative regulations (introduction of unleaded fuels, ban of pentachlorophenol), but demonstrate also the decrease of pollutants in rivers due to reduced industrial or municipal discharges. Moreover, the effectivity of new technologies with respect to environmental protection may be traced back by a specific and retrospective characterization of suitable indicator samples.

In addition to its routine program, the Institute of Applied Physical Chemistry of the Research Centre Jülich (KFA) is performing basic studies on the speciation of selected elements such as arsenic, mercury, and tin, and the determination of new compounds. In this respect, surfactants play an important role because they can influence the immobilization or remobilization of pollutants in soils or sediments. The mobility of other chemicals in such matrices can be estimated, if surfactant concentrations are known. With that, a prediction of possible contaminations of ground or surface waters is possible. Selected examples will be discussed in detail.

Key words bioaccumulation — biomonitoring — environmental specimen bank — mobilization/immobilization of pollutants — retrospective analysis

Introduction

One of the most urgent tasks of the environmental protection policy consists in the regular monitoring of pollutants in water, soil, and air, as well as in various stages of important food chains (plants, animals), finally leading to man. However, this monitoring should not be restricted to the determination of stationary pollutant loads. On the contrary, it requires, in particular, information about their time- and space-dependent behavior under natural environmental conditions. Therefore, the following questions should be answered as a first priority:

— Where do these materials persist and where do they possibly accumulate?

— What chemical form are they present in?

— How mobile are they in the environment?

— Why are they mobilized or immobilized?

— What short- or long-time effect do they have on man and the environment?

— When and how do new pollutants appear in the environment?

— What new substances are environmental chemicals converted into and in what time?

— Do toxic subtances — possibly — result during this process and how stable are they?

With the knowledge and methods previously available, possible influences and impacts of environmental chemicals produced by man and intentionally or unintentionally released into the environment on natural or semi-natural ecosystems, and also on the basic necessities of life and health of mankind can only be inadequately forecast or their potential dangers assessed [1].

According to the "European Inventory of Existing Commerical Substances" EINECS (after GDCh/BUA) [2], there are currently approx. 100 000 different chemical substances whose behavior and action in the environment are still largely unknown [3].

It is therefore all the more important that even the smallest changes in the environment and in the various trophic stages and food chains should be detected by specific observation and monitoring. Their origins have to be elucidated and if necessary their further development should be halted. Corresponding scientific and technical activities place particular emphasis on the protection of mankind and the environment against anthropogenic and geogenic pollutants, as well as their systematic and continuous detection in soil, water, air and selected biological specimens.

On the basis of their specific accumulation potential for certain pollutants, biological samples have the advantage that changes in the local or regional pollution situation can be recognized much more easily. They thus have a special indicator function in the determination of pollutant trends or the early recognition of new chemicals in the environment (see Fig. 1).

mammals (e.g. seal fatty tissue)

birds (e.g.herring gull, fat/eggs)

birds (herring gull brain)

_1 - 10ppm fish (e.g. dab) 0.1 - 1 ppm mussel (e.g. blue mussel) 0.01 - 0.1 ppm

Sea water 0.000001 -0.00001 ppm

PCB food limit value for fish in the U.S.: < 2ppm

Fig. 1 Accumulation of polychlorinated biphenyls (PCB) in various trophic stages of the marine environment

Tasks of the environmental specimen bank

The characterization and evaluation of environmental and human samples — in their actual state, but also in their development over time — creates important prerequisites within the framework of a precautionary policy for the following:

— recognition of impending undesirable developments;

— estimation of nature and extent of undesirable developments already in evidence and their consequences;

— obtaining insights to set priorities for political activities, and

— compiling basic principles for the precautionary policy of the Federal Government in the field of nature conservation and environmental protection and also for human health.

As early as 1973, these insights led to the development of a strategic concept of providing the necessary scientific basis for realizing this precautionary policy by establishing an environmental specimen bank. Special guidelines (Standard Operation Procedures, SOP) were developed for all the operating steps necessary for implementation including the analytical work [4],

The long-term usefulness of the stored samples, particularly for retrospective analysis, is ensured by the fact that all materials are deep frozen at temperatures below —150°C immediately after collection. In this way, any possible changes in chemical composition are completely prevented or reduced to a minimum [5,6], Futher sample

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Fig. 2 Flow chart of the preparation of environmental specimens treatment (processing, homogenization and aliquotization into standardized sub samples) (see Fig. 2) is similarly carried out in the above-mentioned temperature range, and strict compliance with these conditions is monitored by continuous controls.

After preliminary analytical studies in 1976—1978, the logistic and technical prerequisites for the feasibility of an environmental specimen bank were thoroughly investigated between 1979 and 1984 in the pilot project "Environmental Specimen Bank" financed by the BMFT (Federal Ministry for Research and Technology) [7],

Participating institutions

Since January 1, 1985, the Environmental Specimen Bank has been established as a permanent institution under the responsibility of the BMI (later the BMU, Federal Ministry for the Environment, Nature Conservation and Reactor Safety). The Federal Environmental Agency (UBA) is responsible for co-ordination. Two specimen banks are subsumed under the general heading of the German Environmental Specimen Bank:

— the Specimen Bank for Environmental Specimens — at the Institute of Applied Physical Chemistry of the Research Centre Jülich (KFA), and

— the Specimen Bank for Human Organ Specimens — at the Institute of Pharmacology and Toxicology of the Universiy of Münster.

These institutes also take part in the specimen characterization by analyzing heavy metals, metalloids, and essential elements in environmental samples at the Research Centre Jülich, whereas the corresponding activities at Münster comprise both the inorganic and also the organic (primarily chlorinated hydrocarbons) analysis.

Furhtermore, the work of the Environmental Specimen Bank in the field of ecology and in the selection of representative areas and specimen species is supported and guided by

— The Institute of Biogeography at the University of the Saarland.

— The Institute of Ecological Chemistry at the GSF Neuherberg, and

— the Biochemical Institute for Environmental Carcinogens, Grosshansdorf are responsible for the analysis of organochlorine compounds and polycyclic aromatic hydrocarbons (PAH) in the stored terrestrial and aquatic environmental samples (see Fig. 3).

ENVIRONMENTAL SPECIMEN BANK of the

FEDERAL GERMAN GOVERNMENT

Federal Ministry for Environment, Nature Conservation and Reactor Safety

Fedreal Environmental Agency

Environmental Specimen Bank Information System

Specimen Bank for

Environmental Specimens

institute for

Applied Physical Chemistry

Research Centre Jülich, KFA

Institute for Biogeography

University of the Saarland

-

Saarbrücken

Institute for Ecological Chemistry

GSF Neuherberg

Biochem. Inst for

Environm. Carcinogenics

-

Hamburg/G roßhansdorf

Specimen Bank for Human Organs institute for Pharmocology and Toxicology

University of Münster

Specimen Bank for Human Organs institute for Pharmocology and Toxicology

University of Münster

Fig. 3 Organizational chart of the project "Environmental Specimen Bank" of the Federal Republic of Germany

Representatively selected ecosystems

With the operation of the German Environmental Specimen Bank [8—10] as part of the environmental monitoring and ecosystem research network currently in the process of development biological objects in the context of their ecosystem will now be preferentially observed now in addition to the monitoring program for air and water which exists already. An overall concept has been developed for this monitoring and thus also for the environmental specimen bank by a committee of experts under the auspices of the BMU, taking into consideration different types of ecosystems with corresponding representative sampling areas. In these areas (see Fig. 4) continuous sampling has been carried out to some extent since 1985 (up to now, every 2 years). However, this will be converted into a 1-year sampling frequency in accordance with an overall concept to be realized by the year 2000 in order to utilize the analytical, biometric and meteorological data much more effectively in the sense of real-time monitoring. Since the reunification of Germany

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Natl anal parke (f Wattenmeer

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Types oJ Ecosystem:

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Berth tes gad En seml-natura I

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Industrialized i I Im nie forestreai human organ specimens in 1989, representative areas in the former East Germany have also been increasingly studied with the support of local institutions.

Representative specimen species

The selection and assignment of representative specimen species from the terrestrial and aquatic environment, and also from the human field, was similarly undertaken by a committee of experts. This selection is regularly reviewed on the basis of new insights and, if necessary, corrected. However, very serious reasons would be required to eliminate a specimen species that has been collected and stored for a considerable period of time. At present, the following specimen species are collected on a routine basis:

— from the terrestrial field: soil samples, tree samples (leaves and shoots), and animal samples (pigeons' eggs, roe deer liver, earthworms);

— from the limnic field: sediments, fish (muscle and liver), and freshwater mussels;

— from the marine environment: sediments, algae, mussels, fish (muscle and liver), and sea bird eggs (see Fig. 5).

The specimen species from the human field (fatty tissue, liver, kidney, blood, urine, hair, saliva) are stored in the specimen bank for human organ samples at the University of Miinster. The range of analyzed elements and organic pollutants is largely identical with that of the environmental specimens in order to detect any possible connections between the pollution situation in man and his immediate environment.

As part of a supplementary research and development at the Institute of Applied Physical Chemistry, investigations are currently been carried out on materials of the en-

ESB - facilities

algae/plankton

Fig. 5 Various selected sample types from different sectors of the environment algae/plankton

Fig. 4 Geographical map of the representative sampling areas for the Environmental Specimen Bank

Fig. 5 Various selected sample types from different sectors of the environment vironmental specimen bank with the objective of clarifying the possible influences of surface-active substances (surfactants) on the transport behavior and bioavailability of inorganic and organic environmental chemicals in soils and sediments. Particular attention is being paid to the determination of synergistic or antagonistic effects as well as to questions of the immobilization (bound residues) and remobilization of pollutants.

Results

Terrestrial environment — atmospheric input

The initial characterization of environmental specimens from the terrestrial environment — with four complete data sets to date — as well as the regular examinations of human blood from selected parent populations carried out at 6-month intervals has already led to reliable and thus credible results about the ubiquitous decrease in lead pollution. Making use of the Institute's own measuring network to determine pollutant deposition by precipitation, it can be demonstrated without any doubt that the legal measures to reduce lead emissions (introduction of unleaded fuels in 1984) have achieved significant success. The data collections carried out continuously since 1980 — with weekly sampling — indicate, for example, that in rural regions close to industrial centers lead deposition decreased by more than 70% in 1921 in comparison to 1980. A comparable trend is apparent in so-called "background regions," not directly polluted, in which wet lead deposition can be almost exclusively attributed to atmospheric long-distance transport (see Fig. 6).

The tree specimens (spruce shoots, beech leaves) collected and stored since 1985 from the regions of the environmental specimen bank also provide convincing documentation of the decrease in lead pollution (see Fig. 6). The same is also true for the human field, as con firmed by the results of the continuous lead studies of blood from student populations at the University of Münster. On the whole, the results provide clear evidence of the positive effects of the introduction of unleaded fuels.

Cadmium contents in tree specimens (leaves, needles) from various regions display higher concentrations at an agricultural site than in an urban industrialized area. Since the plant uptake of this element essentially takes place via the roots, it must be assumed that the different contents depend on the bioavailability or mobility of this heavy metal in the soil.

The reasons for a varying bioavailability are very complex and extensive site-related studies are necessary to clarify them. For example, differences in humus content or permanent soil moisture are conceivable. A further possibility results from soil acidification caused by acidic rain. Moreover, ubiquitously occurring surface-active substances (surfactants) should also be taken into consideration with respect to a change in mobility. It was thus demonstrated in laboratory experiments that cationic surfactants are basically capable of releasing both essential trace elements (Ca2+, Mg2+, Na+) as well as toxic heavy metals (Cd2+) from degraded loess soil (orthic luvisol — approx. 25% clay mineral fraction). Furthermore, investigations on the clay mineral montmorillonite demonstrated that this release of cations occurs quantitatively and stoichiometrically [11]. In Fig. 7 this change in the balance of nutrients and trace elements is demonstrated by the example of a layer silicate loaded with Na+/Cd2+. The addition of the cationic surfactant initially leads to the replacement of relatively weakly bound Na+ ions. Only after this displacement process has been completed a quantitative release of Cd2+ into the soil solution takes place. However, if the monovalent Na+ ion is replaced by divalent, essential cations (e.g., Ca2+) in the silicate layer, a simultaneous displace-

Fig. 6 Decline in lead pollution from wet deposition in rural areas (site: Jülich) and in spruce shoots from a "background area" (site: Berchtesgaden National Park)

15 4

io 4

sprucc shoots

mobilization [%]

mobilization [%]

DTAB

50 100 150 200

cationic surfactant added [%CEC]

Fig. 7 Displacement of Na+ and Cd2+ ions from a layer silicate by cationic surfactant [11]; (DTAB = dodecyl trimethyl ammonium bromide, CEC = cation exchange capacity)

free DTAB in solution [%]

DTAB

50 100 150 200

cationic surfactant added [%CEC]

Fig. 7 Displacement of Na+ and Cd2+ ions from a layer silicate by cationic surfactant [11]; (DTAB = dodecyl trimethyl ammonium bromide, CEC = cation exchange capacity)

ment by the cationic surfactant takes place because both Ca2+ and also Cd2+ are bound to the exchange sites with comparable strength [11],

Limnic environment — inputs into river water systems

Considerable pollution with heavy metals and chlorinated hydrocarbons was detected in sediments from the River Elbe collected in 1991 and 1992 in co-operation with the Federal Hydrology Agency (BfG, Berlin office). Thus, for example, the salt contents and also the concentrations

Fig. 8 Distribution of mercury concentrations in Elbe sediments from 1991 and 1992 along the Elbe at sampling sites of the International Commission for the Protection of the Elbe; Schmilka — border Czech Republic/Germany; Barby — Saale mouth; Cumlosen — former boundary between the two German states

Fig. 8 Distribution of mercury concentrations in Elbe sediments from 1991 and 1992 along the Elbe at sampling sites of the International Commission for the Protection of the Elbe; Schmilka — border Czech Republic/Germany; Barby — Saale mouth; Cumlosen — former boundary between the two German states of some heavy metals such as mecury, cadmium, lead, and chromium are extremely high in the region of the Saale estuary. Even if the sediment samples from 1992 display declining mercury concentrations for almost all sampling sites, nevertheless, the drastic rise in the region of the Saale mouth (Barby site) is alarming (see Fig. 8).

Likewise, investigations of the Elbe sediments collected in 1991 for chlorinated hydrocarbons and dioxins point to particular pollution problems [12]. However, since these surveys have only recently been included in the analytical program, reliable conclusions about the time sequence and origin of this pollution can only be obtained by the retrospective analysis of corresponding stored samples.

The convention concluded by the International Commission for the Protection of the Elbe (IKSE), the closure of industrial plants, and the improvement in quality of municipal sewage in the upper regions of the Elbe and its tributaries will undoubtedly lead in the future to an improvement of water quality particularly in this region. The same expectations can also be placed in the extension of new environmental technologies. In the same way, an experimental verification of this forecast can only be obtained from a retrospective analysis of different sample types from the Environmental Specimen Bank, for example sediment, freshwater mussels and fish (bream).

In contrast to the systematic investigations of the Elbe, which have started only recently, surface sediments from the Rhine have been analyzed by the Institute of Applied Physical Chemistry since 1978. Samples taken at the Emmerich border station demonstrate a clear reduction in lead and cadmium pollution from 1978 to 1990 (see Fig. 9). The effects of the convention concluded by the International Commission for the Protection of the Rhine (IKSR) are particularly apparent in the same way as the decline in the biological oxygen demand (BOD5) or the rise in the oxygen concentration, which is one reason for a clear increase in the variety of fish species in the Rhine [13].

As part of the continuous expansion of the range of elements characterized in the initial analysis, the thallium concentration in various limnic samples has been determined for some time. The comparison of current data for bream muscle from two different sampling areas (Rhine/Lake Constance and lake land district of Bornhov-ed, Schleswig-Holstein) show that the thallium contents of the samples from Lake Constance are higher than the reference samples from the North German area by approximately a factor of 8 (see Fig. 10). More detailed investigations of stored material from the past 8 years (retrospective monitoring) furthermore revealed that this is a permanent, excessive pollution of Lake Constance. An acute thallium contamination, initially assumed, can thus be ruled out.

Surface-active substances, in particular, cationic surfactants and also the metabolites of the alkyl phenol

i-Rhine -**■ Ell» ■+
Fig. 9 Time curve of the lead and cadmium concentration in surface sediments of the Rhine (site: Emmerich); for comparison, values in Elbe sediments from 1991 at the Cumlosen site

Lake Consta ace

Bornhoved Lakes

as 90 aa 90 92

Fig. 10 Distribution of the thallium concentration in bream muscle from Lake Constance and the Bornhovel Lake district as 90 aa 90 92

Fig. 10 Distribution of the thallium concentration in bream muscle from Lake Constance and the Bornhovel Lake district ethoxylates, possibly also have certain toxic (environmentally toxic) effects in the aquatic environment (surface sediments from rivers, lakes and estuary regions) in the same way as in the terrestrial field. It may also be assumed that a remobilization of heavy metals becomes possible under the influence of surfactants and thus additional quantities of these elements become available for bioaccumulation in various organisms of the limnic or marine food chains.

Marine environment —

impacts on estuary and coastal areas

Both sea water and also sediment analyses have as yet only rarely been implemented with respect to the biological availability of pollutants. However, since only the

Fig. 11 Accumulation of mercury in various trophic stages of the marine environment

available pollutant fraction has toxicological relevance and therefore causes "pollution", it is necessary to use increasingly biological indicators to monitor the pollution and pollution capacity of surface waters.

The special significance of such indicators consists in their accumulation potential, which is described in the literature for various marine organisms [14] (see Fig. 1 and 11). For this reason, mainly sediments, brown algae, common mussels, fish (viviparous eelpout) and herring gull egs are investigated within the framework of the Environmental Specimen Bank program to characterize a marine sampling area. It is planned to sample seal organs (muscle, fatty tissue, liver) as the final link in the marine food chain.

Brown algae (bladder wrack) and common mussels from the same sampling site display quite different accumulation behavior with respect to certain elements. As shown in Fig. 12, As, Ba, Mn, S and Zn are, for example, preferentially accumulated in bladder wrack, whereas an increased accumulation of Cu, Fe and Hg is found in common edible mussels. Furthermore, significant deviations arise for both sample species in a comparison of the North Sea and Baltic Sea (see Fig. 12), which differ considerably in their salt content. Both North Sea specimens conform in displaying a higher accumulation potential for As and Hg, whereas Ba, Mn, and Zn are accumulated to a greater extent in the Baltic Sea specimens. No site-specific allocations of this kind can be made for Cu, Fe, and S. On the whole, apart from the matrix-dependent parameters, in particular the salinity and the temperature seem to play a certain part here.

Hg Ifig/kg x 10), Co |mg/kgx Kl], Fe and Mn |mg/kg x 0.1] ng x 1UJ, LU |iug/Hg x luj, rt aiiu i»in |ing/Hg x u.ij

Fig. 12 Accumulation of various elements in (a) edible mussels and (b) bladder wrack from the North Sea (N) and the Baltic Sea (B)

S 89 9Ü 91 92 93 Elbe estuary

88 B9 90 91 92 93 Weser estuary

Fig. 13 Decline in mercury pollution in the estuary regions of the Elbe (Island of Trischen) and Weser (Island of Mellum) represented by the pollution values of herring gull eggs; FW = fresh weight

S 89 9Ü 91 92 93 Elbe estuary

88 B9 90 91 92 93 Weser estuary

Hg Ifig/kg x 10), Co |mg/kgx Kl], Fe and Mn |mg/kg x 0.1] ng x 1UJ, LU |iug/Hg x luj, rt aiiu i»in |ing/Hg x u.ij

Fig. 12 Accumulation of various elements in (a) edible mussels and (b) bladder wrack from the North Sea (N) and the Baltic Sea (B)

Thus, for example, in the literature a relationship is described in certain marine organisms between increased cadmium uptake at high temperature and low salinity [15].

A clear decline in mercury pollution in the estuary region of the Elbe in the past few years can be documented on the basis of samples of herring gull eggs collected in the "Trischen" bird sanctuary and in which up to more than 90% of the mercury was present in the form of the highly toxic methyl mercury. In comparison to the period before reunification of Germany (1988/89) a reduction in pollution to less than half can be determined for the subsequent years 1991/93 (see Fig. 13). Similar results are also shown by an investigation of poly-chlorinated biphenyls (PCB) [12]. These findings are very probably associated with the closure of industrial plants and municipal sewage disposal in the upper regions of the Elbe and its tributaries. On the other hand, the reduced run-off of the Elbe in the past few years of low

Fig. 13 Decline in mercury pollution in the estuary regions of the Elbe (Island of Trischen) and Weser (Island of Mellum) represented by the pollution values of herring gull eggs; FW = fresh weight rainfall may also have contributed to these results. This urgently requires continuous investigations in the coming years to monitor the new environmental technologies coming into operation. Realistic and reliable statements about the development of the pollution situation however can undoubtedly be made only by a systematic, retrospective comparison with past samples.

Due to the sedentary habits of this species, the determination of the mercury concentration in herring gull eggs also permits a clear distinction between adjacent sampling areas with different degrees of pollution. Thus, for example, samples from the bird sanctuary of "Mellum" (Weser estuary) display considerably lower mercury contents than herring gull eggs from the bird sanctuary of "Trischen" (Elbe estuary) (see Fig. 13).

Additional research activities

Apart from continuous monitoring of known pollutants and operation of the Environmental Specimen Bank, the tasks of prognostic environmental precautions also include, in particular, the investigation of chemicals which, according to the present state of knowledge, do not cause any direct ecotoxicological effects, but whose environmental impacts or possible effects on man and the environment by synergistic or antagonistic effects are as yet completely unknown.

The Institute of Applied Physical Chemistry is therefore involved in investigating those substances which, due to their surface-active properties, may cause an immobilization, remobilization or change of mobility of pollutants — heavy metals and organic substances such as polychlorinated biphenyls (PCB), PAH's or pesticides. The possible surfactant-induced remobilization of pollutants fixed in a "sink" (soils, sediments) is of particular importance since this would make bound residues biologically available again for plant or animal organisms.

Surface-active substances alter the properties of soil minerals (e.g., layer silicates) by adsorption and hydrophobization of the surface. Even slight quantities of surfactants cause significant effects with respect to the transport and biological availability of pollutants in soils and sediments [16]. This may result in the accumulation of pollutants in the trophic stages of the food chain and the elimination of essential trace elements. Cationic surfactants, for example, cause a drastic alteration in the electrolyte equilibrium between the soil and soil solution due to ion exchange. Both essential cations (Ca2+, Mg2+, Na+) as well as toxic heavy metal ions (e.g., Cd2+) are quantitatively displaced [11].

Hydrophobization of the surface causes basic changes in the adsorption properties of the soil minerals. Neutral (hydrophobic) molecules may be taken up into the surfactant layer. On the basis of this knowledge, alkyl ammonium montmorillonites are being investigated and recommended for sealing landfill sites [17, 18]. Similar sorption processes may take place in soils and sediments. Probably, the hydrophobic character of soil minerals will increase due to the accumulation of surfactants, thus promoting the adsorption of non polar less water-soluble substances. That would immobilize them and exclude them from further natural transport or degradation processes.

The following examples are therefore concerned with the impact of surfactants on the interaction between environmental chemicals and the most active clay mineral components (montmorillonite, illite) of the mineral soil horizon or the natural soil structures (e.g. degraded loess soil). Firstly, the influence of surfactants on non-essential elements will be discussed. In examining the interactions of organic substances with surface-active substances, the examples are oriented towards the three surfactant classes in the sequence: cationic, non-ionic and anionic surfactants. Details of the materials and analytical methods used, as well as the nomenclature, are described in the literature [11, 19, 20].

Surfactant interactions with inorganic pollutants

The influence of various classes of surfactants on the transport behavior of Cd2+ in degraded loess soil (B horizon) is shown in Fig. 14 [21]. It is apparent that only cationic surfactants are capable of mobilizing sorbed Cd2+ by an ion exchange mechanism, in the course of which the surfactants are quantitatively bound to the

Cd2</10"9Imol/g]

Cd2</10"9Imol/g]

Fig. 14 Cd2+ mobilization from degraded loess soil by various classes of surfactant: o—o didodecyl dimethyl ammonium bromide; X—X sodium dodecyl sulphate; □—□ alkylphenyl polyethylene glycol ether (Triton-X-100) with 9.5 EO

mineral surface and are not detectable in the equilibrium solution. Non-ionic surfactants (e.g. Triton X 100) are adsorbed much more weakly on degraded loess soil, which may be attributed partially to the van der Waals forces. Accordingly, no Cd2+ mobilization takes place. Anionic surfactants form an only slightly soluble salt with Cd2+, namely Cd(DS)2. Therefore, Cd2+ immobilization occurs due to precipitation.

Surfactant influences on organic pollutants Cationic surfactants

In principle, the adsorption of organic environmental chemicals on layer silicates proceeds extremely slowly so that it may take several weeks to establish an equilibrium state [22], In contrast, if the layer silicate surface is coated with cationic surfactants in different quantities [22] or of different hydrophobicity, e.g., with DTAB (dodecyl trimethyl ammonium bromide) or DDDMAB (didoceyl dimethyl ammonium bromide) [23] then equilibrium in both systems is reached within 30 min, i.e., a drastic increase in the adsorption rate of organic pollutants results. Their residence time or probability of residence in the soil electrolyte is therefore drastically reduced and their bioavailability thus also drops.

Figure 15 shows the influence of added surfactants on the equilibrium states in the form of adsorption isotherms for 2-naphthol. In this concentration range the isotherms can be described by straight lines, which points to a constant distribution of the naphthol between the solid and liquid phases [22, 24], Its adsorption rises with increasing surfactant coverage — relative to the cation exchange adsorbed amount [KT3 mol/g]

adsorbed amount [KT3 mol/g]

equil. concentration [10 mol/1]

Fig. 15 Adsorption isotherms of 2-naphthol on cetyltrimethyl ammonium (CTA+)-illite with increasing surfactant coverage (related to the CEC)

equil. concentration [10 mol/1]

Fig. 15 Adsorption isotherms of 2-naphthol on cetyltrimethyl ammonium (CTA+)-illite with increasing surfactant coverage (related to the CEC)

capacity (CEC) — until the exchange capacity has been reached. With the addition of even higher quantities of surfactant (600% of the CEC), the adsorbed amount of 2-naphthol declines again considerably. Micelles are formed in the solution which then compete with the adsorbed surfactant films for the pollutant molecules, which leads to a decrease of the incorporated, adsorbed pollutant molecules (soil washing effect) [22].

Detailed information about the binding site of the organic compounds and the structure of the adsórbate layer can be obtained by x-ray diffractometry. For example, nitrophenols are intercalated in the interlayers of the swellable, hydrophobed bentonites [23], which may essentially influence their further fate (transport, degradation behavior).

Calorimetric measurements provide information about the binding forces of the pollutant adsorbates. Whereas the low adsorption heat of the phenols on hydrophilic clay surfaces can hardly be measured, clearly exothermal enthalpies were determined for the adsorption of 4-nitro-phenol on surfactant-bentonite complexes [23], Accordingly, the hydrophobic interactions (hydrophobic bond) between the surfactant alkyl chains and the aromatic part of the pollutant molecules are of major importance for these adsorption processes.

On the whole, the displacement of adsorbed environmental chemicals by cationic compounds seems to be a process of general environmental relevance. Thus, for example, the pesticide atrazine adsorbed on layer silicates can be quantitatively displaced by the cationic plant growth inhibitor chlormequat [25], which may lead to a contamination of the ground water with atrazine. Furthermore, as a consequence of similar processes surfactants may also reach deeper layers of the soil and initiate further secondary reactions there.

Non-ionic surfactants

Apart from the cationic surfactants, non-inonic surfactants also cause an increased hydrophobization of the layer silicate surface with increasing concentration, thus promoting, for example, the adsorption of the hydrophobic fungicide biphenyl (see Fig. 16) [26], The increased biphenyl adsorption also measured at a very weakly hydrophobized bentonite (10 |imol non-ionic surfactant/g bentonite) indicates that these effects also become active even with very small (environmentally relevant) surfactant concentrations.

Anionic surfactants

In the case of clay minerals pretreated with small amounts of anionic surfactants (e.g., sodium dodecylsulphate (SDS), c < CMC (critical micelle concentration)), for example, the adsorption of biphenyl is not significantly influenced in comparison to pure layer silicates [26]. These findings may be explained, among other aspects, by the low adsorption potential for anionic surfactants of the negatively charged layer silicate surface (cf. Fig. 17, curve A). Quite different conditions exist in acid soils, in which the soil minerals may be positively charged. As adsorbed amount [mmol/g]

10"

10"

10"

10"

10"

10"® 10"5 10"4 10" 3 10"2 10"1 equil. concentration [mmol/l]

Fig. 16 Adsorption isotherms of biphenyl on bentonite in the presence of the non-ionic surfactant dodecyl octaethylene glycol ether (C12E8): (x —X without surfactant; a—a with 0.013 mmol/g Ci2E8; □—□ with 0.3 mmol/g C12E8) [26]

ads. amount [10-4mmol/m2]

ads. amount [10-4mmol/m2]

Fig. 17 Adsorption isotherms of sodium dodecylsulphate on kaolinite. (A): without non-ionic surfactant; (B): with the addition of dodecyl octaethylene glycol ether in the ratio 1:1 [28]

Fig. 17 Adsorption isotherms of sodium dodecylsulphate on kaolinite. (A): without non-ionic surfactant; (B): with the addition of dodecyl octaethylene glycol ether in the ratio 1:1 [28]

expected, higher adsorbed quantities of anionic surfactants were found, for example, on aluminium oxide at pH 3—7 [27], Even in the neutral pH range, increased anionic surfactant adsorption on soil minerals is possible if cationic or non-ionic surfactants are also present in the system. Adsorption from a mixture of anionic and non-ionic surfactant on kaolinite thus shifts the isotherms of both components towards smaller equilibrium concentrations [28], as illustrated by curve B in Fig. 17 for SDS in the presence of the non-ionic surfactant C12E8. At a mixing ratio of 1:1, a SDS concentration in the bulk phase lower by one order of magnitude is already sufficient to achieve the same SDS adsorption as without the addition of non-ionic surfactant. Since in real systems surfactant mixtures can almost always be expected, the processes shown may play a significant role in the adsorption of organic pollutants on inorganic soil constituents.

Pollutant influences on surfactant adsorption

Just as surfactants may determine the mobility behavior of environmental chemicals in the soil, surfactant transport may also be influenced by other accompanying substances. For example, surfactants adsorbed on layer silicates may be exchanged by ionic pesticides, as illustrated in Fig. 18 for a clay mineral precoated with DTAB [20]. The preferentially adsorbed organic dication paraquat (PQ) displaces the single charged DTAB (the substance quantities are given in equivalent quantities (eq) to clarify the comparison). For each equilibrium concentration, the associated adsorbed amounts of PQ

Fig. 18 Adsorption of paraquat on Ca-bentonite pretreated with cationic surfactant: a—a adsorption isotherm of paraquat, □—□ displacement of dodecyl trimethyl ammonium bromide (DTAB). (DTAB pretreated 0.73 meq/g) [20]

Fig. 18 Adsorption of paraquat on Ca-bentonite pretreated with cationic surfactant: a—a adsorption isotherm of paraquat, □—□ displacement of dodecyl trimethyl ammonium bromide (DTAB). (DTAB pretreated 0.73 meq/g) [20]

and DTAB approximately correspond to the CEC. On the basis of these experimental findings, the following exchange reaction may be assumed:

Since in contrast to cationic surfactants, non-ionic surfactants are largely physisorbed on clay mineral surfaces, they can be relatively easily replaced by monocationic organic substances. If, for example, the monocationic pesticide cyperquat (CQ) is present in the soil electrolyte then apart from the essential cations (Ca2+, Na2+) it also displaces the physisorbed non-ionic surfactant CI2E8 [26]. In order to illustrate the associated structural changes at the layer silicate, Fig. 19 shows the basal spacing of an Na montmorillonite pretreated with C12E8 as a function of the adsorbed amount of CQ. The initial basal spacing of the clay-surfactant complex (1.8 nm) caused by the intercalation of C12 E8 decreases with increasing amount of adsorbed CQ, and at 1.5 nm finally reaches the basal spacing of pure CQ-montmorillonite.

To summarize, the following conclusions may be drawn as provisional results of these model studies:

— Cationic surfactants mobilize essential elements and heavy metals in stoichiometric relations and are quantitatively adsorbed.

— Only cationic surfactants are capable of mobilizing Cd2+, whereas non-ionics do not display any effects and anionic surfactants cause an immobilization.

— The originally hydrophilic surface of the layer silicates is hydrophobized by the adsorption of cationic and non-ionic surfactants resulting in an expanded in-terlayer of the swellable clay minerals.

Fig. 19 Change in the basal spacing of Na montmorillonite with the addition of cyperquat (1), dodecyl octoethylene glycol ether (2) as well as cyperquat to montmorillonite precoated with CpEg (3) [26]

Fig. 19 Change in the basal spacing of Na montmorillonite with the addition of cyperquat (1), dodecyl octoethylene glycol ether (2) as well as cyperquat to montmorillonite precoated with CpEg (3) [26]

— The adsorption of hydrophobic environmental chemicals is enhanced and accelerated at surfactant-clay mineral complexes. The extent of this enhancement depends on the degree to which the surface is hydrophobized.

— The inorganic soil horizon represents an effective sink for organic pollutants, whose effectiveness may increase considerably in the presence of small quantities of surfactant.

— Surfactants adsorbed on clays may be displaced by ionic pesticides, i.e., surfactant transport can also be influenced by other accompanying substances.

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