After the successful conquest of the nano scale by technology (i.e., by nanotechnology), it becomes increasingly obvious that nanostructures play a much bigger role than hitherto assumed also in nature . In particular nanoparticles, often also called colloids, play a big part in our natural environment. Typical environmental colloids are nanoparticles consisting of silicates or oxides, organic colloids such as humic substances or polysaccharides, and biologic particles (bacteria, viruses). Considering how ubiquitous waterborne nanoparticles are in nature, it is not surprising that they also influence the transport of contaminants in the environment.
Traditionally, conduits of groundwaters, mine waters, surface waters etc. are regarded as simple two-phase-systems within which contaminants are distributed between
- a mobile aqueous phase and
- an immobile solid phase.
Sparingly soluble or strongly adsorbing contaminants occur primarily in state 2 according to this approach and should, therefore, be very immobile in nature. However, if - in reality - the contaminants have contact with colloids in the aquatic phase which results in the formation of so-called “pseudocolloids” (Fig. 1) or if they themselves form so-called “eigencolloids” (“real colloids”, “intrinsic colloids”), even sparingly soluble and strongly adsorbing contaminants may become mobile [2-4]. Conversely, there are also cases where truly dissolved contaminants are immobilized by adsorption onto colloids and aggregation/sedimentation of the colloids which may result in natural attenuation (Fig. 2) [5, 6]. The influence of colloidal particles has even been called “a sort of Gordian knot” for our comprehension of the transport of contaminants in natural waters, especially if radiotoxic substances are concerned . Sometimes, it has been distinguished between “well-established processes” and “less-established processes” in contaminant transport research, indicating the different levels of theoretical understanding that exists (cf. ). Definitely, the colloid influences on contaminant transport belong to the “less-established processes” which need intensified research. Our work is aimed at contributing to a better understanding of the formation and the properties of colloidal particles potentially important for the transport of contaminants in the environment.
Fig. 1: Formation of so-called „pseudocolloids“
Fig. 2: Immobilization of toxicants by colloids
In [9,10] we give an overview over the methods for the investigation of natural and artificial nanoparticles in the environment. Among them, we use
- Dynamic light scattering (Multiangle Photon Correlation Spectroscope ALV/CGS-3 Goniometer System)
- Static light scattering (Multiangle Photon Correlation Spectroscope ALV/CGS-3 Goniometer System)
- Zeta potential measurement (Zetasizer Nano ZS, Malvern Instruments)
- Ultracentrifugation (Optima XL 100K, Beckman Coulter)
- Scanning electron microscopy (Hitachi S-4800)
- Transmission electron microscopy.
For the abovementioned reasons, there are lots of systems (in nature and in the laboratory) were colloids influence the behavior of trace componentes such as potential environmental contaminants. We investigated or still investigate for instance
- the effect of colloids on U, As, Pb, Cu etc. in mine waters [5, 11-14],
- the formation of uranium(IV)-silica colloids, thorium(IV)-silica colloids and neptunium(IV)-silica colloids ,
- the colloidal properties of carbon nanotubes and the interaction of carbon nanotube colloids with uranium(VI) ,
- the interaction of milk protein colloids (caseins, whey proteins) with uranium(VI).
- Zänker, H.; Hennig, C. (2014)
Colloid-borne forms of tetravalent actinides: A brief review. Journal of Contaminant Hydrology 157 87-105. →
- Labs, S.; Hennig, C.; Weiss, S.; Curtius, H.; Zaenker, H.; Bosbach, D. (2014)
Synthesis of coffinite, USiO4 and structural investigations of the UxTh(1−x)SiO4 solid solutions. Environmental Science & Technology 48 854-860. →
- Hennig, C.; Weiss, S.; Banerjee, D.; Brendler, E.; Honkimäki, V.; Cuello, G.; Ikeda-Ohno, A.; Scheinost, A.C.; Zänker, H. (2013)
Solid-state properties and colloidal stability of thorium(IV)–silica nanoparticles. Geochimica Cosmochimica Acta 103 197–212. →
- Barnard, A.S.; Guo, H. (Eds.) (2012)
Nature's Nanostructures. Pan Stanford Publishing, Singapore.
- Morel, F.M.M.; Gschwend, P.M. (1987)
The Role of Colloids in the Partitioning of Solutes in Natural Waters. In: Stumm, W. (Ed.), Aquatic Surface Chemistry, Wiley-Interscience, New-York, pp. 405-422.
- McCarthy, J.F.; Zachara, J.M. (1989)
Subsurface transport of contaminants. Environmental Science & Technolology 23, 496-502. →
- Kim, J.I. (1994)
Actinide Colloids in Natural Aquifer Systems. MRS Bulletin 19, 47-53.
- Zänker, H.; Richter, W.; Hüttig, G. (2003)
Scavenging and immobilization of trace contaminants by colloids in the waters of abandoned ore mines. Colloids and Surfaces A: Physicochemical and Engineering Aspects 217, 21-31. →
- Ren, J.; Packman, A.I. (2004)
Modeling of Simultaneous Exchange of Colloids and Sorbing Contaminants between Stream and Streambed. Environmental Science & Technology 38, 2901-2911. →
- Honeyman, B.D. (1999)
Colloidal culprits in contamination. Nature 397, 23-24. →
- Buckau, G.; Duro, L.; Kienzler, B.; Montoya, V.; Delos, A. (2009)
4th Annual Workshop Proceedings of the Intrgraded Project "Fundamental Processes of Radionuclide Migration" (6th EC FP IP FUNMIG). Report FZKA 7461, Forschungszentrum Karlsruhe.
- Zänker, H.; Schierz, A. (2012)
Engineered Nanoparticles and Their Identification Among Natural Nanoparticles. Annual Review of Analytical Chemistry 5, 107-132. →
- Zänker, H. (2010)
In-situ Measurements on Suspended Nanoparticles with Visible Laser Light, Infrared Light and X-Rays. In: Frimmel, F.H.; Niessner, R. (Eds.), Nanoparticles in the Water Cycle, Springer, p.117-138.
- Zänker, H.; Richter, W.; Brendler, V.;.Nitsche, H. (2000)
Colloid-borne uranium and other heavy metals in the water of a mine drainage gallery. Radiochimica Acta 88, 619-624. →
- Zänker, H.; Moll, H.; Richter, W.; Brendler, V.; Hennig, C.; Reich, T.; Kluge, A.; Hüttig, G. (2002)
The colloid chemistry of acid rock drainage solution from an abandoned Zn-Pb-Ag mine. Applied Geochemistry 17, 633-648. →
- Ulrich, K.-U.; Rossberg, A.; Foerstendorf, H.; Zänker, H.; Scheinost, A.C. (2006)
Molecular characterization of uranium(VI) sorption complexes on iron(III)-rich acid mine water colloids. Geochimica et Cosmochimica Acta 70, 5469-5487. →
- Zänker, H.; Hüttig, G.; Arnold, T.; Nitsche, H. (2006)
Formation of Iron-containing Colloids by the Weathering of Phyllite. Aquatic Geochemistry 12, 299-325. →
- Dreissig, I.; Weiss, S.; Hennig, C.; Bernhard, G.; Zänker, H. (2011)
Formation of uranium(IV)-silica colloids at near-neutral pH. Geochimica et Cosmochimica Acta 75, 352–367. →
- Schierz, A.; Zänker, H. (2009)
Aqueous Suspensions of Carbon Nanotubes: Surface Oxidation, Colloidal Stability and Uranium Sorption. Environmental Pollution 157, 1088-1094. →