Geoscience Reference
In-Depth Information
solubility in aqueous solution and a ''microscopic organic environment'' of dis-
solved humic molecules can explain solute solubility enhancement.
When a NAPL reaches the subsurface, it may be subject to mechanical forces
that lead to the formation of a mixed NAPL-water micro-/nano-emulsion char-
acterized by the presence of micro- and nano-droplets of organic compounds.
These micro- and nano-emulsions are transparent or translucent systems, kineti-
cally (nano-) or thermodynamically (micro-) stable, and display an apparent
increase in aqueous solubility as compared to the intrinsic solubility of the NAPL
itself (Tadros
2004
). The very small droplet size (50-200 nm in the case of a nano-
emulsion) causes a large reduction in the force of gravity, enabling the system to
remain dispersed and preventing a coalescence process. In a laboratory experiment
mimicking the contamination of a coastal freshwater aquifer by hydrocarbon-
polluted seawater, Dror et al. (
2003
) report hydrocarbon concentrations in the
source saltwater that are higher than the intrinsic solubilities of the contaminants,
due to the formation of droplets. Contaminant concentrations in the adjacent
freshwater also were higher than the intrinsic aqueous solubilities. The experi-
ments also demonstrated the stability of hydrocarbon-water emulsions as they are
transported through a porous sand layer.
References
Almeida MB, Alvarez AM, de Miguel EM, del Hoyo ES (1983) Setschenow coefficients for
naphtols by distribution method. Can J Chem 61:244-248
Blokzijl W, Engberts BFN (1993) Hydrophobic effects—opinions and facts. Angew Chem Int Ed
32:1544-1579
Chiou CT, Malcom RL, Brinton TI, Kile DE (1986) Water solubility enhancement of some
organic pollutants and pesticides by dissolved humic and fulvic acids. Environ Sci Technol
20:502-508
Dror I, Gerstl Z, Prost R, Yaron B (2000a) Behavior of neat and enriched volatile petroleum
hydrocarbons mixture in the subsurface during leaching. Land Contam Reclam 8:341-348
Dror I, Gerstl Z, Braester C, Rubin H, Yaron B (2000b) In situ effect of amendments on the
dynamics of kerosene dissipation in soil subsurface. Land Contam Reclam 8:349-356
Dror I, Amitay T, Yaron B, Berkowitz B (2003) A ''salt-pump'' mechanism for induced intrusion
of organic contaminants from marine sources into coastal aquifers. Science 300:950
Gordon JE, Thorne RL (1967a) Salt effect on the activity coefficient of naphthalene in mixed
aqueous electrolyte solutions salts 1. Mixture of two electrolytes. J Phys Chem 71:4390-4399
Gordon JE, Thorne RL (1967b) Salt effect on the activity coefficient of naphthalene in mixed
aqueous electrolyte solutions salts 2. Artificial and natural seawater. Geochim Cosmochim
Acta 31:2433-2443
Hartley GS, Graham-Bryce IJ (1980) Physical principles of pesticide behavior, vol 1. Academic
Press, London
Li A, Andren AW, Yalkowsky SH (1996) Choosing a cosolvent: solubilization of naphthalene
and cosolvent properties. Environ Toxicol Chem 15:2233-2239
Meng EC, Kollmann PA (1996) Molecular dynamics studies of the properties of water around
simple organic solutes. J Phys Chem 100:11460-11470
Millero FJ (2000) The activity coefficients of non-electrolytes in seawater. Mar Chem 70:5-22
Millero FJ (1996) Chemical oceanography, 2nd edn. CRC Press, Boca Raton, Florida
