long-term leaching of preservatives from treated wood onto site soils. Their study
concludes the high potential of rhamnolipids (JBR 425) to extract PAHs from such
contaminated soils. However, the ionic strength and the cations present in the soil
solution of creosote-polluted soils should be considered when rhamnolipids are used
as extractants for remediation purposes (Madrid et al. 2019).
5.4.2 Sophorolipids
Of all currently known biological surface-active agents, rhamnolipids are believed to
have the highest potential for becoming the next generation of biosurfactants.
However, the first microbiological surfactants introduced on the market were another
member of glycolipid group – sophorolipids (Müller et al. 2012). Sophorolipids are
synthesized through the fermentation by a number of non-pathogenic yeasts such as
Candida bombicola (Le et al. 2016) which produces high yields of sophorolipids
from vegetable oils and sugars (Mulligan 2005), C. apicola, Rhodotorula
bogoriensis, etc. Like rhamnolipids, they solubilize hydrophobic compounds and
hence increase their bioavailability for subsequent remediation. Sophorolipids lower
the surface tension of water from 73 to about 30–40 mN m
À1 and have a CMC of
40–100 mg L
À1 (Hubert et al. 2012).
There is a growing number of studies that found these biosurfactants to be very
efficient for the remediation of petroleum hydrocarbon-polluted soils, even
outperforming the conventional detergents of chemical origin (such as Triton
X-100), which are in fact considered a new class of chemical pollutants in aquatic
environments. Goswami et al. (2018) compared the performance of environmentally
friendly sophorolipids derived from two yeast, C. bombicola and Yarrowia
lipolytica, with synthetic Triton X-100 on such contaminated soils. The best results
were obtained with the biosurfactants produced by C. bombicola, where 40–68%
reduction of contaminant concentration was achieved using the biosurfactant compared to 37–38% reduction when using Triton X-100.
5.4.3 Lipopeptides
Among other categories of biosurfactants, lipopeptides are particularly interesting
because of their potent surface activity (Meena and Kanwar 2015). They can act as
antibiotics, antiviral and antitumor agents, immunomodulators and specific toxins
and enzyme inhibitors (Rodrigues et al. 2006). Besides their application in medicine,
lipopeptides can be counted among promising dispersants in oil spill remediation.
The one with the greatest potential in the group is probably surfactin, a cyclic
lipopeptide produced by various strains of Bacillus subtilis. It was identified in
1968 and named after its exceptional surfactant activity (Arima et al. 1968). It has
been reported as the strongest lipopeptide surfactant so far (Liu et al. 2015) with the
ability to decrease the surface tension of water from 72 to 27 mN m
À1 at a
concentration as low as 20 μM and the interfacial tension of the water/n-hexadecane
5 The Recent Strategies Employed in Chemical Analysis of Contaminated Waters,. . .
151
concludes the high potential of rhamnolipids (JBR 425) to extract PAHs from such
contaminated soils. However, the ionic strength and the cations present in the soil
solution of creosote-polluted soils should be considered when rhamnolipids are used
as extractants for remediation purposes (Madrid et al. 2019).
5.4.2 Sophorolipids
Of all currently known biological surface-active agents, rhamnolipids are believed to
have the highest potential for becoming the next generation of biosurfactants.
However, the first microbiological surfactants introduced on the market were another
member of glycolipid group – sophorolipids (Müller et al. 2012). Sophorolipids are
synthesized through the fermentation by a number of non-pathogenic yeasts such as
Candida bombicola (Le et al. 2016) which produces high yields of sophorolipids
from vegetable oils and sugars (Mulligan 2005), C. apicola, Rhodotorula
bogoriensis, etc. Like rhamnolipids, they solubilize hydrophobic compounds and
hence increase their bioavailability for subsequent remediation. Sophorolipids lower
the surface tension of water from 73 to about 30–40 mN m
À1 and have a CMC of
40–100 mg L
À1 (Hubert et al. 2012).
There is a growing number of studies that found these biosurfactants to be very
efficient for the remediation of petroleum hydrocarbon-polluted soils, even
outperforming the conventional detergents of chemical origin (such as Triton
X-100), which are in fact considered a new class of chemical pollutants in aquatic
environments. Goswami et al. (2018) compared the performance of environmentally
friendly sophorolipids derived from two yeast, C. bombicola and Yarrowia
lipolytica, with synthetic Triton X-100 on such contaminated soils. The best results
were obtained with the biosurfactants produced by C. bombicola, where 40–68%
reduction of contaminant concentration was achieved using the biosurfactant compared to 37–38% reduction when using Triton X-100.
5.4.3 Lipopeptides
Among other categories of biosurfactants, lipopeptides are particularly interesting
because of their potent surface activity (Meena and Kanwar 2015). They can act as
antibiotics, antiviral and antitumor agents, immunomodulators and specific toxins
and enzyme inhibitors (Rodrigues et al. 2006). Besides their application in medicine,
lipopeptides can be counted among promising dispersants in oil spill remediation.
The one with the greatest potential in the group is probably surfactin, a cyclic
lipopeptide produced by various strains of Bacillus subtilis. It was identified in
1968 and named after its exceptional surfactant activity (Arima et al. 1968). It has
been reported as the strongest lipopeptide surfactant so far (Liu et al. 2015) with the
ability to decrease the surface tension of water from 72 to 27 mN m
À1 at a
concentration as low as 20 μM and the interfacial tension of the water/n-hexadecane
5 The Recent Strategies Employed in Chemical Analysis of Contaminated Waters,. . .
151