Effects-driven chemical design: The acute toxicity of CO 2-triggered switchable surfactants to rainbow trout can be predicted from octanol-water partition coefficients

Article abstract of DOI:10.1039/c1gc15620a

For both environmental protection and improved energy efficiency, CO ₂-triggered switchable surfactants have been developed to change surface activity and solubility upon command. Surfactant activity is turned on by introduction of one atmosphere of CO₂ and reversed by purging with air or nitrogen. These surfactants have numerous potential industrial applications related to their ability to stabilize and destabilize emulsions upon command. To assess their potential environmental impacts, we tested the acute toxicity of nine switchable surfactants to rainbow trout (Oncorhyncus mykiss) at pH ～8.0, typical of natural surface waters. The surfactants were synthesized in several variations, differing in the structure of the hydrophobic tail group, the hydrophilic head group, or both. A strong correlation between the log of the estimated octanol/water partition coefficients (log P) and the toxicity of eight switchable surfactants formed the basis of a structure-activity relationship that was used to design a ninth compound. That new compound had the lowest toxicity of all of the switchable surfactants tested. The effect of log P on acute toxicity was similar to that reported in the literature for other organic compounds. This model shows that despite the addition of varying functional groups, switchable surfactant toxicity remains largely dependent on log P and differs little from traditional non-switchable surfactants. The log P relationship developed provides a very useful tool for screening new compounds for acute toxicity.

Full text of DOI:10.1039/c1gc15620a

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PAPER
Effects-driven chemical design: the acute toxicity of CO2-triggered
switchable surfactants to rainbow trout can be predicted from octanol-water
partition coefficients†
Troy Arthur,a,b Jitendra R. Harjani,c Lam Phan,c Philip G. Jessopc and Peter V. Hodson*a,b
Received 27th May 2011, Accepted 21st October 2011
DOI: 10.1039/c1gc15620a
For both environmental protection and improved energy efficiency, CO2-triggered switchable sur-
factants have been developed to change surface activity and solubility upon command. Surfact-
ant activity is turned on by introduction of one atmosphere of CO2 and reversed by purging with
air or nitrogen. These surfactants have numerous potential industrial applications related to their
ability to stabilize and destabilize emulsions upon command. To assess their potential environ-
mental impacts, we tested the acute toxicity of nine switchable surfactants to rainbow trout
(Oncorhyncus mykiss) at pH ~8.0, typical of natural surface waters. The surfactants were
synthesized in several variations, differing in the structure of the hydrophobic tail group, the
hydrophilic head group, or both. A strong correlation between the log of the estimated
octanol/water partition coefficients (log P) and the toxicity of eight switchable surfactants formed
the basis of a structure–activity relationship that was used to design a ninth compound. That new
compound had the lowest toxicity of all of the switchable surfactants tested. The effect of log P on
acute toxicity was similar to that reported in the literature for other organic compounds. This
model shows that despite the addition of varying functional groups, switchable surfactant toxicity
remains largely dependent on log P and differs little from traditional non-switchable surfactants.
The log P relationship developed provides a very useful tool for screening new compounds for
acute toxicity.
to detergents in use before the 1970s were made to increase
Introduction
biodegradability and reduce persistence, so that waste treatment
A primary goal of green chemistry is to develop compounds
plants could reduce concentrations in effluent and avoid toxicity
that are less environmentally-damaging than chemicals that they
and foaming in receiving waters.
might replace. Characteristics that are important in reducing
Alternatives to traditional surfactants are switchable surfac-
environmental impacts of chemicals include manufacturing and
tants, which are compounds designed with surfactant properties
use properties such as low embodied energy content, use of
that can be changed by a simple adjustment to solution
substrates or feedstocks that have low environmental impacts,
chemistry. To reverse the properties of surfactants at will,
and a low potential for persistence, bioaccumulation, and
structural designs are needed that integrate optimal surfactant
toxicity (PBT). An equally important characteristic is that a new
characteristics with structures and functional groups that are
compound, when used in a process, would make that process
responsive to triggers such as light, heat, oxidants, etc.1–7
A
less environmentally damaging. For aquatic environments, the
past environmental impacts of detergents and surfactants have
been associated with persistence and high toxicity. Changes
recent example is a class of surfactants that are pH sensitive and
specifically designed to respond to the pH changes triggered
by the carbonation of water with 1 atm of CO2.8–10 The
hydrophobic alkyl ‘tail’ of each molecule is similar to that
of traditional surfactants, while the head group is hydrophilic
when protonated and hydrophobic when unprotonated. The
switchable hydrophilicity of the head group gives the surfactant
its switchable surfactancy. Because the head groups of these
molecules are amidines, they are sufficiently basic to be pro-
tonated in carbonated water at only 1 atm. Thus, addition of
carbon dioxide to reduce solution pH can activate the surfactant,
and aeration with inert gases such as nitrogen, argon, or air
aSchool of Environmental Studies, Queen’s University, Kingston, ON,
K7L 3N6, Canada
bDepartment of Biology, Queen’s University, 116 Barrie Street, Kingston,
ON, K7L 3N6, Canada. E-mail: peter.hodson@queensu.ca; Fax: +1
(613) 533-6090; Tel: +1 (613) 533-6129
cDepartment of Chemistry, Queen’s University, 90 Bader Lane, Kingston,
ON, K7L 3N6, Canada
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c1gc15620a
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will inactivate the surfactant by driving off carbon dioxide and
raising pH.
released as oxygen is taken up. As a consequence, there is a
surface or boundary microlayer of water flowing over the gills
that may be at a lower pH, perhaps sufficient to activate the
switchable surfactant.
The advantages of switchable surfactants are many, but the
most important is their ability to make or break emulsions at
will. Switchable surfactants are useful in applications where an
emulsion is needed for one step of a process but is unwanted
in the next step. These include, but are not limited to: micro-
suspension polymerizations, viscous oil transportation through
pipelines, separating oil from a solid substrate, e.g. oil from tar
sands or soybean oil from soybean flakes, and enhancement of
oil recovery over existing methods. However, while switchable
surfactants are ‘greener’ than their traditional alternatives due
to energy savings, are they any more or less toxic than traditional
surfactants if lost to surface waters? Even more importantly, can
ecotoxicity studies be used to guide the design of even greener
switchable surfactants?
The mechanism of toxicity of traditional surfactants involves
both the hydrophilic and the hydrophobic moiety of each
molecule. The hydrophobic end will interact with fish gill
epithelial cells just as it does with liquid oil, while the hydrophilic
end enables the lipidic components of the membrane to be
solubilized in water, destroying cell membranes and causing
suffocation.11,12 In theory, switchable surfactants should have
little effect on gills. While the hydrophobic end will interact with
cell membranes, the hydrophilic end should be ‘switched off’
when added to most surface waters (6.0 to 8.5). However, fish
gills are the site of gas exchange, with carbon dioxide being
Ecological risk assessment is crucial for novel chemicals
destined for commercial or industrial applications. Because a
variety of switchable surfactants have been produced, toxicity
assessment and life cycle assessment, as well as efficacy as a
surfactant will be important factors in determining which, if any,
are best suited for industry. We measured the acute lethality to
rainbow trout of a series of CO2-triggered switchable surfactants
characterized by differing structures of the switchable head
group and differing chain lengths and compositions of the tail.
We tested two alternative hypotheses to explain the variations
in observed toxicities: first, that toxicity would vary primarily
with changes to the structure of the switchable head group; and
second, that toxicity would be determined largely by the degree
of hydrophobicity of the entire molecule, as expressed by the
log octanol-water partition coefficient (log P). The relationship
between toxicity and log P was used to design a surfactant that
was switchable and of low toxicity.
Materials and methods
The acute toxicity of eight novel switchable surfactant com-
pounds (Fig. 1) to 0.5–3 g rainbow trout (Oncorhynchus mykiss)
was evaluated by 96 h static daily renewal lethality tests at 15 ◦C
Fig. 1 Structures and IUPAC names of nine switchable surfactants.
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and a 16 h : 8 h light : dark photoperiod. The relationship
between the toxicity data and log P directed the synthesis of
a ninth compound which was designed to be less toxic by
virtue of its low log P. Tests followed Environment Canada
test guidelines13 with some minor modifications depending on
the availability of test compounds. Animals and test methods
used were approved by the Queen’s University Animal Care
Committee (UACC), the Canadian Council on Animal Care
(CCAC) and the Ontario Ministry of Agriculture, Food and
Rural Affairs (OMAFRA).
0–10 mg L-1. Lake Ontario water is very stable and has a hardness
and alkalinity of 135 and 90 mg L-1 CaCO3, respectively.14
Test methods
Initially, full scale toxicity tests were preceded by a range-finder
test, in which two fish were exposed to each of a broad range
of concentrations to provide a first estimate of the LC50. These
preliminary tests were conducted with 2 L of test solution in
3 L stainless steel bowls. The final toxicity tests were performed
in 5–10 L of solution, depending on the amount of chemical
available, in 20 L plastic buckets lined with a food-grade
polyethylene bag, with 10 fish per treatment and a narrower
range of test concentrations. After three complete tests, we
avoided preliminary tests by estimating the LC50 from log P.
All test solutions were aerated and each test was accompanied
by a water and a 1 mL methanol control test of 10 fish.
Treatments were inspected multiple times each day for dead
or dying fish (gasping, loss of equilibrium, lack of swimming).
Dying fish were counted towards the next time interval
and euthanized humanely by an overdose of the anesthetic
MS-222 (ethyl-3 aminobenzoate methanesulfonate lot:
MKAA2400, Sigma Aldrich Canada, Oakville, ON) at the test
temperature and pH.
Test chemicals
All switchable surfactants (Fig. 1) were synthesized as described
previously.10 Their purity was verified using 1H NMR spec-
troscopy; purity ranged from 70% to >99% (purity data were
not available for compounds 1, 2 and 5). These compounds had
from 7 to 16 carbon alkyl tails, and some tail groups contained
embedded ethoxy groups within the alkyl chain. The switchable
hydrophilic functional groups included amidine, guanidine and
imidazole structures. Two reference toxicant positive controls,
cetyl trimethylammonium bromide (CTAB; CAS # 57-9-0, Lot
# 019K00241) and sodium dodecyl sulfate (SDS; CAS # 151-
21-3, Lot # MKBC3000) were obtained from Sigma Aldrich
Canada, Oakville, ON. Each was added with or dissolved in 1
mL of HPLC grade methanol (Lot # K1552, Fisher Scientific,
Ottawa, ON).
Experiments were terminated after 96 h or when acute toxicity
ceased. Fish remaining alive through the duration of toxicity
tests, as well as fish exhibiting severe signs of toxicity during
tests were euthanized humanely. In early trials, a small number
of exposed fish were dissected to identify external and internal
pathologies, and freshly excised gill tissue was inspected by
microscopy.
Test solutions
For preliminary toxicity tests, a series of dilutions was prepared
with ten-fold decrements in concentration, starting near the
solubility limit. Stock solutions were prepared so that the
amount of methanol for each dose was either 100 ml or 1 mL.
For subsequent full-scale tests, a series of doses was prepared
using methanol as a diluent, and the amount of methanol added
varied according to the test concentration. In some cases, water
bath sonication was needed to dissolve chemicals (switchable
surfactants 3, 4 and 8; reference compounds SDS and CTAB).
Water was used as a solvent in place of methanol for SDS due
to its low solubility in alcohol – methanol was added to the
test solutions of SDS to mimic the conditions of the tests in
which methanol was used as a carrier. For liquid surfactants,
the mean density (n = 5) was determined with an analytical
balance (Denver Instrument Co., model TR-204) to express
concentrations gravimetrically. In addition to positive controls,
negative controls included methanol at the highest concentration
used to deliver test compounds, and water only.
Statistics
LC50¢s were calculated by the probit method or trimmed
Spearman-Karber method (5% alpha) using the LC50 Calcu-
lation Program version 2.0.15 Log P values were estimated using
ALOGPs 2.1,16 and structure data were entered as SMILES
notation (simplified molecular input line entry specification).
These were verified using the Depict imaging tool by Daylight
Chemical Information Systems, Inc. Simple linear regressions of
switchable surfactant log LC50 concentrations and log P values
were performed for both nominal gravimetric concentrations
and molar concentrations. The R2 values for these regressions
were 0.94 and 0.95 respectively.
Results and discussion
All surfactants were toxic to rainbow trout, but only one
mortality was observed among 190 fish tested in methanol and
water control treatments. It occurred in the methanol control
treatment during the test of compounds 3 and 6. The remaining
fish in this tank appeared normal. In surfactant tests, toxic effects
included inflammation of exposed tissues, primarily the gills,
skin and eyes. Excess mucous production around the gills was
observed in treatments of compounds 1, 2, 5 and CTAB. Blood
was visible around the gills in treatments of 1 and 2. Glossy eyes
were observed in 1 and 2 and CTAB treatments. The skin of fish
treated with toxic concentrations of 1, 2, 3, 5, SDS and CTAB
was blanched white, and excess mucous was common. In extreme
Fish
Rainbow trout (0.54–2.22 g) were obtained from a commercial
trout farm (Rainbow Springs, Thamesford, ON) and were
acclimatized to 12–15 ◦C, allowing at least 1 day per ◦C of change
from the hatchery temperature. Prior to testing, fish were held in
260 L tanks with a continuous flow of carbon-filtered municipal
water (Lake Ontario) (>1.5 L/g fish/day) under a 16 h : 8 h
light : dark photoperiod. Measured water quality parameters
during the test period were: pH 7.04–9.36, conductivity 221–
292 mS cm-1, dissolved oxygen 11.1–13.6 mg L-1, and chlorine
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Table 1 The measured acute lethality to rainbow trout and the estimated log P values for nine switchable surfactants and two reference surfactants
Compound
log Pb
96 h LC50 (mg L-1)
Upper C.L.
Lower C.L.
96 h LC50 (mmol L-1)
Switchable surfactants
1
7.3 1.1
5.8 0.8
5.5 0.6
5.1 0.9
4.1 0.6
3.9 0.5
3.8 0.5
3.4 0.5
2.6 0.5
0.08
0.43
0.53
0.73
8.94
17.35
6.89
8.95
52.34
0.08
0.49
n/a
1.50
n/a
18.96
9.43
n/a
0.07
0.37
n/a
0.36
n/a
15.88
5.03
n/a
0.2
1.7
2.0
2.5
45.1
76.3
35.1
49.1
202.5
2
3a
4
5a
6
7
8a
9
68.80
39.84
Reference Compounds
SDS
3.4 1.3
5.9 2.8
15.48
0.14
19.16
n/a
15.51
n/a
53.7
0.4
CTABa
a No confidence intervals defined. b Estimated from ALOGPs 2.1 (Tetko & Tanchuk, 2002).16
cases of skin blanching, the tensile strength of the skin was
lost, and the skin would rupture. This was observed primarily
in 1, 2, and CTAB treatments. Hyperactivity was observed in
compound 4 and CTAB treatments. Decreased activity and fish
lying on the bottom of the test vessel were observed in compound
6 treatments. Loss of equilibrium and death were observed for all
compounds at various concentrations. With some compounds,
certain effects were less pronounced or absent.
Time to death varied by compound, as measured at the lowest
concentration causing 100% mortality. Tests with compounds
5 and 6 had the longest times to 100% mortality at 72 h.
Compounds 1 and 2 caused 100% mortality at 48 h, CTAB at 24
h and compounds 3 and 4 in 4 h. Compound 9 and SDS caused
100% mortalities after 2 h and 7 and 8, within 1 h. Mortality
(and 96 h LC50s) spanned about three orders of magnitude
of test concentrations, increasing with octanol-water partition
coefficients which spanned about 4.5 orders of magnitude
(Fig. 2, Table 1).
able surfactants were congruent with those of the reference
compounds sodium dodecyl sulfate and cetyl trimethylammo-
nium bromide and corresponded to previous observations of
surfactant effects on fish gills in vivo or in vitro.5,17
Each switchable surfactant tested was toxic to rainbow trout
within 96 h. Calculated 96 h LC50¢s ranged from 0.08 mg L-1 to
52.3 mg L-1, and these extreme values correspond to surfactants
with the highest and lowest log P values, respectively. For all
compounds, toxicity varied with log P in a very predictable
manner, and the relationship between log P and LC50 (Fig. 3)
was very strong (R2 = 0.95). These results are based on nominal
concentrations, rather than actual concentrations, as methods
for measuring these compounds in water at the concentrations
tested are not yet available. After the first eight compounds
were tested, the relationship between switchable surfactant
toxicity and log P guided the development of a ninth switchable
surfactant with lower log P and lower toxicity.
The mechanism of toxicity for switchable surfactants sug-
gested by our observations is similar to that of other common
ionic and nonionic surfactants. The signs of toxicity for switch-
Fig. 3 The effect of log P on the toxicity of nine switchable surfactants
(numbers 1 to 9 and solid black line; eqn (1); n = 9, r = 0.98, s = 0.234,
p < 0.001). The relationship developed by Ko¨nemann18 for 50 organic
compounds is shown as a dashed line (eqn (2); n = 50, r = 0.99, s =
0.237; p not reported in ref. 18). 96 h LC50s for sodium dodecyl sulfate
(square) and cetyl trimethylammonium bromide (triangle) are presented
as reference points but are not included in the regression.
Fig. 2 Mortality curves for four switchable surfactants and two
reference compounds. The exposure-response curves for the remaining
six switchable surfactants appeared similar within the range presented,
but were omitted for clarity due to extensive overlap.
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The relationship that was developed between log P and
toxicity for the switchable surfactants was sufficiently predictable
that a Quantitative Structure Activity Relationship (QSAR)
could be developed. The linear equation relating log P and the
log of the inverse of 96 h LC50¢s for the switchable surfactants
(Fig. 3) was:
log(1/LC50) = 0.731log P + 1.628
(n = 8, r = 0.97, s = 0.230, p = <0.001)
(3)
This new slope is closer to the slope of 0.87 observed by
Ko¨nemann (eqn (2)).18 The 96 h LC50s for the reference
compounds SDS and CTAB also fall nearly in line with eqn (2).
Functional groups
log(1/LC50) = 0.667log P + 1.88
(1)
(n = 9, r = 0.98, s = 0.234, p < 0.001)
The switchable surfactants tested are mostly comprised of a
switchable-hydrophilicity amidine head group with a hydropho-
bic alkane tail group. One exception is a guanidine head group
in place of the amidine (compound 6). If the lone guanidine
compound is omitted from the regression, the relationship
between log P and toxicity becomes even stronger (r = 0.99).
Thus, the guanidine version of the switchable surfactant appears
somewhat less toxic than the other versions tested (Fig. 5)
because the LC50 fell outside the 95% confidence limits of
the amidine regression. Since there was only one guanidine test
compound, it is uncertain whether this class of compounds is
less toxic in general or if this compound is the exception.
where s is the standard error of the estimate and p is the
probability that the regression is not significant. This equation is
very similar to that developed by Ko¨nemann18 for a wide array
of organic compounds:
log(1/LC50) = 0.87log P + 1.13
(n = 50, r = 0.99, s = 0.237; p not reported in ref. 18)
(2)
Although derived for compounds that are not surfactants,
Ko¨nemann’s equation (2)18 predicts the toxicity of switchable
surfactants with great accuracy (Fig. 3). This suggests that
the bioaccumulation (and hence exposure and toxicity) of the
surfactants tested in this study, as well as other non-ionic
surfactants, are controlled to the same extent by water-lipid
partitioning as the aromatic compounds and alcohols that
Ko¨nemann18 used to develop eqn (2). This does not mean
that they would have the same proposed general narcotic
mechanism of toxicity,18 because surfactants clearly degraded
exposed tissues by solubilizing lipid membranes.
Eqn (2) was useful only for log P < 6;18 above this value,
compounds were often less toxic than predicted from the
equation. This has been observed previously and is attributed
to deterioration of the log P-bioaccumulation relationship due
to steric hindrance, so that toxicity within 96 h is limited by
uptake kinetics.19 As shown by Fig. 4, removing the switchable
surfactant with the highest log P (1 – log P 7.34) increases the
slope of the resulting equation:
Fig. 5 The effect of log P on the toxicity of switchable surfactants
to rainbow trout (Eq 4; n = 8, r = 0.98, s = 0.192, p < 0.001). The
single guanidine compound tested (compound 6) is not included in the
regression, and falls outside of the 95% C.L. of a regression of the other
switchable surfactants. Two of the amidine compounds (4 and 5) also
fall slightly outside of the confidence limits, but to a lesser degree.
Aside from the guanidine group, no other functional group
seemed to cause a variation in toxicity independent of their
effect on log P. These additional functional groups include
various 7–16 carbon alkyl, ethoxy, and octyloxy groups, as well
as cyclic groups such as aniline, phenyl and imidazoline rings.
The relationship developed between log P and toxicity for this
largely heterologous series suggests that the only apparent way of
decreasing toxicity of the switchable surfactants is by modifying
the structural design to achieve a reduction of log P. The simplest
and most effective way of doing this is by the addition of ethylene
oxide units to the hydrophobic alkyl tail group,20 a strategy
used for traditional non-ionized surfactants.19 After the toxicity
tests were performed with the first 8 compounds, the lessons
learned guided the design of a ninth switchable surfactant. The
addition of two ethylene oxide groups to amidine compound
Fig. 4 The effect of log P on surfactant toxicity for switchable
surfactants with log P < 6 (eqn (3); n = 8, r = 0.97, s = 0.230, p =
<0.001). The relationship developed by Ko¨nemann18 for 50 organic
compounds is shown as a dashed line (eqn (2); n = 50, r = 0.99, s = 0.237;
p not reported in ref. 18). The 96 h LC50s for sodium dodecyl sulfate
(square) and cetyl trimethylammonium bromide (triangle) are presented
as reference points but are not included in the regression.
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2 (log P 5.8 0.8) produced compound 9 (log P 2.6 0.5), a
reduction of approximately 1.6 log P units per ethylene oxide
group and a reduction in toxicity of two orders of magnitude. In
results to be published separately, we have found that this new
less-toxic switchable surfactant, in the presence of CO2, stabilizes
emulsions of water in heavy crude oils.21
2 P. Anton, P. Koeberle and A. Laschewsky, Structure and prop-
erties of zwitterionic polysoaps: functionalization by redox-
switchable moieties, Prog. Colloid Polym. Sci., 1992, 89, 56–
59.
3 P. Anton, A. Laschewsky and M. D. Ward, Solubilization control
by redox-switching of polysoaps, Polym. Bull., 1995, 34, 331–
335.
4 N. Aydogan and N. L. Abbott, Comparison of the Surface
Activity and Bulk Aggregation of Ferrocenyl Surfactants with
Cationic and Anionic Headgroups, Langmuir, 2001, 17(19), 5703–
5706.
Environmental impacts
These switchable surfactants were designed to activate in
carbonated water, while in natural surface waters they would
act as demulsifiers. Our tests however, show that this is not
an advantage in alleviating toxic effects when compared with
common commercial surfactants.
5 S. S. Datwani, V. N. Truskett, C. A. Rosslee, N. L. Abbott and
K. J. Stebe, Redox-Dependent Surface Tension and Surface Phase
Transitions of a Ferrocenyl Surfactant: Equilibrium and Dynamic
Analyses with Fluorescence Images, Langmuir, 2003, 19(20), 8292–
8301.
6 H. Sakai and M. Abe, Control of molecular aggregate formation
and solubilization using electro- and photoresponsive surfactant
mixtures, in Mixed Surfactant Systems, edited by Abe Masahiko
& J. F. Scamehorn, (Marcel Dekker, 2005), vol. New York, pp. 507–
543.
7 M. Schmittel, M. Lal, K. Graf, G. Jeschke, I. Suske and J. Sal-
beck, N,N ‘-dimethyl-2,3 dialkylpyrazinium salts as redox-switchable
surfactants? Redox, spectral, EPR and surfactant properties, Chem.
Commun., 2005, 5650–5652.
8 P. G. Jessop, Reversibly switchable amidine surfactants and meth-
ods of use thereof. Patent Cooperation Treaty Int. Appl., 2006,
CA2006/001877, pp 65.
As with many other surfactants, switchable surfactant toxicity
is driven by the compound’s affinity for a hydrophobic phase
over an aqueous one. The greater affinity for lipids means
higher accumulation of compounds in the tissues of the fish,
and increased toxicity. Additions or subtractions of any of the
functional groups contained within the switchable surfactants
tested did not markedly affect toxicity independent of their
effect on the value of log P. The switchable surfactants have
the same toxicity as conventional surfactants of equal log P.
This does not automatically exclude switchable surfactants from
being classified as ‘green chemicals’ because their switchability
could lead to substantial savings in energy and materials during
the breaking of emulsions or suspensions.
9 Y. Liu, P. G. Jessop, M. Cunningham, C. A. Eckert and C.
L. Liotta, Switchable Surfactants, Science, 2006, 313(5789), 958–
96.
10 J. R. Harjani, C. Liang and P. G. Jessop, Improved Synthesis
of Acetamidines and its Application to the Design of Switchable
Surfactants, J. Org. Chem., 2011, 76, 1683–1691.
By using switchable surfactants during industrial processes,
manufacturers requiring separation of chemicals could reduce
waste by creating and breaking emulsions without addition of
emulsion-breaking additives such as salts, demulsifiers, or strong
acids. Additionally, the application of switchable surfactants
to recover waste oil from products before it reaches landfills,
waterways, or groundwater surely warrants their designation as
a green chemical. In addition to their applications, the nature
of these surfactants could provide a viable method for removing
them entirely from any effluent or discharge in which they may
be entrained.
11 M. A. Partearroyo, S. J. Pilling and M. N. Jones, The lysis of isolated
fish (Oncorhynchus mykiss) gill epithelial cells by surfactants, Comp.
Biochem. Physiol., 1991, 100 C(3), 381–388.
12 C. Gloxhuber and W. K. Fischer, Investigations, of the action of
alkylpolyglycol ethers at high concentrations on fish, Food Cosmet.
Toxicol., 1968, 6, 469–477.
13 Environment Canada. Biological Test Method: Acute Lethality Test
Using Rainbow Trout. EPS1/RM/ 9. Method Development and
Applications Section (MDAS) of the Biological Methods Division.
Ottawa, ON, 2007.
14 P. V. Hodson, B. R. Blunt and D. J. Spry, Chronic toxicity
of waterborne and dietary lead to rainbow trout (Salmo gaird-
neri) in Lake Ontario water, Water Res., 1978, 12(10), 869–
878.
The observed 96 h LC50s for switchable surfactants are not a
complete account of the toxicity, nor of associated potential
environmental impacts. They do, however, provide a sound
metric for comparison between novel switchable surfactants and
traditional surfactants of similar log P, and a basis for designing
a switchable surfactant of lower toxicity that is worth pursuing
as an industrial ‘green’ chemical.
15 Stephan, C.E. Software, to calculate LC50 values with confidence
intervals using probit, moving averages, and Spearman-Karber
procedures. U.S. Environmental Protection Agency, Duluth, MN.
1989.
16 I. V. Tetko and V. Y. Tanchuk, Application of associative neural
networks for prediction of lipophilicity in ALOGPS 2.1 program, J.
Chem. Inf. Model., 2002, 42(5), 1136–1145.
17 P. Part, O. Svanberg and E. Bergstrom, The influence of sur-
factants on gill physiology and cadmium uptake in perfused
rainbow trout gills, Ecotoxicol. Environ. Saf., 1985, 9(2), 135–
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Acknowledgements
This research was funded by a Natural Sciences and Engineering
Research Council (NSERC) Polanyi award to P. G. Jessop and
an NSERC Discovery Grant to P. V. Hodson.
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