1.
Introduction
Enormous
quantities of chemical dyes (something over a million tons) are produced
annually and used world-wide [1]. Effluents
containing these materials can enter the environment through wastewater and runoffs,
constituting a potential hazard. Another group of commonplace dyes are food
dyes, seven of which are commonly used in the United States [2]. They have no food value, but they are added to
our food, mainly to make the food more appealing. They make us feel good to eat
the food, though they have no nutritional value. Moreover, they do not serve as
preservatives [2].
2.
Materials and Methods
2.1.
Sources of
Reagents and Materials
Octolig®, immobilized polyethylenediimine covalently
attached to high-surface-area silica gel (CAS Registry number = 404899-06-5), was
a gift from Metre-General, Inc. (3771 Monarch St, Unit A, Frederick, CO 80530)
and was used as received. Deionized (DI) water and tap water were available in
Our Laboratory. Well water was obtained from a sprinkler attached to a shallow
well aquifer at 3402 Valencia Road, Tampa, FL 33618. It was passed through
fluted filter paper (802; 18.5 cm from Whatman, Inc., GE Healthcare
Bio-sciences, 100 Results Way, Marlborough, MA 01752).
2.2.
Column Chromatography
[3-6].
A
Spectra/chron peristaltic pump was used to deliver standard aqueous “Stock” samples
to a CHEMGLASS chromatography column, 2 cm (id) 30 cm in length and equipped
with a glass frit and a Teflon stopcock. The column was packed with a known
volume of Octolig® resulting in a
void volume of 44%. The substrate had been washed with DI water, and the
supernatant, containing fines, was decanted and discarded. The procedure was
repeated until no fines were noticed, then the column was packed with the
washed Octolig®.
“Stock”
samples (ca.10-5M) were passed over the packed substrate using a rate of about 10
mL/min. Usually, the first four 50-mL aliquots of effluent (a.k.a. “Fractions”)
were discarded, and subsequent seven 50-mL fractions were used for analysis. The
discard procedure was recognition of the consequences of sending a standard
solution into a void volume filled with plain water. Total dissolved solids
were measured using a digital conductivity meter (Fisher Scientific), and used
as a guide to assess a state of equilibrium.
2.3.
Other Analyses
The
pH values were typically obtained using an Orion model 290A pH/ISE meter
connected with an Orion pH triode electrode model 9107BN. Concentrations of
dyes in elements were acquired from the absorbance measurements using a
Shimadzu UV-2401 PC UV-Vis recording spectrophotometer observed in the spectral
region of 200-800 nm. Spectra were saved
to a disk and analyzed using Origin Pro 8.0™.
3.
Results and Discussion
3.1.
Utilization of Octolig® In Management of Non-Food Dyes
Members of our
institute have studied the removal of nuisance species by the use of Octolig®, a commercially available supported chelating
agent, specifically a polyethylenediimine covalently attached to silica gel. The
structure can be represented by an idealized formula: SiO2-O-Si (CH3)2 (CH2)3-NH CH2CH2N (CH2CH2) nNH2. Octolig®
was designed as a means of removing transition metals, but our research
demonstrated that it could also remove nuisance anions, including initially
perchlorate [3], then simple anions phosphate, perchlorate,
nitrite nitrate, as well as larger species as Zinc Phthalocyaninetetrasulfonate
(ZPS) [4,5]. Dye compounds were removed
successfully using Octolig® included
a series of Xanthenylbenzene dyes that included Rose Bengal, Erythrosin, and
eosin. These dyes had functional groups (phenolic or carboxylic) capable of
losing protons in sufficient quantities as to be capable of being converted
mainly to anions and being encapsulated by attraction to protons on the
nitrogens of Octolig® [5]. The three dyes in deionized water or in well
water or tap water could be removed quantitatively (99.9%) by passage over a
chromatography column containing Octolig®.
Effective removal
of organic materials depended on compounds that existed as anions in adequate
supply, e.g., those with sulfonate groups or functional groups leading to pKa
values less than4.5 [6-8].
Another example of
dye management was the green dye Lissamine Green B that we demonstrated could
be removed from aqueous solution by passage over a chromatography column packed
with Octolig®
[6]. Management in this instance
would include removal from clay or other solids after the waste
materials-containing the green dye had been dumped. Rosales and co-workers [1] used electro-Fenton degradation. This procedure,
though effective, may be more demanding of resources, physical and personnel.
We were able to demonstration the efficacy of simple aqueous extraction,
followed by removal using Octolig® [9].
An interesting
alternative approach was the decolorization of textile waste water using granular
activated carbon [10]. Those with memories of
organic chemistry laboratory and subsequent experiences can ponder some side
issues of the approach; include cost and the mess that was associated with this
black powder. But “Circumstances Alter Cases” The procedure was done in
Bangladesh where a supply of locally available granular activated carbon was
available, as well as an adequate supply of conscientious and dedicated
workers, who possibly were not supplied with rubber gloves, just as I was not.
3.2.
Selected Food Dyes
At present, some
seven food dyes are used in the United States, one may argue quite
unnecessarily for any reasons other than aesthetics or salesmanship [2]. They do make the food more appealing. They may
fool customers into a believing that the food has some helpful ingredient such
as fruit. The food dyes are not preservatives, nor do they make the food
healthier [2]. But first and foremost, they
serve a sales function. The additives make us feel good about eating the food, and
having paid more than enough to cover the cost of the additive. We studied six
of the seven were described in the FD&C [Food, Drug and Cosmetic Act (2938)].
These are Blue No.1 and No. 2, Green No.3, Red No. 3 and No.40, Yellow No. 5, 6
[2].
(We did not study
Green No 3). At present, all seven have been used in the United States, but may
question whether this is wise use of resources or wise practices.
3.3.
How Useful/ How
Safe Are Food Dyes?
One might argue
that food dyes listed above are safe or the Food and Drug Administration would
not allow the “Super Seven” to be used.
The prompt answer is that all contingences can’t be envisioned, though
some can.
Uptake of a food
dye can’t be guaranteed to be 100% complete. Accordingly, a problem of disposal
is inevitable, though probably a problem that is ignored. The research at our
institute was concerned with whether a convenient method of removal might be
available, e.g., passage of a sample over a chromatography column packed with
Octolig®.
There may be
reason for concern, though how extensive and intensive is uncertain. For
example, The Food and Drug Administration limited use of Red Dye
No. 3 (January 30, 1990) because very high doses caused cancer in laboratory
rats. Application of the Delany Amendment (relative to carcinogenic properties)
required withdraw of authorization for use, even though the risk of getting
cancer from Red Dye No 3 may have been below “1 In100,000 In A Lifetime of
Consumption.” By comparison, risk from natural disasters was estimated to be70
times the quoted value [10].
Safety
disagreements can arise as noted in a previous summary [11].
Yellow No. 6 (a.k.a. Sunset yellow) was especially useful for fermented foods
that need to be heat treated. Margarine, Doritos, lemon gelatin deserts are
among foods in this category. And though Sunset Yellow was approved by FDA, it
was banned in Norway and Finland. Also, though the Center for Science in the
Public Interest was convinced Blue Dye No.2 was not safe for human consumption,
FDA was not, asserting results of a thorough review of pertinent literature.
Also, a case was
cited of a 55-year-old man who had worked with red, yellow, and blue dyes for
about ten years, but who reported adverse respiratory symptoms when exposed to
Blue Dye No.2 while working, but only as a free-flowing powder [11].
Another cause for
concern is a suspicion that some dyes may cause behavioral problems in some
children. These problems were thought to include aggressiveness, short-term attention
spans, and impulsiveness [12]. One solution
proposed was a “Feingold Diet” that excludes artificial food colorings [13]. Further
studies were described earlier [11], but one
must note the difficulties involved in assessing effects of food dyes on
children or possibly adults.
3.4.
What is the Volume
of Food Dyes Used Annually?
Maybe we shouldn’t
ask the question because we probably still don’t have a good answer. In 2010,
The Food and Drug Administration had adequate information on the total amounts
of specific batches of colors, and this was because of a requirement to provide
certification. In 2010, for example, it was known that over 15 million pounds
of colored batches had been certified. This value, however, covered all uses,
and was, of course, different from the amount of dye used for food. As result
of an earlier study, we raised the question of the incentives for knowing the
amounts of dyes used for food purposes and additional specifics.
A study, reported
by a Purdue group [14], indicated the
consumption of food colorants was an estimated 12 mg/capita/day in 1950, but had
risen to 62 mg/capita/day in 2010. The reported values varied widely with the
choice of food (certain popular breakfast food versus popular energy drinks).
And some suspect the levels are much higher.
3.5.
Can Food Dyes Be
Removed Conveniently?
We believe our
research demonstrated [11] that removal from
aqueous solution could be done and done quantitatively for six of the seven
common food dyes. Our research indicated quantitative removal, e.g., expressed
as Removal Effectiveness (Equation 1) was 99.9±0.0%.
Removal
Effectiveness = (Moles removed) x 100/ moles in stock solution -Equation 1
Where the ± represents the standard deviation of the mean
Deionized (DI)
water was our standard solvent, but for FD&C Red No 3 (Figure 1), tap water was also tested as a solvent,
and so was well water from a shallow aquifer. FD&C Blue No 1 was removed
quantitatively (100.0±0.1%) as was Blue No.2
(100.0±0.2).
The procedure
would require a compound of sufficient acidity or a suitable pH to convert the
dye to an anionic species. And the structure of Red No 3 has an aromatic carboxylic
group. This is adequate for this compound for effective removal [11].
4.
Summary
Synthetic food
dyes are no doubt a valued “Articles of Commerce”, and they have aesthetic
value, and perhaps psychological value. As a pre-teen during World War II
living in Iowa, margarine was sold uncolored, the same color as lard. And the
coloring dye came separately for suitable kneading. A younger friend “Jimmy
Don” achieved certain notoriety for being able to eat bread coated with
non-colored margarine. The dye didn’t add flavor, but it made the bread and
spread palatable to me and others my age. Food dyes may be a small price to pay
for personal comfort.
5. Acknowledgments
I gratefully
acknowledge collaborators and supportive colleagues, especially Dr. Randy
Larsen, who granted access to his Shimadzu UV-2401 PC UV-Vis recording
spectrophotometer.
research article 