Transcript Acrylamide: Contamination in Water and an Assessment of Regulations. Jasmeet Kaur, Laura Smolyar and Antonio F.

Acrylamide: Contamination in Water and an Assessment of Regulations.
Jasmeet Kaur, Laura Smolyar and Antonio F. Machado
Department of Environmental and Occupational Health, California State University, Northridge.
Abstract
Introduction
Metabolism
Acrylamide is a monomer that is used to generate
polyacrylamides (PAMs) via a polymerization reaction. Application
of PAMs as a flocculant is widespread in the industry of waste
water treatment, which resulted in making waste water
treatment the largest contribution of acrylamide into the
environment and drinking water contamination. Acrylamide is
hydrophilic and water soluble molecule with properties that allow
it to leach into the aquatic systems and drinking waters.
Acrylamide is currently classified as a Group B2, probable human
carcinogen by the United States Environmental Protection Agency
(EPA) and International Agency for Research on Cancer (IARC), but
is also known to have adverse effects on nervous system for both
humans and animals. Awareness and knowledge of everyday
exposures to acrylamide through: drinking water, foods,
cosmetics and smoking is a cornerstone in future remediation,
policy re-evaluations, and lowering pollution strategies.
PAMs are used predominantly in water treatment plants as a flocculant but has other uses in plastics, paper,
cosmetics, mineral processing. Acrylamide leaches into aquatic and drinking water via degradation of PAMs that
are used in various industries. Acrylamide is also generated during preparation of food with large starch content
and high temperature cooking. Surprisingly, concentrations of acrylamide around quarries is smaller than in
environment. State of California department of Environmental Protection Agency (Cal/EPA) right to know act,
Proposition 65 regulates that a warning be posted to inform the public potentially hazardous substances, but in
relation to water EPA had set MCGL to 0, and MCL=TT (Treatment technique). There had been risk assessment
studies done, and estimated that risk of developing cancer is 6 out of 10,000 with the current exposures of 0.43
micrograms per a kilogram of body weight. Acrylamide undergoes phase 1 and phase 2 metabolism in
mammalian subjects. Exposure routes consist mostly of ingestion, transdermal and inhalation, however the
drinking water would fall under oral administration. Acrylamide distribution in the body depends on its route of
entry, but it is metabolized by hepatocytes in the liver and is excreted in original and various metabolite forms
mostly via urine. Health effects include: nervous system, neurotoxic, carcinogenicity, reproductive and endocrine
system disrupting effects. Acrylamide does not only impact mammals but also aquatic populations, studies show
necrotic effects on tissues and DNA damage to fish and mussels that were exposed to acrylamide. There are
various remediation strategies in the soil that involve microbial organism degradation of acrylamide, which had
proved to be very efficient. There is also water treatment strategies involving carbon treatments, filtration,
coagulation and chlorine additions.
Industrial Production and Uses
Acrylamide metabolism inside a mammalian body takes a few routes:
• Acrylamide undergoes conjugation reaction with glutathione, and
produces mercapturic acid as a product.
• Acrylamide also undergoes epoxidation reaction with Cyp4502E1,
and produces glycidamide.
• Glycidamide molecule has three possible routes.
•
Uses of Acrylamide by
Industry in Percentages.
Acrylamide is widely used as a building block of PAMs (polyacrylamides) and
acrylamide copolymers. Acrylamide copolymers and PAMs are used in many
industrial processes such as; wastewaters treatment, paper mills, plastics,
dyes, ore processing, and irrigation of water to improve soil texture (L. Brown
et al. 1982),(EU 2000). PAMs are also used in consumer products such as;
caulking, food packaging and processing, manufacturing of adhesives,
pesticide formulations and cosmetic additives (D. Wood et al. 2004).
Polyacrylamide is largely used as a flocculator in water treatment facilities, ore
processing processes and paper mill industries. PAMs are also widely used in
genetic engineering and molecular biology laboratories as a matrix which is
utilized to separate nucleic acid components during analysis of DNA sequence
(Taeymans et al. 2010).
Water Treatment
Oil Drilling
Pulp and Paper
Mineral Processing
Misc.
Glycidamide • Glycidamide undergoes
• Glycemide
conjugation reaction with
can be
molecules that
glutathione and produces
metabolized
have not been
mercapturic acid.
by epoxide
metabolized
Mercapturic acid produces
hydrolase,
stay free and
two metabolites:
creating
unchanged.
glyceramide.
Glycidamide is
1. N-Acetyl-S-(2-hydroxy-2considered to
carbamoylethyl) cysteine.
be genotoxic.
2. Cysteine and N-Acetyl-S-(1carbamoyl-2-hydroxyethyl)
Cysteine.
Figure 1. Metabolism of acrylamide. (Virk-Baker et al. 2014) Running feed.
Distribution/Excretion
Table 1. Use of Acrylamide by industry in percentages directly from
the monograph: acrylamide. (IARC 1985-1986) Pie chart displaying
usages of acrylamide from year 1991 in Table 1.
(E. Dybinga et. Al 2005).
Routes of exposure
Acrylamide Production in Food
Acrylamide is most commonly formed in carbohydrate rich foods which are heated during preparation to or above 120˚C (C. Gertz et al. 2002), (P. Rydberg et al. 2003).
Acrylamide is formed as a by-product of Mailllard browning reaction, the reaction is described in Figure 6 (R. Stadler et al. 2002),(Food Agriculture Organization of the
United Nations 2008), (D. Mottram et al. 2002), (F. Perdreschi et al. 2013).
Figure 6. Acrylamide formation in food. (Mestdagh et al. 2008)
Every six people in out of ten
thousand are expected to
develop cancer as a
result of ingesting acrylamide
containing products. (E.
Dybinga et al. 2005)
Formation of acrylamide begins with reaction of carbonyl compound and amino acid asparagine which results in N-glycosyl conjugation and formation of decarboxylated
Schiff base. After decarboxylation, the Schiff base might decompose into acrylamide and an imine or the reaction might be followed by hydrolysis to aminopropionamide
and carbonyl compounds (R. Stadler et al. 2002),(Food Agriculture Organization of the United Nations 2008), (D. Mottram et al. 2002), (F. Perdreschi et al. 2013).
Cooking methods such as; frying, baking, broiling and roasting are likely to produce acrylamide whereas; boiling and steaming of the foods are less likely to produce
acrylamide. Cooking at high temperatures catalyse a chemical reaction between reducing sugars and amino acids in the food which results in the formation of acrylamide.
Acrylamide is most commonly found in; Potato Chips, French Fries, Roasted Coffee, Cereal Products, Breads and Bakery Products, Dried Foods, Chocolate Products (K.
Skog et al. 2008), (E. Tareke et al. 2002) According to U.S. FDA, there are no guidelines which govern the presence of acrylamide in food but residual amount of acrylamide
is regulated in number of food materials (A. Kita et al. 2004), (H. Mojska et al. 2007).
Figure 3. Distribution and toxicokinetics of
acrylamide in a mammal. Concepts of PBTK
compartment model developed by Kirman et. al.
had been applied in creation of Figure 3, which
represents distribution of acrylamide in a body
with the emphasis to ingestion route of
administration.
Figure 2. Acrylamide exposure routes and average daily exposure dose. (E. Dybinga et al. 2005)
Health Effects
• Nervous system effects:
Negative effects on the nervous system are not generally noticeable in
a large population exposed to lower doses of acrylamide. Study of
• Acrylamide distribution in the body circulates compartments
workers exposed to acrylamide via inhalation found that 71%
PAMs (polyacrylamide) are expected to be highly mobile and biodegradable in soil and water. Residual monomer of acrylamide releases to the soil and lands during
depending on the exposure route. Ingested acrylamide travels experienced numbness in extremities and fatigue, 68% experienced
industrial production of dyes, plastics and grouting agents which might be in wells. Use of PAMs results in small amounts of the PAMs that escapes into the environment, but is
into the stomach, then into liver. Liver cells hepatocytes
unlikely that it will degrade to acrylamide. Residuals of acrylamide monomer mostly end up in the liquid-water effluent.
sweating of hands and feet, 59% skin peeling, 54% loss of pain
Commercially used PAM flocculants in treatment plants contain residual acrylamide monomer, when this residual monomer is released into the environment. Majority of
metabolize acrylamide via pathways described in Fig.1.
sensations and 46% loss of touch sensations. Less than 50% of workers
acrylamide that releases from industrial processes as a discharge, ends up in the water. Acrylamide is known to have high water solubility as a result it leaches into the
Metabolite
of
acrylamide
glycidamide,
may
get
recirculated
groundwater from the soils that are contaminated with toxic releases (S. Touze et al. 2014),(S. Lande et al. 1979).
experienced dizziness, anorexia, loss of vibration sensation, nausea,
Most of acrylamide monomer when used in industrial processes like water treatment facilities ends up in the soil. After the treatment of raw water with the flocculant when
back into the system. Intravenous blood carries compounds to loss of ankle reflexes, headaches, and unsteady gait (C.J Calleman
the left over water from the treatment process stays in the sludges/soil around the treatment facilities. Many studies have shown that AMD (monomer of acrylamide) leaches
the lungs, and lungs bring them back into arterial blood supply.
into the soil and eventually can reach groundwater if proper care is not taken .
1994).
Blood takes compounds into tissues and back into the liver.
Studies conducted by Lande et al, 1979 found that PAMs are mostly mobile in loamy fine sand and least mobile in slit clay.
When PAMs are in water it can undergo either abiotic or biotic degradation. Number of studies showed that PAM will undergo biodegradation after an initial period of
• In humans, half-life of acrylamide in the plasma is short, Half- • Reproductive effects
acclimation (S. Touze et al. 2014),(S. Lande et al. 1979).
Study was conducted on mice affected by obesity and acrylamide.
life
of
acrylamide
in
rodents
ranges
from
1-4
hours
(Sumner
et
Fig 5. represents a diagram of a typical wastewater treatment facility where polyacrylamides are used to
treat waste water. There are a few points in a system where polyacrylamides can be injected, depending on
al. 1992). In a study conducted on human population exposed Obesity had reduced fertility of male mice, but even further
the set up of facility. The system presented in the study by Touze et al, injects polyacrylamides at the
potentiated acrylamide induced toxicity that lead to even greater
to acrylamide, biomarkers are used to determine exposures.
flocculant injection unit, marked in the diagram as P3.
infertility, acrylamide effected both obese and lean males. Obese
Urinary excretion of acrylamide metabolites had been noted.
males displayed greater susceptibility to potentiation of acrylamide
There is a positive significant correlation between the
induced infertility than lean males. The relationship between diet
metabolites located in the urine of exposed humans and the
neurotoxicity index, as well as acrylamide hemoglobin adducts induced obesity and acrylamide toxicity was linked to decreased
fertility, parameters as abnormal sperm morphology and low total
to N-terminal valine (C.J Calleman 1994).
• Smokers were evaluated based on the urine and blood samples, sperm count (Ghanayem et al. 2010).
• Cancer
Figure 5. Water treatment facility/settling basins. (S. Touze et al 2014)
vs the non-smokers. Mercapturic acid (N-acetyl-S-(2Various cohort-studies have been conducted on humans to evaluate
carbamoylethyl)-L-cysteine, AAMA) increased by 2.5 folds,
acrylamide’s carcinogenic effects, and produced some inconclusive
metabolites of glycidamide (N-(R/S)-acetyl-S-(2-carbamoyl-2Acrylamide/polyacrylamide can be found two matrices: water and soil. During the treatment process, the treated water seeps into the soil surrounding the facility as a result.
hydroxyethyl)-L-cysteine, GAMA) increase by 1.7 folds, the N- data. A study about endometrial cancer (EC) concluded that there
Residual of acrylamide can be found in soil. PAMs and acrylamide undergo microbial degradation in the sediment and soils around the water treatment quarries and settling basins.
were no EC risk associated for women with dietary acrylamide intake,
terminal valine adduct of acrylamide (N-2Example of such can be viewed in Fig 5,(Anne Togola 2014).
EU, 2000 risk assessment reports have indicated that photodegradation of acrylamide in surface waters has a half life of about 1 year.
however an increased risk for EC was noted for women who were noncarbamoylethylvaline, AAVal) in blood increase by 3 fold in
Studies conducted by Lande et al, 1979 demonstrated that highest degradation of acrylamide occurs in soil when the soils have an alkaline pH and high temperatures.
smokers and were not treated with oral contraceptives. Human cancer
smokers (Urban et al. 2008).
Sediment around
Sediment in
Water around
Water in
risk assessments are still estimated, through a physiologically based
quarries
environment
quarries
environment
pharmacokinetic and pharmacodynamics (PBPK/PD) model. One such
model had estimated risk to be 1-4 in 10 thousand will be affected by
<0.02 to <0.08 µg/g
<10 µg/L
0.41 to 5.66 µg/L
< 5 µg/L
Carassius auratus (gold fish) manifested histopathological alternations in
cancer, with the average daily consumption dose of acrylamide
hepatopancreas from exposure to acrylamide. Fish were exposed to
(Doerge et al. 2008). Studies show that there is a statistically significant
acrylamide via their water containers that mimic acrylamide contaminated
correlation between acrylamide exposure and rodent carcinogenicity.
Table 2. Environmental levels (S. Touze et al 2014 ), (ATSRD 2012).
aquatic conditions. Lethal Concentration at 50% (LD50) occurred with the
It is important to note that carcinogenicity of acrylamide in rodent
concentration of 119.5 mg/L, while a 100% mortality of fish occurred at 200
studies displayed affinity for reproductive system organs adverse
mg/L. The exposed fish manifested DNA breakage, pancreatic cell necrosis
effects. Acrylamide and it’s metabolite glycidamide are both
EPA
CAL/EPA
European union
Japan
and diffuse intrusions of macrophages and
considered to have mutagenic properties, however glycidamide is
MCGL=0
MCL=TT
0.0005
µg/L.
chromosomal
aberrations-clastrogenesis
0.10 µg/L.
assumed to be a more potent carcinogen.
MCL=TT
(Larguinho et al. 2014). Marine organisms • Endocrine system disruption
Mytilus galloprovincialis (mussels) resembled
Endocrine system disruptions are disruptions in the hormone
Table 3. Regulations of acrylamide.
mammalian GST metabolic activities and
regulations, caused by low doses of acrylamide. Thyroid gland effects
(Treatment Technique (TT) is set instead of MCL for acrylamide because EPA was unable to find any reliable
exhibited cell necrosis of gonads and oocyte
of decreased in the colloid area and follicular area shrinkages were
methods which were economically and technically feasible to measure acrylamide at low concentrations. TT is
atresia (Larguinho et al.2014).
an enforceable procedure which is set by EPA under the Phase II rule. Phase II rule, under the Safe Drinking
noted in a study that exposed female mice to acrylamide (Khan et al.
Water Act requires EPA to review the national primary drinking water regulation periodically. This rule limits
1999). Acrylamide doesn’t only have reproductive effects but it also
the amount of acrylamide use to 0.05% by weight and dosage for the water treatment facilities and requires
influences reproductive organs that produce hormones and
treatment facilities submit in writing that levels specified in phase II rule are not exceeded. Currently
immunohistochemistry. Low body weight, organ weight and
Treatment Technique Process
acrylamide is being reviewed by the EPA during the Second Six Year Review of National Primary Drinking Water
development, progesterone concentration in serum reducing effects
1. Pre-Disinfection:
6. Solids Removal: Solids
5. Filtration: After
Regulations. New technology has been developed by the Swedish National Food Administration in 2002, to
3.
Flocculation:
Commonly used in newer
that settle out of the water
sedimentation, the
had been noted in the study conducted on acrylamide-treated female
treat acrylamide called direct testing procedure. EPA has reviewed the procedure developed by Sweden but
Gentle mixing
plants. Mostly ozone is
are removed to drying
clarified water is
mice (Wei et al. 2014).
process to form
used to remove TOC
EPA is still determining if the cost associated with this procedure is technically reasonable (EPA 2009),(Brown L
lagoons or sludge presses
passed through
Fate and Transport
Levels in the Environmental Matrices
Ecotoxicology/Ecology
Regulations
Remediation/Recommendations
et al. 1980),(EPA 2014). EPA has determined that, “exposure to acrylamide in drinking water at concentrations
of 1.5 mg/L for one day or 0.3 mg/L for 10 days is not expected to cause any adverse effects in a child.”
Whereas, polyacrylamide concentrations near water treatment facilities must be less than 0.08 µg/g. (Anne
Togola 2014). Treatment technique is discussed in detail in remediation/recommendations section.
References
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(Total Organic Carbon)
from raw water.
2. Coagulation: The process of
chemical addition to combine
suspended solids and colloidal solids
creating larger particles that can settle
out and/or be filtered out. Chemicals
commonly used for this process
include aluminum sulfate (alum), ferric
chloride, and synthetic polymers. After
the addition a process called “flash
mixing” occurs, in length of time of 30
to 60 seconds. Flash mixing process
disperses the chemicals to mix with
TSS (Total Suspended Solids).
larger and heavier
particles.
filters to remove
particles of dirt,
algae, and harmful
bacteria and
parasites. Filters can
are usually made
from sand, gravel or
granular activated
carbon.
for dewatering.
7. PostDisinfection: Chlorine and
chlorine containing
compounds are typically
used for disinfection
purposes to disable
bacteria, viruses and
parasites.
4. Sedimentation (Also Known as
Clarification): The particles that are
formed through coagulation and
flocculation become increasingly larger
and eventually settle out of the water
(water.epa.gov)
in large sedimentation basins.
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Rahim MB, Syed MA, Shukor MY. 2012. Isolation and characterization of an acrylamide-degrading yeast rhodotorula sp. Strain mbh23 kctc 11960bp. J Basic Microbiol
52:573-581.
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PAMs degrade into monomers when effected by sunlight, however microbial remediation is more efficient
at breaking down PAMs without leaving monomer residual. Acrylamide is hydrophilic and is hard to eliminate
out of water by filtration.
Degradation of PAMs had been studied in: aeration, light, pH, and sterilization. In a mineral salt medium a
species of Variovorax boronicumulans CGMCC 4969 strain proved to degrade acrylamide, hydrolyzing it to
acrylic acid with a half-life of 2.5 minutes. Escherichia coli strain Rosetta (DE3) pLysS also produced notable
results by hydrolyzing acrylamide into acrylic acid. Not only was acrylamide degraded, but the metabolic
byproducts produced during degradation promoted cell growth (Liu et al. 2013).
Example: Table 5. Concentrations of acrylamide around quarries is smaller than in the environment.
Rhodotorula sp. Strain mbh23 kctc 11960bp was able to degrade a full dose of acrylamide in 5 days (Rahim et
al. 2012).
Acrylamide is degraded into CO2 and ammonium ions in water and soils. The bacterium found to metabolize
acrylamide in aerobic conditions were Bacillus, Pseudomonas, Rhodococcus (Junqua et al. 2014).
Some Recommendations for consumption of food and impact on environment are listed below:
Avoid consumption of fried foods, use alternative methods for cooking such as boiling and steaming.
Better techniques must be utilized at the industries which use acrylamide to reduce the impact on the
environment.
Conclusion
It is important to acknowledge that in contrast to all the studies that have discovered
and determined acrylamide toxic potentials, knowledge is still limited with regards to
effects of acrylamide on a human population. One of the aspects that research can
expand on is producing more risk assessment reports based human population, with
regards to routes of exposure to acrylamide and comparison of effects on different
age groups. Acrylamide is currently classified a possible human carcinogen, however
the metabolite glycidamide is considered to have greater affinity towards
mutagenesis. More research is needed to analyze glycidamide and the overall
possible potentiation of cancer and hormone disrupting effects by acrylamide in
combination with other mutagens.