View
220
Download
0
Category
Preview:
Citation preview
7/26/2019 Literature Review of Monitoring Methods for Formaldehyde
1/26
NATIONAL UNIVERSITY OF SINGAPORE
SH5110 Chemical Hazard Evaluation
Literature Review ofMonitoring Methods for
Formaldehyde
7/26/2019 Literature Review of Monitoring Methods for Formaldehyde
2/26
2 of 26
Executive Summary
Formaldehyde is a known human carcinogen, and yet there is the potential for this chemical
to be present at the workplace, retail spaces and even residential spaces due to its applications
in many building materials. The aim of this literature review is to improve our understandingof the hazards of formaldehyde, how exposure to formaldehyde is being monitored and
regulated at the workplace and also to review the application of new technologies in
measuring airborne formaldehyde concentration.
The TWA and STEL for formaldehyde is at 0.75 ppm (8 hours) and 2 ppm (15 mins)
respectively. NEA recommends a maximum indoor air concentration of 0.1 ppm. Current
standardized methods for compliance measures airborne formaldehyde concentration and
neglects particulate-bound formaldehyde, which is a common occurrence in wood and textile
industries. The applicability and limitations of conventional laboratory methods and direct
reading instruments are discussed. Research into novel methods, which have severaladvantages over the traditional methods for monitoring formaldehyde concentration in the
field, has also been reviewed.
7/26/2019 Literature Review of Monitoring Methods for Formaldehyde
3/26
3 of 26
Contents
Executive Summary ................................................................................................................................. 2
1.0 Introduction ................................................................................................................................ 4
1.1 Industrial applications ............................................................................................................. 4
1.2 Synthesis of Formaldehyde ..................................................................................................... 4
1.3 Safety ...................................................................................................................................... 5
2.0 Standardized Methods ................................................................................................................ 7
2.1 NIOSH 3500 ............................................................................................................................. 8
2.1.1 NIOSH Method 3500 for Formaldehyde Measurement ................................................. 8
2.1.2 Method Evaluation of NIOSH Method 3500 ................................................................... 9
2.2 OSHA 1007 ............................................................................................................................ 15
2.3 NIOSH 5700 ........................................................................................................................... 17
2.4 Other Methods ...................................................................................................................... 18
2.4.1 Direct Reading Instruments .......................................................................................... 18
2.4.2 Emission testing standards ........................................................................................... 18
2.5 Novel Methods ...................................................................................................................... 21
2.5.1 Biosensors ..................................................................................................................... 21
2.5.2 DNAzymes ..................................................................................................................... 22
2.5.3 Formaldehyde dehydrogenase ..................................................................................... 23
3.0 Conclusion ................................................................................................................................. 25
4.0 References ................................................................................................................................ 26
Abbreviations
CARBCalifornia Air Resources Board
DMCDynamic Micro Chamber
FIDFlame Ionization Detector
FLECField and Laboratory Emission Cell
GCGas Chromatography
HPLCHigh Performance Liquid Chromatography
MSMass Spectrometry
NPDNitrogen-specific detector
UVUltraviolet Detector
VASVisible Absorption Spectrophotometry
7/26/2019 Literature Review of Monitoring Methods for Formaldehyde
4/26
4 of 26
1.0 Introduction
Formaldehyde1 is an important precursor to many other materials and chemical compounds.
In 1996, the installed capacity for the production of formaldehyde was estimated to be 8.7
million tons per year. It is mainly used in the production of industrial resins, e.g., for particleboard and coatings. It is also used in pressed-wood products, such as particleboard, plywood,
and fibreboard; glues and adhesives; permanent-press fabrics; paper product coatings; and
certain insulation materials. In addition, formaldehyde is commonly used as an
industrialfungicide,germicide, anddisinfectant, and as a preservative in mortuaries and
medical laboratories. Formaldehyde also occurs naturally in the environment. It is produced
in small amounts by most living organisms as part of normalmetabolicprocesses.
In view of its widespread use, toxicity, and volatility, formaldehyde is a significant
consideration for human health.In 2011, the US National Toxicology Programdescribed
formaldehyde as "known to be a human carcinogen".
1.1
Industrial applications
Formaldehyde is a common precursor to more complex compounds and materials. In
approximate order of decreasing consumption, products generated from formaldehyde
include urea formaldehyde resin, melamine resin, phenol formaldehyde resin,
polyoxmethylene plastics, 1,4-butanediol and methylene diphenyl diisocyanate.
The textile industry uses formaldehyde-based resins as finishers to make fabrics crease-
resistant. Formaldehyde-based materials are key to the manufacture of automobiles, and usedto make components for the transmission, electrical system, engine block, door panels, axles
and brake shoes. The value of sales of formaldehyde and derivative products was over $145
billion in 2003.
1.2
Synthesis of Formaldehyde
Two steps in formation of urea-formaldehyde resin, which is widely used in the production of
particle board.
1Formaldehyde, World health Organization, 2002
http://www.cancer.gov/Common/PopUps/popDefinition.aspx?id=CDR0000642499&version=Patient&language=Englishhttp://www.cancer.gov/Common/PopUps/popDefinition.aspx?id=CDR0000642503&version=Patient&language=Englishhttp://www.cancer.gov/Common/PopUps/popDefinition.aspx?id=CDR0000642495&version=Patient&language=Englishhttp://www.cancer.gov/Common/PopUps/popDefinition.aspx?id=CDR0000044056&version=Patient&language=Englishhttps://en.wikipedia.org/wiki/File:UFresinSyn.svghttp://www.cancer.gov/Common/PopUps/popDefinition.aspx?id=CDR0000044056&version=Patient&language=Englishhttp://www.cancer.gov/Common/PopUps/popDefinition.aspx?id=CDR0000642495&version=Patient&language=Englishhttp://www.cancer.gov/Common/PopUps/popDefinition.aspx?id=CDR0000642503&version=Patient&language=Englishhttp://www.cancer.gov/Common/PopUps/popDefinition.aspx?id=CDR0000642499&version=Patient&language=English7/26/2019 Literature Review of Monitoring Methods for Formaldehyde
5/26
5 of 26
When treated with phenol, urea, or melamine, formaldehyde produces, respectively, hard
thermoset phenol formaldehyde resin, urea formaldehyde resin, and melamine resin. These
polymers are common permanent adhesives used in plywood and carpeting. It is used as
the wet-strength resin added to sanitary paper products such as (listed in increasing
concentrations injected into the paper machine headstock chest) facial tissue, table napkins,and roll towels. They are also foamed to make insulation, or cast into moulded products.
Production of formaldehyde resins accounts for more than half of formaldehyde consumption.
Formaldehyde is also a precursor to polyfunctional alcohols such as pentaerythritol, which is
used to make paints and explosives. Other formaldehyde derivatives include methylene
diphenyl diisocyanate, an important component in polyurethane paints and foams,
and hexamine, which is used in phenol-formaldehyde resins as well as the explosive RDX.
Formaldehyde has been found as a contaminant in several bath products, at levels from 54
610 ppm: it is thought to arise from the breakdown of preservatives in the products, most
frequently diazolidinyl urea. Since 2006, formaldehyde (methylene glycol) is also used inhair smoothing treatments in order to straighten wavy/curly hair and make hair less prone to
frizz under high humid weather. OSHA Oregon has reported these treatments as unsafe for
human health.
1.3 Safety
Formaldehyde is highly toxic to all animals, regardless of method of intake. Ingestion of 30
mL of a solution containing 37% formaldehyde has been reported to cause deathin an adult
human.Water solution of formaldehyde is very corrosive and its ingestion can cause severe
injury to theupper gastrointestinal tract.
Occupational exposure to formaldehyde by inhalation is mainly from three types of
sources:thermalorchemical decompositionof formaldehyde-based resins, formaldehyde
emission fromaqueoussolutions (for example, embalming fluids), and the production of
formaldehyde resulting from thecombustionof a variety of organic compounds (for example,
exhaust gases). Formaldehyde can be toxic, allergenic, and carcinogenic.Because
formaldehyde resins are used in many construction materials it is one of the more common
indoor air pollutants.At concentrations above 0.1 ppm in air formaldehyde can irritate the
eyes andmucous membranes, resulting in watery eyes.Formaldehyde inhaled at this
concentration may cause headaches, a burning sensation in the throat, and difficulty breathing,
and can trigger or aggravate asthma symptoms.
A 1988 Canadian study of houses withurea-formaldehydefoam insulation found that
formaldehyde levels as low as 0.046 ppm was positively correlated with eye and nasal
irritation.A recent review of studies has shown a strong association between exposure to
formaldehyde and the development of childhood asthma.The primary exposure concern is
for the workers in the industries producing or using formaldehyde.
The formaldehyde theory of carcinogenesis was proposed in 1978.In 1987 the U.S. EPA
classified it as aprobable human carcinogen, and after more studies theWHO International
7/26/2019 Literature Review of Monitoring Methods for Formaldehyde
6/26
6 of 26
Agency for Research on Cancer (IARC) in 1995 also classified it as aprobable human
carcinogen. Further information and evaluation of all known data led the IARC to reclassify
formaldehyde as aknown human carcinogenassociated with nasal sinus cancer
andnasopharyngeal cancer.Recent studies have also shown a positive correlation between
exposure to formaldehyde and the development ofleukaemia, particularlymyeloidleukaemia.Nasopharyngeal and sinonasal cancers are relatively rare, with a combined annual
incidence in the United States of < 4,000 cases.About 25,000 cases of myeloid leukaemia
occur in the United States each year.Workplace exposure to inhaled chemicals is among the
most important risk factors for sinonasal cancers.Professionals exposed to formaldehyde in
their occupation, such as funeral industry workers andembalmers, showed an increased risk
of leukaemia and brain cancer compared with the general population. Other factors are
important in determining individual risk for the development of leukaemia or nasopharyngeal
cancer.
In the residential environment, formaldehyde exposure comes from a number of differentroutes; formaldehyde can off-gas from wood products, such as plywood or particle board, but
it is produced by paints, varnishes, floor finishes, andcigarettesmoking as well.
Singapore National Environment Agency recommends that the maximum threshold level for
formaldehyde should not exceed 0.1ppm, based on Guidelines for Good Indoor Air Quality
in Office Premises.2
The purpose of this case study is to review the different methods to determine the
concentration of formaldehyde.
2IAQ, Indoor Air quality website url: http://www.iaqsg.com/chemical-
parameters/formaldehyde/ , accessed on 04/04/2016
7/26/2019 Literature Review of Monitoring Methods for Formaldehyde
7/26
7 of 26
2.0 Standardized Methods
Several standards have been developed to provide guidelines for the sampling and analytical
methods for determining the concentration of formaldehyde in air. The majority of the
methods use a sorbent tube to collect formaldehyde in an active sampling train. Somemethods consider the use of a diffusive sampler to collect formaldehyde in the air passively;
one other method makes use of an impinger to collect formaldehyde in a liquid solution3.
High performance liquid chromatography (HPLC) using an ultraviolet detector is the
analytical method of choice for most of the standards. Other standards recommend gas
chromatography (GC) and visible absorption spectrophotometry (VAS) for the analysis of the
collected samples.
In addition to sampling formaldehyde direct from air, NIOSH has documented a method for
sampling formaldehyde-containing particulates. These particulates are a common occurrencein the wood and textile industries. Legislations has focused on the gas-phase concentration of
formaldehyde based on established interpretation of results from epidemiological studies.
The concentration of formaldehyde-containing particulates at the workplace is not regulated
by either OSHA or the Singapore authorities4.
The list of approved methods for compliance sampling is presented in Table 1. The NIOSH
3500, OSHA 1007 and NIOSH 5700 methods are selected for further discussion below.
Table 1: Approved methods for compliance sampling of formaldehyde in air
Agency Reference Sampler AnalyticalMethod
Applications
NIOSH 2016 Sorbent Tube HPLC-UV
2539 Sorbent Tube GC-FIDGC-MS
For screening only
2541 Sorbent Tube GC-FID
3500 Glass Midget Impinger VAS
5700 IOM ParticulateSampler
HPLC-UV Textile dust or wood dust
OSHA 52 Sorbent Tube GC-NPD Use of formalin solutions
1007 Diffusive Sampler HPLC-UVID-205 Diffusive Sampler VAS Not suitable for STELsampling
EPA IP-6A Sorbent Tube HPLC-UV Environmental sampling(indoor air)
IP-6C Diffusive Sampler HPLC-UV Environmental sampling(indoor air)
IP-11A Sorbent Tube HPLC-UV Environmental sampling(ambient / outdoor air)
ASTM D 5197 Sorbent Tube HPLC-UV
3NIOSH, NOISH Manual of Analytical Methods, Fourth Ed., 19944NEA, National Environment Agency website, url:www.nea.gov.sg,date retrieved: 29th March 2016
http://www.nea.gov.sg/http://www.nea.gov.sg/http://www.nea.gov.sg/http://www.nea.gov.sg/7/26/2019 Literature Review of Monitoring Methods for Formaldehyde
8/26
8 of 26
2.1
NIOSH 3500
2.1.1 NIOSH Method 3500 for Formaldehyde Measurement5
The NIOSH method 3500 is an active sampling approach which uses a sampler attached to a
pump. After collection of the sample, it is analysed through a visible absorption spectrometry
of wavelength 580nm.
Sampler:
The sampler consist of a filter with a PTFE membrane filter (1-3m pore size) supported by
an O-ring followed by 2 midget impingers (Fig 1). During sampling, the two impingers are
filled with 20ml, 1% sodium bisulfite solution. A cassette is attached to the impinger and
impinger to the sampling pump via a flexible inert tubing. The PTFE membrane is necessary
if the sampling is used in a dusty environment. The use of dual impingers in series is
recommended to ensure efficient collection of formaldehyde. After sampling, the contents of
the impingers will be transferred to a polyethylene bottle for shipping.
Figure 1: Midget Impinger Figure 2: Midget Impinger with Sampling Flow Pump
Sample Preparation
When the impingers solution are brought back, the volume of the solution from the front and
back up impinger, Vf and Vb are recorded. 4mL of pipetted sampling solutions is transferred
to a 25mL glass stoppered flask. A 0.1mL 1% chromotropic acid can react with 40
micrograms of formaldehyde. Addition of 6mL of concentrated sulphuric acid is performed
slowly and a gentle swirl to mix. A colour develops as illustrated (Fig 3). The sample is then
5Kennedy, E. R. (1994). FORMALDEHYDE: METHOD 3500, Issue 2. NIOSH Manual of Analytical Methods
(NMAM), Fourth Edition, 8/15/94. Retrieved April 12, 2016, fromhttp://www.cdc.gov/niosh/docs/2003-154/pdfs/3500.pdf
http://www.cdc.gov/niosh/docs/2003-154/pdfs/3500.pdfhttp://www.cdc.gov/niosh/docs/2003-154/pdfs/3500.pdfhttp://www.cdc.gov/niosh/docs/2003-154/pdfs/3500.pdfhttp://www.cdc.gov/niosh/docs/2003-154/pdfs/3500.pdfhttp://www.cdc.gov/niosh/docs/2003-154/pdfs/3500.pdfhttp://www.cdc.gov/niosh/docs/2003-154/pdfs/3500.pdf7/26/2019 Literature Review of Monitoring Methods for Formaldehyde
9/26
9 of 26
placed in a 1cm-cuvette into the spectrophotometer. The reading is recorded at visible
absorption spectrometry at 580nm. Effect of other aldehydes is minimal on this method.
Figure 3: Addition of Chromotropic Acid into Sample solution in Glass Stoppered Flask
Applicability: The working range is 0.02 to 4ppm for an 80L air sample. This is the most
sensitive method and is able to measure ceiling levels as low as 0.1ppm.
Inteferences: Oxidisable organic materials may give a positive interference.
Accuracy, bias and precision of Results
Method Bias should be less than 10% as required by the NIOSH Guidelines. For the NIOSH
Method 3500, there are none identified. The precision expected is 0.09
The accuracy which is determined by the intersections of the bias and precision estimates on
the parabolic grid (nomogram) is 18%
2.1.2
Method Evaluation of NIOSH Method 3500
NIOSH Guidelines for Air Sampling and Analytical Method Development and
Evaluation6
The NIOSH Guide suggest guidelines for the development and evaluation of sampling and
analytical methods for industrial hygiene monitoring For each method under consideration,
the objective of this protocol was to decide if the method would provide results, on the
average, over a concentration range of 0.1 to 2 times the exposure limit, to be within 25% of
the true concentration with a probability of 0.95 for an individual observation.
6Kennedy, E. R., Fischbach, T. J., Song, R., Eller, P. M., & Shulman, S. A. (1996). Summary of the NIOSH
Guidelines for Air Sampling and Analytical Method Development and Evaluation. Analyst, 121. RetrievedApril 4, 2016, fromhttp://www.ncbi.nlm.nih.gov/pubmed/8831274
http://www.ncbi.nlm.nih.gov/pubmed/8831274http://www.ncbi.nlm.nih.gov/pubmed/8831274http://www.ncbi.nlm.nih.gov/pubmed/8831274http://www.ncbi.nlm.nih.gov/pubmed/88312747/26/2019 Literature Review of Monitoring Methods for Formaldehyde
10/26
10 of 26
The sampling of a generated atmosphere is needed to more adequately assess the
performance of a method. The concentration range of the analyte should be at least 0.1 to 2
times of the exposure limit. If it is toxic or suspected to be carcinogenic, there could be a
concentration lower than that calculated which needs to be considered.
NIOSH Method 3500 was checked for reproducibility by having 3 different analysts in 2
different laboratories analysed standard samples containing between 1-20 micrograms of
formaldehyde. The results are approximately the same of 5%.
Evaluation from the sampling of a generated atmosphere determines the following:
1) Capacity of the sampler
2) Efficiency of analyte collection
3) Repeatability
4) Bias
5)
Interferences in the collection by the sampler
Generation of the Analyte
As part of the evaluation method, the collection of samples is needed from an environment
that is as close to the actual sampling conditions as possible. And to fulfil this, the impact of
environmental conditions such as temperature, pressure, humidity and interferences needs to
be in consideration.
Table 2: Effects of surrounding conditions on the analyte
S/N Changed conditions Effect
1 Increased temperature on the
collection medium
Decreased capacity of sampler or decompose
the analyste
2 Reduced pressure Reduced capacity of a sampler
3 High relative humidity Reduced sampler capacity
After the generation of the analyte, its concentration will be verified by a
gravimetric/volumetric means. Ideally, this independent method of verification should not be
biased and should provide an accurate estimated of the concentration. Precision and bias is
also homogenous over the concentration ranges.
Capacity of the Sampler and Sampling Rate
To determine the applicability, the capacity of the sampler should be determined by the
function of flowrate and sampling time.
7/26/2019 Literature Review of Monitoring Methods for Formaldehyde
11/26
11 of 26
Different flow rates typical of the media will be used. Sampling should be performed at 3
different flow rates. The amount of analyte collected at the lowest flow rate and shortest
sampling time should be greater than the limit of quantitation of the method. The generated
analyte should be at least 2 times the highest published exposure limit will be used to
determine the sample capacity to be used.
Sampling should be conducted at various temperatures and humidity to check on its effect of
these parameters on the capacity. 3 replicates at different flow rates should be used to verify
the capacities at each of the different humidity and temperature
Table 3: Temperature and humidity conditions
Parameters High Low
Temperature Ambient >35 C
7/26/2019 Literature Review of Monitoring Methods for Formaldehyde
12/26
12 of 26
Bias is assumed to be homogenous across the evaluated concentration ranges. This
assumption should be evaluated to see if there is homogeneity. Bias is estimated at each
concentration. To fulfil the criterion, method bias should be 10%
Accuracy is the intersections of these points on the parabolic grid in the graph. If the both the
upper confidence limits on the accuracy are less than 25%, it fulfils the accuracy criterion.
Field Evaluation
Field Evaluation is not required in the NIOSH Guidelines for Air Sampling and Analytical
Method Development and Evaluation, as conditions which exist in the field are difficult to
reproduce in the laboratory.
The field evaluation is recommended to further study the performance of the method. Both
the collection of area samples and personal samples should be included in the field evaluation
of the method. Area samples can be used to see if there is field precision and bias. Personalsamples can be used to assess the utility of the method.
In the following is a field precision study extracted from the article, Field Precision of
Formaldehyde Sampling and Analysis using NIOSH Method 3500, the American Industrial
Hygiene Association Journal 58:9,657-6607 The study was designed to examine the field
precision by collecting and analysing a series of replicate samples over an extended period.
The field area is the gross anatomy laboratory during their normal activities. There is also
presence of interferences in the existing work environment (oxidisable organics) where
embalming solutions were used.
Method:
2-4 replicates of airborne samples are obtained in the middle of a gross anatomy lab on 29
days. The inlets of the flow pumps (Fig 5) were positioned upward all at the same level about
120cm from the floor which emulate the breathing zone of the workers during dissection.
Distance between each replicate is about 10cm, as shown below
Figure 4: Set up of the Experiment
7Khanzadeh, F. A., & Park, C. K. (1997). Field Precision of Formaldehyde Sampling and Analysis Using
NIOSH Method 3500.American Industrial Hygiene Association Journal, 58(9), 657-660.doi:10.1080/15428119791012450
120cm
3750cm
750cm350cm
10 cm
7/26/2019 Literature Review of Monitoring Methods for Formaldehyde
13/26
13 of 26
The room temperature and pressure were measured during every collection of the sample.
The sample air flow rate was also determined before and after each sampling by a flow meter,
and the target sampling volume was set to be 0.2-1 L/min. Air volumes are adjusted to 25 deg
Celsius and 760mmHg accordingly to 1-100L
Figure 5: SKC PCXR Constant Flow Pump used to collect replicates
It was decided that the Polytetrafluoroethylene filter would not be used as it is a not a dusty
environment. The assumption is derived due to the whole dissecting operations being
performed on moist tissues without any mechanical tools, there is no evident source of
particulate generation. Even if there is, their effects on the precision will be negligible.
Results & Discussion
A total of 98 air samples were collected. 13 samples did not fulfil the target sampling and
working ranges, 4 of them exceeding sample volume range limit of 100L and 9 samples show
flow rate fluctuations of 10%. Lastly, 7 samples out of the 85 remaining were single and notreplicates. Hence, the remaining samples left for data analysis is 78.
The data were entered into statistical analysis, using Statistical Package for Social Sciences.
The descriptive statistics were used to determine means, standard deviations (SD), and the
ranges of sampling parameters, concentrations and coefficients of variation (CV, precision)
of each set of replicates. A t-test was applied to see the difference between the means of 2
independent groups.
CV = Standard deviation/Mean. A pooled CV is to demonstrate the overall precision of each
sampling and analytical method.
7/26/2019 Literature Review of Monitoring Methods for Formaldehyde
14/26
14 of 26
Table I: Sampling Parameters and Formaldehyde concentrations by Number of Sample
Replicates
Mean
(SD)
Range
Number of Replicates in Each Set2 3 4 Overall
Number of
Samples
16 18 44 78
Sampling
Time (min)
186(18)
160-215
147(26)
120-187
156(28)
115-220
160(29)
115-220
Sampling
Flow (L/min)
0.4(0.1)
0.2-0.5
Sampling
Volume (L)
66(2)
39-89
56 (21)
26-99
60(19)
27-100
60(19)
26-100
Concentration
(ppm)
1.01(0.48)
0.05-1.71
0.84(0.17)
0.62-1.25
0.97(0.28)
0.59-1.72
0.95(0.31)
0.05-1.72
From Table II, the precision of replicate samples ranged from 0.03 to 0.24 with an overall
precision of 0.09. This is equal to the precision of NIOSH Method 3500.
The results of the precision also improve as the number of samples in each case increasedfrom 2-4 replicates. Nevertheless, within the preset target sampling and working ranges, the
results did not demonstrate any significant relationship between the parameters of CV,
formaldehyde concentrations, flow rate, sampling time or sampling volume.
Table II: Coefficient of Variation (CV) by number of Sample Replicates Collected in a Gross
Anatomy Laboratory
Number of Replicates in Each Set
2 3 4 Overall
Number of sets 8 6 11 25
Range of CV 0.035-0.241 0.026-0.108 0.026-0.201 0.026-0.241
Pooled CV 0.116 0.079 0.092 0.093
Conclusion:
The overall precision of the field sampling and analysis was 0.09 which is equal to the
precision of Method 3500 as determined in the laboratory.
7/26/2019 Literature Review of Monitoring Methods for Formaldehyde
15/26
15 of 26
2.2
OSHA 1007
The OSHA Method 1007 describes the validation of diffusive samplers that are meant to
provide an alternative to an existing method, ID-205. ID-205, which validates a diffusive
monitor from 3M (model 3721), is limited by the minimum sampling time of 4 hours, making
it unsuitable to measure STEL level which requires a sampling time of 15 minutes.
The OSHA 1007 method has evaluated and fully-validated three brands of diffusive samplers.
These samplers use 2,4-dinitrophenyl hydrazine (DNPH) to react with formaldehyde in the
presence of an acid to form a unique derivative. Supelcos sampler is found by the authors of
this report to have been replaced by a high efficiency (HE) model which is not suitable for
STEL measurement, and hence not suitable for comparison with the other two brands. Refer
to the Table 4 for other useful information about the samplers.
The laboratory analysis of field samples requires a liquid chromatograph equipped with a UV
detector (set at 365 nm wavelength). Refer to the OSHA document for detailed guidelines for
the analytical procedure8.
Table 4: Diffusive samplers validated by OSHA Method 1007
Specifications
Assay Technology
ChemDisk 571
Aldehyde Monitor
SKC UMEx 100
Passive Sampler
Supelco DSD-DNPH
Diffusive Sampling
Device
High Efficiency (HE)
model
Reagent 2,4-dinitrophenyl hydrazine (DNPH)
Collection medium FiberglassTape (material
unknown)
Spherical silica gel
(105210 m)Capacity 100 ppm-hrs 29 g 150 g for HE model
Lower
Detection
Limits
15 min 330 ppb 200 ppb (0.24 mg/m3)Unknown; HE model
not recommended for
STEL
8 hr 10 ppb 5 ppb (6 g/m3)
24 hr N.A. 2 ppb (2 g/m3)
7 days N.A. 0.2 ppb (0.2 g/m3)
8OSHA, Method 1007: Formaldehyde (Diffusive Samplers), T-1007-FV-01-0505-M, May 2005
7/26/2019 Literature Review of Monitoring Methods for Formaldehyde
16/26
16 of 26
Limitations
This method is not suitable for sampling formaldehyde exposure at workplaces where
formalin solutions, formaldehyde/water solution stabilized with methyl alcohol, is used;
OSHA recommends the active sampling method (OSHA Method 52) to be used when
monitoring exposures resulting from the use of formalin solutions.
This method is not suitable for atmospheres with more than 0.5 ppm ozone concentration due
to interference of DNPH reaction with formaldehyde. DNPH was found to be resistant to
interference from other aldehydes such as, acetaldehyde, butyraldehyde, benzaldehyde and
glutaraldehyde. The samplers also requires at least 10% humidity for best performance and
should be stored at 4 C before and after sampling.
7/26/2019 Literature Review of Monitoring Methods for Formaldehyde
17/26
17 of 26
2.3
NIOSH 5700
In the wood and textile industries, there is potential for airborne formaldehyde to be bound to
inhalable dust. NIOSH Method 5700 is an active sampling method using a sampler
developed by the Institute of Occupational Medicine (IOM). The sample and filter is
designed to collect inhalable dust and comes with a PVC filter with pore size of 5 m.
An example of the sampler is shown in Figure 6. The sampler is fully evaluated for
concentration range of between 0.007 and 0.16 mg/m3.
The recommended analytical method is HPLC using UV detector at 365 nm wavelength.
However, the VAS analytical method used in NIOSH Method 3500 is applicable provided
that there are no substances in the sample which can interfere with the chromotropic acid
analysis. These substances include phenol, oxidizable organic material, other aldehydes and
alcohols.
As the results collected by this method are not required for compliance, the NIOSH manual
cautioned against combining the results from this method together with results collected by
methods which measures the vapour-phase concentration.
Figure 6. SKC IOM Sampler
7/26/2019 Literature Review of Monitoring Methods for Formaldehyde
18/26
18 of 26
2.4
Other Methods
2.4.1 Direct Reading Instruments
Direct reading instruments provide fast access to results at the field and is more useful than
the standardized methods in cases where qualitative measurements are desired in real-time to
pinpoint hot spots. Current direct reading instruments for airborne formaldehyde makes use
of electrochemical sensing, photoelectric photometry, colorimetric or photo-ionization
technologies to detect the target molecules.
These equipment are primarily used as a screening tool to establish the orders of magnitude
of the airborne concentration levels of formaldehyde, where higher than desired levels will
warrant the more costly and time-consuming standardized laboratory methods to be carried
out. The instruments have many limitations affecting the accuracies of the readings. These
limitations include: sensitivity to temperature, pressure and humidity; non-selective toformaldehyde; and prone to contamination and adsorption effects. A recent research
compares two direct reading instruments to NIOSH Method 2016 and found that one of the
instrument significantly underestimated formaldehyde concentration as compare to the
laboratory method whereas the other instrument produced results that are not statistically
significantly different9.
2.4.2
Emission testing standards
Apart from indoor and ambient air concentrations, formaldehyde emissions from
manufactured products are also regulated in countries in North America, Europe and Asia.Different standards are employed in various countries. In the US, the California Air
Resources Board (CARB) approved the use of ASTM E 1333 and ASTM D 6007 as the
standards for emission testing in large and small chambers respectively. A smaller chamber,
known as the Dynamic Micro Chamber (DMC), although not included in the standards, has
shown good comparability with large chambers for measuring formaldehyde emissions. In
Europe, EN 717-1 (large chamber method) and EN 717-2 (gas analysis method) are two
common standards used in emission testing 10 . Other methods includes the EN 120
(perforator method), EN 717-3 (flask method) and JIS A 1460 (desiccator method).
A highly portable and widely tested device, called the field and laboratory emission cell
(FLEC), has been in use since 1991 to carry out emission testing and quality assurance on
location. The major advantages are its portability and that the test procedure is nondestructive
9Hirst, D.V.L; Gressel, M.G.; Flanders, W.D., Short-Term Monitoring of Formaldehyde: Comparison of Two
Direct-Reading Instruments to a Laboratory-Based Method, Journal of Occupational and Environmental
Hygiene, Vol. 8, pg 357-36310Bhm, M.; Salem, M.Z.M; Srba, J., Formaldehyde emission monitoring from a variety of solid wood,
plywood, blockboard and flooring products manufactured for building and furnishing materials, Journal of
Hazardous Materials, 2012, pg 68-79
7/26/2019 Literature Review of Monitoring Methods for Formaldehyde
19/26
19 of 26
in nature11. The design and properties of this type of emission cell is covered by the ISO
16000-10 standard.
Figure 7, 8 and 9 illustrates the various test methods
Figure 7: European chamber method EN 717-1
Figure 8: Other emission testing methods
11
Salthammer, T.; Mentese, S.; Marutzky, R., Formaldehyde in the Indoor Environment, Chemical Reviews,2010, Vol. 110, pg 2536-2572
7/26/2019 Literature Review of Monitoring Methods for Formaldehyde
20/26
20 of 26
Figure 9: Field and laboratory emission cell (FLEC)
7/26/2019 Literature Review of Monitoring Methods for Formaldehyde
21/26
21 of 26
2.5
Novel Methods
Since 2012, the WHO International Agency for Research on Cancer (IARC) has expanded its
classification of formaldehyde as a known carcinogen (Group 1), with positive links to
nasopharyngeal cancer, leukaemia, as well as sinonasal cancer12. As such, with the hazards
of formaldehyde attracting increasing attention, the need for a reliable yet cost effective
method for measuring accurately formaldehyde levels in the environment is apparent.
As discussed in the previous chapters, while NIOSH approved methods are the gold standard
for sampling and analyzing formaldehyde concentration in ambient air for compliance
monitoring, these are primarily chromatography based methods which are ex-situ, requiring
analysis in a lab following collection in the field. These methods are hence not suited for
rapid, real time monitoring of formaldehyde concentration in the environment.
As such, some research have explored novel methods of on-site quantification of
formaldehyde in air, which does not use the traditional methods of liquid or gas
chromatography, but instead uses other methods which fulfil the requirements of being both
simple and portable, as well as being sufficiently specific and sensitive enough for large scale
deployment for environment monitoring in-situ.
While these requirements are partly fulfilled by some currently available direct measurement
methods which uses electrochemical gas sensors and colorimetric detection tabs 13, these
direct measurements methods suffer from several limitations, which affects the accuracies of
the reading. Hence although portable, and able to give fast access to results on the field in
real time, the equipment are not cost-effective, and in some cases of insufficient sensitivityand selectivity to provide reliable measurements.
Thus, one of the new novel method which stands out is biosensors, specifically an enzyme
based detection method, which can give provide readings in-situ, with greater selectivity and
reliability than current commercially available direct measurement methods.
2.5.1
Biosensors
Biosensor is a general term that describe devices which can be used to detect a specific
substances, using a combination of biological components and physiochemical detector. Thebiological component of a biosensor, such as enzymes or cell receptors, are usually highly
specific, reacting or binding only with the specific desired substance. The reaction between
the biological component and the target substance then generate specific physiochemical
signals, such as color or florescence, which can then be detect and quantified by the
physiochemical detector.
12International Agency for Research on Cancer (IARC), Formaldehyde, IARC Monographs on the Evaluation
of Carcinogenic Risks to Humans, 2012, vol. 100F13Hirst, D. V., Gressel, M. G., & Flanders, W. D. (2011). Short-Term Monitoring of Formaldehyde:
Comparison of Two Direct-Reading Instruments to a Laboratory-Based Method.Journal of occupational and
environmental hygiene, 8(6), 357-363.
7/26/2019 Literature Review of Monitoring Methods for Formaldehyde
22/26
22 of 26
The novel methods of formaldehyde measurement in the environment using biosensors hence
could potentially provides several advantages over both the approved NIOSH methods and
commercially available direct measurement methods, These advantages are:
On-situ measurements and reading
High specificity of detection
Cost effective
Two of such novel formaldehyde detection methods using biosensors will be further
discussed below. These two methods make use of DNAzymes and formaldehyde
dehydrogenase respectively, with both having their own which uses and advantages.
2.5.2
DNAzymes
DNAzymes, or catalytic DNA are a kind of artificial enzymes which are capable of specific
catalytic activities. They are widely used for a variety of biochemical reaction, such as DNAglycosidic bond cleavage and DNA self-modification. They have also been used as the
biological component of biosensors, being used to detect nucleic acid, proteins and metal ions.
As such, research has been made to apply the use of DNAzymes into the detection of
formaldehyde, to develop a low cost, sensitive and selective biosensor.
In a research paper by Yang and et al14, they discussed the procedure used for optimizing the
colorimetric property of 2,2-azino-bis(3-ethylben-zothiazoline-6-sulfonic acid)(ABTS) for
the detection of formaldehyde.
ABTS+ is a blue-green-colored free-radical cation, and the reaction of ABTS with H2O2 toform ABTS+ is catalyzed by the hermin-G-quadruples complex (DNAzymes). Formaldehyde
participates in a competing reduction-oxidation reaction with H2O2, which thus prevents the
formation of the ABTS+. As such, the concentration of formaldehyde present can be deduced,
through the indirect measurement of ABTS+ using a colorimetric assay.
One possible advantage of this method of formaldehyde analysis is the selectivity of the
process compared to available direct reading instruments, as various other possible
contaminants tested, such as various alcohols (known interferent for the htV formaldehyde
meter) do not have any significant effect on the measured results.
Through the use of a smartphone application and a portable set up consisting of a dark room
with a LED light, the colorimetric assay can be performed in the field, for rapid assessment of
the results:
14Yang, X., Wang, Y., Liu, W., Zhang, Y., Zheng, F., Wang, S., & Wang, J. (2016). A portable system for on-
site quantification of formaldehyde in air based on G-quadruplex halves coupled with A smartphone reader.Biosensors and Bioelectronics, 75, 48-54.
7/26/2019 Literature Review of Monitoring Methods for Formaldehyde
23/26
23 of 26
Figure 9: Schematic of the portable smartphone-based optical reader
This detector setup was found to be able to detect formaldehyde in a linear range of 0.02 to
14 ppm, and is thus suitable for practical usage, based on the maximum threshold level of 0.1
ppm recommended by NEA.
2.5.3
Formaldehyde dehydrogenase
Similarly, in another research paper by Kudo and et al15, the use of another novel biosensor
for formaldehyde monitoring was demonstrated. Their technique is also enzyme-based,
similar to the previous one discussed, but for this the fluorescence property of nicotinamide
adenine dinucleotide (NADH) was used as an indirect measurement of formaldehyde
concentration.
Formaldehyde dehydrogenase (FALDH), an enzyme which catalyzes the chemical reaction
between formaldehyde and NAD+ (oxidized form) to formate and NADH (reduced form),
was prepared and immobilized on a membrane, which act as the biological component of the
biosensor. Hence, the amount of NADH measured on the membrane after exposure can be
correlated with the amount of formaldehyde originally present.
The membrane was mounted in a flow cell set up, together with a custom fiber-optic NADH
measurement system which can measure the fluorescent intensity of the membrane, to createa formaldehyde-sensitive optode.
By connecting the optode to a pump system for circulation of a phosphate buffer solution
containing NAD+, the membrane can be rinsed, enabling continuous monitoring of
formaldehyde levels, as compared to the previous biosensor setup:
15Kudo, H., Suzuki, Y., Gessei, T., Takahashi, D., Arakawa, T., & Mitsubayashi, K. (2010). Biochemical gas
sensor (bio-sniffer) for ultrahigh-sensitive gaseous formaldehyde monitoring.Biosensors and Bioelectronics,26(2), 854-858.
7/26/2019 Literature Review of Monitoring Methods for Formaldehyde
24/26
24 of 26
Figure 10: Structure of flow-cell and formaldehyde-sensitive optode
The setup was found to be highly sensitive and selective in comparison to conventional
formaldehyde gas sensor. The selectivity was to be expected, due to the specificity of the
FALDH enzyme reaction, and the optode was able to monitor formaldehyde levels
continuously at very low concentrations from 2.5 ppb to 10 ppm.
7/26/2019 Literature Review of Monitoring Methods for Formaldehyde
25/26
25 of 26
3.0 Conclusion
Formaldehyde can be an invisible killer, if not for regulations put in place to limit its
concentration at the workplace. Standardized methods provide a way for enforcing the
regulation at the workplace where formaldehyde is used. However, it can still creep into ourlives unsuspectingly through the use of shoddy building material emitting high concentration
of the chemical. Direct reading instruments utilizing the novel technologies provide a quick
and reliable measurement of airborne formaldehyde concentration. They should be widely
used to provide assurances for indoor air quality in high risk locations such as newly
constructed homes, newly opened underground retail spaces, etc.
The usage of either the direct-reading instruments or the standardized laboratory methods
depend on the objective of the experiment, the condition of the sample, the equipment
available and the requirements of the regulations. All the limitations and the advantages of
the method must be considered before choosing it.
At the cutting edge, there are several novel methods of formaldehyde detection which are
being researched and tested in the lab. These methods use differing principles and concepts,
which have several advantages over the convention and traditional methods, particularly in
for on-site monitoring in the field, and could be of great utility and benefit if realized in the
future.
This literature review exercise has given the group members a more thorough understanding
about the hazards of formaldehyde and the methods of monitoring exposure to this chemical.
7/26/2019 Literature Review of Monitoring Methods for Formaldehyde
26/26
4.0 References
[1] Formaldehyde, World health Organization, 2002
[2] IAQ, Indoor Air quality website url: http://www.iaqsg.com/chemical-
parameters/formaldehyde , accessed on 04/04/2016[3]
NIOSH, NOISH Manual of Analytical Methods, Fourth Ed., 1994
[4] NEA, National Environment Agency website, url:www.nea.gov.sg,date retrieved:
29th March 2016
[5]
Kennedy, E. R. (1994). FORMALDEHYDE: METHOD 3500, Issue 2. NIOSH
Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94. Retrieved April 12,
2016, fromhttp://www.cdc.gov/niosh/docs/2003-154/pdfs/3500.pdf
[6] Kennedy, E. R., Fischbach, T. J., Song, R., Eller, P. M., & Shulman, S. A. (1996).
Summary of the NIOSH Guidelines for Air Sampling and Analytical Method
Development and Evaluation. Analyst, 121. Retrieved April 4, 2016, from
http://www.ncbi.nlm.nih.gov/pubmed/8831274[7] Khanzadeh, F. A., & Park, C. K. (1997). Field Precision of Formaldehyde Sampling
and Analysis Using NIOSH Method 3500.American Industrial Hygiene Association
Journal, 58(9), 657-660. doi:10.1080/15428119791012450
[8] OSHA, Method 1007: Formaldehyde (Diffusive Samplers), T-1007-FV-01-0505-M,
May 2005
[9]
Hirst, D.V.L; Gressel, M.G.; Flanders, W.D., Short-Term Monitoring of
Formaldehyde: Comparison of Two Direct-Reading Instruments to a Laboratory-
Based Method, Journal of Occupational and Environmental Hygiene, Vol. 8, pg 357-
363
[10]
Bhm, M.; Salem, M.Z.M; Srba, J., Formaldehyde emission monitoring from avariety of solid wood, plywood, blockboard and flooring products manufactured for
building and furnishing materials, Journal of Hazardous Materials, 2012, pg 68-79
[11] Salthammer, T.; Mentese, S.; Marutzky, R., Formaldehyde in the Indoor
Environment, Chemical Reviews, 2010, Vol. 110, pg 2536-2572
[12] International Agency for Research on Cancer (IARC), Formaldehyde, IARC
Monographs on the Evaluation of Carcinogenic Risks to Humans, 2012, vol. 100F
[13]
Hirst, D. V., Gressel, M. G., & Flanders, W. D. (2011). Short-Term Monitoring of
Formaldehyde: Comparison of Two Direct-Reading Instruments to a Laboratory-
Based Method.Journal of occupational and environmental hygiene, 8(6), 357-363.
[14]
Yang, X., Wang, Y., Liu, W., Zhang, Y., Zheng, F., Wang, S., & Wang, J. (2016). Aportable system for on-site quantification of formaldehyde in air based on G-
quadruplex halves coupled with A smartphone reader.Biosensors and Bioelectronics,
75, 48-54.
[15] Kudo, H., Suzuki, Y., Gessei, T., Takahashi, D., Arakawa, T., & Mitsubayashi, K.
(2010). Biochemical gas sensor (bio-sniffer) for ultrahigh-sensitive gaseous
formaldehyde monitoring.Biosensors and Bioelectronics, 26(2), 854-858.
http://www.nea.gov.sg/http://www.nea.gov.sg/http://www.nea.gov.sg/http://www.cdc.gov/niosh/docs/2003-154/pdfs/3500.pdfhttp://www.cdc.gov/niosh/docs/2003-154/pdfs/3500.pdfhttp://www.cdc.gov/niosh/docs/2003-154/pdfs/3500.pdfhttp://www.ncbi.nlm.nih.gov/pubmed/8831274http://www.ncbi.nlm.nih.gov/pubmed/8831274http://www.ncbi.nlm.nih.gov/pubmed/8831274http://www.cdc.gov/niosh/docs/2003-154/pdfs/3500.pdfhttp://www.nea.gov.sg/Recommended