Literature Review of Monitoring Methods for Formaldehyde

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NATIONAL UNIVERSITY OF SINGAPORE

SH5110 Chemical Hazard Evaluation

Literature Review ofMonitoring Methods for

Formaldehyde


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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.


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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


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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=English


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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


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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


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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/


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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.pdf


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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/8831274


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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.


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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


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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


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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.


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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.


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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


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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.


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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


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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


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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


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Figure 9: Field and laboratory emission cell (FLEC)


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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.


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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.


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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.


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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.


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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.


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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/

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Literature Review of Monitoring Methods for Formaldehyde