assessment of airborne fine particulate matter and particle size distribution in settled chalk...

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DOI: 10.1177/1420326X11419691 published online 9 September 2011Indoor and Built Environment

Deepanjan Majumdar, D.G. Gajghate, Pradeep Pipalatkar and C.V. Chalapati Raoduring Writing and Dusting Exercises in a Classroom

Assessment of Airborne Fine Particulate Matter and Particle Size Distribution in Settled Chalk Dust

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Original Paper

Indoor and BuiltuiltEnvironment Indoor Built Environ 2011;000;000:111 Accepted: July 15, 2011

Assessment of Airborne FineParticulate Matter andParticle Size Distribution inSettled Chalk Dust duringWriting and DustingExercises in a Classroom

Deepanjan Majumdar D.G. Gajghate Pradeep Pipalatkar

C.V. Chalapati Rao

Air Pollution Control Division, National Environmental Engineering Research Institute, Nehru Marg,

Nagpur-440020, India

Key Words

Air pollution E Health E India E Indoor E Students

AbstractAirborne PM1, PM2.5, PM5 and PM10 generated during

writing with three types of chalk sticks on a board and

particle size distribution of chalk dust fall during writing

and dusting of board were studied by portable aerosol

spectrometer and particle size analyzer. Local Gypsum

chalk led to the highest increase in airborne particulate

matter while Clean-Write the least during writing.

About 10% of particles in chalk dust fall during writing

were finest from: Clean Write (0.5 mm) followed byAbroad Quality (0.67 mm) and Local Gypsum(1.15 mm), while 50% was finest in abroad quality(5.12 mm) followed by Clean Write (6.36 mm) and LocalGypsum (77.65 mm). In dusting samples, 10%, 50% and90% of particles were finest in Clean Write followed by

Abroad Quality and Local Gypsum chalks. Clean

Write chalk produced least total amount of PM1, PM2.4and PM5 and PM10 per unit time in dust fall during

writing. Although short-term exposure to airborne fine

chalk particles may be low in classrooms, several years

of exposure may be a matter of concern. Purpose of this

work was to provide data that would lead to measures

for minimization of health risk due to chalk dusts in

classrooms.

Introduction

Classroom teaching with boards and chalks is one of

the most customary methods of teaching in schools in

many parts of the world. Writing with chalks and

subsequent dusting of boards may generate appreciable

dust of chalk in classrooms and the amount of chalk dust

generation may vary depending on the type of chalks,

types of board and dusting type, e.g. dry or wet or with

vacuum dusters. Chalk dust fall and particulates in

The Author(s), 2011. Reprints and permissions:http://www.sagepub.co.uk/journalsPermissions.navDOI: 10.1177/1420326X11419691Accessible online at http://ibe.sagepub.com

Deepanjan Majumdar,Air Pollution Control Division, National Environmental Engineering ResearchInstitute, Nehru Marg, Nagpur-440020, India, Tel. 91-712-2249895, Fax 91-712-2249895,E-Mail [email protected]


classrooms had been previously measured and reported

[1,2], but real-time airborne chalk dust concentration

during writing has not been measured in classrooms except

in a study where all classroom dust inclusive of chalk

particles were monitored [3]. Few other studies have

monitored particulate matter concentration in classrooms

and resultant human exposure in different countries [46].

Whether chalk dust could pose significant health risks or

not is still inconclusive due to want of medical evidence

but is surely a nuisance in classrooms, especially for those

having dust allergy. Chalk dust is recognized as one of the

irritants that could trigger asthma attacks, the others being

smoke and pesticides [7,8]. Other asthma triggers include

allergens (e.g. pollen, mould, animal dander) and strong

odour apart from infections, physical over-exertion and

emotional factors [7,8]. During teaching, entry of chalk

dust in the respiratory system through nasopharyngeal

region and mouth could be extensive in teachers due to

their proximity to the board and frequent opening of

mouth during lectures and occasional gasping and heavier

breathing due to exhaustion. As per current state of

knowledge on particulate matter vis a vis chalk dust, they

may remain suspended in air for sometime before settling

on the floor and body parts of the teachers and pupils. In

several parts of the world, teaching is nowadays conducted

via overhead projectors or marker boards in classrooms,

but usage of chalk and boards is still common and widely

used in many countries including India. Though monitor-

ing or quantifying classroom chalk dust generation has

been rarely carried out, controlling chalk dust in class-

rooms have attracted researchers attention since the

beginning of this century in many countries and several

devices have been attempted and developed for minimiza-

tion of airborne dust generation from chalks and also from

erasing the board. These patented devices encompassed

efficient chalk board erasers with some of them having

chalk collection devices [913], special vacuum cleaners for

chalk boards [14,15], writing boards [16] and receptacles

for cleaning of board dusters after usage [17]. In spite of

these developments, such types of devices have seldom

found any user in Indian classrooms.

It is pertinent to take a look at the reported effects of

particulate matter on human health, especially on chil-

dren, who spend substantial time in classrooms. Research

results indicate to the active role particulate matter could

play in asthma with effects like decreased lung function

and increased hospital visits [1820]. Interestingly, studies

also have suggested that coarse fraction in PM may be

more strongly associated with asthma [21,22]. Children are

one of the most sensitive population subgroups to

particulate pollution since they may receive an increased

dose of PM to their lungs compared to adults, due to

higher fractional deposition with each breath and/or larger

minute ventilation relative to lung size [23]. Particulate air

pollution has been found to be associated with increased

respiratory symptoms, school absences and medication for

asthmatic children [24]. A long-term study in Southern

California reported growth deficit of childrens lung

function associated with higher ambient PM concentra-

tions [25]. Considering that a child spends most of his/her

time indoors, in which school timings occupy at least one

third, study of the indoor PM concentration levels assumes

a lot of significance as pointed out by researchers [26,27].

Interestingly, few studies have indicated that PM concen-

trations inside classrooms were higher than the corre-

sponding outdoor concentrations and concentrations

inside residences, indicating the importance of school-

microenvironment in childrens particulate exposure [28

30]. But unfortunately, very few studies showed the

magnitude and contribution of chalk dust on total

particulates in classrooms.

In spite of well-known nuisance associated with chalk

dust in classrooms for over a century, as indicated by

research efforts in developing better dusters and writing

boards for chalks in classrooms, very little work has been

done on quantification of airborne chalk particles in

classrooms. This study was undertaken to examine the

particulate generating potential of three different chalks,

viz. a low dust producing chalk named Clean-Write

chalk; a local variety of chalk produced in India and

another variety of chalk used in a foreign country outside

India. The tested null hypothesis was that there was no

increase in airborne chalk dust during writing. The study

was undertaken with the objectives of (i) monitoring of

changes in concentrations of airborne particulate matter

during proxy writing exercises and (ii) determination of

particulate size distribution in chalk dust fall occurred

during proxy classroom writing by the selected chalks and

dusting thereof from the board. So, the study looked into

the real-time particulate generation before, during and

after the writing exercises with the selected chalks and also

the particulate size distribution in the chalk dust fall

during writing on the board and dusting of the board after

writing to understand and comparatively evaluate the

particulate generating potential of the chalks and

the particle size distribution in the chalk dust fall samples.

The purpose of this study was to provide researched data

to contribute to the evaluation of possible risks associated

with chalk dust, which could lead to possible streamlining

2 Indoor Built Environ 2011;000:111 Majumdar et al.


of measures to minimize chalk dust generation and

exposure in classrooms.

Materials and Methods

Experimental Classroom

The experiment was performed in a classroom of a local

school that uses black boards made of cement. The

classroom chosen for the study was of (7.6 4.25 3) m3in dimension with two series of five windows (1.2 0.9)m2each located at opposite sides of the classroom. All the

windows and the only door were closed air tight during the

experiment and no natural draught were allowed inside.

The fans present in the classroom were not operated

during the experiment. Also, personal movement in the

classroom was completely restricted during the experiment

to minimise resuspension of dust from floor.

Chalk Types

All the chalks used for the study were small white sticks

with slightly variable shapes and sizes. The Clean Write

chalk had a length ranging from 5.5 to 6.0 cm, diameter

ranging from 10 to 10.5mm, weight ranging from 7 to 8 g

and a density of 1.52 g cm3. The base material for thechalk is calcium carbonate. The local Variety chalk had

gypsum as the base material and had the following

specifications: 6.46.6 cm length, 0.810 mm diameter

and 3.513.61 g weight while the Abroad Quality chalk

was of length 7.67.8 mm, 910 mm diameter and 11.51

11.62 g weight. While the local variety of chalk had a

rough surface and was soft, which yielded particles on

rubbing by hand, the other two chalk types had much

smoother surface, were hard and yielded very little dust on

rubbing by hand.

Writing Exercise

The writing exercise was started after thoroughly wet

cleaning the classroom floor and the board surface each

day, to negate the chances of residual chalk dust

contaminating the next samples to be collected. Each

writing session was continuously performed for 15min and

a select paragraph was always written to restrict the

writing time within 15min and to allow approximately the

same amount of writing. The writing was performed by a

single person to minimize personal bias as an experimental

error. Dusting of the standard written paragraph was

performed by clean dusters by the same person to negate

personal bias. Every writing and dusting experiment were

repeated three times under similar conditions.

Sampling and Analysis of Chalk Dust

The following types of measurements were made during

the entire study: (i) monitoring of real-time airborne dust

concentration (mgm3) in the classroom, starting fromalmost half an hour before writing, during writing and up

to more than half an hour after writing, until roughly

about the background or lower airborne particulate

concentration was reported by the spectrometer; (ii)

collection of chalk dust fall at the base of board generated

during writing of the sample paragraph; (iii) chalk dust fall

at the base of the board during dusting of the standard

paragraph; (iv) weighing of chalks before and after writing

to estimate their weight loss per unit time during writing.

Chalk dust fall was intercepted and collected during the

writing exercise by placing long and continuous paper

sheets (50 cm150 cm) at the base of the writing board.Three types of selected chalks, as described before, were

used to write on the board. So, three individual chalk dust

samples were generated from the three chalks and taking

three writing exercise replications, a total of nine samples

of chalk dust were collected during writing. Particulates in

chalk dust fall samples were analyzed for determining

volumetric particle size distribution by a particle size

analyzer (Model- CILAS 1180), which generated cumula-

tive volumetric particle size distribution (%) in various

particle size ranges within 0.042500 micron (mm) sizerange. From this database, proportions of particles falling

under various size groups were estimated. Further, the

particle size analyzer also estimated mean diameter of the

dust samples apart from reporting the diameter of particles

falling within 10%, 50% and 90% volume of dust.

Similarly, nine dusting samples were also collected after

dusting with clean and standard dusters. Further, all the

nine writing exercises, each of 15min duration, their pre-

writing period of approximately half an hour and post-

writing periods of almost the same duration were also

monitored for estimating real-time airborne particulate

concentration (PM1, PM2.5, PM5 and PM10), making it 27

number of samples. Real-time airborne dust concentration

(mgm3) analysis was carried out by a portable aerosolspectrometer (Model- GRIMM 1.109).

Uncertainty and Assumptions

The real-time airborne chalk dust concentration meas-

ured by the aerosol spectrometer also included the

background real-time airborne dust concentration in the

classroom, the extent of which was indicated by the data

generated by the instrument before writing started. The

increase in airborne particulate concentration during

writing though was primarily due to chalk dust, assuming

Particulate Pollution from Chalks Indoor Built Environ 2011;000:111 3


that limited or no other dust was generated during this

time, since no other dust generating activity was allowed in

the closed classroom during the experiment. As the input

of outdoor dust was prohibited by closing the classroom

air tight before, during and after writing, it was assumed

that during writing or the collection of chalk dust fall on

the papers at the base of the board, there was negligible

input of outdoor airborne dust in the collected chalk dust

samples. Although there was a very thin gap at the bottom

of the only door present in the classroom that was kept

closed during monitoring and sample collection, the gap

was too insignificant to allow sufficient dust from outside

to corrupt the controlled experimental condition. Also, the

door opened into a veranda that was lined by fully covered

concrete railings, which minimized substantial wind move-

ment or turbulence. No movement was allowed in the

veranda and since the experiment was undertaken during

school holidays, the school was totally vacant except one

attendant. Moreover, the distance of the spectrometer

from the door was large enough and its height good

enough not to be affected significantly by negligible, if

any, entry of outdoor dust during the short experimental

period.

Results and Discussion

Airborne Chalk Dust during Writing

Real-time airborne dust concentration (mgm3) wasmonitored and averaged for a time period before writing,

during writing and after writing and reported in Table 1.

There was slight to moderate increase in airborne

particulate concentration in various size ranges on writing.

Increase in mass of airborne dust on writing was negligible

for PM1 and PM2.5, evidently as smaller particles would

have lesser mass and conversely the increase was more for

PM5 and PM10 (Figure 1). The data in the table and the

figure show that the average concentration of airborne

PM1, PM2.5, PM5 and PM10 during the sampling period

increased slightly during writing over background air-

borne dust concentration and decreased with time after

writing due to natural dispersion and deposition. The non-

alarming increase in real-time airborne dust may have

indicated that there may not be any serious exposure to

airborne chalk dust as regard to their mass within a short

time e.g. during writing, whereas the exposure may

increase on writing for a longer time. Under the conditions

maintained during the writing exercise, no movement was

there on the part of the writer to limit the input from other

dust sources like resuspension from floor or clothes to Table1.Averageairborneparticulate

matter

concentration(m

eanSD)before,duringandafter

writingexperiments(n3)

Chalk

PM

1(mgm3)

PM

2.5(mgm3)

PM

5(mgm3)

PM

10(mgm3)

Before

writing

During

writing

After

writing

Before

writing

During

writing

After

writing

Before

writing

During

writing

After

writing

Before

writing

During

writing

After

writing

LocalGypsum

12.93.53

13.424.64

12.724.13

33.123.62

33.973.48

33.123.36

117.2829.14

120.117.01

116.191.33

170.3441.58

181.3031.08

154.7620.48

AbroadQuality

12.957.51

13.538.64

12.797.32

22.218.6

22.939.55

22.217.97

60.2834.65

63.2135.49

53.7530.23

94.7946.44

101.7052.71

84.1347.16

Clean-Write

12.283.74

12.584.04

12.054.45

21.534.4

21.975.9

21.535.31

85.8538.22

87.2233.15

81.4132.94

112.9555.98

118.1456.93

99.8349.26



allow estimation of chalk dust generated by writing only to

the extent possible. As mentioned earlier, outdoor dust

entry was assumed to be negligible through the thin gap

below the only door of the classroom during writing

exercise. It was assumed here that during real-world

writing in classrooms, deposited chalk dust may get

resuspended in air from floor and clothes due to

movement of the teacher and a substantial increase in

airborne chalk dust concentration may be witnessed.

Further, outdoor dust may also have a substantial

contribution, especially under open door teaching in dry

and windy conditions, to increase the overall dust

concentration during writing. The present results depict

only the real-time chalk dust emission which is critical to

Fig. 1. Increase in airborne particulate concentration over background concentration during writing and its decline after completion ofwriting.

Table 2. Particle size distribution in chalk dust fall samples collected during writing and dusting (n 3)Chalk Volumetric % and

mean diameterDuring writing After dustingDiameter (mm) Diameter (mm)

Local Gypsum 10% 1.15 1.2750% 77.65 5.0390% 225.52 16.49100% 290.66 54.0

Mean diameter 92.91 9.30Abroad Quality 10% 0.67 0.63

50% 5.12 3.0790% 47.37 10.87100% 80.33 25.0

Mean diameter 15.86 4.53Clean-Write 10% 0.45 0.47

50% 6.36 2.5990% 27.92 8.67100% 50.5 28.66

Mean diameter 10.57 3.85



understand the contribution of chalk dust in airborne dust

load during classroom teaching. Government and organi-

zations in various countries have promulgated indoor

PM10 and PM2.5 standards for averaging periods of either 1

or 8 or 24 h. For respirable fraction, Ref. [31] specifies an 8-

hourly permissible exposure limit (PEL) of 5mgm3 (forall inert or nuisance dusts, whether mineral, inorganic, or

organic), Ref. [32] specifies an 8-hourly value of 1.5mgm3

for54mm particles, Ref. [33] specifies 0.1mgm3 (1 h) and0.04mgm3 (long-term) and Ref. [34] specifies 8 hourlyvalue of 3mgm3. For PM10, Federal Republic ofGermany and ACGIH specify 8-hourly values of 4 and

10mgm3, respectively. There is no Indian standardavailable for particulates in indoor air. The obtained

values of PM2.5 and PM10 were various orders of

magnitude less than the indoor PM standard values

mentioned above.

Particle Size Distribution in Chalk Dust Fall

Particle size distribution in chalk dust fall samples

during writing and dusting are presented in Table 2. It was

observed that 10% of particles in chalk dust fall during

writing was finest in Clean Write (0.5 mm) followed byAbroad Quality (0.67 mm) and Local Gypsum (1.15 mm),while 50% was finest in abroad quality (5.12 mm) followedby Clean Write (6.36 mm) and Local Gypsum(77.65mm). In case of after dusting chalk dust fall samples,10%, 50% and 90% of the dust samples were all finest,

respectively, in Clean Write chalk followed by Abroad

Quality and Local Gypsum. Mean diameter of particles

of Clean Write was smallest followed by Abroad

Quality and Local Gypsum. All these results indicated

that though Local Gypsum was more prone to wastage

and breakage on writing and led to more soiling of writers

hands; it produced lesser proportion of fine particles in

dust fall and so was potentially less damaging. It was also

observed that all the chalks produced finer particles on

dusting as compared to writing, barring one case with 10%

of Local Gypsum (Table 2). This can be explained by the

following hypothesis: small pores and cavities on board

can hold fine chalk particles on its surface during writing

and the abrasion with the duster may further disintegrate

fine chalk particles into finer ones, resulting in collection

of finer particulates in the dust fall. Dusting exercise may

throw the chalk particles in air, increasing the exposure.

The residual particles adhered to the duster from previous

dustings also may contribute to every next exposure in

real-life teaching, though in this experiment the duster was

thoroughly cleaned after each dusting, negating this effect.

This implies that exposure to finer dust may be more from

dusting than writing under real-life conditions.

Differential particle size distributions under various size

groups within 10 mm size range in collected chalk dust fallsamples after writing and dusting were plotted and its

moving average trend was drawn for comparison. It was

observed that in dust fall samples during writing, particle

size distribution of Clean Write and Abroad Quality

were comparable while that of the Local Gypsum was

much different (Figure 2), revealing an entirely different

particle size distribution characteristic in the Local

Gypsum within 10 mm size range. Whereas in CleanWrite and Abroad Quality dust samples, 63% and 70%

of the total particulate were within 10 mm size range, thisvalue for local chalk variety was only 22%. This indicated

that most of the particulates generated by Local Gypsum

on writing were beyond 10 mm size range. This implied thatfine particulates (PM10) were generated in more amounts

in Clean Write and Abroad Quality. These results were

in agreement with the earlier observation, that is, local

gypsum chalks appeared much rougher on surface than

the other two chalks, indicating predominating presence of

coarser particles. Further, the coherence of particles in the

local variety was poorer than the other two types as the

particles in local chalk soiled the hand more easily,

indicating a greater scope of chalk particle loss during

writing in the former. In case of chalk dust fall samples

collected after dusting, particle size distribution within

10 mm were slightly different for Clean Write andAbroad Quality as compared to their counterparts in

writing exercise although the appearances of peaks were

almost at identical places, that is, under similar particle

size groups (Figure 3). The similarity in distribution of all

the three dust fall samples from dusting of three different

chalks was probably due to the ability of the board to

retain similar sizes of particulates on itself from all the

three different kinds of chalks. During dusting also, clean

write and abroad quality chalks generated greater

proportion of particles within 10 mm size range, that is,92% and 88%, respectively, as compared to 70% by local

chalk. Best fit equation for all the obtained histograms was

found to be six degree polynomial (Figures 2 and 3).

Average mass of PM1, PM2.4, PM5 and PM10 generated

per unit time in chalk dust fall during writing was

estimated by multiplying their respective fractions (i.e.

PM1, PM2.4, PM5 and PM10) reported by the particle size

analyzer with the actual weight of chalk stick lost during

writing. Interestingly, taking into account this mass of

chalk lost per unit time, a different scenario emerged. The

abroad quality chalk had produced maximum amount of



'Clean-Write'

0

1

2

3

4

5

6

Vo

lum

etric

%

Abroad Quality

0

1

2

3

4

5

6

Volu

met

ric %

Local Gypsum

0

1

2

3

4

5

6

Particle Size (mm)

Vo

lum

etric

%

Fig. 2. Particle size distribution in dust fall collected during writing on board (solid line indicates the two-point moving average trend lineand dashed line indicates the best fit six degree polynomial).



'Clean-Write'

0

2

4

6

8

10

12

14

Vo

lum

etric

%

Abroad Quality

0

2

4

6

8

10

12

14

Vol

um

etric

%

Local Gypsum

0

2

4

6

8

10

12

14

Particle Size (mm)

Vo

lum

etric

%

Fig. 3. Particle size distribution in dust fall collected during dusting of board (solid line indicates the two-point moving average trend lineand dashed line indicates the best fit six degree polynomial).



PM1, PM2.4, PM5 and PM10 per hour, indicating that it

managed to produce maximum mass of fine particulates

amongst the tested chalks (Figure 4). Notably, this aspect

is integrally connected to the deposited dust which gets

airborne when disturbed. The Clean Write chalk was the

best in this respect amongst the three tested chalks as it

produced lowest (0.33, 0.58 and 0.86 g h1 of PM1, 2.4, 5)except for PM10. From durability perspective, clean write

chalk produced the best performance as it wasted least per

unit time amongst all (1.92 g h1 as compared to 5.12 and3.04 g h1 in Local Gypsum and Abroad Type). In aprevious study [2], it was observed that a dusting type

chalk produced more PM4.5 and PM11 than a non-dusting

type chalk on both rough and smooth boards. On the

other hand, writing on rough boards resulted into more

production of PM2.4 and PM11 as rough boards produced

more friction with chalks. Jai Devi et al. [3] reported that

chalk dust was the major source of particulates in the

lecture rooms of the Indian Institute of Technology

(Kanpur) campus.

Conclusions

Very little information is available on airborne chalk

dust, its role in indoor air pollution and effects on human

respiratory health. The present work would definitely add

some immensely valuable scientific information on fine

particulate generation by chalk sticks in classrooms and

may also help assume or hypothesize the possible

repercussions of the fine chalk particulate exposure on

human health. The study revealed that (i) writing with

chalks on boards generated low concentrations of airborne

fine particles in real time; (ii) abroad quality chalk

produced highest mass of PM1, PM2.4, PM5 and PM10 in

chalk dust fall per unit time while Clean Write chalk

produced the least; (iii) Local Gypsum chalk produced

less proportion of fine particles than others; (iv) all the

chalks produced finer particles from dusting as compared

to writing in dust fall, barring a single case; (v) During

dusting also, clean write and abroad quality chalks

generated greater proportion of PM10 in dust fall, that

is, 92% and 88%, respectively, as compared to 70% by

local chalk; (vi) it was noticed that visibility of writing

letters on blackboard by Clean Write chalk was poorer as

compared to the other two chalks and higher pressure was

required to write properly with legible letters.

Though real-time airborne chalk dust generation was

found to be low in this study and chalk dust contained

only calcium carbonate or calcium sulphate predomi-

nantly and did not contain toxic materials, chalk dust

could be harmful to allergic persons and may cause

lacrimation and breathing troubles in the long run and

certainly is a constant nuisance in classrooms as it may

soil clothes, body parts, audio visual aids and study

materials. The issue of allergy, lacrimation and breathing

problem is certainly critical, considering that classroom

teaching involves predominantly children and also in

0.450.52

0.33

0.84

1.03

0.58

1.0

1.48

0.86

1.09

2.14

1.22

0

0.5

1

1.5

2

2.5

3

Local Gypsum Abroad Quality Clean-Write

Chalk Type

Amou

nt G

ener

ated

(g h

-1 )

PM1 PM2.4 PM5 PM10

Fig. 4. Mass (average SD; n 3) of PM1, PM2.4, PM5 and PM10 generated per hour during writing on boards by selected chalks.



many cases teachers who might have crossed the middle

age, thus becoming more susceptible. Exposure to low

concentrations of fine particles for longer durations can be

a matter of concern for children. Use of marker pens and

white marker boards is sometimes advocated for writing

in classrooms, which reduce the generation of fine

particles and also minimize the risk of exposure to chalk

dust. Writing quality of chalks should be improved along

with making the chalks less dust generating. The authors

envisage further studies, preferably long-term, on chalk

dust generation in classrooms under various conditions

for confirmation of the obtained results and observations

along with generation of possible new results and

observations. In-depth studies are welcome on health

impacts of chalk dust on children and teachers.

Acknowledgments

The authors are thankful to Director, NEERI, for providingconstant guidance and encouragement during this study. Theauthors also thank Central Salt and marine Chemicals Research

Institute (CSMCRI) for providing the chalk samples forevaluation studies.

Funding

This research received no specific grant from any

funding agency in the public, commercial, or not-for-

profit sectors.

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