Le Blond JEM 2010

PAPER www.rsc.org/jem | Journal of Environmental Monitoring

Generation of crystalline silica from sugarcane burning

Jennifer S. Le Blond,*ab Claire J. Horwell,c Ben J. Williamsond and Clive Oppenheimera

Received 27th February 2010, Accepted 5th May 2010

First published as an Advance Article on the web 2nd June 2010

DOI: 10.1039/c0em00020e

Sugarcane leaves contain amorphous silica, which may crystallise to form crystalline silica polymorphs

(cristobalite or quartz), during commercial sugarcane harvesting where sugarcane plants are burned.

Respirable airborne particulate containing these phases may present an occupational health hazard.

Following from an earlier pilot study (J. S. Le Blond, B. J. Williamson, C. J. Horwell, A. K. Monro,

C. A. Kirk and C. Oppenheimer, Atmos. Environ., 2008, 42, 5558–5565) in which experimental burning

of sugarcane leaves yielded crystalline silica, here we report on actual conditions during sugarcane

burning on commercial estates, investigate the physico-chemical properties of the cultivated leaves

and ash products, and quantify the presence of crystalline silica. Commercially grown raw sugarcane

leaf was found to contain up to 1.8 wt% silica, mostly in the form of amorphous silica bodies (with

trace impurities e.g., Al, Na, Mg), with only a small amount of quartz. Thermal images taken during

several pre-harvest burns recorded temperatures up to 1056 �C, which is sufficient for metastable

cristobalite formation. No crystalline silica was detected in airborne particulate from pre-harvest

burning, collected using a cascade impactor. The sugarcane trash ash formed after pre-harvest burning

contained between 10 and 25 wt% SiO2, mostly in an amorphous form, but with up to 3.5 wt% quartz.

Both quartz and cristobalite were identified in the sugarcane bagasse ash (5–15 wt% and 1–3 wt%,

respectively) formed in the processing factory. Electron microprobe analysis showed trace impurities of

Mg, Al and Fe in the silica particles in the ash. The absence of crystalline silica in the airborne emissions

and lack of cristobalite in trash ash suggest that high temperatures during pre-harvest burning were not

sustained long enough for cristobalite to form, which is supported by the presence of low temperature

sylvite and calcite in the residual ash. The occurrence of quartz and cristobalite in bagasse ash is

significant as the ash is recycled onto the fields where erosion and/or mechanical disturbance could

break down the deposits and re-suspend respirable-sized particulate. Appropriate methods for

treatment and disposal of bagasse ash must, therefore, be employed and adequate protection given to

workers exposed to these dusts.

1. Introduction

The sugarcane industry is undergoing a period of consider-

able change and, as with other examples of economy-driven

aDepartment of Geography, University of Cambridge, Downing Site,Cambridge, CB2 3EN, UK. E-mail: [email protected]; Fax: +44(0)1223 333392; Tel: +44 (0)1223 339819bDepartment of Mineralogy, Natural History Museum, Cromwell Road,London, SW7 5BD, UKcInstitute of Hazard, Risk and Resilience, Department of Earth Sciences,Durham University, Science Labs, South Road, Durham, DH1 3LE, UKdCamborne School of Mines, College of Engineering, Mathematics andPhysical Sciences, University of Exeter, Penryn, Cornwall, TR10 9EZ, UK

Environmental impact

Our research has shown, for the first time that crystalline silica c

commercial sugarcane-growing estates. Crystalline silica is a know

near estates could be exposed to the combustion products if inadeq

biomass types frequently combusted either for fuel, such as Miscan

crystalline silica. The range of methods detailed in this paper, to ch

other ash and dust mixtures to identify potential sources of crystal

This journal is ª The Royal Society of Chemistry 2010

industrial change, modest consideration has been given to

the potential environmental effects and impacts on human

health. One particular concern is exposure to crystalline

silica (SiO2) which may form during sugarcane burning,1

a practice common on many sugarcane estates (Fig. 1). Two

varieties of crystalline silica—cristobalite and quartz—are

classed as human carcinogens2 and can cause the chronic

disease silicosis.3 If temperatures reached during sugarcane

burning are sufficiently high (i.e. �900 to 1000 �C), amor-

phous silica in sugarcane plants could be converted into

a crystalline variety and exposure to the resulting ash or

particulate matter (PM) may pose a respiratory health

hazard.

an be present in products formed from sugarcane burning at

n respiratory health hazard and people working on or residing

uate disposal procedures are employed. Ash formed from other

thus grass or rice husks, or during wildfires could also contain

aracterize and quantify silica, could also be used to investigate

line silica or other hazardous materials in the environment.

J. Environ. Monit., 2010, 12, 1459–1470 | 1459

Fig. 1 Simplified schematic of the sugar and bioethanol production

process from sugarcane. SCTA – sugarcane trash ash, SCBA – sugarcane

bagasse ash.

1.1. Silica in sugarcane

Broadly speaking, plants can be classified as either Si-accumu-

lators, or Si-non-accumulators.4 Sugarcane and other varieties of

Gramineae (grasses) are Si-accumulators and, in the most

extreme cases, such as the horsetail plant (Equisetum), the silica

content can be up to 25% of the total dry weight of the plant.5

Silicic acid is taken up from the soil by plant roots and precipi-

tated as distinct silica bodies called phytoliths,6 or within tissue

cells such as microhairs, prickle hairs1,7 and guard cells which

surround the stomata (e.g. ref. 8). They can occur as discrete

shapes (e.g. dumbbell) or as fused, elongated structures, and their

size typically varies between <1 and 30 mm in diameter, but can

occasionally occur up to 200 mm.9 Although some plants’ phy-

toliths are composed of calcium oxylate (cystoliths),10 the phy-

toliths in sugarcane are amorphous silica (SiO2$nH2O), with

trace amounts of crystalline quartz.1

1.2. Crystalline silica transition

The conversion of quartz to cristobalite occurs at temperatures

>1300 �C, but the conversion of amorphous silica to a crystalline

state may occur at temperatures #1000 �C.11,12 Feltl et al.13

heated samples of Porasil (amorphous silica) at various

temperatures and found that partial crystallisation of amorphous

silica occurs at 900 �C, whereas complete crystallisation (to

alpha-cristobalite) was observed at 1010 �C. Cristobalite can

form as a metastable phase at lower temperatures when impu-

rities (e.g. Na, K, Al) are present in the structure.14 Similarly, the

temperature at which amorphous silica converts to a crystalline

state increases with increasing sample purity.15

A study of the thermal changes occurring during sugarcane

bagasse burning16 attributed the distinct peak in heat flow

observed (via differential scanning calorimetry) between 900 and

1000 �C, to the melting of amorphous phases or a phase change

in quartz. The crystallisation of amorphous silica to cristobalite

has also been recorded at 1000 �C in rice hulls17,18 and a mixture

of fly ash and burnt clay.19

1460 | J. Environ. Monit., 2010, 12, 1459–1470

1.3. Sugarcane burning

The sugarcane trash (surplus leaf matter) is removed from the

sugarcane stalks, by burning, before they are crushed to extract

sucrose (Fig. 1). During pre-harvest burning, a significant

amount of PM is released into the atmosphere and after the burn,

thick deposits of sugarcane trash ash (SCTA) are left in the field.

The air quality measured within sugarcane growing regions of

Sao Paulo state, Brazil, has been shown to deteriorate dramati-

cally during the burning season: ambient levels of PM can be

double those measured during non-burning periods.20

Bagasse, the fibrous remains left after the sucrose extraction,

can constitute between 20 and 30% of the harvested sugarcane,21

and is routinely combusted in the processing factory boilers to

supply energy (Fig. 1).

1.4. Possible health implications from sugarcane burning

Potential exposure to crystalline silica has been investigated (in

specific locations) during a number of agricultural activities, such

as potato and nut farming,22–25 but much of the exposure has

been attributed to soil re-suspension. Although, acute symptoms

such as cough, shortness of breath and aggravation of pre-

existing conditions (e.g. asthma) can occur after brief, high-

concentration exposure to crystalline silica, silicosis is associated

with chronic exposure.26 Exposure data are crucial in deter-

mining the dose, however, and it is recognised that the mineral-

ogical characteristics of crystalline silica may act to override the

dose-related health effects.27

Newman (1986)28 first speculated that biogenic silica fibres are

responsible for causing mesothelioma and lung cancer in some

sugarcane workers. In India, the incidence of lung cancer was

elevated in long-term sugarcane workers exposed to sugarcane

trash burning in the field29 and mesothelioma has been reported

in sugarcane workers in rural areas.30,31 Conversely, however, no

association was found between mesothelioma and exposure to

biogenic amorphous silica fibres in three subsequent community-

based case-control studies.32,33 Whilst crystalline silica is not

directly associated with mesothelioma, biogenic silica fibres

found in plants have structural similarities to asbestos minerals34

and were shown to promote mesothelial tumours in rats.35

More generally, exposure to the PM from pre-harvest burning

has been associated with a variety of acute and chronic diseases

of the respiratory system, such as asthma.36,37 There is little

detailed information, however, on the health impacts specifically

from sugarcane harvesting and, in particular, sugarcane

burning.38

The bagasse ash (SCBA) remaining after combustion can

represent up to �0.3% of the total weight of sugarcane pro-

cessed21 and is conventionally removed by flushing water

through the boiler. Traditionally, the SCBA is separated from

the water and retained on site and/or used as a fertiliser on

fields.39 People are, therefore, at risk of exposure to the ash as it is

broken down and re-suspended by wind or mechanical distur-

bance during removal, storage and re-distribution on fields.

Although there is increasing research into alternative uses, such

as the addition of SCBA to cement to improve its physical and

mechanical properties,40,41 potential health hazards from

frequent inhalation of SCBA PM have not been investigated.


This study investigates the properties of sugarcane combustion

products from operational sugarcane estates, to identify whether

silica, found naturally in the sugarcane plant, can convert to

a crystalline form during agricultural burning thereby posing

a potential health hazard to exposed workers. A key aim of this

work is to determine whether crystalline silica is found in either

the PM emission or residual ash from real-life sugarcane burning

situations, in a similar way to previously reported experimental

burning.1 Initially the silica in the raw sugarcane leaves and

bagasse was studied to determine chemical composition and

morphology in situ. Conditions during a number of pre-harvest

sugarcane burning events were monitored, to establish whether

temperatures during the fires were sufficient to convert plant

silica into crystalline silica. The presence of crystalline silica

phases within SCBA SCTA and smoke from pre-harvest burning

was investigated and quantified. Other crystalline phases within

the ash samples were also identified to elucidate more informa-

tion regarding the conditions during the burn. A preliminary

assessment of associated occupational exposure is reported

elsewhere.42

2. Field methodology

Samples of raw sugarcane leaves, bagasse, SCTA and SCBA and

auxiliary data were collected from two commercial sugarcane-

growing estates from different South American countries

(including Brazil; Table 1). The species of sugarcane grown at

each of the estates was the same (Saccharum officinarum),

although they differed in genetic variety. Five burning events

were sampled in country A and two in country B. The areas of

Table 1 Sample collection and treatment details

Sample type Sample name Collection details

Raw leaf Country(A/B)_leaf# In each of the 7 plots the third and swere taken from 20 randomly selebefore the burn.

Bagasse A_bag Taken from the processing factory pcombustion (in country A).

SCTA Country(A/B)_ash# Sampled from the top 4 cm of the ac(taking care not to disturb/includesoil), at 12 randomly chosen sites w7 plots, immediately after the pre-

SCBA A_ashbag# Collected directly from the water flubagasse-burning boilers (periodicato clear the residual ash). A_ashbaliquid portion of the water. A_ashin settlement ponds.

Table 2 Summary of sampling sites during pre-harvest burning and atmosp

Samplenumber (#)

Samplingsite Country

Areaburned/ha Date

Localtime of

1 183 A 17.09 26/09/08 12:022 083 A 12.22 30/09/08 14:093 051 A 14.87 01/10/08 14:334 052 A 12.30 02/10/08 13:055 053 A 10.70 03/10/08 14:096 107 B 9.49 10/05/07 18:107 157 B 11.36 15/05/07 18:25


plot burned varied from 12–17 ha. All samples were kept in dry

storage until analysis.

2.1. Burn conditions

The atmospheric conditions were recorded at each of the seven

burn sites studied, including ambient temperature and relative

humidity (Table 2). Duration of burn was also recorded.

Thermal images were acquired with a FLIR Systems� Ther-

maCAM P25 infrared camera to track combustion temperatures.

The instrument’s detector consists of a focal plane micro-

bolometer array composed of 320� 240 elements and is sensitive

in the 7.5–13 mm waveband. The camera was handheld and

operated at distances of a few metres from the burning sugar-

cane. The nominal instantaneous field of view of the detector is

1.3 mrad, corresponding to a ‘‘footprint’’ of order 5 mm pro-

jected to the targeted burning vegetation. At such short obser-

vation distances the transmittance of the atmosphere can be

neglected but the brightness temperatures were adjusted

assuming an emissivity of 0.96 in the instrumental waveband

based on a prior study of burning pine forest.43

2.2. Smoke collection

PM in the smoke was sampled during the pre-harvest burning

using a Sioutas cascade impactor with Isopore� polycarbonate

membranes (25 mm diameter, 0.4 mm pore size, Millipore), which

was attached to a Leland Legacy pump operating at a constant

flow rate of 9 L min�1. Under these conditions, the stages in the

impactor collect particles with the following aerodynamic cut-off

Post-collection treatment

ixth green leafcted plants

Washed thoroughly with deionised water, oven dried(60 �C for at least 24 h), cut into �1 mm sectionsand homogenised (within each plot).

rior to boiler Air dried and cut into �1 mm sections andhomogenised.

cumulated ashthe underlying

ithin each of theharvest burn.

Samples were homogenised (within each plot).

shed out fromlly flushed outg1: supernatantbag2: sediment

The ash–water mixture was desiccated in an oven (60�C for 7 days).

heric conditions

fire

Approximateduration offire/min

Average ambient airtemperature/�C Relative humidity (%)

43 26 84–8725 26 82–8453 26 82–8461 25 80–8342 27 82–8447 18 25–2762 17 26–27

J. Environ. Monit., 2010, 12, 1459–1470 | 1461

diameters, D50 (where at least 50% of the material will be less

than or equal to the cutoff size): <0.25, 0.25–0.5, 0.5–1.0, 1.0–2.5

and 2.5–10 mm. The workers were shadowed (closer than 1 m)

and the impactor inlet was kept roughly at head height, to

reproduce their exposure to PM produced during the burn.

3. Analytical methodology

All of the analyses were carried out at the Natural History

Museum (NHM), London, unless specified.

3.1. Total silica content

The raw sugarcane leaf (air-dried), bagasse and ash samples were

ground to powders in a Retsch Mill (using liquid nitrogen) at the

Department of Chemistry, University of Cambridge. The bulk

oxide composition of the raw leaves, bagasse, SCTA and SCBA

was determined by wet chemical analysis, using an improved

method of closed microwave digestion.44 Carbon, hydrogen and

nitrogen (ultimate analysis) in the samples were also quantified

using a Thermo Finnigan EA1112 CHN-analyser (with BBOT

from FISONS� Instruments: C, 72.53%; H, 6.09%; N, 6.51%, as

a calibration standard).

3.2. Silica in the sugarcane plant

Sections of the raw sugarcane leaf and bagasse samples were

mounted onto carbon sticky pads and coated with �25 nm of

carbon. Silica-rich bodies on the epidermal layer of the sugarcane

leaf were imaged in backscattered electron mode (BSE) under

high vacuum in a LEO 1455 VP Scanning Electron Microscope

(SEM). Elemental composition of features, such as the phytoliths

and prickle hairs on the leaf, was determined using an Oxford

Instruments INCA X-ray analysis system.

3.3. Crystalline composition

Crystalline components of the raw bagasse and ash samples were

identified using X-ray diffraction (XRD), and crystalline silica

phases were quantified in ash samples using an improved meth-

odology for mixed-dust samples.45 Raw leaf samples have

previously been investigated1 and were not therefore analysed by

XRD in this study. For phase identification, sections of filter

membrane (from airborne PM collections) were mounted flat

onto quartz substrates. The bagasse, SCTA and SCBA samples

were ground (grain size z5 to 20 mm) and a thin smear was

placed on a quartz substrate. For phase quantification, ash

Table 3 Wet chemical bulk oxide analysis (wt%) for the raw leaf and bagass

Sample Al2O3 CaO Fe2O3 K2O MgO MnO

A_leaf1 0.18 1.31 0.15 2.11 0.88 0.01A_leaf2 0.22 0.76 0.13 2.21 0.82 0.02A_leaf3 0.20 1.24 0.17 2.47 0.94 0.01A_leaf4 0.14 1.14 0.09 2.52 0.77 0.01A_leaf5 0.22 1.03 0.11 2.50 1.03 0.11B_leaf6 0.23 3.22 0.10 1.68 1.15 0.04B_leaf7 0.26 2.89 0.09 1.50 0.98 0.03A_bag 1.14 0.32 0.61 0.57 0.33 0.01

a bdl ¼ below detection limit.

1462 | J. Environ. Monit., 2010, 12, 1459–1470

samples were ground (as previously stated) and packed into the

deep well of a circular Al mount (for further details see ref. 45).

The samples were analysed on an Enraf-Nonius diffractometer

with a 120� 2q static position sensitive detector (PSD), using

CuKa1 radiation and tube operating conditions of 45 kV and

45 mA, with ZnO as the internal attenuation standard.

3.4. Individual particle analysis

For SEM studies, the SCTA and SCBA were scattered onto the

surface of carbon sticky tabs which were mounted onto 12 mm

diameter Al stubs. Small (�12 mm diameter) portions were cut

(with PTFE scissors) from the polycarbonate filters used to

collect PM from pre-harvest burns and mounted onto Al stubs

using silver dag solution. All stubs were coated with �25 nm of

carbon and analysed in the LEO 1455 VP SEM with EDS.

Samples of ash were also mounted on resin blocks, polished to

a flat surface and coated with �25 nm of carbon for electron

probe microanalysis (EPMA). Selected particles were analysed in

a Cameca SX100 at an accelerating voltage of 10 kV, a beam

current of 20 nA and a spot size of 1 mm. The instrument was

calibrated using a range of natural and synthetic standards:

FOR(std277) for Si and Mg, JAD3(std048) for Na,

COR4(std028) for Al, WOL4(std097) for Ca, MNT(stdIC) for

Ti, FAY(std278) for Fe and KBR3(std075) for K. For each ash

sample, five fields of view were imaged and approximately 8 to 12

particles in each field of view were analysed. The aim of the

EPMA studies was to acquire quantitative elemental data for

individual silica particles, in order to gain an insight into whether

particle purity affects conversion from amorphous silica into the

crystalline forms.

4. Results

4.1. Silica in the raw leaf and bagasse

SiO2 was the most abundant constituent detected in the raw leaf

samples, between 0.45 and 1.8 wt% SiO2 (as a total wt% of the

raw leaf sample, Table 3). The raw leaf samples collected from

country B (B_leaf6 and B_leaf7) contained almost one third of

the amount of silica compared to raw leaf samples from country

A (A_ leaf 1, A_ leaf2, A_ leaf3, A_ leaf4 and A_ leaf5). The raw

bagasse (A_bag) contained 0.7 wt% SiO2. Levels of C, H and N

were similar for all raw leaf samples. Carbon, however, was

slightly higher in the bagasse sample (52.3 wt%) than in the raw

leaf samples (average 46.2 wt%).

e samples, including ultimate (CHN) analysis results (excluding oxygen)a

Na2O P2O5 SiO2 TiO2 C H N

0.16 1.20 1.33 bdl 46.7 5.2 0.90.11 1.14 1.84 bdl 44.6 5.5 0.90.09 0.85 1.59 bdl 45.6 5.9 0.90.10 0.86 1.12 bdl 44.2 5.2 1.00.09 0.76 1.41 bdl 45.6 5.4 0.90.09 0.43 0.45 0.01 48.6 5.8 0.90.08 0.55 0.54 0.01 47.9 5.5 0.90.22 0.15 0.70 0.02 52.3 4.7 0.3


Fig. 2 SEM (backscatter, BSE) images of the adaxial surface of a raw

sugarcane leaf, with EDS analysis spots on a phytolith (Spectrum 1) and

a spine near the margin of the leaf (Spectrum 2).

Fig. 3 XRD pattern with the main crystalline peaks identified for raw

bagasse (A_bag).

Fig. 4 4 FLIR images of the burning sugarcane field, with temperature

scales, a) wide angle image and b) close up of burning leaves.

The BSE images of the sugarcane leaf surface showed distinct

differences in contrast according to chemical composition,

facilitating identification of silica bodies (Fig. 2) on both the

upper and lower surfaces of the leaf. Si and O were the main

elements identified by EDS spot analysis (spectra 1 and 2, Fig. 2)

within the bilobate phytoliths as well as margin hairs, prickle

hairs and bulliform cells. There were other trace elements,

including K (spectrum 2, Fig. 2), Al, Fe and Mg, but these were

rare compared with Si and O.

The XRD pattern for the raw bagasse sample suggests that it

was principally composed of amorphous material (shown as the

broad-angle hump), but quartz, calcite and feldspar were

identified as the predominant crystalline phases (Fig. 3),

although these were not present in sufficient amounts for

quantification.



Images taken with the infrared camera during pre-harvest

burning are shown in Fig. 4. Generally the temperatures recor-

ded (the brightest pixel in the image, n ¼ 174 images) ranged

from <200 to a maximum of 1056 �C, when 3 ¼ 0.96.43

4.3. Silica in the airborne PM

The amount of deposit was too small and the influence of the

polycarbonate substrate too great to ascertain any information

regarding the quantity and form of the crystalline phases within

the airborne PM by XRD. No further analysis of the cascade

impactor samples was carried out.

4.4. Silica in the pre-harvest burning ash

The SCTA from country A (A_ash1, A_ash2, A_ash3, A_ash4

and A_ash5) contains approximately double the amount of silica

(20.2–24.8 wt% SiO2) compared to the SCTA from country B

(B_ash6 and B_ash7; 10.4–10.8 wt% SiO2) (Table 4). The carbon

content is also noticeably different, and tends to be much higher

in the SCTA samples from country B (68.9–69.7 wt% SiO2),

when compared with country A (26.8–30.9 wt% SiO2).

The XRD patterns for country A SCTA samples (Fig. 5a) all

show a distinct hump at �20 to 21� 2q, which may be due to the

amorphous silica component, whereas the patterns from the

country B SCTA (Fig. 5b) appear to have a broader feature

(from a much lower angle 2q) indicative of amorphous carbon,

with a portion of amorphous silica. Quartz was identified in all of

the SCTA samples from country A, but no crystalline silica was

J. Environ. Monit., 2010, 12, 1459–1470 | 1463

Table 4 Wet chemical bulk oxide analysis (wt%) results for the SCTA and SCBA samples, including ultimate (CHN) analysis (excluding oxygen)a

Sample Al2O3 CaO Fe2O3 K2O MgO MnO Na2O P2O5 SiO2 TiO2 C H N

A_ash1 3.87 1.35 2.85 7.64 9.83 0.21 1.21 2.63 24.30 0.05 27.7 0.3 bdlA_ash2 5.59 1.47 3.29 8.24 8.58 0.23 1.06 1.70 20.20 0.07 26.8 0.3 bdlA_ash3 3.57 1.34 1.92 8.61 9.02 0.19 0.93 2.03 23.06 0.06 30.9 0.3 bdlA_ash4 4.42 1.58 2.34 7.81 9.20 0.21 1.11 3.00 22.85 0.07 29.2 0.3 bdlA_ash5 4.13 1.38 2.10 8.84 9.18 0.18 0.92 2.63 24.77 0.08 27.9 0.3 bdlB_ash6 1.68 3.04 8.43 4.88 11.05 2.00 0.34 5.96 10.38 1.12 68.9 2.5 bdlB_ash7 6.36 2.78 8.04 4.81 11.34 1.61 0.49 4.47 10.81 0.88 69.7 2.1 bdlA_ashbag1 10.04 9.46 7.42 11.21 7.26 0.30 4.51 4.21 39.23 0.45 10.8 bdl bdlA_ashbag2 9.40 10.21 7.54 8.69 7.50 0.26 5.68 3.51 40.05 0.52 2.8 bdl bdl

a bdl ¼ below detection limit.

Fig. 5 XRD patterns with the main crystalline peaks identified for a)

SCTA samples from country A, b) country B, and c) SCBA samples

(A_ashbag1 and 2).

Table 5 XRD analysis of the SCTA and SCBA. There is an approxi-mate 1–3 wt% error in the XRD of the calculations (Le Blond et al. 2009),n ¼ 6

Sample

Crystalline silicaidentified in XRDpatterns

XRD crystalline silicaquantification (wt%)

Quartz Cristobalite Quartz Cristobalite

A_ash1 3 — 0.2 —A_ash2 3 — 3.5 —A_ash3 3 — 2.3 —A_ash4 3 — 1.4 —A_ash5 3 — 3.3 —B_ash6 — — 0.4 —B_ash7 — — 0.6 —A_ashbag1 3 3 5.0 1.2A_ashbag2 3 3 15.0 3.0

recognized in the XRD patterns for country B. The other main

crystalline components in the XRD patterns were calcite

(CaCO3) and feldspar (Na/Ca/Al silicates) from country A

(Fig. 5a), whereas calcite, sylvite (KCl) and pyroxene (Ca/Mg/Fe

1464 | J. Environ. Monit., 2010, 12, 1459–1470

silicates) were identified in country B samples (Fig. 5b). The

quantitative XRD analyses confirmed that SCTA samples from

country A contained quartz (Table 5), even at relatively low

levels (0.2 to 3.5 wt%). SCTA ash samples from country B had

very little quartz,�0.5 wt% (average), which was not identified in

the initial XRD pattern. Cristobalite was not identified in any

SCTA samples.

On first observation, SCTA from country B (B_ash6 and

B_ash7) contained abundant woody structures and unburned

leaf material, while samples from country A were dominated by

black ash and entirely lacking material that resembled the orig-

inal sugarcane plant. SEM images of the SCTA (Fig. 6a and b),

however, show many features such as phytoliths, long silica cells

and stomata that are still intact in the SCTA samples from both

countries. The ash commonly had a fluffy and often fibrous

texture, and much of the material was aggregated together in

a fused mass. The individual particles were irregular in shape

with rough surfaces and many have a spongy appearance. SEM-

EDS analysis identified that carbon was the main component in

all SCTA samples, with occasional, irregular-shaped particles of

pure-phase silica and mixed-phase silicates, including fused

bodies (forming elongated lengths of silica; Fig. 6a), carbon

fibres and bundles (Fig. 6b), and individual crystals of calcite and

sylvite.

EPMA on sectioned blocks enabled imaging and analysis of

particle cross-sections, rather than mass aggregations as viewed

under the SEM. Chain-structures common in leaf epidermis were


Fig. 6 SEM (BSE) images of the ash samples; SCTA a) A_ash1 from country A (silica trilobite phytoliths circled, arrow points to elongated silica cells),

and b) B_ash7 from country B (silicaedged stomata circles, arrow points to carbonaceous fibre bundle), and SCBA samples c) A_ashbag2 (spherical

silicate and prismatic silica particles circled) and d) A_ashbag1 (two phytoliths bodies circled).

Fig. 7 Electron microprobe images (BSE) of a) SCTA sample A_ash3

(all probe spots were predominantly silica with trace amounts of Mg, Ca

and very low Fe. The exception was spot number 8, which had a very low

count level) and b) SCBA sample A_ashbag1 (all probe spots were also

predominantly silica, with the following trace elements; Fe, Na, Mg and

Mg. The exceptions were spots 6 that had a low count level, and 8 which

was an Al+Ca+Mg silicate).


seen in BSE images of SCTA (A_ash1; Fig. 7a). EPMA analysis

was selective and only lighter contrast, individual particles were

analysed to investigate whether the silica was pure phase or

contained impurities. Approximately half (�52%) of the

281 particles selected for EPMA were predominantly silica

(i.e. >96 wt% SiO2), with trace amounts of Ca, Al, Mg, Fe and

Na. These selected silica particles, averaged for each sample, are

shown in Table 6.

4.5. Silica in the bagasse ash

The SCBA samples (A_ashbag1 and A_ashbag2) contained

similar levels of silica (39.2–40.0 wt% SiO2; Table 4) and there

was a greater proportion of carbon in A_ashbag1 (10.8 wt%),

when compared with A_ashbag2 (2.8 wt%).

XRD analysis revealed quartz and cristobalite in both SCBA

samples, and quartz was particularly noticeable in A_ashbag2

(Fig. 5c). Other crystalline phases included anhydrite, calcite and

silicate minerals (feldspar and pyroxene). The crystalline silica

quantification showed that SCBA samples contained between 5

and 15 wt% quartz and 1.2 and 3.0 wt% cristobalite (Table 5).

Distinctive morphologies can be seen in A_ashbag2, including

spheres, prismatic particles, blocky and fibrous structures

(Fig. 6c). SCBA sample A_ashbag1 also contains relics of the

parent material, such as phytoliths, or components from the leaf

structure (Fig. 6d), as with the SCTA but with lower abundances.

SEM-EDS showed that the prismatic particles were predomi-

nantly Si- and O-bearing, blocky particles contained Al, Ca, K,

Mg and Na, as well as Si and O, and the spherical forms were

mostly silicates, containing Mg, Al and Fe. All fibrous particles

analysed were carbon-rich.

Although residual plant-like structures were present in the

SCBA, the majority of EPMA images show rounded, vesiculated

particles (Fig. 7b), which predominantly consisted of SiO2 with

J. Environ. Monit., 2010, 12, 1459–1470 | 1465

Table 6 EPMA results for the SCTA and SCBA samplesa

Sample No. of analyses

wt% mg g�1

Total SiO2 Na Mg Al Ca Ti Fe

A_ash1 28 99.9 99.4 bdl 496 134 1962 bdl bdlA_ash2 16 99.9 99.2 136 535 bdl 1445 bdl bdlA_ash3 17 99.9 99.5 487 bdl 757 bdl bdl 2056A_ash4 21 99.9 99.6 554 2160 bdl 2285 bdl bdlA_ash5 28 99.9 99.4 353 1321 bdl 1985 bdl bdlA_ashbag1 23 99.9 99.2 768 619 464 bdl 933.2 2315A_ashbag2 28 99.9 97.4 2286 157 9598 2206 bdl bdl

a bdl—below calculated detection limit.

trace Al, Na, Ca, Ti and Fe. The SCBA particles tended to have

higher levels of Na, Al, Ti and Fe compared to SCTA samples

(Table 6).

5. Discussion

5.1. Silica in the raw leaf and bagasse

The average amount of SiO2 in the whole, raw sugarcane leaves

was �1.5 and 0.5 wt% in countries A and B (respectively).

Previous studies quantified silica as a portion of the dried

material combusted (as part of the analysis), whereas we have

determined the silica by digesting the whole leaf without

combustion. Patel and Kumari46 determined that ashed (at 350–

400 �C) sugarcane leaf from an estate in India contained 7.0 wt%

SiO2, which indicates that either combustion acts to concentrate

the silica or that these Indian sugarcane leaves are much more

SiO2 rich. A previous study by the present authors showed that

the tips of sugarcane leaves cultivated in Kew Gardens, London

contained from �2.5 to 6.5 wt% SiO2,1 but the tips are known to

concentrate silica to a greater extent than the rest of the leaf. The

CHN total can be used to show that results here are comparable

with previous literature values. The CHN totals determined in

raw leaves in our investigation (an average of �46.2 wt%) are

consistent with the 45.4 wt% reported by Jorapur and Rajvan-

shi.47 The CHN totals for raw bagasse samples have been

reported as between 49.4 and 64.9 wt%,48–54 and are comparable

to the value obtained for raw bagasse in this study (52.3 wt%).

The general differences in chemical composition of sugarcane

amongst samples can be attributed to sugarcane variety, growth

conditions,55 fertilisers and climate and the inherent heteroge-

neity of composition resulting from sampling organic material

which consists of a mixture of fibrous bundles and structural

elements (such as parenchyma/epithelial cells and vessels).

Our SEM analyses revealed that some of the phytoliths and

other silica bodies in sugarcane leaves contained trace elements.

This is consistent with findings of Carnelli et al.56 who reported

small amounts of Al in the phytoliths of other Gramineae species.

Trace impurities within the silica bodies may provide a source of

ions that influence (potentially reduce) the temperature at which

the amorphous to crystalline silica phase transition occurs and

may also alter the toxicity of any emitted PM. Trace carbon has

also been identified in phytoliths by Parr and Sullivan57 at levels

of up to 5% of the total weight. Carbon was difficult to determine

1466 | J. Environ. Monit., 2010, 12, 1459–1470

in this investigation as the samples were carbon coated before

they were analysed in the SEM to reduce charging effects.

The XRD pattern of raw bagasse shows that it is largely

amorphous, containing only a low level of quartz. This compares

with other studies that have found that the phytoliths in other

Gramineae are mainly composed of amorphous silica.58 The raw

leaf was not analysed by XRD, but Le Blond et al.1 have previ-

ously identified both quartz and calcite in the XRD patterns of

raw sugarcane leaf samples. Sapei et al.59 speculated that the

quartz may originate from soil contamination, but the leaves

were thoroughly washed during the cited study, so it is unlikely

that the quartz is from soil adhering to the leaf. It is possible that

there is soil (including silicate) contamination in the bagasse

samples analysed in the present study as, although the sugarcane

stalks would have been washed (at the processing factory before

they are crushed to release the sucrose), soil would inevitably still

be present in the mixture and may be incorporated into the

bagasse. This may explain the presence of feldspar in the XRD

patterns for the bagasse, and might also indicate that there are

two sources of silica entering into the boiler: the (mainly)

amorphous silica in the plant and the crystalline silica associated

with particles of soil.


We found that the temperatures achieved during commercial

sugarcane burning are substantial (up to 1056 �C) and reach the

range required for conversion of amorphous silica in the sugar-

cane leaf to crystalline forms such as cristobalite. It is hard to

judge the duration of these high temperatures during pre-harvest

burns, as it seemed dependent on the antecedent and prevailing

meteorological conditions and vegetation conditions at the time

of the burn. It is possible that very high burn temperatures are

only ephemerally maintained on a particular stem or leaf limiting

generation of crystalline silica. The laboratory experiments of Le

Blond et al.,1 however, indicated that only 3 min are necessary for

cristobalite to be formed in the ash and smokes from burning

sugarcane leaves at 1100 �C. We note also that, for obvious

reasons, the temperatures were measured at the periphery of the

burned plots when it was feasible to make a close approach. The

fire intensity in the interior of the plots was surely greater.

Typically the burning of the 12–17 ha plots lasted around 20 min.

There are limited examples in the literature of the temperatures

obtained in other types of biomass burning. Typically, the peak


temperatures are �500 to 700 �C during smouldering and much

higher for the flaming phase at �1500 �C.60 Maximum temper-

atures recorded during savannah fires have been measured as

800–1200 �C, during the flaming phase.61 Infrared and thermo-

couple monitoring of burns of piles of hazel logs have recorded

maximum temperatures of 643 �C, and up to 750 �C with added

wind.62 Although the temperature of combustion in the boilers

was not measured during this study (due to health and safety

restrictions), operating temperatures have been stated to range

from 700–900 �C in sugar-producing factories in Rio de Janiero,

Brazil.63

An indirect way to assess the maximum temperatures reached

during the burn in the ash itself is to determine the presence of

certain temperature-sensitive phases. For example, crystalline

KCl (sylvite) has been identified in some biomass boiler deposits

where rice and wheat straws have been combusted at 525 �C,64

and when woody and herbaceous biomass samples were fired at

500 �C.65 Other biomass combustion experiments have revealed

the breakdown of sylvite and the release of Cl at approximately

700–800 �C, which also plays a role in the rate of K-release,16 and

sylvite was found to disappear from wheat straw completely at

1000 �C.64 Thy et al.64 also suggested that the release of K may be

due to dehydration, re-crystallisation and partial melting of

amorphous silica. Calcite (CaCO3) is also known to begin to

break down at around 500 �C, and disappears if combustion

temperatures exceed 1100 �C.64 The presence of sylvite and

calcite in the ash samples in this study indicates that temperatures

did not regularly exceed �1000 �C and therefore may not have

been sufficient for the large-scale formation of cristobalite.

5.3. Silica formation during pre-harvest burning

The concentration of crystalline silica in the airborne PM was too

low to be detected by XRD on the cascade impactor substrates. It

was, therefore, surmised that there was a low risk from crystalline

silica exposure in smoke of the pre-harvest burning events

monitored here. This is also consistent with the finding that burn

temperatures were not sustained at temperatures high enough to

enable the amorphous silica to convert to a crystalline form.

During pyrolysis (chemical decomposition during burning,

leaving a solid residue), much of the carbon will be lost, leaving

a mineral-rich ash deposit. The average amount of silica

measured in SCTA from country A and country B (23.0 and

10.6 wt% SiO2, respectively) was much lower than previously

reported, XRF-determined, values for silica in sugarcane mate-

rial. For example, Villar-Coci~na et al.66 found that ash from

burning sugarcane straw (i.e. leaves) in a furnace at 800 �C and

1000 �C for 20 min, had 70.2 wt% and 71.0 wt% SiO2, respec-

tively. Similarly, Martirena Hern�andez et al.67 found 59.1 wt%

SiO2 in the ash from open-air burning of sugarcane straw. In

both experiments, XRF was used to determine the SiO2, and the

duration of combustion was most probably longer than that

undergone by the sugarcane leaves analysed here. For example,

Villar-Coci~na et al.66 incinerated samples for 20 min in a furnace

and Martirena Hern�andez et al.67 sampled ash material from

‘heaps of open-air burnt [sugarcane] straw’ which would be

allowed to burn until completely ashed.

The total silica content in the SCTA from country B, however,

was an order of magnitude less than that in samples from country


A. This can, in part, be explained by the original silica content of

the leaves from country B being almost half that of the leaves

from country A (indicating that silica did not concentrate to the

same extent). Combustion dynamics will also be affected by burn

conditions. For example, in country B the average ambient

temperature and relative humidity during the burn were lower

(17–18 �C and 25–27%, respectively), compared with the field

conditions encountered in country A (25–27 �C and 80–87%,

respectively). The amount of carbon in SCTA from the two

different countries also shows that burn conditions were

different, as samples from country A had far less carbon

(�28.5 wt%), compared to those from country B (�69.3 wt%),

consistent with a hotter burn in country A with loss of C as CO2.

Cristobalite was not identified in any SCTA samples. Cristo-

balite has been identified in SCTA produced at 1000 �C (20 min)

in an electric furnace, but was not present in SCTA produced at

800 �C for the same period of time.68 Martirena et al.69 showed

that cristobalite was present in SCTA burned in an uncontrolled

(outdoor) environment, but was not present when the furnace

was kept below 600 �C. The SCTA analysed in this study lacks

cristobalite, perhaps because burn temperatures only occasion-

ally reached temperatures necessary for cristobalite formation in

isolated locations (as indicated by the infrared camera results and

the presence of calcite and sylvite). An alternative suggestion is

that the cristobalite was preferentially released as airborne

particles instead of remaining in the ash deposits,1 however, this

is not supported by our (limited) analysis of PM from pre-harvest

burning here.

Quartz was present at concentrations between 0.2 and 3.5 wt%

in SCTA samples from country A, but was absent in SCTA from

country B. Although care was taken to exclude soil in the ash

collection, quartz and other complex silicate (feldspar/pyroxene)

mineral contamination from soil adhering to sugarcane leaves

during combustion may have occurred. Temperatures of the pre-

harvest burning were suitable for formation of quartz from

amorphous silica in the sugarcane.

Silica-rich elongated structures were seen in SCTA, which

could result from the fusion (either naturally or via burning) of

silica phytoliths. The elongated fibres (observed in �30% of the

SEM images of SCTA) were carbonaceous. Biogenic fibres are

well known in many cultivated plants, such as sugarcane, flax

and rice.70 Whilst these biogenic fibres are not crystalline silica,

they must still be considered in health and exposure assessments

as they have been implicated as a causal factor in mesothelioma

occurrence in exposed populations30,31 and in vivo.35

EPMA results showed that silica particles in SCTA contain up

to �2300 mg g�1 (�0.23 elemental wt%) of impurities such as Al,

Fe, Ca and Mg. Although aluminium may be present in

concentrations from <0.0013 to 1.5 wt% in natural quartz

samples,71 compared with cristobalite and tridymite, quartz has

a closed atomic structure; thus the relatively large quantity of

impurities in biogenic (amorphous) silica may impede formation

of quartz.

5.4. Silica in the bagasse ash

SCBA contained 39.2–40.0 wt% SiO2, which is below the range

of previously reported values (�58 to 86 wt% SiO2),72–75 from

XRF analysis. Again, the variability may reflect the differences in

J. Environ. Monit., 2010, 12, 1459–1470 | 1467

techniques used to quantify silica and the fact that the silica

determined in this study is for the whole material and does not,

therefore, need to account for loss on ignition. Raw bagasse has

a similar level of silica compared to raw leaf, and so the higher

level of silica in SCBA compared with SCTA samples is likely to

be due to different combustion conditions within the processing

factory. Bagasse fed into the combustion furnaces is potentially

subject to conditions that encourage a more complete combus-

tion, and therefore the amount of carbon remaining in SCBA will

be reduced, when compared to SCTA from (uncontrolled) open

air burning.

Due to the demand for SCBA as an additive in

cements,40,63,67,76,77 its chemical composition has been exhaus-

tively studied. We found a CaO-content in SCBA of �9.8 wt%,

comparable to that reported for samples by Chusilp et al.41 and

Fr�ıas et al.,68 at 11 and 12 wt% respectively, but greater than the

�2 wt% reported by Cordeiro et al.63 Our SCBA samples,

however, had �9.8 wt% Al2O3, which is similar to the �9 wt%

reported for other samples by Cordeiro et al.63 but higher than

values reported by Fr�ıas et al.68 (2 wt%) and Chusilp et al.41

(6 wt%). The differences in SCBA composition compared with

previous studies show that bagasse preparation techniques and

combustion conditions vary significantly, as does the starting

composition of the sugarcane.

The crystallinity of biomass ash samples should increase with

increasing temperature and duration of combustion. For

example, Fr�ıas et al.68 found that at temperatures �1000 �C, the

crystallinity of SCBA increased, and there was a commensurate

decrease in the amount of vitreous material associated with lower

temperatures. Increased crystallinity was also observed in the

XRD patterns of sugarcane ash formed at 1100 �C after 10 min

when compared with ash formed after just 3 min in a laboratory

furnace.1 The SCBA samples in this study were more crystalline

than the SCTA, apparent from the less pronounced hump at

�15 to 35� 2q in the associated XRD patterns (Fig. 5c).

Cristobalite was identified in both SCBA samples, at 1.2 and

3.0 wt% in A_ashbag1 and A_ashbag2, respectively, in addition

to quartz (5 and 15 wt% for A_ashbag1 and A_ashbag2).

Although cristobalite has previously been recognized in

SCBA,63,66,78 it is not always observed.74,79 Quartz has been also

identified in SCBA after bagasse was heated at 450 �C.16 The

cristobalite identified here may have been converted from either

the amorphous silica within the sugarcane or the soil quartz

particles adhered to the sugarcane. It is likely, however, that if

boiler temperatures do not exceed 900 �C, then the source of the

silica for cristobalite formation is the silica in the leaf, since the

temperature for the transition from quartz to cristobalite (>1300�C) exceeds that required to alter amorphous silica to cristobalite

(�900 to 1000 �C). The absence of sylvite and calcite in SCBA

samples also suggests that temperatures in the boilers exceed

�700 �C (above the temperature needed for the breakdown of

sylvite).

Prismatic particles in the SCBA were identified as silica (by

SEM), but it is unlikely that these structures are composed

entirely of crystalline silica, as their abundance (observed in

�20% of all SEM images taken of SCTA) would have increased

the crystalline silica quantity detected by XRD. The EPMA

results show that SCBA contains silica-dominated particles, with

minor amounts of Na, Mg, Al, Fe, Ca, Ti and Fe in their

1468 | J. Environ. Monit., 2010, 12, 1459–1470

structure. When compared to SCTA, the total amount of SiO2 is

slightly less in both A_ashbag1 and A_ashbag2 and corre-

spondingly, the amount of impurities (Na, Al, Ti and Fe) is

increased. This increase in the impurities within the silica struc-

ture may be due to the presence of cristobalite in the SCBA,

which was also detected by XRD. The impurities, measured by

EPMA, may be held in the atomic structure of cristobalite,

enabling cristobalite to form outside of its stability field, and

possibly also stabilising it so this form of cristobalite can persist.

Elevated quartz in both of the SCBA samples may effectively

disguise the influence of cristobalite on the EPMA results.

The observation that some SCBA particles were porous

suggests that they may have been in a molten state,77 and can be

compared with some examples of carbon fly ash.79 Erlich et al.80

also found that melting occurred when bagasse pellets were

heated at 900 �C in a furnace, although Cetin et al.52 noted that

the bagasse samples were much less susceptible to melting, when

compared with soft/hard wood species, at high temperatures and

pressures.

5.5. Silica in other biomass fuels

As well as sugarcane burning, consideration must also be given

to the potential for crystalline silica formation and exposure

from combustion of other silica-rich biomass. Agricultural

burning is a widespread issue that affects ambient air quality over

vast areas. A link has already been suggested between rising

hospital admissions for childhood asthma during the rice

burning months in California and Japan.81,82 Another situation

in which silica-rich biomass is burned is the generation of energy

from certain renewable fuels, and this might also represent

a hazard especially where the practice occurs in confined areas,

such as indoor domestic combustion ovens or poorly ventilated

rooms. Many biomass types commonly used as fuels are known

to contain relatively large amounts of silica in their ash products,

for example, wheat straw (48.0 wt% SiO2), olive husk (32.7 wt%

SiO2) and red oak wood (49.0 wt% SiO2) by XRF.83 In the UK,

Miscanthus grass is currently grown as a fuel crop, as it provides

an annual harvest, is relatively easy to cultivate/harvest and gives

a reasonable high dry-matter yield.84 The silica content in ash

from Miscanthus has been reported as �70 wt%85 and it is likely

that crystalline silica is formed during combustion if tempera-

tures exceed �700 �C, which would be typical in biomass boiler

furnaces that operate at 800–900 �C.86 Although renewable fuel

crops are not burned in the field, as with sugarcane, exposure to

crystalline silica could occur during removal of ash from the

combustion furnaces/boilers or re-suspension from stored

deposits of ash.

6. Conclusions

The sugar-producing industry is undergoing a noticeable shift

towards encouraging the utilisation of its waste products, for use

in bioethanol generation and co-generation to provide energy for

the sugar-extraction process. Pre-harvest burning is, however,

still common in many sugar-producing countries and workers

exposed to the ash formed during burning are potentially at risk

from developing respiratory and related problems. Identifying

the presence and conditions under which crystalline silica can


form in the ash created during sugar production is important in

determining the potential risk from silicosis and other silica-

induced diseases, which may take years to manifest symptoms

that can be attributed to crystalline silica exposure.

Our studies have shown that temperatures during pre-harvest

burning of sugarcane are within the range required for the

formation of crystalline silica. However, no cristobalite and only

trace amounts of quartz were found in the residual ash from

sugarcane burning. It is not clear if the quartz was generated as

a result of combustion or incorporation of soil particles. The lack

of crystalline silica in the ash is likely due to the fact most of the

burning occurred at temperatures <800 �C, as evident from the

presence of sylvite in the ash. Fibrous material was present in

the sugarcane ash samples, and should be taken into account in

any risk assessment studying the potential effects from exposure.

Further investigation is also warranted to determine the extent to

which crystalline silica could be emitted in the pre-harvest

burning smoke, especially as sampling only took place at ground

level in this study, rather than in the lofting smoke plumes.

The bagasse ash, however, contained both cristobalite (up to

15 wt%) and quartz (up to 3 wt%). Bagasse ash is an inevitable

and abundant waste product from sugar production,87,88 and

although the amount of cristobalite it contains is relatively low,

when taken together with quartz, its total crystalline silica

content is up to 18 wt%. It may therefore pose a significant health

hazard, especially if the ash is broken down further and re-sus-

pended into the atmosphere. Adequate disposal of bagasse ash

should become an important consideration, and routine moni-

toring of the products formed after the combustion of bagasse

should be in place to identify and reduce possible crystalline silica

release and exposure.

Gaining access to commercial sugarcane estates for such

experimental work is not straightforward (reflected in the rela-

tively small number of samples obtained and analysed here), thus

we are duly cautious in generalising from our results. While we

did identify crystalline silica in the trash and bagasse ash prod-

ucts from sugarcane burning, we could not identify crystalline

silica in the airborne particulate matter. Clearly, burning

conditions, antecedent meteorology, sugarcane species, soils and

harvesting practice vary widely between commercial sugarcane

estates creating very different exposure characteristics. Future

work might also be directed to investigating this variability in

order to determine typical concentrations of crystalline silica that

result from sugarcane burning, and to identify best practice.

Acknowledgements

JSL’s work was supported by a NERC studentship (Grant No.

NER/S/A/2006/14107) with the University of Cambridge and the

Natural History Museum, London. CJH acknowledges a NERC

Postdoctoral Research Fellowship (Grant No. NE/C518081/2),

and CJH and CO acknowledge support from the NERC Envi-

ronment and Health Programme. We thank A. Cardoso, at

UNESP, Brazil for fieldwork assistance and guidance. Thanks

also to the Farm Managers, who allowed me to collect data and

samples on their land. Thanks also to T. Friscic at the Depart-

ment of Chemistry, University of Cambridge for access to the

Reisch Mill. We acknowledge the help of J. Spratt during the

EPMA and G. Cressey for assistance with the XRD analysis,


both at the NHM, London. We would also like to acknowledge

comments from two anonymous reviewers, which greatly

improved the manuscript.

References

1 J. S. Le Blond, B. J. Williamson, C. J. Horwell, A. K. Monro,C. A. Kirk and C. Oppenheimer, Atmos. Environ., 2008, 42, 5558–5565.

2 IARC (International Agency for Research on Cancer), Silica, SomeSilicates, Coal Dust and para-Amid Fibrils, Lyon, 1997, vol. 68.

3 NIOSH (National Institute for Occupational Safety and Health),Health Effects of Occupational Exposure to Respirable CrystallineSilica (No. 2002-129), 2002.

4 D. Neumann, Silicon in Plants, in Progress in Molecular andSubcellular Biology, ed. W. E. G. Muller, 2003, vol. 33, 149–160.

5 C. C. Perry and M. A. Fraser, Philos. Trans. R. Soc. London, Ser. B,1991, 334(1269), 149–157.

6 F. Fraysse, O. S. Pokrovsky, J. Schott and J.-D. Meunier, Geochim.Cosmochim. Acta, 2006, 70, 1939–1951.

7 H. Motomura, T. Fujii and M. Suzuki, Ann. Bot., 2004, 93, 235–248.8 C. K. Morikawa and M. Saiguas, Plant Soil, 2004, 258, 1–8.9 S. Neethirajan, R. Gordon and L. Wang, Trends Biotechnol., 2009,

27(8), 461–467.10 M. Okazaki, H. Setogucji, H. Aoki and S. Suga, J. Plant Res., 1986,

99, 281–287.11 S. Kondo, F. Fujiwara and J. Muroya, J. Colloid Interface Sci., 1976,

55, 421–430.12 M. Muroya and S. Kondo, Bull. Chem. Soc. Jpn., 1970, 43, 3453–

3456.13 L. Feltl, P. Lutovsky, L. Sosnova and J. E. Smolkova, J. Chromatogr.,

A, 1974, 91, 321.14 R. J. Hand, S. J. Stevens and J. H. Sharp, Thermochim. Acta, 1998,

318, 115–123.15 S. K. Milonji�c, L. S. �Cerovi�c, D. M. �Coke�sa and S. Zec, J. Colloid

Interface Sci., 2007, 309, 155–159.16 K. Umamaheswaran and V. S. Batra, Fuel, 2008, 87(6), 628–638.17 A. Boateng and D. Skeete, Cem. Concr. Res., 1990, 20, 795–802.18 P. Khangaonkar, A. Rahmat and K. Jolly, Cem. Concr. Res., 1992,

22, 577–588.19 S. Malhotra and N. Dave, Cem. Concr. Compos., 1999, 22, 285–291.20 M. A. Arbex, L. C. Martins, R. C. Oliveira, L. A. A. Pereira,

F. F. Arbex, J. E. D. Cancado, P. H. N. Saldiva andA. L. F. Braga, J. Epidemiol. Community Health, 2007, 61, 395–400.

21 J. M. Paturau, By-products of the Cane Sugar Industry, Elsevier,Amsterdam, 1989.

22 M. J. Nieuwenhuijsen, K. S. Noderer, M. B. Schenker, V. Vallyathanand S. Olenchock, Ann. Occup. Hyg., 1999, 43(1), 35–42.

23 J. F. Robertson, Farm Build. Progr., 1993, 114, 7–11.24 F. H. Y. Green, K. Yoshida, G. Fick, J. Paul, A. Hugh and

W. F. Green, Int. Arch. Occup. Environ. Health, 1990, 62, 423–430.25 W. J. Popendorf, A. Pryor and H. R. Wenk, Ann. Am. Conf. Gov. Ind.

Hyg., 1982, 2, 101–115.26 OEHHA (Office of Environmental Health Hazard Assessment),

Chronic toxicity summary and chronic reference exposure data,California Environmental Protection Agency, 2005, http://www.oehha.org/air/chronic_rels/silica_final.html, accessed Mar 2010.

27 D. Dahmann, D. Taeger, M. Kappler, S. B€uchte, P. Morfeld,T. Br€uning and B. Pesch, J. Exposure Sci. Environ. Epidemiol.,2008, 18, 452–461.

28 R. H. Newman, Ann. Occup. Hyg., 1986, 30(3), 365–370.29 D. K. Amre, C. Infante-Rivard, A. Dufresne, P. M. Durgawale and

P. Ernst, Occup. Environ. Med., 1999, 56, 548–552.30 P. B. Das, A. J. Fletcher and S. G. Deodhare, ANZ J. Surg., 1976, 46,

218–226.31 H. N. Phoolchund, Occup. Med., 1991, 41, 133–136.32 S. M. Brooks, H. G. Stockwell, P. A. Pinkham, A. W. Armstrong and

D. A. Witter, Environ. Res., 1992, 58, 195–203.33 T. Sinks, M. T. Goodman, L. N. Kolonel and B. A. Anderson,

Epidemiology, 1994, 5, 466–488.34 S. Mann and C. C. Perry, Ciba Found. Symp., 1986, 121, 40–58.35 T. S. Bhatt, S. Lang and M. N. Sheppard, Carcinogenesis, 1991, 12,

1927–1931.

J. Environ. Monit., 2010, 12, 1459–1470 | 1469

36 F. S. Lopes and H. Ribeiro, Revista Brasileira de Epidemiologia, 2006,9(2), 215–225.

37 M. A. Arbex, G. M. B€ohm, P. H. N. Saldiva, G. M. S. Conceicao,A. C. Pope and A. L. F. Braga, Air Waste, 2000, 50, 1745–1749.

38 H. Ribeiro, Rev. Saude Publica, 2008, 42(2), 1–6.39 O. D. Cheeseman, Environmental Impacts of Sugar Production, CABI

publishing, 2004.40 G. C. Cordeiro, R. D. Toledo Filho and K. Thangavel, ACI Mater. J.,

2008, 105(5), 487–493.41 N. Chusilp, C. Jaturapitakkul and K. Kiattikomol, Constr. Build.

Mater., 2009, 23(11), 3352–3358.42 J. S. Le Blond, B. J. Williamson, C. Oppenheimer and C. J. Horwell,

Atmos. Environ., submitted.43 J. K. Hiers, J. J. O’Brien, R. J. Mitchell, J. M. Grego and

E. L. Loudermilk, International Journal of Wildland Fire, 2009, 18,315–325.

44 J. S. Le Blond, C. Unsworth and S. Strekopytov, Commun. Soil Sci.Plant Anal., submitted.

45 J. S. Le Blond, G. Cressey, B. W. Horwell and B. J. Williamson,Powder Diffr., 2009, 24(10), 17–23.

46 M. Patel and P. Kumari, J. Mater. Sci. Lett., 1990, 9, 375–376.47 R. M. Jorapur and A. K. Rajvanshi, Biomass Bioenergy, 1995, 8(2),

91–98.48 P. Sugumaran and S. Seshadri, J. Sci. Ind. Res., 2009, 68, 719–723.49 N. S. Choong Kwet Yive and M. Tiroumalechetty, J. Hazard. Mater.,

2008, 155(1–2), 179–182.50 W. T. Tsai, M. K. Lee and Y. M. Chang, J. Anal. Appl. Pyrolysis,

2006, 76, 230–237.51 V. I. Kuprianov, K. Janvijitsakul and W. Permchart, Fuel, 2006,

85(4), 434–442.52 E. Cetin, B. Moghtaderi, R. Gupta and T. F. Wall, Fuel, 2004, 83,

2139–2150.53 S. Kyritsis, in 1st World Conference on Biomass for Energy and

Industry, Sevilla, Spain, Earthscan, 2001.54 B. M. Jenkins, L. L. Baxter, T. R. Miles, Jr and T. R. Miles, Fuel

Process. Technol., 1998, 54, 17–46.55 S. Al Arni, B. Bosio and E. Arato, Renewable Energy, 2010, 35, 29–35.56 A. L. Carnelli, M. Madella, J.-P. Theurillat and B. Ammann, Am. J.

Bot., 2002, 89(2), 346–351.57 J. F. Parr and L. A. Sullivan, Soil Biol. Biochem., 2005, 37, 117–124.58 S. Mann, C. C. Perry, R. J. P. Williams, C. A. Fyfe, G. C. Gobbi and

J. Kennedy, J. Chem. Soc., Chem. Commun., 1983, 4, 168–170.59 L. Sapei, R. N€oske, P. Strauch and O. Paris, Chem. Mater., 2008, 20,

2020–2025.60 D. Drysdale, in An Introduction to Fire Dynamics, John Wiley and

Sons, Chichester, UK, 2nd edn, 1998.61 S. J. Pyne, P. L. Andrews and R. D. Laven, in Introduction to Wildland

Fire, John Wiley, New York, 2nd edn, 1996.62 E. Pastor, Y. P�erez, A. Aueda, M. Miralles and E. Planas, Fire Safety

Journal, 2010, 45, 69–81.63 G. C. Cordeiro, R. D. Toledo Filho, L. M. Tavares and

E. M. R. Fairbairn, Cem. Concr. Compos., 2008, 30, 410–418.

1470 | J. Environ. Monit., 2010, 12, 1459–1470

64 P. Thy, B. M. Jenkins, S. Grundvig, R. Shiraki and C. E. Lesher, Fuel,2006, 85, 783–795.

65 M. J. Fern�andez Llorente, J. M. Murillo Laplaza, R. EscaladaCuadrado and J. E. Carrasco Garc�ıa, Fuel, 2006, 85(9), 1157–1165.

66 E. Villar-Coci~na, M. Fr�ıas Rojas and E. Valencia-Morales, ACIMater. J., 2008, 105(3), 258–264.

67 J. M. F. Martirena Hern�andez, B. Middendorf, M. Gehrke andH. Budelmann, Cem. Concr. Res., 1998, 28(11), 1525–1536.

68 M. Fr�ıas, E. Villar-Coci~na and E. Valencia-Morales, Waste Manage.,2007, 27, 533–538.

69 F. Martirena, B. Middendorf, R. L. Day, M. Gehrke, P. Roque,L. Mart�ınez and S. Betancourt, Cem. Concr. Res., 2006, 36, 1056–1061.

70 American Thoracic Society, Medical Section of the American LungAssociation, Am. J. Respir. Crit. Care Med., 1998, 158, S1–S76.

71 J. V. Smith and I. M. Steele, Neues Jahrb. Mineral., Monatsh., 1984, 3,137–144.

72 M. C. Borlini, H. F. Sales, C. M. F. Vieira, R. A. Conte, D. G. Pinattiand S. N. Monteira, in REW AS’04, Global Symposium onRecycling, Waste Treatment and Clean Technology, ed. B.Gaballah, R. Mishra, M. Solosabal and M. Tanaka, 1st edn,Fundaci�on INASMET, Madrid, Spain, 2004.

73 M. C. Borlini, J. L. C. C. Mendonca, C. M. F. Vieira andS. N. Monteiro, Rev. Mater., 2006, 11(4), 435–443.

74 S. Rainho Teixeira, A. E. de Souza, G. T. de Almeida Santos,A. Fidel, V. Pena and A. Gil Miguel, J. Am. Ceram. Soc., 2008,91(6), 1883–1887.

75 E. Villar-Coci~na, M. F. Rojas and E. V. Morales, ACI Mater. J.,2009, 105(3), 258–264.

76 N. B. Singh, V. D. Singh and S. Rai, Cem. Concr. Res., 2000, 30,1485–1488.

77 J. Pay�a, J. Monz�o, M. V. Borrachero, L. D�ıaz-Pinz�on andL. M. Ord�o~nez, J. Chem. Technol. Biotechnol., 2002, 77, 321–325.

78 K. Ganesan, K. Rajagopal and K. Thankgavel, Cem. Concr. Compos.,2007, 29, 515–524.

79 J. Pay�a, J. Monz�o, M. V. Borrachero, E. Peris-Mora and E. Gonz�alez-L�opez, Cem. Concr. Res., 1996, 26, 225–235.

80 C. Erlich, M. €Ohman, E. Bj€ornbom and T. H. Fransson, Fuel, 2005,84, 569–575.

81 J. Jacobs, Environ. Health Perspect., 1998, 105(9), 980–985.82 K. Torigoe, Pediatrics International, 2000, 42, 143–150.83 A. Demirbas, Prog. Energy Combust. Sci., 2004, 30, 219–230.84 P. McKendry, Bioresour. Technol., 2002, 83, 37–46.85 H. Spliethoff and K. R. G. Hein, Fuel Process. Technol., 1998,

54(1–3), 189–205.86 L. L. Baxter, T. R. Miles, T. R. Miles, Jr, B. M. Jenkins, T. Milne,

D. Dayton, R. W. Bryers and L. L. Oden, Fuel Process. Technol.,1998, 54, 47–78.

87 D. Dellepiane, B. Bosi and E. Arato, J. Power Sources, 2003, 122,47056.

88 J. Zandersons, J. Gravitis, A. Kokorevics, A. Zhuinsh, O. Bikovens,A. Tardenaka and B. Spince, Biomass Bioenergy, 1999, 17, 209–219.


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