Exposure and potential health effects
associated with the use of PX-10 in the
Dutch Armed Forces
RIVM Report 609037002/2011

RIVM Report 609037002

Colophon

© RIVM 2011
Parts of this publication may be reproduced, provided acknowledgement is given
to the 'National Institute for Public Health and the Environment', along with the
title and year of publication.

Schram-Bijkerk, D. (ed.)1
Tongeren, M. van2
Vermeulen, R.C.H.3

Contact:
Dieneke Schram-Bijkerk
Centre for Environmental Health
Dieneke.Schram@rivm.nl

Contributors:
Heederik, D.J.3
Portengen, L.3
Vlaanderen, J.3
Robertson, A.2
Schmid, K.2
Cherrie, J.W.2
MacCalman, L.2
Reviewed by:
Stayner, L.T.4
Schneider, T.5
1

National Institute for Public Health and the Environment, Bilthoven, The Netherlands
Institute of Occupational Medicine, Edinburgh, United Kingdom
3
Institute for Risk Assessment Sciences/Utrecht University, Utrecht, The Netherlands
4
University of Illinois, Chicago, United States
5
Formerly at National Institute of Occupational Health, Copenhagen, Denmark
2

This investigation has been performed by order and for the account of the Dutch
Ministry of Defence, within the framework of Gezondheidsonderzoek PX-10
(E/609037).

Page 2 of 67

RIVM Report 609037002

Abstract

Exposure and potential health effects associated with the use of PX-10
in the Dutch Armed Forces
The possibility that members of the Dutch Armed Forces developed acute myeloid leukaemia (AML) or other forms of hematopoietic cancer due to exposure to
PX-10 while cleaning and maintaining weapons can be essentially excluded. Until
1970, PX-10 contained small amounts (0.1%) of benzene, a known carcinogen;
thereafter, the concentrations of benzene in PX-10 fell sharply. Consequently,
the total cumulative exposure of military personnel to benzene over the years
was low.
This is the conclusion of a study into the effects and health risks of working with
PX-10. The study was commissioned by the Dutch Ministry of Defence in 2008
after liability claims were filed against it related to serious health complaints due
to activities involving exposure to PX-10.
Three to four per 1,000 Dutch men develop AML during their lifetime without
having had any contact with PX-10. The additional risk of developing AML among
military personnel who worked with PX-10 intensively for many years was determined to be 0.03 extra cases per 1,000 men. Therefore, it is highly unlikely
that additional cases of AML developed, even if a few thousand military personnel were intensively exposed to PX-10.
The exposure to benzene by inhalation and dermal contact varied by time period
and working situation. The yearly average concentrations were 0.5 ppm, which
is below the currently established occupational exposure limit of 1 ppm during
an eight-hour period. PX-10 also contained other volatile components that can
have neurological effects. The study determined that the yearly average concentrations of volatile organic compounds (VOCs) were 2–100 ppm, depending on
the working situation. As dose-response associations have not been established
for VOCs, the risk of developing neurological disorders from exposure to the
VOCs in PX-10 could not be calculated.
Keywords:
soldiers, PX-10, volatile organic compounds, cleaning and maintaining weapons,
health effects

Page 3 of 67

RIVM Report 609037002

Page 4 of 67

RIVM Report 609037002

Rapport in het kort

Blootstelling en mogelijke gezondheidseffecten door het gebruik van
PX-10 in de Nederlandse krijgsmacht
Het is praktisch uitgesloten dat defensiepersoneel acute myeloïde leukemie, of
aanverwante vormen van kanker heeft ontwikkeld door te werken met het wapenonderhoudsmiddel PX-10. Dit middel bevatte tot 1970 lage concentraties
(0,1 procent) van de kankerverwekkende stof benzeen. Daarna daalden de concentraties van deze stof in het product sterk, waardoor de totale blootstelling
voor Defensiepersoneel gering was.
Dit blijkt uit berekeningen van de blootstelling aan en de gezondheidseffecten
van werken met PX-10. Het Ministerie van Defensie heeft dit onderzoek uitgezet,
nadat het in 2008 aansprakelijk was gesteld voor gezondheidsschade door werkzaamheden met PX-10.
Drie tot vier van elke 1.000 Nederlandse mannen krijgen AML, zonder dat ze
ooit met PX-10 gewerkt hebben. Onder defensiepersoneel, dat vele jaren dagelijks intensief met PX-10 werkte, is er volgens de berekeningen sprake van 0,03
extra gevallen per 1.000 mannen. Het is daarom onwaarschijnlijk dat er daadwerkelijk extra gevallen van AML zijn opgetreden, zelfs als een paar duizend
werknemers in hoge mate zijn blootgesteld aan PX-10.
Hoeveel benzeen het defensiepersoneel inademde of opnam via de huid is afhankelijk van de periode waarin de werkzaamheden plaatsvonden en het type
werkzaamheden met PX-10. Het jaarlijks gemiddelde per persoon was maximaal
0,5 parts per million (ppm), wat onder de huidige norm ligt van gemiddeld
1 ppm per werkdag. PX-10 bevat ook andere oplosmiddelen die effecten kunnen
hebben op het zenuwstelsel. Uit dit onderzoek blijkt dat de blootstelling aan de
totale hoeveelheid van deze oplosmiddelen gemiddeld tussen de 2 en 100 ppm
lag, afhankelijk van het type werkzaamheden. Het is echter niet mogelijk aan te
geven wat de effecten hiervan zijn op de gezondheid, omdat de precieze relatie
tussen blootstelling en gezondheidseffecten niet bekend is.
Trefwoorden:
militairen, PX-10, vluchtige organische componenten (VOC’s), wapenonderhoudsmiddel, gezondheidseffecten

Page 5 of 67

RIVM Report 609037002

Page 6 of 67

RIVM Report 609037002

Contents

Summary—9
1
1.1
1.2
1.3

Introduction—13
Background—13
Objectives—13
Organization of the report—14

2

Use of PX-10: Definition of scenarios—15

3
3.1
3.2
3.3
3.4
3.5
3.6

Methods of exposure assessment—17
Benzene and VOCs content of PX-10—17
Modelling approach—17
Laboratory experiments—18
Emission rates of benzene and VOCs—20
Monte Carlo simulation—20
Dermal exposure—21

4
4.1
4.1.1

4.2.4
4.3

Results of exposure assessment—23
Laboratory experiments—23
Evaluating the effect of benzene content in PX-10 on the ‘passive’ evaporation
rate—23
Effects of other components in PX-10 on benzene emission rates—24
Stability of emission rate over time—24
Impact of cleaning activities on the benzene evaporation rate—25
Effect of air speed over evaporation surface on evaporation rate—26
Effect of container dimensions on the benzene evaporation rate—27
Cleaning torpedoes—27
Summary of laboratory experiments—27
Model estimates for benzene exposure—28
Benzene exposure after top-up of PX-10 baths—29
Average daily benzene exposure from near-field and far-field sources—29
Average daily benzene exposure from near-field and far-field sources adjusted
for reported daily working hours at the PX-10 task—33
Sensitivity analysis—35
Model estimates for VOCs exposure—36

5
5.1
5.2

Quantification of potential health effects—41
Methods: life table analysis—41
Results—46

6
6.1
6.1.1
6.1.2
6.1.3
6.1.4
6.1.5
6.2
6.2.1
6.2.2

Discussion—49
Exposure assessment—49
Dealing with uncertainties—49
Evaporation rate of benzene—50
Exposure levels in different use scenario’s—50
Dermal exposure—51
VOCs exposure—52
Potential health effects at low levels of exposure—52
Potential confounding factors—53
Life-table analysis—53

4.1.2
4.1.3
4.1.4
4.1.5
4.1.6
4.1.7
4.1.8
4.2
4.2.1
4.2.2
4.2.3

Page 7 of 67

RIVM Report 609037002

Acknowledgement—55
References—57
Appendix 1: Scenario description and input parameters for exposure modelling—
61

Page 8 of 67

RIVM Report 609037002

Summary
Background
In 2008, liability claims were filed against the Ministry of Defence (MoD) related
to serious health complaints due to activities involving exposure to PX-10. PX-10
is a water displacing substance that has been used for cleaning and maintaining
steel surfaces of weapons until 1995. It contained 0.1% of the carcinogen benzene till 1970. In response, the MoD commissioned the Dutch National Institute
for Public Health and the Environment (RIVM) to quantify the exposure to toxic
substances and potential health effects associated with the use of PX-10. RIVM
coordinated this study, which was performed by the Dutch Institute for Risk Assessment Sciences (IRAS) of Utrecht University and the Institute of Occupational
Medicine in Edinburgh, United Kingdom (IOM). Results of the first part of this
study – an independent review of a report from MoD – have been published previously (1). It was concluded that the report was accurate in that benzene exposure is associated with acute myeloid leukaemia (AML), but that there is also
(limited) evidence for an association with other leukaemia’s and lymphoma (1).
Objectives
The aim of this study was to estimate the exposure to benzene and VOCs from
use of PX-10 and to quantify potential health effects associated with the benzene resulting from past PX-10 use. Although VOCs exposures have been linked
to neurological effects, no consistent information on the specific constituents
causing these effects, nor dose-response relationships were available. Therefore,
it was not possible to quantify the health risks due to exposure to VOCs.
Methods
A workplace exposure model was developed and used to estimate the past inhalation and dermal exposure to volatile organic compounds (VOCs) and, in particular, to benzene from PX-10 use. Six representative use scenarios of PX-10
were defined in focus group meetings with former employees/members of the
Navy who had used PX-10, i.e.:
•
Onshore cleaning of small arms;
•
Cleaning of small arms on board;
•
Onshore small arms workshop in large room;
•
Onshore small arms workshop in small room;
•
Onshore washing room for cleaning of torpedo parts;
•
Onshore torpedo workshop.
Employees from other branches of military service also had been invited for the
focus groups, but did not participate. Estimates of the emission rates were obtained from experiments using a white spirit mixture, similar to PX-10. The information from the focus group meetings and laboratory experiments was used
to model the yearly average exposure to benzene and VOCs for each of the six
use scenarios. Subsequently, two careers were defined to quantify the risk of
developing leukaemia and its subtypes and lymphoma due to exposure to benzene (see box 1). These careers included two exposure scenarios with relatively
high average exposures (cleaning small arms in weapon rooms and on board of
ships) and a civilian who worked many years with PX-10. Therefore, these careers represent worst-case scenarios. Subsequently, the risk of developing leukaemia in general, acute myeloid leukaemia (AML), acute lymphocytic leukaemia
Page 9 of 67

RIVM Report 609037002

(ALL), chronic lymphocytic leukaemia (CLL), non-Hodgkin lymphoma (NHL) and
multiple myeloma (MM) was modelled. The risks were estimated based on life
table analysis of hypothetical cohorts of 100,000 exposed workers in the two
defined careers, as it is not exactly known how many people worked in these
careers and when. Three weighting functions were applied in the life table analysis, addressing different assumptions regarding the reduction in risk with time
since last exposure. In addition, different types of risk models (multiplicative
model vs. additive model) and exposure-response models (spline vs. linear
model) were used. The main reason to present the outcomes of multiple models
is that there is no model that is universally better. As such these different models represent the uncertainty in estimated additional cases. Conclusions were
based on the median of the different estimates.
Table S1: Careers used in the quantification of health effects.
Career 1 ‘military personnel of the
Navy’
Cleaning small arms in weapon rooms and
on ships

Career 2 ‘civilian’

Duration career:
Start career:

38 yrs (age 18-55)
1964

Duration career: 48 yrs (age 18-65)
Start career:
1945
Exposure:
8 hours/day

Rotation land-ship:

3 yrs

Cleaning small arms in small workshops

Full duration of career at the same workplace

Phase 1 (Seaman)
Duration:
Exposure:

6 yrs
4-8 hours/day

Phase 2 (Corporal)
Duration:
Exposure:

9 yrs
1-4 hours/day

Phase 3 (Sergeant)
Duration:
Exposure:

until end of career
several hours/month

Results
The experiments showed that benzene would have rapidly evaporated from an
open bath with PX-10. A half-life of 2 hours was estimated for the benzene content in a PX-10 bath, meaning that the benzene emission rate from an open
bath of PX-10 would have reduced rapidly in the first hours and would have
been negligible at the beginning of the next day. Therefore, the long-term exposure to benzene was, to a large extent, determined by the frequency and
amount of topping–up of the bath (approximately once a week) and the frequency of completely changing the bath with fresh PX-10 in the scenarios using
an open bath (approximately once a month).
Estimates of average yearly benzene exposure ranged for the different use scenarios between 0.009 to 0.4 ppm before 1970, 0.004 to 0.2 ppm between 1970
and 1980, and between 0.001 and 0.04 ppm after 1980. In addition to the inhalable route, exposure via the dermal route would also have contributed to
overall systemic exposure. Due to the manual nature of the cleaning procedures
this exposure route could have been substantial. Modelling of the dermal expoPage 10 of 67

RIVM Report 609037002

sure route showed that this route resulted in yearly inhalation equivalents below
0.2 ppm but was still the main exposure route in certain operations like for instance in the maintenance of torpedoes onshore. Nevertheless, the inhalation
exposure to benzene was the main contribution in most of the tasks. Combining
the dermal and inhalation route resulted in exposure estimates that were on a
yearly average base maximally 0.5 ppm, see Figure S1. VOCs exposure yearly
average levels varied from 2 to 100 ppm depending on the working situation.

1

Total yearly inhalation equivalent (ppm)

0,9
0,8
0,7
0,6
0,5
0,4
0,3
0,2
0,1
0
torpedoes

weapon rooms

ships

large
workshops

small
workshops

torpedo parts

Figure S1: Total yearly benzene exposure before 1970, with error bars indicating
the 5th and 95th percentiles of the estimation intervals.
Despite the differences between the two hypothetical careers, the cumulative
exposure was similar, i.e. 2.42 ppm-years in career 1 and 2.25 ppm-years in
career 2. For career 1 (Cleaning small arms in weapon rooms and on ships) the
estimated additional number of cases per 100,000 exposed individuals ranged
for leukaemia from 3.9 to 26.3 (median 6.5); for AML from 1.4 to 15.0 (median
3.3); for ALL it was 0.3; for CLL it ranged from 1.7 to 2.9; for NHL from 4.7 to
7.1; and for MM from 7.3 to 11.7.
For career 2 (Cleaning small arms in workshops by civilians) the estimated additional number of cases per 100,000 exposed individuals ranged for leukaemia
from 2.6 to 30.3 (median 6.4); for AML from 0.9 to 21.0 (median 2.7); for ALL it
was 0.4; for CLL it ranged from 0.9 to 3.2; for NHL from 2.8 to 8.1; and for MM
from 4.0 to 13.2.
In summary, the additional risk of developing AML, for which the evidence of a
causal association with benzene exposure is most evident, was around 3 cases
per 100,000 exposed people, or 0.03 per 1,000 people in both careers. This
number is however time-dependent and should not be interpreted as an individual risk. The additional risk and subsequent cases for other leukaemia’s and
lymphoma was estimated to be similarly low.

Page 11 of 67

RIVM Report 609037002

Conclusion
It can be concluded that exposure to benzene did occur while using PX-10 and
that these exposures on a yearly average would be likely less than the current
occupational exposure limit of 1 ppm. Yearly average exposure to VOCs was up
to 100 ppm, which equals the (non-legal) current white-spirit 8-hour threshold
value.
Based on the yearly average concentrations and two realistic high-risk careers,
it was estimated that the additional risk of AML is 0.03 per 1,000 subjects exposed to these exposure scenarios. The additional risk for the other leukaemia
subtypes and lymphoma was comparable to the risk of AML. MoD estimated that
the number of exposed subjects in these high-risk careers is likely to be in the
low thousands. Therefore, the possibility that members of the Dutch Armed
Forces developed acute myeloid leukaemia (AML) or other forms of hematopoietic cancer due to exposure to PX-10 while cleaning and maintaining weapons
can be essentially excluded. It should be noted that both the exposure estimates
and risk estimates have considerable uncertainties. As such the estimated number of additional cases should be interpreted with some caution.
VOCs have been linked with some adverse health outcomes, most notably neurological symptoms and disorders. As no dose-response relations exist for VOCs
or specific components with regard to these disorders, no calculation could be
made of the potential health impact. Cases of neurological disorders among subjects that worked with PX10 should therefore probably be referred to specialized
‘solvent teams’ for more specific follow-up.

Page 12 of 67

RIVM Report 609037002

1

Introduction

1.1

Background
In 2008, liability claims were filed against the Ministry of Defence (MoD) related
to serious health complaints due to activities involving exposure to PX-10. PX-10
is a water displacing substance that has been widely used for cleaning and maintaining steel surfaces of weapons. Subsequently, this claim has received attention by the national government, the military union and the media. As PX-10, at
least for part of the time, contained benzene and other organic solvents, the
suggestion has been that the MoD, although aware of the potential health effects, has not acted adequately in eliminating or reducing the exposure or in
providing appropriate personal protection to their employees. In response, the
MoD has agreed to further investigate the use of PX-10, its contents and the
potential associated health effects with the goal to objectively assess the potential health risks that (ex-) military personnel might have been exposed to due to
the historical use of PX-10.
A preliminary evaluation of the composition, use and potential health effects of
PX-10 was made by the Military Medical Service Agency of the Netherlands (2).
MoD commissioned the Dutch National Institute for Public Health and the Environment (RIVM) to independently review this evaluation. Results of this literature review have been published previously (1). In addition, MoD commissioned
RIVM to estimate the exposure to toxic substances in PX-10 and to quantify potential health effects associated with these exposures (this report). This study
was coordinated by RIVM and performed by the Dutch Institute for Risk Assessment Sciences (IRAS) of Utrecht University and the Institute of Occupational
Medicine in the United Kingdom (IOM).
In our previous report (1), it was concluded that:
•
The main constituents of PX-10 were white spirit (including aromatics such
as toluene and benzene), mineral oils and some additives. Of these exposures benzene was identified as being the most important constituent in relation to possible health effects.
•
The concentrations of benzene in PX-10 in the preliminary estimates of MoD
(2) were based on a worst-case scenario; we concluded that 10 times lower
concentrations were more realistic. The benzene level in PX-10 was reduced
from 0.1% before 1970 to 0.03% between 1970 and 1980 and 0.01% after
1980. After 1995 PX-10 was not used anymore.
•
Next to acute myeloid leukaemia (AML), there is evidence that benzene exposure is related to acute lymphocytic leukaemia (ALL), chronic lymphocytic
leukaemia (CLL), non-Hodgkin lymphoma (NHL), and multiple myeloma
(MM).
•
In addition to benzene, exposures to other volatile organic compounds
(VOCs) will have occurred, among which toluene and xylene. Although VOCs
exposures have been linked to neurological effects, the scientific literature is
not consistent.

1.2

Objectives
The aim of this study was to estimate the exposure to benzene and VOCs from
use of PX-10 and to quantify potential health effects associated with the benzene resulting from past PX-10 use. Although VOCs exposures have been linked
to neurological effects, no consistent information on the specific constituents
Page 13 of 67

RIVM Report 609037002

causing these effects, nor dose-response relationships were available. Therefore,
it was not possible to quantify the health risks due to exposure to VOCs.
1.3

Organization of the report
The report consists of the following elements:
•
Use of PX-10: definition of scenarios (chapter 2).
•
Exposure assessment of benzene and VOCs based on the identified scenarios
of PX-10 use (chapter 3 and 4).
•
Quantification of health effects due to exposure to benzene (chapter 5).
•
Discussion (chapter 6)

Page 14 of 67

RIVM Report 609037002

2

Use of PX-10: Definition of scenarios

As no detailed descriptions on the past use of PX-10 were directly available, it
was decided to obtain such information through focus group meetings with (former) long-serving employees of the Dutch Armed Forces. The main aim of the
focus group meetings was to define representative scenarios for the use of PX10 in the Dutch MoD as well as to understand how PX-10 was used within these
scenarios. The 23 focus group members, including both civilians and military
personnel, were asked to provide information on sizes of rooms, amounts of PX10 used and type of ventilation, etc. Two focus group meetings were organized,
one for exposure scenarios during cleaning and handling of small arms, and one
for scenarios during cleaning of large arms. The members of the focus groups,
which included current and retired military and civilian personnel, represented
only the Dutch Navy; there was no representation from other areas of the Dutch
Armed Forces despite the efforts from MoD to include employees from other
branches of services.
As a result of the discussion with the focus groups six different exposure scenarios were identified. These six scenarios are described briefly below and represent
the most important and frequent past usage of PX-10 in the Dutch Navy.
1. Onshore cleaning of small arms (military personnel): Cleaning of small arms
was carried out in a small workshop in the onshore armoury (where handguns were stored). These armouries were well-protected and enclosed
rooms below or above ground with little ventilation. There were typically
three baths in the workshop, each containing about 200 litres of PX-10.
Small arms (guns, pistols) were dismantled; the individual parts soaked in
the baths, cleaned with a brush and often dried using compressed air;
2. Cleaning of small arms onboard (military personnel): Constables were responsible for cleaning of all small arms onboard. The baths for the cleaning
of small arms with PX-10 onboard ships were generally smaller than in the
armoury and typically contained about 20 litres of PX-10. The workspaces
were of variable dimensions, but were generally smaller than the onshore
facilities;
3. Onshore small arms workshop (civilian staff) in small room: Large numbers
of arms were delivered to the workshop where full maintenance was performed. Large baths with hundreds of litres of PX-10 were used for the
cleaning of the weapons;
4. Onshore small arms workshop (civilian staff) in large room: Large numbers
of arms were delivered to the workshop where full maintenance was performed. Large baths with hundreds of litres of PX-10 were used for the
cleaning of the weapons;
5. Onshore washing room: Smaller parts of the torpedoes were cleaned by
soaking and washing in large open baths filled with PX-10. This room was
adjacent to the torpedo hall;
6. Onshore torpedo workshop: The main body of the torpedoes were manually
cleaned by wiping with a cloth soaked in PX-10. This was carried out in a
large hall (torpedo hall).
Following the focus group discussions the exposure scenarios were described in
as much detail as was available and distributed to the participants together with
a list of further follow-up questions. This was done to help refine the scenario
descriptions, in particular for information on essential parameters that were rePage 15 of 67

RIVM Report 609037002

quired for estimation of exposure (e.g. specific sizes of rooms described in the
scenarios etc.). Besides the consensus on the parameter estimates the range
was also recorded and subsequently used in the sensitivity analyses (4.2.4.).
There were two additional scenarios, for which there was not enough information
available to sensibly describe the exposure determinants:
•
Onshore Ammunition Maintenance: Ammunition was dismantled and cleaned
by hand in a bath with PX-10. For the manual cleaning of the large parts of
the ammunition there was a pump dispenser for PX-10, which was applied
directly onto a towel; and
•
Onshore Maintenance of Large Arms (non-torpedo): No former personnel
from the large arms armoury hall were available for the focus group. The
work was carried out mainly by civilians and continued until the late 1980s.
However, the use of PX-10 was less intense compared with use of PX-10 in
the torpedo hall.
Based on the information that was obtained from the focus group it seems that
the exposure to benzene can be assumed to be similar or lower than in the other
scenarios with PX-10 baths.
The six scenarios have been divided into two different exposure types:
a)
Usage of PX-10 in open baths, with continuous evaporation of PX-10 (scenario 1-5). The tasks that were performed at such workplaces consisted of
cleaning metal pieces with PX-10. These tasks have been reported to be
similar to household dish cleaning with a brush and were performed with
completely submerged hands and part of the forearms in the PX-10 liquid;
and
b)
Treatment of metal surfaces with a cloth soaked in PX-10 (scenario 6).
The skin contact with the PX-10 was reported to be less extensive than in
the bath tasks, as the hands were not permanently submerged. In most
cases the contact with PX-10 was limited to the inner side of one hand and
forearm.

Page 16 of 67

RIVM Report 609037002

3

Methods of exposure assessment

As no measurement data are available for benzene exposure during activities
involving PX-10, it was necessary to develop a model to estimate the past exposures. This Chapter describes the methodology used for estimating the past exposure to benzene and total VOCs from use of PX-10.
3.1

Benzene and VOCs content of PX-10
As described previously (1), the main constituents of PX-10 were white spirit
(including aromatics such as toluene and benzene), mineral oils and some additives. Tables 3-1 and 3-2. present the best estimates of the content of benzene
and VOCs respectively, which were described in our previous report and which
were used in the quantification of exposure.
Table 3-1: Best estimates of historical benzene in white spirit.
Period
% Benzene in white spirit
Best estimate
Upper limit
before 1970
0.1
0.2
1970-1980
0.03
0.1
1980 onwards
0.01
0.03
Table 3-2: Reported proportions of toluene and xylene in white spirit (in % volume1).
Solvent
% by volume
Northern Europe
Russia
USA
Toluene
0.005
0.2
0.4
Xylene (o,p & m)
1.1
4.14
1.42
1
Source: http://www.inchem.org/documents/ehc/ehc/ehc187.htm#SectionNumber:2.2,
visited October 26, 2011.
2
C8 aromatics, includes ethyl benzene.

3.2

Modelling approach
To predict the inhalation benzene exposure we adapted a deterministic twocompartment mass-balance model originally developed by Cherrie and Schneider (3). The model consists of two ‘boxes’; a small near-field comprising a virtual cube of 2 metre sides centred on the workers head (8 m3) and a large farfield describing the rest of the room. Each field is assumed to be perfectly mixed
but exchanging air with the other field at a defined rate. This simplification
makes it possible to calculate two components of the exposure, i.e. exposures
originating from near-field sources (e.g. due to a worker’s task) and exposures
originating in the far-field (e.g. due to activities by other workers or other process-related emissions).

Page 17 of 67

RIVM Report 609037002

Figure 3-1: Schematic description of the two compartment model at a workplace
(CFF: concentration in the far-field, CNF: concentration in the near-field).
The basic model is described by two simultaneous differential equations representing the exchange of contaminant mass between the compartments, including mass lost from the system by air exchange with the external environment.

VNF

dCNF
= εNT − CNF .QNF + CFF .QNF
dt

[equation 1]

VFF

dCFF
= εFT + CNF .QNF − CFF .QNF − CFF .QFF
dt

[equation 2]

The volume airflow into and out of the near-field (QNF) defines the exchange between the two compartments (defined by their respective near-field and far-field
volumes, VNF and VFF), while QFF defines the volume airflow from the far-field out
to the external environment (e.g. external ventilation). The mass emission rate
into the near-field (εNT) or into the far-field (εFT) are used to calculate the nearand far-field concentration of a contaminant. These differential equations can be
solved simultaneously over time and allow an iterative calculation of the concentration in each of the compartments.
To be able to implement this model to estimate benzene exposure for a range of
PX-10 exposure scenarios, a number of input parameters were required, including emission rates, room sizes, ventilation rates, bath sizes, working hours,
amounts of replaced PX-10 and the frequency of such replacement (see Appendix 1: Scenario description and input parameters for exposure modelling). The
benzene emission rates were based on experiments carried out at the laboratory
of the IOM (see section 3.3 of this report). The other input parameters were
based on information provided by the focus groups or from information provided
by the Dutch MoD. The airflow between the near- and far-field compartments
(QNF) was arbitrarily set at 10 m3/min, which was based on an estimate of the
airflow arising from convection and some bulk air movement, and was the midvalue chosen by Cherrie (1999) (4). To account for the uncertainties in these
input parameters the model was implemented as a probabilistic model using
Monte Carlo simulations.
3.3

Laboratory experiments
A series of laboratory experiments were carried out at the IOM to estimate the
evaporation rate of benzene from PX-10 and to assess the effect of several factors. In particular the experiments investigated the following:
•
the ‘passive’ evaporation rate of benzene for PX-10 with different levels of
benzene;
Page 18 of 67

RIVM Report 609037002

•
•
•
•
•

the impact of composition of PX-10 such as mineral oil, fatty ester acid on
the benzene evaporation rate;
the change in evaporation rate over time;
the impact of carrying out cleaning activities (i.e. agitating the cleaning solution) on the evaporation rates;
the impact of the air speed over the evaporation surface on the evaporation
rate; and
the impact of the surface area/volume ratio of the container on the evaporation rate.

As production has been discontinued no PX-10 was available for the experiments
and therefore, a mixture of white spirit, mineral oils and fatty acids was prepared for the experiments. The composition was based on the information obtained from the review of the report of the Dutch MoD and based on the old material data sheets (1). Benzene was added for most of the experiments, although
for some experiments simulating cleaning activities, benzene was replaced by
toluene to minimise potential risk for the staff undertaking the experiments.
The experiments were carried out within a fully enclosed box
(31.5 x 31 x 34 cm) inside a ventilated fume cupboard (Figure 3-2). A container
with PX-10 with a volume of 8 cm³ and a surface area of 6.4 cm² was placed
inside the box. The airflow in and out of the box was kept at a constant rate and
mixing of the air was ensured by an internal fan. A carbon filter was used to remove any volatile agents from the air flowing into the box.
The concentration of total VOCs was continuously measured with a direct reading detector (Phocheck photo ionisation detector, model 1000, ION Science Ltd.,
Cambs UK) placed in the box. In addition, benzene in air was sampled with coconut charcoal sorbent tubes which were analysed for benzene according to
NIOSH method 1501.

Volume,
V = 0.033m³

(internal ventilation
assuring complete mixture)

Q1=Q2
(measured)

obstacle

Q2=Q1
(mea sured)

34 [cm]

Filter,
removing
background
aromatic
substances

Ventilator motor: outside box

Airflow 1cm
above the surfa ce
Evapora tion

Pumps
=Q2

Surface
PX-10 liquid

31 [cm]
Figure 3-2: Experimental set up for the determination of the benzene evaporation rate (Q=flow through box [m³/min]).

Page 19 of 67

RIVM Report 609037002

A series of experiments were carried out to test whether the benzene emission
rates increased linearly with the benzene concentration using white spirit mixtures with benzene contents ranging from 0 to 5%.
3.4

Emission rates of benzene and VOCs
The emission rate from the container with PX-10 was calculated from the air
concentration assuming a steady state condition. Under steady-state condition,
the concentration can be associated with the evaporation rate according to the
formula [equation 3].

Css =

G
Q

[equation 3]

Where: Css = Steady state concentration [mg/m³], G = evaporation rate
[mg/min], and Q = Flow through box [m³/min]
The steady state, with stable concentrations of all fractions, could not be maintained as the benzene concentration rapidly declined in the box. Nevertheless
the approach allowed the determination of an initial emission rate and the speed
of the emission decrease over time. The benzene emission rates in the workplaces were estimated using this information on benzene concentration in PX-10
over time and the experimentally determined emission rates. By varying the
benzene concentration in the PX-10 simulation, the relationship between benzene content in PX-10 and emission rate was established. This approach simulated a passive evaporation only. To adjust for active manipulation of PX-10, for
example brush cleaning of items, a test procedure was set up investigating the
impact of active handling of the materials.
The estimation of the benzene emission from the work with soaked PX-10 cloths
was based on the total mass of benzene in the amount of PX-10 that was stated
to be used per day and which was assumed to have evaporated during this day.
The emission rate was calculated as average over the day.
To estimate exposure to total VOCs, it was assumed that white spirit comprised
of a small, highly volatile fraction and a large fraction of medium to low volatile
liquids. The highly volatile part of the aromatic fraction was assumed to consist
mainly of benzene and toluene, while the aliphatic fraction was assumed to consist of hexane and heptane isomers. The evaporation rate of the medium to low
volatile components of PX was essentially constant for the duration of the experiments.
An approximate estimation of the VOCs emission rate was made, assuming that
the information on the evaporation behaviour of benzene in PX-10 (that was determined in the experimental setup) was the same as that for all other highly
volatile components in PX-10.
3.5

Monte Carlo simulation
To take into account some of the uncertainty in the model parameters, a probabilistic approach was used to estimate benzene and total VOCs exposure. For
each model parameter a distribution was provided based on the available information, and a value picked at random for each run of the model. For each scenario the model was run 500 times. The results are provided as the average and
standard deviation over all the runs. The probabilistic model was programmed in
Matlab (Version 7, MathWorks, Natick, Massachusetts, USA).
While running the model for the exposure calculation the input variables for the
model were simulated from triangular distributions, using three defined values:
Page 20 of 67

RIVM Report 609037002

minimum, maximum and mid-point. To determine the sensitivity of the overall
model outcome on changes in the individual input parameters, an additional
sensitivity analysis was performed.
The analysis consisted of the following steps:
•
the mid-points of all the parameters were taken as input parameters for the
model and the resulting exposure estimate was defined as baseline;
•
the model was re-run modifying individually each parameter in the range
from minimum to maximum; and
•
the influence of the individual parameter modification on the outcome of the
model was compared with the baseline value.
3.6

Dermal exposure
Due to the extensive use of PX-10 in the absence of any effective personal protective equipment, the contribution of dermal exposure was considered to be
potentially significant in some of the PX-10 scenarios. Basically two types of
dermal exposure patterns were described for the work with PX-10. The first involved completely submerging the hands in PX-10 for extensive periods. The
second involved manual cleaning of surfaces with a cloth soaked with PX-10.
Both application methods resulted in intense skin contact, although for the latter
the skin surface in contact with PX-10 was smaller (inside palm of only one
hand). Note that the dermal exposure was only estimated for benzene but not
for VOCs as for the latter there were no dermal uptake estimates available.
Reported benzene uptake rates, partially derived from animal toxicological experiments, vary considerably depending on the experimental model used, the
species chosen, the level of benzene applied, length of application, duration of
the contact etc. As a consequence the estimated benzene flux through the skin
varies to a high extent. The dermal contact of the workers with PX-10 was reported to be very intense and there is anecdotal evidence of widespread skin
complaints amongst the former users of PX-10. Therefore, the higher reported
uptake values were considered most appropriate for this population. Based on
the literature review of Nies et al. (5) as well as Nies and Korinth (6) the benzene uptake rates could range from 1 mg/cm²/h for short-term contact to
2 mg/cm²/h for long-term contact with benzene. This value for benzene uptake
rate of 2 mg/cm²/h is furthermore supported by Adami et al. (7) and Sheehan
et al. (8). For the purpose of this study the dermal uptake rate was assumed to
be, on average, 1.5 mg/cm²/h, ranging from 1 to 2 mg/cm²/h.
The internal benzene exposure, resulting from dermal uptake of benzene, was
subsequently converted to equivalent inhalation exposure, based on a model
provided by Nies et al., as well as Nies and Korinth (5, 6):

EIU =

Uptake
BR ⋅ B ⋅ CF

[equation 4]

Where: EIU is the equivalent inhalation unit [ppm];
Uptake is the daily dose of dermal exposure [mg/d];
BR is the breathing rate [m³/8-h d], defined as 10 m³ per shift of 8 h;
B is the inhalation bioavailability factor (no units), defined as 50%; and
CF is the factor to convert concentration to mass per unit volume
[mg/m³], i.e. 1 ppm ≈ 3.2 mg/m³ of benzene.

Page 21 of 67

RIVM Report 609037002

Page 22 of 67

RIVM Report 609037002

4

Results of exposure assessment

4.1

Laboratory experiments

4.1.1

Evaluating the effect of benzene content in PX-10 on the ‘passive’ evaporation
rate
A series of experiments were carried out to test whether the benzene emission
rates increased linearly with benzene content in the mixture, ranging from 0 to
5%. The evaporation rate from the container was estimated under the assumption of steady state conditions. Figure 4-1 shows the measured emission rate in
relation to the level of benzene (%) in the liquid. In experiments without benzene added, the resulting air levels were all below the limit of detection. The
results seem to support a linear relationship between the (initial) evaporation
rate of benzene and the concentration of benzene added to the PX-10 surrogate.

Initial evaporation rate [g/min/m²]

2.0
n=2

y = 0.3482x - 0.0022
R2 = 0.9999
1.5

1.0

0.5
n=6
n=4
n=2
0.0
0

1

2

3

4

Level of added benzene [%]

5

6
linear regression

Figure 4-1: Estimated passive initial benzene emission rate by benzene content
level in PX-10.
The measurement results were extrapolated linearly from the laboratory experiments to provide a benzene emission rate of PX-10 for a bath with a surface
area of 1 m2 using the following linear regression equation:

G = 0.3482 * BC − 0.0022

[equation 5]

Where: G is the evaporation rate (in g/min/m²) and BC is the benzene content
in PX-10 (volume %).
Using this equation and estimates of past benzene levels in PX-10, the benzene
emission rates were estimated for different time periods (Table 4-1).

Page 23 of 67

RIVM Report 609037002

Table 4-1: Estimated benzene emission rates by time period based on benzene
content of PX-10 as estimated previously (1).
Year
Emission rate (g/min/m²)
Average
Minimum
Maximum
<1970
0.03
0.00
0.07
1970-1980
0.01
0.00
0.03
>1980
0.00
0.00
0.01
4.1.2

Effects of other components in PX-10 on benzene emission rates
Experiments were carried out to determine the effect of mineral oil and fatty
ester acid on the benzene evaporation rate. However, the results suggested that
above components did not have any impact on the benzene emission rate from
the PX-10 surrogate (results not shown).
Stability of emission rate over time
Experiments were carried out to determine the stability of the benzene and total
VOCs emission rates over time. The total VOCs concentration in the box remained relatively constant over time at 100 ppm when no benzene was added to
the white spirit mixture, suggesting a stable VOCs emission rate (horizontal grey
line in Figure 4-2). When 5% benzene was added to the white spirit mixture, the
total VOCs levels initially increased dramatically (blue line in Figure 4-2), suggesting the total air VOCs concentration in this situation was dominated by the
benzene levels. However, the total VOCs concentration decreased rapidly over
time because of a decrease in the benzene emission rate. This finding was confirmed by the results of three 10 minute charcoal tube samples, collected at different time periods during the experiment. The implication of the decreasing
emission rate over time was that the benzene content in the PX-10 mixture was
rapidly decreasing, i.e. the mixture is being depleted of benzene.
600

(5% benzene)
500
Benzene and VOC [ppm]

4.1.3

VOC direct measurement

400

Laboratory determined
benzene level
(white spirit ~100ppm)

Measurements

300
VOC best fit extrapolation
(power)
Benzene best fit
extrapolation (exponential)

y = 487.02x -0.60
R2 = 0.9972

200
100

y = 531.36e-0.46x
R2 = 0.9089

0
0

1

2

3

4

5

6

7

8

9

10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Time [h]

Figure 4-2: Total VOCs and benzene concentration over time in the box (measured with 5% benzene in the white spirit mixture). Note the different types of
extrapolation for VOCs (approaching 100 ppm) and benzene (approaching
0 ppm).
Based on these results a half-life of 2 hours was estimated for the benzene content in the PX-10 mixture, which is comparable to results by Nicas et al. (9) who
estimated a half-life of benzene in a petroleum distillates solvent of 3 to 5 hours.

Page 24 of 67

RIVM Report 609037002

Based on the experimental results the emission rate (G) was assumed to decrease exponentially over time according to the following equation:

Gt = e −α ⋅t

[equation 6]

With α as evaporation constant (defining the speed of decrease) and t for time.
In the experiments the α was observed to range from 0.21 to 0.71, the ratio of
the volume to surface area that was used in the experimental set up. In addition, other factors such as sampling and analytical error, as well as any differences in degree of mixing of benzene in the white spirit solution, may also have
played a role. These influences are, however, expected to be minor.
The implication of the exponentially decreasing benzene emission rate over time
was that within a day of filling an open bath with fresh PX-10, the benzene content of the mixture would have been negligible. The long-term average emission
rates of benzene from the PX-10 bath depended therefore on the frequency and
volume of topping up of the bath with fresh PX-10 and on the frequency of complete replacement of a bath with fresh PX-10. According to the focus groups, the
complete replacement of the baths only occurred occasionally (~ once per
month), although topping up of the bath with relatively small amounts of fresh
PX-10 occurred more regularly (~ once per week).
4.1.4

Impact of cleaning activities on the benzene evaporation rate
The emission rates will have been affected by agitation of the liquid in the bath.
Two separate experiments were carried out to simulate the effect of washing
activity on the benzene emission rate. In particular, it was investigated whether
the additional exposure as a result of washing could be thought of as an additional surface equivalent, i.e. passive emission from a notional additional area.
A steel bowl in a fully closed standard laboratory fume hood without ventilation
was used to simulate a washing procedure. The fume hood was transformed into
a glove box (closed lid with inert plastic and gloves to manipulate things inside
the fume hood). Two baths were serially used for this experiment, with surface
areas that differed by a factor 4. For both baths the evaporation rates were
compared between a still bath (no activity) and cleaning activity. The cleaning
activity was simulated by scrubbing a metal piece with a brush dipped every few
seconds in the bowl containing simulated PX-10. To minimise the potential risk
to the person conducting the work, these experiments were carried out with
added toluene instead of benzene. Previous experiments had indicated that the
toluene emission rates were comparable to the benzene emission rates.
The results showed an increased emission rate due to the activity of washing
metal parts. This increase was best described as additional evaporation surface,
not as multiplying factor. An approximation to the added emission was achieved
by calculating the additional surface area for the bath when estimating the total
emission rate of a bath with activity. The additional equivalent bath surface area
required to explain the emission in the experimental setup was estimated to be
800 cm² (uncertainty range 724 cm² to 893 cm²), which corresponded broadly
to the total surface area of the gloves, metal piece, etc. that were in contact
with PX-10. Based on this observation, the influence of the agitation of the passive bath was assumed to be best estimated with the surface that was brought
into contact with PX-10 while carrying out the task. With the help of the task
description this additional evaporation surface was estimated to be around
0.25 m² for each bath (8% of the average batch surface area of 3.2m2). This
Page 25 of 67

RIVM Report 609037002

equivalent surface area due to the cleaning activity was added in the model to
the surface area of the baths to address additional evaporation.
This was a single exploratory experiment in a fume hood, and needed verification before being used in the box model, especially because the results depended on a manual interaction of a person. The setup of the former experiments for the still bath in the box was modified allowing a small metal piece with
a known surface area dipping automatically and repeatedly into the evaporation
container for a PX-10 with 1% benzene. The VOCs emission during this procedure was approximately 9% higher than VOCs emission without the dipper. This
dipping disturbed the surface of the PX-10 and added a known wet surface to
the surface of the evaporation container. A linear correlation was found between
additional evaporation surface ‘x’ and the additional VOCs concentration (VOCs
ppm = 20*x cm² - 2E-13, R² = 0.990). Based on this correlation, the influence
of the disturbed surface was estimated by the surface of the dipper that was in
contact with the mixture. The wet part of the dipper was measured to be around
7.5% which is comparable to the additional solvent emission of 9%.
Both approaches, the up-scaled toluene and the miniature VOCs/benzene, although only explorative, supported the assumption that the emission rates during washing activities could be approximated by simply adding the estimated
equivalent evaporation surface area to the surface area of the bath.
Effect of air speed over evaporation surface on evaporation rate
The air speed over the surface in the box experiment was measured to be
0.24 m/s for the main experiments. To determine the impact of the internal air
speed over the surface, the evaporation was monitored during steady state at
the standard flow rate, the internal ventilation was then increased by having the
fan directly pointing towards the liquid, doubling the air speed over the surface.
This increase approximately doubled the VOCs concentration (Figure 4-3).
1400
Inversed at 16h

1200
VOC [mg/m³]

Steady state

1000
800
600
Steady state

400
200

17:02

16:48

16:33

16:19

16:04

15:50

15:36

15:21

15:07

14:52

0
14:38

4.1.5

Time

Figure 4-3: Effect of increasing air speed (double due to ventilation inversion)
over the evaporation surface on the emission rate.
Although there is a clear effect of air speed on the evaporation rate, it was not
clear whether this has any important implications for the estimated long-term
benzene exposure levels in the PX-10 exposure scenarios. Most of the PX-10
baths were positioned in rooms with little ventilation and the wind speed over
the actual surface was probably low, because the liquid surface would be somePage 26 of 67

RIVM Report 609037002

what below the edge of the bath. Therefore the data collected at 0.24 m/s might
be quite high according to the typical workplace air speed data described by
Baldwin and Maynard (10). On the other hand, use of compressed air was reported to dry the metal components. Clearly this would have resulted in much
higher air speeds and consequently higher evaporation rates. Varying levels of
wind speed over the evaporating surface would result in changes in the half-life
of the benzene content in the PX-10 mixture. While affecting the pattern of exposure, these changes will have little influence on the long-term average exposure to benzene. The baseline VOCs emission, however, will have been influenced by the air speed, which might have led to higher estimates for the VOCs
emission rate. Therefore, the model conditions were assumed to follow the
‘worst case’ conditions with rather high wind speed.
4.1.6

Effect of container dimensions on the benzene evaporation rate
The dimensions of the evaporation container in the experimental box were chosen to approximately reflect the miniaturised dimensions of a bath in a workplace environment of an average room. An additional experiment was carried
out to determine the impact of the shape of the evaporation container on the
benzene emission. A container with double the volume (19 cm³) but the same
surface area of 6.4 cm² was used to obtain an extreme value for the long term
emission rate. With such a container, a half-life value of 13 hours was measured
compared to 2 hours in the used container.
A sensitivity analysis was undertaken to assess the impact of different decrease
rates, comparing the model outcomes. The daily average for the exposure to
benzene did not change very much using either of the decrease rates. A 2 hour
half-life was therefore applied in the main modelling assuming that the chosen
dimensions are closer to the up-scaled bath dimensions.

4.1.7

Cleaning torpedoes
It was assumed that the emission rate for situations like the washing of torpedoes with a cloth was best described as a repeated total evaporation of a certain
amount of PX-10. The situation is similar to the situation described by Nicas et
al. (9) for the liquid wrench (a cleaning, lubricant agent). However, it was very
difficult to determine the correct surface area for PX-10 in this task. The calculation of a surface evaporation was therefore omitted and the exposure to benzene and total VOCs for this scenario was estimated by the daily amount of PX10 used for this activity as estimated by the focus groups. It was assumed that
all of the benzene evaporated quickly from the thin layer when applied with a
cloth to a metal surface. For the estimation of the daily exposure to benzene in
the model a total evaporation in the near-field of a worker of all benzene (estimated by the amount of PX-10 used per day) was therefore assumed.

4.1.8

Summary of laboratory experiments
The main conclusion from the laboratory experiments was that the emission rate
for benzene from PX-10 was not constant but decreased rapidly over time because of its higher vapour pressure compared to white spirit. This observation
had significant implications for the predicted benzene exposure level for the exposure scenarios where metal parts were cleaned in an open bath (scenario 15). In contrast, this observation has limited or no impact on the exposure during
the scenario that involved cleaning metal surfaces with a cloth soaked in PX-10
(scenario 6), as it was assumed that this activity will have always been carried
out with fresh PX-10.

Page 27 of 67

RIVM Report 609037002

4.2

Model estimates for benzene exposure
To account for the uncertainties in the various input parameters a deterministic
model was implemented using probabilistic techniques. There was uncertainty in
the emission rate, room size, air change rate and the parameters associated
with the likely dermal uptake.
Table 4-2 lists the input parameters used with triangular distribution and the
sources on which they were based (see Appendix 1 for detailed information on
the ranges used in each of the scenarios). For each scenario the outcomes of the
model are presented as average and standard deviation of the simulations. The
values are presented as inhalation exposure (in ppm) and as dermal uptake, the
latter expressed as inhalation-equivalent (in ppm-eq.), according to the model
by Nies et al. (5, 6) and Williams et al. (11).
The emission rates in the model were either based on the results of the experiments (for cleaning parts within a bath, scenario 1-5) or based on the total
amount of (fresh) PX-10 used (for cleaning of the torpedo tube, scenario 6). The
latter was calculated, given the amount used per day and the assumption that
all benzene contained within the fresh PX-10 evaporated during eight hours.
The percentage of benzene content in PX-10 during various time periods was
based on information obtained from the literature and expert review, and are
lower than were originally estimated by the Dutch MoD (1). For the exposure
scenarios where metal parts were cleaned in an open bath, two events occurred
with certain regularity in the scenarios: a) the weekly top-up of PX-10 in a bath
and b) much less frequently, a complete renewal of the bath.
Table 4-2: List of input parameters for the modelling (see Appendix 1 for more
details).
Parameter

Source the parameter is based on

Scenarios

Obtained from focus group discussions

Emission Rate

1)
2)
3)

Experiments
Amount of PX-10 used daily
Benzene level of PX-10 for specified time
periods, as estimated previously (1)

Emission decrease rate

Experiments

Air change rate

Focus groups

Room Volume

Focus groups

Hours worked

Focus groups

Percentage of time spent in NF & FF

Focus groups

Local ventilation

Focus groups

Dermal uptake rate

Literature

Fraction of benzene in solution

Benzene level of PX-10 for specified time periods, as estimated previously (1)

Exposure duration

Focus groups

Surface area

Literature

Breathing rate

Literature

Inhalation bioavailability factor

Literature

Conversion factor (from mg/m3 to ppm)

Literature

Page 28 of 67

RIVM Report 609037002

4.2.1

Benzene exposure after top-up of PX-10 baths
The probabilistic model was run for the different time periods, scenarios and the
two exposure routes (inhalation and dermal). Due to the rapid evaporation of
benzene from the open bath of PX-10, the actual benzene content in the bath
would have been negligible within a day of topping up a bath with fresh PX-10.
Note that the added amount of benzene following a top-up was rather limited
compared to the size of the bath. In general this was assumed to have occurred
once a week. Information on the frequency and the amount of PX-10 top-up was
obtained from the focus groups. The evaporation rate was calculated for the
bath scenarios by calculating the concentration of benzene in the bath given the
amount of added PX-10 and dividing it by the volume of the bath.
C bath = C PX − 10 ⋅

Volume

top − up

Volume

bath

[equation 7]

In the case of replacement of all PX-10 in the bath, the whole volume of added
PX-10 was considered to have the benzene concentration as estimated previously (1).
4.2.2

Average daily benzene exposure from near-field and far-field sources
Tables 4-3 and 4-4 show the 8 hour-Time Weighted Average (TWA) predicted
inhalation, dermal and combined benzene exposures for working with a source
in the near-field (NF) only (Table 4-3) and for working with a source in the farfield (FF) only (Table 4-4).
The frequencies with which the baths of PX-10 were completely replaced substantially influenced the exposure to benzene. For each scenario the frequency
of total PX-10 replacement has been estimated using information obtained during the focus groups:
•
Armouries: from 12/year to 2-3/year;
•
Ships: from 12/year to 4/year;
•
Workshops: 12/year (one response only); and
•
Washing room: 40/year (one response only). This last statement has been
ignored, as, firstly, it contradicts the focus group discussion where a less
frequent ‘topping up’ was stated.
Weekly average exposures were estimated for weeks with 1) a complete bath
replacement and 2) PX-10 top-up. The top-ups and full bath replacements were
assumed to occur at the start of the week. The weekly average exposures were
estimated based on the declining exposure levels during the week, with relatively high exposures on the day of full PX-10 replacements and top-ups. The
yearly average exposure was calculated based on the information obtained from
the focus groups on the frequencies of bath replacements and top-ups. Exposure
was assumed to occur only during week days; no holiday breaks were included
for the calculation of annual average exposure.

Exposure year Ø = α ⋅ Exposuretop − up Ø + β ⋅ Exposure full − replacement Ø
[equation 8]
Where: Exposuretop-up is the exposure during top-up and Exposurefull-replacement is
the exposure during full replacement of the bath. Appendix 1 provides
the values for the ranges for the top-up and PX-10 replacement frequencies for each scenario.
Page 29 of 67

RIVM Report 609037002

Table 4-3 shows the average benzene exposure based on 8 hour work shifts that
are exclusively spent with a source in the near-field, i.e. next to a bath or working with the soaked cloth. These results do not reflect the actual work hours.
Results are presented for the inhalation exposure and the dermal exposure as
well as the combined exposure. The combined exposures show values in the
range of 0.02 to 0.9 ppm for the highest exposure estimates (i.e. years before
1970). The dermal exposure was much lower than the inhalation exposure for
scenarios 1 to 5. However, for scenario 6 the (inhalation equivalent) exposure
by the dermal route was similar as the inhalation exposure. This was due to
intense dermal contact with fresh PX10, increasing the dermal exposure, and the
large size of the torpedo hall, which resulted in a reduction of the inhalation exposure compared with similar activities in a small room.
Table 4-4 shows the average benzene exposure based on the weekly average of
8 hour work shifts that are exclusively spent with a source in the far-field but
not in the near-field. Due to the small dimensions of some of the rooms and the
low ventilation rates, the inhalation exposure levels for far-field sources are
similar to the near-field values except for the large torpedo halls. No dermal exposure was calculated for these situations, because a far-field source would not
lead to dermal exposure (Table 4-5).

Page 30 of 67

RIVM Report 609037002

Table 4-3: Yearly average benzene exposure based on weekly average of 8 hour work ONLY in the near-field (NF).
Yearly 8h NF inhalation
Yearly 8h dermal estimation
No Description
Year
(inhalation equivalent)

1

Cleaning small
arms in weapon
rooms

2

Cleaning small
arms onboard of
ships
Cleaning small
arms in small
workshops

3

4

5

6

Cleaning small
arms in large
workshops
Washing of torpedo parts in the
adjacent room
Maintenance torpedoes onshore

Before 1970
1970-1980
After 1980
Before 1970
1970-1980
After 1980
Before 1970
1970-1980
After 1980
Before 1970
1970-1980
After 1980
Before 1970
1970-1980
After 1980
Before 1970
1970-1980
After 1980

Mean
[ppm]
0.505
0.225
0.049
0.272
0.114
0.026
0.071
0.029
0.005
0.014
0.006
0.001
0.174
0.080
0.026
0.528
0.233
0.072

5th
[ppm]
0.213
0.089
0.019
0.104
0.041
0.010
0.027
0.011
0.002
0.005
0.002
0.001
0.057
0.025
0.008
0.202
0.074
0.024

95th
[ppm]
0.914
0.406
0.087
0.472
0.208
0.048
0.125
0.054
0.009
0.025
0.011
0.003
0.331
0.154
0.054
0.875
0.415
0.132

Mean
[ppm eq.]
0.011
0.005
0.002
0.011
0.005
0.002
0.011
0.005
0.002
0.011
0.005
0.001
0.011
0.005
0.002
0.368
0.159
0.050

5th
[ppm eq.]
0.004
0.002
0.001
0.003
0.002
0.001
0.004
0.002
0.001
0.004
0.002
0.001
0.004
0.002
0.001
0.102
0.048
0.013

95th
[ppm eq.]
0.021
0.010
0.003
0.022
0.010
0.003
0.021
0.010
0.003
0.020
0.010
0.003
0.021
0.010
0.003
0.672
0.314
0.097

Total (inhalation and dermal)
yearly 8h NF inhalation equivalent
Mean
5th
95th
[ppm eq.] [ppm eq.] [ppm eq.]
0.516
0.218
0.935
0.231
0.091
0.416
0.051
0.020
0.090
0.283
0.107
0.494
0.119
0.043
0.218
0.028
0.010
0.051
0.082
0.031
0.146
0.034
0.013
0.063
0.006
0.002
0.012
0.025
0.010
0.045
0.011
0.004
0.021
0.003
0.001
0.005
0.185
0.061
0.352
0.085
0.027
0.163
0.028
0.009
0.057
0.896
0.304
1.547
0.392
0.122
0.729
0.122
0.037
0.230

Note that these numbers are NOT the peak exposure values after a top-up or full replacement – the values of this table take into consideration the decrease over
the week.
The values are shown with a resolution of three digits after the decimal separator, be aware that this high resolution is provided to avoid zero values.

Page 31 of 67

RIVM Report 609037002

Table 4-4: Yearly average benzene exposure based on 8 hour work ONLY in the far-field (FF).
Yearly FF inhalation
Yearly dermal estimation
No Description
Year

1

Cleaning small
arms in weapon
rooms

2

Cleaning small
arms onboard of
ships
Cleaning small
arms in small
workshops

3

4

5

6

Cleaning small
arms in large
workshops
Washing of torpedo parts in the
adjacent room
Maintenance torpedoes onshore

Before 1970
1970-1980
After 1980
Before 1970
1970-1980
After 1980
Before 1970
1970-1980
After 1980
Before 1970
1970-1980
After 1980
Before 1970
1970-1980
After 1980
Before 1970
1970-1980
After 1980

Mean
[ppm]
0.511
0.223
0.049
0.273
0.113
0.026
0.066
0.026
0.005
0.007
0.003
0.001
0.170
0.078
0.026
0.041
0.019
0.005

5th
[ppm]
0.208
0.088
0.020
0.104
0.043
0.011
0.024
0.010
0.002
0.003
0.001
0.000
0.057
0.026
0.008
0.016
0.006
0.002

95th
[ppm]
0.933
0.397
0.090
0.476
0.208
0.049
0.119
0.048
0.009
0.013
0.005
0.001
0.330
0.152
0.051
0.081
0.040
0.011

No dermal exposure

No dermal exposure was assumed
to occur as this is the far-field of a
working person

Total (inhalation and dermal)
yearly FF inhalation equivalent
Mean
5th
95th
[ppm eq.] [ppm eq.] [ppm eq.]
0.511
0.208
0.933
0.223
0.088
0.397
0.049
0.020
0.090
0.273
0.104
0.476
0.113
0.043
0.208
0.026
0.011
0.049
0.066
0.024
0.119
0.026
0.010
0.048
0.005
0.002
0.009
0.007
0.003
0.013
0.003
0.001
0.005
0.001
0.000
0.001
0.170
0.057
0.330
0.078
0.026
0.152
0.026
0.008
0.051
0.041
0.016
0.081
0.019
0.006
0.040
0.005
0.002
0.011

Note that the far-field inhalation exposure for the scenario ‘washing of torpedo parts in the annexed room to the torpedo hall’ is based on the FF of the ‘maintenance torpedoes in the torpedo hall’ and therefore based on the less accurate total mass-approach. Note furthermore that these numbers are NOT the peak exposure values after a top-up or full replacement – the values of this table take into consideration the decrease over the week. The values are shown with a resolution
of three digits after the decimal separator, be aware that this high resolution is provided to avoid zero values.

Page 32 of 67

RIVM Report 609037002

4.2.3

Average daily benzene exposure from near-field and far-field sources adjusted
for reported daily working hours at the PX-10 task
Using the average work hours that were reported by the focus group members
for the PX-10 activities, the yearly exposure estimates were adjusted using the
following procedure:
•
The time spent on working with PX-10 (NF source) was introduced in the
probabilistic modelling, using the range described by the focus group members; and
•
The total working time on a day was assumed to be 8 hours. If the time
spend on the activity was less than 8 hours, then the remainder of the 8
hours was taken to be the time spent elsewhere. The remainder of the time
was selected to be in the far-field for this PX-10 activity, in the far-field for
another PX-10 task or in a non-exposed area, depending on the scenario description (see Appendix 1).
Based on these calculations an estimated average exposure for a worker was
calculated for each scenario. Table 4-5 presents the results for the inhalation
exposure and the dermal exposure as well as the combined exposure. The combined results show values in the range of 0.01 to 0.5 ppm for the highest exposure estimates (years before 1970). These average values were only slightly
lower than the estimated 8 hour values, which can be explained by the fact that
for many tasks the focus group stated long working hours – either in the nearfield or in the far-field, but only little time at another places.

Page 33 of 67

RIVM Report 609037002

Table 4-5: Yearly average benzene exposure based on the reported work hours spent in the near- and far-field (NF&FF) respectively.
Yearly NF&FF inhalation
Yearly dermal estimation (inhalaTotal (inhalation and dermal)
No Description
Year
tion equivalent)
yearly inhalation equivalent
Mean
5th
95th
Mean
5th
95th
Mean
5th
95th
[ppm]
[ppm]
[ppm]
[ppm eq.]
[ppm eq.]
[ppm eq.]
[ppm eq.]
[ppm eq.]
[ppm eq.]
1
Cleaning small
Before 1970
0.444
0.300
0.598
0.007
0.004
0.010
0.451
0.304
0.608
arms in weapon
1970-1980
0.194
0.127
0.265
0.003
0.002
0.005
0.197
0.129
0.270
rooms
After 1980
0.043
0.029
0.056
0.001
0.001
0.001
0.044
0.029
0.058
2
Cleaning small
Before 1970
0.284
0.194
0.378
0.004
0.002
0.006
0.287
0.196
0.384
arms onboard of
1970-1980
0.120
0.081
0.163
0.002
0.001
0.003
0.122
0.082
0.165
ships
After 1980
0.028
0.019
0.038
0.001
0.000
0.001
0.029
0.019
0.039
3
Cleaning small
Before 1970
0.070
0.047
0.096
0.004
0.002
0.006
0.074
0.049
0.101
arms in small
1970-1980
0.029
0.019
0.039
0.002
0.001
0.003
0.030
0.020
0.041
workshops
After 1980
0.005
0.003
0.007
0.001
0.000
0.001
0.006
0.003
0.008
4
Cleaning small
Before 1970
0.129
0.066
0.201
0.008
0.004
0.013
0.137
0.070
0.213
arms in large
1970-1980
0.059
0.029
0.093
0.004
0.002
0.006
0.062
0.031
0.099
workshops
After 1980
0.020
0.010
0.032
0.001
0.001
0.002
0.021
0.010
0.034
5
Washing of torBefore 1970
0.009
0.006
0.013
0.004
0.002
0.005
0.013
0.008
0.018
pedo parts in the
1970-1980
0.004
0.003
0.005
0.002
0.001
0.003
0.006
0.004
0.008
adjacent room
After 1980
0.001
0.001
0.001
0.000
0.000
0.001
0.001
0.001
0.002
6
Maintenance torBefore 1970
0.307
0.160
0.522
0.199
0.043
0.435
0.506
0.203
0.957
pedoes onshore
1970-1980
0.136
0.065
0.241
0.086
0.021
0.199
0.222
0.086
0.44
After 1980
0.044
0.022
0.075
0.027
0.006
0.063
0.071
0.028
0.138
The values are shown with a resolution of three digits after the decimal separator, be aware that this high resolution is provided to avoid zero values.

Page 34 of 67

RIVM Report 609037002

Sensitivity analysis
Sensitivity analyses were carried out to test whether one of the main input variables dominated the results. The calculations used only the deterministic model
with average parameter values and the outcome of the individual modifications
of the parameters ‘air exchange rate’, ‘room volume’ and the two emission rates
in the near- and far-field using the minimum and maximum value of their range.
The subsequent input variables influenced the model similarly in all scenarios
which suggested that none of them dominated the results.

Scenario 2

Scenario 3

Scenario 4

Scenario 5

Scenario 6

Table 4-6: Sensitivity analysis of the parameters used in the Monte Carlo model.
The influence on the outcome was expressed relative to the average outcome.
Scenario 1

4.2.4

Minimum

2.49

1.43

2.73

2.06

2.43

1.57

Maximum

1.11

1.11

1.1

1.06

4.26

1.04

Minimum

0.91

0.91

0.92

0.95

0.51

0.97

Maximum

1.52

1.61

1.56

2.98

1.78

1.93

NF emission rate

Minimum

0.35

0.44

0.39

0.6

0.58

0.71

Maximum

2.49

1.43

2.73

2.06

2.43

1.57

FF emission rate

Minimum

0.63

0.77

0.65

0.78

0.64

0.88

Maximum

0.91

0.91

0.92

0.95

0.51

0.97

Minimum

1.56

1.56

1.56

1.56

1.56

1.56

Maximum

0.83

0.83

0.83

0.83

0.83

0.83

Air exchange rate
Room volume

Half-life *

Scenario 1: Weapon room maintenance (military): small arms
Scenario 2: Onboard maintenance (military): small arms
Scenario 3: Workshop in small room (civilians): small arms
Scenario 4: Workshop in large room (civilians): small arms
Scenario 5: Washing room: small parts of torpedoes in bath
Scenario 6: Torpedo hall: the main body of the torpedoes
*) Calculation based on the values of α ranging from 0.6 - 2.3. No estimation for the scenario d without a bath was calculated.

As expected of a multiplicative model that depends equally on the emission rate,
size of room and rate of air exchange, the outcome of the sensitivity analysis did
not show a dominating variable.
A sensitivity analysis for different emission rate decreases (expressed as the
evaporation constant: α) were carried out. The half-life time of 1.2 hour (alpha
0.6) was used to calculate the baseline of the model and other half-lifes were
compared to it. The initial emission rate was adjusted to account for the change
in the decrease rate so that the same total amount of benzene was emitted over
time, regardless of the half-life. As would be expected the shorter half-life (α
=1.2) resulted in most of the benzene being emitted during the first 8 hours
(workday). The slower decrease rate (α = 0.3) resulted in lower exposures during the first 8 hours, and as the remainder of the benzene would have been
emitted overnight when no operators were present, the overall average exposure would have also been lower.
Page 35 of 67

RIVM Report 609037002

Table 4-7: Sensitivity analysis for the half-life of the benzene emission rate used
in the Monte Carlo model.
Approximated
0.6
1.2
2.3
4.6
9.2
18.5
half-life [h]
α [h-1]
1.2
0.6
0.3
0.15
0.075
0.0375
Exposure relative to α=0.6
1.56
1.00
0.83
0.76
0.73
0.70
α = the evaporation constant (see equation [6])

4.3

Model estimates for VOCs exposure
The total VOCs emission rate from fresh PX-10 was initially dominated by the
highly volatile components of the mixture. In addition to benzene, other highly
volatile agents would have been present in PX-10, both aromatic (e.g. benzene,
toluene) and aliphatic hydrocarbons (e.g. hexane and heptane). This approach
of distinction between a highly and a lower evaporative fraction is supported by
Kopstein (12). The total highly volatile fraction in the PX-10 was unknown and
had therefore to be estimated using the following assumptions:
1. the highly volatile fraction was the same for the aromatic and aliphatic fraction in PX-10;
2. PX-10 consisted of 80% aliphatic and 20% aromatic hydrocarbons. This is
based on the safety data sheet information on the composition of PX-10 over
time which suggests that the aromatic content was around 20% until approximately 1987, after which time PX-10 was no longer used in large quantities (1); and
3. the highly volatile components in the aromatic fraction consisted of benzene
and toluene in equal quantities (see Table 3-2).
Table 4-8 provides the estimates of the total highly volatile faction of PX-10 for
three different time periods.
Table 4-8: Estimation for the composition of the total highly volatile fraction of
PX-10.
Before 1970
1970-1980
After 1980
Average Upper
Average Upper
Average Upper
limit
limit
limit
Total aromatic
20%
20%
20%
20%
20%
20%
Benzene total
0.10%
0.20%
0.03%
0.10%
0.01%
0.03%
Toluene total
0.10%
0.20%
0.03%
0.10%
0.01%
0.03%
Total highly
0.20%
0.40%
0.06%
0.20%
0.02%
0.06%
volatile aromatic
Total aliphatic
80%
80%
80%
80%
80%
80%
Hexane total
0.40%
0.80%
0.12%
0.40%
0.04%
0.12%
n-Heptane total
0.40%
0.80%
0.12%
0.40%
0.04%
0.12%
Total highly
0.80%
1.60%
0.24%
0.80%
0.08%
0.24%
volatile aliphatic
Total highly
1.0%
2.0%
0.3%
1.0%
0.1%
0.3%
evaporative
To estimate the emission rate for the highly volatile components of PX-10 it was
assumed that they all evaporated at the same rate as benzene. After the highly
volatile fraction was evaporated, VOCs continued to be emitted from the mixture
at a constant rate. This constant emission rate was estimated based on the ex-

Page 36 of 67

RIVM Report 609037002

perimentally determined evaporation rate of modern white spirit, which has a
very small highly volatile fraction.
In the experimental box, the baseline of white spirit was measured to be
100 ppm (under the given box properties and flow rates). This was extrapolated
to a 1 m² bath (by analogy with the benzene rate, a flow of 2 L/min and a surface of 6.4 cm² but with the weight conversion for white spirit of
1 ppm = 5.5 mg/m³ (13)). This corresponded to a constant VOCs emission rate
of 100 ppm or 1.7 g/min/m² of modern white spirit and provided the estimation
for the constant baseline VOCs emission of PX-10. Sizes of the baths were also
adjusted to account for active washing of equipment in the VOCs emission modelling.

Evaporation rate [g/min/m²]

Figure 4-4 shows the resulting VOCs emission rate for fresh PX-10 before 1970,
when the total highly volatile fraction of PX-10 was assumed to be 1%. The
highly volatile fraction rapidly evaporated out of the bath, leading to elevated
VOCs concentrations, followed by a decrease in VOCs emission, until the system
reached the baseline emission rate.

highly evaporative fraction < 1970

2.4
2.2

baseline evaporation

2
1.8
1.6
1.4

Calculated VOC (4 highly evaporative at totally 1%, decreasing with EXP (0.45*t) [g/min/m²]

1.2

Measured constant VOC evaporation rate of white spirit [g/min/m²]

1
0

1

2

3

4

5

6

7

8

9

10 11 12
Time [h]

13

14

15

16

17

18

19

20

21

Figure 4-4: Estimated VOCs emission rate over time of PX-10 – example of new
PX-10 bath.
According to equation [5] the highly volatile fraction in PX-10 had an initial
emission rate of 0.346 g/min/m², assuming that all the highly volatile components evaporated at the same rate as benzene.
Based on this decreasing emission rate, which approximates the baseline after
about 6 hours, the probabilistic exposure model was used as described for the
benzene concentration modelling. The subsequent tables show the results for
total VOCs exposure. They are presented in the same manner as above, however, only for inhalation exposure due to badly defined dermal uptake of VOCs:
•
Long-term average exposure from near-field activities assuming the activity
takes up the entire working day (Table 4-9);
•
Long-term average exposure from far-field activities, assuming the activity
takes up the entire working day (Table 4-10); and
•
Long-term average exposure, based on the reported actual duration of exposure to VOCs from near-field and far-field sources (Table 4-11).
It is apparent in the subsequent three tables that the highly volatile fraction was
a minor part of the average yearly exposure to VOC.

Page 37 of 67

22

23

24

RIVM Report 609037002

Table 4-9: Yearly average VOCs exposure based on 8 hour work ONLY in nearfield (NF).
No Description
Year
Yearly 8h NF inhalation
mean
5th
95th
[ppm]
[ppm]
[ppm]
1
Before 1970
96
76
118
Cleaning small
arms in weap1970-1980
92
72
113
on rooms
After 1980
95
74
118
2
Before 1970
55
48
63
Cleaning small
arms onboard
1970-1980
54
46
62
of ships
After 1980
53
46
61
3
Before 1970
14
11
17
Cleaning small
arms in small
1970-1980
14
10
17
workshops
After 1980
13
10
17
4
Before 1970
3
2
3
Cleaning small
arms in large
1970-1980
3
2
3
workshops
After 1980
3
2
3
5
Washing of
Before 1970
33
23
45
torpedo parts
1970-1980
34
22
47
in the adjacent
34
23
48
room
After 1980
6
Before 1970
168
152
183
Maintenance
torpedoes on1970-1980
153
138
168
shore
After 1980
149
134
163
Note that these numbers are NOT the peak exposure values after a top-up or full replacement – the values of this table take into consideration the decrease over the week.

Table 4-10: Yearly average VOCs exposure based on 8 hour work ONLY in farfield (FF).
No Description
Year
Yearly 8h FF inhalation
mean
5th
95th
[ppm]
[ppm]
[ppm]
Before 1970
95
75
118
Cleaning small
1
arms in weap1970-1980
91
72
112
on rooms
After 1980
93
71
119
Before 1970
55
47
62
Cleaning small
2
arms onboard
1970-1980
53
46
61
of ships
After 1980
52
45
60
Before 1970
12
9
16
Cleaning small
3
arms in small
1970-1980
12
9
16
workshops
After 1980
12
9
16
Before 1970
1
1
2
Cleaning small
4
arms in large
1970-1980
1
1
2
workshops
After 1980
1
1
2
Washing of
Before 1970
32
21
43
torpedo parts
1970-1980
33
21
46
5
in the adjacent
room
After 1980
33
21
46
Before 1970
16
12
22
Maintenance
6
torpedoes on1970-1980
15
11
19
shore
After 1980
14
10
19
Note that the far-field inhalation exposure for the Scenario ‘washing of torpedo parts in the
annexed room to the torpedo hall’ is based on the FF of the ‘maintenance torpedoes in the
Page 38 of 67

RIVM Report 609037002

torpedo hall’ and therefore based on the less accurate total mass-approach. Note furthermore that these numbers are NOT the peak exposure values after a top-up or full replacement – the values of this table take into consideration the decrease over the week.

Table 4-11: Yearly average VOCs exposure based on the reported work hours
spent in the near- and far-field respectively.
No Description
Year
Yearly NF&FF inhalation accounted
for work hours and location
mean
5th
95th
[ppm]
[ppm]
[ppm]
1
Before 1970
78
69
88
Cleaning small
arms in weap1970-1980
75
65
84
on rooms
After 1980
77
68
88
2
Before 1970
54
50
58
Cleaning small
arms onboard
1970-1980
53
49
57
of ships
After 1980
53
49
56
3
Before 1970
13
11
14
Cleaning small
arms in small
1970-1980
12
11
14
workshops
After 1980
12
11
14
4
Before 1970
2
2
2
Cleaning small
arms in large
1970-1980
2
2
2
workshops
After 1980
2
2
2
5
Washing of
Before 1970
27
20
43
torpedo parts
1970-1980
27
19
46
in the adjacent
room
After 1980
27
20
46
6
Before 1970
97
60
148
Maintenance
torpedoes on1970-1980
88
53
132
shore
After 1980
86
51
128
Note that the far-field inhalation exposure for the Scenario ‘washing of torpedo parts in the
annexed room to the torpedo hall’ is based on the FF of the ‘maintenance torpedoes in the
torpedo hall’ and therefore based on the less accurate total mass-approach. Note furthermore that these numbers are NOT the peak exposure values after a top-up.

Page 39 of 67

RIVM Report 609037002

Page 40 of 67

RIVM Report 609037002

5

Quantification of potential health effects

5.1

Methods: life table analysis
In life table analysis a hypothetical cohort of subjects is followed from birth
through death. For each age (year) the following aspects are calculated: the size
of the population at risk, the number of cases of a specific health outcome that
arises in an unexposed population, the (cumulative) exposure for exposed individuals in the populations, and the number of cases of a specific health outcome
in the exposed population. By combining this information the Excess Risk (ER)
(the number of additional cases per 100.000 exposed individuals) can be expressed as a function of age. The steps in the life table analysis are illustrated in
Figure 5-1.
Estimate the size of the population at risk (Figure 5-1A)
Data from Statistics Netherlands (CBS) were used to estimate the population at
risk for each age (in years) between the ages 0 to 100 years. The population at
risk is defined as the percentage of the population at age 0 that is still capable of
developing health effects associated to benzene exposure. In case of death individuals leave the population at risk. Between the ages 0 and 100 years the population at risk decreases from 100% (at age 0) to <1% (at age 100).
Number of cases in the unexposed population (Figure 5-1B; 5-1C;
Table 5-1)
Data from the Comprehensive Cancer Centre (IKC) were used (1989-2008) to
estimate age-specific incidence rates for the relevant diseases in a population
that is not occupationally exposed to benzene. The age-specific incidence rates
are combined with the age-specific size of the population at risk to calculate the
number of incident cases in the unexposed population at risk.
Table 5-1: Expected number of cases in unexposed population (100,000) till the
age of 120 (source: Comprehensive Cancer Centre).
# Cases
Total Leukaemia

1121

Acute Myeloid Leukaemia (AML)

334

Acute Lymphocytic Leukaemia (ALL)

118

Chronic Lymphocytic Leukaemia (CLL)

496

Non-Hodgkin Lymphoma (NHL)

1769

Multiple Myeloma (MM)

1446

Exposure (Figure 5-1D)
In life table analyses of chronic exposures, cumulative exposure is generally
used as exposure metric. Cumulative exposure is the product of intensity and
duration of exposure. It is a standard exposure metric used in many occupational studies of chronic health effects as index of the target tissue dose. Here
we generate cumulative exposure estimates for two hypothetical individuals
based on two realistic exposure scenarios and the yearly average benzene exposure estimates incorporating the inhalation and dermal route of exposure (Table
Page 41 of 67

RIVM Report 609037002

4-5). These scenarios (one military and one civilian) were chosen as they are
two ‘high’ exposed scenarios as provided by MoD. The career scenarios are presented in Table 5-2. The exposure scenarios are presented in Tables 5-3 and 54.
Table 5-2: Assumptions exposure scenarios.
Career 1 ‘military personnel of the
Navy’
Cleaning small arms in weapon rooms and
on ships

Career 2 ‘civilian’

Duration career:
Start career:

38 yrs (age 18-55)
1964

Duration career: 48 yrs (age 18-65)
Start career:
1945
Exposure:
8 hours/day

Rotation land-ship:

3 yrs

Cleaning small arms in small workshops

Full duration of career at the same workplace

Phase 1 (Seaman)
Duration:
Exposure:

6 yrs
4-8 hours/day

Phase 2 (Corporal)
Duration:
Exposure:

9 yrs
1-4 hours/day

Phase 3 (Sergeant)
Duration:
Exposure:

until end of career
several hours/month

Table 5-3: Scenario ‘Cleaning small arms in weapon rooms and on ships’.
Year
Year
Age
Age Duration Work locaRank
Hrs/day
start end
start end (years)
tion
1964
1967
1970
1973
1976
1979
1981
1982
1985
1988
1991
1994
1997
2000

1966
1969
1972
1975
1978
1980
1981
1984
1987
1990
1993
1996
1999
2001

Page 42 of 67

18
21
24
27
30
33
35
36
39
42
45
48
51
54

20
23
26
29
32
34
35
38
41
44
47
50
53
55

3
3
3
3
3
2
1
3
3
3
3
3
3
2

weapon room
ship
weapon room
ship
weapon room
ship
ship
weapon room
ship
weapon room
ship
weapon room
ship
weapon room

Seaman
Seaman
Corporal
Corporal
Corporal
Sergeant
Sergeant
Sergeant
Sergeant
Sergeant
Sergeant
Sergeant
Sergeant
Sergeant

6
6
2.5
2.5
2.5
1
1
1
1
1
1
1
1
1

Cumulative
exposure
(ppm-yr)
1.16
1.78
2.00
2.11
2.32
2.35
2.35
2.37
2.38
2.40
2.41
2.42
2.42
2.42

RIVM Report 609037002

Table 5-4: Scenario ‘Cleaning small arms in workshops’.
Year
Year
Age
Age Duration Hrs/day Cumulative
start end
start end (years)
exposure
(ppm-yr)4
1945 1947 18
20
3
8
0.22
1948 1950 21
23
3
8
0.44
1951 1953 24
26
3
8
0.67
1954 1956 27
29
3
8
0.89
1957 1959 30
32
3
8
1.11
1960 1962 33
35
3
8
1.33
1963 1965 36
38
3
8
1.55
1966 1968 39
41
3
8
1.78
1969 1969 42
42
1
8
1.85
1970 1971 43
44
2
8
1.91
1972 1974 45
47
3
8
2.00
1975 1977 48
50
3
8
2.09
1978 1980 51
53
3
8
2.18
1981 1983 54
56
3
8
2.20
1984 1986 57
59
3
8
2.22
1987 1989 60
62
3
8
2.23
1990 1992 63
65
3
8
2.25
The cumulative exposure was derived from the exposure estimates described in
chapter 4.
Risk function (Figure 5-1E)
A risk function (dose-response relation) is needed in life table analysis to quantify the relation between cumulative exposure to benzene and the relative risk of
developing an adverse health effect. In the life table analysis multiplicative relative risk functions were derived from meta-regressions of studies on humans
occupationally exposed to benzene, see Table 5-5. A multiplicative relative risk
model assumes that benzene increases the background incidence rate by a multiplicative factor that depends on prior benzene exposure (14). Multiplicative
linear models were fitted for all endpoints (15). In addition, nonlinear models
were fitted for leukaemia and AML (15). These were fitted with and without an
intercept. The intercept in the regression model represents the difference between the background disease rate in the study population as compared to the
referent population. In the life table analysis this difference in background rate
was addressed by subtracting the intercept from all predictions (effectively lowering the predicted (increased) risks for benzene at each exposure level). In addition to the multiplicative models a set of additive models published by the US
Environmental Protection Agency (U.S. EPA) (16) for leukaemia and AML were
applied in the life table analysis. An additive risk model assumes that benzene
increases the background mortality rate by an additive amount that depends on
prior benzene exposure. In Table 5-5 the general form and parameter estimates
for the risk functions used in the life table analyses for leukaemia, AML, MM, and
NHL are presented. Because of the relative high uncertainty in the risk estimates
for CLL and ALL we used the risk function estimate of total leukaemia.

Page 43 of 67

RIVM Report 609037002

Table 5-5: Risk functions used in the life table analysis.
Multiplicative
Multiplicative
Multiplicative
Health
Spline
Spline
Linear
outcome
Intercepta,b
No interceptb,c
No interceptd
β0 = 0.288
β1 = 0.012
β1 = 0.005
Leukaeβ1 = 0.013
β2 = -0.04
e
mia
β2 = -0.024
β0 = 0.273
β1 = 0.023
β1 = 0.005
AMLf
β1 = 0.018
β2 = -0.148
β2 = -0.115
ALL
β1 = 0.005g
CLL
β1 = 0.005g
MM
β1 = 0.006
NHL
β1 = 0.003

Additive
Linear
No intercepte,f
β1 = 1.9e-6

β1 = 2e-6

Risk functions used in the life table analysis
a
General form of a multiplicative model based on a natural spline with intercept:
Ln(RR) = β0 + β1 (X) + β2 [X – ξ1]+3 + β3 [X – ξ2]+3 (16)
b
For the leukaemia spline knots were located at 2.9, 22.7, and 125.5 ppm-yr. For the AML
spline knots were located at 4.3, 17.4, 247.1 ppm-yr. (16)
c
General form of a multiplicative model based on a natural spline without intercept:
Ln(RR) = β1 (X) + β2 [X – ξ1]+3 + β3 [X – ξ2]+3 (16)
d
General form of a linear multiplicative model without intercept: Ln(RR) = β1 ln(X) (16)
e
General form of a linear additive model without intercept: AR= β1 *X (16)
f
Additive models originally published by the U.S. EPA (15)
g
Risk function of leukaemia

Temporal variation in the association between benzene and adverse
health outcomes (Figure 5-1F; 5-1G)
Multistage cancer models predict that the effect of an increment of exposure on
cancer risk may vary with time since (last) exposure. Several studies have
shown that the effect of benzene exposure on leukaemia appears to diminish
with time since exposure (17, 18). Richardson estimated that the relative risk of
leukaemia as the result of exposure to benzene was reduced by 50% every ten
years after effective exposure (17). However, this observation is not unique for
benzene and leukaemia but has also been observed for other exposure-cancer
associations. For example, Hornung et al. (19) showed that in a study of radon
exposure and lung cancer in uranium miners the relative risk for a given cumulative exposure was reduced by 50%, 15 years after effective exposure, compared to current miners and those within 5 years of last exposure. Therefore
there was an exponential decay in relative risk with a half-life of age-specific
relative risk of approximately 15 years.
Three weighting functions were applied in the life table analysis to address reduction in risk with time since last exposure.
1. No weighting function was applied. Additional number of cases were calculated up to 75 years of age. This is the standard procedure used in the calculations of additional cases by the Dutch Health Council.
2. The effect of benzene exposure on the health outcome decreased exponentially with a half-life of 10 years. Additional number of cases calculated at
120 years of age (age at which the full cohort is deceased).
3. The effect of benzene exposure on the health outcome decreased exponentially with a half-life of 15 years. Additional number of cases calculated at
120 years of age (age at which the full cohort is deceased).
Page 44 of 67

RIVM Report 609037002

Excess risk (Figure 5-1H; 5-1I)
By combining information on the size of the population at risk, the number of
cases in the unexposed population, the cumulative exposure, the risk function,
and the temporal variation in the association between benzene and adverse
health outcomes, the Excess Risk (ER) (the number of additional cases per
100,000 exposed individuals) is expressed as a function of age.
(A)

(B)

(C)

(D)

(E)

(F)

(G)

(H)

(I)

Figure 5-1: Illustration of the steps in a life table analysis; demonstrated for
health outcome Acute Myeloid Leukemia (AML) and an exposure of 45 years at
1 ppm.
(A) Estimate of the size of the population at risk. Line indicates the percentage
of the population that is still capable of developing health effects associated
to benzene exposure.
(B) Estimate of the incidence in the unexposed population. Dotted lines are 95%
confidence intervals for the estimate.
(C) Estimate of the absolute number of cases in the unexposed population
(D) Cumulative exposure scenario. Continuous line indicates cumulative exposure. Dotted line is the average intensity of exposure.
Page 45 of 67

RIVM Report 609037002

(E) Relative risk function
(F) Weighting function. Three types of weighting functions are illustrated. From
top to bottom: No weighting, the effect of benzene exposure on the health
outcome decreased exponentially with a half-life of 15 years, the effect of
benzene exposure on the health outcome decreased exponentially with a
half-life of 10 years.
(G) Relative risk function with application of the weighting function
(H) Estimate of the absolute number of cases in the exposed and unexposed
population. Continuous line represents the unexposed population. Dotted
line is the exposed population.
(I) Estimate of the absolute number of excess cases in the population due to
exposure to benzene.
5.2

Results
In Tables 5-6 and 5-7 the outcomes of the life table analysis are presented. The
outcomes are based on a combination of the type of risk model (multiplicative
model vs. additive model), the type of exposure response model (spline vs. linear model), whether an intercept is allowed in the exposure response model
(yes vs. no), and three different approaches to address the temporal variation in
the association between benzene and adverse health outcomes. The main reason to present the outcomes of multiple models is that there is no model that is
universally better. As such these different models represent the uncertainty in
estimated additional cases.
For scenario ‘Cleaning small arms in weapon rooms and on ships’ the additional
number of cases per 100,000 exposed individuals ranges for leukaemia from 3.9
to 26.3 (median 6.5); for AML from 1.4 to 15.0 (median 3.3); for ALL 0.3; for
CLL from 1.7 to 2.9; for NHL from 4.7 to 7.1; and for MM from 7.3 to 11.7.
Table 5-6: Additional number of cases of hematopoietic cancer per 100,000 individuals exposed to benzene according to exposure scenario ‘Cleaning small arms
in weapon rooms and on ships’.
Multiplicative
Multiplicative
Multiplicative
Additive
Spline
Spline
Linear
Linear
Intercept
No intercept
No intercept
No intercepta
1
2
3
1
2
3
1
2
3
1
2
3
Leukae17.7 4.1
7.0
26.3 6.1
10.4 6.0
3.9
4.8
14.1 5.1
6.9
mia
AML
7.5
1.8
3.0
9.5
2.2
3.8
2.1
1.4
1.7
15.0 5.5
7.4
ALL
0.3
0.3
0.3
CLL
2.9
1.7
2.2
NHL
7.1
4.7
5.6
MM
11.7 7.3
9.0
a
Additive model originally published by the U.S. EPA (15)
Where;
1. No weighting function applied to address the temporal variation in the association
between benzene and the health outcome. Additional number of cases calculated at
75 years of age.
2. Effect of benzene exposure on the health outcome decreases exponentially with a
half-life of 10 years. Additional number of cases calculated at 120 years of age (age
at which the full cohort is deceased).
3. Effect of benzene exposure on the health outcome decreases exponentially with a
half-life of 15 years. Additional number of cases calculated at 120 years of age (age
at which the full cohort is deceased).

Page 46 of 67

RIVM Report 609037002

Table 5-7: Additional number of cases of hematopoietic cancer per 100,000 individuals exposed to benzene according to exposure scenario ‘Cleaning small arms
in small workshops’.
Multiplicative
Multiplicative
Multiplicative
Additive
Spline
Spline
Linear
Linear
Intercept
No intercept
No intercept
No intercepta
1
2
3
1
2
3
1
2
3
1
2
3
Leukae20.3 2.6
5.2
30.3 3.9
7.8
6.9
2.6
3.6
19.8 6.0
8.2
mia
AML
8.7
1.2
2.3
11.0 1.5
2.9
2.4
0.9
1.3
21.0 6.4
8.8
ALL
0.4
0.4
0.4
CLL
3.2
0.9
1.5
NHL
8.1
2.8
4.1
MM
13.2 4.0
6.2
a

Additive model originally published by the U.S. EPA (15). For explanation of 1 -3, see
Table 5-6.

For scenario ‘Cleaning small arms in workshops’ the additional number of cases
per 100,000 exposed individuals ranges for leukaemia from 2.6 to 30.3 (median
6.4); for AML from 0.9 to 21.0 (median 2.7); for ALL 0.4; for CLL from 0.9 to
3.2; for NHL from 2.8 to 8.1; and for MM from 4.0 to 13.2.
The calculated additional cases of total leukaemia, lymphoma and its subtypes
per 100,000 benzene exposed subjects according to a certain scenario ranges
between 0.3 to a maximum of 30 cases. This ratio is however time-dependent
and should not be interpreted as an individual risk. For AML, the median of the
estimates for the number of additional cases per 100,000 benzene exposed subjects was 3, or 0.03 per 1,000. How many additional cases can be expected
within military and civilian personnel that has worked with PX-10 is difficult to
predict as the number of exposed subjects per exposure scenario is not exactly
known. However, estimates of MoD are that the number of exposed subjects in
these described scenarios is likely to be in the low thousands. Therefore, the
possibility that members of the Dutch Armed Forces developed acute myeloid
leukaemia (AML) due to exposure to PX-10 while cleaning and maintaining
weapons can be essentially excluded. The additional risk and subsequent cases
for other leukaemias and lymphoma was estimated to be similarly low. Of note,
the risk estimates for lymphoma (ALL, CLL, NHL, MM) should be interpreted with
caution because the exposure-response functions used were based on limited
quantitative data or extrapolated from total leukaemia.

Page 47 of 67

RIVM Report 609037002

Page 48 of 67

RIVM Report 609037002

6

Discussion

This study showed that the estimated average yearly benzene exposure by
working with PX-10 ranged between 0.009 to 0.4 ppm before 1970, 0.004 to
0.2 ppm between 1970 and 1980, and between 0.001 and 0.04 ppm after 1980.
When exposure by dermal contact was added to these inhalation levels, exposure estimates were maximally 0.5 ppm. These yearly average benzene exposures are below the current eight-hour occupational exposure limit of 1 ppm.
VOCs exposure yearly average levels varied from 2 to 100 ppm depending on
the working situation. VOCs exposure was rather constant over the years.
Based on the yearly average concentrations and two realistic high-risk careers,
it was estimated that the additional risk of AML is around 0.03 per 1,000 PX-10
exposed subjects. The additional risk for the other leukaemia subtypes and lymphoma was comparable to the risk of AML.
MoD estimated that the number of exposed subjects in these high-risk careers is
likely to be in the low thousands. Therefore, the possibility that members of the
Dutch Armed Forces developed acute myeloid leukaemia (AML) or other forms of
hematopoietic cancer due to exposure to PX-10 while cleaning and maintaining
weapons can be essentially excluded. The potential health impact of VOCs other
than benzene could not be calculated because of the lack of dose-response relations.
6.1

Exposure assessment

6.1.1

Dealing with uncertainties
The exposure levels were estimated based on a combination of laboratory experiments, focus group discussions and historical documents as no measurements or detailed records were available regarding important exposure determinants of PX-10. This will inherently have led to uncertainties in the input parameters. However, this has been taken into account by documenting estimated
ranges in the input parameters, which were subsequently used in the probabilistic modelling to quantify the likely exposure distributions. The model input parameters (e.g. room sizes, bath sizes, amount of PX-10 used etc.) were used in
a multiplicative way and a model sensitivity analysis did not reveal a predominant para-meter.
A two-box exposure model was developed based on the model described by
Cherrie and Schneider (3) to estimate past exposure. The application of the twobox model is a simplification of the complex processes around the emission and
dispersion of solvents which allows running a Monte Carlo simulation. The emission of benzene from the PX-10 mixture in open baths was assumed to be proportional to the surface area. This was based on experiments carried out in the
laboratory under controlled conditions. Clearly, other parameters, such as geometry of the bath and the air velocity over the surface of the bath are other
important determinants of the evaporation rate of benzene (20). Although the
air velocity over the surface of the bath was expected to have been low for the
majority of the time, the use of pressurized air to dry metal parts was also reported, and would have increased for short time the air velocity over the surface
and therefore the benzene evaporation rate.
Furthermore, the model assumed perfect mixing of the vapours in the near- and
far-fields. This is also a simplification, however, since there may have been disPage 49 of 67

RIVM Report 609037002

tinct and consistent plumes of contaminated air in the near-field, in particular if
PX-10 was spilled on clothes (21), which could have led to higher short-term
personal exposure levels. Finally, the airflow between the near- and far-field
compartments was arbitrarily set at 10 m3/min, which was the mid-value chosen
by Cherrie (1999) (22). The author concluded that within a plausible range of
airflow rates from the near-field there was little variation in the magnitude of the
difference between near- and far-field concentrations. However, the use of pressurized air would significantly affect the airflow between the near- and far-field.
It needs to be noted that the estimates of the focus group related to the average work circumstances and practices. This does not preclude that PX-10 was
used in different ways or in different settings as described in this report. However, the exposure scenarios described in this report cover the largest and most
likely uses of PX-10 in the Navy. Unfortunately, it was only possible to collect
information for exposure scenarios from the Navy. Although the conditions of
use may be slightly different within other sections of the Armed Forces, it was
expected that the benzene estimates for the scenarios in the Navy were broadly
comparable to the exposure in other branches.
6.1.2

Evaporation rate of benzene
The emission rate was estimated based on the result of laboratory experiments
and on information collected during focus group meetings. The experiments
showed that benzene would have rapidly evaporated from an open bath with PX10. Based on the experiments, a half-life of 2 hours was estimated for the benzene content in a PX-10 bath, meaning that the benzene emission rate from an
open bath of PX-10 would have reduced rapidly in the first hours and have been
negligible at the beginning of the next day. Such decrease was also confirmed
by Nicas et al. (23), who saw a similar decrease (even though with a longer halflife) of benzene in a mixture of similar solvents. For simplicity reasons the model
was run for 24 hours a day with the emission rate for a cleaning activity in the
bath, even though the active washing was presumably only performed during
work time, which might have lead to a shorter half-life time of the benzene in
the PX-10 mixture. However, the level of benzene in PX-10 was also for passive
baths rather low at the end of the first working day.
The rapid depletion of benzene from the PX-10 mixture has important implications for the estimates of exposure for the first group of scenarios (using an
open bath). The long-term exposure to benzene is, to a large extent, determined by the frequency and amount of topping–up of the bath and the frequency of completely changing the bath with fresh PX-10. Information on the
frequency of top-up and the amount used was obtained during the focus group
meetings (once per week). With regard to the frequency of replacing all the PX10 in a bath, the information we obtained pointed to a monthly replacement,
although some indications were provided by the focus group members that the
PX-10 in the baths was replaced at an irregular frequency.

6.1.3

Exposure levels in different use scenario’s
For scenarios with open baths of PX-10 the maximum inhalation exposure values
were reached in the time before 1970 and ranged from 0.009 ppm for cleaning
of torpedo parts in a room next to the torpedo hall up to 0.44 ppm for cleaning
of small arms in the weapon room. The difference in the exposure between the
two scenarios was mainly due to the room size and the duration of the activities.
The annual average inhalation exposure during the cleaning of the torpedo tubes
with a soaked PX-10 cloth was estimated to have been 0.307 ppm. The benzene
Page 50 of 67

RIVM Report 609037002

exposure was generally lower in later periods of time, due to the reduction in the
benzene content of the PX-10.
Rather similar results were found for the benzene levels in the near-field and the
far-field of the scenarios except for the two scenarios in larger facilities. The
similarity of the values is explained by the assumed low air exchange values.
Cherrie (22) showed that at low air exchange rates the near-field and the farfield levels are rather similar. These similar values can be furthermore explained
by the fact that there were also sources of benzene placed in the far-field (i.e.
other baths, or part of a bath that was out of the dimension attributed to the
near-field: 8 m³).
The results from the retrospective exposure assessment were compared with
workplace benzene exposure assessment levels described in published peer review articles (8, 9, 11, 23-28). It is clear that any comparison with results from
other studies is very limited. The large differences in the scenarios studied mean
that other studies can only be used as contextual information and not as material to validate our model estimates. Benzene concentrations of <0.007 up to
0.55 ppm have been reported. The studies cover different solvents being used in
quantities from a few millilitres up to 100 litres, with benzene content from
0.00001% to 0.01% and cleaning tasks that lasted minutes up to hours, and
workplaces from 7 m³ to 70,000 m³. These massive differences in exposure affecting factors make it almost impossible to use the studies as validation for the
model described here.
One study should be highlighted. It provides estimates for benzene exposure
during a task that is very similar to the cleaning with PX-10 by Fedoruk et al.
(24). This study describes the measurement of exposure during a simulation of
the work with Safety-Kleen 105, a substance similar to PX-10, used for similar
purposes of cleaning/de-greasing. The Safety-Kleen 105 was used in a half open
degreaser station similar to a PX-10 bath. Benzene was added at two levels to
the substance: 0.0009% and 0.0058% by weight (lower than the assumed levels in PX-10). The study reported short-term concentrations measured in the
breathing zone of <0.03 ppm and 0.44 ppm, respectively. Note that these results relate to short-term exposure and not long-term exposure and therefore do
not take into account any declining emission rates for benzene. These data are
fairly similar to predicted benzene exposure levels for the first day exposure at
the later periods (with 0.01% benzene in PX-10) after a complete replacement
of the baths with fresh PX-10 (data not shown in detail: values from 0.02 to
1.2 ppm were calculated in the different scenarios for the exposure in the nearfield).
6.1.4

Dermal exposure
Dermal exposure to benzene was estimated using a model by Nies et al. and
Williams et al. (5, 6, 11) and expressed as inhalation exposure equivalent. The
estimated dermal exposure was relatively low compared to the inhalation exposure. On average, the inhalation exposure was found to be 10-30 times higher
than the dermal exposure in the bath scenarios. The relative contribution of
dermal exposure was only equivalent to the contribution from inhalation exposure in the very large torpedo hall. Note that similar application with a towel and
fresh PX-10 was reported to have occurred onboard ships but in smaller
amounts. However, there was insufficient information available to model these
situations as independent scenarios.

Page 51 of 67

RIVM Report 609037002

In addition to the nature of the task and the benzene content in the PX-10, the
estimated dermal exposure to benzene depends largely on the assumed uptake
rate. There is a wide range in reported dermal uptake values for benzene, based
on different experimental approaches. Skin condition is likely to play an important role, with enhanced uptake of benzene where there is damage to the outer
layers of the skin, e.g. dermatitis. We have decided to adopt a relatively high
dermal uptake rate, as there was anecdotal evidence of widespread dermal
symptoms amongst users of PX-10. Despite this assumption, in most cases
dermal exposure was not considered to be an important contributor to systemic
benzene exposure.
6.1.5

VOCs exposure
VOCs exposure from the open baths or the use of PX-10 on surfaces has been
estimated based on the amount of PX-10 used and the experimentally determined VOCs emission rate of white spirit. Additional to this basic level of white
spirit emission, it was considered that a fraction of white spirit consisted of the
highly evaporative substances benzene, toluene, hexane and heptane isomers.
This fraction was estimated to have been around one percent of the PX-10 in the
time period before 1970 and was decreased over the years to a very low level
after 1985.
As for benzene, the highest modelled levels for VOCs exposure were found before the 1970s, with annual average levels up to 100 ppm in the large torpedo
halls. The emission of VOCs was shown to be mainly due to the evaporation of
white spirit and was little influenced by the evaporation of the highly evaporative
fraction. For the scenarios with open baths these values were therefore only
slightly lowered after 1970 when the highly evaporative fraction was lowered in
white spirit (benzene, toluene, hexane and heptane). The current Dutch 8 hour
threshold value for white spirit is 575 mg/m³ (about 100 ppm).

6.2

Potential health effects at low levels of exposure
The exposure estimates showed that yearly average levels of benzene were below 1 ppm. There have been numerous studies of benzene-induced haematotoxicity (15), but few have been able to study effects at low levels of exposure.
Ward et al. (29) found no evidence of a threshold for haematotoxic effects of
benzene and suggested that exposure to <5 ppm benzene could result in haematological suppression. Occupational exposure decreased white blood cells
(WBCs) in petrochemical workers exposed to <10 ppm benzene (30), and Qu et
al. reported that WBCs and other cell types were decreased in workers exposed
to <5 ppm benzene (31). In contrast, Collins et al. (32, 33) and Tsai et al. (34)
did not detect decreased blood cell counts based on routine monitoring of workers exposed to low levels of benzene. A study by Lan et al. (35) showed that
total WBCs, granulocytes, lymphocytes, B cells and platelets significantly declined with increasing benzene exposure and were lower in workers exposed to
benzene at air levels of 1 ppm or less compared to controls. In this study an extensive exposure assessment over a 16-month period was conducted and individual air-monitoring data was linked to the endpoints measured. Although confirmation of these findings in other studies is needed, these data strongly suggest that benzene causes haematological effects at or below 1 ppm. This is in
line with our conclusion that working with PX-10 may have been associated with
an additional risk of AML, although exposure levels were low.

Page 52 of 67

RIVM Report 609037002

6.2.1

Potential confounding factors
Benzene is not the only exposure that is capable of inducing haemato- and lymphopoietic cancers. However, it is important to realize that for an exposure to
confound the association between exposure to benzene and hemato- and lymphopoietic cancer it needs to be correlated to benzene exposure as well. In general, two factors are considered as potential confounding factors: cigarette
smoke and ionizing radiation.
Ionizing radiation is the best studied risk factor for hemato- and lymphopoietic
cancer and there is convincing evidence that this exposure is indeed causally
related to hemato- and lymphopoietic cancer subtypes (36). It is however unlikely that exposure to ionizing radiation was associated with exposure to benzene due to working with PX-10. Primarily because exposure to ionizing radiation above background levels is not expected in the exposure scenarios discussed in this report.
Based on the results of several large cohort studies (37-39), cigarette smoking
is associated with an increased risk of leukaemia. The relative risks range from
1.5 to 2.0. The association with leukaemia is primarily thought to be related to
exposure to benzene present in cigarette smoke. There are other known or suspected leukemogens present in cigarette smoke, including urethane, 1,3butadiene, radioactive elements, N-nitrosodi-n-butyulamine, and styrene. Benzene is therefore unlikely responsible for all smoking induced-leukaemia. However, based on current knowledge of the leukemogenicity of these compounds
and their relative concentrations in tobacco smoke, it seems likely that benzene’s contribution is substantial (40). The evidence for the association between
cigarette smoke and other lymphohematopoietic cancers is less convincing (41).
Due to the strength of the association between smoking and leukaemia and because it is unlikely that smoking behaviour would be related to occupational
benzene exposure it is not likely a potent confounder and would be unlikely to
affect the shape of the dose-response relation. However, tobacco smoke is an
additional source of benzene. In Table 6-1 estimates of the lifetime cumulative
exposure to benzene for an individual only exposed to environmental sources, a
light smoker, and a heavy smoker are summarized.
Table 6-1: Estimate of lifetime cumulative exposure to benzene.
Exposure source
Lifetime expoSource
sure (ppmyear)
Background exposure
0.35
(42)*
Light smoker (20 cigarettes/day)
3
(40)
Heavy smoker (40 cigarettes/day)
6
(40)
*

6.2.2

Assumed 75 years of exposure to calculate background exposure

Life-table analysis
A limitation in the calculations is that only for leukaemia and its subtype AML
quantitative exposure response associations (multiplicative and additive models)
have been published. Although lymphoma has been linked to benzene exposure
no quantitative exposure-response relations have been published. We derived
quantitative estimates of the dose-response of MM and NHL by fitting a linear no
intercept model to the available risk estimates for which a quantitative exposure
estimate was available. These estimates however are rather imprecise and
should be interpreted cautiously. For CLL and ALL we used the leukaemia risk
estimate to calculate the additional cases that could be expected for CLL and
Page 53 of 67

RIVM Report 609037002

ALL. We furthermore, used several different models to account for a temporal
decrease in risk. These models differ from counting only cases till the age of 75
(standard in calculations of the Dutch Health Council), and two models in which
the risk declined after exposure with 50% in 10 or 15 years. These models provide as such a bandwidth of expected additional cases.
As no dose-response relations exist for VOCs or specific components with regard
to neurological disorders no calculation could be made of the potential health
impact. Subjects with neurological disorders who worked with PX-10 should
therefore probably be referred to specialized solvent teams for more specific follow-up.

Page 54 of 67

RIVM Report 609037002

Acknowledgement

We would like to thank Jurgen van Belle, Nicole Janssen, Ingrid van Kuilenburg,
Erik Lebret, Carla van Wiechen and Kees van Luijk (National Institute for Public
Health and the Environment) for their contributions to this study. We are grateful to the members of the focus groups for providing information for the exposure assessments.

Page 55 of 67

RIVM Report 609037002

Page 56 of 67

RIVM Report 609037002

References

1.

2.
3.

4.

5.

6.

7.

8.

9.
10.
11.

12.
13.

14.
15.

16.

17.

Belle NJCv, Janssen N. Evaluatie van het PX-10 rapport van het ministerie
van Defensie. Bilthoven: National Institute for Public Health and the Environment 2010. Report No.: 609037001.
Neuteboom MJW, Gerretsen HA, Leenstra T, Sijbranda T. PX-10: Intern
Onderzoek. Soesterberg: Dutch Ministry of Defence 2009.
Cherrie JW, Schneider T. Validation of a new method for structured subjective assessment of past concentrations. Ann Occup Hyg. 1999;May;
43(4):235-45.
Cherrie JW. The effect of room size and general ventilation on the relationship between near and far-field concentrations. Appl Occup Environ Hyg.
1999;14(8):539-46.
Nies E, Barrot R, Drexler H, Hallier E, Kalberlah F, Prager H-M, et al.
Perkutane Aufnahme von Benzol‚ Folgerungen für die retrospektive Expositionsabschätzung. Arbeitsmed Sozialmed. 2005;(40):585-94.
Nies E, Korinth G. Commentary on ‘Penetration of benzene, toluene and
xylenes contained in gasolines through human abdominal skin in vitro’.
Toxicology in vitro : an international journal published in association with
BIBRA. 2008;22(1):275–7.
Adami G, Larese F, Venier M, Barbieri P, Coco F, Lo, Reisenhofer E. Penetration of benzene, toluene and xylenes contained in gasolines through
human abdominal skin in vitro. Toxicology in vitro : an international journal published in association with BIBRA. 2006;20(8):1321-30.
Sheehan P, Bogen KT, Hicks J, Goswami E, Brorby G, Lau EC, et al. Benzene inhalation by parts washers: new estimates based on measures of
occupational exposure to solvent coaromatics. Risk analysis : an official
publication of the Society for Risk Analysis. 2010;30(8):1249-67.
Nicas M, Neuhaus J. Predicting benzene vapor concentrations with a near
field/far field model. J Occup Environ Hyg. 2008;5(9):599-608.
Baldwin PEJ, Maynard AD. A survey of wind speeds in indoor workplaces.
Ann Occup Hyg . 1998;42(5):303.
Williams PRD, Knutsen JS, Atkinson C, Madl AK, Paustenbach DJ. Airborne
concentrations of benzene associated with the historical use of some formulations of liquid wrench. J Occup Environ Hyg. 2007;4(8):547-61.
Kopstein M. Estimating airborne benzene exposures from air monitoring
data for mineral spirits. J Occup Environ Hyg. 2011;8(5):300-9.
WHO-UNEP-ILO. White spirit (Stoddard solvent) [WHO Task Group on Environmental Health Criteria for White spirit met at BIBRA Toxicology International, Carshalton, UK, 13-17 November 1995]. Geneva: WHO1996.
Crump KS. Risk of benzene-induced leukemia predicted from the Pliofilm
cohort. Environ Health Perspect. 1996;104 Suppl 6:1437-41.
Vlaanderen J, Portengen L, Rothman N, Lan Q, Kromhout H, Vermeulen R.
Flexible meta-regression to assess the shape of the benzene-leukaemia
exposure-response curve. Environ Health Perspect. 2010;118(4):526-32.
U.S. EPA. Carcinogenic Effects of Benzene: An Update. EPA/600/P97/001F. Report. Washington, DC: United States Environmental Protection
Agency 1998.
Richardson DB. Temporal variation in the association between benzene
and leukaemia mortality. Environ Health Perspect. 2008;116(3):370-4.

Page 57 of 67

RIVM Report 609037002

18.

19.

20.

21.

22.

23.
24.

25.
26.

27.

28.

29.

30.

31.

32.

33.

34.

35.

Silver SR, Rinsky RA, Cooper SP, Hornung RW, Lai D. Effect of follow-up
time on risk estimates: a longitudinal examination of the relative risks of
leukaemia and multiple myeloma in a rubber hydrochloride cohort. Am J
Ind Med. 2002;42(6):481-9.
Hornung RW, Deddens J, Roscoe R. Modifiers of exposure-response estimates for lung cancer among miners exposed to radon progeny. Environ
Health Perspect. 1995;103 Suppl 2:49-53.
Lennert A, Nielsen F, Breum NO. Evaluation of evaporation and concentration distribution models – a test chamber study. Ann Occup Hyg.
1997;41(6):625-41.
Breum NO, Soehrich E, Lund Madsen T. Differences in organic vapour concentration in the breathing zone resulting from convective transport from
spillage on clothing. Appl Occup Environ Hyg. 1990;(5):298-302.
Cherrie JW. The effect of room size and general ventilation on the relationship between near and far-field concentrations. Appl Occup Environ Hyg.
1999;14(8):539-46.
Nicas M, Plisko MJ, Spencer JW. Estimating benzene exposure at a solvent
parts washer. J Occup Environ Hyg. 2006;3(5):284-91.
Fedoruk MJ, Bronstein R, Kerger BD. Benzene exposure assessment for
use of a mineral spirits-based degreaser. Appl Occup Environ Hyg.
2003;18(10):764-71.
Kopstein M. Benzene levels in hydrocarbon solvents. J Occup Environ Hyg.
2006;3(9):D85–7; author reply D7–90.
Madl AK, Paustenbach DJ. Airborne concentrations of benzene and mineral
spirits (stoddard solvent) during cleaning of a locomotive generator and
traction motor. J Toxicol Environ Health, Part A. 2002;65(23):1965-79.
Plisko MJ, Spencer JW. Evaluation of a mathematical model for estimating
solvent exposures in the workplace. J Chem Health Safety.
2008;15(3):14-21.
Sheehan P, Malzahn D, Goswami E, Mandel J. Simulation of benzene exposure during use of a mineral spirit solvent to clean elevator bearing housings. Human and Ecological Risk Assessment. 2008;14(2):421–32.
Ward E, Hornung R, Morris J, Rinsky R, Wild D, Halperin W, et al. Risk of
low red or white blood cell count related to estimated benzene exposure in
a rubberworker cohort (1940-1975). Am J Ind Med. 1996;29(3):247-57.
Zhang B. Investigation of health status in workers exposed to low-level
benzene. Zhonghua yu fang yi xue za zhi [Chinese journal of preventive
medicine]. 1996;30(3):164-6.
Qu Q, Shore R, Li G, Jin X, Chen LC, Cohen B, et al. Hematological changes among Chinese workers with a broad range of benzene exposures. Am J
Ind Med. 2002;42(4):275-85.
Collins JJ, Conner P, Friedlander BR, Easterday PA, Nair RS, Braun J. A
study of the hematologic effects of chronic low-level exposure to benzene.
J Occup Environ Med. 1991;33(5):619-26.
Collins JJ, Ireland BK, Easterday PA, Nair RS, Braun J. Evaluation of lymphopenia among workers with low-level benzene exposure and the utility
of routine data collection. J Occup Environ Med. 1997;39(3):232-7.
Tsai SP, Wendt JK, Cardarelli KM, Fraser AE. A mortality and morbidity
study of refinery and petrochemical employees in Louisiana. J Occup Environ Med. 2003;60(9):627-33.
Lan Q, Zhang L, Li G, Vermeulen R, Weinberg RS, Dosemeci M, et al. Hematotoxicity in workers exposed to low levels of benzene. Science.
2004;306(5702):1774-6.

Page 58 of 67

RIVM Report 609037002

36.

37.

38.
39.

40.

41.

42.

Linet M, Devesa S, Morgan G, Schottenfeld D, Fraumeni J, Jr. The Leukaemias. Cancer Epidemiology and Prevention. New York: Oxford University Press; 2006. p. 841-71.
Garfinkel L, Boffetta P. Association between smoking and leukaemia in two
American Cancer Society prospective studies. Cancer. 1990;65(10):235660.
Kinlen LJ, Rogot E. Leukaemia and smoking habits among United States
veterans. BMJ (Clinical research ed). 1988;297(6649):657-9.
Siegel M. Involuntary smoking in the restaurant workplace. A review of
employee exposure and health effects. JAMA : the journal of the American
Medical Association. 1993;270(4):490-3.
Korte JE, Hertz-Picciotto I, Schulz MR, Ball LM, Duell EJ. The contribution
of benzene to smoking-induced leukaemia. Environ Health Perspect.
2000;108(4):333-9.
Morton LM, Hartge P, Holford TR, Holly EA, Chiu BC, Vineis P, et al. Cigarette smoking and risk of non-Hodgkin lymphoma: a pooled analysis from
the International Lymphoma Epidemiology Consortium (interlymph). Cancer epidemiology, biomarkers & prevention : a publication of the American
Association for Cancer Research, cosponsored by the American Society of
Preventive Oncology. 2005;14(4):925-33.
Wallace L. Environmental exposure to benzene: an update. Environ Health
Perspect. 1996;104 Suppl 6:1129-36.

Page 59 of 67

RIVM Report 609037002

Page 60 of 67

RIVM Report 609037002

Appendix 1: Scenario description and input parameters for
exposure modelling

As a result of the discussion with the focus groups six different work scenarios
were developed. These were considered to be the jobs that were likely to have
endured exposure to vapours of PX-10 and physical contact with the mixture.
Scenarios for small arm maintenance
1) Armoury (military personnel): In the armoury store, cleaning of small arms
was performed. These armoury stores were generally small, well-protected
and enclosed rooms below or above ground with little ventilation. The scenario description was based on a store visited during the day of a focus
group meeting. Small arms were kept in racks of relatively large size. PX-10
was used in large stainless steel containers (baths). Sailors/marines stationed at the armoury store took weapons apart and put loose items in the
baths to clean them. After a certain time in this bath (often overnight) they
were manually cleaned with brushes. During this task hands and arms were
often immersed in the PX-10. PX-10 was never sprayed, neither was there a
manual dispenser of PX-10. However, the weapons were often dried with
compressed air to aid drying, especially in the holes and crevices. The farfield (FF) of this scenario was defined as performing other maintenance task
with weapons in the background of the same rooms without direct contact to
PX-10.

Page 61 of 67

RIVM Report 609037002

Table A1-1: Parameters of the scenario ‘Armoury (military personnel)’ that were
used in the Monte Carlo model to determine the range of expected exposure to
benzene.
Parameter

Unit

Minimum

Distribution

Source

Room size

[m³]

24

Mode
27

Maximum
30

Triangular

Vis / FG

Ventilation

[ACH]

0.2

0.5

0.8

Triangular

Lit / FG

NF Bath surface *)

[m²]

NF volume PX-10 in bath

[m³]

NF amount PX-10 topped up

[L/week]

FF Bath surface *)

[m²]

FF volume PX-10 in bath

[m³]

FF amount PX-10 topped up

[L/week]

Daily duration in NF

0.6

Fix

FG

0.07

0.08

0.09

Triangular

FG

6

6.67

7.33

Triangular

FG

Fix

FG
FG

1.20
0.14

0.16

0.18

Triangular

12

13.33

14.67

Triangular

FG

[h]

4.05

4.50

4.95

Triangular

FG

Daily duration in FF

[h]

1.80

2.00

2.20

Triangular

FG

Daily duration non-exposed

[h]

0.85

1.50

2.15

Triangular

FG

Top-up frequency

[/year]

40

47

52

Triangular

FG

Full bath replacement frequency

[/year]

2

12

24

Triangular

FG

[g/min/
m²]

0.000

0.033

0.067

Triangular

Exp

Initial emission rate 19701980

[g/min/
m²]

0.000

0.008

0.033

Triangular

Exp

Initial emission rate >1980

[g/min/
m²]

0.000

0.001

0.008

Triangular

Exp

Triangular

Exp

Triangular

Lit

Initial emission rate <1970

Half-life of benzene in PX-10

[h]

0.5

1.3

3.7

Dermal uptake rate

[mg/cm²
/h]

1.0

1.5

2.0

Dermal surface exposed

[cm²]

1179

1525

1872

Triangular

Lit

Dermal exposure time

[h]

4.05

4.50

4.95

Triangular

FG

ACH: Air changes per hour, NF: near-field, FF: far-field. The source of information is provided with the abbreviation FG for focus group, Lit for literature, Vis for visited or estimated from photo. *) Additional 0.25 m² were accounted for the active washing. The exponent α of the decrease rate is provided for the calculation by the formula for exponential
decrease: Emission (t) = Initial emission rate * t(– α). The non-exposed working time was
calculated subtracting from 8 hours the work in NF plus the work in FF and was set to 0 if
NF+FF was more than 8 hours. The values of the initial emission rate were measured experimentally 30 minutes after the start of emission.

2) Maintenance of small arms on board of ships: Constables were cleaning all
small arms on ships. The main task of these constables was to clean weapons, up to the 3rd step (only main parts disassembled). This task was performed daily for a long time. This weapon maintenance aboard took place in
different parts of the boat that had in common that they were much smaller
than the armoury on the mainland. The baths for the cleaning of small arms
with PX-10 on board of ships were much smaller than the ones in the other
scenarios and could be anywhere, e.g. in the corridor or in designated weapon rooms. Usually there was no ventilation used while working with these PX10 baths. On board of the ships, the baths were not completely filled with PX10 (to be prepared for a movement of the ship) and the PX-10 was replaced
irregularly, depending on dirtiness and missions. The stainless steel containers were additionally closed with lids that when the bath was not in use.
Similar to the mainland the weapons were removed after soaking for 10-15
Page 62 of 67

RIVM Report 609037002

minutes and dry cleaned with compressed air. The manipulation of the weapon cleaning and drying was performed with bare hands.
Table A1-2: Parameters of the scenario ‘Maintenance for small arms on board of
ships’ that were used in the Monte Carlo model to determine the range of expected exposure to benzene.
Parameter

Unit

Minimum

Mode

Maximum

Distribution

Source

Room size

[m³]

7

8

9

Triangular

Vis / FG

Ventilation

[ACH]

0.8

1.2

1.5

Triangular

Lit / FG

NF Bath surface *)

[m²]

NF volume PX-10 in bath

[m³]

0.45

0.49

NF amount PX-10 topped up

[L/wee
k]

0.06

0.07

FF Bath surface *)

[m²]

FF volume PX-10 in bath

[m³]

0.09

0.10

FF amount PX-10 topped up

[L/wee
k]

0.45

0.51

Daily duration in NF

[h]

2.25

2.50

Daily duration in FF

[h]

5.50

5.50

Daily duration non-exposed

[h]

0.00

Top-up frequency

[/year]

Bath replacement frequency

0.2

Fix

FG

0.54

Triangular

FG

0.08

Triangular

FG

Fix

FG

0.11

Triangular

FG

0.56

Triangular

FG

2.75

Triangular

FG

5.50

Triangular

FG

0.00

0.25

Triangular

FG

40

47

52

Triangular

FG

[/year]

2

12

24

Triangular

FG

Initial emission rate <1970

[g/min/
m²]

0.000

0.033

0.067

Triangular

Exp

Initial emission rate 19701980

[g/min/
m²]

0.000

0.008

0.033

Triangular

Exp

Initial emission rate >1980

[g/min/
m²]

0.000

0.001

0.008

Triangular

Exp

Half-life of benzene in PX-10

[h]

0.5

1.3

3.7

Triangular

Exp

Dermal uptake rate

[mg/cm
²/h]

1.0

1.5

2.0

Triangular

Lit

0.25

Dermal surface exposed

[cm²]

1179

1525

1872

Triangular

Lit

Dermal exposure time

[h]

2.25

2.50

2.75

Triangular

FG

*see explanation Table A1-1.

3) Civilian workshop (smaller size): Large numbers of arms were delivered to
the workshop where the full maintenance of them was performed. Very large
baths with PX-10 were used for the cleaning of the weapons. The parts of
the weapons were placed in the bath with PX-10. Small parts were put in a
basket, while larger parts were placed individually in the bath. Gun barrels
were put vertically above the bath all night. The parts were often left to soak
in PX-10 overnight. The next day, the components were manually cleaned
with brushes, a task during which the hands were often immersed in PX-10.
PX-10 was never sprayed, nor was there any use of a manual dispenser.
However, compressed air was often used to aid the drying of the weapons.
Different locations were used for full maintenance of the weapons, the main
difference between these workplaces was the room size.

Page 63 of 67

RIVM Report 609037002

Table A1-3: Parameters of the scenario ‘Civilian workshop (smaller size)’ that
were used in the Monte Carlo model to determine the range of expected exposure to benzene.
Parameter

Unit

Minimum

Distribution

Source

Room size

[m³]

68

Mode
75

Maximum
83

Triangular

Vis / FG

Ventilation

[ACH]

0.8

2.4

4.0

Triangular

Lit / FG

NF Bath surface *)

[m²]

NF volume PX-10 in bath

[m³]

NF amount PX-10 topped up

[L/week
]

1.6
1.30

1.44

1.58

60

66.67

73.33

FG

Triangular

FG

Triangular

FG

Fix

FG

Triangular

FG

Triangular

FG

FF Bath surface *)

[m²]

FF volume PX-10 in bath

[m³]

2.59

2.88

3.17

FF amount PX-10 topped up

[L/week
]

120

133.3
3

146.67

Daily duration in NF

[h]

2.25

2.50

2.75

Triangular

FG

Daily duration in FF

[h]

4.95

5.50

6.05

Triangular

FG

Daily duration non-exposed

[h]

0.0

0.0

0.8

Triangular

FG

Top-up frequency

[/year]

40

47

52

Triangular

FG

Full bath replacement frequency

[/year]

2

12

24

Triangular

FG

[g/min/
m²]

0.000

0.033

0.067

Triangular

Exp

Initial emission rate 19701980

[g/min/
m²]

0.000

0.008

0.033

Triangular

Exp

Initial emission rate >1980

[g/min/
m²]

0.000

0.001

0.008

Triangular

Exp

Triangular

Exp

Triangular

Lit

Initial emission rate <1970

3.20

Fix

Half-life of benzene in PX-10

[h]

0.5

1.3

3.7

Dermal uptake rate

[mg/cm
²/h]

1.0

1.5

2.0

Dermal surface exposed

[cm²]

1179

1525

1872

Triangular

Lit

Dermal exposure time

[h]

2.25

2.50

2.75

Triangular

FG

*see explanation Table A1-1.

4) Civilian workshop (larger size): The same task as described for the small
workshop was performed in a larger workshop. Large numbers of arms were
delivered to the workshop where the full maintenance of them was performed. Large baths with hundreds of litres of PX-10 were used for the
cleaning of the weapons. Different locations were used for this full maintenance of the weapons was performed, the main difference between the
workplaces was the size of the room. Due to the larger size of the room this
location was better designed for tasks that were not related to the bath.

Page 64 of 67

RIVM Report 609037002

Table A1-4: Parameters of the scenario ‘Civilian workshop (larger size)’ that
were used in the Monte Carlo model to determine the range of expected exposure to benzene.
Parameter

Unit

Minimum

Mode

Maximum

Room size

[m³]

900

1000

1100

Triangular

Vis / FG

Ventilation

[ACH]

0.8

2.4

4.0

Triangular

Lit / FG

Fix

FG

1.30

1.44

1.58

Triangular

FG

60

66.67

73.33

Triangular

FG

Fix

FG

Triangular

FG

Triangular

FG

NF Bath surface *)

[m²]

NF volume PX-10 in bath

[m³]

NF amount PX-10 topped up

[L/week
]

1.6

Source

FF Bath surface *)

[m²]

FF volume PX-10 in bath

[m³]

2.59

2.88

3.17

FF amount PX-10 topped up

[L/week
]

120

133.3
3

146.67

Daily duration in NF

[h]

2.25

2.50

2.75

Triangular

FG

Daily duration in FF

[h]

4.95

5.50

6.05

Triangular

FG

Daily duration non-exposed

[h]

0.00

0.00

0.80

Triangular

FG

Top-up frequency

[/year]

40

47

52

Triangular

FG

Bath replacement frequency

[/year]

2

12

24

Triangular

FG

Initial emission rate <1970

[g/min/
m²]

0.000

0.033

0.067

Triangular

Exp

[g/min/
m²]

0.000

0.008

0.033

Triangular

Exp

[g/min/
m²]

0.000

0.001

0.008

Triangular

Exp

Triangular

Exp

Triangular

Lit

Initial
1980

emission

rate

1970-

Initial emission rate >1980

3.20

Distribution

Half-life of benzene in PX-10

[h]

0.5

1.3

3.7

Dermal uptake rate

[mg/cm
²/h]

1.0

1.5

2.0

Dermal surface exposed

[cm²]

1179

1525

1872

Triangular

Lit

Dermal exposure time

[h]

2.25

2.50

2.75

Triangular

FG

*see explanation Table A1-1.

Scenarios for heavy arm maintenance
5) Torpedo parts washing: In the room where smaller elements were soaked in
large baths with PX-10. After disassembly, the single parts of the torpedoes
were washed in a PX-10 bath. This was performed in a small cleaning chamber, adjacent to the main torpedo hall, which had a number of PX-10 baths
along its walls. Compressed air was used to dry the parts. Due to proximity
of the large torpedo hall, it is to assume that the personnel did not perform
much work in the FF but rather moved out of the room when not performing
cleaning activities. This only influences the interpretation of the model outcome, where the far-field of the activities in the washing room was therefore
assumed to be in the far-field of the larger torpedo hall. Note that for the
modelling of the washing room far-field concentration, the parameters of Table A1-5 were used to calculate the near-field concentration.

Page 65 of 67

RIVM Report 609037002

Table A1-5: Parameters of the scenario ‘torpedo part washing’ that were used in
the Monte Carlo model to determine the range of expected exposure to benzene.
Parameter

Unit

Minimum

Room size

[m³]

22

Mode
95

Maximum
195

Triangular

Vis / FG

Ventilation

[ACH]

0.2

0.5

0.8

Triangular

Lit / FG

Fix

FG

Triangular

FG

Triangular

FG

Fix

FG

Triangular

FG

Triangular

FG
FG

NF Bath surface *)

[m²]

NF volume PX-10 in bath

[m³]

1.22

1.35

1.5
1.49

NF amount PX-10 topped up

[L/week
]

31.50

35

38.5

0.5

Distribution

Source

FF Bath surface *)

[m²]

FF volume PX-10 in bath

[m³]

0.41

0.45

0.50

FF amount PX-10 topped up

[L/week
]

10.5

11.67

12.83

Daily duration in NF

[h]

3.5

5.2

8.0

Triangular

Daily duration in FF

[h]

1.8

2.0

2.2

Triangular

FG

Daily duration non-exposed

[h]

0.0

0.8

2.7

Triangular

FG

Top-up frequency

[/year]

40

47

52

Triangular

FG

Bath replacement frequency

[/year]

2

12

24

Triangular

FG

Initial emission rate <1970

[g/min/
m²]

0.000

0.033

0.067

Triangular

Exp

Initial emission rate 19701980

[g/min/
m²]

0.000

0.008

0.033

Triangular

Exp

Initial emission rate >1980

[g/min/
m²]

0.000

0.001

0.008

Triangular

Exp

Triangular

Exp

Triangular

Lit

Half-life of benzene in PX-10

[h]

0.5

1.3

3.7

Dermal uptake rate

[mg/cm
²/h]

1.0

1.5

2.0

Dermal surface exposed

[cm²]

1179

1525

1872

Triangular

Lit

Dermal exposure time

[h]

3.5

5.2

8.0

Triangular

FG

*see explanation Table A1-1.

6) Torpedo hall: The cleaning and protecting of torpedoes was performed in a
large hall. PX-10 was poured from large containers in buckets of 10 litres to
be used for cleaning the body of a torpedo. Cleaning of the torpedo body was
carried out using cloths soaked with PX-10. One or more such buckets were
used per day. There were six teams of torpedo washers. On one side of the
hall were large hangar doors. These were open only in summer. PX-10 was
used in above described way every day, sometimes during 8 hours a day.
Sometimes the job was rotated and a person was not exposed for a whole
day. It is to assume that the personnel were mainly using this location to
perform the background work of both the scenarios ‘torpedo hall’ and ‘torpedo parts washing’. The far-field concentration of this scenario was therefore used as the far-field exposure for both scenarios.

Page 66 of 67

RIVM Report 609037002

Table A1-6: Parameters of the scenario ‘Torpedo hall’ that were used in the
Monte Carlo model to determine the range of expected exposure to benzene.
Parameter

Unit

Minimum

Mode

Maximum

Distribution

Source

Room size

[m³]

15750

17500

19250

Triangular

Vis / FG

Ventilation

[ACH]

0.8

2.4

4.0

Triangular

Lit / FG

NF daily amount PX-10

[L/day]

-

10

-

Fix

FF daily amount PX-10

[L/day]

-

50

-

Fix

FG

Daily duration in NF

[h]

1.50

3.25

8.00

Triangular

FG

Daily duration in FF

[h]

0.0

4.75

6.5

Triangular

FG

Daily duration non-exposed

[h]

0.0

0.0

0.0

Triangular

FG

Dermal uptake rate

[mg/cm
²/h]

1.0

1.5

2.0

Triangular

Lit

Dermal surface exposed

[cm²]

295

381

468

Triangular

Lit

Dermal exposure time

[h]

1.5

3.25

8.0

Triangular

FG

*see explanation Table A1-1.

Three further scenarios were identified but not modelled
The exposure to benzene was estimated to be lower than in the other scenarios.
Based on the information about amounts of PX-10 used, room sizes or ventilation situation etc. However, due to a lack of data the exposure could not be
modelled.
1. Large gun workshop.
2. Ammunition was maintained and cleaned with PX-10.
3. Maintenance of torpedoes and other equipment on board of vessels.
Note that due to smaller amounts of PX-10 and slightly better ventilated facilities the first two scenarios are expected to have shown smaller exposure than
the scenarios described in detail above, however, the exposure on vessels was
reported to have been very variable in task and location. An application of larger
amounts of PX-10 in places with limited space and ventilation might have led to
high short-term exposure to benzene.
Full bath replacement frequency
The frequency of the total replacement of the PX-10 in a bath (in comparison to
topping up the bath with PX-10) was found to predominantly influence the benzene exposure level. The focus group members were therefore specifically asked
to estimate the replacement frequency for each scenario.
The answers of the focus group showed a rather large range for the frequencies.
Range of answers:
Small arm maintenance in armouries onshore: 12/year; 2-3/year
Small arm maintenance on board of ships:
12-16/year; 5-6/year; 2-3/year
Small arm maintenance in civil workshops:
12/year
Torpedo parts washing:
more frequent than 2/year
Ammunition maintenance:
12/year
As none of the scenarios was clearly reported to have a much more frequent or
much less frequent replacement of the whole PX-10 in the bath, the range was
defined as between two weeks and twice a year for all scenarios with PX-10
baths.

Page 67 of 67

FG