Workshop of the Latest Developmenton the Evaluation Method of
PBT (Persistent Bioaccumlative Toxic)
Chemicals― Focusing on the Environmental Fate,
Bioaccumulation, and Safety Assessmentof Cyclic Siloxane ―August 29, 2017
The Society of Silicon Chemistry Japan

PROGRAMThe Symposium was held on 29th August 2017 in Tokyo. It is organized by The Societyof Silicon Chemistry of Japan, and co-sponsored by International Council of Chemical
Association, American Chemistry Council, The Chemical Society of Japan, Japan Chemical
Industry Association, and Silicone Industry Association of Japan.

Opening Speech

Mitsuhiro Takarada

Vice Chairman, The Society of Silicon Chemistry, Japan (SSCJ)

		
……… 3
Overview of Silicon Chemistry, Application/Physical-Chemical Properties
Ralf Maecker

Chair, CES-Silicones Europe / Momentive Performance Materials

		
……… 4
Science of PBT Assessment: Overview of Safety Assessment of cVMS
Kathleen Plotzke

ICCA-LRI Chair, Dow Chemical USA

		
……… 7
Dietary Exposure Bioaccumulation Fish Test to Evaluate Bioaccumulation
Potential of Chemical: Current Progress in Japan
Naoki Hashizume

Chemicals Evaluation and Research Institute (CERI), Japan		……… 13
Environmental Monitoring of cVMS in Japan

Yuichi Horii

Center for Environmental Science in Saitama (CESS)		……… 17

1

Silicone Industry Association of Japan

Cyclic Volatile Methyl Siloxanes: Environment Canada D5-Board of
Review and the Science and Process Used in Risk-Based Weight of Evidence
Assessment of cVMSs
Keith Solomon
Centre for Toxicology, University of Guelph, Canada		……… 22Ecological Risk Assessment of cVMS

Ellen MihaichDuke University Environmental and Regulatory Resources		……… 27
Pharmacokinetic Behavior of D4 and D5 in Fish and Mammals: Why D4 and
D5 Do Not Accumulate
Kathleen Plotzke
ICCA-LRI Chair, Dow Chemical USA

		……… 32
Hazard Assessment and Health Risk Characterization for D4 and D5
Wolfgang Dekant

Department of Toxicology, University of Wurzburg, Germany		……… 36

Round Table/Wrap Up		……… 40
Closing Comments

Eriko Sakurai

President, Silicone Industry Association of Japan		……… 45

2

Silicone Industry Association of Japan

Opening Speech
Mitsuhiro Takarada

Vice Chairman, The Society of Silicon Chemistry, Japan (SSCJ)

About SSCJ
The society was founded in 1996 with the aim of promoting silicon development as well as
development in other related chemistries. We currently have 424 members in Japan and abroad.
We welcome researchers in silicon chemistry and related industries with an inexpensive
membership fee of ¥2,000 (USD19)/y.
SSCJ has the following four missions:
1. Support the growth of young scientists
2. Strengthen cooperation with scientists in Asia and beyond
3. Expand membership and exchange knowledge between various fields
4. Enhance silicon chemistry literacy by various fields
The activities of SSCJ include the following: Holding domestic two-day seminars each year Holding ASIS symposium once every two years
 Dispatching young members to overseas conferences Presenting awards to scientists in academia and industry with outstanding achievements
each year

3

Silicone Industry Association of Japan

Overview of Silicon Chemistry, Application/Physical-Chemical
Properties
Ralf Maecker

Chair, CES-Silicones Europe / Momentive Performance Materials

Introduction
Silicones are specialty products. The backbone of inorganic silicon and oxygen atoms drives
the unique properties of this chemistry set which makes them distinctly different from carbon
chemistry. Silicones are only used where their special performance is needed. Siloxanes areindispensable, critical building blocks for all silicone products.
Chemistry and characteristics of Si-based materials‘Silicone’ is a generic term referring to a class of synthetic polymers based on a frameworkof alternating silicon and oxygen (siloxane) bonds with at least one organic group attached tothe silicon atom via a direct carbon-silicon bond. The silicone family includes siloxanes andsilanes, all of which are widely used in thousands of products. Due to their molecular structure,silicones can be manufactured in many forms such as solids, liquids, semi-viscous pastes,
greases, oils, and rubber.
Silicone polymers are typically liquids of varying viscosity that may be linear or branched,
but are individual polymer strands. Structuring of the polymer can occur by cross-linking theindividual chains. Cross-linking is accomplished by synthesizing polymers with functionalgroups on the chain that either react with each other or with moisture in the atmosphere.
Cross-linked silicone polymers can have very different properties dependent on the degree ofcross-linking. Gels are lightly cross-linked and can flow. Foam and rubber silicone features ahigher degree of cross-linking and may be reinforced. Hard coats are highly cross-linked andreinforced.
Silicone materials offer a host of useful physically and chemically useful characteristics
that include thermal stability; resistance to oxidation, ozone, and UV exposure; low surface
tension for good wetting, spreading, and flow; good dielectric properties; water repellency(hydrophobicity); low flammability; high gas permeability; high compressibility and shear
resistance; limited organic compatibility; and softness and flexibility. The structure ofsilicones gives them unique properties critical to demanding applications such as: personalcare (antiperspirants and hair conditioners); automotive (coatings, lubricants, ignition cables,and engine gaskets); construction (sealants and adhesives); electronics (smart phones, tablet
computers, and keyboards); health care (tubing, syringe coatings, cushioning, catheters, andmasks); textiles (coatings for water resistance, improvements for tear strength and abrasion
4

Silicone Industry Association of Japanresistance); as well as renewable energy applications (insulators in solar and wind energy
solutions).
Introduction to cyclic and volatile methyl siloxanes (cVMS)
Manufacturing of silicones start with silicon metal sourced from natural SiO2 (quartz). Figure
1 describes the main steps in manufacturing silicone.
> 99,5% of D4 volume isused asintermediate/monomer

In the manufacturing process, thehydrolysis of methylchlorosilanes
always produces a mix of siloxanes

Figure 1: D4 is a vital building block for all silicones
It is important to note that in the manufacturing process the hydrolysis of methylchlorosilanes
always produces a mix of siloxanes that are then separated. Once separated, cVMSs can bedirectly used in products. cVMSs are basic members of the family of silicone materials andare raw materials for the manufacture of silicone polymers. cVMSs are clear, volatile, lowmolecular weight liquids with very low water solubility with D4, D5, and D6 as examples.
Figure 2 shows the chemical structure of these cVMSs.

Figure 2: Chemical structure of cVMSs
Challenges of cVMS: Silicone chemistry
The backbone of inorganic silicon and oxygen atoms combined with the organic functionality
drives the unusual combination physical and chemical properties including high hydrophobicity
and lipophilicity; low water solubility; volatility; large molecular size; very low polarizability;
significant hydrogen bond acceptor characteristics; higher bond strength of Si-O bonds
compared to Si-C bonds; and undergo biotransformation in both aquatic and terrestrialorganisms.
In summary, the industry has invested and investigated the properties and chemistry of silicones
5

Silicone Industry Association of Japanover the past four decades. Much information needs to be looked at in order to understandthem. Silicones are very different from organic chemistry.
It is important to note that silicone chemistry is fundamentally different from carbon chemistry.
Silicon is one period lower than carbon in the periodic table of elements and silicon has agreater capacity than carbon to share electrons with oxygen. This leads to stronger bonds withhigher bond energies, higher bond angles, and shorter than expected bond lengths as comparedto the carbon-oxygen bond. The nature of the silicon-oxygen bond makes siloxanes molecules
like D4 flexible, which results in weak interactions between other siloxane molecules. This is
illustrated by the lower surface tension, viscosity, and vapor pressure of siloxanes compared tohydrocarbons of similar molecular weight. Their large size combined with a moderate ability
to accept hydrogen bonds leads to differences in the ability of D4 and other siloxanes to interact
as solutes with environmental ‘solvents’ or environmental media such as water, organic carbon
in soil or sediment, and lipids in biota. These characteristics lead to different behavior in theenvironment as compared to carbon compounds.
Summary
Silicones are among the most extensively studied materials used in consumer and industrial
applications today with over 1000 studies over more than 35 years. Silicones are extremely
versatile with wide-ranging properties that make them key component in thousands ofconsumer and industrial materials. The beneficial characteristics of silicones enable them tobe used in a wide variety of applications and products including in construction, transportation,
electronics, manufacturing, engineering, health care, cosmetics, and personal care

6

Silicone Industry Association of Japan

Science of PBT Assessment: Overview of Safety Assessment ofcVMS
Kathleen Plotzke

ICCA-LRI Chair, Dow Chemical USA

The issue
On a global scale, regulatory agencies are implementing risk management measures to control
exposure to chemicals considered to be persistent, bioaccumulative, and toxic (PBT) or very
persistent and very bioaccumulative (vPvB). In some jurisdictions these decisions are based
solely on screening-level criteria with no risk-based assessment. Restrictions based solely onscreening-level criteria without consideration of a weighted evaluation of all scientific evidence
will drive promising technologies with promising benefits out of the market, which will thenlimit innovation and commercial growth.
Scientific evolution of PBT criteria
The Stockholm Convention is a global treaty that was adopted in 2001 and ratified in 2004 toprotect human health and the environment from persistent organic pollutants (POP) and PBTchemicals. Growing concern for these chemicals was the impetus for the classification schemesof POPs/PBTs since they last for long time in the environment (persistent), bioaccumulate infatty tissue of living organisms and magnify as they move up the food chain, are toxic, andtravel long distances far from emission sources.
Criteria for the classification of the POPs were developed in the late 1990s by the Criteria
Expert Group for Persistent Organic Pollutants. The criteria were based on the properties of anumber of compounds, all of which were subsequently classified as POPs under the Stockholm
Convention.
Unfortunately, the criteria used to identify a chemical as PBT is based on the state of thescience in the late 1970s and early 1980s. It was assumed to reflect all chemistries and is notalways consistent from one jurisdiction to another.
Protection goals for POPs
The goal for classifying POPs are to ensure that both humans and the environment areprotected. Indeed, UNEP in 2001 stresses, “…significant adverse human health and/or
environmental effects…”

7

Silicone Industry Association of Japan

ICCA LRI Workshop
The 2016 ICCA LRI Workshop held in Japan focused on new approaches for weight-ofevidence decision making for PBT chemicals and POPs compared to criteria-based approaches.
The session focused on front-line approaches to evaluate PBT chemicals and POPs.
Discussions included: development of a quantitative and transparent weight of evidence (WoE)
approach for characterization of PBT/POPs compared to criteria-based assessments; revisionof the guidance on REACH’s PBT/vPvB criteria; importance of dietary exposure in evaluating
the bioaccumulation of poorly water soluble substances; Multibox-AQUAWEB model forbioaccumulation assessment; the measurement and influence of metabolism in bioaccumulationassessments; challenges in assessing the toxicity of poorly water soluble chemicals; weight ofevidence (WoE) approach for assessing literature on concentrations of environmental chemicals
in breast milk and formula; and the challenges of assessing persistence in a regulatory context.
What follows are the major findings and recommendations from the workshop. There is aweaknesses of the current numerical POPs/PBT criteria including a lack of realism in existing
standardized testing guidance and a lack of understanding/use of realistic exposure potentials
for humans and the environment. It is important and opportune time to step back and redefine
PBT and POP concerns and the protection goals and design higher tiered standardized testing toprotect against false negatives and false positives in achieving this goal. Decisions based solely
on numerical criteria without a weighted evaluation and integration of all scientific evidence
could drive technologies with promising benefits out of the market, which would then limit
innovation and commercial growth and could miss chemicals of real concern. The chemicalindustry is ideally positioned to collaborate and develop partnerships to develop specificproposals for enhancing the realism of PBT/POP assessments globally and share best practices
for acceptance of new methods and approaches. ICCA-LRI can help develop new methods
for assessment of substances that may exhibit PBT/POP properties under real life conditions
by working collaboratively across sectors with academics and regulators. ICCA-LRI cancatalyze the education of the next generation of experts and also serve as a forum for transfer of
information on these new methodologies/best practices especially for emerging countries.
Key science for cVMS PBT/POP assessments
Current environmental screening criteria predict that some cVMS have PBT or POP properties.
Research shows that information beyond screening criteria must be evaluated to understandcVMS behavior in the environment. A robust quantitative WoE assessment conducted byAcademic experts concluded that all lines of evidence shows that the cVMSs have very
different, physical, chemical, and biological properties from the legacy POPs. Refined
approaches are needed, and when applied these show that these materials should not beclassified as P, B, or T or as vP or vB.
Some jurisdictions only look at screening-level criteria. Not looking at the overall science
could prevent the development of important technologies. The criteria for determining which
chemicals are PBT or persistent organic pollutants (POP) are to prevent damage (adverse
effects) from them to human health or the environment. Unfortunately, the criteria for
determining a PBT was based on the science of the 1970s and were assumed to reflect all
8

Silicone Industry Association of Japanchemistries, which is not appropriate for many of the new chemistries today. .
Regarding the key science of persistence, it is important to look at both laboratory and fielddata on cVMS to fully understand persistence of cVMS in the environment. Many chemicals
partition into multiple environmental compartments, but persistence in the major compartment
or final sink is most appropriate for assessing persistence in the global context. The overallpersistence (POV) is more important for the cVMSs than for other classes of chemicals, suchas the classical POPs. Since the cVMSs partition readily to atmosphere (major compartment)
where they are degraded more rapidly than in other matrices, their presence in the global
environment is much shorter (months) than the classical POPs where global lifetimes are much
longer (several years). Due to the physical properties of the cVMSs, traditional laboratory tests
for persistence even in sealed systems are not appropriate for extrapolation to the environment
because they do not consider rapid partitioning to air, which is the final sink in the environment.
Figure 1 shows how cVMSs are exchanged between media and how they react in theenvironment.

Figure 1: Understanding cVMS Persistence
Regarding bioaccumulation concerns in the food web, it is important to remember that
substance must accumulate or biomagnify sufficiently to potentially cause significant adverse
effects in populations and ultimately affect ecosystems. An example would be DDT metabolites
that affected raptor populations in the USA. When these criteria were put into place, the intent
was to prevent significant and adverse effects on human health and the environment. However
the criteria were only intended to screen for problem substances and then use current science
to determine their actual impacts. The question is how to best predict biomagnification, which
is a complex ecosystem phenomenon that is difficult to model in the laboratory taking into
consideration the intrinsic properties of substances being evaluated. Bioconcentration factor(BCF) is typically used as a surrogate for biomagnification.
Regarding the evolution of PBT criteria for bioaccumulation, when assessing bioaccumulation
potential it is important to consider the intrinsic properties of chemicals for which the criteria
were derived, i.e. organochlorines. KOW, BCF, and BAF criteria were developed as screening
tools with the intention to identify biomagnifying substances. However, since these areproxies, they do not apply to all chemicals equally and vary as a result of the unique intrinsic
9

Silicone Industry Association of Japan

properties of chemical substances relative to properties of organochlorines.
Figure 2 shows how bioconcentration is typically used in regulatory assessment.

Figure 2: BCF Background
However, the behavior of cVMS in natural systems is very different from laboratory water
exposure testing. Indeed, the standard laboratory BCF tests fail to accurately predict theability of a highly lipophilic, poorly water soluble, and metabolizing substance such as D4,
D5, or D6 to biomagnify in the environment. Dietary exposure is the main route of uptake forbioaccumulation of highly lipophilic substances. It is important to understand the behavior ofD4 and other cVMSs following dietary exposure for a better comparison to what will actually
happen in the field. Several recent field studies from locations in Europe, North America,and Asia have shown that cVMS D4 biodilutes as you move up the food chain. For D5 andD6 there is a lack of full agreement of the TMF across various study areas and this may
reflect differences in TMF study design. TMFs may also be biased because of environmental
conditions and sample collection. There is also a lack of common sampling areas for the
species considered in the TMF calculation and the presence of point sources such as waste
water treatment plants can cause concentration gradients in the sampling area. These gradients
can have a significant impact on study outcomes, as shown by Gobas et al. in 2014 and2016. Additional work is currently underway with external experts to validate a MultiboxAQUAWEB model that takes into consideration these variables and confounding factors.
Figure 3 shows D4 TMF behavior in aquatic and terrestrial food webs at Lake Pepin in the
USA show that it does not bioaccumulate, in contrast to the results for PCB 180.

Figure 3: D4 TMF Behavior: Aquatic/Terrestrial Food Web: Lake Pepin (USA) example
Trophic food web biodilution behavior of D4 has been documented in systems varying from
freshwater to marine and pelagic to benthicpelagic in food web structure, and reported D4
10

Silicone Industry Association of Japan

Relative D4 Biota Concentration (e.g., ng/g-lipid weight)

TMV values are generally less than one, as shown in figure 4.
10000

Reported D4 TMF values are
generally <1 (P<0.05)

1

1000

Median D4 TMF = 0.6(Biodilution)

100

10

0.2
Piscivorous fish

Zooplankton/Benthic Invert

Trophic Level

Tokyo Bay (2016)

Inner Oslofjord (2010)

Outer Oslofjord 1 (2010)

Daltian Bay_China (2015)

Lake Pepin_USA (2009)

Lake Mjosa_Norway (2013)

Lake Randsfjord_Norway (2013)

Lake Erie_Env Canada (2015)

Oslofjord_NIVA Norway (2016)

Figure 4: D4 Trophic Biodilution Behavior Observed – new data available from Oslofjord Norway
Two new publications indicate 1) there was no evidence from any of the regression models tosuggest biomagnification of cVMS in Tokyo Bay. Rather, the regression models indicated thattrophic dilution of cVMS, not trophic magnification, occurred across the sampled food web and2) . there was no evidence to suggest biomagnification of cVMSs in Oslofjord. Rather, results
indicated that trophic dilution of cVMS, not trophic magnification, occurred across the sampled
food webs.
Key science on LRT and back deposition
The ultimate goal of the POP convention is to protect humans and the environment in local
and distant or remote locations from adverse outcomes. LRT and deposition of a chemical toa receiving environment in a remote region is a complex interaction, and this is especially true
for substances with unique physical-chemical properties such as cVMSs.
Since half-lives based only on laboratory studies are predicted to be greater than two days,
cVMSs may have the potential to undergo long-range transport to remote regions via theatmosphere. However, they are readily degraded in air. It is well established that cVMSs
degrade by interaction with OH radicals in the air. cVMSs are mainly released from the urban
centers where the OH radical concentrations are much higher than the global average OH
radical concentration used to estimate their current half-lives. Very recent work using actual
monitoring data demonstrates the real life degradation of VMS in air may be much faster(between 1.7 and 2.7 days) and involve other mechanisms beyond OH radical degradation thanwhat is currently estimated. Discussions with experts from Norway, Stockholm University,
and Canada at the SETAC conference provided support for this hypothesis and all expressed
an interest to collaborate. Work is underway with external partners to better understand thisuncertainty on air half-life.
Although D4, D5 and D6 have been reported in Arctic air, the concentrations are much lower
11

Silicone Industry Association of Japanthan in source regions. For example the measured cVMS (D5 and D6) concentrations in the
Arctic air are hundreds of times lower than those in the source region, and D4 detection inremote air may be due to analytical artefact. From a report by NILU in 2016, they indicatedthat “D4 data should be treated with caution as the measured concentrations of D4 might havebeen affected by degradation effects during storage as shown by Kierkegaard et al. (2013).
Thus no firm conclusions can be made regarding the presence of D4 in Arctic air nor any trends
in concentration based on findings in this monitoring study.”
Very little airborne cVMS will deposit from air to surface compartments in the environment
due to their unique combination of partition coefficients. Thus airborne VMS in the remotepart of the atmosphere will result in little exposure to surface media. No detections for cVMS
in surface media when there is no local release confirmed their low deposition potential. The
presence of cVMS does not represent any real exposure risk to biota/humans in remote regions.
Therefore, there no potential for adverse outcomes.
Summary of cVMS WoE assessment: PBT
Combining all of these lines of evidence shows that the cVMSs have very different,
physical, chemical, and biological properties from the legacy POPs. The traditional criteriaof persistence, biomagnification used to classify the legacy POPs are not suitable for thecVMSs. Overall, the QWoE analysis shows that there is moderate to strong evidence of no
adverse effects from concentrations of D4, D5, and D6 as measured or expected to be in theenvironment.
In conclusion, refined approaches are needed, and when applied show that cVMSs should not
be classified as P, B, or T or as vP, or vB and will not back deposit.

12

Silicone Industry Association of Japan

Dietary Exposure Bioaccumulation Fish Test to Evaluate
Bioaccumulation Potential of Chemical: Current Progress inJapan
Naoki Hashizume

Chemicals Evaluation and Research Institute (CERI), Japan

CERI is one of the biggest laboratories in Japan that conducts the chemicals safety assessmentswith 40 years of experience in bioaccumulation assessment. CERI has provided thebioconcentration study data for more than 3000 chemicals and has contributed to the progressof bioaccumulation assessments.
Bioaccumulation assessment in Japan
Bioaccumulation assessment of chemicals is an important issue for chemical management. The
bioaccumulation of chemicals has been assessed since the Chemical Substances Control Law(CSCL) was enacted in 1973. Bioaccumulation assessment is required for chemicals when
production or import volume is higher than one ton per year and BCF is used as endpoint.
Bioaccmulation criteria in the CSCL state that a chemical is highly bioaccumulative if BCF is
greater than 5000 L/kg, and not highly bioaccumulative if log POW is less than 3.5 or BCF isless than 1000 L/kg.
Regarding the dietary exposure test, in 2004 CERI starting examining the test. In 2010 theOECD conducted the ring test for dietary exposure test and in 2012 the dietary exposure test
was included during a revision of the OECD guidelines. In 2013 Japan conducted the ring testfor dietary exposure test. In 2016 a committee was formed to discuss the dietary exposure test
in CSCL. This year or in 2018 the CSCL will be revised to include the dietary exposure test.
Biomagnification is the increase in concentration of the test substance in or on an organism(or specified tissues thereof) relative to the concentration of test substance in the food. This isdefined in OECD TG 305. In fish the BMF is calculated by dividing the dietary uptake by thesum of gills elimination, fecal egestion, metabolic biotransformation, and growth dilution.
Figure 1 details the dietary exposure test according to OECD TG 305.

13

Silicone Industry Association of Japan

Figure 1: Dietary exposure test (OECD TG 305)
Advantages of the new dietary exposure bioaccumulation fish test include that it is suitable fortesting poorly water-soluble chemicals, which may not be technically feasible for an aqueous
exposure test. In addition, BMF is a meaningful measure of the potential for the chemicals toundergo dietary biomagnification in the environment.
Ring test in Japan
Japan’s Ministry of Economy, Trade and Industry (METI) conducted the ring test for the
dietary exposure test to fill the data gap for using the results of dietary exposure tests forregulatory purposes. Six GLP laboratories in Japan were selected to perform the test oncommon carp (Cyprinus carpio) using hexachlorobenzene (HCB) in the test diet routinely usedin each laboratory. Results showed that BMFKgL and BMFKg for HCB were below one in alllaboratories, that BMFKgL varied more than 10 times between the laboratories, and that BMFKg
varied approximately three times between the laboratories.
Challenges for the dietary exposure test include the fact that the result of ring tests in Japan
indicate that BMFKgL may differ depending on test conditions such as the test diet. Therefore,
it was decided to conduct the dietary exposure test in different test conditions to investigate theinfluence of the test conditions on BMF values. Four different feeds were used differing in sizeand protein/lipid/phosphorus content (Figure 2).

14

Silicone Industry Association of Japan

Figure 2: Influence of test conditions
In addition to these differences, the medium was also different with acetone being used in two
tests, fish oil at 10% in three tests, fish oil at under 1% in three tests, and corn oil at 10% in one
test. This also created differences in the lipid content with the acetone medium tests being at
5.67% and 5.23%, while in the other tests the lipid content varied between 13.9% and 17.1%.
There were also different feeding rates with two tests at two and the remaining tests at three.
Test condition may influence the BMFKgL values of HCB, and correcting the BMFKg values bylipid content in the test diet might lead to misunderstanding the results. After normalizing lipid
content at 5%, the results still showed a difference of approximately double, but this was lessvariation than for BMFKgL (Figure 3).

Figure 3: Influence of test conditions
Dietary exposure test in Japan’s CSCLMETI held a committee to discuss the dietary exposure test in Japan’s CSCL. Major commentsfrom experts included that the dietary exposure test is useful for poorly water soluble
chemicals, and there is difficulty in conducting the aqueous exposure test. Expert comments
also indicated that it was too early to include the dietary exposure test to evaluate highlybioaccumulation substances since there needs to be more experimental data. Therefore, METI
decided to use the dietary exposure test to identify non-highly bioaccumulative substances.
15

Silicone Industry Association of Japan

According to a provisional agreement, test methods were adopted that are similar to theOECD TG 305, but with three additional points. 1) Dietary exposure tests are applicable inchemicals which have water solubility bellow 0.01 mg/L and log KOW higher than five or forchemicals which are not stable in water. 2) Test diets have a lipid content of between 10% and15%. 3) It is recommend to add reference substances to both control and treatment diets. As
for bioaccumulation criteria in the provisional agreement, there is no definitive criteria if it
is highly bioaccumulative. If it is not highly bioaccumulative, then growth-corrected kinetic
dietary the BMFKg should be less than 0.007. If BMFKg is greater than or equal to 0.007 thenit is left up to an expert judge to consider the accumulation to edible part and/or results ofreference substance, etc.
In the field, BMFL equals the accumulated chemical in predator divided by accumulated
chemical in prey. A BMFL greater than one indicates biomagnification, while a BMFL ofless than one indicates no biomagnification. In the lab we can use a similar formula for thechemical concentration in fish where the source of the chemical is spiked feed. However, thefeed content will be an artificial concentration, so you will end up with similar BMF but witha different meaning. Therefore, we can think of not using a BMF value of one as the standard.
Therefore, at CSCL the BMF/BCF correlation is used to calculate the figures. Furthermore, forthe provisional agreement on bioaccumulation criteria, the current criteria for not being highlybioaccumulative corresponds to a BCF of 1000, which is a BMFKg of 0.017. Meanwhile, intraand/or inter-individual variation of BMFKg is approximately 2.4 times BMFKg, which meansthat it is not highly bioaccumulative if BMFKg is less than 0.007.
In conclusion, if water solubility less than 0.01 mg/L and log KOW is greater than five thenit is difficult to conduct the aqueous exposure test. In this case, the dietary exposure test
is conducted by adding a reference substance to both control and treatment groups. If theconcentration of the reference substance does not differ greatly between the control andtreatment group fish and the BMF Kg is greater than 0.007 then determining whether thesubstance is bioaccumulative is left up to an expert judge. If BMFKg is less than 0.007 then thesubstance is determined to be not highly bioaccumulative.
Questions
1. When you conducted the BMF test you used fish oil, corn oil, and acetone but in the caseof acetone the substance will only stay on the surface of the feed since it is volatile. Is
adsorption a factor here?
Only two tests used acetone. The lipid content is low, so that is why we think BMFKgL is low.
Is bioavailability different between the tests? This is a conversation to have in the future, but it
is possible.
2. If you spike the feed then the test substance may be released into the water. What is thepossibility of that and what will be different because of it?
The release to water will be higher with spiked feed, but the substance is not water soluble. We
measured the amount of substance in the water, but it did not reach the detection limit using theflowing water method, so accumulation of the substance in fish from water is minimal.
16

Silicone Industry Association of Japan

Environmental Monitoring of cVMS in Japan
Yuichi Horii

Center for Environmental Science in Saitama (CESS)

Silicone is widely used in our lives and is used in construction, electric and electronic
apparatuses, personal care and lifestyle items, transport equipment, and in general industry,so there is a need to understand the impact of cVMSs on health and the environment in
the Japanese context where there is less information. cVMSs are very volatile, so 90% ofemissions are into the air. Most of the remaining emissions are through the sewage treatment
facilities. Although most cVMSs are eliminated, some may be accumulated in the environment.
We investigated the distribution of atmospheric siloxanes. We placed focus on analyzing
accumulation in aquatic environments and at sewage treatment plants we looked at the behaviorof these substances as well as emissions into the air. In order to assess the accumulationof cVMSs we need a sophisticated approach and we have based our methodologies on ISO
standards.
Determination of VMS in the aquatic environment
We used the purge and trap extraction method in determining VMSs in the aquatic environment.
We targeted seven VMSs, the cyclic D3, D4, D5, and D6 as well as the linear L3, L4, and L5.
Since siloxanes are present in much laboratory equipment, it was difficult to have high sensitiveand high precision analysis without good blank control. We had to use silicone-free materials,
analysts had to take great care in sample handling to reduce contamination, and carried out
daily blank checks that include instrumental, procedural, and trip blanks. In addition, due tothe high volatility and adsorption of VMSs into organic carbon, we applied PT extraction withultrasonic assistance to get good extraction efficiency from aqueous and particulate phases.
For purge and trap extraction, the sample liquid is put into a one-liter gas wash bottle. Then thesample is purged using a vacuum pump. The sample is therefore gasified and trapped in thisabsorber and then measured after elution with small volume of hexane.
Investigation of sewage treatment plants (STPs)
Through STPs some substances are emitted into the environment. We decided how to look at
how siloxanes move in facilities and how much is eliminated. We sampled 25 STPs for D4,
D5, and D6. The concentrations are shown in figure 1.

17

Silicone Industry Association of Japan

Figure 1: Concentrations of cVMS in effluent from 25 SPTs
Small-scale STPs indicate rural plants serving around 1000 people. D5 accounted for 85% of
the total with 530 ng/L being the mean concentration, which seems to be twice or thrice thevalues found in the river environments, so STPs seem to be the main source of emissions. Next
we looked at the Mass balance of D5 in a sewage treatment plant as shown in figure 2.

Figure 2: Mass balance of D5 in a sewage treatment plantD5 removal efficiency was 94% with most of D5 (73%) being removed by adsorbing withactivated sludge. Almost 100% of D5 in aeration gas was removed by AC treatment at
deodorization, and more than 99.9% of D5 contained in sewage sludge was decomposed byincineration. We estimated the emission of D5 via STP effluent around Tokyo Bay and foundthat there was a total emission of about 2000 kg per year. The Sumida River having the highest
share at 380 kg per year and the Arakawa River at 320 kg per year. Numerous STPs aroundTokyo Bay emit water into Tokyo Bay for a total of about 800 kg per year of emissions.
VMS monitoring in Tokyo Bay watershed
We took 84 samples from river that had an average total concentration of 212 ng/L for
the seven VMSs we tested for. In Tokyo Bay the concentrations were very low at 11 ng/L,
18

Silicone Industry Association of Japanwhich is close to the measurable limit. In downstream STPs in the urban area highconcentrations were observed. In the northern part of Saitama Prefecture septic tanks are stillused and concentrations were very high. In the downstream of rivers, near the river mouths
concentrations of siloxanes in sediment were found to be high. Therefore, high accumulationof siloxanes were observed in the sediment.
Figure 3 shows the relationship between cVMS concentrations (ng/L) and suspended solids(SS) (mg/L) or total organic carbon (TOC) (mg/L).

Figure 3: Relationship between cVMS concs (ng/L) and suspended solid (mg/L) or TOC (mg/L)
There was no correlation with SS in river solids, but significant correlation with SS in effluent,
as well as significant correlation with TOC in river water and effluent, which is dependent upon
the amount of organic materials found in effluent. We have published a paper on this topic
in the journal Science of the Total Environment titled ‘Distribution characteristics of volatile
methylsiloxanes in Tokyo Bay watershed in Japan: Analysis of surface waters by purge and trap
method’. If you are interested, please read the paper.
Fish investigation in Tokyo Bay and inflow rivers
In rivers we tested carp and black bass. In Tokyo Bay we looked at sea bass and eel as hightrophic level samples. As for concentration profiles of VMS (µg/g-lipid) in fish samples, thehighest values were found near the discharge point of STP water. Therefore, the location is an
influencing factor with concentrations lower in Tokyo Bay as compared with rivers. We did not
find high concentrations in high trophic level samples.
Regional characteristics and temporal trends of methylsiloxanes in the atmosphericenvironment, Saitama, Japan: simultaneous analysis for 20 compounds
We determined cyclic methylsiloxanes D3 through D9 and linear methylsiloxanes of L3
through L15 in the atmosphere. We used a small mass-flow pump attached to an SPE cartridge
to capture siloxanes at nine locations in Saitama Prefecture over one week. We have conducted
continuous measurements since June, 2016. We divided the prefecture into the three sections ofurban, mountainous, and agricultural. We find higher concentrations of methylsiloxanes in thesouth of the prefecture and lower concentrations in the north with D3, D4, and D5 accounting
19

Silicone Industry Association of Japan

for the vast majority of emissions and D5 having the highest concentrations especially inurban areas due to its use in aerosol products. However, D4 concentrations were higher in thenorthern agricultural region, which may be due to differences in half-life between D4 and D5,or there may be a source of D3 and D4 that we are not yet aware of.
We used the AIST-ADMER model to estimate D5 emissions from the use of personal careproducts that 281 grams are emitted per day. High levels of emissions were found in the urban
area, southern Saitama Prefecture. The concentration distribution and the emissions scenario of
D5 seems to match.
At CESS we do continuous monitoring throughout the year. We found concentrations in therange of 100 to 960 ng/m3 and an average of 390 ng/m3. We have seen that concentrations
vary over the year with the highest numbers being found in autumn and winter and the lowest
in summer. Interestingly, the ratio of D4 and D5 is low when concentrations are low and highwhen concentrations are high.
Finally, figure 4 shows the compositions of cVMSs in each environmental media.

Figure 4: Compositions of cVMS in each environmental media
In each medium D5 has the highest percentage since it is added to personal care products.
Interestingly, however, those proportions were slightly altered in each environmental media,
depending on the physico-chemical properties of cVMS.
Further questions
What are the temporal trend for cyclic and linear? Will they increase, decrease, or not change?
What is the composition of cVMS in dissolved and particulate phases in a water environment?
This is an important factor to predict environmental fate and bioavailability of cVMS. What is
the factor for seasonal variations of cVMS (D4) in the atmosphere? What are the D3 sourcesin the environment? Is it from impurities in silicone products or any specific source, or do they
originate from degradation or transformation in the atmosphere?
20

Silicone Industry Association of Japan

Questions
1. In water and fish you investigated the concentration and you have looked at thebioaccumulation factors. Have you looked at the ratio between fish and water?
This looks at the changes in ratio between fish and water. For BAF, the ratios ranged several
thousands to tens of thousands different in concentrations seen.

21

Silicone Industry Association of Japan

Cyclic Volatile Methyl Siloxanes: Environment Canada D5Board of Review and the Science and Process Used in RiskBased Weight of Evidence Assessment of cVMSs
Keith Solomon

Centre for Toxicology, University of Guelph, Canada

As background, it is important to keep in mind that all things are toxic and can present a
hazard, but that no or minimal exposure is equal to no harm. It is when exposure above acertain amount is reached that there will be harm. It is when you include probability into themix is when you will be able to characterize risk (Figure 1).

Figure 1: Probability must be considered to characterize risk
Risk is totally ignored in current POPs and PBT regulations. It must have a component ofprobability of exposure and sensitivity. The only way that risk can be managed is to reduce
intensity and probability of exposure.
Legislative background
The legislative background of the D5 board of review (BoR) is the Canadian Environmental
Protection Act (CEPA) of 1988, and the Toxic Substances Management Policy 1995. These
were adopted to protect the environment and human health by the virtual elimination ofsubstances that are toxic, persistent, and bioaccumulative, as well life-cycle management of
22

Silicone Industry Association of Japanother toxic substances and substances of concern to prevent or minimize their release into
the environment. The Canadian Environmental Protection Act of 1999 detailed screening
assessments of substances to determine if they present risk to the environment or human healthwith three outcomes: no further action, further assessment, or virtual elimination.
Siloxane D5 board of review
CEPA Screening concluded in November 2008. D5 was entering the environment in a quantity
concentration or under conditions that may have harmful effect on the environment or its
biological diversity, so it was to be added to schedule 1 of CEPA. In July 2009, an affectedindustry stakeholder filed a Notice of Objection and requested that a BoR be established. In
August 2010, the Minister of the Environment published notice of his intention to establish
a BoR to review D5 but not D4. The members of the BoR were John Giesy, Keith Solomon,and Sam Kacew. The key question for the board was whether D5 presented a ‘danger tothe environment’. Based on legal precedent, this was determined to require “…a de novo
assessment of risks posed by D5, taking into account all of the available, relevant, scientificinformation…” The members of the board had judicial status. Witnesses were called bycounsel for Environment Canada, the appellants, and the BoR. Witnesses were cross-examinedby counsel for EC, the appellants, and the BoR. The BoR then produced a report that wasprovided to the Minister of the Environment.
The BoR on D5 concluded that D5 exceeded the regulatory threshold for persistence, did notexceed the thresholds for bioaccumulation, does not biomagnify through the food chain, that
there is no evidence to demonstrate that D5 is toxic to any organisms tested up to the limit ofsolubility in any environmental matrix, that D5 does not pose a danger to the environment,
and that projected future uses will not pose a danger to the environment. Aside from thelegal aspects of the BoR, the panel followed good scientific methods for review and analysis,used probabilistic risk assessment for their assessment, recommended the use of transparent
modelling approaches, and did not use weight of evidence in the formal sense.
Weight of evidence (WoE)
The term weight of evidence originated in the legal system, but as a process has been
misused in the scientific arena. WoE is widely used but seldom formalized. WoE has threecharacteristic uses in the literature related to risk assessment for human health. The first is
metaphorical where WoE refers to a collection of studies or to an unspecified methodologicalapproach. Most uses of WoE have been metaphorical and no better than a magician’s wand.
The other two characteristic uses are methodological where WoE points to establishedinterpretative methodologies, and theoretical where WoE serves as a label for a conceptual
framework.
As scientists, we are faced by the data paradox. Published studies are often incompletely
documented, raw data is rarely available, most studies do not follow standardized protocols,
there is selection bias, and there is publication bias since negative results are not published.
Therefore, studies need to use good laboratory practice, have quality assurance, and quality
control. This is required by regulation and means that studies are completely documented,
23

Silicone Industry Association of Japan

that raw data is available, standardized protocols are used for most studies, and that there is no
selection or publication bias.
Quantitative WoE (QWoE)
There is too much data with a large number of studies reported in the literature, some showing
adverse effects and some not. Proponents for each side of the question will select conclusions
from studies that support their position. This results in arcane arguments from experts involvedin a ‘he-says—she-says’ debates. QWoE is the exit strategy. However, QWoE is not about
criteria. Criteria for protection of the environment use data on P, B, T, etc. The best data areusually selected based on the quality (reliability) of the studies. Therefore, some studies are
excluded. QWoE includes all studies that have enough data to allow quality to be assessed.
QWoE is not a simple scientific review, a meta-analysis, or risk assessment. Instead, QWoE
assesses the consistency and coherence of data on the biological or environmental behaviorof a stressor (chemical or otherwise). QWoE can address risk but not yet in the fully
probabilistic sense. Observed responses that are relevant can be compared to criteria, NOECs,
or probabilistic values. QWoE does provide a consistent and transparent process to bring all
relevant studies together with minimal bias and to show overall relevance. The process of
QWoE assessment is shown in Figure 2.

Figure 2: Process of QWoE assessment
As for scoring for quality, the scoring guide acts as a filter based on the methods and reportingof a study to assign a quality score. Studies with a high score are good studies for setting
criteria, while those with a low score are unsuitable for setting criteria. However, regardlessof the score, all studies are used for QWoE. QWoE is about maximizing consistency andtransparency so the reasons for the scores are provided. There are two components of a QWoE,
the narrative and the supplemental information (scoring sheets).
24

Silicone Industry Association of Japan

The results of QWoE assessments for TMF data for D5 and toxicity data for both D4 and D5
are shown in Figures 3 through 5.

Figure 3: Example of TMF data for D5 (nR=11)

Figure 4: Example of toxicity data for D4 (nR=32)

Figure 5: Example of toxicity data for D5 (nR=36)
25

Silicone Industry Association of Japan

Conclusions of the QWoE are as follows: 1) cVMSs are persistent in some studies in somematrices (sediment) but it is Poverall or P in the final compartment (air) that matters. 2) Studies infood-webs support a conclusion that the cVMSs do not meet the criteria for biomagnification;
consistent with toxicokinetic studies and modelling. 3) Toxicity of cVMSs was not observed
less than or equal to solubility in water or the maximum sorption capacity in soils andsediments. Concentrations in the environment were not measured at greater than or equal to
the solubility in water or the MSC. 4) Concentrations in air in remote locations are small, and if
deposition occurs it is very unlikely to be biologically relevant.

26

Silicone Industry Association of Japan

Ecological Risk Assessment of cVMS
Ellen MihaichDuke University and Environmental and Regulatory Resources, LLC

Risk assessment methodology
Risk is a function of both hazard and exposure. Risk assessment is the use of the factual database to define the health or environmental effects of exposure of individuals or populations
to materials or situations. There are four steps involved. The first is problem formulation or
hazard identification to find out what is known about the situation or material and to develop
hypotheses. The second is the characterization of ecological effects or a dose-response
assessment to determine the inherent toxicity under defined conditions. The third is an
exposure assessment to determine how much is out there. The final step is risk characterization
to determine how risky something actually is by comparing the toxicity and exposurecomponents.
Overview of risk assessment process for cVMS
The chemical properties of cVMSs are shown in figure 1.
H3C CH3H3C CH3Si
O Si OO
H3C O
CH3CH3 H3C
Si
Si
Si
Si
H
C
CH3 3
H3C
O CH3
O
O
O
Si
H3C Si O Si CH3
H3C CH3CH3CH3

H3C CH3H3C O Si O CH3
H3C Si
Si CH
3OO
Si CH3H3C Si
CH3
O
O
Si
H3C
H3C CH3

D4

D5

D6

• Molecular Weight: 296• Water
Solubility: 56 µg/L
• Henry’s Law constant: 12
atm-m3/mol• Log Kow: 6.98
• Hydrolysis
half-life: 3.3 days

• Molecular Weight: 370• Water
Solubility: 17 µg/L
• Henry’s Law constant: 33
atm-m3/mol• Log Kow: 8.03
• Hydrolysis
half-life: 73 days

• Molecular Weight: 444• Water
Solubility: 5.1 µg/L
• Henry’s Law constant: 49
atm-m3/mol• Log Kow: 8.87
• Hydrolysis
half-life: ~400 days

Figure 1: Chemical properties of cVMSs
As background, cVMSs are a very well-researched class of materials. Through their
manufacturing, handling, use and disposal, traces of cVMS may enter sewage treatment plants
and receiving waters. Due to their properties, accumulation in sediments is possible andvolatilization is likely. Assessing ecotoxicity, exposure, and risk in the water and sedimentcompartments is warranted but challenging. Problem formation is based on protection goals to
27

Silicone Industry Association of Japan

protect human health and the environment from adverse effects and involves the developmentof working hypotheses as to how cVMS might distribute in the environment and affectcomponents of the ecosystem.
The properties of D4, D5, and D6 exert control over test designs. First, they have low
aqueous solubility so it is a challenge to prepare test solutions and a challenge to conduct
analytical measurements. They have a combination of low water solubility, high KOW, andhigh Henry’s Law values, and therefore have a tendency to escape the water through sorption
and volatilization but not redeposit once in the air. In order to conduct aquatic tests, closed,
no-head space, flow-through test systems (except for algae) are generally used. In addition,
it is important to make careful measurement of test concentrations, understand the maximum
sorption capacity in the matrix, and consider water solubility.
cVMSs have unusual properties that constrain exposure. Despite unusually small KOC, they
partition to organic carbon in soil and sediment but not at concentrations greater than the
maximum sorption capacity. This limits exposure in toxicity tests. Data from tests conducted atconcentrations above the maximum solubility or MSC are not ecologically relevant.
Results of cVMS toxicity testing
To summarize aquatic toxicity results, for D4 there were no acute 96-hr effects at solubility
limits for fish, invertebrates, and algae. The lowest 14-day LC50 for rainbow trout is 0.010 mg/
L in an enclosed system. There was a marginal effect on Daphnia survival at the highest test
concentration in a 21-day study with no effect on reproduction. For D5 there were no effects atsolubility limits in acute and chronic tests with fish, invertebrates, and algae, and no effect onfish in the dietary dosing study. For D6 there were no effects at solubility limits in acute andchronic tests with fish and invertebrates.
To summarize sediment toxicity results, for D4 there were NOECs of 13 to 44 mg/kg dw inchronic tests in natural sediments with synchronized Lumbriculus and Chironomus. There
was also no obvious effect of varying OC in 14-day tests with Chironomus with a NOEC of
54 to 120 mg/kg dw and an LC50 of 130-170 mg/kg dw. For D5, acute and chronic tests with
Hyalella and Chironomus gave similar results of 69 to 130 mg/kg dw based on survival ordevelopment. Lumbriculus was relatively insensitive to D5 with NOEC equaling 1272 mg/
kg dw. For D6 there were no effects on Lumbriculus at the highest concentration tested of 484
mg/kg dw, and no effects on other benthic species are expected.
The D5 avian reproduction study followed OECD 206 guideline with Japanese quail. There
were no statistically significant effects observed on any parameter measured during the 22week JQ reproduction study with D5. The NOEC during the study was 1000 mg/kg feed, or
143.5 mg/kg body weight per day. The NOEC determined in the D5 avian reproduction study
is at a concentration approximately 10,000 times higher than what has been measured in soil,
sediment, and fish samples in the environment.

28

Silicone Industry Association of Japan

Exposure assessment
Models are being developed to consider unique properties of cVMSs, and monitoring data
will help validate models. Field monitoring is ongoing around the world, for example for the
Voluntary Product Stewardship Initiative in Inner Oslo Fjord, Lake Ontario, Lake Pepin, andTokyo Bay. Challenges in cVMS trace analysis include contamination issues during sampling,transport, storage, and analysis. Quality control measures are also critical since the measured
data are generally at or below detection limits.
The critical body burden (CBB) is the lowest total body concentration of a chemical whichis associated with adverse toxic effects. The first order pharmacokinetic model is: Cfish = K1/
k2*Cw*(1-exp-(k2+km)*time. As for predicting chronic NOEC using CBB, rainbow trout NOEC
from the early life-stage study is 4.4 μg/L at the highest concentration tested and the highconcentration was based on the acute study. Using the CBB model, the exposure time to reacha concentration that would cause adverse effects ranges from 27 to 269 days depending on fish
size and concentration. For the 93-day trout ELS, concentrations equal to or less than 12 μg/L
could have been used without adverse effects occurring. Mortality after seven days in the acutestudy was unexpected and may indicate issues with the non-standard test conditions.
As for pelagic risk characterization of cVMSs, the compounds exhibit low toxicity to pelagic
species. Field Cbiota is much less than CBBs, and NOECs are often greater than water solubility
as shown in figure 2.

Figure 2: Pelagic Risk Characterization of cVMS

29

Silicone induStry ASSociAtion of JApAn

As for sediment risk characterization with D4, figure 3 shows Probability Density Function(PDF) and Cumulative Distribution Function (CDF) for D4 field sediment exposure andchronic benthic invertebrate toxicity NOEC values (mg/kg-OC) in a benthic species sensitivity
distribution.

Figure 3: Sediment Risk Characterization with D4
As for sediment risk characterization with D5, figure 4 shows PDF and CDF for D5 field
sediment exposure and chronic benthic invertebrate toxicity NOEC values (mg/kg-OC) in abenthic species sensitivity distribution.

Figure 4: Sediment Risk Characterization with D5
The fact that exposure and chronic NOEC in the previous two graphs do not overlap indicates
low risk. Results were also the same for D6 at low concentrations.
ConclusioncVMSs have robust ecotoxicity and monitoring databases and have unique physical andchemical parameters that limit the chance for significant exposure in the environment.
30

Silicone induStry ASSociAtion of JApAn

Concentrations in the environment are low and cVMSs preferentially partition to sedimentand air. Probabilistic effects and exposure assessments do not indicate the risk to aquatic or
sediment organisms. Finally, using a quantitative WoE procedure and risk assessment, it can beconcluded that cVMSs do not present a risk to human health or the environment when used asintended.
Questions
1. I understand that siloxanes are safe with no risk, but there is one study that is an outlier.
Could you explain why you reject this data?
The problem with the Lumbriculus variegatus study was that the organic material for theartificial sediment was not the best when the test was being made up. Also, the worms were
not synchronized by cutting off their heads, which was at odds with the guidelines. Therefore,
there is a lot of variability that could have caused this result by chance. That is why we did
another study with natural sediment and made sure that the worms were synchronized per theguidelines.
2. Could you explain about the relationship between the plots of quality score and the graphin figure 4?
We use all of the monitoring data we have to develop a cumulative distribution or a probability
density function. The quantitative weight of evidence helps us know how everything fits. We
developed a regression and then plotted the lowest no effect level. This is probabilistic since
you have distributions with the 95th percentile of concentration and the 5th percentile of theeffect, so this is very conservative.

31

Silicone Industry Association of Japan

Pharmacokinetic Behavior of D4 and D5 in Fish and Mammals:
Why D4 and D5 Do Not Accumulate
Kathleen Plotzke

ICCA-LRI Chair, Dow Chemical USA

The concern with bioaccumulation: biomagnification
It is important to determine whether a chemical movement in food webs magnifys or biodilutes.
For high uptake or a non-metabolizing chemical there will be an increase in concentration
as it moves up in trophic levels, while low uptake rate or highly metabolized chemicals will
decrease in concentration as it moves up the trophic levels. The reasons why a standard BCF is
not a good measure for biomagnification of cVMS is because standard laboratory BCF tests failto accurately predict the ability of a highly lipophilic, poorly water soluble, and metabolizing
substance such as D4, D5, and D6 to biomagnify or not in the environment. Dietary
exposure is the main route of uptake for bioaccumulation of highly lipophilic substances inthe environment. Understanding uptake, metabolism, and elimination of these substances indifferent organisms in the environment is critical for understanding biomagnification potential.
Processes affecting biomagnification in aquatic organisms
Mackay et al. in 2015 examined the importance of the role of physical-chemical properties in
evaluating the potential for accumulation from ‘superhydrophobic’ compounds such as cVMSs.
The term ‘superhydrophobic’ is applicable to compounds with log KOW greater than about
seven, which includes D4, D5, and D6. The authors compiled a series of conventional uptake
equations and a simple accumulation model for aquatic organisms. Among the importantfactors that were examined were the roles of hydrophobicity and metabolism. Bioaccumulation
results when uptake is significantly greater than elimination. As for the processes affecting
biomagnification in aquatic organisms, ADME processes are critical. Biota concentrationof a chemical equals uptake through the gills and diet minus loss via the gills, egestion, andmetabolism.
Taking the example of D4 metabolism in fish, metabolism in vivo has been measured in lab
studies with rainbow trout as shown in figure 1. Very little to no parent D4 is found in bile orurine respectively following administration of D4 to rainbow trout. This example of a 96-hour
trout metabolism study following bolus doses also had estimated kM of greater than 0.01 per
day..

32

Silicone Industry Association of Japan

Figure 1: D4: Metabolism in Fish (example)
Results of this study were similar with D5. Clearance occurs via enterohepatic circulationof metabolic products in bile with excretion via the digestive tract and urinary clearanceof metabolites. D4 and D5 are metabolized in rainbow trout with similar estimatedbiotransformation half-lives of less than seven days. There is biodilution of cVMS in foodwebs due to metabolism and/or lack of uptake. Results on cVMSs both in vitro and in vivo
demonstrated metabolism in fish. The silicone industry is funding additional metabolism
work performed via Henriette Selck of Roskilde University on benthic organisms and Frank
Gobas of Simon Frazer University on fish regarding more environmental relevant dosing andconcentrations.
Processes affecting biomagnification in terrestrial organisms and humans
Again, ADME processes are critical for understanding biomagnification potential interrestrial organisms and humans. Biota concentration equals uptake via skin/inhalation plus
diet minus loss via exhaled air, metabolism, and egestion. This is a simple mass balance
process where bioaccumulation results when uptake is significantly greater than elimination.
Extensive pharmacokinetic studies in mammals for D4 and D5 (including rodents andhumans) demonstrate that D4 and D5 are readily eliminated either by exhalation in breathor via metabolism to polar metabolites excreted in urine. It is not possible for D4 or D5 tobioaccumulate due efficient elimination processes in mammals. This process is detailed infigure 2.

Figure 2: D4: Exhalation and Metabolism in Mammals (example)
33

Silicone Industry Association of Japan

Figure 3 shows the mammalian urinary metabolite profile post exposure to D4 and showsthat no parent D4 is found in urine. Similar results were seen following exposure to D5.

Figure 3: Mammalian Urinary Metabolite Profile Post Exposure to D4
SummarycVMSs undergo metabolism/biotransformation in a salmonid species, the rainbow trout.
Further studies are ongoing with fish and benthic invertebrates under relevant exposure/dose conditions in the environment. cVMSs are readily metabolized or exhaled in terrestrialorganisms, and field data indicate biodilution. cVMSs are readily metabolized or exhaled inhumans and concentrations will not increase over time.
Questions
1. For the fish metabolism study, how did you calculate the bio-transformation half-lives? Are
these values from the whole body?
We looked at the whole body as well as the blood concentrations over time. It is similar towhat we do for mammals.
2. I think you suggest low bioaccumulation of D4 or D5 by fish, but this morning we were toldthat the bioaccumulation factor is around 5000. What do you think about this point?
With the BCF, you are maintaining concentrations of these substances in the water, you will get
partitioning of these lipophilic substances into lipophilic fish. However, in the environment theconcentrations in the water re low so this will not be a major exposure pathway. However, you
do find these substances in the sediment, therefore, it is important to look at exposure throughthe diet where metabolism will play a significant role34

Silicone Industry Association of Japan

3. Can we think that this is different from traditional POP substances?
It is very different since metabolism plays a key role for these substances where the traditional
POP substances were not readily metabolized
4. What kind of reaction is happening in the metabolism of these substances?
It is enzymatic metabolism. We have studied this in detail in the rodents. It is a P450 enzyme
demethylation, which destabilizes the ring. Then it undergoes simple hydrolysis.
5. When D4, D5, D6 are metabolized you have alcohol which is soluble in water. What is the
toxicity of these compounds? You may need to think about the long transport characteristicsof these substances as well.
From a toxicity perspective, we have done acute aquatic toxicity tests and you see nothing evenat the highest concentrations tested. From long-range transport or PBT perspective, they arehighly water soluble and have very low log KOW so they will not bioaccumulate. . They might
be found in the atmosphere in remote regions but that would be from degradation of cVMS. .
6. CYP P450 is an enzyme in the liver, and for just-hatched fish CYP levels are low, so I am
concerned for juvenile fish. Do you have evidence of low toxicity in juvenile fish?
The real key is the exposure component. You will not have enough exposure for it to build up
to achieve a narcotic mode of action, which is the only mode of action that would cause adverse
effects. You have to get to high concentrations to achieve that.

35

Silicone Industry Association of Japan

Hazard Assessment and Health Risk Characterization forD4 and D5
Wolfgang Dekant

Department of Toxicology, University of Wurzburg, Germany

Available studies on the toxicity of D4 and D5
Guideline-compliant studies cover all endpoints considered relevant for hazard assessment.
Studies were performed using inhalation exposure due to specific characteristics of absorptionof D4 and D5 from the gastrointestinal tract after oral administration with micro-emulsions.
Concentrations used in inhalation studies are limited by aerosol formation above approximately
160 ppm for D5 and approximately 700 ppm for D4. From the available studies, there werea number of endpoints affected in repeated-dose studies with D5. There were reversible
increases in liver weight with a NOEC greater than 28 ppm in a 28-day study. There wereincreased lung weights and alveolar macrophage accumulation with a NOEC of 10 ppm in a
28-day study. There were no effects on development and fertility in one- and two-generation
studies. There were small increases in the incidences of uterine endometrial carcinoma after
two-year inhalation exposure at 160 ppm.
Risk characterization for D5
Reversible liver changes due to the induction of CYP450 mediated by CAR are not considered
as adverse, but represent an adaptive response due to absence of histopathological changes inliver. Mild lung effects represent the typical response to repeated inhalation exposures to amild irritant. Induction of uterine tumors is caused by a dopamine-like mode of action altering
the estrous cycle in the rat that increases exposure of the target tissue to endogenous estrogen.
As for risk characterization for lung effects, SCCS used the NOAEC of 49 ppm for local effects
on the respiratory tract as a point of departure (POD) for risk characterization after inhalation
exposures to D5. SCCS compares air concentrations of D5 using a POD of 740 mg/m3 toderive the margin of exposure/safety. The margin of safety/exposure (MoS, MoE) calculationneeds to be based on a comparison of the dose of D5 received per unit of lung weight in theinhalation studies and dose of D5 received per unit of lung weight in consumers. The local
effect is determined by dose to target. In addition, the particle sizes of D5 aerosols needs to beconsidered since only small particles penetrate into the lung.
Local respiratory tract PoD was derived from a 90-day vapor inhalation study with D5. PoD
equal to a NOAEC for lung effects is 49 ppm or 0.75 mg/L. Inhalation volume in male rats is20.5 L/h. Exposure time is six hours per day and was converted from five to seven days per
week. The average lung weight in male rats in the study was 1.02 g. The resulting inhalation
36

Silicone Industry Association of Japan

PoD was 65 mg of D5 per gram of rat lung per day.
The calculated consumer respiratory tract exposure to D5 from inhalation of aerosols
products and margins of exposure to adjusted PoD in rats shows that there is no risk
from D5 from hair styling aerosols, hair treatment aerosols, and deodorant sprays.
As for uterine tumor induction, D5 is not genotoxic, not estrogenic, and does not induce acytotoxic response in the uterus. The dopamine-like activity of D5 results in increased numberof estrogenic days in aging Fischer 344 rats. However, tests did show increased estrogen
exposure as shown in figure 1.

Figure 1: Uterine tumor induction
Endpoints affected in repeated-dose inhalation studies with D4
The hazard data was very good. There were reversible increases in liver weight similar to D5.
There was also slight nasal mucosal goblet cell proliferation and interstitial inflammation of
the lung and increased kidney weights. Although there was chronic progressive nephropathy,
this does not happen in humans and is not relevant. There were no effects on development,
but in Sprague Dawley rats there were decreased numbers of implantation sites and a reduced
mean live litter size at 700 ppm in a one-generation reproductive toxicity study by whole bodyinhalation of D4 for six hours a day a minimum of 28 days prior to mating and through theday. Exposures of females suspended from GD 21 to lactational day four and offspring were
examined after sacrifice on PND 28.
There was also a two-generation reproductive toxicity study by whole body inhalation of D4
for six hours a day for at least 70 consecutive days prior to mating through weaning of pups
on postnatal day 21. This study showed reduced mating and fertility index in F1 at 700 ppm,
a reduction in mean live litter size and mean number of pups in F0 and F1 at 500 ppm and 700
ppm, an increased estrous cycle length in F1 females at 700 ppm, and a reduction in corpora
lutea and reduced numbers of pregnancies at 700 ppm. There were, however, no adverse
effects on male reproductive endpoints.
37

Silicone Industry Association of JapanAs for the effect of inhalation exposure to D4 for 24 months on uterine histopathology inFischer 344 rats, the only statistically significant difference from control was an increase ofendometrial epithelial hyperplasia at 700 ppm. A statistically significant trend for endometrial
adenoma was also observed.
Figure 2 shows how the dopamine-like activity of D4 increases estrogen exposure of the uterus.

Figure 2: Dopamine-like activity of D4 increases estrogen exposure of the uterus
D4 was found not to be genotoxic, has only a weak affinity to estrogen receptors, and does not
act as estrogen.
Human relevance of uterine tumor induction by D4 by alteration of prolactin through adopamine-like activity of D4
Figure 3 shows the mode of action in rat from a decrease in prolactin that leads to endometrial
hyperproliferation.

Figure 3: Human relevance of uterine tumor induction by D4 by alteration of prolactin througha dopamine-like activity of D4.

38

Silicone Industry Association of Japan

It is important to note, however, that the LH suppression/delay found in rat is of little relevanceto humans. Indeed, figure 4 shows how the chain of events that leads to decreased mating andfertility in rats is broken at the point of decreased LH surge, since a decrease in prolactin is not
associated with a decrease in LH surge in humans.

Figure 4: Human relevance of a dopamine-like mode of action of D4 regarding female fertility
Summary
Modes of action have been developed for all toxicity endpoints for D4 and D5 relevant to risk
characterization. Experimentally-supported modes of action for uterine tumor induction by D4
and D5 and for female-specific effects on fertility (D4) have no human relevance. Local effects
of D4 and D5 on the lung may be used for characterization of health risks after inhalation using
appropriate dosimetry.
Questions
1. If you were responsible for CLP classifications on these two materials, what would be yourconclusion on the GHS classification?
I would issue no classification. In Europe they would probably end up with a CMR 2classification because you see tumors. Due to regulatory issues it is difficult to not issue aclassification even in the absence of human relevance.

39

Silicone Industry Association of Japan

Round Table/Wrap Up
Questions:
1. Regarding cyclics in the environment and their degradation, could you talk about themechanism and how stable cyclics are in the environment?
2. Regarding health, what are the respiratory effects on the body either in the nose or in thelungs?
3. For Dr. Dekant, what is the number of rats used in individual experiments?
(Plotzke) There is a lot of published data on the persistence of these substances. About water,
with particularly D4 you have simple hydrolysis that happens in water. The ring structure
opens up and breaks down into more water soluble materials and there may be more hydrolysis
at different pH levels. Clay catalysis is what breaks down the cyclic materials in the soil. It
happens faster in drier soil. When soil is moist cVMS moves into the air. There is also dataon the air degradation by hydroxyl radicals. We are currently looking at other mechanisms ofdegradation, but is rapid in the air and it is broken down into water soluble substances. Whereyou see more persistence is in sediment. Therefore, you need to know about the concentrationsof the parent material and whether there is potential for adverse outcomes associated with thiscompartment this can easily be assessed with a risk assessment approach. About metabolism,
the processes are similar in that you get break down into water soluble substances that are
excreted and should eventually degrade to silica and CO2.
(Maecker) Laboratory studies are done at a pH of seven for regulatory purposes, but a study
found that the average pH of surface water is 7.9 in Europe. Hydrolysis rates happen really fast
and are not temperature dependent.
(Plotzke) About human health, I think Professor Dekant answered this at the end. Looking
back at the lung effects, it is important to point out that a number of authorities looked at therobust data such as Health Canada, Cosmetic Ingredient Review Board, and the UK Health
Safety Executive. When they apply a risk assessment approach it shows there is no risk tohuman health. It is important to remember that GHS is hazard-based. Sometimes we have to
make decisions about GHS before we have mode of action data looking at relevance. If weknew what we know today, even D4 would not be classified. Australia has done a review onhuman health and has stated that there is no risk to human health in how these substances areused.
(Dekant) The issue is that you have Australia, the UK, and the US on one side and Europe
on the other side that is more conservative. The Anglo-Saxons are more risk-focused. That
there is no risk is well-supported by the evidence. There is no mode of action that supports
genotoxicity. When EFSA looks at that, they probably will also conclude that there is no risk
under present applications.
40

Silicone Industry Association of Japan

(Solomon) Assessments are done by Environment Canada and Health Canada, and they nevertalk to each other except through an intermediary. The conclusion was that risk is minimum, so
as a board we were instructed not to look at human health issues.
(Plotzke) One additional point testing, it is important to look at how we do toxicology studies
for human health or even terrestrial organisms. We are required to expose organisms to thehighest possible concentrations. From a terrestrial perspective it is important to understand thedifference between what is being done in the laboratory and how organisms in an environment
will be exposed. You will not get an inhalation exposure of 500 ppm or 700 ppm terrestriallyor environmentally. We can look at the kinetics and see that at high concentration we are ina non-linear range of kinetics. Therefore, the same effects will not be seen at the lower doses
found in the environment.
(Dekant) Rodent data is quite good as experimental support of the kinetic model. Predictions
are supported by measurements of the repeated inhalation by rats.
4. Talking about assessment methods, what is the recommended method for testing cyclics? Is
BMF good for assessing cyclics?
(Solomon) To have adverse effects you must have exposure at levels that would cause adverse
effects. If the bioconcentration due to lack of exposure is negligible or very small you cannot
get reactions that cause events. If you do not see toxicity at the maximum concentration thatyou can achieve in the matrix then bioaccumulation or biomagnification is irrelevant.
(Plotzke) About biomagnification factors, I know we cannot do trophic magnification studies
in the field on every chemical, so we need another way to understand the behavior of how
biomagnification happens in the field. For these substances, one way to do that is metabolism
and looking at the metabolic transformation rates in different organisms.
(Hashizume) I agree. For cVMSs BMF studies are more relevant than BCF studies. For
cVMSs we have field data, TMF data, and in vitro data. We should combine data to find out
what we know.
(Plotzke) We can also learn from this dataset about what happens in the field to inform how
we better understand biomagnification for other chemicals. It is quite difficult to analyze thesesubstances due to potential for contamination. You need to be extremely careful on the analysis
side. If you use a silicone-based column then you could create misleading final data. Talking
about what is going on with air and using an absorption matrix to capture the molecules,
sometimes D5 on that absorbent will break down into D4 and D3. You need to make sure thisis not happening in order to record the correct levels of each substance.
(Horii) We are using many siloxanes in our lives, so we need to pay attention when analyzing
those compounds. If we have those compounds on our body then concentrations in the indoor
air in the laboratory will increase. We need to use a simple and quick method to measure thecompounds. In our lab we always use fresh solvents. That kind of attention is important.
41

Silicone Industry Association of Japan

(Solomon) The people at Environment Canada were trying to get measurements of D5 in theenvironment and had extreme problems. They had to set up a clean room to do so. Anyone
using cosmetics or hair treatments were banned from the facility. When your blanks are higher
than environmental readings then there is problem. A paper on siloxanes in the Antarctic
showed that many mistakes were made while taking measurements. The quality score they
got was 0.05 out of four because they made all the mistakes possible, yet it was published in apeer-reviewed journal.
(Dekant) The general issue is that with trace analysis you have to be extremely careful
especially in chemicals that are widely used.
(Mihaich) That means we have to be careful when reading peer-reviewed papers. Whenyou dissect papers and find mistakes, we as scientists need work with people in the field tounderstand what is really going on.
5. With the absence of metallic ions, does it affect absorption in the human body? If siloxanes
have chelation with metallic ions, what is impact on the absorption in the skin?
(Plotzke) About the dermal absorption data, we see that regardless of the formulation (D4/D5)
it stays stable on the skin. Most of it volatilizes off the skin as parent D4 or D5, so there are noreactions on the skin. What influences the penetration is the ability to volatilize.
(Dekant) Volatility is important. The chemistry does not support complex formation because
there are no sites for chelation. The material volatilizes and absorption is very low.
(Plotzke) Absorption is 0.1% for D4 and even less for D5.
(Solomon) Human skin is very wet and these materials are not soluble in water, so we would
not expect them to penetrate the skin. I have not seen data on insects, but that would beinteresting because they have lipophilic exterior membranes.
6. About decomposition, one specific characteristics of silicone is resistance to oxidation,ozone, or UV exposure. Therefore, how can it be that D4 or D5 decompose easily in theatmosphere?
(Plotzke) D4 and D5 are the small monomers that make up the long-lasting and stable
polymers that resist degradation. D4 and D5 can interact, but the polymer behavior is very
different.
(Maecker) Reactions in polymerized compounds are very different. With respect to the halflives of D4, D5, and D6, they degrade relatively fast compared to what you would expect if
only the hydroxyl radical mechanism was at work. This implies there are more mechanismsthat break them down. We need to find those mechanisms.
(Solomon) I agree that the molecule in the air is because of volatility, but on a surface of a
42

Silicone Industry Association of Japan

product there would be a smaller probability of reactions by hydroxyl radicals, which makes it
more stable.
7. You suggested CAR-induced CYP 1/CYP 2B, but I think there is crosstalk of the gene
expression. There may be indirect effects due to this crosstalk.
(Dekant) There is fairly good characterization about which P450 activities are induced, so
this is the major pathway. There is always overlap of P450 activities, but the major point isthat P450 induction is very similar to phenobarbital. Second, there are liver weight increases
without any histopathology which indicates events are not adverse. As for interactions, youhave to have fairly high concentrations, which means when you do drug interactions the
blood levels of the drugs are at least micrograms or milligrams per liter, so there are specificinteractions possible depending on the cytochrome P450 is blocked or induced. There is noevidence that changes in the biotransformation of another agent occurs. Even if you haveagents with high environmental exposure higher than D4 and D5 it is difficult to see anything.
(Plotzke) Are you referring to cross talk between nuclear receptors? We compared it tophenobarbital, and specifically looked at CAR and PXR interaction. Even though you haveliver enlargement and some similarity to phenobarbital, you do not have liver tumors after even
two years.
8. Regarding regulatory status, in Europe there may be restrictions on wash off for personalcare applications. What is your forecast regarding this?
(Maecker) The wash off personal care restriction is decided by the European Commission.
There needs to be publication in the official European journal and then a 24-month phase out
compliance period. After that no products are allowed to have more than 0.1% of D4 or D5.
It was foreseen that this goes together with a monitoring program of the waterways on theinfluence on water treatment plants to see if that restriction is effective. If not effective, what
other additional measures that could be taken would be discussed. Then all member states haveto agree. Unfortunately, the European Commission asked the European Chemicals Agency
to develop another form of restriction for personal care products, and they cannot deny that.
The European Chemicals Agency has to look at the details, and asked all parties in Europe toprovide relevant data. The next step is for the European Chemicals Agency to review this datawith no time limit. They will then create an Annex-15 dossier and have a year to publish it.
As an industry we are convinced that these compounds are not PBT. Therefore, we
are in constant debate with member states and authorities in Europe to help them to come tothe same conclusion. At a workshop with German authorities in November we talked about
this. On the first of August they announced that they would conduct a risk management
option analysis (RMOA), which surprised us. However, they are starting at the level hazard
assessment, so they are trying to do the PBT assessment again taking into account all of thelatest information. In principle it is a good development since we can inform the process with
QWoE in a structured way. It is getter clearer to people in Europe that the chemistry is different
and that the evaluation process needs to be adapted.
For the PBT heuristics and how to apply standards, once a substance like D4 makes a
POP listing, it does not matter what evaluations had been done in the states that are a part of the
43

Silicone Industry Association of Japan

Stockholm Convention. Member states would lose the ability to make their own decision on
the matter.
9. The weight of evidence description for PBT assessment annex was updated, so could you
talk about that?
(Maecker) There are two REFIT programs ongoing in Europe for POPs and PBTs. In principlethat is not a new thing. Chemical industries can now give input and an opinion on how toassess substances. Even in annex XIII there is talk about weight of evidence in addition tonumerical criteria. However, no one does it correctly, transparently, or in a repeatable way,
which is a problem. Make sure there is a transparent way as described in a guideline on how
to apply WoE so that everyone can apply it in the same transparent way. In Europe we are notthere yet.
10. How do you introduce a weight of evidence approach?
(Solomon) It is not difficult. All you need is a scoring guide and to use it on studies andreports, but doing so takes longer than you think, especially for published studies. Sometimes
it is extremely difficult to understand what they did. A badly-written paper can take you twodays to understand and GLP studies can take an hour. Also, a QA process as you do in GLP isimportant to catch any mistakes. As long as it is transparent, the exact scoring system is notthat important. We should get the same results regardless of scoring mechanism. Transparency
is essential
Ellen talked about comparing 95th percentile concentrations to NOECs. When we did
the sediment deterministic risk assessment, for sediment we used the 99.9th centile, which isvery conservative. This was deliberate because we think these things are not likely to cause
problems. The only reason we could do so was because the datasets were very good.
(Plotzke) It is important to look at new methodologies, how to apply them, and looking at
all the data. We understand that criteria for screening are important, but you must look atadditional data in a weight of evidence type of approach. The most important thing to keep inmind is to document the process, be transparent, and discuss it with other experts.

44

Silicone Industry Association of Japan

Closing Comments
Eriko Sakurai

President, Silicone Industry Association of JapanAt first, we appreciate all the speakers, who are the leading researchers in this area globally.
And thanks to the workshop attendees to make the workshop successful by your active
participation. All the high quality of questions and discussions prove that this is a really hot
topic for many of us. It was great to learn about the scientific processes of Weight of Evidence.
We now believe more about the relevance of Weight of Evidence as a part of regulation
method. I hope Dr. Solomon would be able to give us a short course on Weight of Evidence as
he does at Universities in the near future. One of our important missions in Chemical Industry
is the innovation. Our innovation supports the innovation at downstream industries such as
Automotive, Electronics, Personal Care and more. Another important mission for us is ourcontribution to sustainability. We will continue to provide our knowledge to the science based
chemical management.

45

Silicone Industry Association of Japan