Opinion on the results of the Risk Assessment of: Dimethyl Sulphate [DMS], CAS N°: 77-78-1, EINECS N°: 201-058-1 carried out in the framework of Council Regulation (EEC) 793/93 on the evaluation and control of the risks of existing substances - Opinion expressed at the 15th CSTEE plenary meeting, Brussels, 5th of May 2000.
Terms of reference
The CSTEE on the basis
of the examination of each Risk
Assessment Report is invited to
examine the following issues:
1. Does the CSTEE agree with
the conclusions of each Risk
Assessment Report?
2. If the CSTEE
disagrees with such
conclusions, the CSTEE is
invited to elaborate on the
reasons for this divergence of
opinion.
GENERAL COMMENTS
ENVIRONMENT
The information on
toxicity both for aquatic
organisms and the terrestrial
compartment is very limited.
However, due to the negligible
releases of DMS into both
compartments no further data
are needed; thus the
conclusions in the Risk
Assessment Report are
justified.
HUMAN HEALTH
Although there is
general agreement with the
results of the Risk Assessment
Report the CSTEE disagrees with
some conclusions or proposals
given in the document for
Consumers and Workers.
The CSTEE also disagrees
with the proposed
classification only as a skin
sensitiser, the quantitative
cancer risk assessment, the
risk characterisation of
reproductive toxicity and the
Risk Assessment Report proposal
for occupational exposure limit
values.
Final general remark
Literature citations
should be checked, as some
inconsistencies between
citation in the text and in the
reference have come to our
attention.
SPECIFIC COMMENTS
Environment
Short-term toxicity data
are available for all trophic
levels of the aquatic ecosystem
(fish, invertebrates, algae,
bacteria). Nevertheless, in
most cases, data reliability is
low or methodological details
are not sufficiently described
for an appropriate judgement.
In general, it is
proposed in the report that
available toxicity data refer
to the mixture of DMS and its
hydrolysis products
(monomethylsulphate and
sulphate). These latter are
very less toxic than DMS. Thus
the reported toxicity is mainly
attributed to DMS.
Long term toxicity data
are not available for any
aquatic organism.
A PNECwater of 14m g/L
was calculated from the lowest
acute toxicity figure. This
lead to a PEC/PNEC values
always lower than 1.
The CSTEE can agree with
the judgement of low concern
for treatment plants, for
sediments and for soil
compartments, even if no data
are available on sediment
dwelling organisms, on the
understanding that it is
rapidly hydrolysed.
The risk for the
terrestrial (soil) compartment
was assumed to be negligible
due to the lack of exposure.
A potential risk related
to atmospheric exposures has
been identified for humans
exposed through the local
environment. The ecological
consequences of this exposure
should also be identified. As
indicated in the report, this
risk has not been assessed due
to the lack of ecotoxicological
information.
Human Health
1. Classification as a
sensitiser
The presence of a skin
sensitisation potential and the
general reactive nature of the
compound suggest that it is
also a respiratory sensitiser.
This contrasts with the
conclusions in chapter 4.1.3.1
(p. 61). Since the major route
of exposure is inhalation, an
experimental evaluation (in the
absence of an OECD validated
guideline) of the sensitising
potential upon inhalation is
needed.
2. Quantitative cancer risk
assessment
The rapporteur proposes
a quantitative cancer risk
assessment for DMS. Based on
his calculations reference
concentrations with acceptable
cancer risk levels in the range
from 0.09 to 9 microg/m³ (p.
66) are given. This approach
and the calculations are not
justified. Moreover, the
current analytical detection
limit for DMS in air is 10
µg/m³.
A scientifically based
risk assessment process is only
justified if sufficient
toxicological data are
available, e.g. mechanistic
data or dose-response
relationships. As mentioned
repeatedly in the Risk
Assessment Report, the database
on DMS carcinogenicity is very
limited. The shortcomings of
the carcinogenicity studies
(Druckrey et al. 1970; Schlögel
1972) on DMS are adequately
addressed by the rapporteur
(e.g. group size,
concentrations above MTD,
unusual study design). Using a
crude linear extrapolation
model as a default method to
calculate cancer risk
regardless of the underlying
database is not justified from
a scientific point of view.
There is a great degree of
uncertainty in the
corresponding figures. This
uncertainty must be indicated.
There is no controversy
that DMS should be regarded as
a potential human carcinogen
with a genotoxic mode of
action. Therefore, it has to be
assumed that even at low doses,
any exposure leads to a certain
health risk, which, however, is
not quantifiable so far (see
above).
Instead of dealing with
unreasonably low occupational
exposure levels having no
scientific background, risk
minimisation for workers should
be based on adequate personnel
protection equipment and on
technical measures to reduce
exposure.
Due to the
above-mentioned reasons, the
cancer risk calculation (pp
62-63) and the derivation of an
occupational exposure limit
based on cancer risk (pp 65-66)
is not acceptable.
Alternatively, the uncertainty
of the risk estimation must be
described.
3. Risk characterisation of
reproductive toxicity
tly, the second
conclusion (iii) concerning
reproductive toxicity is not
justified.
4. Occupational exposure
limit values
There is agreement that
information on dose-response
relationships for critical
non-tumorigenic effects (e.g.
respiratory irritation) are
lacking. This strengthens the
demand for exposure
minimisation.
The toxicological data
on DMS do not allow any
conclusion on a scientifically
based occupational exposure
limit. Taking this as a fact,
any attempts to extrapolate or
calculate a number are not
justified.
Again, risk limitation
by exposure minimisation and by
personnel protection equipment
should be recommended in this
section.