Opinion on the results of the Risk Assessment of : Benzene, C10-13-alkyl derivs 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 6th CSTEE plenary meeting, Brussels, 27 November 1998
Terms of
reference
1. Are the conclusions of the
Risk Assessment Report justified?
2. Are the Risk Assessment Reports
presented by the Member States
Rapporteur
of good quality?
Physico-chemical properties and
environmental partitioning
Even if precise figures cannot be defined
for a technical mixture, it is reasonable to
assume that different congeners in the mixture
of Benzene C10-13 alkyl derivatives have very
similar properties. Thus the technical mixture
of linear alkylbenzenes (LAB) can be defined
as low water soluble (in the order of a few
tens of µg/L) highly lypophilic (log Kow>7)
and highly volatile.
Volatility data are quite controversial and
different vapour pressure figures are reported
in the literature, but always higher than 1Pa.
Taking into account the low water solubility,
Henry's Low Constant (either calculated or
experimentally determined) is very high,
indicating significant volatilisation from
water to air. This in contradiction with the
statement at page 6 of the report indicating
"moderate volatilisation from the water
medium".
In conclusion, in function of the
partitioning among environmental compartments,
LAB can be classified as follows:
- moderate
affinity for water
- high
affinity for air
- high
affinity for soil, sediments and organic
matter.
Persistence
LAB is readily biodegraded in the aquatic
environment and in soil. In natural river
water, a half-life of about 4 days was
observed at a concentration of 100 ppb and a
half-life of about 9 days was observed at a
concentration of 500 ppb (far above water
solubility). The product is readily
mineralised to CO2.
In sewage sludge treatment plants, removal
is >98%.
No photochemical transformation was
observed.
Environmental assessment
Bioaccumulation
LAB has a very high bioaccumulation
potential, but experimental BCF in fish is
very low. Experiments on fish bioaccumulation
were well done and methodologically sound,
therefore BCF figures are highly reliable. The
hypothesis of metabolisation in the liver
seems to be confirmed by some experiments on
mammals, nevertheless, metabolic patterns are
not well known. Therefore, the possibility of
bioaccumulation in other animals (e.g.
invertebrates) cannot be completely excluded.
Environmental exposure
Aquatic and terrestrial environment
The application of the tables of the
Technical Guidance Document (TGD) indicates
relatively high figures of emissions in water
and soil during production and processing.
Nevertheless, taking into account the results
of Life-Cycle Inventory studies, it seems
reasonable to accept the assumption that
emissions in the environment during production
and processing are negligible in comparison to
emission in sewage due to the use of
LAS-containing detergents.
On these bases, local exposure is
calculated according TGD, and the results are
the following:
Cuntreated
sewage |
0.075 mg/l |
Ctreated
sewage (activated sludge) |
0.0045 mg/l |
Csludge |
93 mg/kg |
PECmicro-organism |
0.0045 mg/l |
PECsurface
water (treated effluents) |
0.0005 mg/l |
PECsurface
water (without treatment) |
0.0075 mg/l |
PECsediment |
0.24 mg/kg |
PECsoil
(av. time: 30 d) |
0.076 mg/kg |
PECsoil
(av. time: 180 d) |
0.017 mg/kg |
PECgrw. |
4.4 x 10-5
mg/l |
Regional exposure is
calculated according to the EUSES program and
results are the following:
Compartments | PECs |
Surface
water |
7 x 10-5
mg/l |
Sediment |
0.06 mg/kg |
Agricultural
soil |
6.5 x 10-4
mg/kg |
Natural soil |
7 x 10-7
mg/kg |
Groundwater |
1.6 x 10-6
mg/l |
Calculated figures are
generally in agreement with some monitoring
data available.
Atmosphere
The statement that no atmospheric emissions
are expected due to the very low vapour
pressure of LAB is unacceptable, as
highlighted above.
Nevertheless, the value calculated by EUSES
for a local PEC in air (3.2 ng/m3) is
acceptable.
Food Chain
Assuming a scenario where food sources are
50% local and 50% regional is not very
correct. A worst case of sedentary predators
eating on a local basis should be assumed.
Thus, the following concentrations for fish
and earthworm should be taken:
PEC
fish = 0.017 mg/kg
PEC
worm = 5.5 mg/kg
Toxicity on aquatic and terrestrial
organisms
Surface water
Data on aquatic organisms show some
contradictions. Experiments on several
organisms (bacteria, algae, crustaceans and
fish) show no adverse effects at saturated
concentrations. Nevertheless, acute and
chronic experiments on
Daphnia magna
carried out using a carrier solvent indicate
very high toxicity levels (LC50 48h ranging
from 80 to 9 µg/L; 21 days NOEL= 7.5 µg/L). In
the report it is suggested to reject these
results, supporting the suggestion with the
hypothesis that "the toxicity mechanism in
presence of a carrier is different".
Nevertheless, the use of carriers for
testing aquatic toxicity of low soluble
substances is a commonly accepted procedure
and the results obtained must be taken into
account. Moreover, for substances carried into
natural waters through sewage containing a
number of unknown organic substances
(including solvents) the possibility of
interference cannot be excluded.
Therefore, there are no reasons for
rejecting the hypothesis that, at least in
particular conditions, LAB could be toxic for
aquatic organisms.
The PNEC, based on the lowest NOEL on
aquatic organisms, is set at 0.00075 mg/l.
Sediment, Terrestrial compartment and
Atmosphere
The PNEC for sediment and soil organisms is
calculated on the basis of the previously
defined PNEC on aquatic organisms, thus, it
can be assumed as very conservative.
No data are available for the setting of a
PNEC for air compartment.
Food chain
The assessment of a PNEC for food of 50
mg/kg seems reasonable.
Risk characterisation
Some problems arise from the evaluation of
the risk for the aquatic ecosystem on a local
basis.
If risk is based on the surface water
concentration resulting from an activated
sludge (AS) Sewage Treatment Plant (STP)
effluent, the result is the following:
PEC/PNEClocal
= 0.0005 / 0.00075 = 0.68 |
Nevertheless, if the worst
monitoring data of 0.001 mg/l, referring to a
trickling filter STP effluent, is used, one
obtains a PEC/PNEC
local = 1.3.
Moreover, if calculation is made considering
surface water receiving a non-treated
effluent, PEC/PNEC
local = 10.
It must be underlined that situations of
inadequate or completely lacking sewage
treatment are not unlikely to occur in
European surface waters.
Therefore, risk for the aquatic environment
on a local basis cannot be excluded.
For all other compartments, the statements
of negligible risk for the environment are
reasonable.
Human health
Exposure assessment
Because alkylation of benzene is a step in
the production of linear alkyl benzene (LAB),
rigorous procedures have been set up in order
to control exposure to this toxic compound.
This, in turn, ensures «negligible» exposure
to LAB.
Occupational exposure
No monitoring data are available. The
estimation of possible exposure in the
workplace was carried out using an EASE model
and indicated very limited dermal and oral
exposure.
Consumer exposure
The scenario used for calculation was very
conservative and the data provided are
indicative of a safe situation.
Indirect exposure via the environment
The EUSES calculations for local and
regional total daily intakes were 2.5 10
-4
mg/kg and 1.5 10
-5 mg/kg
respectively.
Hazard identification and dose
(concentration)-response (effect) assessment
Toxico-kinetics, metabolism and
distribution
The distribution, metabolism and excretion
of 2-(14C)-phenyl dodecane have been studied
in male and female rats up to 96 hours
following intravenous, oral or dermal route
exposure. Metabolism has been studied by thin
layer chromatography analysis, distribution by
whole body autoradiography and excretion by
liquid scintillation counting.
LAB and its metabolites (up to 9
identified) were rapidly excreted in the
urine.
Radioactivity persisted a longer time in
organs of high lipid content. It is noticeable
that radioactivity has been detected
constantly in the stenos gland following
intravenous and oral route.
After oral and dermal dosing, no
radioactivity was detected in the central
nervous system (except in the pituitary sinus
of the brain).
Acute toxicity
No deaths were observed in acute oral and
dermal toxicity limit tests on rats. LAB is
not classifiable as either toxic or harmful
under current EU legislation. The aerosol size
used for inhalation studies should be
indicated.
Irritation
Properly conducted assays indicated that
LAB is not an irritant neither for the eye nor
for the skin.
Corrosivity
LAB is not corrosive
Sensitisation
No sensitising potential was demonstrated
for human and guinea pigs.
Repeated dose toxicity
Inhalation and oral NOAEL in rats were 102
mg/m
3 (6 hours/day for 14 weeks)
and 50 mg/kg/day (2-generation fertility
study) respectively
Mutagenicity
All tests were negative :
- Ames
(with and without metabolic activation)
- Mammalian
cell systems (V79 and CHO /HGPRT gene
mutation),
- Rat bone
marrow chromosome assay.
Carcinogenicity
Although there is only one rat study
available which was limited to 18 months
duration, there is no reason to suspect that
LAB poses a carcinogenic hazard.
Toxicity for reproduction
Reproductive (fertility and developmental
teratogenicity) toxicity have been adequately
studied and no sign of these toxic effects
were detected.
Risk characterisation
Workers
Margins of safety (MOS) are 41.6 and >100
for dermal and inhalation exposure
respectively.
Consumers
MOS for dermal and oral exposure are 8475
and 263158 which is very high.
Man exposed indirectly via the environment
Here again the MOS are extremely high: 2 X
10
5 and 3.3 X 10
6 for
local and regional models respectively.
Some gaps do exist with hazard
identification to the lung. For instance, due
to an unclear protocol, acute toxicity is
questionable. In addition neither
toxicokinetic nor metabolic and distribution
studies have been conducted whereas both
volatilisation to air and high lipophilicity
indicated high possible air pollution and lung
targeting respectively. However, due to very
low exposure, these gaps are not interpreted
by the CSTEE as sufficient to alter the risk
characterisation.
Conclusions
Referring to environmental aspects, the
report provides enough information for a Risk
Assessment of LAB. Procedures for calculating
PECs and for risk characterisation are
adequate and, notwithstanding some minor
inconsistencies, correctly applied.
Referring to human health, the general
conclusion that there is at present no need
for further information and/or testing or for
risk reduction measures beyond those which are
being applied already is deemed consistent
with the available data and calculations
presented in the document.
The major criticisms to the document are
the following:
1. The statements about the low volatility
of LAB cannot be accepted if a vapour pressure
higher than 1Pa is assumed. Anyway, this is
not very relevant for the risk assessment,
because the risk for the environment due to
atmospheric pollution can be assumed as
negligible.
2. The report tends to minimise the risk
for the aquatic environment, even if a PNEC as
low as 0.00075 mg/l is correctly used for the
evaluation. Taking into account the
environmental fate of the product and, in
particular, the low persistency, it is
reasonable to confirm that the risk on a
regional scale is negligible. Nevertheless, on
a local basis, in the absence of adequate
treatment facilities, a risk for the aquatic
environment is likely to occur.