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EC number: 295-442-6
CAS number: 92045-60-8
A complex combination of hydrocarbons obtained by subjecting a petroleum naphtha to a sweetening process to convert mercaptans or to remove acidic impurities. It consists of hydrocarbons having carbon numbers predominantly in the range of C4 through C5, predominantly C5, and boiling in the range of approximately minus 10°C to 35°C (14°F to 95°F).
undertaking environmental risk assessments the best use of all available
ecotoxicity data should be made. However, the assessment of ecotoxicity
data for many petroleumproducts
is complicated since several different test methods and procedures have
been used. As petroleum products contain a mixture of substances with a
range of solubilities a critical aspect with respect to interpreting the
validity of ecotoxicity tests is how the test media is prepared.
Although not always explicitly stated most of the data
generated in the period up to the early 1990s originated from
experiments in which a "water soluble fraction" (WSF) was tested. WSFs
are prepared by mixing the petroleum product with the aqueous test
medium (e. g. 25 to 50 mL product with 1 L of medium). After mixing the
test solutions are then allowed to stand, the aqueous phase is separated
and dilutions of this medium are used in testing the species under
study. The results areexpressed either
as (a) the dilution, or % WSF, or (b) the concentration of dissolved
hydrocarbons expressed in mg/L (CONCAWE, 1995). A disadvantage with
these WSF studies is that it is not possible to convert the quoted
result to the amount of product that must be added to a given volume of
aqueous medium to produce the effect.
problems of preparing test media for oil products were recognised in the
early 1990s. As a consequence the recommended method, which enables
ecotoxicity assessments of petroleum products to be interpreted, was to
determine the amount of test substance that must be equilibrated with
the test medium to produce a specified level of effect. This is the
so-called "loading rate" or water accommodated fraction (WAF)
methodology as developed by Girling et al. (1992) and reported in
CONCAWE (1992). Even with these laboratory based studies there are
doubts about their value in the context of risk assessment owing to the
fact that once a petroleum product is released to the environment its
constituent substances will partition to the various compartments
(water, sediment, soil and air) in accordance with their
physico-chemical properties. The assumption being that in the receiving
environment the substances will be degraded and transformed in
accordance with their individual susceptibilities to physical, chemical
and biological degradation processes and will exhibit effects in
accordance with their individual toxic potencies.
on mechanisms of toxicity and PNEC derivation
an attempt to better understand the potential for adverse effects an
attempt to integrate the effects of a products constituent substances
(hydrocarbon blocks) in such a way that an overall assessment of their
combined effects can be made. For the assessment of toxic effects it is
important that the method of integration meets the assertion that
effects can only be integrated for substances that share the same mode
of toxic action. All components of petroleum products exhibit non-polar
narcosis effects on organisms.
ideal circumstances a PNEC for a hydrocarbon block would be derived from
ecotoxicological test data for one or more components that are
representative of that block. The TGD sets out how this can be done
either by applying an Assessment Factor to the lowest acute
ecotoxicological effect or chronic no effect concentration or by
applying statistical extrapolation methods to a number of data points.
For petroleum products this was not a practical option since the
majority of its mass is comprised of chemical components that cannot be
accurately described by a chemical structure (and which may not have a
unique CAS number) and for which there is an absence of ecotoxicological
data. Under such circumstances the only practical option is to estimate
a PNEC using a relationship between physico-chemical descriptors of a
component or a hydrocarbon block and concentrations resulting in
ecotoxicological effects or absence of an effect. This is the hypothesis
encompassed by the Target Lipid Model (TLM) described by McCarthy et al.
theory underpinning the TLM is that the concentration of a substance in
a lipid that is responsible for the onset of a non-polar narcosis effect
is the same when expressed on a molar basis for a range of taxonomic
groups e. g. fish, invertebrates and algae. Consequently the toxic
potency of a substance depends upon its capacity to achieve the
threshold concentration within an organism. There are a number of
variables that determine this capacity, key of which are the solubility
of the substance in water and lipid and its molecular size. In an
application of the theory, DiToro et al. (2000) have published a
non-polar narcosis-based QSAR for predicting the aqueous concentration
of a hydrocarbon substance that induces a specified level of biological
effect. The QSAR relates biological effect to the log Kow of the
substance. Log Kow is a function of the solubility of a substance in
water and lipid (octanol) but is limited by molecular size because large
molecules cannot pass through biological membranes.
the absence of measured ecotoxicity data for a substance the TLM and
associated QSARs provide a theoretical basis for predicting the
ecotoxicity of a substance. By extension of the theory it should also be
possible to evaluate the toxicity of a mixture of substances provided
that they have the same mode of toxic action. McGrath et al. (2004) have
validated the theory by characterising the aquatic toxicity of six
gasoline blending streams and have showed that predicted and measured
toxicity were in good agreement.
established procedures that enable the toxicity of a mixture of
hydrocarbons to be predicted, McGrath et al. (2004) have also utilised
statistical theory developed by a number of workers to define an acute
species sensitivity distribution for narcotic chemicals. A relationship
has been established enabling the concentration of a hydrocarbon
substance to be determined that will affect a specified proportion of
the species present in a community. By setting the proportion to a
notional low level (e. g. 5%), a hazard concentration (HCx where x is
the proportion that might be affected i. e. 5%) is obtained. The HCx has
similarities with a hazard concentration derived by applying statistical
extrapolation procedures described in the TGD to a set of test substance
data. It can also be considered analogous to, and used for risk
assessment in the same way as, a PNEC derived by applying an Assessment
Factor (AF) specified in the TGD to a lowest acute EC50 or LC50 value in
a data set.
According to the EU CLP Regulation (EC
No. 1272/2008) criteria, substances in the low boiling point naphtha
category are classified as Chronic Category 2 (H411) for the environment
based on acute invertebrate and alga toxicity.
Information on Registered Substances comes from registration dossiers which have been assigned a registration number. The assignment of a registration number does however not guarantee that the information in the dossier is correct or that the dossier is compliant with Regulation (EC) No 1907/2006 (the REACH Regulation). This information has not been reviewed or verified by the Agency or any other authority. The content is subject to change without prior notice.Reproduction or further distribution of this information may be subject to copyright protection. Use of the information without obtaining the permission from the owner(s) of the respective information might violate the rights of the owner.
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