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Reprotoxic effects of
benzene
The European Commission have recently completed an extensive review of
benzene's health and environmental effects under its existing
substances regulation. The EU appointed Germany as the Rapporteur
for developing the risk assessment on behalf of the other member states.
During the course of this work, two articles were identified that appeared
to indicate that benzene may have adverse effects in the offspring of
exposed rats. Because the findings were unique and had not been encountered
in other similar studies, Professor Richard Irons, the leading world authority
on the biology of benzene, was asked to provide a review of the significance
of these findings in the context of current understandings of the molecular
biology of benzene. Professor Irons findings demonstrate that whilst benzene
has many toxic properties, it is no more toxic to the offspring for children
than to adults. These same conclusions were also reached by the EU.
Biodegradability of benzene
It is important that an accurate understanding of a substance's biodegradability
in the environment is available in order that suitable judgements can
be made on the nature of controls that may be necessary to reduce any
emissions. Over the past 30 to 40 years, several studies have been undertaken
on the biodegradation of benzene. Unfortunately, many of these testing
methods are not of an acceptable quality today. This has meant that interpreting
the findings of the studies has been very difficult as, in some cases,
the results are conflicting.
In view of the importance of having a sound understanding of benzene's
biodegradability, a series of tests were performed by a number of laboratories.
Three laboratories performed five different tests in order to ensure that
minor variations in the testing protocol would be accounted for in the
resulting test data. The results show that benzene is readily biodegradable
in the environment.
The significance of the Morris Water Maze Test
The Morris Water Maze Test (MWMT) is a test that is been developed to
help try to understand how drugs and similar substances may affect a person's
memory. In the MWMT, rats swim in a pool which contains a simple maze.
Within the maze are a series of platforms that the rat is able to climb
on to. The rats' swimming performance is observed with or without administration
of the drug, in order to investigate the effect of the drug.
Recently, the test has been used to evaluate whether solvents may have
similar effects to drugs. Certain articles have been published on the
topic. APA commissioned Dr Sandra Allen, a
specialist in the field,
to
review the relative strength and weaknesses of the MWMT, particularly
as it applies to materials other than pharmaceuticals. Dr Allen's report
has been published in the literature.
A summary of the report is available.
Fate of benzene in waste water treatment plants
It is important to demonstrate the effectiveness of control technologies
used for the treatment of any benzene that is released from the aqueous
effluent of aromatic production facilities. In Europe, most emissions
from production facilities are predicted using mathematical models. Although
these models may be accurate in many cases, they are not a substitute
for real data.
A study was commissioned from a US leading company of environmental engineers and scientists (Hydroqual)to review the information that is available on the real life fate of benzene in waste water treatment plants (which are installed at production facilities to ensure that any benzene is effectively removed). They were asked to answer a specific question: what is the reason for the measured outlet concentrations of benzene at aromatics production plants being so low? One explanation may be that benzene is evaporated to air during the course of treatment. Another reason may be the fact that the micro-organisms in the treatment plant are particularly effective at digesting benzene.
Reassuringly, the answer is the latter. Waste water treatment plants
that are associated with aromatic production plants and have become "acclimatised"
to benzene are extremely efficient at removing benzene from waste water.
So, the reason that so little benzene is found at the outfall is a result
of the voracious appetite of these micro-organisms and not to the fact
that it has been lost to air during the course of treatment.
Toxicity of benzene to algae
Although benzene is
a substance for which much environmental information is available, some
of the information is now more than 20-30 years old and, as such, no longer
meets the standards expected of current laboratory tests. Therefore, a
laboratory test was commissioned to ensure that a current OECD
test was available to inform any decisions which need to be made in this
area.
The study demonstrates that benzene is of low toxicity to algae.
Ecotoxicological database for xylenes
APA is committed to ensure that the database supporting its products is
the best available. It recognised that several of the studies that describe
the effects of xylenes in the environment were not to present day requirements.
Therefore, it sought to ensure the database contained relevant, high quality
data. After a general call for tender, TNO has been chosen to perform
the following tests on para-xylene according to the OECD protocols.
Determination of the effect of p-xylene (CAS#106-42- 3) on the growth of the fresh water green alga Selenastrum capricornutum (OECD Guideline No. 201).
The differences between the observed effect that xylene had on algal growth rate and growth under the test conditions are not indicative of toxicological relevance.
Daphnia Magna reproduction test with p-xylene
The data processing showed a No Observable Effect Level at 1.57 mg/l.
Screening of the effect of p-xylene (CAS# 106-42-3)
on the respiration of activated sludge (OECD Guideline No. 209)
It was concluded that no inhibition of the respiration rate of activated
sludge took place at the limit concentration of p-xylene (water saturation).
Information on emissions from aromatics production
facilities
Information on the nature of emissions to the environment from
production facilities was collected by APA in the 1990s, and 
this
has been updated in 2005. APA gathered information from
all its member companies, enabling a full assessment
of the nature of human and environmental exposures. The exercise was
performed by an independent institution, the Royal
Haskoning laboratories in the Netherlands who are experienced in these
fields and have advised the Commission and governments on this task.