Abstract
The objective of this M.Sc. research project, conducted in the framework of ENFIRO, a project within the
Cooperation Program of the EU 7th Research Framework Programme, was to assess the aquatic toxicity of
organophosphorous flame retardants (FRs) tetraphenyl resorcinol bis(diphenylphosphate) (RDP), bisphenol-
A bis(diphenylphosphate) (BDP). This was done by testing the inhibitory effect
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of FRs on the degradation of
glucose.
In the first experiment Guideline 301 of the Organisation for Economic Co-operation and Development
(OECD) for ready biodegradability testing was applied and CO2 production was measured continuously using
the automatic respirometer Respicond VI. To overcome the challenge of obtaining a constant dissolved
concentration of the strongly hydrophobic substances, RDP and BDP were loaded onto, and passively dosed
to the inoculums from PDMS silicone devices. The loading of the PDMS passive dosing devices was
unsuccessful; only 1.87% and 2.41% of the intended loaded mass of RDP and RDP was found to be present
on the PDMS tubing respectively. Although the automated respirometer Respicond VI has proven to be
convenient in use, it has also shown to be prone to contamination when used for liquid samples.
In the second experiment, applying the head space test (OECD guideline 310), the CO 2 evolution was
measured with gas chromatography. The concentrations of saturated RDP and BDP solutions were shown to
increase with dilution factor. Also, sedimentation occurred after ~10 days. Rather than a true solution, the
solutions therefore likely were colloidal micro-emulsions.
In neither experiment a decrease in degradation rate or ultimate percentage degradation with increasing FR
concentration was observed. The percentage degradation of glucose in the first experiment was
90.05±4.03% for RDP and 86.03±3.83% for BDP, and in the second experiment was 39.79±6.16% RDP and
34.91±4.56% on average for BDP. Thus, no toxicity effect was observed. However, from these data no
conclusions can be drawn about the FRs toxicity; no measurable concentrations of the target FR were
present in the Respicond study. In the head space test, the test medium likely was a micro-emulsion rather
than a true solution, which must certainly have had implications for the FR bioavailability to the test
organisms. Further, the pass level of 60% degradation was never reached for any of the samples nor for the
controls, and the test is therefore invalid.
In the absence of a reliable means to obtain a constant aquatic concentration of RDP and BDP, the toxicity
and persistence tests as designed are not likely to be successful in the future. Different research strategies
may be considered; passive dosing may be optimized for use with these phosphorous based compounds, or
the hypothesis that RDP and BDP form aggregates may be confirmed, after which these substances may be
investigated further as colloid particles.
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