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Environmental fate & pathways

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Due to the complex composition ofthe substance distillates (coal tar), heavy oils (anthracene oil >50 ppm BaP, AOH [CAS no. 90640-86-1]),a single BCF value cannot be determined for the substance. Relevant components (all PAH) will have their individual BCF values. Main constituents of AOH are among others phenanthrene and pyrene (see Chapter 1.2). These substances are considered to represent the bioaccumulation potential of total AOH as other PAH present in AOH will exhibit similar characteristics (see below, reference WHO (2003)). Bioaccumulation properties of these two substances together with other more general information on the bioaccumulation potential of PAH will characterise sufficiently the bioconcentration potential of AOH as a whole.

BIOCONCENTRATION in fish focused on selected PAH as marker substances

In both, the risk assessment report on coal-tar pitch (EU 2008) and the expertise for CONCAWE (Lampi and Parkerton 2009), the study by Jonsson et al. (2004) on BCF of PAH received the highest rate of reliability. Therefore, this work is given highest priority.

In this obviously well-performed bioconcentration study similar/according to OECD 305 (flow-through conditions), BCF values were determined using concentrations in fish and water at steady state (BCFSS) and uptake and depuration rate constants (BCFK). For phenanthrene, BCFSS were 700 and 1623 respectively (low and high exposure), while BCFK were 810 and 2229. Corresponding data for pyrene were 50 and 53 (BCFSS) and 145 and 97 (BCFK). Calculation of steady state BCFS resulted in lower values than using rate constants in the BCF calculation.

For phenanthrene, less test substance accumulated in the tissue at the low exposure level (0.12 µg/L) compared to the high level (1.12 µg/L) due to a lower uptake rate, while the high excretion/depuration rates were almost the same at either exposure condition. Lower BCF for pyrene resulted from reduced uptake as apparent from the much lower uptake rate constants for pyrene compared to phenanthrene while depuration was somewhat higher as the already high depuration rate constants of phenanthrene.

Lipid content of the fish used in this experiment was high (approx. 10%). According to OECD Guideline 305 - Bioaccumulation in Fish, adopted October 2012, it is recommended to normalise BCF with regard to lipid content of test organisms for substances with high lipophilicity (i.e. with log Pow > 3) in order to reduce variability of test results caused by variable lipid content of test fish. A lipid content of 5% has been widely used and is considered as standard, as this represents the average lipid content of fish commonly used in studies on BCF.

In their expertise, Lampi and Parkerton (2009) re-calculated the kinetics-based BCF values (BCFK) by accounting for the high lipid content of the fish (approx. 10 %). Normalised by this way down to the standard lipid level of 5 % in fish, the adjusted BCFS (BCFKL) arrived at 417 and 1149 for phenanthrene and at 76 and 59 for pyrene, respectively. BCFSS normalised this way resulted in BCFSSL of 381 and 837 for phenanthrene and 26 and 27.3 for pyrene.

Based on this data, overall evidence indicates that AOH has a low to moderate bioconcentration potential. PAH are absorbed to different degrees in fish but metabolism and depuration rate is high that resulting bioconcentration factors are only moderate. However, the extent of bioconcentration is mainly determined by the metabolic and excretory capacity of the target organism and can be different for other organisms with lower metabolic capacity.

Lampi and Parkerton state that - "with the exception of phenanthrene - reliable fish BCF data indicate that the EPA PAH show BCFs below 2000" (note: Anthracene had been excluded from their treatise). They continue: "In the case of phenanthrene, there are two high quality BCF values, both below 2000 and several values that are judged to be reliable with restrictions that fall between 2000 to 5000. Thus, a weight of evidence approach for phenanthrene would suggest it fulfils the B criterion, if based only on bioconcentration data.

Taking into account the complementary information for assessing bioaccumulation properties along the food chain, available data clearly demonstrate that all PAHs investigated, including phenanthrene, exhibit a low biomagnification potential (WHO 2003; EU 2008; Lampi and Parkerton 2009).

Conclusion according to WHO:

"Aquatic organisms that metabolize PAHs to little or no extent, such as algae, molluscs and the more primitive invertebrates (protozoans, porifers and cnidaria) accumulate high concentrations of PAHs, as would be expected from their log Kow values, whereas organisms that metabolise PAHs to a great extent, such as fish and higher invertebrates, accumulate little or no PAHs.

The concentration of PAHs in vegetation is generally considerably lower than that in soil, the bioaccumulation factors ranging from 0.0001 to 0.33 for BaP and from 0.001 to 0.18 for 17 other PAHs tested.

Biomagnification (the increase in concentration of a substance in animals in successive trophic levels of food chains) of PAHs has not been observed in aquatic systems and would not be expected to occur, because most organisms have a high biotransformation potential for PAHs. Organisms at higher trophic levels in food chains show the highest potential for biotransformation (WHO 1998)." [from WHO (2003), p.147]

References:

EU (2008) Coal-Tar Pitch, high temperature - Risk Assessment. European Union Risk Assessment Report. The Netherlands [http://echa.europa.eu/documents/10162/433ccfe1-f9a5-4420-9dae-bb316f898fe1]

Lampi and Parkerton (2009) Bioaccumulation Assessment of PAHs - Review Paper Prepared for CONCAWE. ExxonMobil Biomedical Sciences, Inc.

WHO (2003) HEALTH RISKS OF PERSISTENT ORGANIC POLLUTANTS FROM LONG-RANGE TRANSBOUNDARY AIR POLLUTION, JOINT WHO/CONVENTION TASK FORCE ON THE HEALTH ASPECTS OF AIR POLLUTION. WHO Regional Office for Europe, World Health Organization 2003