Toxicokinetics of pyrene in the freshwater alga Chara rudis

• Uptake and degradation of pyrene in Chara rudis was studied over 22 days.
• Exposure to pyrene during epilimnetic conditions gave significant growth compared to hypolimnetic.
• Pyrene dissipated more rapid from water during epilimnetic conditions.
• Pyrene was metabolised to 1-OH-pyrene, and both translocated from cortex to cytoplasm.
• The mass balance indicate a ring fission of pyrene and metabolites after 4 days.

Chara has been suggested a good model to study uptake of xenobiotics into cytoplasm due to their large internode cells surrounded by a layer of cortex cells. We studied the uptake and elimination of pyrene (nominal concentration of 5 μg L−1) in the freshwater alga Chara rudis during 22 days in two treatments mimicking epilimnetic (warm and light) and hypolimnetic (cold and dark) conditions. The growth of Chara during the exposure was higher in epilimnetic conditions (40%) compared to both hypolimnetic pyrene exposed Chara and controls (epilimnetic and hypolimnetic, no pyrene). In the water, a more rapid dissipation of pyrene was observed in epilimnetic conditions, possibly as a result of the increased algal growth. In the cortex, pyrene, 1-OH-pyrene (minor metabolite) and an unknown hydrophobic major metabolite was measured. Pyrene amounts decreased over time, while amounts of the unknown metabolite increased. In internode cytoplasm, pyrene and 1-OH-pyrene showed initially increasing followed by decreasing trends, while the unknown metabolite was not detected. The total mass balance showed that we were able to account for the applied pyrene until 4 days of exposure. However, after this time, there was a significant decrease in amounts accounted for by fluorescence, suggesting that the metabolism of pyrene involves degradation of the ring structure. The degradation was larger in epilimnetic than hypolimnetic conditions.

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