Equilibrium partitioning behavior of naphthalene and phenanthrene with axenic microplantlets of the temperate green seaweed Acrosiphonia coalita

The partitioning behavior of the polycyclic aromatic hydrocarbon (PAH) compounds naphthalene and phenanthrene with the temperate green seaweed Acrosiphonia coalita was characterized. The uptake and partitioning experiments were designed to prevent PAH volatilization, and the PAH concentration was measured in both the seawater liquid medium and in the algal biomass. Axenic microplantlets of A. coalita were used in all experiments to eliminate the possibility of microbial PAH biotransformation. Gas chromatography/mass spectrometry analysis did not reveal any putative metabolites of phenanthrene oxidative biotransformation in either the seawater medium or the algal biomass, but did show that dissolved organic matter from algal biomass constituents were in the liquid medium. The algal biomass grew by 30% over the 114 h duration of the partitioning experiments, suggesting PAH compounds did not harm the organism. Both living and heat-killed microplantlets partitioned PAH compounds into the biomass. Naphthalene and phenanthrene reversibly partitioned into the lipid fraction of the algal biomass with equilibrium partitioning constants of 0.130 ± 0.007 and 1.58 ± 0.03 L g−1 dry cell mass, respectively, which scaled proportionally to their octanol–water partitioning constants. The PAH material balance for the partitioning process closed between 86% and 100% for naphthalene adsorption and phenanthrene desorption, but closed at 52% for phenanthrene adsorption. To account for the loss, it was proposed that phenanthrene interacted with dissolved organic matter released by the living algal biomass. This study has provided fundamental information needed to assess how seaweeds can play a role in the bioaccumulation and bioremediation of PAH compounds in the marine environment.