The environmental ubiquity of perfluorooctane sulfonate (PFOS) is well-known. However, little is known about the environmental fate of individual PFOS isomers. In this study, we investigated the fractionation and the bioaccumulation of PFOS isomers in water, sediment and biota collected from Lake Ontario. A total of six isomers, three perfluoro-monomethyl-substituted compounds, and three perfluoro-dimethyl isomers in addition to the linear PFOS (L-PFOS) were detected in water, sediment and biota. L-PFOS represented a much higher proportion of total PFOS (sum of linear and branched) in all organisms (>88%) compared to its proportion in technical PFOS (77%). The predominance of L-PFOS suggests a reduced uptake of branched isomers, a more rapid elimination of the branched isomers and/or a selective retention of the L-PFOS. The PFOS isomer profile found in biota was very similar to sediment, even for pelagic organisms such as zooplankton, suggesting greater partitioning of L-PFOS to biota and to sediment. The bioaccumulation factor (BAF) for L-PFOS between lake trout (whole fish) and water was estimated to be 3.4 x 10(4) L/kg compared with 2.9 x 10(3) L/kg for the monomethyl-substituted group (MM-PFOS). The remarkable difference between L-PFOS and branched isomer BAFs is due to an enrichment of branched isomers in water. The trophic magnification factor of L-PFOS (4.6 +/- 1.0) was greater than MM-PFOS isomers (1.3 +/- 0.17 to 2.6 +/- 0.51), whereas dimethyl-PFOS showed no biomagnification. The results illustrate the important influence of molecular structure on the bioaccumulation of perfluoroalkyl sulfonates.

Aggregation of algae, mainly of diatoms, is an important process in marine pelagic systems, often terminating phytoplankton blooms and leading to the sinking of particulate organic matter in the form of marine snow. This process has been studied extensively, but the specific role of heterotrophic bacteria has largely been neglected, mainly because field studies and most experimental work were performed under non-axenic conditions. We tested the hypothesis that algae-bacteria interactions are instrumental in aggregate dynamics and organic matter flux. A series of aggregation experiments has been carried out in rolling tanks with two marine diatoms typical of temperate regions (Skeletonema costatum and Thalassiosira rotula) in an axenic treatment and one inoculated with marine bacteria. Exponentially growing S. costatum and T. rotula exhibited distinctly different aggregation behavior. This was reflected by their strikingly different release of dissolved organic matter (DOM), transparent exopolymer particles (TEP) and protein-containing particles (CSP), as well as their bacterial biodegradability and recalcitrance. Cells of S. costatum aggregated only little and their bacterial colonization remained low. Dissolved organic matter, TEP and CSP released by this alga were largely consumed by free-living bacteria. In contrast, T. rotula aggregated rapidly and DOM, TEP and CSP released resisted bacterial consumption. Experiments conducted with T. rotula cultures in the stationary growth phase, however, showed rapid bacterial colonization and decomposition of algal cells. Our study highlights the importance of heterotrophic bacteria to control the development and aggregation of phytoplankton in marine systems.

A fugacity-based, nonsteady state, mechanistic model called ACC-HUMAN was developed to describe bioaccumulation of lipophilic organic pollutants from air, water, and soil to humans. The physical environment was linked via a marine and an agricultural food chain model to a human bioaccumulation model. Contaminant uptake via the primary dietary sources of persistent lipophilic contaminants in industrialized countries was addressed, namely fish, dairy products, and beef. In addition, uptake from air and water was considered, allowing the model also to treat less lipophilic compounds. To evaluate the model, the food chain characteristics were parameterized for southern Sweden and historical scenarios of polychlorinated biphenyl (PCB) concentrations in air, water, and soil in this region were constructed from published data. The resulting model predictions of PCB concentrations in fish, milk, beef, and human tissue agreed well with measured concentrations from Swedish monitoring programs. This suggests that ACC-HUMAN is a useful tool for predicting human exposure to bioaccumulative organic compounds. It can be linked easily to existing multimedia fate and transport models.

A model was used to explore the influence of physicalchemical properties on the potential of organic chemicals to bioaccumulate in humans. ACC-HUMAN, a model of organic chemical bioaccumulation through the agricultural and aquatic food chains to humans, was linked to a level I unit world model of chemical fate in the physical environment and parametrized for conditions in southern Sweden. Hypothetical, fully persistent chemicals with varying physical-chemical properties were distributed in the environment, and their bioaccumulation to humans was calculated. The results were evaluated using the environmental bioaccumulation potential (EBAP), defined as the quotient of the chemical quantity in a human divided by the quantity of chemical in the whole environment. Since the latter is closely related to emissions, EBAP is potentially a more useful tool for comparative risk assessment of chemicals than currently used medium-specific measures such as the fish-water bioaccumulation factor. A high environmental bioaccumulation potential, defined as > 10% of the maximum EBAP, was found for chemicals with 2 < log KOW < 11 and 6 < log KOA < 12. While these chemical partitioning properties clearly influenced bioaccumulation at each trophic level, these effects tended to equalize over the food web. The fact that the transfer from the environment as a whole to humans was quite uniform over a large chemical partitioning space suggests that these partitioning properties are relatively unimportant determinants of human exposure compared to other factors such as the substance's persistence in the environment and in the food web.