During the next 50 years, which is likely to be the final period of rapid agricultural expansion, demand for food by a wealthier and 50% larger global population will be a major driver of global environmental change. Should past dependences of the global environmental impacts of agriculture on human population and consumption continue, 10(9) hectares of natural ecosystems would be converted to agriculture by 2050. This would be accompanied by 2.4- to 2.7-fold increases in nitrogen- and phosphorus-driven eutrophication of terrestrial, freshwater, and near-shore marine ecosystems, and comparable increases in pesticide use. This eutrophication and habitat destruction would cause unprecedented ecosystem simplification, loss of ecosystem services, and species extinctions. Significant scientific advances and regulatory, technological, and policy changes are needed to control the environmental impacts of agricultural expansion.

The objectives of this study were to test the hypothesis that bioaccumulation of hydrophobic organic compounds (HOCs) by phytoplankton is correlated to the compound's octanol/water partition coefficient (Kow) in a predictive relationship in laboratory experiments, and to confirm these findings with field observations. In laboratory experiments we measured the uptake of 40 representative polychlorinated biphenyl (PCB) congeners over time under conditions that inhibited and allowed phytoplankton growth. Results indicated that the bioaccumulation process is consistent with partitioning from water into cell lipids but is slower than previously thought. The uptake of PCBs was slow relative to growth of phytoplankton, preventing the chemical from reaching thermodynamic equilibrium in algal cells under conditions promoting growth (nonwinter). Thus under nonwinter field conditions, many PCB congeners never reach equilibrium concentrations. Food-chain models that assume equilibrium between HOCs and the primary trophic level could be inaccurate and may need to use a kinetic framework.

This study reports on the development and evaluation of a predictive model for the accumulation of polychlorinated biphenyls (PCBs) in phytoplankton which incorporates the kinetics of the process. The model includes a surface sorption term, uptake and loss rate coefficients, and a biomass dilution term. Laboratory data collected from the accumulation of 40 representative PCB congeners in four representative algal species were used to parameterize the model, and the performance of the model was evaluated on a set of independent laboratory data and a set of field data collected from Green Bay, Lake Michigan. Model predictions were compared to predictions from an equilibrium model. Under low growth conditions, the predictions of the kinetics model and the equilibrium model were similar. However, for data collected during periods of intense growth, equilibrium predictions deviated significantly from the observed values and from the kinetics model predictions by as much as 3 orders of magnitude. Concentrations calculated on a lipid basis by both models significantly underestimated the observed accumulation and questioned the hypothesis that PCBs accumulate in the lipid portion of phytoplankton. However, on a relative basis, the kinetics model reproduced the observed accumulation significantly better than the equilibrium approach.

Five sediment cores from a north-south transect of Lake Michigan were collected using box cores deployed from the RV Lake Guardian and from a submersible (Johnson Sea Link II, RV Seward Johnson). The sediments, analyzed for PAHs (n ) 28) and 210 Pb to obtain accumulation rates and inventories of PAHs, were used to determine the role of the atmosphere in contaminant loading to Lake Michigan. The accumulation of PAHs in the sediments increased dramatically around 1900, reached a plateau around 1930-1975, and decreased slightly in recent time. Surface sediment accumulation rates and inventories for ∑PAHs (n ) 17 parent), corrected for sediment focusing with 210 Pb, equaled 50-70 ng cm -2 yr -1 and 5000-7000 ng cm -2 , respectively. The relative abundances of individual PAH compounds from Lake Michigan sediments, PM-10 aerosol of Chicago, and a coke oven signature are statistically similar establishing a linkage between combustion sources in the south, atmospheric deposition, and sediment accumulation. Further support for this linkage is the historical PAH accumulation in lake sediments and historical coal use in Illinois over the same time period. The major source of PAHs to Lake Michigan sediments is coke and steel production found in the urban/industrial complex around Chicago, IL, and Gary, IN. These PAHs are deposited primarily in the southern basin after which they are redistributed throughout the lake as a result of in-lake integration processes (water and sediment transport).

A wide range of chlorinated organic compounds was measured in different size classes of lake trout (Saluelinus namaycush namaycush) and whitefish (Coregonus culpeaformis neohantoniensus) from Siskiwit Lake, a remote lake on Isle Royale in Lake Superior. Our results confirm the long-range transport of several chlorinated pesticides and polychlorinated biphenyls (PCBs) and, in addition, indicate that technical chlordane constituents, octachlorostyrene, pentachloroanisole, and decachlorodiphenyl ether also are transported to remote locations. Chemical concentrations as a function of fish age (size) were not similar between species and were not consistent among compounds. Differences in bioaccumulation with age between species for a given compound indicated that physical-chemical properties alone do not determine bioaccumulation in a species; fish characteristics are also important. The relationship of the bioconcentration factor (BCF) and the octanol-water partition coefficient (Kow) was examined. The correlation was weak (r2 = 0.73) for pesticides and poor (r2 = 0.46) for PCB congeners when compared to published relationships based on laboratory data.

Water from Lake Michigan and fish from all five Great Lakes have been sampled and analyzed for a suite of six polybrominated diphenyl ether (PBDE) congeners and 110 polychlorinated biphenyl congeners (PCBs). The Lake Michigan dissolved phase PBDE congener concentrations (0.2 to 10 pg/L) are similar to dissolved phase PCB congener concentrations (nondetected to 13 pg/L). Partitioning of PBDEs between the particulate and dissolved phases exhibits behavior similar to that of PCBs. Organic-carbon-normalized water-particle partition coefficients (log K(OC)s) ranged from 6.2 to 6.5. Lake trout are depleted in BDE-99 relative to dissolved phase concentrations, and in contrast to what is expected from the PCB congener patterns. This reflects suspected debromination of BDE-99 in the food web of Lake Michigan. A regression of the log of the bioaccumulation factor (BAF) and the log of the octanol-water partition coefficent (K(OW)) indicated a positive relationship for both PCB congeners and PBDE congeners. BDE-99 does not appear to followthe same trend, a further indication that it is subject to biotransformation. Using the PBDE BAFs for Lake Michigan and the PBDE fish concentrations from the other Great Lakes it is expected that the dissolved phase concentrations of congeners in the other lakes would range from 0.04 to approximately 3 pg/L.

Air-water exchange of PCBs was determined in Lake Michigan on an event and seasonal basis in 1991 -1993. Instantaneous fluxes of CPCB (sum of 77 congener peaks) based on air-water concentration gradients drawn from air and water samples collected simultaneously aboard ship demonstrated net volatilization in September 1991. Air samples collected on the northeastern shore of Lake Michigan (Sleeping Bear Dunes State Park) between December 1991 and July 1993 showed no seasonal trend in vapor-phase CPCB concentrations and ranged from 30 to 400 pg/m3. These air concentrations were used to calculate seasonal water-air fluxes of CPCB that ranged from -18 ng m-2 day-' (net deposition) to 60 ng m-2 day-' (net volatilization). The seasonal variation of vapor-phase and dissolved-phase PCBs in the impacted southern quarter of the lake are unknown, thereby hindering estimation of fluxes in this region. The estimated annual net CPCB flux is 12.3 p g m-2 yr-', which corresponds to 520 kg for the northern three-quarters of Lake Michigan.

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