This study creates a compendium of gene expression in normal human tissues suitable as a reference for defining basic organ systems biology. Using oligonucleotide microarrays, we analyze 59 samples representing 19 distinct tissue types. Of ∼7,000 genes analyzed, 451 genes are expressed in all tissue types and designated as housekeeping genes. These genes display significant variation in expression levels among tissues and are sufficient for discerning tissue-specific expression signatures, indicative of fundamental differences in biochemical processes. In addition, subsets of tissue-selective genes are identified that define key biological processes characterizing each organ. This compendium highlights similarities and differences among organ systems and different individuals and also provides a publicly available resource (Human Gene Expression Index, the HuGE Index, http://www.hugeindex.org ) for future studies of pathophysiology.

The interplay between the hydrologic processes that supply, store, and route water in catchment systems and the chemical weathering reactions that add and remove solutes acts as an important control on chemical weathering fluxes. In this study, we use paired measurements of solute chemistry and runoff in four nested catchments that span the transition from the Andes Mountains to the Amazonian foreland floodplain in Peru in order to investigate the links between hydrology and weathering processes and to determine how these links change across a geomorphic gradient. All of the sites show variation in elemental concentrations and ratios with runoff consistent with hydrologically driven changes in lithologic sources, the extent of secondary mineral precipitation, and, potentially, fluid flow paths. In the Andean sites, solute concentrations are relatively constant despite large changes in runoff. This is in direct contrast to the foreland floodplain site, where solute concentrations are diluted as runoff increases. In the Andes-Amazon, the concentration-runoff behavior is correlated with the mean catchment slope angle, which suggests that erosional processes, by modulating the timescales over which weathering reactions occur within the critical zone, can be an underlying control on solute production and therefore on chemical weathering. Due to the co-variation between the geomorphic and hydrologic controls on chemical weathering, weathering fluxes in Andean sites are more sensitive to seasonal changes in runoff than in the foreland floodplain site.

Bioconcentration data are reported for a series of superhydrophobic chemicals including polybrominated biphenyls, brominated benzenes, mirex and polychlorinated biphenyls in the guppy (Poecilia reticulata). The observed bioconcentration factors follow a linear relationship with the 1‐octanol/water partition coefficient for chemicals with a log Kow of up to 6. For chemicals with higher Kow values, the bioconcentration factors were lower than expected from the linear relationship. This loss of linear correlation is shown to be caused by (a) a low fraction of bioavailable chemical in the water, (b) elimination of chemical into the feces, (c) an insufficient exposure time to achieve equilibrium and (d) fish growth. Procedures are presented by which the magnitudes and relative contributions of these factors to reducing the apparent bioconcentration factor from linearity can be determined.

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