water, which presumes that soil bioavailability is identical to that of arsenic in drinking water. Noting that the equal-availability assumption of arsenic may not be valid, A. Davis and colleagues evaluated mineralogic controls on the bioavailability of arsenic in smelter-impacted soils. They proposed that the lower bioavailability of arsenic in soils near Anaconda, Mont., smelters may be related to arsenic's location in lesssoluble mineral phases. Specific examples include arsenic oxide-metal and phosphate phases. The authors attributed the site's low bioavailability of arsenic in soil to the lower solubility of these arsenic-bearing phases, inaccessibility of included arsenic, and kinetics of dissolution. {Environ. Sci. Technol. 1996, 30(2), 392-99)
Lead bioaccumulation Organolead compounds such as alkylleads from gasoline combustion have concentrated in mussel populations along the eastern Adriatic Coast. N. Mikac and colleagues evaluated the alkyllead levels and the relative bioconcentration of specific alkyllead species in mussels. They found organolead compounds occurred at levels between 0.1 and 45 ppb (wet weight). Tetraalkyl, trialkyl, and cKalkyl species occurred at maximum levels of 45, 32, and 9 ppb, respectively. They conclude that organic lead levels are better indicators of pollution than total lead given the number of other potential lead sources in the environment. Results show that the bioconcentration rate of organolead species from seawater was lower than that of total lead, which suggests that mussels are not as efficient bioaccumulators of organic lead relative to total lead. {Environ. Sci. Technol. 1996, 30(2), 499-508)
Tracking dioxins in an English pasture Atmospheric transport and deposition are considered important mechanisms in the dispersal of polychlorinated dibenzodioxins and dibenzofurans (PCDD/F) throughout the environment. L-0. Kjeller and colleagues studied the historical data on vegetation, which they used to infer changes in atmospheric deposition of PCDD/F from 1861 through 1993. Vegetation samples from an undisturbed pasture in southeast England have been collected and archived since 1861. Five-year composite samples were prepared and analyzed for PCDD/F. Concentrations of these compounds in the vegetation remained constant until 1945, rose to a peak in the mid-1960s, declined, then reached a lower peak in the late 1970s, and finally declined through the last sampling period in 1993. The authors infer that the peaks may be the result of byproducts of the production of chloro-aromatic compounds, superimposed on a background of dioxins from combustion sources. {Environ. Sci. Technol., this issue, 1398-1403)
Lead dissolution in the stomach decreased significantly as pH rose from 1.3 to 2.5, and arsenic solubility also decreased but not as dramatically. Lead was preferentially adsorbed and precipitated relative to arsenic in the near-neutral conditions of the small intestines. The method also can estimate lead and arsenic bioavailability in soils for risk assessments. The authors note that the test is designed to evaluate lead and arsenic bioavailability in the absence of animal study results. {Environ. Sci. Technol. 1996, 30(2), 422-30)
Lead bioavailability The form and solubility of lead and site-specific soil conditions are believed to affect lead bioavailability. M. V. Ruby and colleagues tested lead and arsenic for bioavailability using an in vitro, physiologically based, extraction-designed representative of human gastrointestinal parameters. Their results for lead correlated significantly with results from a Sprague-Dawley rat model. They predicted arsenic bioavailability that was comparable to results from rabbit and primate models.
MEASUREMENTS Analyzing VOCs in blood Standard methods for analyzing volatile organic compounds (VOCs) in aqueous systems do not work well for analyzing VOCs in small volumes of blood. F. St. Germain and colleagues developed an inertial spray extraction interface that allows VOC analysis in blood without sample pretreatment. The aqueous sample is sprayed downward through a nozzle
generating an aerosol, which allows the VOCs to equilibrate rapidly between gas and liquid phases. Gasphase VOCs are swept by a countercurrent flow of helium through an off-axis port and into a jet separator. This leads to an ion trap mass spectrometer for detection and quantification. Detection limits following injection of 1 mL of aqueous sample were
