Natural organic matter in drinking water New and pending regulations have created a need for better mathematical models to predict organic charge and metal complexation of natural organic matter (NOM) in drinking waters. These properties can affect removal of IMOM during water treatment. P. Bose and D. A. Reckhow report development of a model that describes the effect of ionic strength on the protonation of fulvic acid and the effect of pH and ionic strength on complexation of calcium by this natural ligand. The authors report that the model provided a good description of their measured data sets and could account for the effects of ionic strength and pH. They propose that the model can be calibrated with data from conventional methods and used to extrapolate behavior to dilute drinking water conditions. {Environ. Sci. Techno!., this issue, pp. 765-70)
RISK Dose—route extrapolation Risk assessments for airborne carcinogens are often limited by lack of cancer potency factors (termed unit risk or slope factors) specific to inhalation exposure. G. L. Ginsberg and co-workers evaluated the feasibility of extrapolating across three dose routes (oral, gavage, inhalation) with a case study of the contact-site carcinogen, epichlorohydrin. Their comparison included the use of dosimetry to adjust for delivery to contact sites. Results indicated a large disparity in potency across the three routes of administration. When dosimetry adjustments were made the inhalation-to-oral potency difference was minimal The dose rate rather than the dose route appears to be the primary determinant of epichlorohydrin cancer potency (Risk Analysis 1996 16(5) 667-81)
SEDIMENTS Bioturbation effects Acid volatile sulfides (AVS) can decrease the bioavailability of metals in sediments under anoxic conditions. Aquatic organisms burrowing in the sediment may promote oxidation, which may in turn affect sediment metal bioavailability. G. S. Peterson and co-workers studied the bioavailability of metals in sediments in the presence of a burrowing oligochaete (Lumbriculus variegatus). Bioavailability of cadmium in the surface centimeter of the sediments increased with oligochaete density and was attributed to the oxidation of the AVS as a resuit of the bioturbation. Cadmium
bioavailability in the sediments located below bioturbation depth did not change. The authors conclude that bioturbation can enhance bioavailability of some cationic metals in surficial sediments. (Environ. Toxicol. Chem. 1996, 15, 2147-55)
SOIL Protecting phytoremediators Plants used for stabilization and phytoremediation of contaminated surface soils are also susceptible to the toxic effects of the contaminants. W. F. Pfender reported use of Pseudomonas strain SR3 to protect proso millet {Panicum miliaceum L.) growing in soil contaminated with high levels of pentachlorophenol (PCP). Simple coating of the millet seeds at planting with Pseudomonas (a known PCP-degrader) was enough to protect the plants after germination. Pfender found that treated millet seedlings grew at the same rate as seedlings planted in uncontaminated soil Non-inoculated seedlings showed reduced growth rates PCP was concentrated in plant roots 13fold over the soil concentrations when were not inoculated with hacteria hut onlv 0 09-fnlrl h innnila'tprl (I Frwirnn 1996, 25, 1256-60)
SURFACE WATERS Acid mine drainage Assessment of surface waters contaminated with acid mine drainage is difficult because of the complex physicochemical nature of this pollutant. N. F. Gray reported development of an index to detect and
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quantify contamination from acid mine drainage waters and to monitor the recovery of receiving waters. The parameters used for assessment were pH, sulfate, iron, zinc, aluminum, copper, and cadmium. Each parameter was assigned a weighting based on its concentration, sorption properties, effect of neutralization, importance of its concentration to drainage formation, and die detection limit of the analytical technique used to measure it. When applied to a mining site in Ireland, the index allowed discrimination between different sites. (Water Environ. Manag. 1996, 10(5), 332-40)
Exxon Valdez PAHs The Exxon Valdez grounding in 1989 led to the accumulation of PAHs in fish, mussels, and other marine animals in the surrounding area. J. F. Neff and colleagues estimated PAH concentrations in the water at the time of the exposure and related tissue residues from mussels and pink salmon to water concentrations through an equilibrium partitioning approach. Estimated PAH concentrations were similar to the dissolved PAH concentrations directiy measured from the water but were lower than the dissolved plus particulate PAH concentrations. The authors conclude that this method allows the estimation of concentrations at times and locations that were not directly monitored Their data indicate that PAH concentrations generally did not exceed water quality standards for Drotection of marine lifp (Fnvr'rnn Tnxirnl Chpm 1999 75, 2240-53)
TOXICOLOGY Copper bioavailability Bioavailability data are necessary to assess the toxicity of copper in aquatic systems, but few analytical mediods can measure the bioavailable fraction of metals in aqueous or sediment phases. E. Deaver and J. H. Rodgers, Jr., measured copper concentrations in five waters by atomic absorption spectroscopy (AA) and differential pulse anodic stripping voltammetry (DPASV). Ten-day LC50 values for Hyallela azteca in these waters ranged from 42 to 142 ug/L measured by AA. Measured by DPASV LC ranged only from 17 to
