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 varie-gatus). 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 re-suit 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 Pseudo-monas 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 uncontami-nated soil Non-inoculated seedlings showed reduced growth rates PCP was concentrated in plant roots 13-fold 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

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 bioavail-able 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

1 1 8 A • VOL. 31, NO. 3, 1997 / ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS