Tracing trace metal complexation Chemical reactions determine the fate of trace metals released into aquatic environments. J. M. Gamier and colleagues investigated the kinetics of trace metal complexation by monitoring chemical reactions in suspended matter from a French river. Radiotracer experiments on Mn, Co, Fe, Cd, Zn, Ag, and Cs identified seasonal variations in the predominant species. In summer, Cd and Zn were complexed by specific natural organic matter ligands. Cs remained in an inorganic form, whereas Fe and Ag were either organic complexes or colloidal species. In winter, a two-step process occurred for Mn and Co. They were rapidly complexed by weak ligands, followed by slower complexation by stronger ligands. The authors conclude that low concentrations of natural ligands may control the speciation of trace elements. (Environ. Sci. Techno!..,his issue, pp. .597-1606)
incorporates uncertainty and variability, calculating risk with variables that include resources expended and policy mandates. Despite these advantages, there are significant barriers to its widespread use, including risk managers' inexperience with probabilistic risk assessment results and general suspicion of the method. The authors describe ways to promote the proper use of probabilistic risk assessment. (Hum. Ecol. Risk Assess. 1996,2(4), 1008-34)
Uncertainty modeling ity to air pollution among different population subgroups. (Am. J. Respir. Crit. Care Med. .197,155, ,68-76)
MEASUREMENTS Dioxin trends in fish Concentrations of PCBs, polychlorinated dibenzo-p-dioxins, and polychlorinated dibenzofurans are often gauged in terms of toxic equivalence factors. S. Y. Huestis and co-workers reported temporal (1977-93) and age-related trends in concentration and toxic equivalencies of these compounds in Lake Ontario lake trout. Analysis of the stored frozen fish tissue used a single analysis protocol, which allowed improved comparison of data from different time periods. Results showed that contaminant levels have declined substantially since 1977 but concentration levels have stabilized approaching a steady state or a very slow decline The proportion of the total toxic equivalency ascribed to each compound has changed little in each of the three sets examined (Environ Toxicol Chem 1997 16(2) 154-64)
Herbicide extraction Efficient extraction and analysis of phenoxyacid herbicides are difficult because of their high polarity and low volatility. T. S. Reighard and S. V Olesik reported the use of methanol/ C0 2 mixtures at elevated temperatures and pressures to extract these herbicides from household dust. The experiments were done at conditions covering both subcritical and supercritical regimes. They found that the highest recoveries (between 83% and 95% for the four herbicides studied) were observed at 20 mol % methanol and at temperatures of 100 °C or
150 °C. In addition, when a 200-uL volume of hexane was added to the 1-g dust sample, a preextraction with C0 2 and no methanol removed much of the extraneous matrix. These matrix compounds, when present, create a more complex chromatogram and require more reagent. (Anal. Chem. 1997, 69, 566-74)
POLICY Overcoming NIMBY Public participation programs can help citizens get past "not-in-mybackyard" (NIMBY) responses to the siting of hazardous waste facilities. J. J. Duffield and S. E Depoe described the effects of citizen participation in the storage of 2.4 million cubic yards of low-level radioactive waste from the Fernald, Ohio, nuclear weapons complex. Among the participants were labor representatives, academicians, 8X63. residents, and activists. Because the task force had the opportunity to question technical experts and dispute evidence a democratic format ated for two-way communication between officials and citizens (Risk Pol Rev 1997 3(2) 31-34)
RISK Probabilistic techniques Efforts to improve risk characterization emphasize the use of uncertainty analyses and probabilistic techniques. K. M. Thompson and J. D. Graham describe how Monte Carlo analysis and other probabilistic techniques can be used to improve risk assessments. A probabilistic approach to risk assessment
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Monte Carlo modeling is a powerful mathematical tool with many advantages over traditional point estimates for assessing uncertainty and variability with hazardous waste site exposure and risk. However, a lack of variability information hinders Monte Carlo modeling. As a solution, W. J. Brattin and colleagues proposed running repeated Monte Carlo simulations using different combinations of uncertainty parameters. The amount of variation among the different simulations shows how certain or uncertain any individual estimate of exposure or risk may be An example of this proach is provided including an estimation of the average exposure to radon daughter products in indoor air (Hum Ecol Risk Assess .199 2(4) 820-40)
SOIL Decomposition model Clay has a stabilizing effect on organic matter in soil and thus reduces the rate of decomposition. Current computer simulation models, however, do not adequately describe the protection of organic matter by clay. J. Hassink and A. P. Whitmore developed and tested a model that predicts the preservation of added organic matter as a function of the clay fraction and the degree of or~ ganic matter saturation of the soil. It closely followed the buildup and decline of organic matter in 10 soils to which organic matter was added Better than conventional models this model was able to predict the accumulation and degradation of organic matter in soils of different textures and the contents of initial organic matter (Soil Sci Soc Am J 1997 61 131-39)
