temperatures also increase SOC content. [Global Biogeochem. Cycles 1994, 8, 237-54)
The results provide new insight into redox controls on trace element be havior in the environment. [Geochim. Cosmochim. Acta 1994, 58, 3993-4008)
MEASUREMENTS Thermospray MS The unambiguous determination of iV-methyl carbamate pesticides and their degradation products is impor tant because of their potential envi ronmental impacts. Gas chromato graphic methods are hampered by thermolability, low volatility, and high polarity; liquid chromatographic methods can be sensitive but do not yield mass spectral conformation. D. Barcelo and colleagues at the CID/ CSIC (Barcelona, Spain) and Vrije Uni versity have been studying the use of thermospray mass spectrometry to provide sensitive determination of Λί-methyl carbamates and their degra dation products with mass spectral conformation. They analyzed the ther mospray mass spectra for a series of 19 carbamates and 12 products of car bamate degradation. Spectra were ob tained using two solvent systems, three modifiers, and both positive and negative ionization modes. It was not possible to create a single set of opti mal thermospray conditions for all carbamates. Detection limits as low as 1 ng of an individual carbamate can be achieved. [J- Am. Soc. Mass Spectrom. 1994, 5, 913-27)
METALS Trace element cycling The behavior of metals in the envi ronment is often controlled by their speciation. Balistrieri, Murray, and Paul selected Hall Lake in Washing ton to thermodynamically model the effects of redox conditions on a suite of metals (As, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, V, and Zn). Hall Lake is ideal because it is stratified, grading from oxic surface waters to anoxic bottom waters. Redox-sensitive ele ments (Cu, Ni, Pb, and Zn) exist in their reduced form as metal sulfide solution complexes in the anoxic region. Transformations of dissolved elements between oxidation states are predicted for As, Cr, Cu, Fe, Mn, and V; solubilities of these elements increase with depth in the anoxic layer. All elements studied are pre dicted to cocycle with Fe and Mn.
growth of the species in soils with high levels of zinc and cadmium. (J. Environ. Qual. 1994, 23, 1151-57)
RISK ASSESSMENT Exposure parameters
REMEDIATION Extract and wash Removal of hazardous contaminants from soil by extraction and washing is a potential alternative for waste site remediation. Vijay S. Raiput and col leagues of Unitech Engineers, Inc., and Rutgers University conducted ex periments to investigate this tech nique using a sandy loam soil. Model contaminants studied were 1,2,4-trichlorobenzene (TCB), aniline, phenol, and 2,4-dichlorophenol (DCP). As much as 99% of the hydrophilic com pounds aniline, phenol, and DCP were effectively removed by washing with deionized water only. A combina tion of washing with surfactant and rinsing with water was required for removal of 90% to 97% of TCB. Reme diation costs will depend upon vari ables such as process efficiency, type of soil contaminants, method of sur factant treatment, and soil sludge gen eration. {Water Environ. Res. 1994, 66, 819-27)
Metal-hungry plant Specialized plants that can accumu late high concentrations of heavy met als from contaminated soils while tol erating the adverse growth conditions at these sites are referred to as hyperaccumulators. Removal of heavy met als from the soil could be achieved by successive croppings of hyperaccumulators and either disposal of the har vested material or recycling of the metals by smelting. S. L. Brown and J. S. Angle of the University of Maryland studied the uptake of zinc and cad mium by a hyperaccumulator (Thlaspi caerulescensJ. and C. Presl) grown on contaminated soils. The total amounts of heavy metals translocated (metal concentration in the shoots times shoot biomass) were significantly greater in T. caerulescens than in other indicator plants. Maximum transloca tion of metals by T. caerulescens oc curred at near-neutral pH values. The authors concluded that the effective ness of T. caerulescens for phytoremediation, in comparison to other plants, was the result of its ability to tolerate higher levels of zinc and cadmium in the shoot tissue, and of the greater
Monte Carlo techniques are increas ingly being applied to estimate uncer tainty in risk assessment. These tech niques require "standard" data distributions for common parameters. Brent Finley et al. from ChemRisk propose such distributions for a num ber of exposure parameters frequently required in health risk assessments. They report age-specific distributions for body weights, skin surface areas, tap water and fish consumption, inha lation and soil ingestion rates, soil-onskin adherence, and tenure in resi dences and occupations. Using these standard distributions in risk assess ments would speed the replacement of single-point estimates with more reasonable probabilistic assessments. (Risk Anal. 1994, 14(4), 533-53J
RISK
ASSESSMENT
Plant toxicity data Regulation of herbicides and pesti cides is just beginning to include the considerable research in the past de cade on toxicity to plants. Canada is drafting test guidelines for nontarget plants in pesticide registration. Kathryn Freemark and Céline Boutin of the Canadian Wildlife Service describe the basis for these guidelines. Plant screening test data routinely generated by herbicide manufacturers can be incorporated into the first tier of a cost-efficient risk assessment. Ecosystem approaches to risk assessments in other areas will require integration of more diverse information, including data on plant toxicity. (Environ. Manage. 1994, 18, 841-54) Contributors to Research Watch are Brian Eitzer, Connecticut Agricultural Experiment Station, New Haven, CT; Stephen Geiger, Remediation Technologies, Inc., King of Prussia, PA; Vincent Hand, Miami University, Institute of Environmental Sciences, Oxford, OH; Richard Hurst, CHEMPET Research Corp., Moorpark, CA; Louis Kovach, Ecolife Associates, Wilmington, DE; and Margaret Whittaker, NSF International, Ann Arbor, MI.
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