limiting conditions in a chemostat. Results indicate that degradation rates of TCE using methanol are comparable to values for cells grown on methane. Methanol- or oxygenlimited cultures also had degradation rates that approached those of cultures grown on methane. (Appl. Environ. Microbiol. 1996, 62, 1124-28)
RISK Aquatic benchmarks Ecological risk assessors often begin evaluation of a contaminated site by screening out many of the chemicals present so they can focus risk assessment on a few compounds that are most representative of the site. Screening involves comparing ambient concentrations with "benchmarks"—concentrations regarded as nonhazardous. G. W. Suter II discussed 13 methods for deriving benchmarks for aquatic organisms and presented benchmarks for 105 compounds. The report compares each in terms of sensitivity, availability, magnitude in relation to background levels, and conceptual basis. No one benchmark proved superior. Suter recommends use of multiple benchmark values in conjunction with other factors to identify contaminants of concern. (Environ. Toxicol. Chem. 1996, 15, 1232-41)
Ecological exposure Ecological risk assessments for hazardous waste sites, now being conducted with increased frequency, estimate exposure for different animal species living in the area. Researchers include animals representative of different trophic levels and typically use the oral pathway as the animals' main route of exposure. T. M. Carlsen presents the results of exposure assessments on burrowing vertebrates found in upper and lower trophic levels of a waste site. Carlsen identified inhalation of contaminated subsurface burrow air as a significant but previously unrecognized exposure pathway for exposure to trichloroethylene (TCE). (Risk Anal. 1996, 16, 211-17)
Dermal exposure Many toxic environmental chemicals can be absorbed through the skin,
Residue transport into homes by shoes and feet Studies of routes of human exposure to pesticides have devoted little attention to transport of pesticide residues into homes on the shoes and feet of people walking over treated lawns. M. G. Nishioka and colleagues studied this process on turfs treated with 2,4-D and dicamba. They used a polyurethane foam (PUF) roller to sample dislodgeable residues from the turf and carpet surfaces and a modified vacuum to collect carpet dust. Samples were analyzed by gas chromatography with electron capture detection or mass spectrometry with negative chemical ionization. The researchers found that the turf dislodgeable residues were 0.1-0.2% of the application level. Pesticide levels in the carpet dust and carpet surfaces were 3% and 0.3%, respectively, of the turf dislodgeable residues. (Environ. Sci. Techno!., this issue, 3313-20)
and thus the transdermal route is a major contributor to an organism's total accumulated internal dose. Current models used to estimate dermal doses are based on assumptions that are invalid for short-term exposures to VOCs. A. Roy and colleagues present a generalized distributed-parameter, physiologically based pharmacokinetic model (DP-PBPK) that describes dermal transport of VOCs through the outer layer of the skin. The authors compare the DP-PBPK model with two simpler PBPK models by creating parameters for all three models for chloroform and applying them to various inhalation and dermal exposure scenarios. Although the three models produced nearly identical results, the DP-PBPK model predicted a substantially lower net dermal dose because of postexposure volatilization. (Risk Analysis 1996, 16, 147-59)
Communication efforts Several barriers discourage organizations from evaluating customer satisfaction with risk communications activities. A. Fisher and Y-C. Chen report on the first federal agency to overcome these barriers and sponsor a baseline study. The U.S. Department of Agriculture's
Animal and Plant Health Inspection Service (APHIS) mailed questionnaires to 2000 customers of its services. Respondents said that many risk communication activities are important, but they think that APHIS is not especially effective in those activities. Customers were moderately satisfied with much of the risk information they received. The study provides valuable baseline data for measuring future changes in the effectiveness of APHIS risk communication. (Risk Anal. 1996, 16, 177-84)
WASTEWATER Heavy metal sorbents Heavy metal ions are among the most common toxic components in industrial effluents. Existing methods, such as chemical precipitation, sorption, and ion exchange, have low efficiency in removing trace levels of metal ions. M. Weltrowski and co-workers synthesized chitosan TV-benzyl sulfonate derivatives as sorbents for the uptake of metal cations from acidic solutions. Chitosan is a derivative of chitin, a natural polymer extracted from Crustacea shells. They tested mono- and disulfonate chitosan derivatives on numerous heavy metal cations, including cadmium, zinc, nickel, lead, copper, iron, and chromium. Disulfonate compounds had better sorption capacities than the monosulfonates because of their amphoteric nature, but sorption of the raonosulfonate and disulfonate compounds improved after the researchers protected the amino groups with benzyloxycarbonyl groups. (J- Appl. Polym. Sci. 1996, 59, 647-54)
Contributors: Brian Eitzer, Connecticut Agricultural Experiment Station, New Haven, Conn.; Stephen Geiger, Remediation Technologies, Inc., King of Prussia, Pa.; Vincent Hand, Miami University, Institute of Environmental Sciences, Oxford, Ohio; Richard Hurst, CHEMPET Research Corp., Moorpark, Calif; Louis Kovach, Ecolife Associates, Wilmington, Del; Raewyn Town, Queen's University of Belfast, Northern Ireland; and Margaret Whittaker, NSF International, Ann Arbor, Mich.
VOL. 30, NO. 11, 1996/ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS • 4 7 1 A
