ronmental laws date to 1940, though until the current administration, environmental regulations were enforced by large agencies that also oversaw development as well. Understanding how the Mexican situation is different from those of the U.S. and Canada will help manage environmental issues in Mexico and at the border. [The Environmental Professional 1995, 17(2), 137-52]
Decision-analytic tests To manage an ecosystem, appropriate data must be gathered that establish the significance of biological effects of a stressor. M. Power and colleagues showed that the most popular statistical tests of significance are designed to draw conclusions about a system, rather than aid in management decisions. Conclusion-drawing tests have two drawbacks: They require strong evidence about the system, because conclusions will be accepted as truth, and popular statistical tests ignore the consequences of decisions on the tests. The authors conclude that decision-analytic tests avoid these drawbacks, improving the ability of environmental managers to implement cost-effective strategies based on available knowledge. [Environ. Manage. 1995, 79(5), 629-39]
REMEDIATION Vapor extraction Vapor extraction of contaminated soils removes volatile hydrocarbons and, to a lesser extent, enhances in situ biodégradation of hydrocarbons. Decreased soil moisture content, increased soil temperature, substrate removal, and soil gas level variations affect in situ biodégradation during vapor extraction. W. J. Hickey studied vapor extraction in a gasoline plume, observing substantial reduction of the gasoline fraction and microbial activity within the first 60 days. Although soil moisture content decreased and temperature increased during vapor extraction, microbial activity decreased. Hickey attributed this to preferential removal of the lower molecular weight gasoline fraction. Gasoline vapor reaccumulation was not maximized until two or three months after the vacuum stopped. Results indicate that monitoring soil vapor concentrations within the first few weeks
after the termination may not provide an accurate assessment of soil remediation. (/. Environ. Qual. 1995, 24, 571-82)
RISK Comparative risk limits E. Silbergeld studied the scientific and social limitations inherent in comparative risk assessment. Comparative risk assessments are weakened by the multifactorial nature of risk, voluntary versus involuntary exposures, and comparisons of cancer versus noncancer endpoints. She proposes reforms, including standardized risk methodology for noncancer endpoints, improved and ensured public access to risk debates, and increased health effects data collection and analyses. [New York University Environmental Law Journal 1995, 3(2), 405-30]
SEDIMENTS Pore-water methods Sediment pore-water collection methods can significantly influence analysis results. N. Sarda and G. A. Burton, Jr., studied four pore-water collection methods to ascertain the effect on ammonia analysis. They collected sediments using a hand corer with a 5-cm diameter dredge and a standard 15.5-cm2 Ekman dredge. Pore-water was extracted from each sediment sample using centrifugation. Pore-water also was directly sampled in the field using a suction technique and a "peeper" method involving sample jars fitted with mesh. The hand corer and Ekman dredge resulted in the highest pore-water ammonia concentrations for all three study sites. The authors conclude that these methods could result in artificially elevated porewater chemical analyses. [Environ. Toxicol. Chem. 1995, 14&), 1499-506]
WASTEWATER Wetlands treatment Several parameters must be considered when designing an effective constructed wetlands for wastewater treatment, such as the effects of plant types and draining, system ki-
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netics, aerobic and anaerobic respiration contributions to biochemical oxygen demand (BOD) removal, and characterization of oxygen transport effects. P. S. Burgoon and colleagues evaluated these parameters for a subsurface flow wetlands under batch and continuous flow conditions. Pilot-scale wetlands were constructed and subjected to primary or secondary wastewater. Plants enhanced the removal of carbonaceous and nitrogenous BOD but increased hydraulic retention times (HRT). Periodic draining did not affect BOD removal. BOD removal kinetics were first order for HRT of less than 24 h. Oxygen transport through plants did not significantly affect BOD removal at > 24 h HRT. Methanogenesis was found to be a major respiratory pathway for BOD removal. [Water Environ. Res. 1995, 67(5), 855-62]
Removing heavy metals Heavy metal concentrations
