Toxicity of organic mixtures saturated in water to Daphnia magna. Effect of compositional changes

The toxicity of aqueous solutions saturated with mixtures of hydrophobic organic liquids is contrasted to that of solutions prepared from solids. Data for a variety of mixtures are presented and are related to the solubilities of the components. It is shown that in the absence of biological interactive effects, the toxicity of a component in a saturated mixture of liquids will be equal to or less than that of a corresponding solution of its most toxic component. In contrast, for solutions derived from a mixture of solids, the toxicity will equal or exceed that of a corresponding saturated solution of its most toxic component, and will tend to increase with the complexity of the mixture.     

The new approach to wilderness preservation through benefit-cost analysis

Over the last 15 years, economists of Resources for the Future led by John Krutilla have been developing a new approach to wilderness preservation. This paper offers a concise exposition of their approach and adds a few steps. The basic ingredient of the new approach is a perception of declining net benefits of wilderness development and rising net benefits of wilderness preservation over time. These alter the entire shape of the benefit-cost analysis of potential development. The new steps involve reversibility, postponability, and recognition of multiple interest rates.     

Short run aspects of a genetic control program for Heliothis virescens (Lepidoptera: Noctuidae)

The possibility that suppressing the tobacco budworm, Heliothis virescens (F.), by means of genetic control will lead to short run crop yield sacrifices is examined. A simulation model of budworm/backcross population dynamics is used to investigate the effects of backcross releases which are too small or improperly timed. Apart from its potential for ultimate long-term suppression of the tobacco budworm, adverse short-term effects on crop yields are not likely to be a serious problem with a genetic control program. Furthermore, backcross release appears to have some potential as a substitute for chemical pesticides during the period prior to budworm elimination by genetic control.     

Development of quantitative estimates of uncertainty in environmental risk assessments when the scientific data base is inadequate

The reasons for developing quantitative estimates of uncertainty in environmental risk assessments are discussed along with a method for developing them which involves scientific judgement. In the situation considered here the regulatory needs are ahead of the science, which makes the development of the estimates on uncertainty more difficult, but not impossible. Quantitative estimates for all uncertainties involved in the estimation of risk resulting from exposure to volatile organic compounds (VOCs) in drinking water are developed and tabulated. By far the largest contribution to the uncertainty in the risk estimates for VOCs in drinking water are due to uncertainty in the extrapolation of the dose-response curve to low levels. The uncertainty due to extrapolation is on the order of 10⁴ and 10⁶. Other components of the analysis may contribute uncertainties of a few orders of magnitude. In general the largest uncertainties are in the toxicological data base and the manipulation of it needed to estimate risk. The data base and manipulations needed to estimate exposure due to VOCs in drinking water were at the more an order to magnitudes in uncertainty.