Statistical hypothesis testing formulations for U.S. environmental regulatory standards for ozone

Environmental regulatory standards are intended to protect human health and environmental welfare. Current standards are based on scientific and policy considerations but appear to lack rigorous statistical foundations and may have unintended regulatory consequences. We examine current and proposed U.S. environmental regulatory standards for ozone from the standpoint of their formulation and performance within a statistical hypothesis testing framework. We illustrate that the standards can be regarded as representing constraints on a percentile of the ozone distribution, where the percentile involved depends on the defined length of ozone season and the constraint is stricter in regions with greater variability. A hypothesis testing framework allows consideration of error rates (probability of false declaration of violation and compliance) and we show that the existing statistics on which the standards are based can be improved upon in terms of bias and variance. Our analyses also raise issues relating to network design and the possibilities of defining a regionally based standard that acknowledges and accounts for spatial and temporal variability in the ozone distribution.     

Amniotic band syndrome causing fetal head deformity

Amniotic band syndrome is a rare cause of fetal head deformity. We report a case in which antenatal ultrasound in the first half of pregnancy indicated the presence of a fetal cranial deformity, reported as either anencephaly or encephalocele. At assessment autopsy, disruption of the fetal skull was associated with amniotic band formation. Appropriate genetic counselling can be offered to such patients only when detailed pathological examination of the aborted fetus is made. The recurrence rate of amniotic band syndrome does not warrant amniocentesis in a subsequent pregnancy.     

Adsorption and precipitation of tetracycline with struvite.

The interaction of tetracycline with struvite during adsorption and precipitation processes was investigated. Tetracycline removal by adsorption was affected by solution pH, contact time, and struvite concentration. The lowest tetracycline removal (8.4%) was observed at pH 7.7, the dissociation constant (pKa2) of tetracycline. Because of the electrostatic repulsion, the amount of tetracycline adsorbed on the surface was low. The small amount of adsorption was the result of surface complexation between tetracycline ions and metal ions. Calcium (Ca2+) ions in the adsorbent enhanced the binding of tetracycline. Freundlich (KF: 0.04, n: 1.49) and Redlich-Peterson (KR: 0.08, alphaR: 0.98, betaR: 0.49) models best defined the equilibrium data. In the case of struvite precipitation, approximately 22% of tetracycline was removed as a result of binding to struvite alongside struvite formation.     

Sorption of Zn(II) in aqueous solutions by scoria

We conducted kinetic and equilibrium sorption experiments on removal of Zn(II) from aqueous solutions by scoria (a vesicular pyroclastic rock with basaltic composition) from Jeju Island, Korea, in order to examine its potential use as an efficient sorbent. The batch-type kinetic sorption tests under variable conditions indicated that the percentage of Zn(II) removal by scoria increases with decreasing initial Zn(II) concentration, particle size, and sorbate/sorbent ratio. However, the sorption capacity decreases with the decrease of the initial Zn(II) concentration and sorbate/sorbent ratio. Equilibrium sorption tests show that Jeju scoria has a larger capacity and affinity for Zn(II) sorption than commercial powdered activated carbon (PAC); at initial Zn(II) concentrations of more than 10mM, the sorption capacity of Jeju scoria is about 1.5 times higher than that of PAC. The acquired sorption data are better fitted to the Langmuir isotherm than the Freundlich isotherm. Careful examination of ionic concentrations in sorption batches suggests that the sorption behavior is mainly controlled by cation exchange and typically displays characteristics of 'cation sorption'. The Zn(II) removal capacity decreases when solution pH decreases because of the competition with hydrogen ions for sorption sites, while the Zn(II) removal capacity increases under higher pH conditions, likely due to hydroxide precipitation. At an initial Zn(II) concentration of 5.0mM, the removal increases from 70% to 96% with the increase of initial pH from 3.0 to 7.0. We recommend Jeju scoria as an economic and efficient sorbent for Zn(II) in contaminated water.     

Impact of heating and air conditioning system operation and leakage on ventilation and intercompartment transport: studies in unoccupied and occupied Tennessee Valley homes

Forced-air heating and air conditioning (HAC) systems caused an average and maximum increase in air infiltration rates of 1.8- and 4.3-fold, respectively, during brief whole-house studies of tracer gas decay in 39 occupied houses. An average increase in air infiltration rate of 0.33 +/- 0.37 h-1 corresponded to an incremental air leak of 240 m3/h, based on approximate house volume. More detailed tracer gas decay studies were performed in basement, kitchen and bedroom locations of six homes with low air infiltration rates (i.e., less than 0.25 h-1). The HAC mixed the indoor air efficiently between measurement sites. HAC operation also caused 1.1- to 3.6-fold increases in air infiltration rates, corresponding to absolute increases of 0.02 to 0.1 h-1. In an unoccupied research house, three-fold increases in average air infiltration rate with HAC operation (i.e., from 0.13 to 0.36 h-1) were reduced to two-fold (i.e., from 0.10 to 0.18 h-1) by sealing the external HAC unit and crawlspace ductwork system. This sealing also resulted in a 30 percent reduction in crawlspace-to-indoor transport rates with the HAC turned on. Blower door tests indicated a less than 20 percent reduction in house leakage area.     

Agrobacterium-mediated transformation of Nicotiana attenuata, a model ecological expression system

Summary. Research into the genetic basis of the ecological sophistication of plants is hampered by the availability of transformable systems with a wealth of well-described ecological interactions. We present an Agrobacterium-mediated transformation system for the model ecological expression system, Nicotiana attenuata, a native tobacco that occupies the post-fire niche in the Great Basin Desert of North America. We describe a transformation vector and a transformation procedure that differs from the standard cultivated tobacco transformation protocols in its use of selectable markers, explants, media and cultivation conditions. We illustrate its utility in the transformations with genes coding for key enzymes in the oxylipin cascade (lipoxygenase, allene oxide synthase, hydroperoxide lyase) in antisense orientations and present high-throughput screens useful for the detection of altered phenotypes for the oxylipin cascade (green leaf volatiles and jasmonic acid after wounding). Received 14 March 2002; accepted 10 May 2002     

Development of rapid ammonium uptake during starvation of batch and chemostat cultures of the marine diatom Thalassiosira pseudonana

Cell nitrogen quotas and uptake rates following ammonium additions were measured during ammonium-limited growth transients obtained by starving batch and chemostat cultures of Thalassiosira pseudonana (Clone 3 H). During starvation, cell quotas decreased by more than 50% in batch cultures. In chemostat cultures, the drop in cell quota during starvation decreased with dilution rate, from more than 50% at 1.45 d^-1, to less than 10% at 0.22 d^-1. Minimal levels of 3 to 4×10^-2 pg-at. N cell^-1 were reached after 24 h starvation in both batch and chemostat cultures. Uptake rates over the first minute of perturbation experiments were 3 times the long-term (10 to 30 min) rates. In batch cultures, specific uptake rates increased from 4 d^-1 to 20 d^-1 after 24 h starvation. Uptake rates per cell were independent of starvation time and dilution rate in chemostat cultures, but lower in non-starved batch cultures. The implications of these data for models of phytoplankton growth are discussed: the data support models which predict a depression in average growth rates when diatoms encounter microscale patches in oligotrophic environments.     

Influence of irradiance on the nutritional value of two phytoplankton species fed to larval Japanese scallops (Patinopecten yessoensis)

Japanese scallop (Patinopectin yessoensis Jay) larvae grew faster and were larger after 18 d when fed a diet of high-light(HL)-grown Chaetoceros simplex or HL Pavlova lutheri relative to diets of the same phytoplankton species grown at low light (LL). When provided as saturating rations to larval scallop, these diets could be ranked: HL C. simplex>LL C. simplex>HL P. lutheri>LL P. lutheri. In both phytoplankton species, HL-grown cells contained more of the short-chain saturated fatty acid (FA), 16:0 than LL-grown cells. Scallop growth rates were a significant function of the amounts (mg g^-1 dry wt) and the proportions (as percentage of total FAs) of the FAs 14:0 and 14:0+16:0 (total saturated FAs) in their diet. The proximate biochemical composition of HL- versus LL-grown phytoplankton showed no significant differences in protein, total lipid, carbon, carbohydrate or nitrogen per cell which were consistently associated with the greater nutritional value of HL cells. In spite of this high variability in proximate composition, the larval growth rate was a significant function of the average carbon content, nitrogen content and cell volume of the phytoplankton cells. Increased amounts of the essential polyunsaturated FAs 20:5 3 and 22:6 3 in the phytoplankton were negatively correlated with larval scallop growth rates. Thus HL-grown phytoplankton cells were nutritionally superior to LL-grown cells. This nutritional superiority seems to be determined by the fatty acid composition of the cells which, in turn, is controlled by variation in irradiance. The general tendency of predator FA profiles to resemble that of their prey was not observed in larvae fed P. lutheri. The much greater amounts of 18:4 3, 20:5 3, and 22:6 3 FA in P. lutheri relative to C. simplex were not evident in the scallop larvae fed these cells.