Direct comparison of 210Po, 234Th and POC particle-size distributions and export fluxes at the Bermuda Atlantic Time-series Study (BATS) site

Particle-reactive, naturally occurring radionuclides are useful tracers of the sinking flux of organic matter from the surface to the deep ocean. Since the Joint Global Ocean Flux Study (JGOFS) began in 1987, the disequilibrium between ²³⁴Th and its parent ²³⁸U has become widely used as a technique to measure particle export fluxes from surface ocean waters. Another radionuclide pair, ²¹⁰Po and ²¹⁰Pb, can be used for the same purpose but has not been as widely adopted due to difficulty with accurately constraining the ²¹⁰Po/²¹⁰Pb radiochemical balance in the ocean and because of the more time-consuming radiochemical procedures. Direct comparison of particle flux estimated in different ocean regions using these short-lived radionuclides is important in evaluating their utility and accuracy as tracers of particle flux. In this paper, we present paired ²³⁴Th/²³⁸U and ²¹⁰Po/²¹⁰Pb data from oligotrophic surface waters of the subtropical Northwest Atlantic and discuss their advantages and limitations. Vertical profiles of total and particle size-fractionated ²¹⁰Po and ²³⁴Th activities, together with particulate organic carbon (POC) concentrations, were measured during three seasons at the Bermuda Atlantic Time-series Study (BATS) site. Both ²¹⁰Po and ²³⁴Th reasonably predict sinking POC flux caught in sediment traps, and each tracer provides unique information about the magnitude and efficiency of the ocean's biological pump.     

Review of PCBs in US schools: a brief history,an estimate of the number of impacted schools,and an approach for evaluating indoor air samples

PCBs in building materials such as caulks and sealants are a largely unrecognized source of contamination in the building environment. Schools are of particular interest, as the period of extensive school construction (about 1950 to 1980) coincides with the time of greatest use of PCBs as plasticizers in building materials. In the USA, we estimate that the number of schools with PCB in building caulk ranges from 12,960 to 25,920 based upon the number of schools built in the time of PCB use and the proportion of buildings found to contain PCB caulk and sealants. Field and laboratory studies have demonstrated that PCBs from both interior and exterior caulking can be the source of elevated PCB air concentrations in these buildings, at levels that exceed health-based PCB exposure guidelines for building occupants. Air sampling in buildings containing PCB caulk has shown that the airborne PCB concentrations can be highly variable, even in repeat samples collected within a room. Sampling and data analysis strategies that recognize this variability can provide the basis for informed decision making about compliance with health-based exposure limits, even in cases where small numbers of samples are taken. The health risks posed by PCB exposures, particularly among children, mandate precautionary approaches to managing PCBs in building materials.     

Osmotic adjustment and organic solute accumulation in unicellular cyanobacteria from freshwater and marine habitats

The intracellular concentrations of low-molecular weight carbohydrates and quaternary ammonium compounds present in 26 axenic isolates of unicellular cyanobacteria have been studied over a range of external salinity from freshwater up to 300% seawater (100%=35 S). In all cases, a single carbohydrate, either sucrose or glucosylglycerol, was identified as the principal organic osmoticum, showing major variation in response to the external salt concentration; quaternary ammonium compounds were present in osmotically insignificant amounts. Glucosylglycerol was accumulated as primary osmoticum by nine of the isolates from saline habitats and by five of the freshwater isolates; trace amounts of sucrose were also prsent. The remaining twelve freshwater strains accumulated sucrose as sole osmoticum. Glucosylglycerol-accumulating strains grew over the widest salinity range (up to 200 to 250% seawater), whether isolated from saline or non-saline habitats. Sucrose-accumulating strains were more stenohaline, growing only in up to 50 to 100% seawater and showing no sustained growth in hypersaline media (>100% seawater). The data suggest that (1) glycosylglycerol accumulation is not unique to marine cyanobacteria, and (2) the upper salinity limit for growth may be linked to organic solute accumulation, rather than habitat, with glucosylglycerol-accumulating isolates having a greater potential for growth in salt-stressed conditions than sucrose accumulators.     

Judgments of photographs vs. field observations in studies of perception and judgment of the visual environment

The use of photographs as surrogates for field observations is common in studies of perception and judgment of the visual environment despite theoretically important differences between photographs and three-dimensional scenes. The few available empirical studies of the validity of photographs as representations of the visual environment have methodological weaknesses. We describe a method for investigating the representativeness of photographs that differs from previous approaches in three important respects. First, individual subjects rather than group averages are analyzed. Second, multiple judgments are obtained so that the relations among judgments of photographs can be compared with the environment. Third, a ‘lens model equation’ analysis is used to examine relations among systematic components of variation in judgments. An illustrative study of visual air quality judgments is presented. It was found that, in the case of judgments of visual air quality, photographs provide a good representation of the visual environment.     

Urban visual air quality judgments: Reliability and validity

A procedure based on judgments of human observers for measuring visual air quality in urban areas is described, and its reliability and validity are examined using the results of several studies conducted in a metropolitan area. It is concluded that the procedure provides a measure that is sufficiently reliable and valid to warrant its use in studies of the causes and consequences of changes in visual air quality. Substantial agreement was found among individuals with regard to judgments of visual air quality, but the possibility of differences between experienced and inexperienced observers requires further investigation. The paper provides an example of methods that can be used, and issues that should be addressed, in the development of perceived environmental quality indices.     

Microplankton population structure in Southern California nearshore waters in late spring

Taxonomic composition, biomass as organic carbon, numerical abundance, and size distribution of the microplankton were determined at 6 Southern California nearshore locations in late May–early June, 1970. Samples were taken at approximately 5 m (10 m at one station) intervals through the upper 40 to 50 m to reveal some of the small-scale differences and levels of variability in the populations. Total microplankton biomass over all euphotic zone samples varied by more than two orders of magnitude (7.6 to 1,200 g C l^-1). Average biomass at comparable sites (n=5) ranged from 48 to 240 g C l^-1; biomass range within stations varied from about 5-fold to 120-fold. Total microplankton numbers varied approximately 22-fold (4.3×10⁵ to 9.5×10⁶ organisms l^-1) over all euphotic zone samples, but the range within stations was always less than an order of magnitude. At comparable stations, nanoplankton biomass had ranges extending from 3.7-fold to 12-fold; its average percentage contribution (±1 SD) to the total microplankton biomass varied from 39±5% to 54±13%. Netplankton biomass showed a similar minimal range, but its greatest range was more than two orders of magnitude. Ranges of abundance of major taxonomic groups within stations varied considerably from about 2-fold to more than three orders of magnitude. The small-scale variability of the populations probably affects the reliability of the microplankton as a food source for pelagic consumers.     

Prenatal ultrasonic diagnosis of familial asymmetric septal hypertrophy

Hypertrophic cardiomyopathy usually manifests clinically in the second or third decade of life. Two dimensional echocardiography is a reliable indicator of the presence of the disease. This technique is of use in the screening of fetuses at risk for familial cardiomyopathy. This report describes the prenatal echocardiographic detection of hypertrophic cardiomyopathy in the fetus of a mother with hypertrophic cardiomyopathy localized to the apical region of the left ventricle.     

Prenatal ultrasound diagnosis of congenital heart disease associated with intrauterine growth retardation. A report of 2 cases

Two fetuses with extreme growth retardation (IUGR) of 31 and 34 weeks gestation were studied using a combination of two dimensional echocardiography (2DE), pulse wave Doppler (PWD) and differential measurement of the instantaneous vessel diameter techniques. The first fetus was diagnosed as having univentricular heart or possible double outlet right ventricle (DORV). Descending aorta blood flow was reduced as was indexing for weight. The second fetus was diagnosed as having univentricular heart with periodic bigeminal and trigeminal rhythm. Descending aorta blood flow was measured on two occasions and was reduced both times. Indexing for weight was within normal limits the first time and showed gross reduction on the second occasion prior to fetal demise. Fetal death occurred in both cases at 34 weeks gestation. Cardiovascular evaluation in fetuses with IUGR is useful as the detection of severe congenital cardiac abnormalities may substantially alter the management of these pregnancies, in particular caesarean section may be avoided when the prognosis for the fetus is considered hopeless.