Monitoring total suspended solids by using nephelometry

Correlation curves were developed relating nephelometric turbidity units (NTU) with total suspended solids (TSS) for diked upland dredged material placement site effluents of three US Army Corps of Engineers (COE) maintenance dredging projects in the Chesapeake Bay, Maryland. The procedure was developed in an effort to ensure compliance with Maryland's 400 milligrams per liter (mg/l) TSS standard for COE dredging projects. Samples of the sediments to be dredged were collected and analyzed, correlating turbidity readings with TSS determined by standard gravimetric techniques. The correlation curves were provided to the COE inspectors to measure the effluent with a turbidity meter and to extract a TSS concentration from the correlation curve. Samples collected and analyzed after initiation of the dredging indicated that the correlation curves were an overestimate of the actual TSS concentrations of the effluent discharges. The procedure, endorsed by the State of Maryland, provided immediate on-site TSS analysis eliminating the previously encountered delays in obtaining gravimetric analysis of effluent discharges and potential contract management problems.     

Does a ‘notched’ nuchal translucency indicate Down syndrome fetuses or other adverse pregnancy outcome?

The aim of the present study was to assess the sonographic contour of the increased nuchal translucency (NT) and to correlate this with pregnancy outcome. Fifty sonographic images of fetuses with increased NT [>95th centile thickness of the normal range for crown–rump length (CRL) between 38 and 84 mm] were retrospectively assessed. In all the cases a complete pregnancy and even infancy follow-up (<36 months) was available. The NT appearances were subdivided into two forms: a ‘notched’ or ‘uniform’ appearance. The images were correlated with karyotype results [trisomy 21 (DS) vs euploid cases] and pregnancy outcome. Complicated outcomes were classified as being either DS fetuses, miscarriage or termination of pregnancy because of structural anomaly. Thus 30/35 (86%) of the euploid fetuses had a ‘uniformly’ increased NT, whereas 8/13 DS cases (62%) had a ‘notched’ appearance (Fisher's exact test, p=0.004). Additionally, 27/29 fetuses (93%) which had an uneventful pregnancy outcome had a ‘uniform’ increased NT, whereas 12/26 (57%) of the fetuses which had adverse pregnancy outcome had a ‘notched’ appearance of their NT (Fisher's exact test, p<0.001). Although it was not possible to correlate the sonographic data with post-evacuation microdissection findings, it is possible that a uniformly shaped, increased NT may be more representative of a developmental delay in a normal fetus. Conversely, a ‘notched’ nuchal surface may represent abnormal lymphatic or cardiovascular development more commonly seen in DS fetuses. Copyright © 2001 John Wiley & Sons, Ltd.     

Online single particle analysis of chemical composition and mixing state of crop straw burning particles: from laboratory study to field measurement

Fresh straw burning (SB) particles were generated in the laboratory by the combustion of rice straw and corn straw. The chemical composition and mixing state of the fresh SB particles were investigated by an Aerosol Time-of-Flight Mass Spectrometer (ATOFMS). Based on the mass spectral patterns, the SB particles were clustered into four major types: Salt, Organic Carbon (OC), Elemental Carbon (EC), and internally mixed particles of EC and OC (EC-OC). In addition, particles containing ash, polycyclic aromatic hydrocarbons, heavy metals or nicotine were also observed. Physical and chemical changes of the SB particles immediately after the emission were analyzed with highly time-resolved data. During the aging processes, the average particle size increased steadily. Freshly emitted organic compounds were gradually oxidized to more oxygenated compounds in the OC-containing particles. Meanwhile, an important displacement reaction (2KCl+ SO42−→ K₂SO₄ + 2Cl⁻) was observed. The marker ions for SB particles were optimized and applied to identify the SB particles in the ambient atmosphere. The fluctuation of the number fraction of ambient SB particles sorted by ATOFMS agrees well with that of water soluble K⁺ measured by an online ion chromatography, demonstrating that the optimized marker ions could be good tracers for SB particles in field measurements.     

Trace metals used as natural markers for discriminating some karstic freshwaters near Trieste (Italy)

Some heavy metals have been determined using voltammetry in freshwaters forming part of a karstic hydrological system (the Timavo River, north of Trieste), during attempts to characterize and discriminate the different sources of the springs. The trace elements can be considered natural markers, with lead appearing to be the most discriminating variable. Non parametric statistics and cluster analysis were used to estimate the significance of the determined parameters with respect to the considered ecosystem.     

A multilevel analysis of private-vehicle evacuation clearance times along the US Gulf Coast

This study uses multilevel regression analysis to examine the effect of social characteristics and the built environment on clearance time under an evacuation scenario. The primary unit of analysis is the US Census tract (N?=?1660), nested within 31 incorporated places spanning five US states. The dependent variable is an estimate of clearance time in hours derived using network analysis techniques within a geographic information system. We find that tracts with a more peripheral location, more female residents, a higher proportion of Hispanic residents, and higher median household incomes are associated with higher clearance times, on average. Our research suggests the relationship between suburbanization and clearance time is complex and evolving, mediated by past investments in the built environment and shifting social conditions. In addition to facilitating the evacuation of areas with low access to personal vehicles, urban planners and emergency management officials should also consider how the degree of connectivity in the street network impacts congestion and clearance time.     

Indoor and outdoor air PBDE levels in a Southwestern US city

Levels of polybrominated diphenyl ether (PBDE) flame retardants have been increasing in humans and the environment for the past few decades. Human levels are markedly higher in the US than Europe. Although food appears to be a significant route of intake, food PBDE levels are not substantially higher in the US than Europe. House and office dust appear to be major routes of exposure with air believed to usually provide a lesser route of intake. Because there are very few measurements of airborne PBDE that have been performed in relevant microenvironments in the US, increased efforts to assess airborne PBDE in the US as sources of exposure are needed. This study reports, for the first time from a Southwestern US city in Texas, the results of measurements of airborne PBDE in multiple locations, two outdoor and six indoor (residential and office) from active air sampling with collection of a combination of both vapor- and particulate-phase PBDE. Higher PBDE levels were measured in indoor than outdoor air, which confirms previous findings. Of 11 measured congeners including BDE 209, total PBDE levels in two outdoor air samples were 112 and 125 pg m^?3 and the indoor air levels ranged from 175 to 1232 pg m^?3 with a median of 572 pg m^?3. These findings suggest that sources of air contamination with PBDE may be similar in Texas as elsewhere in North America. However, more sampling is required to (1) better determine if this is the case and (2) attempt to characterize potential sources of PBDE contamination in both indoor and outdoor air by analysis of congener patterns.