David L. Johnson

Differences in accumulation of PAHs and metals on the leaves of Tilia × euchlora and Pyrus calleryana

The accumulation of substances associated with PM2.5 [polycyclic aromatic hydrocarbons (PAHs) and metals] on leaves of Pyrus calleryana (pear) and Tiliaxeuchlora (linden) along an urban road was investigated. These species have similar leaf morphology and were exposed to the identical environmental conditions. The accumulation of both PAHs and metals per leaf area was significantly higher on linden leaves than on pear leaves.

Biological oxidation of arsenite in seawater

The biological mediation of arsenic speciation has been shown to include oxidation, reduction, methylation and demethylation mechanisms. This study examines the biological oxidation of arsenite in seawater at low levels (100 parts 10 −9 , 1·3 μ m ). Experimental results indicate that abiotic oxidation proceeds at a slow, constant rate, as can be predicted from a consideration of physical and chemical variables only. In the presence of certain aquatic bacteria, however, oxidation is rapid, and the As(III) concentration decreases exponentially with time. Aspects of bacterial oxidation which are investigated include qualitative characteristics of the organisms, enzyme-substrate relationships and kinetic considerations in relation to chemical, physical and biological variables. The distribution of this phenomenon in natural waters is evaluated, and the importance of bacterial oxidation assessed relative to an overall arsenic budget. Results of this study are compared to those of previous investigations of bacterial arsenite oxidation.

A Tale of Two Swaths: Urban Childhood Blood-Lead Levels across Syracuse, New York

A growing body of research documents various prominent and important geographic dimensions to pediatric lead poisoning. This paper uses the Onondaga County Health Department database for 1992–1995 and the 1990 Census of Population and Housing data to analyze the spatial distribution of blood-lead levels in Syracuse, New York. Analyses are conducted at the individual, census block, census block group, and census tract resolutions. Regardless of geographic resolution, pediatric blood-lead levels contain positive spatial autocorrelation, with two conspicuous swaths being visible on maps. In apparent support of some previous research, average housing value is found to be a principal predictor of blood-lead levels; so is population density. The primary conclusion of the paper is that intervention strategies should focus on the old and poor neighborhoods of the city and ones housing minority groups, and should address issues of housing quality and maintenance practices, as well as soil contamination.

Impacts of Positional Error on Spatial Regression Analysis: A Case Study of Address Locations in Syracuse, New York

Positional error is the error produced by the discrepancy between reference and recorded locations. In urban landscapes, locations typically are obtained from global positioning systems or geocoding software. Although these technologies have improved the locational accuracy of georeferenced data, they are not error free. This error affects results of any spatial statistical analysis performed with a georeferenced dataset. In this paper we discuss the properties of positional error in an address matching exercise and the allocation of point locations to census geography units. We focus on the errors spatial structure, and more particularly on impacts of error propagation in spatial regression analysis. For this purpose we use two geocoding sources, we briefly describe the magnitude and the nature of their discrepancies, and we evaluate the consequences that this type of locational error has on a spatial regression analysis of pediatric blood lead data for Syracuse, NY. Our findings include: (1) the confirmation of the recurrence of spatial clustering in positional error at various geographic resolutions; and, (2) the identification of a noticeable but not shockingly large impact from positional error propagation in spatial auto-binomial regression analysis results for the dataset analyzed.

Seasonal variation in paediatric blood lead levels in Syracuse, NY, USA.

Venous blood lead values for 2,633 children aged 0–4 years in Syracuse, New York, collected between 1 April 1992 and 31 March 1993 were summarised by census tract for study of geographic variability. A demographic exposure model is presented showing housing stock and SES (socioeconomic status) parameters as the most significant predictor variables. A seasonal trend in blood lead levels was observed with late summer values about 40% higher than late winter values for census tracts with the highest geometric mean PbB levels. Seasonal variation is compared with a biokinetic uptake model to examine hypotheses about temporal variations in soil and dust lead exposure patterns.

Rapid search and quantitative analysis of gunshot residue particles in the SEM.

Automated scanning electron microscopy coupled with image analysis and X-ray micro analysis was used to characterize a variety of gunshot residue (GSR) samples. More than 500 rounds of commercially available ammunition and six different types of hand gulls were used in the study of 17 GSR and 19 reference specimens. The individual particle X-ray composition was determined for 12 different elements. Elemental composition of GSR particles was highly variable but consistent with compounds mixed into or associated with a barium oxide matrix. When present in a specimen, GSR could be adequately characterized with automated procedures in less than an hour by restricting analyses to features larger than 2 microm. In clean samples, a higher resolution particle search was required to avoid reporting false negatives. Careful control of the back scattered electron signal strength threshold, by reference to a standard, was needed to ensure both time-efficient and accurate analyses. Samples collected from non-shooting subjects. active in a physical environment which contained firearms discharge residue were seen to be easily contaminated by sub-micron GSR particles.

Handguns and ammunitions indicators extracted from the GSR analysis.

The computer automated scanning electron microscope. X-ray microanalysis of Firearms Discharge Residue (FDR) can reveal substantial information about the circumstances of their generation beyond the presence of characteristic gunshot residue (GSR). Indicators of the type of weapon and ammunition used can he obtained from the distribution of GSR particle shapes and from the multi-element analysis of the FDR sample. This is demonstrated for a large database of GSR samples from nine different handguns and over 60 different ammunitions. An example classification scheme is presented for the supporting particles generally found present in FDR. When particle type area concentration ratios are normalized to the iron (Fe) particle type, results show it is possible to distinguish much about the metal used in the weapon manufacture, whether it was of large or small caliber, whether the bullets were jacketed or plated, and whether the cartridge cases were of aluminum, brass, or nickel-plated brass. Standardization of such analytical schemes would be advantageous.