A risk-based screening approach for prioritizing contaminants and exposure pathways at Superfund sites

Contamination at Superfund sites can involve mixtures of chemicals and radionuclides in a variety of environmental media. Determining priorities for evaluation and remediation of various contaminants is an important part of the initial phases of any site investigation. An effective screening analysis at the beginning of the project can help by identifying both those situations in need of immediate remedial attention and those which require further sampling and evaluation. The screening approach discussed here is made up of two sets of calculations designed to provide upper- and lower-bound estimates of health risk to individuals likely to receive the highest exposures. This approach allows rapid identification of contaminants which pose a negligible risk and can be assigned a low priority for remedial attention or which pose a substantial risk and should be given the highest priority for appropriate remediation efforts. Contaminants designated as neither high- nor low-priority should be investigated in more detail prior to making decisions regarding the need for or method of remediation. The utility of this approach has already been demonstrated in the evaluation of contamination in the Clinch and Tennessee River systems originating from historical operations of atomic weapons and energy research facilities near Oak Ridge, Tennessee.     

The economics of uranium demand

The major characteristics of the demand for uranium are identified, and a number of factors which determine the actual level of uranium requirements of the nuclear power industry are discussed. Since the role of inventories is central to the process of short-term price formation, by comparing projections of uranium production and apparent consumption, the relative level of total inventories is calculated and an assessment is made of its likely impact on the uranium market during the 1980s.     

Effectiveness of Panama as an intercontinental land bridge for large mammals

Habitat fragmentation is a primary driver of wildlife loss, and establishment of biological corridors is a common strategy to mitigate this problem. A flagship example is the Mesoamerican Biological Corridor (MBC), which aims to connect protected forest areas between Mexico and Panama to allow dispersal and gene flow of forest organisms. Because forests across Central America have continued to degrade, the functioning of the MBC has been questioned, but reliable estimates of species occurrence were unavailable. Large mammals are suitable indicators of forest functioning, so we assessed their conservation status across the Isthmus of Panama, the narrowest section of the MBC. We used large-scale camera-trap surveys and hierarchical multispecies occupancy models in a Bayesian framework to estimate the occupancy of 9 medium to large mammals and developed an occupancy-weighted connectivity metric to evaluate species-specific functional connectivity. White-lipped peccary (Tayassu pecari), jaguar (Panthera onca), giant anteater (Myrmecophaga tridactyla), white-tailed deer (Odocoileus virginianus), and tapir (Tapirus bairdii) had low expected occupancy along the MBC in Panama. Puma (Puma concolor), red brocket deer (Mazama temama), ocelot (Leopardus pardalis), and collared peccary (Pecari tajacu), which are more adaptable, had higher occupancy, even in areas with low forest cover near infrastructure. However, the majority of species were subject to ≥1 gap that was larger than their known dispersal distances, suggesting poor connectivity along the MBC in Panama. Based on our results, forests in Darien, Donoso–Santa Fe, and La Amistad International Park are critical for survival of large terrestrial mammals in Panama and 2 areas need restoration.     

A simulation model of rhizome networks for Fallopia japonica (Japanese knotweed) in the United Kingdom

Fallopia japonica (Japanese knotweed) is an aggressively invasive herbaceous perennial that causes substantial economic and environmental damage in the United Kingdom (UK). As such, it is of considerable concern to councils, environmental groups, private landowners and property developers. We construct a 3D correlated random walk model of the development of the subterranean rhizome network for a single stand of F. japonica. The formulation of this model uses detailed knowledge of the morphology and physiology of the plant, both of which differ in the UK to that of its native habitat due to factors including a lack of predation and competition, longer growth seasons and favourable environmental conditions in the UK. Field data obtained as a part of this study are discussed and used in the model for parameterisation and validation. The simulation captures the field data well and predicts, for example, quadratic growth in time for the stand area. Furthermore, the role of a selection of parameters on long-term stand development are discussed, highlighting some key factors affecting vegetative spread rates.     

Seasonal and areal changes in standing stocks of phytoplankton,zooplankton and micronekton in the eastern tropical pacific

Five standing stocks were measured together at similar latitudes and longitudes on seasonally repetitive cruises in 3 areas — western, eastern, and southern — of the eastern tropical Pacific. The stocks were chlorophyll a at 0 to 150 m depth (mg/m²), night and day zooplankton at 0 to 200 m depth (ml/1000 m³), and night crustacean micronekton and fish-pluscephalopod micronekton at 0 to 200 m depth (ml/1000 m³). The logarithms of the measurements of each stock in each area were subjected to analysis of variance with the following factors: season (2 month period), latitude, and longitude. Seasonal coverage was most comprehensive, with 7 successive periods, in the western area (approximately 16° N to 3° S latitude, 100° to 122° W longitude). Most stocks in most parts of the western area had a simple seasonal cycle of low amplitude, with a single maximum and minimum that usually differed by a factor <2; some stocks in some parts of the area exhibited no seasonal cycle; all statistically significant cycles, except for fish-plus-cephalopod micronekton, were similar in phase. In the other two areas, located broadly to the east and south of the western area, suitable measurements were made at only 2 periods (opposite seasons) of the year. There were indications of phase differences between chlorophyll a and zooplankton in the eastern area, which should be further investigated. Most standing stocks declined gradually from east to west, and were higher in known upwelling areas and areas of shoal thermocline than elsewhere.     

Toward modeling regionally specific human security using GIS: case study Cambodia

A new methodology for measuring human security is presented. The three stages of the methodology are: i) threat assessment, ii) data collection and organization, and iii) data visualization and analysis, using Geographic Information Systems. Results from a Cambodia case study are highlighted. The United Nations Development Program's notion of human security, which gives equal weight to economic, health, food, political, personal, and environmental factors, is used. Country-specific threats in each category are determined, and local, spatially referenced data are collected. In this paper, poverty, dengue fever, and tuberculosis are used as examples of the analytic process. Regions of Cambodia exposed to all three of these threats ("hot spots") are located, and spatial correlation between poverty, dengue fever, and tuberculosis is calculated. The methodology i) advances a broad concept of human security, ii) will potentially assist policy and decision makers, and iii) identifies research questions that cannot be resolved using single-sector analysis.     

Validation of pyrithiobac sodium (Staple herbicide) ELISA for Australian cotton soils

An enzyme-linked immunosorbent assay (ELISA) for pyrithiobac-sodium (Staple) produced by DuPont was validated in Australian soils. This pyrithiobac-sodium ELISA was shown to be highly sensitive with the limit of detection of 4-5 ppt. Soil samples were extracted either in PBS buffer by shaking or by accelerated solvent extraction (ASE). While pyrithiobac sodium can be analyzed directly by ELISA after ASE extraction with 1/10 or more dilutions, the analysis of PBS extract required filtration and dilution 1/20 or more depending on the concentration. Immunoassay results compared favorably with GC-MS results for both ASE and PBS extract of incurred residue of pyrithiobac sodium in soil samples, indicating that this ELISA can be an inexpensive and reliable alternative to conventional residue analysis methods for quantification of pyrithiobac-sodium. This validation provided the basis for applying the ELISA to a field study of pyrithiobac-sodium.     

Antimony bioavailability in mine soils

Five British former mining and smelting sites were investigated and found to have levels of total Sb of up to 700 mg kg(-1), indicating high levels of contamination which could be potentially harmful. However, this level of Sb was found to be biologically unavailable over a wide range of pH values, indicating that Sb is relatively unreactive and immobile in the surface layers of the soil, remaining where it is deposited rather than leaching into lower horizons and contaminating ground water. Sb, sparingly soluble in water, was unavailable to the bacterial biosensors tested. The bioluminescence responses were correlated to levels of co-contaminants such as arsenic and copper, rather than to Sb concentrations. This suggests that soil contamination by Sb due to mining and smelting operations is not a severe risk to the environment or human health provided that it is present as immobile species and contaminated sites are not used for purposes which increase the threat of exposure to identified receptors. Co-contaminants such as arsenic and copper are more bioavailable and may therefore be seen as a more significant risk.