Application of phytoscreening to three hazardous waste sites in Arizona

Abstract

The great majority of prior phytoscreening applications have been conducted in humid and temperate environments wherein groundwater is relatively shallow (~1-6m deep). The objective of this research is to evaluate its use in semi-arid environments for sites with deeper groundwater (>10m). To that end, phytoscreening is applied to three chlorinated-solvent hazardous-waste sites in Arizona. Contaminant concentrations were quantifiable in tree-tissue samples collected from two of the sites (Nogales, Park-Euclid). Contaminant concentrations were detectable, but not quantifiable, for the third site. Tree-tissue concentrations of tetrachloroethene (PCE) ranged from approximately 400-5000ug/kg wet weight for burrobrush, cottonwood, palo verde, and velvet mesquite at the Nogales site. In addition to standard trunk-core samples, leaf samples were collected to test the effectiveness of a less invasive sampling method. Leaf-sample concentrations were quantifiable, but several times lower than the corresponding core-sample concentrations. Comparison of results obtained for the test sites to those reported in the literature suggest that tree species is a major factor mediating observed results. One constraint faced for the Arizona sites was the relative scarcity of mature trees available for sampling, particularly in areas adjacent to industrial zones. The results of this study illustrate that phytoscreening can be used effectively to characterize the presence of groundwater contamination for semi-arid sites with deeper groundwater.

An assessment of correlations between chlorinated VOC concentrations in tree tissue and groundwater for phytoscreening applications

“…Significant differences in tree-tissue VOC concentrations as a function of tree species were also observed in prior analyses of phytoscreening data collected from sites with deeper groundwater 11,37 . Sorek et al 11 reported significant differences in concentrations as a function of tree species for multiple sampling sites in Tel Aviv.…”

“…core or branch) is likely a primary source of variability given that prior studies have indicated that tissue concentrations measured for trunk core samples are significantly higher than those measured for branch or leaf samples for the same conditions. 6,8, 10, 37 Thus, the aggregate data were first parsed to include only those representing trunk core samples (95 out of the 100 total samples). A correlation between core tissue and groundwater concentrations was determined to have an r-squared of 0.56 for the aggregated data set.…”

“…For these conditions, the source of contaminant for tree uptake is hypothesized to be diffusive vapor-phase transport of the contaminant from the groundwater, through the vadose zone, to the root zone. 9, 37 These different routes of exposure may have a significant impact on resultant tree-tissue concentrations. In addition, the specific subsurface conditions at a site (e.g., soil type, physical heterogeneities, water content, microbial activity), and the associated potential for attenuation, are likely to exert greater influence when roots are not in direct contact with groundwater.…”

“…Sorek et al 11 reported significant differences in concentrations as a function of tree species for multiple sampling sites in Tel Aviv. Duncan et al 37 evaluated 6 phytoscreening applications for deeper-groundwater sites and the results indicated that tree species was a likely primary cause of the observed differences in tree-tissue concentrations. For example, tree-tissue VOC-concentrations reported for eucalyptus were approximately 1.5 to 3 orders-of-magnitude larger than those reported for cottonwood, oak, and fir for similar groundwater concentrations.…”

Application of the Hazardous Waste Vitreous Enamel Generated in the Production Process of Heating Devices as a Partial Replacement for Cement

“…However, in this way, natural resources are consumed while the amount of waste is not reduced, so that only in the short time can the problem be mitigated or solved. Some authors [8,9] examined various methods by which it is possible to monitor the impact of hazardous waste from landfills on the environment, while other authors [10,11] examined the possibility of legislation to solve the problem of illegal landfills or to find ways for more efficient networking between hazardous waste producers and plants that deal with its processing. Additionally, the problem of hazardous waste, such as bottom ash [12] or fly ash [13][14][15], can be solved by applying it in the construction industry, as a substitute for cement in the production of mortar and concrete.…”