Phytoremediation: An ecological solution to organic chemical contamination

Twelve organic compounds commonly found at hazardous waste sites were studied for uptake by hybrid poplar trees. The vegetative uptake of many of these compounds has not previously been demonstrated for plant species being utilized for phytoremediation, such as hybrid poplar trees. Experiments were conducted hydroponically utilizing 14C-labeled compounds to ascertain translocation and fate. Predictive relationships for the translocation and partitioning to plant tissues were developed from the experimental data. Translocation and partitioning relationships based on compounds' octanol−water partitioning coefficients (log Kow) produced the best results, but the relationships did not allow for fully accurate prediction of each contaminant's fate. Translocation and subsequent transpiration of volatile organic compounds (VOCs) from the leaves to the atmosphere was shown to be a significant pathway. As full-scale phytoremediation systems are deliberated, the pathways investigated here should be considered in te...

http://lib3.dss.go.th/fulltext/Journal/Environ%20Sci.%20Technology1998-2001/1998/no.21/21,1998%20vol.32,no.21,p3379-3385.pdf

Predictive Relationships for Uptake of Organic Contaminants by Hybrid Poplar Trees

The literature on heavy metal toxicity to vascular plants is reviewed. Special attention is given to forest plant species, especially trees, and effects at low metal concentrations, including growth, physiological, biochemical and cytological responses. Interactions between the metals in toxicity are considered and the role of mycorrhizal infection as well. Of the metals reviewed, Zn is the least toxic. Generally plant growth is affected at 1000 μg Zn L−1 or more in a nutrient solution, though 100 to 200 µg L−1 may give cytological disorders. At concentrations of 100 to 200 μg L−1, Cu and Cd disturb metabolic processes and growth, whereas the phytotoxicity of Pb generally is lower. Although a great variation between plant species, critical leaf tissue concentrations affecting growth in most species being 200 to 300 μg Zn g−1 dry weight, 15 to 20 μg Cu g−1 and 8–12 μg Cd g−1. With our present knowledge it is difficult to propose a limit for toxic concentrations of Zn, Cu, Cd and Pb in soils. Besides time of exposure, the degree of toxicity is influenced by biological availability of the metals and interactions with other metals in the soil, nutritional status, age and mycorrhizal infection of the plant.

Toxicity of heavy metals (Zn, Cu, Cd, Pb) to vascular plants

Nitroaromatic compounds, including 2,4,6-trinitrotoluene (TNT), hexahydro-1,3, 5-trinitro-1,3,5-triazine (RDX), octahydro-1,3,5,7-tetranitro-1,3,5-tetrazocine (HMX), N-methyl-N,2,4,6-tetranitroaniline (tetryl), and associated byproducts and degradation products, were released to the environment during manufacturing and load, assembly, and pack (LAP) processes at U.S. Army Ammunition Plants (AAPs) and other military facilities. As a result of the release of these nitroaromatic compounds into the environment, many AAPs have been placed on the National Priorities List for Superfund cleanup (Fed. Reg. 60:20330). Many of these sites cover a wide expanse of relatively undisturbed land and provide diverse habitats that support a variety of aquatic and terrestrial species. Nitroaromatics are potentially toxic to the indigenous species at these sites and present a significant concern for site remediation. Table 1 presents an overview of ranges of detected concentrations of the nitroaromatic compounds in groundwater, surface water, sediment, and soil at military and manufacturing sites.

Nitroaromatic Munition Compounds: Environmental Effects and Screening Values

Response of roots of trees to heavy metals

The uptake of bromacil, dichlorobenzonitrile (DCBN), nitrobenzene (NB) and dinitrobenzene (DNB) was studied in isolated barley roots and mature soybean plants. The uptake rate constants for soybean plants were in the order of DCBN = bromacil < NB < DNB. The same pattern was evident for the root tissue test, except for DNB. Metabolism of the (14)C-labeled chemicals indicated that DCBN was metabolized in the leaves but not in the roots. DNB was metabolized in the roots, and bromacil remained primarily as parent compound. A method for obtaining uptake rate constants is described.

The uptake, distribution and metabolism of four organic chemicals by soybean plants and barley roots

Soybean [Glycine max (L.) Merr.] cultivars Dare and Hood were exposed to ozone (980 μg/m3) for 2 h to determine if differences in cultivar sensitivity were associated with differential activation of selected enzymes. The first trifoliate leaves of the cultivars were in similar stages of development (14 days from sowing) when exposed. The ozone treatment increased the activities of glucose 6-phosphate dehydrogenase, phenylalanine ammonia lyase, polyphenol oxidase and peroxidase above the control in both cultivars within 30 h after exposure. However, the activity of all these enzymes increased several hours sooner in Dare (sensitive) than in Hood (tolerant). Our data suggest that the differential sensitivity of these two cultivars to ozone could be based on the differential ozone induced activation of the enzymes involved in the lesion formation process.

Differential Foliar Sensitivity of Soybean Cultivars to Ozone Associated with Differential Enzyme Activities

Red alder (Alnus rubra Bong.) was grown in sand culture in the greenhouse to obtain data on the effects of cadmium (Cd) on a symbiotic nitrogen (N) fixation system which contributes to the fertility of forest soils. Treatment of red alder seedlings for 11 weeks with 0.545 to 136 ..mu..M CdCl/sub 2/ in N-free nutrient solution decreased in situ nitrogenase activity 25 to 89%, N fixation 23 to 98%, and the number of nodules per plant 29 to 74%, when compared to plants receiving no Cd. Similar reductions were observed in plant growth. Treatment with 0.054 to 0.545 ..mu..M CdCl/sub 2/ decreased nitrogenase activity 6 to 31%. When non-nodulated A. rubra seedlings were inoculated in the presence of 0.054 and 0.109 ..mu..M CdCl/sub 2/, N fixation decreased 52 and 89%, respectively. Plant growth decreased in a similar fashion. When non-nodulated seedlings were given 0.545 ..mu..M CdCl/sub 2/ and 6 mM NH/sub 4/NO/sub 3/ or Ca(NO/sub 3/)/sub 2/, nitrate reductase activity decreased 22 and 24%, respectively, when compared to plants receiving no CdCl/sub 2/. Nitrogen accretion and plant dry weights were decreased by treatments in which plants were supplied with Ca(NO/sub 3/)/sub 2/ and 0.273 and 0.545 ..mu..M CdCl/sub 2/, whenmore » compared to controls without CdCl/sub 2/. These results suggest that Cd can inhibit nitrogenase activity and therefore N fixation. Growth, nodulation, and nitrate reductase activity are also inhibited by Cd.« less

Cadmium effects on the nitrogen fixation system of red alder

Influence of root exposure concentration on the fate of nitrobenzene in soybean.

The Kenaga nomogram was developed by the U.S. Environmental Protection Agency (EPA) in the mid 1970s and has since been used prior to the registration of a pesticide to estimate the maximum potential pesticide residue level on plant material in the food chain of wildlife. The objective of this study was to evaluate the nomogram using field data. Six pesticides representing a variety of pesticide classes were applied to 15 plant species. Five of the six nomogram categories were tested with plant parts representing differences in surface morphology (i.e., glabrous vs. pubescent leaves). The sixth category was a mixed-grass community seeded with three grass species. Pesticide residue levels were determined the day of application and up to 32 d afterward. While the linear nomogram model does not represent the data as well as other models, relatively few data points (10%) collected on the day of pesticide application exceeded the nomogram predictions. The one systemic pesticide tested had degradation rates similar to nonsystemic pesticides in most categories. Present nomogram categories were significantly different from each other in most cases. However, the forage category should be combined with the leaves and leafy-crop category and have higher estimated residue levels than the Kenaga nomogram. A considerable amount of variation occurs in the level of pesticide residue on plant materials even under controlled experimental conditions and therefore nomogram values should be used as an estimate only until actual field residue data are available. The nomogram, with modifications, appears to be a reasonable regulatory device if careful thought is given in selecting the plant category for making residue estimates.

Carlos Wickliff

Papers

The uptake, distribution and metabolism of four organic chemicals by soybean plants and barley roots

Differential Foliar Sensitivity of Soybean Cultivars to Ozone Associated with Differential Enzyme Activities

Cadmium effects on the nitrogen fixation system of red alder

Influence of root exposure concentration on the fate of nitrobenzene in soybean.

Field evaluation of the EPA (kenaga) nomogram, a method for estimating wildlife exposure to pesticide residues on plants