RESULTS OF A FIELD TRIAL EXPERIMENT OF A HYDROPONIC GROWING SYSTEM POWERED BY SOLAR ENERGY USING ALL PLASTIC MATERIALS IN ITS CONSTRUCTION. THE SYSTEM INCLUDED UTILIZATION OF DISCARDED PLASTIC MATERIALS CONTAINING HEAVY METAL CONTAMINANT AS SOIL MATRIX. BY AL MATTES, Phytoremediation, Botanist, Ottawa October 1996

Executive Summary

During the summer of 1996 five research lines were established at the University of Lethbridge for the purpose of investigating several aspects of plant response to use of Automobile Shredder Residue (ASR) as a soil matrix in a hydroponic garden. This material presents a considerable disposal problem for the automobile recycling industry. It is a heterogeneous mixture that contains glass, fibres, plastic, urethane foam and metals in a variety of forms. Some of the metals can leach into solution and contaminate ground water supplies. The levels of leachable heavy metals present, particularly Pb & Zn, can exceed provincial limits for non-hazardous disposal protocols and therefore it is of considerable interest to develop a system which can safely remove and sequester these. The purpose of the research developed this summer was to investigate the possibility that plants, especially those that have been described as hyperaccumulaters by other researchers, could effectively deal with some or all of the heavy metals present. The design of the hydroponic system, Elevated Wetlands, is a copyright technology developed by Noel Harding. The systems utilize all plastic components to both contain plants and to provide a support matrix for their roots. This matrix provides a medium through which nutrient solution can be delivered and offers sufficient support to the plants to ensure stability in various outdoor weather conditions. Power is provided to operate continuous circulation pumps by solar panels. With the assistance of Dr. Fred Edgecombe and EPIC, 2500 pounds of ASR was obtained from a recycling plant in Edmonton and shipped to Lethbridge. A sample was taken using the cone and quartering procedure as outlined by Day (1995) and shipped to the Institute for Chemical Process and Environmental Technology at the National Research Council in Ottawa for characterization under the direction of Group Leader Dr. Michael Day.

V - No Plants

One of the lines was designated as a control line and contained no ASR. A second control line contained ASR but no plants. The three other lines were planted with species of plants that had previously been described in the literature as hyperaccumulaters or contained plants that were gathered from the vicinity of a lead zinc smelter where contamination from the plume had resulted in Pb and Zn levels in the soil of from 500 to more than 1500 parts per million (ppm). Various testing protocols were designed to release the bound heavy metals in order to test the efficacy of plant uptake. Initially, attempts were made to reduce the pH of the system, a procedure which results in the release of substantial levels of Pb and Zn according to research, (Day 1995). Subsequently Ethylene Diamine Tetra-acetic Acid (EDTA) was added. This chelator had been used by researchers (Raskin, 1995) to assist in solubilizing metals bound to soil particles in order to facilitate plant uptake. Tests for the presence of Pb, Zn, Cd, and Fe were made weekly by Dr. Scott Hinman at the University of Calgary using Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP - AES). Additional tests were made using ion chromatography to ascertain the levels of various ions present in solution including nitrates, sulphates, potassium and phosphate. Plants were monitored closely for evidence of both nutrient deprivation and signs of phytotoxicity indicative of excess heavy metal uptake. This was undertaken by Dr. John Harder a plant water relations expert and authority on hydroponics gardening techniques. He was also responsible for the weekly testing procedures. In addition to tests of plants viability in the systems as described, the volume of water added was monitored in order to allow for calculations of effective evapotranspiration rates of the systems. This was accomplished by recording weekly additions using an inline meter attached to the water supply line. Highlights: Plants grew exceptionally well in the control line which used all plastic soil and to which nutrients were added regularly. A variety of plants were introduced into this line including several indigenous species of both grasses and flowering plants including red root pigweed, plantain and mint. Typical marsh plants included cattails and sedges. Biomass produced exceeded that from any similar native plant species growing locally, the tomato plant produced hundreds of flowers and many fruit as did the pepper plant. The tobacco plant grew to a height of nearly 2 meters and was in full flower by the time the experiment terminated. This line clearly shows the efficacy of the Elevated Wetlands system and the reliability of plastic soil as a growing medium for hydroponic culture. There were insignificant levels of Zn and Fe measured in this system and both Cd and Pb were not detected.

IV - ASR Testline

When water is added to a system containing ASR, the amount of Pb, Zn and Cd released into solution is very low, certainly not sufficient to exceed any guidelines for ground water release. Pb was present at less than 0.75 ppm, Zn at 3.04 ppm and Cd at levels of 0.006 ppm. This indicates that in a system containing ASR which has only water added to it, there is no concern regarding excessive amounts of heavy metals released. In the three systems that contained plants and ASR, the levels of Pb detected after 6 weeks of operation had declined to 0.00 in two instances and in the third to 0.01 ppm (which represents 1.2% of the highest amount determined). In the system with no plants, however, 14.08% of the highest recorded level of Pb in solution remained after 6 weeks. For Zn the results are not as dramatic but nonetheless they still appear to be significant. In the line with no plants levels declined to 31.25% of the highest level recorded whereas in lines with plants the levels declined to a low in one of 4.8% and a high in another of 15.8%. After 6 weeks of operation the third line had levels measured of 7.7% of the highest initial level determined. The decline of Pb present can be attributable to one of two processes which take place, either plant uptake or precipitation as insoluble salts. In the case of the line with no plants the only possibility is a precipitation process whereas in the test lines the results obtained could be the result of either plant uptake or of root exudate mediated precipitation, a process described by Raskin and named phytostabilization. A similar process was likely responsible for the reduction in levels of Zn found. Absolute results which would determine whether the absent metals were precipitated or were taken up by plants and sequestered will be determined by additional tests still to take place. Testing of the levels of metals remaining in the ASR, in precipitates taken from each system and from sludge found at the bottom of each system will be made at the NRC by Dr. Day. Following this analysis and a subsequent mass balance with initial levels known to be present in this ASR sample if it is shown that there are still unaccounted for differences, samples of plants from each system will be tested for presence of heavy metals at NorWest labs.

III - ASR Testline

Despite frequent repeated attempts to reduce the pH of the system to 7 or lower, it was not possible to do this even when as much as 1 liter of 1 molar acid was added to the 1500 liters of solution present in each system. This is not surprising given the basic nature of ASR. When tested for pH, ASR is shown to be about 8.2 (Day, personal communication). Beyond this, however, it is also a buffering substance and therefore it takes considerable quantities of acid added to overload the buffering capacity inherent in a solution which constantly circulates through ASR. When to this is added the fact that the irrigation water at the University of Lethbridge is itself at a pH of 8.0, the difficulties in lowering the pH to 7.0 or below and keeping it there are easily understood. This is an important result from the summer's research, and one that is essential to keep in mind when determining the possibility of using ASR as a component of a sculpture to be built in a public place with water passing through eventually returning to the natural ecosystem. The amount of Pb leached from the ASR sample using the Ontario Government Ministry of Environment and Energy protocols was found to be 9.5 ppm, for Zn 220 ppm and for Cd 0.565 ppm. whereas the maximum levels obtained in the Elevated Wetlands system, even when acid was added remained at levels far below these (Pb 0.74, Zn 3.96, Cd 0.08). When EDTA is added to a system there is a marked change in levels of metals present in solution which rose to the point where the ICP-AES instrument had to be recalibrated. The level of metal present is related to the molar concentration of EDTA used and as additional amounts were added on a weekly basis to reach a maximum concentration of 0.02 M, the levels of Pb, Zn, CD and Fe increased correspondingly. In fact the levels of Pb present far exceeded those obtained using MOEE protocols and peaked in one line at a level of 33.8 ppm, (compared to 9.5 ppm). Level of Zn reached a maximum of 286.8 ppm (compared to 220 ppm) but Cd remained below the MOEE obtained level of 0.565 ppm and reached a maximum level of 0.167.

II - ASR

The high levels of Pb and Zn that resulted from the addition of EDTA might point the way to a possible treatment process for partial remediation of ASR prior to landfill. If it were to be shown that addition of EDTA would result in the solubilizing of sufficient recoverable quantities of Pb, Zn and Cd, such that subsequent leachate tests gave levels of these metals sufficiently low enough to allow for non-hazardous landfill disposal, depending on cost effectiveness, it might be possible to develop an industrial level treatment procedure to do this. Recovery of the metals from the resultant water might be necessary to ensure cost effectiveness and this might be accomplished by either chemical means, or using Elevated Wetlands technology by using the water in a diluted form as part of the nutrient solution for hydroponic plant irrigation. For an Elevated Wetlands system operating at full capacity with close to 100% biocover and warm dry sunny weather, we were able to demonstrate that 66 liters of water per m2 were effectively cleaned of all contaminants by evapotranspiration each week. Depending on the final size of an installation, meaningful volumes of water can, therefore, be successfully remediated using this technology throughout a growing season. In addition to plants which were known to be hyperaccumulaters and therefore expected to survive the presence of heavy metals in solution, during the course of the summer we found additional plants that hold promise for further investigation of their metal tolerant ability. These are plantain, a variety of Epilobium ( a common member of this family is fireweed) and Lamb's quarters. Seeds from each of these were gathered and are available if subsequent research into this area develops.

I - No ASR

Seeds from all plants which grew to maturity in the systems containing ASR were gathered and stored for possible future research as well. There were two aspects of the research that took place that proved to be negative in terms of the effectiveness of the system. 1) When the high volumes of heavy metals were moved into solution as a result of the addition of the chelating agent, most plants died, even some of those described in the literature as hyperaccumulaters. The reason for this is not clear from the summers research. Some plants, however, did not seem to be affected and these hold promise for future investigations. 2) High levels of Fe present in the system (as much as 12% of the ASR was determined to be Fe) result in the deposition of a layer of rust coloured material over the system's surface. This layer also builds up on plant root interfaces at the surface level as well. Whether or not it has an effect on the plant growth was not determined. It does not appear to be possible to remove the Fe from ASR and therefore a decision to use ASR in a sculpture must be done with the knowledge that like sculptures and fountains around the world that include running water, there will be an inevitable build-up of rust material deposited on many surfaces.

REFERENCES: Budd A.C. 1979, Budd's Flora of the Canadian Prairie Provinces, Research Branch Agriculture Canada, pp 539 Baker A.J.M. 1989, Terrestrial Higher Plants Which Hyperaccumulate Metallic Elements - A Review of Their Distribution, Ecology and Phytochemistry, Biorecovery, Vol. 1, pp 81-126 Day M., 1996, Characterization of Automobile Shredder Residue (ASR) Sample Supplied by Environment and Plastics Institute of Canada (EPIC) as part of the University of Lethbridge, Alberta Wetiand Study, unpublished report Day M., Awadalla F. T., 1995, Leachability of Lead from Auto Shredder Residues: A Canadian Perspective, Environmental Technology, Vol. 16, pp 785-793 Day M., Farouk T. A. Lynhiavu A., 1994, Chemical Association of Lead in Auto Shredder Residue, Environmental Technology, Vol. 16, pp 585-592 Dushenkov V., Kumar P.B.A., Mofto H., Raskin I., 1995, Rhizofiltration: The Use of Plants to remove Heavy Metals from Aqueous Streams, Environmental Science and Technology, Vol. 29, pp 1239 -1245 Harter R. D., 1982, Effect of Soil pH on Adsorption of Lead, Copper, Zinc and Nickel, American Joumal of the Soil Science Society, Vol. 47, pp 47-51 Jorgensen S.E., 1993, Removal of Heavy Metals from Compost and Soil by Ecotechnological Methods, Ecological Engineeiing, Vol. 2, pp 89 -1 00 Kumar P.B. A., Dushenkov V., Mofto H., Raskin I., 1995, Phytoextraction: The use of Plants to Remove Heavy Metals from Soils, Environmental Technology Vol. 29, pp 1232 - 1238 Norvell W.A. 1984, Comparison of Chelating Agents as Extractants for Metals in Diverse Soil Materials, American Joumal of Soil Science Society, Vol. 48, pp 1285-1292 Salt D.E., Slaycock M., Kumar P.B.A., Dushenkov V., Ensley B.D., Chet I., Raskin 1. 1995 Phytoremediation: A Novel Strategy for the removal of Toxic Metals from the Environment Using Plants, Biotechnology, Vol. 13, pp 468 - 474 Salisbury F.B., Ross C. W. , 1992, Plant Physiology, Wadsworth Inc. Belmont California, pp 119 Smith R.A. H., Bradshaw A.D., 1979, The Use of Metal Tolerant Plant Populations for the Reclamation of Metalliferous Wastes, The Joumal of Applied Ecology, Vol. 16, pp 595 - 612

	Corporate Contribution
	CPIA EPIC Polywheels Manufacturing Ltd. NOVA Chemicals Ltd. Plasti-Fab Division of PFB Corporation Columbia Geosystems Ltd. Flexahopper Plastics Ltd. IPEX Inc. W. Ralston (Canada) Inc. Alta Steel Co. Polytubes Ltd. Enviroscapes Frontier Irrigation Australian-Canadian Machinery Ltd. Phillips Farevaag Smallenberg Inc.