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Phytoremediation of Lead Using Sunflowers and EDTA
and J.L. Schnoor, Department of Civil and Environmental Engineering,
Lead is rather difficult to separate from polluted soils because it precipitates with most common anions, such as SO42-, PO43- , CO32-, S2-. Current cleanup methods are either too expensive, time-consuming, or devastating to soil properties.
In this research, common sunflowers were grown hydroponically and their potential for uptake and translocation of lead was assessed. EDTA was added to Hoalgand nutrient solution to study its role in lead transport between sunflower tissues. Daily gravimetric transpiration data were also recorded to examine toxicity of lead to sunflowers.
Pre-rooted sunflowers were relocated from soil to 400 ml bioreactors. About 200 ml Hoalgand solution was initially put into each flask. Hoalgand solution was resupplied when about 30 ml was left in the flask. After 7 days of cultivation, sunflowers were weighed and divided into four groups: control (1), lead-added (2), EDTA-added (3), and lead-EDTA-added (4). The concentration of lead was set to about 50 PPM above soil background (a representative soil-water concentration) in order to assess lead toxicity. The ratio of lead to EDTA was 10: 1. After exposure, each sunflower was cut into roots, shoots, and leaves. Samples were treated and measured with recommended method in AA WinlabTM Software by Perkin Elmer 3300.
The uptake efficiency of whole sunflower was calculated with mass balances. Lead uptake varied from 59% to 78% for the individual sunflowers. There was no significant difference of uptake efficiency between group 2 and group 4 (no EDTA versus added EDTA) which was 67% (stdv.=8%, n = 3) and 74% (stdv.=6%, n = 4), respectively. These results indicate that lead availability in hydroponic solution was not limited and chelation by EDTA may only increase the bioavailability of lead in soil. Soil experiments are currently underway to investigate this possibility.
Although the presence of EDTA did not affect lead uptake, it did significantly influence lead transport between plant tissues. Generally, roots of groups 2 and 4 showed a great ability to retain lead (from 28,000 to 42,000 mg Pb/ kg Dry Weight). This conclusion, that roots accumulate lead, was similar to other reports. The effect of EDTA on lead transport is clear when shoot and leaf concentrations are compared for the two groups. The sunflowers in group 2 showed higher shoot uptake than group 4, 563 (stdv.=286, n = 4) and 232 (stdv.=44, n = 3) mg Pb/kg DW, respectively. This trend was reversed with respect to leaf tissues where about 1000 mg Pb/kg DW (stdv.=207, n = 3) was translocated for group 4 and no lead was detected in leaves of group 2.
During 10 days of exposure, the normalized transpiration (defined as 1 for controls) decreased slightly for group 4. Although no distinct visible symptoms such as chlorosis were noticed for any group, the trend of transpiration decline for group 4 indicated a slight toxicity for the 50 mg/L dosage. Longer toxicity experiments are needed and the ability of sunflowers to complete the life-cycle (go to seed) should be determined since the accumulation of lead in aerial tissues may present larger bioaccumulation issues.
Key words: remediation, sunflower, lead, EDTA
Abstracts From The 1997 Conference on Hazardous Waste Research
Dont forget the final talk in the series of "City Talks" organised by: SMOGBUSTERS
Thursday 17 December: Speaker: Felix Laube, transport consultant
Swiss clockwork: lessons from Switzerland's cities and towns
$7 / $5. Join us for wine and cheese after the talk.
6pm - 8pm, Room A, Level 2, Parramatta Civic Building (behind Parramatta Town Hall)
For more information: Christine Laurence, Smogbusters, Nature Conservation Council, ph: 9279 2944
[Also ask about the new Smogbusters Education Team. First meeting is Tuesday 15 December 1998.]
John Ralston Saul, Sydney Jan 99
Eminent Canadian environmental educator, John Ralston Saul is one of five keynote speakers at the International Conference on Environmental Education to be held at University of NSW in Sydney on 14-18th January 1999. The Conference will draw together environmental educators and decision-makers from around the world at a time when both the Australian and NSW Governments are developing either a legislative or policy frameworks on environmental education. Contact Peter Layton at NSW EPA for info on ph (02) 9325 5845, fax (02) 9325 5601 or email: firstname.lastname@example.org ¨
Indian Lead Conference, Feb 99
Professor Brian Gulsons research has again been acknowledged internationally (why not more so in Australia?). Brian is the only Australian to be asked to speak at the Indian lead conference that promises to be "the largest ever held on the topic of lead poisoning". Brian will speak on several days (on two panels): the first panel will be on day 1 with the topic
"Investigating environmental lead sources and pathways". The second topic will be on his work with bone lead and pregnancy along with Dr. Morri Markowitz, with a working title "Assessing the lead in bone: the main reservoir for lead in the body". The date of the conference is February. 8,9 and 10, 1999 and the venue is in Bangalore in Southern India.
This conference is being sponsored by the US Centers for Disease Control, US Environmental Protection Agency, The World Bank, and the host The George Foundation of India. Friends of Lead Free Children, along with Johns Hopkins University is a co-sponsor.
There will be over 72 speakers, so to find out who they are, send an email to email@example.com to request a copy of the conference invitation brochures, ie to Steve Null of Friends of Lead Free Children.
Kate Hayter, Coordinator of Hunter LEAD Group Branch is particularly keen to get to the conference in order to catch up with the US lead researchers she has been corresponding with and to set up a south east Asian network of parents of lead poisoned kids. Can anyone help Kate and a colleague to get there?
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