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Relationship between sediment phase Pb and As speciation and

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Relationship between sediment phase Pb and As speciation and Powered By Docstoc
					Relationship between sediment phase Pb and As speciation and accumulation in Chironomids

Colleen McPike & Theresa Smigelski

Abstract
Chironomids are a geographically widespread benthic invertebrate found in fresh waters throughout North America. This research project involves raising chironomids in contaminated sediments to determine if they accumulate and/or redistribute lead and/or arsenic found in the sedimentary phase. Sediments were prepared from Ottawa sand spiked with arsenic (III) oxide, arsenic (III) sulfide and lead (II) oxide. The chironomids were raised in contaminated sediment through the larvae stage and then removed from the tank for testing. In addition, larvae raised in a control system as well as water samples and sediments from the experimental mesocosms were analyzed for lead and arsenic. Samples were analyzed by atomic absorption spectrophotometry following acid digestion. Although difficulties in obtaining suitable chironomid egg masses limited the range of experiments that could be conducted, preliminary results will be presented.

What are Chironomids?
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Family Name: Chironomus Riparius Similar to mosquitoes, except they don’t bite!! More commonly called lake flies or midges Immature chironomids exist as larvae at the sediment water interface Adult midges do not have a functional digestive system, therefore they do not feed Life span: About 1 week- sole purpose is to reproduce

Adult Chironomid Larvae & Experimental Aquaria

Objectives
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Raise chironomid adults in an uncontaminated system to provide egg masses for experiments with contaminated sediments Prepared sediment with 500 ppm As or Pb in either the sulfide or oxide form Raise chironomids from egg-masses in As and Pb contaminated sediments Analyze chironomids to determine As and Pb concentration in larvae

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Experiment Design
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Prepare surrogate sediment from As and Pb compounds mixed with standard Ottawa sand Add ~1L of tap water, air stone and surrogate sediment to 10 liter aquarium. Add 1 gram Tetramin fish food. Allow to equilibrate for 1 week. Add 1-2 egg masses from adults raised in maintenance tank. Feed 1 gram Tetramin fish food/week. Incandescent light on 12 hours/day. Remove larvae after 30 days. Analyze for As or Pb

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pH Measurements (end of experiment)
Tank
Tap Water (starting material) Maintenance (control) As2O3 As2S3

pH
7.34 8.63 7.52 5.98

PbO

7.61

Analysis of Samples by AAS
Condition Pb As

Wavelength
Flame Condition Calibration Range Sample Digestion

217 nm
Lean (blue) 0-100 ppm in solution Hot HNO3 Digestion

197 nm
Rich (yellow) 0-100 ppm in solution Hot HNO3 Digestion

Pb Analyses
Sample Measured Anticipated [Pb] in ppm [Pb] in ppm

Maintenanc e Tank Water PbO Sand
PbO Larvae

Not Detected
456 No Sample

-

500 -

As Analyses
Sample Measured [As] in ppm Anticipate d [As] in ppm

Maintenanc e Tank Sand

Not Detected
466 Not Detected (only 2 larvae found) 527 Not Detected (only 2 larvae

500 -

As2O3 Sand
Larvae

As2O3

As2S3 Sand
Larvae

500 -

As2S3

Conclusions
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We were able to successfully prepare 500 ppm As and 500 ppm Pb spiked surrogate sediment Although the pH values in the experimental mesocosms varied, a near neutral pH was maintained Few eggs placed into the spiked tanks developed, limiting the quantity of sample available for analysis
– Chironomids have been successfully raised in 500 ppm zinc sulfide, zinc carbonate and lead carbonate spiked sediments – Liberty and Schaumloffel, 2001 and Martinez, Moore and Schaumloffel, 1999

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Additional experiments at lead and arsenic concentrations at less than 500 ppm are justified

Acknowledgements
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Research Committee for Funding Dr. Hugh Gallagher for organizing today’s symposium Mike Kahl (USEPA ) for providing initial chironomid egg masses Anne Liberty for sharing her earlier results


				
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