Date of Award

8-2012

Document Type

Thesis

Degree Name

Master of Science (MS)

College/School

College of Science and Mathematics

Department/Program

Biology

Thesis Sponsor/Dissertation Chair/Project Chair

Ann Marie DiLorenzo

Committee Member

Sandra Adams

Committee Member

Lee H. Lee

Abstract

The terrible events of the September 11, 2001 World Trade Center (WTC) tragedy left many dead, injured, devastated and emotionally scarred. The effects of the tragic event were noticed even after a decade in upper-respiratory ailments resulting from the exposure of the toxic dust. WTC dust contained many toxic heavy metals including lead (Pb) and zinc (Zn) that might be responsible for upper respiratory complications. The very high concentrations of Zn (ranging from 1000 ppm to 3000 ppm ) together with high concentration of Pb (100 ppm to 500 ppm ) might create toxicity alone or in combination. Synergistic effects of heavy metals are the possibility in WTC dust which might be causing different health problems. The interaction of Pb with Zn is like a double-edge sword and the overall toxicity depends upon the ratio of their concentrations and on the type of the test tissues.

The first part of the project studied the effects of the extremely high concentration of Zn and Pb on cytotoxicity and apoptosis of MRC-5 human lung cells in vitro. Also, the experiment elucidated how different combinations of Pb and Zn at a specific ratio (1:1, 1:5, 1:10, 1:15) altered the cytotoxicity and apoptosis of MRC-5 cells. Assays were performed utilizing a 96 well plate reader and Triplex Assay (Promega) in vitro. Data showed that in unstressed condition Pb at 50 ppm and Zn at 500 ppm generated a toxicity of 289690 RFU and 21144.5 RFU respectively. Combination of these two treatments, in which Pb is 50 ppm and Zn is 500 ppm (producing a ratio of their concentration of 1:10 that mimics WTC dust Pb and Zn ratio) created a toxicity of 2117.5 RFU. This toxicity is very low as compared to individual toxicity of Pb or Zn. Similar findings were also noticed in low serum stressed condition. It was noticed that higher amount of toxicity and apoptosis were produced in stressed cell than in unstressed cell. The second part of the project tested two variables: quality of bone growth and the competitive incorporation of Pb and Ca into the cultured chick femurs. Data demonstrated that there was 5 % growth of bone at 1000 ppm Pb ( showing a reduction of 11 % growth than control). The combination treatment of Ca and Pb (constituting a total of 1000 ppm) produced a bone length of 22 % which was even higher than control and calcium treated bone. This data indicated that Ca and Pb had antagonistic interaction with each other where Ca was able to reduce the damaging effects of Pb.

Overall, this research found that the amount and concentration of Pb present in WTC dust is highly damaging to human lung cells both in stressed and unstressed condition. However, the damaging effects may not be felt by people exposed to WTC dust because the high amount of Zn is able to reduce the toxicity of Pb. Zn, contrary to the expectation, has antagonistic effect with Pb. The metal Zn is a reward in disguise to WTC people. The toxic effects of Pb when combined with Zn may not be damaging to normal people because of the protective role of zinc; however both the metal could be troublesome to infants, diseased, sick, old and low resistance people. The in vitro bone culture of chick femur also demonstrated that Pb would be damaging on bone growth and quality. Calcium might be able to mitigate the damaging effects of lead. Further research is needed to know the impact of Ca and Pb interaction in lung cells.

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