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Study on the Combined Toxic Effects of Nano Titanium Dioxide and Lead Acetate on Escherichia coli

Author: FanChuanGang
Tutor: ZhouYiKai
School: Huazhong University of Science and Technology
Course: Occupational and Environmental Health
Keywords: Titanium Dioxide Lead Toxicity Combined effects Escherichia coli Oxidative Stress
CLC: TB383.1
Type: Master's thesis
Year: 2011
Downloads: 47
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Abstract


Background: With the development of nanotechnology, nano-TiO2 is applied in more and more fields, such as cosmetics, painting, and wastewater treatment. At the same time, masses of production and abandonment of nano-TiO2 have followed up: not only the natural processes of nano TiO2 is released into environment, but the manufactured nano-TiO2 used in painting for about 10 years can also be released into environment, causing pollution. Safety and pollution of Nano TiO2 have attracted more and more attentions. As we know, lead is one of the most important heavy metal pollutants and the American Conference of Governmental Industrial Hygienists （ACGIH） categorizes lead as one of animal carcinogenic materials. State Environmental Protection Administration of China （SEPA） has reported that: the dose of lead in two thirds of China’s coastal waters is excessive and about one fifth of the land in our country is contaminated by lead. During the process of wastewater treatments, waste abandonment and others, nano-TiO2 contacts with lead compounds and may influence each other. The interaction and combined effects of them to surrounding environment livings have not been known until now.Objective:⑴Investigating the interaction between nano-TiO2 and PbAc （lead acetate）;⑵Investigating the relationship between OD600 （600nm absorbance value） and E. coli concentrations;⑶Investigating the combined effects of nano-TiO2 and PbAc on growth of E. coli;⑷Investigating the combined effects of nano-TiO2 and PbAc on E. coli antioxidant enzymes, proteins, and DNA.Methods: By scanning electron microscopy and dynamic light scattering technique TiO2 nano particle size and particle surface properties are characterized; by flame atomic absorption method, nano TiO2 adsorptions of PbAc are investigated; by plate count and spectrophotometer method, the mathematical relationship between the concentration of E. coli and OD600 is studied. The combined toxic effects of nano-TiO2 and PbAc on E. coli growth, antioxidant enzymes, proteins, genetic material DNA are explored in 4×4 full factorial design, and their interactions are identified using response surface analysis.Results: SEM results show that compared with single nano TiO2, adding PbAc induces the aggregation and surface property changes of TiO2 nanoparticles. DLS results show that nano-TiO2 particle size is significantly increased with decreased concentration of nano-TiO2 or combined with an increasing dose of PbAc （P <0.05）. Flame atomic absorption results show that nano-TiO2 adsorbs Pb2+ iron, and its adsorption rates are significantly increased with increasing concentration of nano-TiO2（P <0.05）. The relationship between OD600 and E. coli concentration is not linear, but curved; a mathematical model is fitted and checked. The results prove that the model has a high accuracy and compared with the plate counted numbers its error is within±3%. Growth curves of E.coli showed that nano-TiO2 and PbAc inhibit its growth, and the combined mixtures exhibit severer inhibitions. Full factorial analysis showed that nano-TiO2 and PbAc both have adverse effects on E. coli growth, antioxidant enzymes, protein carbonyl levels, DNA oxidation levels; and in their mixtures, compared with the corresponding effect of single substance, the combined toxicity is not significant at low doses of nano TiO2 or PbAc. Response surface analysis showed that there is a significant interaction between nano TiO2 and PbAc, it is identified as antagonism.Conclusion: Nano TiO2 and PbAc significantly influence each other: nano TiO2 adsorbs PbAc, reducing its effective concentrations; PbAc induces the aggregation and surface property changes of nano TiO2. Nano-TiO2 and PbAc have toxic effects on E. coli growth, antioxidant enzymes, proteins, DNA, while the combined effects are less than the sum of the single toxic effects, the interaction is antagonistic. It is the first time to investigate the mathematical relationship between OD600 and E. coli concentrations and fit a mathematical model based on it.

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