Study On The Combined Toxic Effects Of Nano Titanium Dioxide And Lead Acetate On Escherichia Coli

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:â‘´Investigating 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;â‘·Investigating 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.