Study On The Combined Toxicity Of Nano-TiO₂and Heavy Metals To Bacteria

Nano-particles have unique physical and chemical properties, but in the process of its using, it maycause health and environmental hazards. Although, in recent years, the toxicity of nano-particles toaquatic organisms have a certain understanding, but the combined toxicity mechanism is not clear,especially the combined toxic effect on bacteria.In this study, it will consider the nature of the nano particles, environmental factors, and the natureof the bacteria. Using heavy metals in water as the sample for the study, and choose E.coli as test strains,to carry out the following research:(1) Investigate the adsorption behavior of nano-TiO2on heavymetals in water. Determine the adsorption properties of nano-TiO2on the heavy metals (Cd (II), Zn (II)).(2) Determine the impact of water quality on the nano-TiO2adsorption of heavy metal ions.(3)Determine the complex toxic effects of nano-TiO2and heavy metal ions to bacteria. And clarifycomplex mechanism of toxic effects of pollution on bacteria.Studies have shown that, in the determination of adsorption kinetics of metal ions Cd (II) andZn (II), interaction between nano-TiO2and heavy metal ions (Cd (II), Zn (II)) is similar to Lagergrenpseudo-second adsorption kinetics equation. In the determination of metal ions (Cd (II), Zn (II)) of theadsorption isotherm, nano-TiO2of metal ions Cd (II) and adsorption characteristics Zn (II) is more inline with Freundlich isotherm equation. The study found that, under the conditions of this experiment,(soft water, medium hard water, and hard water) adsorption of metal ions (Cd (II), Zn (II)) on nano-TiO2as a result of the greater impact of water hardness, and nano-TiO2in hard water have more adsorptioncapacity. Along with the increase of hardness of water, calcium and magnesium ions, carbonate,bicarbonate is increased. This phenomenon will affect the combination of nano-TiO2and heavy metalions in water, because of the adsorption of nano-particles.In the study of combined toxicity of nano-TiO2and heavy metals to bacteria, with the analysis ofthe experimental results, we found that, nano-TiO2have inhibition effect on the E.coli. when thesolution concentration of nano-TiO2is between50mg/L and200mg/L, the inhibition effect ofnano-TiO2is increased. And the inhibition effect showed a downward trend. However, when its solutionconcentration reached about200mg/L, the inhibition effect to E.coli showed a rising trend. But in general, the law of the inhibition effect showed irregular change. In the study of toxicity of heavy metalto bacteria, when the solution concentration of metal ion (Cd (II), Zn (II)) is between0mg/L and0.5mg/L, the mortality rate of E.coli rose rapidly, almost tending to a straight line. And when its solutionconcentration is between0.5mg/L and5mg/L, with the solution concentration increasing, the mortalityrate of E.coli is increasing slowly. According to the studying of the heavy metal ions (Cd (II), Zn (II))single-toxic to E.coli, the fact is that Cd (II) of the LC50is2.7075mg/L, Zn (II) of the LC50is5.6521mg/L. In the study of the water quality effect on the bacterial toxicity test, we found that, withthe increase of hardness of water quality in the experiment, the toxicity of heavy metal ions (Cd (II), Zn(II)) to E.coli weakened. The reason is that when the water hardness is increased, the calcium andmagnesium ions, carbonate and bicarbonate root in the water are also increased. They formed complexions or precipitation with heavy metal ions, then reducing the toxicity.In the study of the effects of water quality on bacterial toxicity test, with the increase of waterhardness, the toxic effect of heavy metal ions (Cd (II), Zn (II)) on E.coli weakened. Complex toxicitytest of nano-TiO2and heavy metal ions (Cd (II), Zn (II)) provided that, under the conditions of thisexperiment, the LC50of the metal ions Cd (II) and nano-TiO2is1.4332mg/L, the LC50of Zn (II) andnano-TiO2is2.4029mg/L. Compared to a single heavy metal ions (Cd (II), Zn (II)), the coexistence ofheavy metals and nano-TiO2have more toxic to E.coli. And the combined toxicity show synergisticeffects. This may be due to:1) The interaction between nano-particles and bacteria. Nano-particles maybe adsorbed to the bacterial surface or go through the channel into the inside of bacteria, and then itproduces toxicity to bacteria.2) Nano-particles adsorb heavy metals, enlarge the contact area of theheavy metals and bacteria.3) Nano-particles and the residue of heavy metalsin water reacted on bacteria.And the nano-particles absorbed heavy metals. Heavy metal Attached to the nano-particle metal mayimprove the toxic effect on bacteria.