Oxidation process of lead sulfide nanoparticle in the atmosphere or natural water and influence on toxicity toward Chlorella vulgaris.

Lead sulfide nanoparticle (nano-PbS) released into environment can cause hazards to human or ecosystem. Nano-PbS potentially undergoes oxidation in the environment, but oxidation mechanism is not understood yet. Herein, oxidation kinetics and products of nano-PbS by ozone (O), hydrogen peroxide (HO) and hydroxyl radical (HO·) in the atmosphere or natural water were investigated. Results show that oxidation process of nano-PbS can be divided into three stages, producing sulfate, ions and oxides of lead in sequence. O or HO·leads to faster release of ionic lead from nano-PbS in the initial stage than HO, but causes significant decrease of ionic lead by transforming divalent lead to tetravalent lead oxides in the second or third stage. Toxicity determined taking Chlorella Vulgaris as an example follows an order of PbO < PbO < nano-PbS < PbO < PbSO. Toxicity of lead particles is mainly determined by sizes influencing cellular uptake and solubility product constant (K) related with dissolution of lead in cells. The results indicate that the toxicity of nano-PbS increases in an initial oxidation stage and decreases in further oxidation stages. This study provides new insights into environmental behavior of nano-PbS and mechanism understandings for assessing ecological risks of nano-PbS.