Heating at 100 °C for 5-10 min is a common method for treating wastewater containing recombinant DNA in many bio-laboratories in China. In this experiment, plasmid pET-28b was used to investigate decay efficiency of waste recombinant DNA during thermo-treatment. The results showed that the decay half-life of the plasmid was 2.7-4.0 min during the thermo-treatment, and even heating for 30 min the plasmids still retained some transforming activity. Low pH promoted the decay of recombinant DNA, but NaCl, bovine serum albumin and EDTA, which existed in the most wastewater from bio-laboratories, protected DNA from degradation. Thus, the decay half-life of plasmid DNA may be longer than 2.7-4.0 min practically. These results suggest that the effectiveness of heating at 100 °C for treating waste recombinant DNA is low and a gene pollution risk remains when those thermo-treated recombinant DNAs are discharged into the environment. Therefore other simple and effective methods should be developed. Heating at 100 °C for 5-10 min to treat waste recombinant DNA has potential eco-risk.

This study aims to investigate the influence of the coexistence of halogen ions (bromide/iodide) and biological source matters on the speciation and yield of trihalomethanes (THMs), haloacetic acids (HAAs), and N-nitrosodimethylamine (NDMA) during the ozonation and subsequent chlorination of water. The results show that the concentrations of brominated THMs and iodinated THMs increased with increasing bromide and iodide concentration. These results may be attributed to the higher reactivity of hypobromous acid and hypoiodous acid generated from the ozonation and subsequent chlorination in the presence of bromide or iodide ions. The presence of bromide increased the species of brominated HAAs. There was a shift from chlorinated HAAs to brominated HAAs after increasing the concentration of bromide. The effect of iodide on HAA formation was more complex than bromide. For most samples, the concentration of total HAAs (T-HAAs) increased to the maximum and then decreased with increasing iodide concentration. The components of the organic precursors also significantly influenced the formation of brominated and iodinated disinfection by-products (Br-DBPs and I-DBPs). Humic acids produced more CHBr₃(596.60 μg/L) than other organic materials. Microcystis aeruginosa cells produced the most tribromoacetic acid (TBAA, 84.16 μg/L). Furthermore, the yield of NDMA decreased with increasing bromide concentration, indicating that the formation of NDMA was inhibited by the high concentration of bromide.