Assessment of the relative toxicity of Cu2+ by measuring structural changes of supercoiled DNA

A method for the measurement of the relative toxicity of Cu2+ in aquatic environments is proposed. It is based on the quantitative measurement on the shape change of the supercoiled DNA after it is contacted with different levels of Cu2+ for various time intervals. In the absence of any redox reagents, all supercoiled DNA degraded into other forms of DNA after 24 h incubation in the presence of 5.13 × 10−3, 5.08 × 10−4 and 5.35 × 10−5 mol/L Cu2+. At a lower Cu2+ concentration (10−6 mol/L), 44% of supercoiled DNA retained its original supercoiled form after 24 h, and 29% after 48 h. The concentration of RC50, i.e. concentration of pollutants at which 50% of the supercoiled DNA was relaxed compared to control samples, can be obtained from the does–response curves at different exposure time, which may provide a rapid and convenient approach to assess the relative toxicity of environmental pollutants.