Exposure of mayfly Ephemera orientalis (Ephemeroptera) eggs to heavy metals and discovery of biomarkers

The objective of this study was to assess acute toxicity of heavy metals in eggs of mayfly Ephemera orientalis McLachlan, and to elucidate relationships between heavy metal toxicity and protein expression patterns determined using surface-enhanced laser desorption/ionization time-of-flight mass spectrometry (SELDI-TOF-MS). Acute toxicity analysis was conducted using five heavy metals (cadmium, chromium, copper, lead, and mercury), and the toxicity endpoint was established from the egg hatching rate during a 14-day exposure period. Median hatching toxicity (HC₅₀) values were determined for each heavy metal, and the most toxic heavy metal was found to be mercury (0.11mg/L), followed by copper (0.32mg/L) and lead (4.39mg/L). E. orientalis eggs were highly tolerant to cadmium and chromium (>120mg/L). Proteinchip^® array analysis using a strong anion exchange proteinchip (Q10) in conjunction with SELDI-TOF-MS was used to assess the protein expression patterns after exposure to heavy metals at the EHC₁₀ (prohibiting hatching concentration to 10% eggs), except for cadmium and chromium, which were used at concentrations of 1, 10, and 100mg/L. Three novel biomarker candidate proteins, i.e., 4269, 4283, and 4623 m/z, were identified for the detection of heavy metal toxicity in aquatic ecosystems at the level of HC₁₀ in E. orientalis eggs. SELDI-TOF MS analysis for detecting differential expression of proteins was found to be more effective than Q10 proteinchip separation in the mayfly eggs.