Degradation of methyl and ethyl mercury into inorganic mercury by various phagocytic cells

In connection with the dealkylation of methyl mercury (MeHg) and ethyl Hg (EtHg) with reactive oxygen-producing systems, we examined the ability of phagocytic cells to degrade MeHg or EtHg into inorganic mercury in vitro by collecting them from blood or peritoneal cavity of several species of animal. EtHg was readily degraded by human polymorphonuclear leukocytes (PMN), rat PMN, guinea-pig PMN, rabbit PMN, guinea-pig macrophages (M phi), human monocytes and guinea-pig eosinophils. In contrast, rat hepatocytes and the M phi hybridoma clone 39 cells were weaker in their degrading ability. Degradation of MeHg by these cells was always much weaker than EtHg, under identical conditions; however, by increasing the cell numbers, MeHg was appreciably degraded by human PMN, rat PMN and rabbit PMN. The reactive oxygen species mainly responsible for alkyl Hg degradation seemed to be hydroxyl radicals produced by M phi, and hypochlorous acid produced by PMN, monocytes and eosinophils. It was also suggested that the degradation of alkyl Hg by these cells might be an intraphagosomal event.