The toxicity of DDE to a marine dinoflagellate

DDE, the nearly ubiquitous metabolite of DDT, has been found to be highly toxic to Exuviella baltica, a widely distributed marine dinoflagellate. Concentrations as low as 0·1 part per thousand million (10⁹; ptm) significantly inhibited growth for at least 24 h, as measured by cell numbers and growth rate. Thereafter, growth rate in 0·1 ptm-treated cultures slightly exceeded control values but cell numbers remained lower than controls for three to four additional days. Exposure to higher concentrations of DDE (1 to 10 ptm) resulted in greater inhibition, the extent and duration depending upon dose. At 10 ptm, cell numbers doubled only once in seven days compared with six times in control cultures. DDE was more toxic than DDT or polychlorinated biphenyls (PCB). Inhibition caused by DDE and PCBs in combination was approximately additive. Estimated lowest cellular concentrations of DDE in this study were two to 13 times higher than concentrations of total chlorinated hydrocarbons found in samples from natural marine phytoplankton communities.