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Uptake and Metabolism of 2,2-bis-(p-Chlorophenyl-1,1,1-trichloroethane (DDT) by Marine Phytoplankton and Its Effects on Growth and Chloroplast Electron Transport ¹

^a Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California 92037

The effects of DDT (2,2-bis-(p-chlorophenyl)-1, 1, 1-trichloroethane) on the growth of seven marine phytoplankters, representative of five algal divisions, were studied. At a concentration of 80 parts per billion (0.23 µM) DDT, growth of Dunaliella tertiolecta was unaffected, and there was slight, if any, influence on the development of Cyclotella nana, Thalassiosira fluviatilis, Amphidinium carteri, Coccolithus huxleyi, and Porphyridium sp. Skeletonema costatum exhibited a 9 day lag before cell division commenced, the rate of growth subsequently being the same as in the control (no DDT). A further inoculation of this culture of S. costatum into 80 parts per billion DDT gave another 9-day lag before initiation of normal growth.

The ability of marine phytoplankton to metabolize DDT varied. DDE (2,2-bis-(p-chlorophenyl)-1, 1-dichloroethylene) was the only significant hexane-soluble metabolite detected. It occurred in cells of S. costatum, C. nana, T. fluviatilis and D. tertiolecta. Maximum degree of conversion was 7.5% and was based on the total DDT found in the cell-water system of 9-day D. tertiolecta cultures. The total amount of DDT recovered from cultures in 2- to 3-week experiments ranged from 63.5% for T. fluviatilis to 90.7% for S. costatum. The amount of DDT found associated with the cells, collected by centrifugation, in the cell-water system ranged from 70.8 to 99.5%.

Chloroplast particles were isolated from a "resistant" species, D. tertiolecta. Noncyclic electron flow, as measured by ferricyanide reduction, was inhibited by DDT and DDE, and could explain growth inhibition in other phytoplankters. Fifty percent inhibition occurred at 20 µM DDT. Sensitivity of phytoplankton to toxic hydrophobic chlorinated hydrocarbons may be dependent upon penetration of the molecules to active sites within membranes.

¹ This research was supported by the Institute of Marine Resources of the University of California, San Diego.