The unicellular green alga, Chlorella sorokiniana Shihira and Krauss, was cultured in vitro using an inorganic growth medium with various concentrations of the herbicide glyphosate [N-(phosphonomethyl)glycine]. Growth rates, in terms of ceil doublings per day, were determined for cells inoculated into media containing from 5.91 × 10−6 M to 591 × 10−6M glyphosate. Comparisons with a control, which supported 10.4 doublings/day, showed growth only slightly reduced at 5.91 × 10−6M and 11.8 × 10−6M, with averages of 9.7 and 9.5 doublings/day; reduced by more than half at 17.7 × 10−6M with an average of 4.4 doublings/day; and prevented at all higher concentrations. In addition to completely preventing growth at 23.7 × 10−6M and above, glyphosate seemed to cause a deterioration of the inoculum cells. Filtering the media containing 5.91 × 10−6M, 11.8 × 10−6M, and 17.7 × 10−6M through kaolinite prior to introduction of the alga reduced the inhibition previously noted at 17.7 × 10−6M and resulted in growth rates from 9.1 to 9.5 doublings/day.
