The Effect of 2,4-D and Atrazine on the Growth Rate of a Mixed Algae Culture

The application of herbicides to both aquatic and terrestrial environments is increasing at a very rapid rate. In the Weed Control Handbook (Blackwell 1960), 71 herbicides are named. Yet today, approximately 3/4 of all weed control is accomplished by 2,4-D, simazine (similar in action to atrazine) and diuron. This application is even more pronounced in predominately agricultural areas such as eastern South Dakota. Both 2,4-D and atrazine are used extensively for weed control in agriculture, and it is not being presumptuous to assume that they are finding their way into our lakes and streams. It is the purpose of this paper to determine what the effects of these two herbicides are on the growth rate of a mixed culture of algae which is composed predominately of one blue-green species. By determining the effects in the laboratory, it may be possible to relate this information to natural environmental conditions. A mixed culture of algae was selected for this research in order to approximate natural conditions as much as possible. The two herbicides were chosen because they are used extensively, and at least one of them (2, 4-D) is becoming a common pollutant. Workers, such as Janke and.Weij, have known since the early 1930\u27s that algae produce such auxin and auxin-like compounds as NAA,IAA and IBA (1). It has also been pointed out that these · substances can affect growth in many ways when applied exogenously. However, none of the studies have involved the common blue-greens found in this area, nor has the compound 2, 4-D been identified as one of the auxins being produced by the algae. No less than 17 metabolic inhibitors and 19 antibiotics which inhibit algae are known, yet only a very few are known to affect some of the forms of algae present in this research, and none of these involve 2,4-D or atrazine