Effects of Soil Applications of 10 Chlorinated Hydrocarbon Insecticides on Soil Microorganisms and the Growth of Stringless Black Valentine Beans

Heptachlor, chlordane, methoxychlor, lindane, aldrin, toxaphene, dieldrin, TDE, DDT, and BHC were applied to Arredondo fine sand at rates of 12.5, 50, and 100 ppm. of the active ingredient. The soil was placed in 2-gallon pots and maintained in a greenhouse throughout the study. The first crop of Stringless Black Valentine beans, planted 2 weeks after treatment, showed that BHC decreased germination; all other insecticides increased germination or had no effect. Root and top weights were decreased by chlordane, lindane, aldrin, dieldrin, TDE, DDT and BHC. Only top weights were reduced by methoxychlor. Heptachlor and toxaphene had no effect on growth. Germination and root growth of a second crop of beans, seeded 11 months after application of the insecticides, were not affected; top growth was significantly reduced by lindane, aldrin, TDE, DDT, and BHC. Microbial data, obtained 1 month after application of the insecticides, indicated that they had no effect on the numbers of bacteria in the soil. Dieldrin increased the numbers of fungi; all others had no effect. Carbon dioxide evolution was increased by toxaphene, dieldrin, TDE, DDT, and BHC; the others had no effect. Nitrate production was decreased by heptachlor, lindane, and BHC; increased by toxaphene, TDE, and DDT; and unchanged by the others. Sixteen months after application of the insecticides no significant changes occurred in numbers of fungi and bacteria or carbon dioxide evolution. Nitrate production was reduced by DDT and BHC. Based upon the measurements made in this study, the growth of Stringless Black Valentine beans was influenced more than the microorganisms by the presence of insecticides in the soil. Until more specific information on microbial responses to these materials has been obtained, it appears that toxicity of higher plants will be the earliest warning of phytotoxic amounts of chlorinated hydrocarbon insecticides in the soil.