Effects and persistence of baygon (Propoxur) and temik (Aldicarb) insecticides in soil

Abstract

The effects of two carbamate insecticides, Baygon and Temik, on microbial processes in soil were investigated. Total plate counts revealed that Baygon and Temik at field rate applications (5 ppm) did not greatly influence the microbial populations in the soil. At a concentration of 500 ppm the fungal and actinomycete populations showed a marked increase in response to Temik and Baygon. Nitrification was severely inhibited by the granular (formulated) Baygon and Temik at 500 ppm, but was much less inhibited with the technical grade (technical) insecticides. The discrepancy appeared due to metabolism of the corn cob grits carrier, the resulting immobilization of nitrogen causing an apparent ‘inhibition’ of nitrification. At the approximate field rate applications of 5 ppm, only slight inhibition was observed with formulated Baygon or Temik. An accumulation of nitrite was noted, especially with technical Baygon at 500 ppm. Populations of the autotrophic nitrifying bacteria were depressed for 2–3 weeks by application of either Baygon or Temik to the soil at 500 ppm. Pure culture studies on Nitrobacter agilis and Nitrosomonas europaea indicated that Baygon and Temik were toxic to both organisms, but particularly the latter. The toxicity to Nitrosomonas was more severe in pure cultures than in soil. Oxygen uptake studies showed that formulated Baygon (but not Temik) added to soil at 500 ppm resulted in high respiratory activity, mostly due to metabolism of the carrier. The technical insecticides had little effect on respiration as measured by carbon dioxide evolution, although there were indications that Temik was being metabolized during the interval from 16 to 30 days. Baygon was found to be quite resistant to degradation in the test soil. Temik residues decreased by about 50% during the 30-days test period.