Degradation of parathion in culture by microorganisms found in cranberry bogs.

Oxygen concentration and different carbon sources drastically altered parathion degradation in culture media inoculated with microorganisms from Wisconsin cranberry (Vaccinium macrocarpon Ait.) growing soils. These microorganisms also grew in basal salts media utilizing parathion as the sole carbon source. 14CO2 was produced only from [phenyl-14C]parathion, whereas [ethyl-14C]parathion-derived radiocarbon remained in the stale media of the soil-free cultures. Addition of 0.05% glucose to basal salts medium inhibited [phenyl-14C]parathion degradation, whereas the addition of 0.05% yeast extract to basal salts medium also inhibited microbiological degradation of the insecticide to 14CO2, but to a lesser extent. Aminoparathion and aminoparaoxon were formed only in basal salts medium with 0.05% yeast extract. Aerobic cultures produced more 14CO2 and less aminoparathion from [phenyl-14C]parathion than did anaerobic cultures. Aminoparathion was more abundant in cultures with inocula obtained from the 18- to 23-cm soil layer than with culture inocula obtained from the 0- to 5-cm soil layer under both aerobic and anaerobic conditions.

Degradation of [14C]photodieldrin by Trichoderma viride as affected by other insecticides.

Various soil fungi were tested for their capacity to degrade the insecticide [14C]photodieldrin. Of nine species investigated, Trichoderma viride was the only one which degraded the insecticide to an appreciable extent into water-soluble, non-insecticidal compounds within 4-5 weeks. These products amounted to 32-41% of the radiocarbon applied to the culture media. The degradation was a function of live mycelia, which metabolized the insecticide and excreted water-soluble compounds into the culture media. Since soils usually contain a mixture of pesticide residues, the effects of several chlorinated hydrocarbon insecticides on the capacity of the fungus to degrade [14C]photodieldrin were studied. Thus, in fungal cultures treated with compounds structurally similar to photodieldrin, such as aldrin and dieldrin, only 4-17% of the applied radiocarbon was water-soluble and more photodieldrin remained. In controls, however, 35% of the applied radiocarbon was in the form of water-soluble products and less photodieldrin remained. The degradation of [14C]photodieldrin by T. viride, with time, was associated with a continuous decline of hexane-soluble radiocarbon and a steady increase of water-soluble metabolites, which appeared in the fungal media. The amount of hexane-soluble radiocarbon in mycelia was directly related to the fungal mass.

Binding of (14C) parathion in soil: a reassessment of pesticide persistence.

A steady decrease of extractable [14C] parathion residues in soils over a 1-month incubation period was accompanied by an increase of unextractable, bound 14C-labeled residues, resulting finally in total recoveries of extracted plus bound residues of 80 to 87 percent of the applied radiocarbon. Soils containing bound residues were nontoxic to fruit flies. Binding of 14C-labeled residues was related to the activity of soil microorganisms; soil sterilization resulted in a reduction of binding by 58 to 84 percent. Under flooded (anaerobic) conditions, the binding of compounds labeled with 14C doubled, and parathion was reduced to aminoparathion. Reinoculation of sterilized flooded soil fully reinstated the binding capacity. [14C] Aminoparathion was preferentially bound to soil, since its binding within 2 hours was 30 times greater than that of [14C] parathion. Because of the existence of formerly "unseen," unextractable residues, the concept of "persistent" and "nonpersistent" pesticide residues might have to be reconsidered.

Environmental factors affecting the degradation of Dyfonate by soil fungi.

The ability of selected fungi to degrade the soil insecticide Dyfonate (O-ethyl S-phenyl ethylphosphonodithioate) into water-soluble, noninsecticidal metabolites was found to be dependent on the supply of nutrients, incubation time, temperature, pH, as well as other factors. With yeast extract as the carbon source (5 g/liter) and ammonium nitrate (1 g/liter) as the nitrogen source, both Rhizopus arrhizus and Penicillium notatum degraded the insecticide to a larger extent than with any other combination of nutrients used. With glucose as the carbon source, concentrations of ammonium nitrate above 5 g/liter inhibited the degradation of Dyfonate by R. arrhizus. Time-course studies on the metabolism of the insecticide indicated that Dyfonate was first absorbed by the fungal mycelium, where it was metabolized followed by the release of water-soluble, noninsecticidal, breakdown products into the culture media. The degradation appeared to involve the breakdown of Dyfonate into ethyl acetate soluble metabolites, such as ethylethoxyphosphonothioic acid, ethylethoxyphosphonic acid, methyl phenyl sulfoxide, and methyl phenyl sulfone. These compounds were then further degraded into water-soluble products. The optimum conditions for the degradation of the insecticide by R. arrhizus were observed at pH 6.0 to 7.0 and at 15-25 degrees C. Aged fungal mycelia were as active as mycelia in the logarithmic growth phase.

Synergism of insecticides by herbicides: effect of environmental factors.

The synergism of parathion and p,p'-DDT [1,1,1-trichloro-2,2-bis-(p-chlorophenyl)ethane] by atrazine was investigated as a function of soil type, age of pesticide soil residues, and the presence of soils in quiet or turbulent water. Compared to previous tests in which the pesticides were applied on glass surfaces, a significant reduction of the toxicity of the insecticides to fruit flies and of the synergistic effects of atrazine was observed with soils, particularly a silt loam. The effects of atrazine as a synergist in soil declined rapidly within 4 days. The toxicity of parathion in water and its synergism by atrazine were significantly reduced by soil sediments, depending on the type and amount of soil present. Soils were highly effective in turbulent water: in water containing the relatively high parathion concentration of 0.3 part per million, 93 percent of the mosquito larvae present died within 24 hours, yet this solution was rendered nontoxic by being mixed with 5 grams of a loam soil. With atrazine present in the latter system, however, 38 percent of the mosquito larvae died. Thus, insecticides can be more or less toxic, depending on their concentrations, the presence of synergists, and the environmenetal conditions.