Effects of light and the importance of living plant tissues on the fate of [14C]phorate in water and Elodea plants

Abstract

The importance of living plant tissues and light on the uptake and metabolism of [14C]phorate-derived residues from water by Elodea nuttallii plants was investigated. Plants growing for 2 weeks in water with a bottom deposit of [14C]phorate-treated soil accumulated in their tissues up to 30% of the originally soil-applied radiocarbon and 56% when the insecticide had been directly applied to the water. Most of the 14C-labeled compounds thus taken up were bound to plant tissues, which might explain the small amounts of radiocarbon released later from these plants into insecticide-free water. The uptake of insecticides from water was a function of the living plant, since dead plant tissues contained only small amounts (2.6% of that found in living plants) of 14C-labeled compounds after having been exposed for 72 h to [14C]phorate-contaminated water. Moreover, most of the [14C]phorate-derived compounds (38.4% of applied) were taken up by Elodea plants when exposed to light, while plants incubated in the dark contained only 9% of the radiocarbon originally applied to the water.Lakes and rivers are often contaminated with pesticide chemicals, after their use for soil and plant pest control.This contamination is to some extent a result of soil runoff due to heavy rainfall, causing a transport of soil particles previously contaminated with pesticide chemicals. In the case of relatively water soluble chemicals, transport of pesticides with water through soils (leaching) is also possible, in particular with sandy soils. Once water has been contaminated, plant and animal life as well as microorganisms within the water are exposed to these chemicals.Studies conducted previously in our laboratory dealt with the effects of lake bottom mud on the movement and metabolism of [14C]phorate in a soil-lake mud-water system (Walter-Echols andLichtenstein, 1977, 1978a). Phenomena related to the accumulation of the insecticide in Elodea nuttallii, a common macrophyte in North American lakes, have also been reported (Walter-Echols and Lichtenstein, 1978b) and were further investigated in this study relative to the effects of light and living plant tissues on the fate of [14C]phorate in water. MATERIALS AND METHODSChemicals.[methylene-14C]Phorate (sp act. 9.7 mCi/mmol) was obtained through the courtesy of American Cyanamid Co. The insecticide was diluted with nonradioactive phorate before its addition to soils or water.Nonradioactive phorate, phorate sulfoxide, phorate sulfone, phoratoxon sulfoxide, and phoratoxon sulfone were also obtained from the American Cyanamid Co. These chem-

Effects of light on the organophosphorus pesticides bromophos and iodofenphos and their main degradation products examined in rainwater and on soil surface in a long-term study

“…It may occur in water and air as well as on target organisms and on soil surface. Useful data on the photolysis of pesticides in water (Burkhard et al, 1975;Hautala, 1978; Koshy et al, 1983;Nilles andZabik, 1974, 1975; Walter-Echols and Lichtenstein, 1983) are available, but published information on photochemical degradation on soil surface is relatively scarce (Burkhard and Guth, 1979; Liang and Lichtenstein, 1976; Nilles andZabik, 1974, 1975;Smith et al, 1978).…”