Effects of lake bottom mud on the movement and metabolism of14C‐phorate in a flooded soil‐plant system

Abstract

Abstract The movement and metabolism of 14C‐phorate were investigated in flooded loam soils deposited on lake mud sediments. A layer of lake mud underlying insecticide‐treated loam soil significantly increased the persistence of phorate and reduced the amounts of 14C‐phorate residues that were released from the sediments into the water. After a 2‐week incubation 62% of the applied phorate was recovered undegraded, 13% as phorate sulfoxide, but no phorate s;ulfone could be detected in the presence of lake mud. When insecticide‐treated loam soil was mixed with lake mud sediments, the metabolism of phorate was further reduced and even less radiocarbon moved into the water. Varying the amount of lake mud or of insecticide‐treated soil did not affect the insecticide distribution in the system, nor its metabolism. The evolution of 14CO2 and the release of volatile lipid‐soluble metabolites were both depressed by underlying lake mud. Studies pertaining to the rate of metabolism and movement of 14C‐phorate in a soil‐lake mud‐water‐plant system during a 2‐week incubation period, indicated a decline in the radiocarbon content of the soil‐lake mud mixture during the first 3 days of incubation, with a concomittant increase of 14C in the water. After that, the amounts of 14C‐compounds remained constant in the soil‐lake mud, decreased in the water and increased steadily in the Elodea plants, which picked up these compounds from the water. Most of the plant associated radiocarbon could not be extracted and was bound to the plant tissue, amounting finally to 81% of all the radiocarbon recovered from the Elodea plants.