Behavior of Pesticides in Soil and Other Environment

Abstract

In Saitama prefecture, the investigations and experiments for pesticide residue were started in 1971. Since the residue of organochlorine insecticides on crop and soil was one of problem awaiting solution at that time, the investigation into the actual condition of the residue of BHC, DDT, aldrin and dieldrin on the fields was performed at the first time. The residue amounts of all of them on soil were higher level in 1971. But, after 1 year, they decreased to about 1/2. BHC and DDT decreased with the lapse of year after 1972, but, aldrin and dieldrin were not decreased and about 0.1ppm of concentration was kept up on soil. Then, the effects of promoting decomposition on soil and suppressing absorption to crops to aldrin and dieldrin were experimented with using soil conditioner. In this experiment, 5 kinds soil conditioneres, fused magnesium phosphate, calcium carbonate, calcium cyanamide, magnesium nitrohumate and compost, were used. By application of fused magnesium phosphate and calcium cyanamide to soil, the pH of soil was rised from acidity to about neutrality, and absorption of aldrin and dieldrin to crops were increased, further, the oxidation from aldrin to dieldrin was promoted. The application of magnesium nitrohumate and compost suppressed absorption of aldrin and dieldrin by crops. The residue amounts of aldrin and dieldrin on soil were decreased by the application of fused magnesium phosphate or calcium cyanamide with compost. And, same effect was recognized in the application of magnesium nitrohumate. Since about 1975, many problems on herbicides were brought with rapid increase of used amount of herbicides. Then, the behavior of herbicides was investigated in paddy fields. In water for irrigation or drain, the detectable times of chloronitrofen, benthiocarb, molinate and simetryne were in conformity with used time in paddy fields. When, the residue on soil was experimented with pot, the residue amounts of benthiocarb and simetryne under watering condition were more little than under flooding condition. Then, the leaching tests of several herbicides were performed with lysimeter. In this experiments, it became clear that the amounts of herbicides moving to a lower soil layer and leached out increased with the increase in water solubility of the herbicide. In 1976, the problems on paraquat was brought at the first time. In connection with this, the residue of several herbicides on soil in tea fields in which several herbicides were used twice per year among seven years was investigated. It became clear that the residues of paraquat and diquat on soil were not decrease after stopped application of herbicides. Since accumulation of paraquat to soil was anxious, the influence of paraquat to the growth of some crops, turnip, carrot and so on, was experimented with used two type soils, alluival soil and volcanic ash soil, to which paraquat was added with high concentration. The influence of paraquat was more clearly in volcanic ash soil for weak soil adsorption of paraquat. On the crops in volcanic ash soil over 100ppm soil concentration of paraquat, chlorosis was appeared and the yield was decreased clearly. It became clearly by the investigation into the actual condition that the residues of paraquat in fields were related with used amount in fields.