Suppressive effect of soil application of carbonaceous adsorbents on dieldrin uptake by cucumber fruits

Abstract

The use of aldrin and dieldrin as pesticides was prohibited in 1975 in Japan. However, some of the soils still remain contaminated with dieldrin, because aldrin is easily oxidized to dieldrin and dieldrin is extremely stable in soil. In recent years, dieldrin at concentrations exceeding the limit set by the Food Sanitation Law of Japan (dieldrin < 0.02 mg kg–1 fresh weight) has been detected in cucumber fruits produced in some areas of Japan. We examined the effect of the soil application of selected adsorbents on reducing dieldrin concentrations in cucumber fruits in three steps of pot experiments. Among the three types of biochar made from wood chip, rice husk, and bamboo, wood chip charcoal was found to be the most effective (pot experiment 1). The effect of wood chip charcoal was enhanced by high-temperature burning and crushing (pot experiment 2). However, the effect of activated carbon was superior to that of optimized (high-temperature-treated and crushed) wood chip charcoal (pot experiment 3). Therefore, activated carbon was selected as the most effective adsorbent. The effect of activated carbon to reduce dieldrin concentrations in cucumber fruits was confirmed in a field experiment, and the effect continued to a certain extent for at least four years after the application. We calculated the cost of activated carbon necessary to maintain a sufficient suppressive effect in the field, and this cost would appear to be acceptable to cucumber farmers. Consequently, application of activated carbon to dieldrin-contaminated soils can be considered a promising practical technique for reducing dieldrin concentrations in cucumber fruits.