Fate, degradation and dissipation of DDT in tropical environment

The dissipation of DDT was characterized by a rapid decline during the first four weeks which then gradually slowed down with time. Extractable radioactivity decreased with time while bound activity increased to 8.5 percent and 10 percent for the two field trials p,p'-DDE was the major metabolite of DDT and DDD was formed only after 120 days from date of application. The half-life of DDT including its metabolic products in soil was 235 days. Laboratory studies showed that temperature had a direct effect on the rate of volatilization of DDT. Organic volatile formation increased with increase in temperature. However, temperature had an inverse relationship with CO2 formation. Increase in temperature brought about by solar radiation caused faster degradation of DDT. DDE and DDD formation were 1.6 and 2 times faster in quartz tube which allows penetration of solar radiation compared to glass tube. Binding of DDT to soil may be promoted by microflora content through metabolic binding. The faster degration of DDT to DDE in quartz tube suggested that solar radiation plays an important role in the degradation of DDT. Volatilization was one of the major pathways for loss of DDT in soil. In water, DDT declined rapidly compared to its disssipation in soil with a half life of 31 days. Within 7 days, 30 percent of the applied 14C-DDT dissipated. Decline of DDT on wood surface was gradual with a half-life of 60 days. Microorganisms can release DDT bound to soil by as much as 80 percent. Under field conditions, 14C-DDE dissipated with a half life of 151 days which is comparable with half-life of 105 days for extracted DDT. Unchanged DDE accounted for the bulk of the residues following DDE treatment in soil. The result indicated that DDT and its metabolite DDE dissipate from Philippine soil at a rate faster than that reported from temperate countries