| Research Abstract |
The valuation of decrease of pesticide loadings during flowing down of two small rivers by loading budget method and of degradation rate of pesticides as organic matter. The runoff of pesticide applied to paddy fields were observed every three days during flowing down in the two rivers, the Akuta and the Amano, which were branches of the Yodo. In the Akuta the main stream and its irrigation waterway were observed together during their flowing down reaches (length : 2.5km)in 1996. The conditions of their flowing water courses which ran parallel side by side were different from one another. In the main stream which were separated into small shallow pools as fishing spots by small stones the decrease of pesticide loadings became to larger. In the water way of which three surfaces were made of concrete their decrease became smaller than in the main stream. In the lower reaches of the Amano the loadings of pesticides were decresed as following : MEP 87%, Pyroquilon 32%, Esprocarb 3%, BPMC 1
… More
% in 1997 ; Piributylcarb 7%, IEP 43%, Pretilachlor 42%, Simetryn 30%, Esprocarb 20%, Pyroquilon 19%, BPMC 17%, Diazinon 5% in 1998. However, the loadings of other five pesticides(Thiobencarb, Isoprothiolane, Oxadiazon, Dymron and Piperophos), which were detected at times as high concentration level, increased by 5-20%. The decrease of pesticide I oadings during flowing down was evaluated as the degradation of organic matter assuming that its reactin followed with first-order equation as well as self-purification coefficient. These phenomena were considered to be cased by two factors.One was the difference between the sampling time-lag at upper and lower points and the flowing down time of riverwater in the reach. Other was contributed to the adsorption of pesticides to particulates and sedimentation of their particulates to riverbed and the degradation by attached biofilm on the riverbed. The pesticides were detected in attached biofilm as following : Esprocarb 95ppb, Mefenacet 47ppb, Simetryn・IBP・Butachior l0ppb, thiobencarb 3ppb, Disulfoton O.4ppb in R.Akuta ; Esprocarb・IBP 5-10ppb in R.Amano. Less
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