The Impact of Pesticides - Academy Publish

VARIATION OF PESTICIDES IN RIVER WATERDaily VariationRivers with cultivated areas in their basins are affected directly by these appliedpesticides in the areas. Therefore, these rivers have been used to evaluate thepesticide runoff events from the cultivated areas. The pesticide concentrations in thewaters from these rivers varied markedly during short periods. Hourly and bihourlyvariations in 11 pesticide concentrations in river waters after aerial applicationsduring August 7 to August 12 were reported (Tanabe and Kawata, 2009). Thetargets were mainly applied aerially to paddy fields in the contributory area duringthe investigated period. The pesticides were detected at high concentrations aftertheir applications. Differences in the times between the applications and highconcentrations depended on the distances of the applied area and the sampling siteas well as their properties and applied amounts (Tanabe and Kawata, 2009).Figure 2 presents the relative concentration ratios of four kinds of concentrations ofthe eight pesticides out of the 11 compounds for the daily representative meanvalues from August 8 to 11. Buprofezin, fenitrothion and fenobucarb areinsecticides; flutolanil, isoprothiolane, mepronil, pencycuron and phthalide arefungicides. The pesticide concentrations at 10 a.m. and the mean values at 10 a.m.and 4 p.m. were within 70–150 % of the daily mean concentrations, except for thevalues (less than 70%) of flutolanil, mepronil and phthalide on August 8. Data ofthat day showed increases of pesticide concentrations during 6 to 10 p.m. Theconcentrations at 10 a.m. for flutolanil on August 10-11 and mepronil on August 11were greater than 150% of the corresponding daily means, because theconcentrations increased at around 10 a.m. In these cases, the pesticide applicationsduring the day or the previous day caused significant variations in theirconcentrations in the river waters. However the mean values at 10 a.m., 2 p.m. and 6p.m. were within 70–150% of the daily mean concentrations. Therefore, theconcentration at 10:00 a.m. is regard as the representative daily value in many casesin the river. However, the concentration might be different from the daily meanvalue during the day or on the day following the pesticide application. Therefore,the mean concentrations at 10 a.m., 2 p.m. and 6 p.m. of a day were recommendedas the best representative value of the day in this case (Tanabe and Kawata, 2009).Long Term VariationIt is difficult to evaluate the appropriate variations and the maximum concentrationsin river waters by daily or weekly samplings immediately after the applications.However, long- term variations of pesticide concentrations in river waters werecommonly evaluated based on weekly or biweekly samplings. The concentrationlevels of some pesticides in river waters are presented in Table 2. The concentrationlevel of a pesticide in a river was affected mainly by the amount of a pesticideapplied in the basin, the distance from paddy fields, and the flow rate of the riverwater.Typical weekly variations of pesticide concentrations in the Shin River, NiigataPrefecture, are depicted in Fig. 3. The maximum concentrations of herbicidesAcademyPublish.org - The Impact of Pesticides207