Saturday, 15 July 2006

Adsorption of Carbofuran in Wet Zone Soils of Sri Lanka.

Janitha A. Liyanage1, Ransilu C. Watawala1, Ananda P. Mallawatantri1, and Rai Kookana2. (1) Dept of Chemistry, Univ of Kelaniya, Kelaniya, Sri Lanka, (2) CSIRO Land and Water, PMB 2, Glen Osmond, SA 5064, Australia

Wet zone of Sri Lanka has a high potential of agriculture and also consists with a large number of water catchments. Pesticides application in this zone is very high and it would badly affect the ground and surface water resources as the fate of these pesticides are still known in the soils of Sri Lanka. Therefore sorption behavior of pesticides in soils is highly necessary for better understanding and good environmental management. The pesticide soil sorption coefficient (Kd) for all types of soil series in the Wet zone of Sri Lanka was calculated for carbofuran as carbofuran usage is very high in this area. Previously classified 28 types of soil series were identified, samples of the surface soil (0 - 15 cm) were collected, air-dried in the laboratory, ground and passed through a 2mm sieve prier to use. The soil pH and the electrical conductivity were measured for all soils. 5g of each soil was mixed with 1ppm pesticide solution and shaken in the room temperature for 16 hours. The supernent was analysed using HPLC 18 C Apollo column and Kd values were calculated for each soil series. Kd for carbofuran was highest in Wagura soil which has the highest soil organic carbon (SOC) content of 8.5 L/kg soil and the Kd was lowest for the Pugoda soil series which has the lowest SOC content of 0.2 L/kg soil. Kd values vary from 0.02 to 3.7 (mean 0.74; median 0.58) and Koc ranged from 0.7 to 70 (mean 32.59; median 31.75) in the 28 soils. The variation in Kd values indicates the different sorption capacities of the soils for carbofuran and the vast range of Koc indicates the differences in the SOC content in different Wet zone soil series in Sri Lanka. Wagura soil has the highest acidic conditions having the soil pH of 3 and an unusually high EC value of 19.9 which is far different from other soils in the Wet zone. Carbofuran is non-ionic in nature and the pH is not expected to be affected the sorption directly but may have indirect effects by its influences on the nature of organic carbon. The multiple regressions of the Kd for carbofuran against % SOC, % Clay and pH were not very significant.

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