Sublethal effects of chlorpyrifos and cypermethrin on Octolasion cyaneum (Annelida: Oligochaeta, Lumbricidae).

SALVIO C., LÓPEZ A.N. , MANETTI P.L. , CLEMENTE N.L. , MENONE M.L.

Montevideo

Workshop; 3rd Latin American Pesticide Residue Workshop, Food and Environment; 2011

Pharmacognosy and Natural Products , Faculty of Chemistry- Uruguay

Insecticides chlorpyrifos and cypermethrin are widely used in agriculture and therefore, they can accumulate in the soil becoming an ecotoxicological risk to invertebrates such as earthworms that eat large amounts of soil. Earthworms are key organisms in the soil ecosystem for the impact they produce on soil structure and for its action on nutrients decomposition and mineralization. The aim of this work was evaluated the toxic effect of chlorpyrifos and cypermethrin insecticides on earthworm Octolasion cyaneum (Oligochaeta, Lumbricidae).The experimental unit was a plastic container of 1000 cc which was placed 750 g of soil moist (29% clay, 21% fine silt, 16% coarse silt, 35 % sand and 5.98 % organic matter, ph=6) mixed with pesticide doses and 10 adult individuals with a weight of 500-700 mg. One assay were made with chlorpyrifos and doses were 0, 120, 240, 480, 960 and 1440 g ha-1 (48% active ingredient (a.i.), emulsifiable concentrate) and other assay were made with cypermethrin at 0, 12.5, 25, 50, 75 and 100 g ha-1 (25% a.i. emulsifiable concentrate). The containers were placed in a chamber at 20+2¨¬C and 14L:10O and the observations were made at 7, 14, 21 and 28 days after application (DAA). Biomass in wet weight, individual dead and/or alive, cocoon and juveniles production was determined. The assay was extended to 60 DAA to observe cocoon and juveniles production. In both assays, the experimental design was completely randomized with 4 replicates. Data were analyzed using ANOVA and when significant treatment differences were detected, means were separated by least significant difference (¥á=0.05). With chlorpyrifos 235 individuals were recorded live and 5 dead. According to biomass, differences were detected at 7, 14 and 28 DAA (p<0.05). Both at 7 and 28 DAA, the biomass was higher in the control compared to other treatments (p = 0.0001 and p = 0.04, respectively). The cocoon production increased in control with respect to the other treatment at 60 DAA. Furthermore, increased juveniles production in the control and 480 g ha-1 for chlorpyrifos (p<0.05). On the other hand, there were 237 individuals alive and 3 dead with cypermethrin. With regard to biomass differences were obtained at 14 and 28 DAA, with an increase in the control compared with other treatments (p <0.05). At 60 DAA, cocoon and juveniles production were increased with the lower dose (12.5 g ha-1) and decreased with higher doses, 75 and 100 g ha-1 (p <0.05). It is concluded that chlorpyrifos and cypermethrin to the doses used in the field, 480 g and 50 g ai ha-1 respectively, did not affect survival but caused sublethal effects on O. cyaneum.