Abstract
Laguna Lake is the largest inland water resource in the Philippines and an important source of fisheries in the area. The Pagsanjan-Lumban catchment is the main freshwater input of the lake but contaminants resulting from agricultural activities within the catchment may impact fisheries. Laboratory-based acute toxicity data was generated on selected non-target aquatic species native to Laguna Lake for pesticides used in the catchment. Freshwater shrimp, Macrobrachium lar, were found to be the most sensitive species for the pesticides used in the areas surrounding the catchment compared to Tilapia sp. embryos, newly hatched Tilapia and 22mm Tilapia fingerling. Of the pesticides used in the catchment, the pyrethroids (lambda cyhalothrin, deltamethrin and cypermethrin) were found to be highly toxic under laboratory conditions to freshwater shrimp and Tilapia fingerling. Malformations, such as spinal deformities and abnormal yolk sac distribution, were observed in the fish embryos at pesticide concentrations below LC50 values. Currently there are no water quality guidelines available in the Philippines for pesticides. Such toxicity data on local species is highly beneficial in developing site-specific water quality guidelines. An acute hazard assessment was conducted for risk ranking of pesticides used in the Philippines by comparing the 48h LC50 values of selected pesticides to M. lar and actual concentrations of the pesticides detected in selected sampling areas within the Pagsanjan-Lumban catchment. The maximum measured concentration of profenofos (15.4μg/L) and pyrethroids (3–6μg/L) in the field samples collected in the Pagsanjan-Lumban catchment were above the 48h LC50 values. These compounds posed a high acute hazard (HQ>1) to freshwater shrimp in the Pagsanjan-Lumban catchment. Poor management practices in pesticide use could result in decline of rice-fish cultures and other economical invertebrates in some catchments in the Philippines.
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