Determination of Toxicity Level of Laguna Lake Waters using Hydra sp. and Lactuca sativa L. (lettuce)

Abstract

Laguna Lake, the largest freshwater body in the Philippines, serves as a multipurpose resource. This important water source has been greatly affected by development pressures like rapid population growth, industrialization, and urbanization. The study aimed to determine the toxicity risk of the waters using selected bioindicators such as, Hydra sp. and lettuce (Lactuca saliva). Water samples were collected from Northwest bay (NWB) and East Bay (EB) of the lake. A 96h (4 days) Hydra assay was done to initially assess the median effective dose (ED50) and lethal dose (LDS0) while in the 120h (5 days) lettuce assay, the inhibitory concentration (IC50) was determined. No Hydra sp. ED50 and LD50 and lettuce IC50 values were taken from the water samples. Only the positive control for Hydra sp. (Cr6+) and L. saliva (Zn2+) showed significant results (95% level). The values for Hydra sp. ED50 and LD50 for the 1st trial were 0.84 mg/L Cr6+ and 28 mg/L Cr6+ respectively, whereas the 2nd trial yielded 2.8 mg/L Cr6+ and 14 mg/L Cr6+ respectively. The IC50 values for the lettuce assay were <7.1 mg/L Zn2+ on both trials. Results showed the water samples had no significant toxicity on the two test organisms. The lake does not pose a toxic risk at present.