Abstract

Deformities in the mouthparts of Chironomidae larvae, particularly of the teeth on the mentum, have been proposed as a bioindicator of anthropogenic impacts on water quality. Therefore, this study was used the deformities of Chironomid larvae for assessing water quality of Huai Kakang stream (Maha Sarakham Province, Thailand). The effect of lead exposure in the mentum deformities of Chironomus spp. was also studied to confirm the relationship between the toxicant and the deformities. Water, sediment and chironomids larvae, were collected from Huai Kakang stream. Water and sediment were analyzed for nitrate (NO₃^-),total phosphate (TP), chemical oxygen demand (COD),and heavy metals (i.e. Cd,Cu, Ni, Pb, andZn).  Chironomids larvae were examined for the mentum deformity. For the bioassay test, the larvae were raised in 4 different concentrations of lead, including 0, 10, 20 and 30 mg_Pb/L. The results indicated that the lower stream site of Huai Kakang was polluted with the exceeding limits of Lead and cadmium.  The 53.33% of chironomid larvae exhibited mentum abnormality.  The bioassay test showed the high concentration of lead caused the larvae to reduce in number. The 50% lethal concentration (LC₅₀) was 34.74 mg_Pb/l. The experiment of 20mg_Pb/L showed the highest percentage of deformity and bioaccumulation of chironomids.

Key words: MouthpartDeformities, Lead, Stream and River Pollution, Chironomids