LAUSR

Deformities in the mouthparts of non-biting midge larvae, particularly in the teeth of the mentum, were studied in cadmium polluted areas in Mae Tao Stream, Mae Sot District, Tak Province, Northern Thailand. Non-biting midge larvae were sampled together with water and sediment from 4 study sites: sites MT1 and MT2 were upstream to a zinc mine and unpolluted by cadmium; sites MT3 and MT4 were downstream and polluted with cadmium. From the water temperature, pH, electrical conductivity, total dissolved solids, dissolved oxygen, nitrate-nitrogen, ammonia-nitrogen, and orthophosphate, the stream water quality was classified as moderately clean. The cadmium concentrations MT3 and MT4 exceeded the European maximum permissible level of 3.0 mg/kg for agricultural soil. A total of 3067 larvae and 21 taxa representing 3 subfamilies (Chironominae, Orthocladiinae, and Tanypodinae) from the four sampling sites were screened for mentum deformities. The results indicated that the deformity incidence of larvae was 5% at MT3 and MT4 and 0.20% at MT1 and 0.75% at MT2. Hence the mouthpart deformities of non-biting midge larvae could be potentially used as a bio-indicator for cadmium pollution.