EVALUATION OF TRICHOPTERA AS AN INDICATOR ORGANISM FOR ENVIRONMENTAL-POLLUTION BY HEAVY-METALS

A method of analysis for heavy metals in trichopteran larvae by AAS wa s established to evaluate this aquatic insect as an indicator organism for environmental pollution by heavy metals. A wet digestion method w ith nitric acid and hydrogen peroxide was found to be suitable for the decomposition of trichopteran larva samples. No serious variation in heavy metal contents was found in individual samples collected from on e sampling point. A weak negative correlation was observed between the body length and the heavy metal ,contents of trichopteran larvae. In addition, the heavy metal content of trichopteran larvae seems to show a seasonal fluctuation. Trichopteran larvae in the Watarase River, wh ich has abandoned copper and manganese mines along its upper stream, s how an enriched heavy metal content as compared with those in other no n-polluted rivers. Moreover, this aquatic insect in the Kiryu River al so shows enrichment of manganese due to abandoned manganese mines situ ated upstream. These facts suggest that the trichopteran larva is a us eful indicator organism for environmental pollution by heavy metals.