FIELD AND EXPERIMENTAL MORPHOLOGICAL RESPONSE OF CHIRONOMUS LARVAE (DIPTERA, NEMATOCERA) TO XYLENE AND TOLUENE

The morphological response of Chironomus gr. thummi larvae after a spi ll of xylene (10 000 l) and toluene (7500 l) in a brook was investigat ed. At the site of the spill, the proportion of larvae with mentum and antennal deformities increased in the following months. Downstream (5 00 m), no such clear response could be discerned. Mandible deformities occurred as well, but the fluctuations could not be related to the pu lse pollution. Fugacity and concentration models predict a higher affi nity of xylene to sediments and biota. Therefore, a short term 72 h ex posure test with xylene (0, 10, 100, 1000 mu l/l) was performed on ear ly instar larvae. Fourth instar larvae with a split medial mentum toot h represented 15% of the surviving population (mortality was 44%) at a concentration of 10 mu l/l xylene.