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(T/EH005) Bioaccumulation and deformities in third and fourth instars Chironomus gr. thummi give clues about ontogeny of deformities. Janssens de Bisthoven, Luc1, 1 ABSTRACT- The heavy metals Cu, Pb, Cd and Zn and the frequencies of head deformities were compared in third and fourth instars of Chironomus gr. thummi from the Laan stream, a polluted tributary ('SAL') of the River Dijle, and two sites in the River Dommel, polluted with Cd and Zn ('NP' and 'SCH'). Body concentrations of Cd were 10 (SCH) to 30 (NP) times higher in the Dommel than in the Laan; Pb was 1.5 to 2 times higher, Cu 5 and Zn 6 (SCH) to 10 (NP) times higher in the Dommel larvae than in the Laan larvae. No difference in metal concentrations were found between both instars in the Laan population. Copper was found in higher concentrations in the third instars than in the fourth instars of both Dommel sites. The same for Pb in site NP. In SAL the deformity frequencies were similar in both instars (5-30%). In NP the % of larvae with a deformed pecten epipharyngis was 3 times higher in the fourth instars (12%). The same was noted for the larvae of SCH, where also the antennal deformities increased from 3 % in third instars to 24 % in fourth instars. The SAL deformities are induced by other unknown pollutants, since the deformity percentages were as high as in the Dommel, despite the much higher metal concentrations in the Dommel. Higher accumulation of metals in younger instars must be attributed to (1) higher metabolic rate, (2) higher surface to volume ratio in the younger larvae, hence enhancing bioaccumulation, and (3) shedding of metal-loaded third instar larval exuvia during moulting to fourth instar (1,2, and 3 demonstrated in other studies). Higher deformity frequencies in older instars occur when (1) a fraction of the normal third instars moult into deformed fourth instars, (2) normal fourth instars emerge before their deformed counterparts, thus disappearing from the ecosystem (demonstrated in Janssens de Bisthoven et al., Freshw. Biol. 39, 179-191 (1998), and (3) a significant fraction of the deformed third instars moult into deformed fourth instars (1 and 3 demonstrated in Vermeulen, PhD, KULeuven, pp. 207 (1998). Key words: Chironomus, bioaccumulation, deformities, ontogeny |
