Although natural( 17β-ocstradiol) and synthetic( 17a-ethinylestradiol)oestrogens in sewage effluent have been shown to disrupt hormonally controlled processes in a number of animal groups, understanding of their effect upon British freshwater molluscs is limited. The effects of exposure to high (0.1 to 10 mg/L EE2) and low (I to 10,000 ng/L EE2) nominal concentrations of 17acthinylestradiol (EE2 on the freshwater pulmonate gastropod Lyninaea stagnalis were assessed using studies designed to interfere with normal control processes in the life cycle of the animal. At 15degC,the snail was found to spend about 2 weeks developing as an embryo, 3 months growing as a juvenile and up to 2 years producing egg masses as an adult (shell height 22 to about 50 mm). The earliest life stages (embryo and neonate) were most sensitive to the toxicant in short-term exposure studies (e. g. neonate 24h LC50 = 9.4 mg/L; adult 24h LC50 = 14.2 mg/Q. Embryonic development was inhibited and a higher frequency of morphological malformations was found in animals exposed to environmentally relevant levels of EE2 compared to control animals. The animals' sensitivity toward the toxicant lessened following gastrulation. Neonate growth was promoted by the presence of the toxicant at 32-100 ng/L EE2 Whereas it was greatly reduced following exposure to the toxicant at the high μg/L concentration range. Reproduction was greatly influenced by the presence of the toxicant. For example, the quality, though not the quantity, of egg capsules produced was reduced. A number of morphological malformations to the egg capsule were observed and the possible sites of EE2 action on the reproductive tract were discussed. Allocation of packaging material to the egg mass occurred in a triphasic manner with the increased packaging observed at environmentally relevant levels of EE2 (10 ng/L EED lessened in samples from the 1000 ng/L exposure group yet significantly elevated at 10,000 ng/L EE2- Significant mortality was observed in groups exposed to treated sewage treatment plant effluent and control groups. However, the reproductive output, measured as the number of egg masses and capsules, was significantly reduced by the presence of effluent. Several previously unseen malformations to the egg capsule and egg mass were observed. Allocation of packaging material to the egg mass was inhibited by the effluent. As a consequence hatchability of the embryos was reduced in 50 and 100% effluent exposure groups. The implementation of novel bioassay endpoints in L. stagnalis toxicity tests has proven useful in identifying the effects of EE2 on freshwater pulmonate molluscs. The potential for further use of this species as a bioindicator in both laboratory and in situ studies is considered promising and is recommended
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:491416 |
| Date | January 2006 |
| Creators | Casey, Daire C. |
| Publisher | Cardiff University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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