A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science, Asian Institute of Technologh; Inter-University Program in Environmental Toxicology, Technology and Management, Chulabhorn Research Institute and Mahidol University

Thesis (M.Sc.) - Asian Institute of Technology, 2004

Penaeus monodon and wtes calcarifer have been used as test species for Whole Effluent Toxicity Testing (WETT) in order to assess toxicity of effluent that is discharged into the Gulf of Thailand. However, these two species are not widespread in the Gulf of Thailand. Major sources are commercial aquaculture. For protection of native species in the Gulf of Thailand, their suitability as surrogate WETT test species was studied. In this study, the acute toxicity of effluent from natural-gas drilling platforms, and potassium chloride (KCl), as a reference toxicant, were conducted in two standard test species, mysis stage Penaeus monodon (Black tiger prawn) and larval wtes calcarifer (Asian seabass), and in newly hatched Sepia pharaonis (Pharoah cuttlefish), a native species in the Gulf of Thailand, in order to compare relative sensitivity among these species. The potential for use of Sepia pharaonis as WETT native species was also determined. For toxicity testing of KCl, a reference toxicant, the average 48-h LCso's for Penaeus monodon and Sepia pharaonis were 0.8868 g/l (n = 3) and 0.2432 g/l (n = 3), respectively, while the 96-h LCso for La-tes calcarifer was 1.0025 g/l (n = 3). For toxicity testing of natural-gas drilling platform effluent, the average 48-h LC5o's for Penaeus monodon and Sepia pharaonis were 3.2722 % (n = 3) and 0.6792 % (n = 2) of effluent, respectively, while the average 96-h LCso of Lates calcarifer was 10.1848 % effluent (n = 3) by assigning an LC so of 10 % effluent for the second and the third experiment where the LC5o was greater than 10 % effluent to allow the comparison of the average LC5o's across species. From the species sensitivity comparisons, Sepia pharaonis was observed to be the most sensitive species to natural gas drilling platform effluent. Their responses to the natural gas drilling platform effluent were significantly different from wtes calcarifer (p < 0.05) but the difference was not found when compared to Penaeus monodon though the average LC5o of Penaeus monodon was relatively higher than Sepia pharaonis. This may be the result of low power of statistical analysis. Based on the results from this study, the responses of the two standard test species may not be representative for native species in the Gulf of Thailand. Great care should be exercised when interpreting results from WETT using these standard test species for protecting species in the Gulf of Thailand. Sepia pharaonis could be easily cultured and handled under laboratory conditions. Further studies in Sepia pharaonis should be conducted to ascertain the potential to develop it as a standard test species for WETT. These results also prove the important of carrying out similar studies in other native species to determine the relative sensitivities. Only then can a standard test species be used to gauze the potential sensitivities of all native species to a toxicant. Information on the application of WETT in Thailand is limited. However, it certainly has the potential to be used as a tool for assessing the toxicity of complex effluents. This does require the development of standard protocols with suitable test organisms.