Title The Study on the Susceptibility for Chemicals and Their Difference between Marine Test Fishes
Authers Akira KAKUNO
Keywords chemicals,marine fish,toxicity test,susceptibility,critical body residues
Citation Bull. Fish. Res. Agen. No.33, 1-70, 2010
Recently, studies on fish toxicity has shifted from acute to chronic tests since long-term effects of chemicals on fish appear to be more important than short-term effects. Yet the protocols for chronic toxicity tests using marine fish have developed slowly compared to their freshwater counterparts. In addition, the difficulty of handling fry has restricted the development of a chronic toxicity test using an early life stage of a Japanese marine fish. These situations have now interfered in the conduct of environmental risk assessments of chemicals in the coastal environments of Japan. Thus, acute and chronic toxicity tests were conducted using Japanese marine fish, red sea bream (Pagrus major), and American marine fish, mummichog (Fundulus heteroclitus)for 4 chemicals: bis-n-tributyltin oxide (TBTO), triphenyltin chloride (TPTC), cadmium (Cd), and naphthalene (Nap). Median lethal concentrations (LC50)were derived from acute toxicity tests. On the other hand, chronic tests were early life stage toxicity test (ELS)and long-term toxicity test (LT)for mummichog and red sea bream juvenile, respectively, with growth (body length and weight)as test endpoints. Results show that relationship between LC50s and chronic toxicity values for both red sea bream and mummichog were linear implying that chronic toxicity values can be estimated through their acute-to-chronic toxicity ratios. Moreover, red sea bream was adversely affected at lower concentrations of the chemicals than mummichog suggesting that LT can replace ELS as chronic toxicity test for red sea bream juvenile. Hematological parameters such as red blood cell count, hematocrit, or hemoglobin concentration were also efficient when used for evaluating non-lethal toxicity of the chemicals in red sea bream. Additionally, we determined the bioconcentration factors (BCF)of TBTO, TPTC, Cd and Nap in both mummichog and red sea bream to investigate the cause of the differences in their susceptibility to these 4 chemicals. The critical body residues (CBR), which were calculated from BCF and LC50 values, were also compared to the dead fish body residues (DFBR)collected during the acute toxicity tests. Results show that it took about six weeks for TBTO, TPTC and Cd to reach their steady state while Nap reached steady state within 1 week only and was quickly eliminated. Interestingly, the concentrations of the test chemicals in dead mummichog were higher than in dead red sea bream for all chemicals. In addition, CBRs were comparatively higher than DFBRs for all chemicals except for Nap. Hence, it seems toxicity was underestimated by CBR. It was, however, evident that DFBR of the test chemicals in the acute toxicity test and 96hr-LC50 were very strongly correlated. For instance, red sea bream, which has a lower 96hr-LC50, die at a lower body residue concentration than mummichog. This indicates that red sea bream is a more sensitive marine test fish compared to mummichog. Finally, body residue such as DFBR is a useful indicator of fish susceptibility to chemicals.
URI http://www.fra.affrc.go.jp/bulletin/bull/bull33/1-70.pdf