| Experimental population dynamics of freshwater rotifer Brachionus calyciflorus exposed to sublethal concentrations ofβ-hexachlorocyclohexane (β-HCH) and chlordecone (kepone) were studied by means of life-table, three-day population growth, four-day resting egg production and environmental capacity tests. The main contents and results were presented as the following:1. The experimental population dynamics of B. calyciflorus exposed to sublethal concentrations (0.001, 0.01, 0.1, 1, 10, 100 and 1000μg/L) ofβ-HCH were studied by means of life-table, three-day population growth and four-day resting egg production tests. The results showed that compared to the controls, 10, 100 and 1000μg/Lβ-HCH shortened significantly the embryonic development time of rotifers, 0.1, 10, 100 and 1000μg/Lβ-HCH prolonged significantly the duration of juvenile period of rotifers, 0.1 and 1000μg/Lβ-HCH prolonged significantly the life expectancy of rotifers at hatching, 100 and 1000μg/Lβ-HCH prolonged and increased significantly the generation time and the intrinsic rate of population increase of rotifers, respectively. 1000μg/Lβ-HCH increased markedly the population growth rate of rotifers. 0.1μg/Lβ-HCH increased significantly the ratio of mictic females/amictic females, but the reverse was true for 1000μg/Lβ-HCH. 100 and 1000μg/Lβ-HCH decreased significantly the mictic rate. 10, 100 and 1000μg/Lβ-HCH increased significantly the fertilization rate of mictic females and resting egg production. A significant dose-effect relationship existed between the concentrations ofβ-HCH and the population growth rate, the mictic rate, the fertilization rate of mictic females as well as the resting egg production, and all the four parameters could be used to monitor sublethal concentration ofβ-HCH in water environment, with the resting egg production and the fertilization rate of mictic females being the most sensitive endpoints.2. The experimental population dynamics of B. calyciflorus exposed to sublethal concentrations (0.0005, 0.005, 0.05, 0.5, 5 and 50μg/L) of chlordecone were studied by means of life-table, three-day population growth and four-day resting egg production tests. The results showed that compared to the controls, 5 and 50μg/L chlordecone shortened markedly the embryonic development time of rotifers, but prolonged significantly the duration of juvenile period. 50μg/L prolonged significantly the duration of productive period and mean life span. 0.05 and 5μg/L chlordecone shortened significantly the duration of post-productive period. 0.5-50μg/L chlordecone increased significantly the lifetime egg production and net-reproductive rate of rotifers. 0.5 and 50μg/L chlordecone prolonged significantly the generation time of rotifers. 50μg/L chlordecone increased significantly the intrinsic rate of population increase of rotifers and the ratio of ovigerous females/non-ovigerous females. 0.0005 and 50μg/L chlordecone increased significantly the fertilization rate of mictic females. 0.05-50μg/L chlordecone increased significantly the resting egg production. A significant dose-effect relationship existed between the concentrations of chlordecone and resting egg production, and the resting egg production could be used to monitor sublethal concentration of chlordecone in water body. In addition, the fertilization rate of mictic females is also a sensitive endpoint.3. The effects of sublethal concentrations ofβ-HCH (0.001, 0.01, 0.1, 1, 10, 100 and 1000μg/L) and chlordecone (0.0002, 0.002, 0.02, 0.2, 2 and 20μg/L) on the population growth of B. calyciflorus were studied by means of environmental capacity tests. The results showed that the rotifer population exposed to 100μg/Lβ-HCH grew slower than the others after 6 days, and its density was also lower than the others. The rotifer population exposed to 1000μg/Lβ-HCH grew fast in the initial six days, but declined at the 7th day, and its density was lower than the others too; from the 10th day on, the rotifer population grew and tended to be stable. The rotifer population exposed to 0.0002μg/L chlordecone grew faster than the others at the 4th-6th day, however, the rotifer population exposed to 20μg/L chlordecone grew slower than the others after 3 days, and its density was also lower than the others, but from the 10th day on, its density was equal to the others. Compared to the controls, 100 and 1000μg/Lβ-HCH decreased significantly the maximum population density of rotifers, 10, 100 and 1000μg/Lβ-HCH, and 20μg/L chlordecone decreased significantly the population growth rate of rotifers. A significant dose-effect relationship existed between the concentration ofβ-HCH and the maximum population density, and the population growth rate, and both the two parameters could be used to monitor sublethal concentration ofβ-HCH in water environment.
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