Abstract
A freshwater shrimp, Paratya compressa improvisa (Decapoda), was exposed in flowthrough aquariums to lake sediment contaminated with etofenprox (EFP, a synthetic pyrethroid insecticide) at 0.49, 9.98, 32.6 and 128 ng/g (wet wt.) for 30 h by spiking with EFP at 0,1, 2,0, 6,4, and 25.6 mg/L. Concentrations of EFP in the sediment decreased slowly in the flowthrough aquariums for 30 d, and remained at 60 and 70% of the initial concentration in the sediment treated with 6.4 and 25.6 mg/L EFP, respectively. Neither mortality nor growth of the. shrimps exposed to the sediment treated with 0.1 or 2.0 mg/1, EFP were affected. On the other hand, the mortality of the shrimps exposed to sediment treated with 6.4 mg/L EFP reached 100% by 7 days in the first part of the 35-d experiment, and was still approximately 76% in the latter period of the experiment. When the shrimps exposed to sediment treated with 6.4 mg/L EFP with commercial fish food, their mortality decreased to 20% compared to 76% of the unfed shrimp. Mortality of the shrimps exposed to the sediment treated with 25.6 mg/L EFP was 100% within 24 or 48 h throughout the 35-d experiment. However, shrimps introduced into the overflow water from this exposure-aquarium were not affected in either their growth or mortality. The EFP concentration of the sediment treated with 25.6 mg/L EFP was diluted with control sediment to 50%, 2.5% and 12.5%. Mortality of the shrimps exposed to these sediments decreased in relation to EFP concentration in the mixed sediment. All experimental results suggested that the high mortality of the shrimps is due to ingestion of EFP in the sediment rather than waterborne EFP exuded from the sediment.
