Estimating biological half-lives of 137Cs in a cyprinid fish Tribolodon hakonensis by a one-compartment model considering growth dilution effect

Japanese daceTribolodon hakonensisrearing experiments were conducted to estimate parameters related to(137)Cs uptake and excretion processes. Fish (initial mean total length 256 mm, 136 g) were reared at 20 degrees C for 182 days using the same daily ingestion rate (1% of body weight for 6 days per week) with three feeding regimens: feeding contaminated pellets (80.7 Bq/kg-dry of(137)Cs) throughout the experiments (Cs-137 uptake group), feeding contaminated and non-contaminated pellets respectively for days 0-40 and days 42-180 (Cs-137 uptake-excretion group), and feeding non-contaminated pellets throughout the experiments (control group). Samples were taken periodically. The(137)Cs concentrations in muscle tissues (MU) and whole bodies (WB) were measured using Ge detectors. The(137)Cs concentrations in fish that had grown to 240 g by day 182 reached 45.5 Bq/kg-wet in MU and 37.0 Bq/kg-wet in WB in the(137)Cs uptake group. A one-compartment model incorporating the growth coefficient estimated that the biological half-lives of(137)Cs in MU and WB excluding the growth dilution effect (216 days and 233 days, respectively) were longer than the apparent biological half-lives (100 days and 104 days) observed in the(137)Cs uptake-excretion group. The developed method can contribute to promoting precise prediction of radiocesium contamination of fish affected by the Fukushima fallout.