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

Abstract

Japanese dace Tribolodon hakonensis rearing experiments were conducted to estimate parameters related to ¹³⁷Cs uptake and excretion processes. Fish (initial mean total length 256 mm, 136 g) were reared at 20 °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 ¹³⁷Cs) throughout the experiments (¹³⁷Cs uptake group), feeding contaminated and non-contaminated pellets respectively for days 0–40 and days 42–180 (¹³⁷Cs uptake–excretion group), and feeding non-contaminated pellets throughout the experiments (control group). Samples were taken periodically. The ¹³⁷Cs concentrations in muscle tissues (MU) and whole bodies (WB) were measured using Ge detectors. The ¹³⁷Cs 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 ¹³⁷Cs uptake group. A one-compartment model incorporating the growth coefficient estimated that the biological half-lives of ¹³⁷Cs 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 ¹³⁷Cs uptake–excretion group. The developed method can contribute to promoting precise prediction of radiocesium contamination of fish affected by the Fukushima fallout.