The Activity of Natural Radionuclides Th-232, Ra-226, K-40, and Na-22, and Anthropogenic Cs-137, in the Water, Sediment, and Common Carp Produced in Purified Wastewater from a Slaughterhouse

Abstract

In the immediate vicinity of a slaughterhouse, a fishpond was built that uses treated wastewater from the slaughterhouse, and in this way integrates a new value chain in the form of purification and use of slaughterhouse wastewater in an aquaculture production system. The negative aspect of such integrated production systems is the concern related to the safety of fish meat produced in these systems. The aim of this research was to determine the activity level of Cs-137, K-40, Ra-226, Th-232, and Na-22 in water, sediment, and carp harvested from a pond that received purified water from a slaughterhouse. All samples were collected in spring and in autumn. The activity concentrations of selected radionuclides were determined by gamma spectrometry (HPG-e detector). The activity of K-40 in water samples ranged from 8.4 to 15.6 Bq L−1. The specific activity concentrations of the Ra-226 in water samples ranged between 1.02 ± 0.11 and 2.76 ± 0.49 Bq kg−1. The results of the activity of natural radionuclides (Bq kg−1) in the sediment samples were in the following ranges: 440–629 for K-40, 10.7–15 for Th-232, 20.2–44.4 for Ra-226, and 1.08–2.04 for Na-22, with average values of 531.75, 12.3, 32.97, and 1.75, for K-40, Th-232, Ra-226, and Na-22, respectively. The average content of Th-232 (12.3 Bq kg−1) did not exceed the world UNSCEAR average value of 45, while the average content of Ra-226 (32.97 Bq kg−1) slightly exceeded the UNSCEAR value of 32 Bq kg−1. The K-40 concentration activity of 531.75 Bq kg−1 was much higher than the UNSCEAR weighted average value of 420 Bq kg−1. In the fish samples, natural radionuclide Na-22 was detected only in autumn (2.74 ± 0.32 Bq kg−1). Results of Cs-137 and Th-232 concentrations were below the method detection limit in all samples, ˂0.5 Bq kg−1 and ˂2 Bq kg−1, respectively. The activity of K-40 was in the range from 121 to 160 Bq kg−1. The activity concentrations of the Ra-226 in carp samples ranged between 9.5 and 54.4 Bq kg−1. The results indicate that consumption of fish meat obtained from this integrated system does not pose a significant health concern in the case of the usual consumption rate that is typical for the population of Serbia. Almost no statistically significant seasonal variations were observed.