Chapter 48, Problem 1DAA

Bioaccumlation in tuna Bluefin tuna are among the fishes that were exposed to radioactive material released into the sea by the damaged Fukushima nuclear power plant (Section 47.1). These tuna breed in the western Pacific, and some migrate to the Eastern Pacific when they are 1 to 2 years old. Daniel Madigan suspected that migrating tuna would transport radioactive material to the waters off the coast of California. To test this hypothesis, he and his collaborators analyzed the concentration of cesium radioisotopes (¹³⁷Cs and ¹³⁴Cs) in bluefin tuna and yellowfin tuna caught near San Diego in August 2011. Yellowfin tuna do not cross the Pacific; they spend their lives in California's coastal waters. The scientists compared these data with the radioisotope content of bluefin tuna that had been caught near San Diego in 2008. FIGURE 48.9 shows their results.

FIGURE 48.9 Radioactive cesium (Cs) concentration in two species of tuna caught along the coast of California.

¹³⁷Cs has a half-life of 30 years and some persists in the Pacific from weapons testing. ¹³⁴Cs has a half-life of 2 years and was undetectable in the Pacific prior to the accident at Fukushima. Becquerels (Bq) is a measure of radioactivity.

How did the radioisotope content of the bluefin tuna caught in August of 2011 compare to that of bluefins caught in 2008 (before the Fukushima accident)?

Summary Introduction

To determine: How the radioactive content of the bluefin tuna caught in August of 2011 compare to that of bluefins caught in 2008 (before the Fukushima accident).

Concept introduction: Bioaccumulation is the concentration of a pollutant inside an organism’s tissues causing the amount of the pollutants to increase over time. Trophic level also affects the pollutant concentration by the process of biological magnification The concentration of the chemical increases as the pollutant moves up the food chain. Bioaccumulation and biological magnification even in low concentrations (depending on toxic potential) can have detrimental effects on a species.

Explanation of Solution

The powerful earthquake occurred in the northeast coast of Japan in March 2011 caused tsunami that killed 15,000 people. During this time, the nuclear power plant on the shore of the city Fukushima became damaged and released some radioactive materials into the air and sea. The water was polluted with cesium 137 (¹³⁷Cs), a radioactive material having a half-life of 30 years.

The bluefin tuna are among the fishes that were exposed to radioactive materials released into the sea. These tuna fishes breed in the western Pacific and some migrate to the Eastern Pacific when they are 1 to 2 years old. Researcher D suspected that the tuna might have transported the radioactive material off the coast of California. To test this hypothesis, the concentration of cesium radioisotopes (¹³⁷Cs and ¹³⁴Cs) in bluefin tuna and yellowfin tuna caught near the San Diego in August 2011were analyzed for the presence of cesium.

The yellowfin tuna reside in the California’s coastal water and they do not cross the Pacific. Therefore, the presence of cesium in yellowfin tuna was compared with bluefin tuna.

Refer to Fig. 48.9, “Radioactive (Cs) concentration in two species of tuna caught along the coast of California” in the question. From the figure, the bluefin tuna caught in 2011 have 6.3 Bq and 4 Bq of ¹³⁷Cs and ¹³⁴Cs, respectively; whereas the bluefin tuna caught in 2008 have 1.4 Bq and 0 Bq of ¹³⁷Cs and ¹³⁴Cs, respectively.

Therefore, the bluefin tuna caught after the Fukushima nuclear plant incident (2011) have a higher level of cesium radioactivity than the bluefin tuna caught before the incident (2008).

Conclusion

¹³⁴Cs radioisotope and a lower level of ¹³⁷Cs were found in the bluefin tuna caught in 2008; however, the tuna caught after the accident in 2011 contained a higher level of both radioisotopes.