Evaluation of Chlorella as a Decorporation Agent to Enhance the Elimination of Radioactive Strontium from Body

Abstract

Background: Release of radionuclides, such as 137Cs and 90Sr, into the atmosphere and the ocean presents an important problem because internal exposure to 137Cs and 90Sr could be very harmful to humans. Chlorella has been reported to be effective in enhancing the excretion of heavy metals; thus, we hypothesized that Chlorella could also enhance the elimination of 137Cs or 90Sr from the body. We evaluated the potential of Chlorella as a decorporation agent in vitro and in vivo, using 85Sr instead of 90Sr.

Methods: In vitro experiments of adsorption of 137Cs and 85Sr to Chlorella were performed under wide pH conditions. The maximum sorption capacity of Chlorella to strontium was estimated using the Langmuir model. A 85Sr solution was orally administrated to mice pretreated with Chlorella. At 48 h after 85Sr administration, the biodistribution of radioactivity was determined.

Results: In the in vitro experiments, although 85Sr barely adsorbed to Chlorella at low pH, the 85Sr adsorption ratio to Chlorella increased with increasing pH. The maximum sorption capacity of Chlorella to strontium was 9.06 mg / g. 137Cs barely adsorbed to Chlorella under any pH conditions. In the biodistribution experiments, bone accumulation of radioactivity after 85Sr administration was significantly decreased in the Chlorella pretreatment group compared with the non-treatment control group.

Conclusions: In conclusion, these results indicated that Chlorella could inhibit the absorption of 90Sr into the blood and enhance the elimination of 90Sr from the body through adsorption in intestine. Further studies are required to elucidate the mechanism and the components of Chlorella needed for adsorption to strontium and could promote the development of more effective decorporation agents.

Fig 1. Adsorption of radionuclides to Chlorella.

Binding ratios of ⁸⁵Sr at pH 1.2 (closed circles), ⁸⁵Sr at pH 6.8 (open circles), ¹³⁷Cs at pH 1.2 (closed diamonds), or ¹³⁷Cs at pH 6.8 (open diamonds) to Chlorella depended on the Chlorella concentration. Data are expressed as the mean ± SD of three samples.

Fig 2. pH dependence of Chlorella adsorption.

Binding ratios of ⁸⁵Sr (open circles) or ¹³⁷Cs (open diamonds) to Chlorella depended on the pH conditions. Binding ratios of ⁸⁵Sr (closed circles) after exposure to acidic conditions. Data are expressed as the mean ± SD of three samples.

Fig 3. Langmuir model.

Adsorption capacity of Chlorella to strontium. Data are expressed as the mean ± SD of three samples.

Fig 4. Adsorption of ⁸⁵Sr to Chlorella in the presence of cations.

Binding ratios of ⁸⁵Sr to Chlorella in the presence of Na⁺ (closed circles), K⁺ (open circles), or Ca²⁺ (closed diamonds). Data are expressed as the mean ± SD of three samples.