Antarctic krill are a potential food source for humans and animals, but krill are known to contain high levels of fluorine (F). In this study, we investigated the toxicity of F in Antarctic krill using Wistar rats. There were three experimental groups: The control group were fed a basal diet, the krill treatment group were fed the same basal diet mixed with krill powder (150 mg/kg-1 F), and the sodium fluoride (NaF) treatment group were fed the basal diet with added NaF (150 mg/kg-1 F). General toxicity indicators including body weight and food intake were measured during the experiment. After three months the rats were dissected and tissue samples were collected from the liver, kidney, spleen, brain, and testis. Morphological changes in the cells of these tissues were assessed using HE staining. There were no significant differences in the body weight, the food intake, or the viscera coefficients among the three groups. In both treatment groups some pathological changes were observed in all soft tissue samples except the testis, although there were fewer and less severe pathological changes in the krill treatment group than in the NaF treatment group. The results showed that the toxicity of F in Antarctic krill was lower than for an equivalent amount of F in NaF, but it was still toxic to rats consuming large quantities of krill. The findings of this study highlight the need for further investigation into potential F toxicity if krill is to be used for human consumption.
3.3 Histological analysis
The histological sections of liver from rats in the control group and two treatment groups are shown in Figure 2. The sections from rats in the control group appeared normal and healthy (Figure 2 A1, A2, A3). However, the liver sections from the Antarctic krill treatment group showed some vacuolization in the cytoplasm, hepatic sinus expansion, and loss of integrity of the epithelium lining the central veins (Figure 2 B1, B2, B3). The same abnormalities were observed in the NaF treatment group, but to a greater extent than in the krill treatment group (Figure 2 C1, C2, C3), and some of the liver cells in the NaF treatment group showed signs of necrosis.
In the control group, the histoarchitecture of the kidney sections was normal (Figure 3 A1, A2, A3). A small degree of vacuolar degeneration in kidney cells and some loss of integrity in the epithelial lining of the renal tubules were observed in the krill treatment group (Figure 3 B1, B2, B3). Similar but more advanced changes were seen in the slides from the NaF treatment group (Figure 3 C1, C2, C3).
The histopathological sections of spleen from the control group and the two treatment groups are shown in Figure 4. Compared with the control group, lymphocyte nodules increased and white pulp decreased in the two treatment groups. The increase in lymphocyte nodules and the decrease in white pulp were more pronounced in the NaF treatment group than in the krill treatment group.
Compared with the control group (Figure 5 A1, A2, A3), the number of neurocytes decreased and the number of spongiocytes increased in brain sections from the two treatment groups (Figure 5 B1, B2, B3 and C1, C2, C3). The sections from the NaF treatment group revealed large areas of vacuolar degeneration and there was a greater reduction in neurocyte numbers compared with the krill treatment group.
There were no significant histopathological changes seen in the sections of testis from the three groups. The number and development of sperm cells showed no obvious pathological changes.