Toxicity study of Chlorella vulgaris water extract on female Sprague Dawley rats by using the Organization for Economic Cooperation and Development (OECD) Guideline 420

Chlorella vulgaris, a coccoid green eukaryotic microalga, is a popular food supplement and has been marketed as a nutritional supplement in Asia. Despite numerous reports on the antioxidant property of this species, its toxic effect has not been extensively studied. The aim of this study was to determine the acute oral toxic effect of C. vulgaris on female Sprague Dawley (SD) rats. An acute oral toxicity assessment of C. vulgaris was performed based on the Organization for Economic Cooperation and Development (OECD) Guideline 420. These guidelines are divided into a sighting study and a main study. In the sighting study, C. vulgaris extract was administered orally in sequential doses of 5, 50, 300 and 2000 mg kg−1 body weight (BW) with one rat used for each dosage. Clinical observation and mortality were observed for each rat to monitor signs of toxicity for 14 days. BW and relative organ weight (ROW) were recorded. Blood was collected for liver function test (LFT). Gross pathological evaluations were performed after euthanasia of rats. Haematoxylin and eosin (H&E) staining of the liver and kidney was also performed. The main study was performed based on the highest dose in the sighting study that did not exhibit any signs of toxicity and mortality. For 14 days, clinical observations, BW, and ROW were recorded. Blood from rats in the main study was also measured for LFT, and gross pathological evaluations and H&E staining of the liver and kidney were also performed. The highest dose of 2000 mg kg−1 BW C. vulgaris was used in the main study. No toxicity and mortality were observed in both the sighting study and the main study. Increases in BW were observed in both studies. Gross pathological evaluations showed no signs of organ abnormalities on each organ in the sighting and main studies. The ROW also showed no differences. The values of biochemical parameters in the liver function test showed no differences in the sighting study. However, in the main study, significant decreases in alkaline phosphatase (ALP) and aspartate aminotransferase (AST) were observed on day 14 compared with day 0 (p < 0.05). Chlorella vulgaris showed no toxicity at the dose of 2000 mg kg−1 BW. In conclusion, C. vulgaris can be categorized as unclassified according to the Globally Harmonised Classification System (GHS) for chemical substances and mixtures.