In the Philippines, carrageenan from Eucheuma seaweeds produced by the alternative refining process is known as Philippine Natural Grade (PNG) carrageenan. Philippine Natural Grade (PNG) carrageenan refined by the altenative process from Eucheuma cottonii was orally administered to male and female specific pathogen-free Sprague-Dawley rats at 0.5, 1.5 and 5.0% level admixed with the standard laboratory diet in a 3-month subchronic toxicity test. The standard laboratory diet served as the negative control and the conventionally processed refined carrageenan (CP carrageenan) admixed at 5.0% level served as the positive control diet.
The average daily intake of PNG carrageenan at different mixing levels were 382, 1140 and 3887 mg/kg/day in male rats and 410, 1292 and 4170 mg/kg/day in female rats, respectively. On the other hand, the average daily intake of CP carrageenan in male and female rats were 3917 and 4249 mg/kg/day, respectively. There were no evidences observed which showed that PNG carrageenan, a high molecular weight substance, was observed at the gastrointestinal tract and no toxic manifestations or adverse effects were observed in rate as a result of ingesting PNG carrageenan for 3 months based on the clinical signs and behavioral changes, body weight gain, feed consumption and efficiency of utilization; clinical examinations, consisting of hematology, blood coagulation tests, serum biochemistry, urinalysis, and fecalysis; and pathological examinations, consisting of necropsy, organ weight and histopathology. The same findings were observed with CP carrageenan.
Apparently, the principal effect induced by PNG carrageenan and CP carrageenan in rats was the passage of soft formed stools which did not have any toxic or adverse consequences. However, fecal softening with PNG carrageenan was sporadic and involved only a few rats; while with CP carrageenan, fecal softening was frequently observed in all rats. Passage of soft stool may be attributed to the laxative effect (aperient) of carrageenan. The difference in the observed frequency of fecal softening may be partially due to the presence of higher cellulose content.
The absence of subchronic oral toxicity in rats at 5.0% dietary level suggests that PNG and CP carrageenan share the same toxicological attributes. Furthermore, in this toxicity test, the high cellulose content of PNG carrageenan may have contributed to the improvement of the consistency of feces excreted.(Author)

BFAD Laboratory Information Bulletin, 1996 2 (1) pages 20-34