Ricin is a toxic glycoprotein (with several minor variants) belonging to the type II group of ribosome inactivating proteins (type II RIP) found in the seeds (beans) of the castor oil plant (Ricinus communis L. (Euphorbiaceae)). It is composed of two polypeptide chains of approximately 30 kDa joined by a disulfide bond. A limited number of other plants in the same family contain type II RIPs, i.a. subtropical leguminous climber Abrus precatorius L. and, Croton tiglium L. which contain abrin and crotin I, respectively. The seeds of Croton tiglium contain a number of other toxins which make it unsuitable as a feed for livestock. In the Terms of Reference, the plant Jatropha curcas was also requested to be considered, however, it does not contain a RIP II protein. The toxicity of its seeds can be ascribed to the oil, which contain phorbol esters and this plant is therefore not relevant for this opinion on ricin.
Following extraction of castor oil, ricin is left in the press-cake/castor bean meal. Castor oil production mainly takes place outside the EU. Because of its low value of the press-cake as feed no import to the EU is expected.
Following cell uptake by endocytosis, ricin causes acute cell death by inactivation of ribosomal RNA. Acute symptoms in humans after intake of castor beans are hematemesis (vomiting containing blood), diarrhoea, haemorrhagic necroses in several organs, renal failure, circulatory collapse and death after 6 to 14 days with a fatal oral dose of about 1 mg/kg b.w. (5-10 castor beans). Because of its destruction in the intestinal tract, ricin is approximately 1000-fold more toxic following parenteral administration or inhalation, than by the oral route. Oral LD50 values in rats and mice were 20 to 30 mg/kg b.w., and the corresponding intra peritoneal LD50 value for mice is 22 μg/kg b.w. There are no data on chronic or reproductive toxicity, or genotoxicity of ricin. Crotin I showed LD50 i.p. values in mice of 20 mg/kg b.w.
The very limited data on acute toxicity in target animals comprise mainly information on castor bean products rather than on purified ricin. Amongst ruminants, cattle appear to tolerate higher intakes than sheep. In horses severe colic and death have been observed after a single dose of approximately 7-8 mg ricin/kg b.w. Toxic effects in pigs and birds have been reported as well as accidental poisonings in dogs with vomiting, depression and diarrhoea as the main clinical signs. No- or lowest observed adverse effect levels (NOAELs or LOAELs) for acute effects of ricin could not be identified for any of the animal species.
The Panel on Contaminants in the Food Chain (CONTAM Panel) is not aware of any feed producers using castor seed meal as a feed for livestock in the EU, and therefore subject to this caveat, exposure of animals would only be expected as a result of accidental contamination. There are limited data on the toxicokinetics and carry-over of ricin to products of animal origin (milk, meat or eggs). Livestock has a very low tolerance to ricin exposure via feed before clinical symptoms of toxicity are manifest. It is therefore unlikely that highly exposed animals would enter the food chain, and the CONTAM Panel considers the risk of ricin transfer to livestock products to be negligible.
Except for exposures to ricin via the accidental intake of castor beans (Ricinus communis) human exposure via food, under normal circumstances, is unlikely to occur.