CASTOR plant, locally known as ‘arind’, is grown in warm temperate and tropical areas of the world. The plant has been cultivated for centuries for oil produced by its seeds. The Egyptians burned castor oil in their lamps more than 4,000 years ago. The oil was used thousands of years ago in wick lamps for lighting. To many people the castor plant is just an overgrown, undesirable weed and yet it produces one of nature’s finest natural oils.
The oil extracted from the castor bean has a growing international market, assured by more than 700 uses, ranging from medicines and cosmetics to substituting petroleum in the manufacturing of bio-diesel, plastics and lubricants.
Castor plant has many uses, particularly the thick, yellowish or almost colourless oil obtained from the seeds. The seeds with hulls removed contain 40 to 60 per cent oil. There are various industrial applications for castor oil and its derivatives and new ones are continually being discovered. When dehydrated, castor oil is converted into quick-drying oil used extensively in paints and varnishes. Dehydrated castor oil is said to have qualities superior to linseed oil and tung oil, two of the most important drying oils. The oil is water resistant making it ideal for coating fabrics and for protective coverings, insulation, food containers and guns.
The oil is the source of several synthetic flower scents and fruit flavours, such as jasmine, apricot, peach, plum, rose, banana, and lemon. The chemicals for these flavours and aromas are obtained from ricinoleic acid, ingredients of natural castor oil. In fact, ricinoleic acid consists of about 90 per cent of the total triglyceride fatty acids of castor oil. The oil is also used in manufacture of soap, ink and plastics, for preserving leather, and as an illuminant. Red oil is also used for dyeing and finishing textiles and in brake fluids and certain insecticidal oils.
The seeds, leaves, and stems of the plant contain ricin and ricinine, which are poisonous to humans and animals. Eating a castor bean causes nausea, and eating several may cause death. These toxic compounds are not present in the oil.
Ricin has been shown to possess anti-tumor qualities and has been used in cancer research and chemotherapy during recent years. One of the most promising uses of ricin is in the production of immunotoxins used in treatment of tumour.
Castor oil is also used as personal lubricant. It is sometimes applied externally as a soothing emollient for dry skin, dermatitis, other skin diseases, sunburn, open sores and it is the primary ingredient of several brand name medications. Several additional uses for castor oil include hair tonics, ointments, cosmetics, and contraception creams and jellies.
Castor oil is the primary raw material for the production of sebacic acid, which is the basic ingredient in the production of nylon and other synthetic resins and fibers. Approximately three tons of castor oil can produce one ton of nylon.
Castor oil is also a strong laxative and in higher doses is purgative. The oil is so effective that it is regularly used to clear the digestive tract in cases of poisoning. Castor oil is well tolerated by the skin and it is sometimes used as a vehicle for medicinal and cosmetic preparations. In some areas, the oil is massaged into the breasts after childbirth to stimulate milk flow. Indian herbalists use a poultice of castor oil seeds to relieve swollen and tender joints. In China, the crushed seeds are used to treat facial palsy.
Castor oil as a “bio-diesel” has proven to have technical and ecological benefits and stands as an opportunity for agricultural development. For arid and semi-arid regions, growing castor plant in conjunct with Jatropha offers the only viable solutions for turning marginal lands into viable economic lands. Each hectare of castor planted in arid and semi-arid regions produces 350-650 kg of oil, which in turn produces 350-650 kg of bio-diesel per hectare.
Castor oil is soluble in alcohol and does not require heat and the consequent energy requirement of other vegetable oils in transforming them into fuel.
The oil is also used as a lubricant, lamp fuel, as a component of cosmetics, in the manufacture of soaps, printer’s ink, plastics, fibers, hydraulic fluid, break fluid, varnishes, paints, embalming fluid, textile dyes, leather finishes, adhesives, waxes, and fungicides. It is gradually being replaced as a raw material for some of the uses by petroleum-based products.
In India, the leaves are used as food for silk worms. The stalks from fields are burned for fuel in India and have been shown to be suitable for short-fiber pulp. The species has been planted for dune stabilisation. Castor plant is also widely grown as ornamental plant. Its large, star-shaped leaves make it a bold foliage plant. Some varieties have red or purplish colored leaves and stems.
Castor plant has large, palm-shaped leaves, green female flowers and prickly red seed capsules. In its native habitat, the castor plant is 30 to 40 feet in height bearing broad, deeply-lobed leaves on long stalks. The leaves are purple-bronze when young, gray-green or dark maroon when mature. The female flowers without petals, borne in clusters above the male flowers, develop into bur-like capsules containing three seeds each. When the capsules are mature and dry out, they explode scattering their beans. Shrubby dwarf strains no more than five feet high have been developed in cultivation, bearing non-explosive capsules.
Castor plant is grown as an annual herb in temperate countries but grows to tree-like proportions on fertile ground in tropical climates. Castor bean is herbaceous when young but becomes woody with age. The wood is soft and light with thick central pith. Occasionally, irregular brown heartwood develops. The bark is light brown, smooth and exhibits rings at the nodes and raised lenticels. There are a moderate number of large, star-shaped leaves with seven to nine long pointed lobes.
After decorticating, they are subject to a series of hot or cold presses followed by solvent extraction, each step yielding a different grade of oil. The largest producers are Brazil and India. The principal consumer is the United States and Europe. The seedcake remaining after extracting the oil is used as fertiliser or cooked to destroy the toxin and incorporated into animal feeds.
Castor beans are planted in rows spaced from one to two metre apart with spacing within the rows of about 0.5 m. When grown as an annual crop, it takes five to nine months from planting to harvest. Castor beans are reported to survive for eight to ten years and may reach six metre in height. Annual varieties reach one to two metre in height. Seed yields under cultivation vary from 200 to 1,700 kg/ha, depending on variety and site quality.
The bean may become a weed in neglected cropland and pasture. It is not difficult to control through cultivation and mowing. Of greater concern than its weedy potential is the high toxicity of its seeds, which contain ricin, a water-soluble protein. Even a small amount of masticated seed is likely to cause death. Humans and horses are especially vulnerable. Fatal doses are from 2.5 to six seeds for humans and about six seeds for horses. Symptoms are stomach irritation, diarrhoea, abdominal pain, increased heart rate, profuse sweating, collapse, and convulsions. Broken seeds can cause skin irritation. The foliage is only slightly toxic. It is advisable to completely eliminate castor bean from pastures, especially horse pastures, and pinch off flowers of ornamental plants to prevent possible poisoning of children.