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Biodiversity has an economic value, with local, regional, national and international implications. Consequently, biodiversity is often an issue of economics and so of politics. Biodiversity has also an alternative value, an intrinsic value (Pearce and Moran, 1994), which is academic/scientific, that is unrelated to direct human use. However, the intrinsic value studies form the basis for economic valuation and exploitation.
ECONOMIC VALUE OF MEDICINAL PLANTS
Plant species are used for medicinal purposes in two ways:
a) as traditional medicines, singly or in formulations, such as those prepared and dispensed by traditional medical practitioners, which may or may not attract a market price; and
b) commercial products, dispensed by prescription or over the counter sales, such as patented/licensed medical products of allopathy or traditional systems of medicine.
Both these uses have economic value. For the lack of adequate and appropriate data, it is near impossible to evaluate the returns from the first category. The economic value of plant based drugs, therefore, largely rests on the second category uses. It is estimated that in the rich world, 25 per cent of all medical drugs are based on plants and their derivatives (Principe, 1991). In the poor world, this is closer to 75 per cent.
The economic value of a particular species of plants in medicinal use depends upon a number of factors, among which the following are important:
a) Certain plant species are used in a large number of formulations. The use of a particular species with reference to the number therapeutic effects it exerts or the number of formulations in which it is an ingredient, is expressed as the therapeutic index and frequency index, respectively. A higher index reflects a higher economic value attributable to a particular species. Such species are often referred to as the ‘elite species’. For example neem (Azadirachta indica) is indicated for use against 10 out of 18 symptoms in gastro-intestinal disorders (Sharon, 1994) and against eight out of 11 symptoms in dental care (Shubharani, 1995). Neem has several other medicinal and non-medicinal uses as well. Consequently, neem is one of the elite species of Indian medicinal plants.
b) Certain species are of great importance in the treatment of a particular disease as they happen to be the only (or one of very few) species with that therapeutic potential, as the alkaloids of Catharanthus roseus in the treatment of leukemia. The importance of the disease also is a factor. Such species attract high market rate.
c) Some species have a narrow distribution and/or occur in small populations. Some may be difficult to cultivate. Such species also command a higher price. For example, Trichopus zeylanica, occurring in south India, Sri Lanka and the Malay peninsula, is recently projected as the Indian equivalent of ginseng. This species now attracts a high market value.
d) Certain species of medicinal plants like Rauvolfia serpentina and Saraca asoca have been over exploited and so now occur rather scarcely in nature. It is difficult to cultivate Rauvolfia serpentina on a large scale while Saraca asoca is rather easier to propagate. The market value of some species, thus depends upon such criteria.
e) There are synthetic substitutes for several originally plant derived products, as for example clove oil. If the synthetic substitute is cheaper to produce than the plant based product and/or if the natural products have no other uses, the economic value of the natural product falls. However, certain therapeutically active constituents produced by plants like digoxin and digitoxin have not been produced synthetically. Some like vincristine, vinblastin, opiates, etc., that have been synthesised have proven to be less efficient than the natural products. The economic value of a species of medicinal plants depends upon this situation as well.
f) The economic value of a particular species varies with time. An effective synthetic substitute, or the discovery of a better natural alternative or the disuse of the species/product over a period of time, may deplete the species of its market value. For example, till sulphonamides came into use, sandalwood oil was the most widely used effective antispetic. Subsequently, sandalwood oil (Saantalum album) has fallen into disuse as an antiseptic. Its economic value should have come down but did not as sandalwood oil has other uses with higher economic returns.
g) The costs involved in isolation and purification of an active principle involve several considerations. It requires about a tonne of leaves of Catharanthus roseus to obtain one gram of the alkaloid vincristine, essentially needed to treat leukaemia. Vincristine is one of the expensive plant products costing about US$ 24,000/g. Vinblastin, another alkaloid from the same species, used to treat Hodgkin disease, is present in quantity 1,000 more times than vincristine. One gram of vinblastine costs about US$ 6,800. It is now possible to convert vinblastine into vincristine through biotransformation. There is also a growing interest in the other alkaloids present in Catharanthus roseus. Thus, several factors govern the cost of the raw material and the final product of a medicinal plant, from time to time.
The potential of plants as sources of medicine is often taken in support of identification and preservation of the world’s most species rich ecosystems. Such assessments are speculative and totally based on chance. Screening the vast vegetable world for potential sources of medicine and their use in the traditional way or through the application of biotechnology for a large scale industrial production of the active constituents or by chemical synthesis, is a very uncertain and a long term proposition that involves heavy financial investment with no certainty of the economic returns. There is no guarantee that the future drugs will all be derived from plants.
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