"Dehydration. Loss of balance. Sterility."The warnings are part of an anti-drugs campaign on Colombian television. Their purpose, though is not to point out the pernicious effects of drugs on the human body - but on the environment. By latest estimates Colombia has more than 100,000 hectares of coca - and these crops were not planted on prime agricultural land. Each hectare of coca grown implies a further two or three hectares of forest being felled, and biologists fear valuable bio-resources could be disappearing as the forest is cut down.