A letter in the Lancet for May 20 from a group of Italian scientists draws attention to possible contamination of the environment by discarded therapeutic drugs. It is pointed out that thousands of tons of pharmacologically active substances are used yearly in various branches of medicine, as well as many more used in animal farming. Some of these compounds may be excreted unmetabolised or in the form of active metabolites, and may escape degradation in waste treatment plants, thus entering the environment. Further pollution may be caused by improper disposal of time-expired medicines.
Pharmaceutical products can have long half-lives, and so may accumulate and reach detectable and biologically active concentrations in soil and water. Some commonly used drugs such as erythromycin, cyclophosphamide, naproxen, sulphamethoxazole and sulphasalazine may persist for longer than a year, and clofibric acid, the metabolite of clofibrate, may persist in lakes and rivers for 21 years. An analysis of selected drugs in drinking waters and river sediments in Italy indicated that some 16 drugs were detected in the nanogram per litre concentration range, but were not associated with specific sources of contamination, apart from diazepam in one drinking water supply, which apparently derived from a point source. Human exposure might occur within the nanogram per day range, but three to four orders of magnitude less than those required for any pharmacological effect. Risks from acute exposure are therefore considered unlikely, but the possible adverse effects of life-long exposure remain to be determined.