Other issues Other suspected adverse effects of low doses of POPs for which evidence is being accumulated include porphyria, disturbance of hormonal function and suppression of the immune system in exposed individuals. Deleterious effects of many POPs on beneficial species are well documented. This particularly applies to aquatic organisms. Environmental aspects of DDT use in public health programmes, and malaria control in particular, have been the subject of much controversy for many years. The impact of DDT on the environment has been greatly reduced since its use in food production was banned in most countries many years ago.
Many countries rely on the use of DDT for the control of malaria and visceral leishmaniasis.
In the early seventies, considerably more acutely toxic organophosphorous and carbamate insecticides were introduced in vector control operations, which resulted in a considerable increase in incidences of acute poisoning, both accidental and occupational. Resistance to them has also developed in a number of malaria vectors. In recent years, pyrethroids started to replace both chlorinated hydrocarbons and organophosphorous compounds. Being aware of the need for chemical insecticides as an essential tool in integrated pest management programmes in controlling vector-borne diseases, WHO is encouraging the development of new classes of pesticides through the WHO Pesticide Evaluation Scheme. Unfortunately, this development is much slower than insect resistance development, and there is a fear that the few available insecticides may not be sufficient in the near future especially taking into consideration the implications of resistance and cross-resistance in the vectors.