Development of resistance

One of the first discovered problems of pesticides was that pests can become resistant to the chemicals. Unaware of how to deal with this issue, farmers then decide to spray more frequently and to apply higher doses. This just causes more problems.

Within a pest population there is genetic variation in their resistance to pesticides. If pests have not been previously exposed to a new pesticide, most individuals in the population are susceptible, but some individuals are resistant. Pesticides that are used to control the pest will kill most of the susceptible individuals, but the few resistant individuals survive. In this way the proportion of resistant individuals in the population increases. Repeated selection of resistant individuals will make that every succeeding generation of the pest will have a higher proportion of resistant individuals than the original population. Eventually, after repeated and more intensive use of the same pesticide to the same pest population, the pesticide becomes ineffective. Unfortunately, even under ideal IPM conditions pests can become resistant to pesticides. However, IPM can help in delaying the development of resistance. 

The economic problems

There are two sides to the economics of pesticide use. 

• Direct costs

This refer to buying the products, which requires by the farmers.

• While many argue that pesticides are cheap, they form a major part of the farm inputs.
• Many farmers have become trapped in a dependence on pesticides. By using pesticides they have disrupted natural control, which results in more pests and which leads to more pesticide use.
• Indirect costs

This refers to all kind of expenses related to pesticide use, most of which are paid by the government spending tax payers' money.

• A hidden cost is all the medical costs related to health problems and accidental deaths as a result of pesticide use. 

• Governments spend millions on laboratories for residue testing, laboratories for testing the quality of pesticides, field testing of pesticides, testing of side effects, etc.
• Other costs born by the government include: costs for staff involved in registration, labeling, inspectors for implementing legislation, disposal of obsolete pesticides, cleaning of contaminated sites, etc.
• The import of pesticides requires large amount of foreign currencies.
• The pesticide residue issue is becoming more and more important in world trade. This is a development which is likely to have an adverse effect on the export market for countries that rely heavily on agriculture as a major part of their economy. 

Conclusion

Air pollution has always been with us. Pollution is the introduction of contaminants into a natural environment that causes instability, disorder, harm or discomfort to the ecosystem i.e. physical systems or living organisms. Pollution can take the form of chemical substances or energy, such as noise, heat or light. Pollutants, the elements of pollution, can be foreign substances or energies or naturally occurring; when naturally occurring, they are considered contaminants when they exceed natural levels. Pollution is often classed as point source or nonpoint source pollution.

Pollution became a popular issue after World War II, due to radioactive fallout from atomic warfare and testing. Then a non-nuclear event, The Great Smog of 1952 in London, killed at least 4000 people.

Growing evidence of local and global pollution and an increasingly informed public over time have given rise to environmentalism and the environmental movement, which generally seek to limit human impact on the environment.

Adverse air quality can kill many organisms including humans. Ozone pollution can cause respiratory disease, cardiovascular disease, throat inflammation, chest pain, and congestion. Water pollution causes approximately 14,000 deaths per day, mostly due to contamination of drinking water by untreated sewage in developing countries.

To protect the environment from the adverse effects of pollution, many nations worldwide have enacted legislation to regulate various types of pollution as well as to mitigate the adverse effects of pollution.

Indoor environment is a complex issue in terms of toxicology and health risk assessment. There are many different types of pollutants which may give rise to combined effects. The exposed population is the general public including vulnerable groups.

References

1. Spengler, John D. and Sexton, Ken (1983) "Indoor Air Pollution: A Public Health Perspective" Science (New Series)
2. Ernest Hodgson (2010). "A Textbook of Modern Toxicology
3. US Environmental (July 24, 2007), What is a pesticide? epa.gov. Retrieved on September 15, 2007.
4. Gilden RC, Huffling K, Sattler B (January 2010). "Pesticides and health risks".
5. Report on Carcinogens, Eleventh Edition; U.S. Department of Health and Human Services, Public Health Service, National Toxicology Program (2011).
6. Secretariat of the Stockholm Convention. "Measures to reduce or eliminate POPs" Geneva. Retrieved 12 June 2009.