Human Impacts on Ecosystems - Literature review Example

Pesticides have been known to exist for thousands of years. Sulfur burning was a method used in ancient Sumer as well as ancient Rome for killing insects; the Romans were also known to use salt to kill weed (Wikipedia,2010). In the 1400s, lead, mercury and arsenic were effectively used for this purpose. Similarly, in 1600s, the problem of ants was tackled by the use of a mixture of honey and arsenic. In the later of part of the 1800s, US farmers used various arsenites as well as tobacco derivatives to control pests. The greatest expansion in the pesticides was seen after World War II. Chemicals like DDT, aldrin, diedrin and 2,4 – D came into use due to their low cost and high degree of efficacy (Delaplane, 1996). DDT took the cake as wiping out major portion of vectors responsible for typhus and malaria. Although being in existence since the latter half of 19th century, its true potential was understood in 1939. It was so successful that the inventor Paul Müllen was awarded Nobel prize in 1948 for his achievement. It was not until 1962 when the ground breaking book of Rachel Carson, Silent Spring, made a connection between environment pollution, major health hazards and DDT. Carson (1962) argued that the chemicals like DDT are not only toxic to the insects but to the birds and fish as well. It was proposed that this was because of a direct mechanism as well as an indirect mechanism. After a ban on the use of DDT in the US, the enthusiasm was shifted to production of newer compounds which were safer and better than the conventional ones and methods of crop production that discouraged pests. Integrated pest management (IPM) was introduced as a multipronged strategy to focus on newer crop production methods, increased growth of pest-specific predators and timing of pesticide spray so that maximum damage to the pests could be incurred ultimately increasing the yield (Delaplane, 1996). It is interesting to note that the pesticide consumption has increased dramatically over the last 50 years. As opposed to 2kg/ha in 2004, in 1961, it was just 0.49kg/ha. In one estimate, France and US spray 35% and 20% of their total surface area respectively every year (Goodplanet.info, 2010). In spite of having very potent newer agents, the figures keep on rising. Europe represents almost one third of the world pesticide market share standing at 30 billion dollars a year. North America and Asia constitute a quarter each. US is the leading consumer of the pesticide industry with a figure of 2.5kg/ha. Europe consumes 3kg /ha, while India is at only 0.5kg/ha. In a report by PAN Europe (2007), it was stated that the pesticide consumption was on the rise despite newer agents that act at a lower dose. This shows that the pest control is still dependent on the use of these products. The big question is why they are used? According to a report, approximately one third of the agriculture production is destroyed with the brunt faced by developing countries because of pests. This amounts to a whopping 300 billion dollar annual losses with an average yield loss ranging from 30 to 40% (Plucknett and Kagbo, 2010). More than 1600 types of different pesticides are listed in the Compendium of Pesticide Common Names. These are classified according to their area of action such as Herbicides, Insecticides and Nematicides. Other major categories include Acaricides, Antimicrobials, Attractants, Avicides, Fungicide, Molluscicides, Predacides, and Rodenticides (Wood, 2010). The WHO Recommended Classification of Pesticides by Hazard and Guidelines to Classification 2009, divides these chemical compounds into Class Ia compounds, which are extremely hazardous, Class Ib as highly hazardous, Class II as moderately hazardous, Class III as slightly hazardous and Class U as unlikely to be acutely hazardous based on LD50 for the mice. An important fact worth mentioning is that since there are a huge variety of products available for different types of pests, similarly there is also a tremendous variability in the mechanism of action of these pesticides. One chemical may act at one or more critical cellular pathway of the pest. According to Hayes’ Handbook of Pesticide Toxicology (2010, pp. 106 – 117), this can be explained for a category of a chemical. Insecticides, Nematicides and Acaricides act as Acetylcholine esterase inhibitors or agonists. Some of them also block glutamate gated chloride channels and mitochondrial complexes. A variety of them are ryanodine receptor modulators. Pyrethrum derivatives such as pyrethrins and pyrethroids that act on sodium channels are quick in action. Rodenticides may either form an acute toxin such as phosphine in the stomach of the rodent or cause hypercalcemia. Examples include zinc phosphide and bromethalin. Warfarin may exert an anti-coagulant effect, hence the animal to spontaneously hemorrhage till it dies. Herbicides target plant specific mechanisms. They act on photosystems thereby disrupting the respiration of the weed. They also block amino acid and fatty acid synthesis and can also cause cell membrane disruption. Molluscicides disrupt cellular respiration of snails and slugs. Phasmohabditis hermaphrodita; a pathogenic nematode, is a biological molluscicide. Pesticides, when applied are either adsorbed, may be transferred to some other location or degraded into non-active components depending on the type of pesticide. Adsorption is a process by which these chemicals directly bind to the soil particles. Transfer is the phenomenon by which these compounds are dispersed away from the application site. According to Nebguide (1993), absorption, crop removal, leaching, spray drift and run off. Micro-organisms and plants uptake these compounds by absorption. Mechanisms like volatilization and run off are important as they distribute the pesticides to other location to eradicate the pests but this is not always they case as it is also one of the reasons of environmental pollution. Similarly, spray drift causes these chemicals to be dispersed to other location at the time of application. Leaching is dependent on the water-solubility of the pesticide and can either be downwards, upwards or sideways. Degradation takes place either by, microbial action, sun light or photodegradation or by a chemical reaction (Nebguide,1993). In a study by McBride (1989), it has been postulated that the risk of water contamination is determined by characteristics of the pesticide used, the characteristics of soil and the water volume; A chemical with high water solubility, low soil adsorption, high persistence applied on a coarse and low organic matter soil with shallow ground water and frequent irrigations has a high risk of contaminating water source. In an article by PAN Europe (2010), Belgium, France, Netherlands and UK have highest pesticide contamination in lowland river areas; the annual cost in cleaning up the water resource is around 170 million euros in UK annually with a share of this burden passing on to the consumer. Several techniques can be used to minimize the pesticide pollution. Integrated pest management (IPM) is an excellent way to start with. It involves a holistic approach of selecting resistant plant species, cultivation and scouting to minimize the chemical usage. There should be repeated checks on the crops to measure the pest population before a pesticide attack could be ensued. Crop rotation methods should be employed to discourage the harmful organisms. Educational programs should be encouraged so that all the individuals involved in the process know exactly what they are doing. This can be done by strong media campaigns backed by pertinent legislation. Research into biological and other non-chemical pesticides should be sought for. Pesticide selection should be appropriate and after use disposal according to recommended way. Tanks and reservoirs should never be filled with pesticides while being close to a water reservoir to avoid contamination. Preferably, a water source should be covered to prevent pollution. Detailed weather forecast should be taken into account before spraying to minimize run off and spray drift. The equipment used should be in tip top shape so that there are no leaks and droplet size is appropriate. Muir, PS, 2010, Biology 301 Human impacts on Ecosystems, Oregon State University, Oregon, viewed 21 November 2010, < http://people.oregonstate.edu/~muirp/index.htm> DDT Wiki 2010, wiki article, 20 November 2010, viewed 21 November 2010, Pesticide Wiki 2010, wiki article, 20 November 2010, viewed 21 November 2010, Rachel Carson Wiki 2010, wiki article, 10 November 2010, viewed 21 November 2010, < Wood, A 2010, Compendium of pesticide common names: Classified list of pesticides, viewed 21 November 2010, Goodplanet.info, 2010. Issues: Pesticides, viewed 21 November 2010, Plucknett, DL, Kagbo, RB, 2010. Pest Management: Crop Losses, Use of Agrochemicals, Recent and Future Strategies, Integrated pest management, Azadirachta indica Bacillus thuringiensis, viewed 21 November 2010, < http://www.libraryindex.com/pages/3374/Pest-Management.html> McBride, DK, 1989. Managing pesticides to prevent groundwater contamination. North Dakota State University Extension Service, Publication E-979. Nebguide, 1993. Best management practices for agricultural pesticides to protect water resources, viewed 21 November 2010, < http://www.p2pays.org/ref/20/19700.htm> PAN Europe, 2010. Water Pollution, viewed 21 November 2010, < http://www.pan-europe.info/Issues/Pesticide_Pollution.html> Krieger, R (ed), 2010. ‘Pest Toxicology: The primary mechanisms of pesticide actions’, Hayes’ Handbook of Pesticide Toxicology, 3rd Edition, Elsevier, USA. WHO, 2009. WHO Recommended Classification of Pesticides by Hazard and Guidelines to Classification 2009, viewed 21 November 2010, Carson, R 1962. Silent Spring, Houghton Mifflin, Boston. Delaplane KS 1996. Pesticide Usage in the United States: History, Benefits, Risks, and Trends, viewed 21 November 2010, < http://ipm.ncsu.edu/safety/factsheets/pestuse.pdf> Read More