With global population levels soaring to more than 7 billion,1 it is often taken for granted how the world has been able to sustain such a large population that is increasingly reaching its carrying capacity. While the unequal distribution of wealth does question the notion of a population that is being “sustained,” a more fundamental question of how 7 billion people are being fed leads us to an emerging hot topic that has, to a certain degree, spawned the organic food movement in California. As an agricultural state responsible for generating $43.5 billion in agricultural revenue in 2010 produced by 81, 500 farms,2 the use of pesticides in California and around the world has been key to producing yields capable of feeding a population that is still growing. While there are many arguments concerning the use of pesticides, these arguments are better substantiated with a modern understanding of pesticides and how they are used today.
What are Pesticides
A pesticide can be simply described as any chemical agent used to repel or kill harmful pests,3 but technological advancements within the genetic revolution have further complicated this rather simplistic definition. Increasing activism against pesticides has perhaps acted to over-simplify the perception of pesticides, which are sometimes viewed exclusively in the context of dusting crops. Mosquito repellants, however, responsible for preventing the spread of harmful disease such as malaria and West Nile virus, are other examples of pesticides that been instrumental in saving human lives.
Pesticides are classified into several categories based on the type of “pest” the chemical is attempting to target.4Herbicides, insecticides, and fungicides are the three major categories with the highest usage and market share.5 The general trend in pesticide use has been a reduction in the amount of pesticides used per square area with the advancement of better chemistry that has been able to create more potent compounds. Although the volume of pesticides used is progressively decreasing, there is still an increasing global demand for pesticides such that four (4) pounds of pesticides are used per person annually!6
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The Environmental Protection Agency’s (EPAs) latest estimates from 2007 place pesticide expenditures at a whopping 39 billion dollars globally, with the U.S. owning a near 32%, or 12.5 billion dollars, of the total market share.8 In fact, between 2006 and 2007, there has been an increase in expenditures of around 3.5 billion dollars that illustrates a growing market for pesticides. Therefore, in the chemical industry, pesticides occupy a very special and important niche in the overall market. Quite counter intuitively, the largest pesticide firm in terms of revenue shares history with the production of one of the world’s first pain killers, aspirin. Bayer AG is estimated to control 19% of the market share with Syngenta following very close behind,9 and it is interesting to note that the three largest pesticide companies are European with several of their products banned in the European Union.
Given the constant conversation—mostly negative—going around about pesticides and their impact on human society, it is perhaps a good idea to delve into a discussion of the major types of pesticides used today as well as some of the major discussions surrounding them. Perhaps the best way to understand today’s pesticides, however, is to look at their historical development.
History of Pesticides
The world of pesticides was much simpler a long time ago, and a look into the history of pesticides better illustrates the development trends of these compounds. The first pesticides were sulfur based and identifiably a Chinese concoction dated to 1000BC.10 These early pesticides formed part of a general category of pesticides known as first generation pesticides that usually include heavy metals such as arsenic.
Second generation pesticides, also known as synthetics, were born out of the world of organic and natural chemistry following World War II. Compounds such as rotenone and pyrethroids were identified in various plant species as powerful insecticides that were eventually synthesized synthetically in laboratories for chemical use.11 Pyrethroids still find broad application today as household insecticides that include over 3500 registered products.12 While pyrethroids were first identified in nature and thereafter synthesized in the lab, there are other synthetic compounds that were born directly in the laboratory. Such compounds include certain notorious names such as DDT as well as 2,4D—known as “agent orange” to those familiar with the Vietnam War. While DDT is currently discontinued the United States and European Union due to severe ecological effects linked to bioaccumulation, 2,4D has interestingly found use in the laboratory as an artificial growth regulator in plant cell cultures.13
Today: Third Generation Pesticides
Incredibly, the majority of pesticides used in the United States are actually herbicides, with $5.8 billion in sales attributed to herbicide alone according to the EPA’s latest statistics from 2006 to 2007 estimates.15 The most common pesticides used in the U.S. today come in the form of more potent agents whose delivery may be physical or genetic in nature. The so called third generations of pesticides do not represent a complete evolution from synthetic pesticides. Rather, they highlight a novel approach of using biochemical knowledge to target pests on the molecular level along with delivery mechanisms that have dramatically increased pesticide potency while improving specificity for insects, weeds, and fungi as opposed to human beings. Here is an overview of some of the most important pesticides used today.
- Glyphosate
One of the most common pesticides and herbicides used in the United States is glyphosate, marketed as Roundup by Monsanto. Without going into much technical detail, glyphosate is an inhibitor targeting the shikimate biosynthetic pathway16 in plants that is crucial for the production of important amino acids, electron carriers and growth hormones for plant survival. As a pesticide designed to affect a plant specific molecular pathway, the chemical is relatively safe to wildlife and has even been genetically engineered into plants such that the crop itself can produce glyphosate without the farmer having to physically dust his/her crop. The chemical is poorly absorbed by the human gastrointestinal tract,17 and has a tendency to absorb tightly onto soil particles and tends not to leach into water supplies. The use of glyphosate, however, has been so indiscriminate in recent years that concerns for water supplies being contaminated by glyphosate are quite widespread as large concentrations of glyphosate can lead to kidney damage and reproductive issues.18 While glyphosate is selective for plant species, it is actually a fairly broad use weed killer that is used in everything from corn and soybean to forest plantings and grasses.19 The Safe Drinking Water Act of 1974 grants the EPA the jurisdiction to monitor levels of glyphosate that could be accumulating in the water supply, with revisions in 1994 to account for newer research on threshold contaminant levels for glyphosate.
- Atrazin
contaminating water supplies, and the EPA is conducting numerous studies to assess the levels of atrazine in water as well as the short and long term effects of low concentrations of atrazine. Atrazine specifically operates by targeting and inhibiting electron shuttles in photosystem II of plant chloroplasts.23 Photosystem II is a crucial pathway in plant photosynthesis, and therefore the inactivation of such a pathway interferes with the weed’s ability to fix carbon from atmospheric carbon dioxide and produce glucose. Although the use of Atrazine has become more localized in the mid-west than California, it use still persists as a broadleaf weed killer for crops such as corn and sugar cane. - Neonicotinoids
Neonicotinoids are also a new generation, biochemically targeted pesticide that has recently grabbed headlines as a potential contributor to colony collapse syndrome24 in 28 - BT Endotoxin
One of the major developments in generation three pesticides has been the genetic delivery of chemical agents by programming their production in plants. These modified plants, known as genetically modified organisms (GMOs) have been at the heart of numerous debates surrounding the lack of long term exposure data that could implicate health issues due to the consumptions of GMOs. One of the most popular GMOs in America is Bt-Corn,29 or in other words corn infused with the genetic code to make a bacterial derived toxin that is capable of warding off pests. Bt endotoxin is not only highly effective against a major pest—Lepidoptera larva—but also the genetic engineering of the toxin means that the levels of the toxin are highly controlled by the plant’s biochemical machinery. The risk of over-exposure is greatly reduced, but the consequence is that human beings will consume the endotoxin with the crop itself as it cannot simply be washed off. The toxin has not been determined to be harmful to human beings, since toxins themselves are highly organism selective, and the European Union has not banned this pesticide for use. There are still concerns regarding BT-produced corn, especially since corn derivates are a staple in the American diet and there have been no longer term studies that will validate the toxin’s safety with absolute certainty. Perhaps the idea of being a “genetic” pesticide adds to the fears of food science penetrating a mysterious and fundamental domain of life, but such fears should hopefully mitigate with greater scientific backing and public education.
The Next Generation of Pesticides
As mentioned earlier, there is a major movement underway by consumers to shift away from the abundant use of pesticides given the potential ecological damage and health effects. The next generation of pesticides are appearing to be even less chemical in nature and more biological, and may not even make use of pesticides at all. Let’s take a look at a couple of these options currently underway.
Integrated Pest Management (IPM) is a broad term for a series of practices that are more environmentally sensitive and ecologically informed.30 IPM is multifactorial, and makes use of intelligent monitoring of pest life cycle, pest predators and spatial variables to determine the type of pest control that is most effective in a certain environment. The methodology prioritizes the use of low risk pesticides such as pheromones—hormones that may act to attract pests to specially designed traps—and stresses the use of informed decision making along a continuum of seasonal variations to ensure the smartest regulation of pests within a farm. An example of IPM motivated decision could be the selection of a pest-resistant variety of a crop for planting and perhaps the rotation of certain crops over seasons during times when target pests are least present. Organic production methods fall under the umbrella of IPM, but make use of naturally derived pesticides over synthetic analogs.
RNAi: In the same way that personalized medicine seeks to use genetics to improve the efficacy of treatment, scientists are turning more towards genetics as a means of pest management that greatly reduces the need for artificial chemicals. Many of us are familiar with DNA (Deoxyribonucleic acid), which is essentially the language in which genetic code is written. In other words, our genetic code is composed of DNA subunits, and through various complex mechanisms this code is translated into cellular products that regulate our internal processes. There is another nucleic acid known as ribonucleic acid (RNA) that is involved in the execution of our genetic code, and a special type of effect known as RNA interference (RNAi) is being investigated as a potential means of regulating future pests. The general theory behind RNAi is based off of short segments of ribonucleic acids known as micro-RNAs that work to silence the translation of gene products post-transcriptionally.31 Perhaps in the future, micro-RNAs coded on a DNA vector such as a plasmid could essentially disable critical enzymes within pests. There is, however, a long way to go before such a move becomes a reality as the effective targeting of micro-RNA is still somewhat an art in the world of molecular biology.
The Future of Pesticides
In the 21st century, the gift of chemical and biological knowledge has spawned the production of safer and more potent pesticides around the world. While the use of chemical agents in controlling pests have its potential drawbacks, it is important to underscore the growing need for pest management in the light of current population growth rates. As synthetic agents are being retired around the world in favor of safer and sounder pest management solutions that may or may not make use of pesticides, there is hope that greater research and development is able to minimize the hazards of pesticides and hopefully bring a more positive light on genetically engineered crop that are overall acting to reduce human exposures to pesticides. It is not often discussed that the biggest victim of the conventional chemical pesticide is the farmer and field worker who is in direct contact with these agents at high concentrations for sustained periods of time. The greatest benefit to the people who feed our planet’s mouths is a solution that minimizes risk while broadening the public understanding for emerging science.
