Environmental Risk and Pest Management
Leon G. Higley
Entomology, University of Nebraska-Lincoln
Considering questions of environmental risk as we take action against pests has become an increasingly important issue. Environmental risk involves technical understandings of risk, public perceptions, and public influence, as well as fundamental questions about the principles and goals for pest management. Although some questions of risk date back to the origins of the concept of pest management, many modern issues are relatively recent developments. This chapter will briefly address environmental risk in pest management and will try to highlight key references that provide more detailed information. One important point to make at the outset is that much work on environmental risk in pest management is ongoing, and many of the issues we will discuss retain considerable controversy and are by no means fully developed.
A key question to be asked is if pest management even needs to address issues of environmental risk. As Perkins (1982) has pointed out in his seminal book, Insects, Experts, and the Insecticide Crisis, the goal of many workers in pest management is to address the needs of farmers. As we consider issues in environmental risk, we must recognize that there can be conflicts between the needs of agricultural producers and the concerns of society in general. Is it part of the explicit goals of pest management to deal with these greater societal concerns on issues like environmental risk? In other words, is pest management only about dealing with pests and maintaining profitability or are other, noneconomic considerations important?
We, like many individuals working, thinking, and writing about pest management, believe pest management must address environmental risk. However, this is not a universally held viewpoint. In our view, goals of pest management include economic sustainability through minimizing the economic impact of pests, ecological sustainability through employing management tactics to minimize selection pressure, and environmental sustainability impact of management tactics on the environment. It is this latter point, of course, that is the focus of these comments, and it seems an important one to make about any technology. While society may be willing to accept some environmental deterioration in association with certain technologies (air pollution associated with generating power and use of automobiles is an obvious example), nevertheless, we would like to have technologies with minimal impacts. Because pest management is a philosophy addressing how we should employ technologies against pests, it follows that minimizing environmental impacts of those methods should be one of our goals.
We will consider this question in more detail, but you should be aware of a number of important references. Pimentel and Lehmen (1993) offer various perspectives on issues of pesticides and environmental quality. Another good book on broader questions of risk and risk perspective is a recent volume by Cothern (1995), which discusses decision making relative to risk perception and ethical implications of questions about risk. Also, the National Research Council (1989) publication Improving Risk Communication is another valuable reference on fundamental definitions of risk.
Our own work on environmental risk and IPM addresses areas including national pesticide policies (Higley et al. 1992), pesticide risk communication (Peterson and Higley 1993), and reducing risk through IPM. Regarding pest management broadly, Pedigo and Higley (1992) and Higley and Pedigo (1993) offer perspectives on improving responsiveness to environmental questions through consideration of the economic injury level. Another approach employing the economic injury level is that of Higley and Wintersteen (1992) in which they present an environmental EIL (which we will discuss in more detail).
These references are only a fraction of the large literature that is available on risk, but they do offer a starting place to begin more detailed investigations. The remainder of this chapter will look at two issues. First, we will consider what exactly risk is and discuss the importance of perceptions on risk in defining risk. Second, we will look at approaches for addressing risk in pest management, and, specifically, we will consider some new proposals (in which we've been involved), such as the environmental EIL.
Risk and Risk Perception
What is risk? Why do public perceptions of risk differ from expert assessments of risk? Is it possible for risk to be an objective measure, or will it always be subjective? In this section, we will address these questions; for a more comprehensive discussion see Peterson and Higley (1993).
Public perceptions of pesticide safety increasingly influence pesticide legislation and regulation. Unfortunately, although public concerns about pesticides do, and should, contribute to the formation of pesticide legislation and policies, perceived risks may contribute to irrational, even counterproductive, regulations (Higley et al. 1992). Misunderstandings about public perceptions of risk and failure to address the key issues of risk perception, are important barriers to consensus about the risks posed by pesticide use.
What is Risk?
Does the number of fatalities associated with a risk solely represent the magnitude of the risk? Some experts would say yes. However, risk assessments usually include broader definitions of risk. For example, is swimming riskier than nuclear power? Yes, if we consider fatalities alone. (Approximately 3,000 people die each year from swimming-related accidents in the United States alone.) But, swimming is not riskier than nuclear power if we consider other factors.
Although definitions of risk vary, most recognize risk as:
R = P * C (1)
where R is risk, P represents the chance or probability of an undesirable event, and C represents the adverse consequences of the event (Lowrance 1980). You might say that risk is a measure of how often something will happen and how bad it will be. Differences in risk perception involve different perspectives on both probability and consequence.
Risk perception research began in earnest soon after the accident at the Three Mile Island Nuclear Power Plant in Harrisburg, PA. Researchers were intrigued that expert estimates of risk from technologies such as nuclear power did not mirror public estimates of risk from the same technologies. Therefore, risk perception research seeks to understand how people perceive risk presented by different circumstances and activities.
The public continually ranks certain risks much higher than experts. Why is this so? According to Slovic (1987), "Lay people can assess annual fatalities [from a given factor] if they are asked to (and produce estimates somewhat like the technical estimates). However, their judgments of `risk' are related more to other hazard characteristics (for example, catastrophic potential, threat to future generations) and, as a result, tend to differ from their own (and experts') estimates of annual fatalities."
Perceptions of Pesticide Risk
Public perceptions of risk from pesticides usually are greater than the risks determined by experimentation. Experts determine risk from pesticides based on empirical estimates of chronic and acute human and animal toxicity and environmental fate. Although in most cases human health risks associated with pesticide use are very low, the public consistently ranks pesticide use as being very risky (Slovic 1987). Indeed, the public perception of risk posed by most synthetic chemicals is inordinately great (Hart and Turturro 1987, Kraus et al. 1992). Too often, people who work with pesticides and have a more complete understanding of the risks often dismiss public concerns as irrational or misinformed. Consequently, many technical people react defensively to public concerns. Even worse, some regard public fears as so irrational that they do not attempt to explain risks and the risk assessment process to lay people. This is dangerous behavior, because the public needs to understand and be involved in pesticide issues to improve the policy making process (Higley et al. 1992).
Responses to public concerns by experts are often inadequate, doing little to seriously address public risk perceptions. A traditional approach has been to respond to public concerns by comparing highly visible, well-understood risks to less visible, less well-understood risks (National Research Council 1989). Some responses have compared the risks from pesticide exposure to the risks presented by everyday activities, such as driving an automobile or riding a bicycle. Although most risk comparison statements by pesticide experts are more accurate than public perception of the risks, these responses do little to correct the public's misconceptions about the unfamiliar risks of pesticide use (Slovic 1987, National Research Council 1989). Most experts fail to consider the criteria the public actually use to evaluate risks.
Although the risks associated with driving an automobile are more serious, the public perceives using pesticides as being much riskier. Why is this so? Researchers recently have explored the mental processes people use to assess risks from many types of modern technologies and activities. This body of research demonstrates that lay people use a different set of criteria than experts for evaluating risk. Specific factors that influence public risk perception include:
- Control - the ability of the individual or society to control the risk.
- Catastrophic potential - the possibility of fatalities or ill effects grouped in time and space as an epidemic.
- Dread - the fear of the possibility of serious delayed effects, such as cancer. Dread is related to catastrophic potential, but the impact does not necessarily need to be grouped in time or space.
- Familiarity - the degree of familiarity lay people have with risk.
- Equity - the equal distribution of risks and benefits throughout society.
- Level of knowledge - the general understanding lay people have with the process or activity posing the risk.
- Voluntariness of exposure.
- Effects on children and future generations - concerns about possible delayed effects on humans and the environment posed by the risk.
- Clarity of benefits - represents the awareness and understanding of the benefits provided by the activity posing the risk.
- Media attention.
- Trust in organizations or institutions.
The public uses these characteristics to judge the acceptability of a risk, rather than using risk estimates based on experiments. Such a view of risk is more encompassing and powerful than simple estimates of mortality. In addressing risk, we should especially consider catastrophic potential, control, level of knowledge, and effects on children and future generations.
One reason the public may view pesticides in food as riskier to their health than the natural carcinogens in common foods and beverages is because consumers have no control over the pesticide content of food. In contrast, people can choose which types of foods they eat, and, therefore, they have a sense of control over this activity. Similarly, people may accept the risks from driving an automobile much more readily than the risks from pesticide exposure, because they have control over the automobile.
The public also will not readily accept the risk associated with a potential catastrophe (Slovic 1987). And yet, catastrophic potential is seldom discussed by the experts. For example, public fear of nuclear power is largely based on vivid images of millions of radiation deaths, massive environmental devastation, and threats to future generations should an accident occur (Slovic et al. 1982). Consequently, the public's perception of risk from nuclear power is far greater than the experts'. More to the point, the pesticide disaster at Bhopal, India, although it was an industrial accident, is a vivid example of the catastrophic potential of pesticides (Shrivastava 1987).
The public views pesticides as having both catastrophic potential and posing a dread risk (Slovic 1987). First, pesticides are feared because of their possible harmful delayed effects such as cancer. Second, the public is greatly concerned about environmental damage caused by pesticide use. It was, after all, Rachel Carson's 1962 book, Silent Spring, documenting the ill effects from pesticide use that sparked the environmental movement. Widespread knowledge of the problems with biomagnification and contamination of groundwater by pesticides and their metabolites, coupled with the reality that pesticides are among the most extensively broadcast synthetic chemicals in the environment, makes dread risk a very real concern to the public.
Coverage of a risk by the mass media can reinforce existing public risk perceptions (Wilson 1991). Media coverage often reveals the dangerous activities that are so pervasive in today's technological world. The mass media provide visual images of risks, enhance the imaginability of a problem, and concentrate on the human aspects (Hart and Turturro 1987, Valenti 1987). The media may also remind the public that they have little or no control over these activities.
The public is unlikely to accept risks from an activity if experts openly disagree over the magnitude and nature of the risk. Indeed, the public knows that experts have advocated the use of pesticides without full knowledge of their potential hazards, DDT being a prime example. The public views pesticides as risky, in part, because of a justified lack of confidence in expert opinion. Once the credibility of experts and government institutions has been damaged, it is very difficult to regain public confidence (National Research Council 1989). To complicate matters further, the public realizes that experts can be found to support any position in a risk argument because attitudes about risk are inherently subjective.
Public perception of risk also is influenced by individual and group goals, values, and politics (National Research Council 1989). Some groups may want to see all pesticides banned; other groups may want less government regulation of pesticides. The goals and values expressed by individuals in these diverse groups will influence their risk perceptions. Similarly, members of society do not equally accept the benefits from a technology (National Research Council 1989).
The understanding, or clarity, of benefits associated with pesticide use also is considered by the public in conjunction with pesticide risks. Where benefits relate directly to questions of risk, for example, accepting one risk (such as pesticides) to avoid a greater risk (such as tick- or mosquito-borne diseases), benefits may have a direct bearing on risk perception. More commonly, discussions of benefits focus on economic impacts or crop yields which the public does not regard to be as important as health or environmental risks (Slovic 1990). Assessing benefits is very much a matter of opinion and because benefits do not directly apply across society, discussions of pesticide benefits are unlikely to quell public concerns about pesticide risks.
Much more risk-perception research is needed, especially as it relates to pesticides. Slovic (1987) eloquently stated that, "Lay people sometimes lack certain information about hazards. However, their basic conceptualization of risk is much richer than that of the experts and reflects legitimate concerns that are typically omitted from expert risk assessments. Each side must respect the insights and intelligence of the other." Unless these valid public attitudes regarding pesticide risks are acknowledged and addressed by experts and public agencies, conflict over these risks seems inevitable.
Addressing Risk in Pest Management
Tactics and Frequency of Use
Historically, two approaches have dominated the question of environmental quality in pest management: frequency of use and choice of management tactic. Regarding frequency of use, many efforts in pest management are directed at reducing unnecessary management action (typically, eliminating unneeded pesticide use). The development of the economic injury level (EIL) and associated economic thresholds (ET) is one clear reflection of this trend (Pedigo et al. 1986). In most cases where the issue has been studied, the use of pesticides is reduced with thresholds. These reductions are a consequence of conservative attitudes toward protecting crops with pesticides. Relative to other costs of production, pesticides often provide relatively inexpensive insurance against catastrophic losses from pests. However, although thresholds have been important in reducing frequency of use, it is not an intrinsic feature of EILs or ETs that necessarily lead to a reduction in use. For example, in situations where a crop is not intensively managed, such as with forages or other low-value crops, the use of thresholds can cause an increase in pesticide use.
The second important way that pest management can address environmental risk is through the choice of management tactic. If we associate most risk with the use of pesticides, then the use of alternative tactics such as host plant resistance, cultural techniques, or biological control, provide more environmentally-friendly alternatives. Sometimes we will use such tactics in combination with pesticides, in which case the use of alternative tactics may impact frequency of pesticide use. (As an aside, it's interesting to note that it was exactly this issue of using biological control in conjunction with pesticides that led to the development of the EIL and ET by Stern et al. .)
Although alternative practices are usually regarded as less risky than pesticides, risk is associated even with these tactics. For example, an increased chance of soil erosion is associated with certain rotational patterns or tillage practices. Similarly, very high levels of an antibiotic factor in a crop can, of themselves, prove to be of risk. (One example of this was the development of a potato cultivar with strong insect resistance but such high levels of alkaloid in the tubers that it was unsafe for human consumption.) Even with biological control, there have been recent arguments about assessing risk to native species from natural enemy introductions (for perspectives, see Caruthers and Onsager , Lockwood [1993a,b]). One problem with the use of alternative tactics is that most of these tactics have to be used in a preventive fashion. One of the outstanding limitations in pest management, particularly relative to finding alternative practices, is that we have few alternatives to pesticides for therapeutic management actions.
One development that does relate to the choice of management tactic for improving environmental quality has been changes in pesticide development over the past thirty years. Since the discovery of the deleterious environmental impacts of DDT and other chlorinated hydrocarbons, there has been a very strong effort to find compounds that not only have good properties with regard to human safety, but also good properties with regard to environmental safety. Environmental safety includes such considerations as effect on non-target species (birds, mammals, fish, etc.) and reduced potential for long-term environmental contamination. In this arena, there have been remarkable improvements in environmental safety. Development of the pyrethroids and some of the new, so-called "biorational compounds" clearly have resulted in chemicals that present much less environmental risk. Ironically, in developing such compounds a conflict arises between desirable properties in terms of affecting pests (such as longevity) versus desirable properties from an environmental standpoint (such as short life in the environment). Nevertheless, the gradual transition in insecticide development toward environmentally safer compounds is a major contribution to risk reduction.
Environmental Risk and the EIL
Can pest management move beyond frequency of use or developing safer tactics to more directly address environmental risk? Pedigo and Higley (1992) have argued that by considering components of the EIL from an environmental standpoint, it may be possible to identify approaches that could be pursued in pest management to try to improve environmental quality. In their original article and a subsequent paper (Higley and Pedigo 1993), they discuss potential approaches. Preferential taxation of pesticides based on environmental risk is one approach they identified, although they note that this would undoubtedly have the potential to reduce proof of producer profitability and therefore runs in conflict to other goals of pest management. Regarding plant response to pest attack, they note that emphasis on improving the ability of plants to tolerate or compensate for pest injury offers the potential for reducing the need for intervention and for providing longer-term solutions to pest management tactics. In reviewing injury per pest, they note that although this has been proposed with respect to medical pests, there seems to be little likelihood that it would be of use for agronomic pests, given that changing the amount of pest attack requires changes in an entire pest population. However, one example that may be useful is with respect to weeds, where there are demonstrations that extremely low concentrations of herbicides can be used to impair the competitiveness of weed species sufficiently to reduce the need for subsequent management action (Mortensen and Coble 1997). A final area they identify has to do with the proportion of the pest population affected by management action. A number of studies suggest that current rates of pesticide use are well in excess of what is actually needed for reliable management, so reduced pesticide rates may be a simple approach that could considerably reduce pesticide loads, provided that pesticides are properly applied.
The Environmental EIL
The Pedigo and Higley arguments regarding environmental quality and the EIL are largely theoretical, in that they have tried to view the EIL as a framework for identifying areas in pest management where efforts might be directly focused on questions of environmental quality. Another, more controversial, approach is to use the EIL itself to address environmental risk directly. Higley and Wintersteen (1992) first proposed this approach, which has a relatively simple premise. Because the EIL relates insect damage to economic costs of that damage, why not include in the economic costs the indirect effect of the pest on environmental quality. In other words, in addition to assigning a cost to crop losses as part of the EIL, why not also assign an environmental cost, which is a reflection of the environmental risk posed by the management tactic.
The central difficulty in such a proposal is establishing exactly what environmental costs would be. As one solution, Higley and Wintersteen proposed a scheme for developing estimates of the environmental costs for different pesticides. Once they have these cost estimates, it is relatively straightforward to reflect costs in an EIL. The procedure Higley and Wintersteen proposed employs a technique called contingent valuation, which has been used by economists to try to put a dollar value on what are called "non-market goods" (goods whose value is not directly estimable). Contingent valuation uses opinion surveys to try to estimate costs. For example, a typical use of a contingent valuation survey might be to ask how much you would be willing to see your taxes increase to clean up a polluted lake. Higley and Wintersteen used contingent valuation to ask field crop producers in the Midwest how much they would be willing to pay to avoid different levels of environmental risk. From these cost estimates, they associated a value with different levels of risk. They went on to define risk by looking at chemical properties of pesticides and the effect of pesticides on a variety of non-target species. Additionally, as part of their survey procedure they also asked field crop producers to define the relative importance of these different areas of environmental risk.
Accompanying this document are examples of data for calculating environmental risks and formulas for calculating environmental EILs themselves on computer spreadsheets.
- Spreadsheet #1 (view as an HTML file or as a Microsoft Excel file): Environmental risk ratings for a variety of insecticides, based on formulated product - Note that these rankings differ from those reported in Higley and Wintersteen (1992), because the Higley and Wintersteen values were for risk based on active ingredient whereas those in the spreadsheet are for formulated product.
- Spreadsheet #2 (view as an HTML file or as a Microsoft Excel file) How environmental EILs can be calculated, and illustration of the range of values seen in these EILs.
To view spread sheets as Microsoft Excel files you must have Excel installed as a helper application in your browser. If you do no have Excel installed on your computer you can download a shareware Excel viewer from Microsoft. Alternatively, save the files to a disk and view using Excel.
To date, the use of environmental EILs has been theoretical, although as estimates are refined they will be made available for pesticide users.
The use of an environmental EIL could potentially reduce frequency of pesticide use in that a less-safe insecticide would have a much higher EIL, indicating that it would only be used when pest populations are larger and therefore more damaging. However, another important potential use of environmental EILs and/or environmental cost data is in pesticide selection. Because it's difficult to differentiate among pesticides based on issues of environmental risk, an index like the environmental EIL provides one way to compare pesticides based on something other than efficacy and cost. Improving procedures to select pesticides based on questions of environmental risk is an important issue, and there is at least one alternative procedure to that proposed by Higley and Wintersteen. Kovach et al. (1992) developed a procedure whereby they rank pesticides based on a variety of criteria (including features beyond those in Higley and Wintersteen), so that pesticide users can select pesticides based upon an environmental risk index.
Some criticisms of both the Higley and Wintersteen (1992) and Kovach et al. (1992) approaches have been made in the literature. Higley and Wintersteen (1997) review these critiques in some detail. Hutchins and Gehring (1993) argue against environmental EILs on philosophical grounds, based on how environmental risks are assessed and costs are assigned. Their arguments rest on the premise that environmental risk is either already considered in the registration process or is so subjective that it would seriously weaken the value of objective decision-making tools. Hutchins and Gehring's discomfort with the subjectivity of environmental risk determinations is common among scientists and represents an important issue in broadening perspectives on risks by experts. A good discussion of this controversy regarding risk perception and subjectivity is provided in Cothern (1995). Another criticism of the Kovach et al. and Higley and Wintersteen approaches is that of Dushoff et al. (1994) who argue that single index methods for evaluating risk are conceptually flawed. In our opinion, this is really more a question of differences of philosophy and opinion about how assessments of risk should be made rather than a legitimate criticism of flawed techniques or other absolute limitations. Higley and Wintersteen (1997) offer a more detailed discussion of the Dushoff et al. arguments.
Much emphasis on environmental quality in pest management will undoubtedly continue to focus on issues of alternative, environmentally-safe tactics. In particular, developing non-pesticidal alternatives and more environmentally benign pesticides will no doubt continue to be emphasized. Nevertheless, we see a broader need for mechanisms within pest management to address issues of environmental safety. In this effort, a variety of approaches are likely to have merit. In particular, looking at aspects of pest management and identifying ways we might change practices to improve environmental safety, as well as developing new tools such as pesticide selection criteria and environmental EILs, are among the most immediate approaches that can be used in this enterprise. Given the many difficulties in implementing IPM programs, many barriers to implementing new techniques (like the environmental EIL or the Kovach et al. index) clearly exist. Nevertheless, because our pest management programs must be responsive to the needs of the general public as well as to individual growers, developing procedures to improve environmental safety in pest management will remain a priority for the foreseeable future.
Disclaimer: "The thoughts, beliefs, and proposals presented do not necessarily represent the consensus opinion of DowElanco or the Agricultural Products Industry."
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Other Suggested Readings
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- Czerwinski, C. & M.B. Isman. 1986. Urban pest management: decision-making and social conflict in the control of gypsy moth in west-coast cities. Am. Entomol. 32(1):36-41.
- Fisher, A. 1991. Risk communication challenges. Risk Analysis. 11:173-179.
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- Rowan, K.E. 1994. Why rules for risk communication are not enough: a problem-solving approach to risk communication. Risk Anal. 14:365-374.