SCOPE 49 - Methods to Assess Adverse Effects of Pesticides on Non-target Organisms

	6.1 OBJECTIVE AND SCOPE
	6.2 THE NATURE OF THE PROBLEM
	6.3 PESTICIDES
	6.4 ECOSYSTEMS
		6.4.1 SOIL
		6.4.2 WATER
		6.4.3 TERRESTRIAL
	6.5 RESISTANCE
	6.6 INTEGRATED PEST MANAGEMENT
	6.7 RISKBENEFIT ANALYSIS
		6.7.1 RISK ANALYSIS
		6.7.2 BENEFIT ANALYSIS
	6.8 SUMMARY AND RESEARCH PRIORITIES
	6.9 REFERENCES

 6.1 OBJECTIVE AND SCOPE

The primary objective of this chapter is to identify the problems, evaluate the methodology available, and indicate priority areas for research required to assess potential or actual adverse effects of pesticides upon non-target organisms (NTO). The breadth and scope of the subject necessitates extensive reliance upon reviews and texts as references for the reader.

NTOs will be taken to mean man, other vertebrates, invertebrates, microorganisms, and plants which are unintentionally exposed to pesticides or toxic derivatives. Voluntary exposure resulting from occupational sources such as manufacture, formulation, and application will not be covered here, because, although the people thus affected are NTOs, their exposure cannot be said to be unintentional; the risk is accepted, and full safety precautions can be followed to minimize exposure (Holden, 1986). Ambient exposures near manufacturing sites, landfills, and sewage treatment plants have been discussed (NRCC, 1982c). Occupational health risks and the problems and errors associated with epidemiological studies have been described (Elwood, 1986; Roberts et al. 1985a). The risks associated with re-entry of agricultural workers to recently sprayed areas have also been amply reviewed (Kahn, 1979; Gunther, 1980; Gunther et al., 1977). Methods for evaluating human exposures to pesticides are dicussed elsewhere in this volume.

6.2 THE NATURE OF THE PROBLEM

The annual worldwide agricultural use of pesticides has been estimated to be of the order of 5 x 10⁶ tons with a value of about $16.3 billion (US) (Helsel, 1987). The same source estimates that some 52 per cent of applied pesticides are herbicides, 26 per cent insecticides, 17 per cent fungicides, and 5 per cent other. Global pesticide use continues to grow, especially in developed countries that account for about 80 per cent of the total use (Helsel, 1987).

Despite the use of pesticides, about 35 per cent of crops are estimated to be lost (Pimentel and Pimentel, 1979). Approximately another 20 per cent of the crops are lost post-harvest. Thus, nearly 50 per cent of food in the world is being lost annually despite all pest control procedures.

It is estimated that less than 0.1 per cent of the pesticides applied to crops reach the target pests (Pimentel and Levitan, 1986). Thus, more than 99 per cent of applied pesticides have the potential to impact NTOs and to become widely dispersed in the environment.

Exposure routes include inhalation, dermal absorption, ingestion, and systemic action through plant surfaces and roots and cell surface of microorganisms. Direct exposures through dietary intake of food or water are of particular concern to all organisms since they cannot be avoided. The young may be at particular risk. Levels of persistent organochlorine compounds in human milk (Jensen, 1983) suggest that suckling vertebrates may be exposed to low levels of pesticides in areas still using organochlorine pesticides. Many third world countries still continue to use DDT and other persistent organochlorine pesticides. Levels in soil and water are of special concern to NTOs confined to these media and thus subjected continually to a pesticide, its contaminants, and its decomposition products.

Acute adverse effects on NTOs are more easily measured and have been reasonably well documented in many cases, albeit mostly through laboratory studies. Regulatory authorities now require such data as part of the registration submission.

The potential for subtle, sublethal effects has been increasingly recognized. These effects are far more difficult to measure, and adequate models for their measurement are lacking. Attempts have been made to use behavioural responses to sublethal levels of pesticides as indicators of potential adverse effects (Beitinger and Freeman, 1983; Peakall, 1985; Haynes, 1988). It is likely that behavioural parameters are sensitive indicators of ecosystem damage, but they are more difficult to investigate than biochemical or physiological parameters. The roles of biochemical indicators and their development and validation as indicators of ecosystem health has been reviewed (NRCC, 1985a). Baseline data from which comparisons can be made are universally lacking. For this reason, it is difficult to determine impacts on communities and populations which are ecologically more significant than effects on a few individuals.

In the `real world', NTOs are subjected to a wide number of pesticides and byproducts together with a larger number of non-pesticide industrial chemicals. This chemical barrage occurs via a variety of routes, at varying levels of exposure, and over most of the life-span of the organism. These chemicals are present in very small quantities, often at the limit of analytical detection. The impact, if any, on NTOs remains to be established and awaits the development of suitable methodology. This problem has been addressed at length in a recent publication which identifies the limitations, methodologies, practicalities, and utility of dealing with chemicals in mixtures (Vouk et al., 1987).

The pesticides themselves consist of hundreds of compounds differing significantly in structure, chemical and physical properties, modes of action, persistence, and toxicity. Thus, the effect of over 600 insecticides, herbicides, defoliants, acaricides, and fungicides on honeybees has been described (Johansen, 1977; NRCC; 1981). The basic active pesticide ingredients are formulated with surfactants, carriers, solvents, and other adjuvants that can affect persistence and toxicity in an unpredicted mannera topic that has not been extensively investigated (Graham-Bryce, 1987; Hartley and Graham-Bryce, 1980; Matthews, 1979).

Pesticides themselves have varying levels of impurities depending on the purity of the starting materials, synthetic routes, and quality control by the manufacturer. Some of these impurities, such as the dioxins and nitrosamines, are extremely toxic to animals. Furthermore, after release to the environment, there may be formed a wide variety of products by a range of mechanisms resulting in materials with toxicities different from the parent compound. Thus, simple cause-effect relationships in the `real world' are virtually impossible to establish, making the findings of much of the control laboratory experimentation at elevated dosage levels of questionable value.

The levels of exposure to NTOs vary considerably over time, ranging from fully registered application rate arising from drift or soil application, to the nanogram or picogram levels usually found by environmental monitoring. These lower concentrations, while usually insignificant to large organisms, are potentially more significant to microorganisms weighing approximately 10^-12g. 

6.3 PESTICIDES

Many compilations of pesticides exist (CPCR, 1986; Reynolds, 1987; Spencer, 1982; Worthing, 1987). Classification of pesticides may be based on structural similarity (e.g., organochlorines, OPs, carbamates, and pyrethroids) or by function (insecticides, herbicides, and fungicides). Structural similarities are convenient, but many compounds do not fit into the main categories. Functional organization is helpful for the user, but may hide the fact that the compound has several activites (e.g, pentachlorophenol is an insecticide, fungicide, defoliant, and a herbicide).

From the point of view of the potential impact of pesticides on NTOs, the mode of action is the most significant parameter. This approach, however, has the difficulty that in most cases the mode of action is unknown in detail, but nevertheless still identifies the potential area of concern for environmental impact on NTOs. In some cases the mode of action is completely unknown. The lack of detailed knowledge regarding the mode of action of most pesticides highlights one of the areas of research requiring intenive effort. Table 6.1 summarizes current thoughts on modes of action but does not detail secondary effects or uncertainties (Coats, 1982; Corbett et al., 1984; Hassall, 1982).

Table 6.1. Illustrations of pesticides and their sites of action

Thus, although primarily used in crop protection, many organophosporus compounds are of low toxicity to vertebrates and are used to control animal pests. Some are too phytotoxic for use on crops but may be fed to cattle to control a variety of parasites (e.g., fenchlorphos).

Unfortunately, laboratory determination of LD₅₀s on a limited number of laboratory species does not usually allow extrapolation of potential effects on other species under field conditions (Moriarty, 1983). Thus the exceptional sensitivity to grain contaminated with carbophenothion of grey geese but not other game birds, pigeons, corvids, rabbits, or rats was discovered after the death of overwintering geese in Britain (Dempster, 1987).

One of the great unknowns in measuring the potential impact of pesticides on NTOs and the environment is the almost complete lack of data on the effect, if any, of the so-called non-active ingredient in formulations. This is not altogether surprising, since laboratory studies aimed at establishing simple causeeffect relationships are much easier to perform using solutions of analytical grade material. Such experiments, while useful to provide clues as to real-world possibilities, are often extrapolated beyond the limits imposed by the experimental conditions and those intended by the original workers.

The primary purpose of a formulation is to improve the efficiency of the pesticide, but in so doing, another large unknown is introduced for NTOs. There are literally thousands of possible adjuvants which may be used, many of them complex mixtures whose composition is not known fully. No information is more subject to secrecy than the composition of pesticides' formulations. It is an accepted maxim in the pesticide industry that no active ingredient can perform more efficiently in the field than its formulated ingredients will allow.

Formulated ingredients may include emulsifiers, dispersing agents or stabilizers, spreading or wetting agents, sticking agents, humectants, synergists, activators, inert mineral carriers, and organic solvents. These adjuvants are used to formulate the active ingredient as dusts, granules, aqueous concentrates, wettable powders, emulsifiable concentrates, and less frequently as aerosols, poison baits, and microcapsules (Hassall, 1982). The use of microencapsulated materials caused massive bee kills, because foraging bees took the capsules back to their hive and stored them in brood frames together with pollen. Thus foraging bees were killed transporting and collecting contaminated pollen; young hive bees were killed by the poisoned food (Aitkins et al., 1978; Johansen, 1977).

In other cases granular formulations, but not the emulsifiable concentrate of carbofuran, have been implicated in bird kills. The potential influence of surfactants on soil and aquatic organisms with regard to the biological availability of the active ingredient is obvious, especially those solvents or surfactants that modify cell membranes and protective coat properties. The degree of impact on both game and useful insects by the fungicide triphenyltin hydroxide has been shown to be greatly influenced by the nature of the formulation (Pieters, 1961). The relative phytotoxicity of solvents has been described (Krenek and King, 1987).

The method of application is also important, since, in the majority of cases, efficiency is poor: most of the formulation is not applied to the target organism, but is lost through drift or fall out. The types of machinery and structure of equipment have been described (Matthews, 1979). High, medium, low, and ultralow volume sprays, and fumigation, each pose a different set of problems for NTOs (Corbett et al. 1984; Hassall, 1982; Vander Hooven and Spicer, 1987). 

6.4 ECOSYSTEMS

To determine the impact of pesticides on NTOs, one must first know much about the ecosystem in which the NTOs exist. Such information is lacking due to the complexity of the problem and the absence of multidisciplinary research teams.

The intended direct impact of pesticide application is the reduction of target pests below economic thresholds. An indirect effect of this treatment is to kill NTOs since by their nature most pesticides are broad spectrum toxicants designed to kill living organisms. Many indirect effects are not measurable as acute toxicity. Thus, biocontrol agents not directly affected by an application may find that their food supply has been either seriously depleted or contaminated with sublethal levels of pesticides. Herbivores feeding largely on weeds may find that their food supply has virtually disappeared. Additionally, sublethal levels of pesticides may continue to exert subtle effects, reducing the ability of the NTO to reproduce, feed, or avoid its predators.

Ignorance of the population dynamics of NTOs and of the interactions with the microecosystem of which NTOs are components make it extremely difficult to predict from laboratory studies the impact of pesticides. Such studies cannot mimic 'real-world' situations and should simply serve to establish priorities for large-scale and lengthy field studies conducted by multidisciplinary teams. Laboratory studies focus on effects on relatively few individuals, usually using pure materials under artificial conditions. Ecological effects occur in populations or communities, necessitating a knowledge of population dynamics.

Some of the problems encountered in studying the impact of pesticides on NTOs in soil, water, air, and forest ecosystems will be briefly discussed. Many publications now adopt the ecosystem approach and identify deficiencies and research priorities (NRCC, 1975b, 1978a, b, 1979, 1983a; Osborne, 1986).

6.4.1 SOIL

Soil constitutes a medium of such complexity and variability that relatively few scientists have attempted to work in this area. It has been stated that on average a temperature zone meadow in mid-summer will have the following population per 100 m²: approximately 150 000 individual plants, several hundred guilds of herbivores and carnivores; diverse populations of insects, birds, and mammals totalling approximately 30 000; above and below ground, 1000 billion bacteria, fungi, algae, and protozoa; and around the plants' roots, a billion nematodes, 5 million microarthropods, 2 million oligochaetes, and 30 000 earthworms (Rhoades and Cates, 1976; Swain, 1977). Much of the communication and interaction between this ecological complex will occur by chemical signals which may be interrupted or modified by the influx of outside chemicals in a pesticide formulation. Attention has been focused on soil microorganisms because of the vital role these organisms play in the recycling of wastes, nitrogen, and carbon. The literature on the impact of pesticides on soil microorganisms is voluminous (Butler, 1977; Edwards and Thompson, 1973; Lal and Saxena, 1980; McCann and Cullimore, 1979; Padhy, 1985; Rajagopal et al., 1984; Tu and Miles, 1976). Ignorance of ecological interaction and population dynamics of soil organisms makes it difficult to achieve definitive conclusions, but attempts to develop ecologically-based `yardsticks' are vital (Domsch et al., 1983).

6.4.2 WATER

The aqueous medium probably has been studied more than any other, due to the relative ease of investigation in the laboratory. This has led to the development of a multiplicity of experimental techniques utilizing static, recirculation, renewal, and flow-through systems. Comparison of results from different workers is virtually impossible, and whether laboratory results can in fact be extrapolated to field conditions is doubtful. These problems are discussed, and the evaluation in the field of the pesticide impact on many pest control projects internationally is given by Muirhead-Thomson (1987).

The behavioural avoidance of fish to sublethal levels of pesticides has been demonstrated (Beitinger and Freeman, 1983) and an evaluation made of the various experimental designs used to examine behavioural responses (Giattina and Garton, 1983).

The impact of pesticides on NTOs in aquatic ecosystems under field conditions has also been the subject of numerous publications and reviews (Hart and Fuller, 1974; Hurlbert, 1975; Hurlbert et al., 1972; Mulla et al., 1979; Mulla and Mian, 1981; NRCC, 1982b, 1983b, 1985b, c, 1986; Smith and Stratten, 1986). The same difficulties discussed under soil apply here, and are just as difficult to resolve. 

6.4.3 TERRESTRIAL

It is impossible to study the infinite variety of complex subsets of the terrestrial ecosystem. Application of pesticides for crop (food and forestry) protection and health purposes covers a wide range of climatic, cultural, social, and economic conditions. The transport and transformations of pesticides in the environment have been reviewed recently (Jury et al., 1987). Of necessity, studies have focused on systems where the greatest impact might be expected on NTOs. Forestry has been the subject of many such studies, because of the large areas involved and of the use of aerial application techniques (NRCC, 1975a, 1977, 1982a; Norris, 1981; Symons, 1977). Pesticides are distributed widely, and organisms in vegetation, forest floor, soil, water, and air are exposed to levels of pesticide not necessarily allowed on food crops. The general impact of pesticides on NTOs in a forest ecosystem is well documented, but again inadequacies in knowledge and detailed understanding of the forest ecosystems' population dynamics and their interactions with climatic factors present do not allow predictions of the impact on NTOs, especially at the sublethal level of exposure.

Because of these deficiencies, Symonds (1977) has suggested that use of bacterial insecticides, such as Bacillus thuringiensis (BT), would be beneficial for NTOs because of its more specific toxicity. However, the field effects of BT on non-target insect populations has been reviewed, and the conclusion reached that the same incomplete picture emerges (NRCC, 1976). Similar studies on the impact of pesticides on a large variety of agricultural food crops have been carried out with essentially the same conclusions, namely the inability to predict the likely impact of an applied pesticide stems largely from our ignorance of the basic ecology of most species, their interactions, and population dynamics. Arthropod community structure complexity in agricultural crops has been reviewed (Liss et al., 1986).

 6.5 RESISTANCE

One of the impacts of pesticides on living organisms has been the widespread development of resistance. Pesticide resistance occurs when some individuals of the target species are no longer killed by the pesticide at the prescribed dosage formerly found to be lethal. Resistance results in higher rates of application to effect control with potentially larger impact on NTOs. Ultimately control breaks down.

 Since the first reported case of resistance to a pesticide (Melander, 1914) there has been an exponential increase in reported cases with a doubling in the number of resistant arthropod species from 1970 to 1980 (Georghiou and Mellon, 1983). Over 432 insect species have been found to be resistant to insecticides, to a total of 829 pesticide groups. Fungicide resistance has also developed with some 90 species resistant to 34 fungicides and bactericides (Ogawa et al., 1983). Herbicide resistance is also slowly developing with the triazines and other classes of herbicides (Lebaron and Gressel, 1982).

While some progress has been made in understanding the biochemical basis of resistance, very little is known about the genetic basis for resistance (Plapp and Wang, 1983; Tsukamoto, 1983). Such an understanding is required before biotechnology can be used effectively. Most of the research on pesticide resistance has understandably been directed at the target species due to the impact this phenomenon has had with regard to increased pesticide use, breakdown of crop and animal protection, and the useful life of new materials which may have limited marketability due to cross resistance, e.g., pyrethroids and DDT.

One effect of pesticides on soil microorganisms has been the acceleration of their ability to degrade pesticides. This rapid breakdown of pesticides may have been confused with resistance problems in some cases, since the results are the same: breakdown in control and increased use of the pesticide. Evidence for this has been accumulating since the early 1970s, and has been the subject of many recent publications (Williams et al., 1976; Read, 1986; Camper et al., 1987).

Increasingly, with the emphasis on integrated pest management (IPM) and biological control, there is a need to know more about mechanisms of resistance in NTOs. It appears that less than 3 per cent of the published literature is involved with NTO resistance (Booth et al., 1983). Pesticide resistance in NTOs that are beneficial insects or other types of biocontrol agents is an obvious advantage, if these agents are to be used in conjunction with pesticides in an IPM program (Hassan, 1987). In the laboratory, attempts to induce resistance to pesticides has usually resulted in failure or, at best, a low level of resistance which regressed rapidly back to the original level within a few generations. In the 1970s, resistance of predatory phytoseiid mites to organophosphorus pesticides was confirmed, and has been utilized in IPM programs. Toxicology and mechanisms of resistance and the application of resistant biocontrol agents in IPM programs has been reviewed by Croft and Strickler (1983).

6.6 INTEGRATED PEST MANAGEMENT

IPM has become a buzz-word with a multiplicity of meanings ranging from intensive monitoring studies of insect pest populations as a prerequisite to pesticides use to a total holistic approach. The latter involves detailed knowledge of the microecosystem of croppestbiocontrolclimatic factors. Such holistic approaches are difficult to organize due both the complexity of the systems being examined and to the difficulty in assembling the multidisciplinary teams required to carry out the long-term research essential to answer the, problems.

Many definitions have been used for IPM. The term was coined some time in the 1950s, although the concept has evolved over thousands of years (Newsome, 1975). Typical of the many definitions used is the following (Flint and Van den Bosch, 1981):

IPM is the use of the best possible combination of methods to reduce and maintain pest populations below a level that would cause economic damage. It is based on a principle of optimum rather than maximum pest control. It constitutes a major component in an agricultural production system which will allow sustained agricultural production with minimal deleterious effects on the producer, consumer, the agrosystem, and the environment in general.

Such a definition leaves open the choice of the `best possible combination of methods', and what would constitute an economic threshold of damage would vary on geographic and market conditions. Most workers agree that pesticides will continue to be used as part of IPM.

One aftermath of the influx of new pesticides available in the 1950s and 1960s was the loss of the IPM approach and the adoption of the philosophy of eradicaton rather than reduction of pest levels to below economic thresholds. More importantly, the concept of the older pest control methods (cultural, biological, host resistance, mechanical, monitoring) were discarded in favour of prophylactic treatment of pesticides with rigid spray schedules that resulted in maximum impact on NTOs, including biocontrol agents, and in the development of resistance.

One of the impacts of the prophylactic use of pesticides is the destruction of the natural abiotic and biotic natural control mechanisms (Brown, 1978; Van den Bosch et al., 1982), many of these controls being insects themselves.

Naturally, these are targets for broad spectrum pesticides and often result in species normally controlled naturally becoming significant pests (MacPhee et al., 1976). Furthermore, destruction of natural biocontrol agents may allow rapid repopulation of target pest populations due to destruction of controlling NTOs by the pesticide treatment. This lack of understanding of the arthropod pest-predator complex often results in outbreaks of non-target pests. Thus use of synthetic pyrethroids against the main pest of apples has resulted in outbreaks of phytophagous mites. This has been ascribed to destruction of natural control agents or sublethal effects on their behaviour (Hull and Starner, 1983; Hull et al., 1985).

Thus the movement towards IPM, while highly desirable and a great improvement over the prophylactic use of pesticides, does not eliminate the need for more extensive research in the following areas:

1. Understanding the total interaction of the components of the pestcrop microecosystem

2. Understanding the basic biology involved in pestbiocontrol systems 

3. Understanding the plantpest system (what differentiates a resistant host from a susceptible one?)

4. Understanding of pest resistance mechanisms

5. Simplified models for determining economic threshold sufficiently rugged to be of universal use.

The development of thresholds used in IPM requires years of research followed by care, use, and fine tuning of operational IPM programmes (Poston et al., 1983). The problems of developed versus developing countries is strikingly different, as are the resources required for IPM implementation.

Although most examples cited under the IPM heading relate to insect pests, it is essential to start developing the knowledge required to consider diseases and weeds as part of the system. Factors involved in the development and implementation of IPM, together with examples, are given in numerous publications (Glass, 1975; Perkins, 1982).

The current emphasis on biological control agents (Caltagirone, 1981) will undoubtedly help to reduce pesticide input into the environment. The use of biocontrol insects in an IPM programme requires differential toxicity studies on the pesticides used to control pests and on their potential impact on the biocontrol agents. Pathogens may, in the long term, prove to be more efficient than insect parasitoids as biocontrol agents (Kurstak and Tijssen, 1982). From the point of view of potential impact on NTOs, however, one would need to have detailed knowledge regarding specificity and factors controlling infection and virulence to target pests. This will undoubtedly add to the problems already being encounterd in the registration of these materials for pest control (Summers et al., 1975).

A recent publication outlines the theory and reviews the practical aspects of IPM implementation (Burn et al., 1987). The editors considered that widespread application of IPM was not possible due to the lack of fundamental understanding of the interactions between pest, crop or animal, climate, and biocontrol agents.

6.7 RISKBENEFIT ANALYSIS

In essence, a risk-benefit analysis is a process whereby a decision may be reached regarding whether the continued use of a pesticide is justified, taking to account the latest information regarding the risk. It is a method whereby existing data and information are organized and analysed. Of necessity, it involves the retrieval of all available data on the material, critical evaluation of the methodology, and verification of the data. Increasingly the process is being used by regulatory officials to reach decisions regarding continued pesticide use. Successful application of the riskbenefit analysis process requires availability of information that is, for the most part, incomplete or completely lacking. Attempting such analyses helps to identify inadequacies in databases and to pinpoint areas of particular concern. The risk assessment and benefit assessment are essentially separate processes carried out independently, and brought together for the final decision process.

6.7.1 RISK ANALYSIS

Generally, it seems to be easier to produce data for risk assessments. Partly, this may be attributed to the registration process which requires toxicological data on NTOs. In addition, the riskbenefit analysis is usually carried out in response to new toxicological or environmental concerns.

Risk analysis is dealt with in numerous publications which deal at length with the problems and processes involved in risk assessment (Lovell, 1986; Ragsdale and Kuhr, 1987; Willes et al., 1985; Tardiff and Rodricks, 1988). The WHO Recommended Classification of Pesticides by hazard has gained wide acceptance, and provides a comprehensive listing of current pesticides based on the technical materials used in formulations rather than the pure active ingredient (WHO, 1988). Data sheets are published on the impact of specific pesticides on NTOs.

While there are many weak areas in the risk analysis of NTOs exposed to pesticides, exposure estimates are one of the most difficult. The need to develop new techniques and approaches and their validation has often been identified. Exposure assessment is based largely on disparate approaches using invalidated and unpublished models. The US Environmental Protection Agency's Science Advisory Board further indicated that `biomarkers' seemed to be a research area of particular promise and was being evaluated by a National Academy of Sciences Committee. Biomarkers are defined as indicators of variation in cellular or biochemical components or processes, and in structure or function in biological systems or samples. Thus, current interest stems in part from advances in the area of biotechnology (Anonymous, 1987). 

6.7.2 BENEFIT ANALYSIS

All too often, this consists of an economic benefit analysis (Krystynak, 1983; Dunnett, 1983; Stemeroff and George, 1983). Health and social benefits, while often apparent, are more difficult to document (Spindler, 1983).

The recent series published by the National Research Council of Canada (NRCC) critically reviewed the riskbenefit process. The NRCC assessed the strengths and weaknesses of available information and processes using case studies of pesticides to evaluate current measures of benefits (Roberts et al., 1985b; Victor, 1985).

6.8 SUMMARY AND RESEARCH PRIORITIES

In summary, research priorities are as follows.

1. To develop an understanding of community population dynamics of the microecosystem being investigated by utilizing a multidisciplinary team approach. This is essential to establish baselines from which effects can be measured over the short and long terms. This holistic, integrated, multidisciplinary approach is essential for ecotoxicological studies requiring extrapolation of laboratory findings to the field.

2. To develop reliable, biological, biochemical, physiological, and possibly behavioural indicators of environmental pesticide impact. This is required to deal with the real-world conditions of varying levels of exposure to pesticides mixed with numerous other potential toxicants, the wide variation of climatic and geographic conditions, and inherent problems with estimation of exposure-time relationships.

3. To expand research into mode-of-action studies including secondary effects. This will indicate where adverse effects may be expected and which particular groups of organisms are particularly at risk.

4. To investigate the impact of non-active ingredients in formulations, of impurities, and of variability of active ingredients, and formulation components.

5. To determine whether causeeffect relationships can be established in the majority of cases.

6. To establish whether sublethal effects are of concernthis again requires knowledge of what we are looking for and the methodology.

7. To carry out more research on the impact of formulation types.

8. To establish whether some particular groups of pesticides merit a more detailed investigation (e.g., chitin-active materials) because of the  potential impact on NTOs (Marks et al., 1982). Impact on the basic photosynthetic mechanism also would be an area of particular concern (Murthy, 1983).

9. To develop a basic understanding of the interactions between pest, crop or animal, climate, and biocontrol agents.

10. To establish the impact of changing agricultural practices (e.g., no-tillage techniques) on NTOs in relation to the increased use of pesticides necessitated by such changes.

6.9 REFERENCES

Anonymous (1987) Exposure estimates seen as weak link in EPA risk assessment. Pest. Toxic Chem. News, Dec. 23, pp. 5-7.

Atkins, E. L., Kellum, D. and Atkins, K. W. (1978) Encapsulated methyl parathion formulation is highly hazardous to honeybees. Am. Bee J. 118, 483-485. 

Beitinger, T. L. and Freeman, L. (1983) Behavioral avoidance and selection responses of fishes to chemicals. Residue Rev. 90, 35-55.

Booth, G. M., Weber, D. J., Ross, L. M., Burton, S. D., Bradshaw, W. S., Hess, W. M. and Larsen, J. R. (1983) Mechanisms of pesticide resistance in non-target organisms. In: Georghiou, G. P. and Saito, T. (Eds), Pest Resistance to Pesticides, Plenum Press, New York, pp. 387-409.

Brown, A. W. A. (1978) Ecology of Pesticides, Wiley-Interscience, New York. 

Burn, A. J., Coaker, T. H. and Jepson, P. C. (Eds) (1987) Integrated Pest Management, Academic Press, London, New York, Sydney, Tokyo, 474pp.

Butler, G. L. (1977) Algae and pesticides. Residue Rev. 66, 19-62.

CPCR (1986) Crop Protection Chemicals Reference (2nd edn), Chemical and Pharmaceutical Press, Wiley, New York, 2030pp.

Caltagirone, L. E. (1981) Landmark examples in classical biological control. Ann. Rev. Entomol. 26, 213-233.

Camper, N. D., Fleming, M. M. and Skipper, H. D. (1987) Biodegradation of carbofuran in pretreated and non-pretreated soils. Bull. Environ. Cntam. Toxicol. 39, 571-578.

Coats, J. R. (Ed.) (1982) Insecticide Mode of Action, Academic Press, New York, London, 470pp.

Corbett, J. R., Wright, K. and Baillie, A. C. (1984) The Biochemical Mode of Action of Pesticides (2nd edn), Academic Press, London, New York, Tokyo, 382pp. 

Croft, B. A. and Strickler, K. (1983) Natural enemy resistance to pesticides: documentation, characterization, theory and application. In: Georghiou, G. P. and Saito, T. (Eds), Pest Resistance to Pesticides, Plenum Press, New York, pp. 669-702. 

Dempster, J. P. (1987) Effects of pesticides on wildlife and priorities in future studies. In: Brent, K. J. and Atkin, R. K. (Eds), Rational Pesticide Use, Cambridge University Press, Cambridge, Melbourne, New York, pp. 17-25.

Domsch, K. H., Jagnow, G. and Anderson, T. H. (1983) An ecological concept for the assessment of side effects of agrochemicals on soil microorganisms. Residue Rev. 86, 66-105.

Dunnett, E. (1983) An economic assessment of the benefits of captan use in Canada. Can. Farm Econ. 18, 31-40.

Edwards, C. A. and Thompson, A. R. (1973) Pesticides and the soil fauna. Residue Rev. 45, 1-79.

Elwood, P. C. (1986). Interpretation of epidemiological datapitfalls and abuses. In: M. Richardson (Ed.), Toxic Hazard Assessment of Chemicals, The Royal Society of Chemistry, London.

Flint, M. L. and Van den Bosch, R. (1981) Introduction to Integrated Pest Management, Plenum Press, New York, 240 pp.

Georghiou, G. P. and Mellon, R. B. (1983) Pesticide resistance in time and space. In: Georghiou, G. P. and Saito, T. (Eds) Pest Resistance to Pesticides, Plenum Press, London, New York, pp. 1-46.

Giattina, J. D. and Garton, R. R. (1983) A review of the preference-avoidance responses of fishes to aquatic contaminants. Residue Rev. 87, 43-90.

Glass, E. H. (1975) Integrated Pest Management. Rationale, Potential, Needs and Implementation. Special Publication 75-2, Entomological Society of America, Lanham, Maryland, 141pp.

Graham-Bryce, I. J. (1987) Chemical methods. In: Burn, A. J., Coaker, T. H. and Jepson, P. C. (Eds) Integrated Pest Management, Academic Press, London, New York, Sydney, Tokyo.

Gunther, F. A., Iwata, Y., Carman, G. E. and Smith, C. A. (1977) The citrus re-entry problem: research on its causes and effects and approaches to its minimization. Residue Rev. 67, 1-139.

Gunther, F. A. (Ed.) (1980) Minimizing occupational exposure to pesticides (research conference and workshop). Residue Rev. 75, 1-183.

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