, USES AND EFFECTS OF

Paul C. Jepson Oregon State University

I. Classification and Uses cides. Benefits that include improved yield, crop quality, II. Efficiency and food safety and reductions in vector-borne disease III. Ecotoxicology and Management incidence have driven, and will continue to drive, their use. The earlier synthetic organic compounds were, however, flawed in their environmental behavior. They were persistent, they had a very broad spectrum of GLOSSARY toxicological activity, and they displayed a tendency to be magnified in concentration through food chains, A chemical substance used for controlling, such that damage was inflicted to populations preventing, destroying, or mitigating a pest or- that lived beyond the treated area in habitats that were ganism. not intentionally contaminated. The discovery of some of these limiting impacts was only made possible through technical advances in, for example, analytical PESTICIDES HAVE BEEN IN RECORDED USE since chemistry and conceptual advances where, for example, 1000 B.C. Arsenic was in regular use as a garden insecti- the ability to predict environmental behavior from cide in China by A.D. 900 and chemicals of one form chemical properties only developed after pesticides had or another have protected humans and their crops and been in use for decades. New pesticide discoveries are livestock throughout the development of modern civili- no longer accompanied by the marvel and optimism zation. In comparison with this long time scale, we are that characterized the first synthetic insecticides. Our still in the earliest phases of the use of synthetic organic ability to exploit these materials has, however, advanced pesticides, which were first used over large areas in the considerably in recent years, and the chemicals them- 1940s. There has, nonetheless, been sufficient time for selves are increasingly specific in their impacts and several generations of pesticide chemistry to evolve, appear to pose reduced risks. Scientists still question and pesticides have influenced all habitats and have the value of reliance upon chemical pesticides, however, affected the lives of all their inhabitants over this period. and modern is characterized in general by a cautious approach to their management and use. Set in a volume that will be consulted largely by I. CLASSIFICATION AND USES biologists and ecologists with an interest in biodiversity, this article summarizes the chemicals that are in most Nowhere have the costs and benefits of modern technol- widespread use and outlines the processes that contrib- ogy been more difficult to reconcile than with pesti- ute most to efficient delivery to the biological target. The

Encyclopedia of Biodiversity, Volume 4 Copyright  2001 by Academic Press. All rights of reproduction in any form reserved. 509 510 PESTICIDES, USES AND EFFECTS OF

TABLE I dients in a pesticide formulation include the AI, sol- Classification of Pesticides by the Type of Pest Controlled vents, carriers, surface-active agents, and specialized additives. Solvent choice is determined by the solubility Acaricide Mites, ticks, and spiders of the AI, potential toxicity to target plants (phytotoxic- Adulticide Adult ity), toxicology, flammability, volatility, and cost. Some Algicide Algae solvents are not miscible in water and cause emulsions Arboricide Trees, brush, and scrub to be formed (e.g., xylene), whereas others are selected Avicide Birds because of their ability to dissolve the AI and their Bactericide Bacteria ability to dissolve in water (e.g., isopropyl alcohol). Fungicide Fungi Carriers can include inert clays that disperse the active Plants ingredient through a powder or granular formulation. Insecticide and sometimes related pests, Surface-active ingredients are used to assist in the pro- including mites cess of emulsion formation (the dispersion of the pesti- Ixodicide Ticks cide liquid within the liquid diluent), but they also Larvicide Insect larvae include wetting agents (materials that reduce surface Miticide Mites, ticks, and spiders tension and enhance wetting and coverage of surfaces), Molluscicide Mollusks, such as slugs and snails dispersing agents (materials that maintain the emulsion Nematicide Nematodes as microscopic droplets within the diluted formula- Ovicide Invertebrate eggs tion), and spreading agents (materials that enhance cov- Piscicide Fish erage of waxy plant foliage and insect cuticles). Predacide Vertebrate Predators The pesticide formulation may be in solid (i.e., Rodenticide Rodents, including rats and mice powder or granule) form, or it may be a liquid or gas Silvicide Trees, brush, and scrub concentrate. Modern pesticides may achieve their Termiticide Ants and termites intended effects at rates of less than 10 g per hectare (10,000 m2 ϭ 1 ha), and the formulation blend enables these tiny quantities to be distributed evenly over the intended target surface. nature and importance of toxicological and ecological A two-letter code denotes the formulation type on all effects are then reviewed, followed by a summary of pesticide labels, and this is a fundamentally important procedures through which pesticides are regulated and aspect of the selection of a pesticide for a particular managed. This article does not provide detailed reviews use. There are four groups of formulation types: of biochemical mode of action, application, formula- tion, or environmental fate and behavior in any detail, • Group 1: Concentrates for dilution in water, includ- and readers are recommended to pursue some of the ing DC (dispersable concentrate), EC (emulsifiable literature in the bibliography to gain insight into these concentrate), SC (suspension concentrate), and WP important areas of pesticide science. (wettable powder) • Group 2: Concentrates for dilution with organic sol- A. Uses of Pesticides vents, including OL (oil-miscible liquid) and OP (oil-dispersable powder) Pesticides may be classified by the types of pest they • Group 3: Formulations to be applied undiluted, in- control (terms often bearing the suffix-cide; Table I) or cluding GR (granules) and UL (ultra-low-volume by the effects that they have upon the pest organism (ULV) liquids) (terms that do not bear the suffix-cide; Table II). • Group 4: Miscellaneous formulations, including RB (bait) and AE (aerosol dispenser) B. Classification of Pesticides 1. Formulations Pesticides are marketed in complex mixtures, or formu- 2. Pesticide Types lations, containing the pesticide chemical itself, the ac- Pesticides are characterized by their chemical diversity tive ingredient (AI), and additives that enhance mixing also. The summary below includes many of the most and dilution in water or oil and release or deliver the important groups of chemicals used in crop protection, toxic material once it has been applied. Common ingre- but it is not exhaustive. Some pesticide properties are PESTICIDES, USES AND EFFECTS OF 511

TABLE II Classification of Pesticides by Effects on Pests

Antifeedant Inhibits feeding while insects remain on the treated plant Antitranspirant Reduces transpiration Attractant Lures pest to a specific location Chemosterilant Prevents reproduction Defoliant Removes foliage without immediately killing plant Desiccant Causes plant parts to dry Disinfectant Destroys or inactivates harmful organisms Feeding stimulant Causes vigorous feeding Growth regulator Stops, speeds up, or retards growth in insects or plants Repellent Drives away pests without killing them Semiochemical Pheromones and other substances emitted by plants or that alter animal behavior Synergist Substance that enhances the effects of a pesticide

sufficiently uniform within the major classes of chemi- toxicity. Some have adverse effects on wildlife, includ- cals for this broad classification to be used in selection ing toxicity to fish. Examples include neem tree (Azadi- of chemicals for a particular use. Biochemical mode of racta indica) oil, which is used to protect stored prod- action, for example, tends to be similar within major ucts from insects; pyrethrum, from Chrysanthemum classes, and many crop protection programs use materi- cinerariaefolium, a powerful but rapidly degraded insec- als from several classes to avoid excessive selection ticide that affects the peripheral nervous system, caus- pressure for resistance to pesticides. Other properties, ing paralysis, known as ‘‘knockdown’’; nicotine (from are, however highly variable within pesticide classes as Nocotiana tabacum), an alkaloid insecticide that is also well as between them. These include vapor pressure a neuromuscular poison in vertebrates; and rotenone, (volatility) and the various partitioning coefficients that from the roots of Derris and Lonchocarpus spp., also determine the distribution and fate of the active ingredi- used as a piscicide. Some of these materials are widely ent in the environment. These properties determine the used in locally made or commercial formulations, and effectiveness of the pesticide against a specific target although they may be highly toxic, many are not persis- or in a specific climate type or habitat, and detailed tent in the environment and degrade rapidly in sunlight knowledge of these properties is required for pesticide or when exposed to microbial activity in soil or water. selection to be effective. Some aspects of properties will Each material has unique properties, and it is not possi- be dealt with in Section II. ble to make generalizations about toxicology or envi- ronmental impact. 3. Major Classes of Insecticides ii. Organochlorines Organochlorines are synthetic a. Inorganic pesticides, among the first to be developed. Early materi- These are mainly nonvolatile and water-soluble com- als, including DDT, had dramatic early successes in vec- pounds that often have high mammalian toxicity and tor-borne disease control, but most have adverse envi- may also be cumulative poisons. Many are now discon- ronmental impacts, resulting from persistence in the tinued or banned. They include materials such as boric environment, accumulation through food chains, global acid, copper sulfate, mercurous chloride, and sodium redistribution of residues, and ecotoxicological impacts. arsenite. Many organochlorines are now banned internationally. Examples include diphenyl aliphatics (DDT, dicofol, b. Organic methoxychlor), benzene derivatives (HCH, pentachlo- i. Botanical These pesticides are derived from rophenol), cyclodienes (chlordane, endosulfan, endrin), plant materials, some of which have low mammalian and polychloroterpenes (camphechlor). 512 PESTICIDES, USES AND EFFECTS OF

iii. Organophosphates Organophosphates, or OPs, mum flowers. They have similar toxicological proper- are esters of phosphoric acid. Many have high mamma- ties but tend to be much more photostable and lian toxicity and may require frequent application persistent. Natural pyrethrins occur in mixtures of six because they are generally not persistent. Organophos- esters, and resistance is rare in the insects that they are phates are nerve poisons, acting through inhibition used against. The synthetic pyrethoids are generally of cholinesterase. The fall into three groups: (1) marketed as a single ester, and resistance may develop Aliphatic organophosphates, which are the oldest rapidly. Pyrethoids are generally of low mammalian group, some with low mammalian toxicity (e.g., mala- toxicity but are highly toxic to fish and bees and benefi- thion, which has been in use for 40 years) but others cial predatory or parasitic invertebrates. Pest resur- having high mammalian toxicity, but short persistence. gence, or population outbreaks that result from the Short persistence makes many OPs of use in short- destruction of natural enemies, may occur in certain season crops, where the plant or the consumer has crops. Examples include allethrin, bioresmethrin, a low tolerance for pests (e.g., vegetable crops). Exam- cyfluthrin, deltamethrin, and permethrin. ples include, acephate, dichlorvos, dimethoate, mala- thion, and phorate. (2) Phenyl organophosphates, ix. Fumigants Fumigants are insecticides that kill which are more stable and persistent but which include by vapor or gas action, have low molecular weight, and materials with high mammalian toxicity. Examples often contain halogen radicals. They can be highly toxic include fenitrothion, methyl parathion, and temephos. to vertebrates, particularly in enclosed spaces. Exam- (3) Heterocyclic organophosphates, which may be ples include chloropicrin, ethylene dibromide, and more persistent and active in soil. Examples include methyl bromide. azinphos-methyl, chlorpyriphos, phosmet, and pyra- zophos. x. Petroleum Oils Petroleum oils, also known as mineral oils, have insecticidal properties. Light applica- iv. Carbamates Similar to organophosphates, car- tions of refined paraffin oils can be made to trees in bamates are esters of carbamic acid, with short residual leaf. Lower viscosity, semirefined oils can be applied life and a wide spectrum of activity. This group also to dormant trees in winter to kill invertebrates and includes some and fungicides. Some of the their eggs. pesticides with highest mammalian toxicity are carba- mates. Again, they divide into three groups: (1) Methyl carbamates with a phenyl ring structure, including car- xi. Antibiotics One antibiotic, abamectin, derived baryl and methiocarb; (2) methyl and dimethyl carba- from Streptomyces, is an effective insecticide and anti- mates with heterocyclic structures, including aldicarb parasitic agent also in veterinary use. There is evidence and methomyl; and (3) methyl carbamates of oximes, that when used in cattle, it can harm dung-feeding having a chain structure, including bendiocarb. invertebrates. It has some systemic properties (i.e., it can penetrate leaves and be carried within the plant v. Formamidines Formamidines are used as insec- vascular system). ticides and acaricides, have the characteristic nitrogen structure –NuCHN–, and are effective against the eggs xii. Semiochemicals Semiochemicals are behavior- and larvae of (butterflies and moths). They modifying compounds, including pheromones, particu- are useful alternatives to organophosphates, where re- larly the sex attractants of female moths. These may sistance has developed. Examples include amitraz. attract male moths for monitoring or be dispersed by spraying or formulation into controlled-release devices vi. Dinitrophenols Dinitrophenols are broad-spec- to establish false trails and disrupt mating of pest spe- trum insecticides that have two nitro groups (NO2) cies. These compounds have very low environmental attached. Examples include binapicryl and dinocap. hazards, and the development of resistance is rare.

vii. Organotins Organotins are tin-based organic xiii. Insect Growth Regulators Insect growth regu- compounds that act as acaricides and fungicides, some lators are compounds derived from, or inhibitory to, with long residual activity. Examples include cyhexatin. insect hormones and include methoprene, a juvenoid or juvenile hormone mimic, effective against mosquitoes, viii. Pyrethroids Pyrethroids are synthetic com- and diflubenzuron, which disrupts the synthesis of chi- pounds based upon pyrethrins, found in chrysanthe- tin and kills insects when they molt. PESTICIDES, USES AND EFFECTS OF 513

xiv. Microbials Included in this group are bacterial b. Organic agents, particularly Bacillus thuringiensis, which is used Organic fungicides have the reputation of being safer against Lepidoptera, Diptera, and Coleoptera. A pro- and less persistent than some of their inorganic counter- teinaceous inclusion or endotoxin, which constitutes parts, and they are often used at very low doses. 40% of cell weight at sporulation, breaks down in in- sects with alkaline midguts to an active protoxin. This category also includes fungal diseases of insects, includ- i. Dithiocarbamates Dithiocarbamates are deriva- ing Beauvaria bassiana, Metaryzium anisopliae, and Ver- tives of sulfur-containing dithiocarbamic acid, in com- ticillium lecanii, some of which can be formulated and bination with zinc salts, ferric salts, and manganese sprayed like conventional insecticides. Some viral salts. These fungicides have greater efficacy, better sta- agents are also used on a large scale, including nuclear bility, and less phytotoxicity than elemental sulfur. polyhedrosis viruses (NPV) of Lepidoptera. Microbial Their toxicity derives from the formation of the isothio- u u insecticides tend to have very limited effects on organ- cyanate radical (–N C S–) in breakdown. Com- isms that they do not directly parasitize, and vertebrate pounds in this group include thiram, maneb, metham- effects are almost unknown. sodium, and zineb.

xv. New Insecticides A series of new insecticides ii. Organometallics This group of fungicides in- belonging to several previously unexploited classes of cludes the following: (1) Mercury compounds, formerly chemistry have been introduced in recent years. Some popular for disinfective and protective action as well of these pose greatly reduced environmental risks, al- as volatility. They have high mammalian toxicity and though this does not apply to all of the newer materials. are no longer available for any purpose. (2) Organocop- These include imidacloprid (in the class chloronicoti- per compounds, including copper acetate, which was nyls), a highly systemic pesticide that is now used on first synthesized in 1899. These fungicides are not easily a very wide scale. Research on these newer insecticides washed off leaves, being insoluble in water, and give is limited at present, but there is optimism that ecologi- persistent protection. They act by the nonspecific dena- cal impacts and risks to wildlife will be greatly reduced turing of proteins. Examples include cuprobam. (3) as they become more widely used. Organotins, triphenyltin salts, including fentin, which 4. Major Classes of Fungicides can be both toxic and phytotoxic. a. Inorganic Inorganic fungicides are derived from sulfur or simple iii. Substituted Aromatics These compounds in- metal salts. They are generally stable, persistent, and clude derivatives of benzene and phenol, with hydrogen insoluble in water. They include sulfur, which was orig- atoms replaced by chlorine, nitrogen, and oxygen, and inally applied as flowers of sulfur, in dust form, and are suited for seed treatment and control of soil-borne which is still used, but in a more highly ground colloidal fungi. Examples include chlorthalonil and pentachloro- suspension. It has both direct contact and fumigant phenol (PCP). activity at temperatures above 20ЊC, but above 32ЊC the vapor may cause phytotoxicity (toxic harm to the iv. Dicarboximides Also called sulfenamides, these target plant). Environmental damage and toxicological compounds are considered to be among the safest pesti- impacts to nontarget organisms are otherwise limited. cides in seed treatment and protectant sprays. Examples Copper-based fungicides include Bordeaux mixture, an include iprodione and vinchlozin. early fungicide that consists of a solution of copper sulfate and hydrated lime. With 12% copper, this fungi- v. Phthalamides Phthalamides are used as nonsys- cide has low mammalian toxicity. A more stable form temic, broad-spectrum, foliar fungicides on fruit, vege- of copper (e.g., copper oxychloride) is used in modern tables, and ornamentals. Examples include captafol and formulations, enabling the slow release of copper into captan, which is used widely in the tropics, but increas- leaf surface water film and toxic buildup in fungal tis- ingly subject to restrictions. sue. Other inorganic fungicides have included heavy- metal-containing materials that incorporate mercury, zinc, nickel, or chromium. These are normally highly vi. Dinitrophenols These nonsystemic fungicides toxic and persistent, and they have been banned inter- are used against powdery mildew and include the com- nationally. pounds binapacryl and dinocap. 514 PESTICIDES, USES AND EFFECTS OF

vii. Triazines This group consists mainly of herbi- viii. 2-Aminopyrimidines This small group of sys- cides, with anilazine as the only fungicide, used as a temic fungicides has activity against powdery mildew protectant treatment in vegetables. and includes bupirimate. c. Systemic Compounds ix. Quinones This group includes benodanil and These fungicides are absorbed and translocated through futonil. plant tissues and provide longer term, protective con- trol, with some curative and therapeutic effects for plants that are already infected. There are many groups, x. Other Organic Fungicides A number of impor- some of which are summarized below: tant fungicides do not belong to the groups above, but comprise a random selection of compounds with unre- i. Oxathiins Oxathiins control basidiomycete lated chemical structures. They include chlorothalonil, fungi and include the compounds carboxin and meth- dodine, guazatine, and thiocyclam. Most are nonsys- furoxam. temic, protective fungicides.

ii. Benzimidazoles and Thiophantes Benzimidaz- 5. Major Classes of Herbicides oles and thiophantes are broad-spectrum fungicides and Herbicides kill or interrupt the growth of plants. Some are widely used in the tropics; intensive use has often are selective, but others kill all plants that come into led to resistance. Some of these compounds replaced contact with them and are used in industrial settings organomercury fungicides as seed dressings. They in- and in rights-of-way maintenance. clude benomyl, carbendazim, and thiabendazole.

a. Inorganic Herbicides iii. Pyrimidines Included in this class of com- pounds are bipirimate and ethirimol. This class includes mostly salts that have been in use for a considerable time. Sodium arsenite solutions and arsenic trioxide were popular in the 1960s but are now iv. Acylalanines This class of compounds in- banned. This class also includes iron and copper sul- cludes metalaxyl. fates, which are used for foliar application. Sulfuric acid has been widely used in horticulture and cereal crops v. Ergosterol Biosynthesis Inhibitors (EBIs) Er- as a selective herbicide. These materials are water solu- gosterol biosynthesis inhibitors are a heterogeneous ble and readily leach from soil. Further examples in- group of compounds with a common mode of action. clude sodium salts of boric acid (borates) and so- They can have systemic, protective, and curative prop- dium chlorate. erties. They include (1) imidazoles (e.g., imazalil and prochloraz), (2) piperazine, pyridine, and pyrimidine b. Organic Herbicides compounds (e.g., pyrifenox and triforine), (3) morpho- lines (e.g., dodemorph and tridemorph), and (4) i. Organic Arsenicals These materials are much triazoles (e.g., flutriafol, myclobutanil, and propo- less toxic to mammals than inorganic arsenic salts. They conazol). inhibit metabolism, competing with phosphate in es- sential reactions. These compounds include disodium methanearsenate (DSMA). vi. Organophosphates Organophosphates are a group consisting mainly of neurotoxic insecticides but also include fungicides such as pyrazophos. ii. Phenoxyaliphatic Acids Herbicides in this group are a series of compounds in which the phenoxy nucleus vii. Phenylamide and Other Fungicides against Oo- is linked with acetic, propionic, and butyric acids. Solu- mycetes This is another heterogeneous group, sharing bility in water is high relative to that of many herbicides. the property of toxicity to oomycete fungi. High speci- They have selective, hormone-type effects on broad- ficity and systemic activity help to confer resistance leaved weeds, but grasses are tolerant. 2,4-D, 2,4,5-T, when used intensively. Included in this group are (1) and MCPA were immensely popular and once regarded phenylamides (e.g., benalaxyl and metalaxyl) and (2) as safe. In the 1970s, dioxin contamination was sus- the compounds cymoxanil and prothiocarb. pected in 2,4,5-T and its registration was canceled. PESTICIDES, USES AND EFFECTS OF 515

iii. Substituted Amides This is a large group of or- Metham sodium is a soil fumigant, converted in the soil ganic nitrogenous herbicides, including amides and ani- to methyl isothiocyanate. Examples include diallate, lides. Amides primarily act in soil against annual grass metham sodium, and thiobencarb. weeds, causing stunting. They have low mammalian toxicity and include chlorthiamid and propyzamide. ix. Heterocyclic Nitrogens These compounds have Anilides, which have numerous subgroups, are used in a ring structure where the carbon atoms are replaced by postemergence grass and broad-leaved weed control as nitrogen or sulfur. They include triazines, triazinones, wells as in preemergence compounds to control germi- triazoles, pyridines, and uracils. Triazines are a very nating weeds and grasses. All have low mammalian selective group of compounds; selectivity depends upon toxicity (e.g., and ). the plant’s ability to metabolize the AI. They are soil applied and absorbed through roots, inhibiting photo- iv. Diphenyl Ethers These compounds possess two synthesis once the plant has emerged. Mammalian tox- benzene rings, joined through oxygen or a more com- icity is generally low, and intense application in some plex chain of molecules. They include preemergence areas has led to groundwater contamination and restric- and selective postemergence compounds of low mam- tions upon use. Examples include and sima- malian toxicity. They are fairly insoluble in water, do zine. Triazinones have six-membered rings and include not leach, and may be persistent for several months. hexazinon. Triazoles, with a five-membered-ring struc- Examples include diclofop methyl and oxyfluorofen. ture, are active against broad-leaved weeds (e.g., ami- trole). Some pyridines are effective against deep-rooted v. Dinitroanilines Dinitroanilines are the most herbaceous weeds, and others are selective brush killers widely used group of herbicides in agriculture. They (e.g., and trichlopyr). Uracils, another substi- have a dinitroaniline nucleus in common and are effec- tuted, six-membered-ring family of chemicals with two tive against annual grasses and broad-leaved weeds nitrogen atoms and a double bond, are primarily for when applied preemergence. Degradation occurs preemergence application and uptake by roots. They through volatilization and photodecomposition. Mam- are effective at controlling annual grasses and broad- malian toxicity is low, and in soil persistence can be leaved weeds over an extended period by inhibition of quite long. This class of compounds includes benflura- photosynthesis. Uracils may be very persistent. Exam- lin and trifluralin. ples include bromacil and lenacil.

vi. Substituted Ureas Based on the simple nitro- x. Bipyridiliums, Also Termed Pyridines Con- gen-containing molecule urea, the first example, mon- taining two pyridyl rings, this group includes some uron, was discovered in the 1950s as a total herbicide. extremely well known and widely used compounds More modern compounds are used as selective, pre- (e.g., and ). They have contact action emergence herbicides that are strongly adsorbed to soil. on the above-ground parts of plants and in the plant They inhibit photosynthesis, causing chlorosis. These they are reduced to free radicals that destroy tissue compounds have low mammalian toxicity and their under light. They are widely used as desiccants. These efficacy is influenced by temperature, rainfall, and soil compounds are deactivated by sorption to the soil and type. Examples include chloroxuron, diuron, isopro- slow to degrade, leading to increasing restrictions. Both turon, and . AIs are hazardous, being the main cause of pesticide- related death in many countries. There is no known an- vii. Carbamates In addition to many insecticides tidote. and fungicides, a number of herbicides have been devel- oped from this chemical group. They include pre- and xi. Aliphatic Acids This group includes chlori- postemergence materials that inhibit germination and nated derivatives of acetic acid, trichloroacetic acid cell division. They have low mammalian toxicity and (TCA) and dalapon. These compounds are used on non- short persistence. Examples include and phen- cropland and in forestry, killing the plant by causing medipham. precipitation of proteins within cells.

viii. Thiocarbamates The thiocarbamates are a xii. Phenol Derivatives Herbicides in this group group of carbamates containing sulfur, including selec- are highly toxic, selective, foliar herbicides and include tive pre- and postemergence compounds. The -allate dinitrophenols and one chlorinated phenol, pentachlo- compounds may persist for many months in soil. rophenol. Dinitrophenols, primarily contact herbicides, 516 PESTICIDES, USES AND EFFECTS OF

TABLE III Utilization Efficiency of Pesticidesa

Utilization Pesticide Method of application Target organism efficiency (%) Explanation

Demeton-S-methyl Foliar spray Aphids on sugar beet 0.000008 Insects located in heart leaves, an effective refuge from direct spraying Dieldrin Seed treatment Wheat bulb fly larvae 0.0015 Pests less likely to encounter seed as plant develops Dimethoate Foliar spray Aphids on field beans 0.03 Relatively low efficiency of spray retention by plant Lindane Foliar spray Capsids on cocoa 0.02 Pesticide losses due to drift when treating large trees Lindane/dieldrin Aerial spraying Locusts 6.0 Pesticide applied by aircraft within swarm, of swarms maximizing chance of contact

a From data summarized by Graham-Bryce (1977): Graham-Bryce, I. J. (1977). Philos. Trans. R. Soc. London, B 281, 163–179.

inhibit respiration and photosynthesis (e.g., infestations ensue, and pests are few in number or (DNBP), DNOC) and are now banned in the United widely dispersed. It is generally agreed, however, that States. Pentachlorophenol is now being banned in Eu- there is considerable scope for improvement in the effi- rope and the United States. ciency of pesticide delivery, through attention to appli- cation, formulation, and the optimum delivery of the xiii. Benzonitriles or Substituted Nitrites These AI through attention to the physicochemical properties compounds consist of a benzene ring with a cyanide of the compound. The interaction between the pesticide (CIN)- radical and are broad spectrum, acting on vari- and organism that leads to chemical exposure and up- ous processes of growth and tissue disruption (e.g., take is termed bioavailability. The term availance de- dichlobenil and ioxynil). scribes the profile of chemical concentration over time, a function of physicochemical properties, transfer, and xiv. Miscellaneous Herbicides Herbicides with un- sorption within the treated environment. related chemical structures include some widely used materials such as endothal sodium, an aquatic weed killer, , a nonselective, residual, postemer- gence herbicide, and alloxydim sodium, fluazifop-butyl, A. Delivery and Bioavailability and other selective, postemergence systemic herbicides, The toxic effects of a pesticide against any intended used against perennial and annual grasses. target or unintended nontarget organism are a function of intrinsic toxicity (the activity when it is directly applied to the organism) and the amount that reaches II. EFFICIENCY the organism under the conditions of application. The amount that the organism is exposed to depends upon Ideally, the receiving organism receives a toxic dose of placement (which is a function of application method), pesticide and nontarget organisms escape injury, pattern of release (a function of the formulation), redis- achieving high efficiency of use. Efficiency is, however, tribution and transfer processes (a function of the physi- very rarely measured. When it has been, efficiency is cochemical properties of the pesticide, environmental far from ideal when expressed as the proportion of the conditions, and the nature of the substrate), and the applied dose taken up by the target organism or the location and receiving characteristics of the organism. amount needed to directly combat an infestation by The latter is a function of the degree of contact or treating it directly (Table III). avoidance of the chemical, the activity of the organism What should our expectation for efficiency be? High in question, and, on a large scale, the spatial dynamics efficiency can-not be expected in all circumstances. For of the organism as it relates to the pattern of treatment example, many applications are made before serious and the persistence of the chemical. PESTICIDES, USES AND EFFECTS OF 517

B. Application, Formulation, and Delivery of the volume contains drops with a diameter less than the VMD, and the other half contains drops of the Toxic Dose with a diameter greater than the VMD. Through application and formulation, it is possible to • Number median diameter (NMD): If the drops are manipulate the placement, size, and composition of divided in half by number, independent of volume, the discrete units or drops of pesticide in which it then the diameter of half of the drops is larger than is dispensed and the rate of release from those units the NMD, and the diameter of the other half is or particles. smaller.

1. Soil Treatment The NMD : VMD ratio indicates the spread of drop Some of the most difficult challenges relate to the prob- sizes: the larger the ratio, the broader the spectrum. If lem of delivering sufficient pesticide to small targets the ratio approaches 1, the drops are all of a similar distributed in a bulk medium in which mobility is re- size and behave in a similar way. stricted and the chemical subject to rapid degradation. Conventional spray application through hydraulic It is therefore important to localize the pesticide to the nozzles presents a major challenge for optimization of vicinity of the target and plant part that needs protec- pesticide use efficiency, and their widespread use ac- tion. For example, granular formulations and seed treat- counts for a great deal of pesticide drift and off-target ments can both be used to increase efficiency of transfer exposure and contamination. Table IV provides details of pesticide to organisms in the soil. Once applied, the of the drop spectrum from a conventional fan jet hy- chemical must move into the soil matrix and the rate draulic spray nozzle. Drops of between 1 and 50 Ȑm of release determines the concentration in the soil. Dif- in diameter account for only 4.2% of the volume, but fusion and redistribution can be achieved by bulk flow 90.8% of the total drops in the sample. In addition, of water moving down through the soil profile after 61.9% of the volume of the spray liquid is in drops of rain or irrigation. Contact between the water network greater than 160-Ȑm diameter. In 1 liter of spray liquid, in soil pores and the coated seed is very important. this would yield nearly 90 million drops with a diameter Efficiency, or the toxicity of soil-applied AI per unit of less than 50 Ȑm, and therefore susceptible to drift. of material released, is determined by the way in which Drop behavior has been the subject of detailed re- the chemical partitions between the solid, liquid, and search. Drops are subjected to various forces as they air phases of the soil. The partition coefficients between leave the nozzle and before they impact on a surface. these different phases can be used to accurately predict the rate of movement of pesticides within a given soil • Gravitational forces: Small drops have a low termi- type. nal velocity. For example, a 5-Ȑm-diameter drop falls at 0.075 cm/sec and often drifts from the tar- 2. Spray Application get area, whereas a 500-Ȑm-diameter drop falls to Spray application is the commonest method of pesticide the ground at 213.9 cm/sec. delivery. It is convenient, flexible, and simple, but it • Movement induced by air movement: Wind carries lacks selectivity and there is a risk of contaminating drops away from the target area. For example, in a nontarget areas. Hydraulic sprayers give a range of pesti- wind of 1 m/sec, a 5-Ȑm-diameter drop released cide drop sizes, at the smallest extreme of which there is from 1 m experiences 350 m of sideways transport, a tendency to drift away from the target area. Controlled whereas a 500-Ȑm drop moves 0.48 m. To deposit droplet application (CDA) sprayers are much rarer, but within5mofthetarget area, a drop must have a they control drop size and as a consequence may reduce diameter of greater than 67 Ȑm in a wind speed of drift and increase efficiency. 0.7 m/sec and it must have a diameter of greater The main function of spray machinery is to transfer than 168 Ȑm in a wind traveling at 3 m/sec. The energy to the liquid pesticide formulation to atomize friction of the air rapidly decelerates drops from it into droplets by means of a nozzle. The drop size the velocity at which they left the nozzle. For exam- distribution is typical for the nozzle in question and it ple, a 5-Ȑm drop is decelerated to its deposition ve- is characterized by the volume median diameter and locity in 0.33 cm and a 200-Ȑm drop is brought to the number median diameter of the drops. the equivalent velocity in 630 cm.

• Volume median diameter (VMD): If a sample of Drift is worse where relative humidity is low. Drops spray is divided into two equal volumes, then half become smaller as spray liquid evaporates and sedimen- 518 PESTICIDES, USES AND EFFECTS OF

TABLE IV Drop Sizes from a Hydraulic Spray Nozzle Measured with a Laser Particle Size Analyzera

Drop range (Ȑm) Volume (%) Cumulative volume (%) Number (%) Cumulative number (%)

563–262 26.17 61.94 0.07 0.80 262–160 35.77 0.75 160–113 17.52 1.36 113–84 8.78 33.84 1.82 8.39 84–65 4.81 2.31 65–50 2.73 2.86 50–30 2.66 8.45 30–15 1.12 4.22 21.90 90.81 Ͻ15 0.27 60.46

a Data from Micron Sprayers, UK. Nozzle, Fan Jet SS8002 operating at a pressure of 3 bar and a flow rate of 700 ml/min. VMD ϭ 192 Ȑm, NMD ϭ 12 Ȑm, VMD : NMD ratio-16.

tation takes longer. If 1 liter of liquid is atomized to ogy limits the efficiency, effectiveness, and safety of the 10-Ȑm drops, then the cumulative surface area is 600 spray application process. m2. If it is atomized to 100-Ȑm drops, then the surface area falls to 60 m2. Evaporation is therefore exacerbated by the shrinkage of drops and the increase of relative III. ECOTOXICOLOGY AND surface area. MANAGEMENT Large drops pose an equivalent problem: not de- flected by air currents, they gain momentum and either Pesticides pose challenges through being toxic to organ- miss the plant target and hit the soil or strike the plant, isms other than the specific pests, diseases, or weeds shatter, and fall to the ground. The cubed relationship they are targeted against. Relative toxicity is expressed between diameter and volume means that the volume in a number of ways, but the most prevalent relates to of a 100-Ȑm-diameter drop is 1 million times that of a oral and dermal exposure of mammals, which equates 1-Ȑm-diameter drop. The variation in pesticide dose to both human and vertebrate wildlife toxicological between a 4- and 400-Ȑm-diameter drop (common in risks for organisms that are directly exposed (Table V). a hydraulic nozzle drop spectrum) is 1 million fold. Table VI lists some representative active ingredients Many drops of a diameter greater than 300 Ȑm fall to by toxicity and demonstrates that in all major pesticide the ground, and a large proportion of the pesticide types and range of classes, there is a considerable variety applied by a hydraulic nozzle never comes into contact in intrinsic toxicities to mammals. with the pest, disease, or weed it is intended to control. It is extremely difficult to translate these data, or toxicological data for any other species, into predictions 3. Deposition on Obstacles of ecological risk. Very toxic materials may be relatively Objects are surrounded by a cushioning layer of air, nonhazardous in the environment, because they are and spray drops require considerable momentum to hit rapidly sorbed or dissipated, whereas less toxic materi- a target. Larger drops strike targets, and smaller drops als may prove hazardous because they readily leach or move around them. The probability of striking depends runoff into water or because they are persistent. upon the shape of the object; hairs, for example, pick Recent attempts have been made to bridge the gap up small drops. Flying insects such as mosquitoes are that exists between basic toxicology and environmental best hit by drops of 10–20 Ȑm in diameter, resting flies chemistry and the potential ecological impact of pesti- require drops of 30–40 Ȑm, diameters of 90–130 Ȑm cides in ecosystems. Van Straalen and van Rijn (1998) are needed where crop penetration is needed, and a computed species sensitivity distributions for soil fauna diameter of Ͼ250 Ȑm is optimal for horizontal surfaces (soil invertebrates that contribute to biogeochemical such as weeds. cycling), based upon laboratory test data for toxic ef- Continuing reliance upon hydraulic spray technol- fects in soil, and calculated the concentration that PESTICIDES, USES AND EFFECTS OF 519

TABLE V Pesticide Toxicity Classes

LD50, single oral dose LD50, single dermal dose Probable lethal oral Toxicity rating for rats (mg/kg) for rabbits (mg/kg) dose for humans

6, supertoxic Ͻ5 Ͻ20 A taste, a grain 5, extremely toxic 5–50 20–200 A pinch, 1 teaspoon (5 ml) 4, very toxic 50–500 200–1,000 1 teaspoon (5 ml) to 2 tablespoons 3, moderately toxic 500–5,000 1,000–2,000 1 liquid ounce (30 ml) to 1 pint (470 ml) 2, slightly toxic 5,000–15,000 2,000–20,000 1 pint (470 ml) to 1 quart (950 ml) 1, practically nontoxic Ͼ15,000 Ͼ20,000 Ͼ1 quart (950 ml)

would be below the no-effect concentration (NOEC: reach this ‘‘95% protection level.’’ This time, referred the highest dose not to cause a specific effect) for repro- to as the ‘‘ecotoxicological recovery time,’’ can be used ductive inhibition for 95% of the species that are theo- as a basis for calculating the minimum time for ecologi- retically present within the soil arthropod community. cal recovery to take place after pesticide application. Using a simple model for pesticide fate, based upon There is considerable scope for further development of exponential decay, they then calculated for a series of this technique, built upon readily collected toxicologi- compounds the time that each product would take to cal data sets. Such data are, however, surprisingly diffi-

TABLE VI Examples of Pesticide Toxicities to Vertebrates from Laboratory Test Data Used in Registration

Pesticide technical Oral LD50 Dermal LD50 Pesticide type and class name (rat, mg/kg) (rat (a), rabbit (b))

Insecticides Organochlorine Dieldrin 46 10 (a) Endosulfan 80 359 (b) Organophosphate Azinphos-methyl 16 222 (a) Chlorpyrifos 135 2000 (b) Dichlorvos 56 75 (a) Dimethoate 320 Ͻ130 (b) Malathion 2800 4100 (b) Carbamate Aldicarb 0.7 5 (b) Carbaryl 850 Ͼ2000 (b) Pyrethroid Deltamethrin 135 Ͼ2000 (b) Allethrin 930 — Bioresmethrin 7070 — Fungicides Dithiocarbamates Thiram 780 Ͼ5000 (a) Maneb 7990 Ͼ5000 (a) Dinitrophenol Dinocap 980 — Herbicides Inorganic Sodium arsenite 39 — Bipyridiliums Paraquat 157 — Triazines 5000 Ͼ3100 (b) 520 PESTICIDES, USES AND EFFECTS OF

TABLE VII Rankings of 10 Selected Pesticides According to Three Criteriaa

Rank based Joint Rank based on assessment Pesticide on toxicity persistence (recovery time)

Lindane (organochlorine insecticide) 6 2 2 Dimethoate (organophosphate insecticide) 8 8 7 Parathion (organophosphate insecticide) 5 6 6 Chlorpyrifos 1 7 4 (organophosphate insecticide) Carbofuran (carbamate insecticide) 4 3 3 Carbaryl (carbamate insecticide) 2 10 5 Methomyl (carbamate fungicide) 7 9 8 Benomyl (benzimidazole fungicide) 3 1 1 Atrazine (triazine herbicide) 10 4 10 Fentin (organotin fungicide) 9 5 9

a The score 1 is given for the highest toxicity (the 95% protection level referred to in the text), the greatest persistence (soil half-life), and the longest predicted ecotoxicological recovery time (i.e., the time it takes the pesticide concentration to decline to the 95% protection level).

cult to find in the published literature, and they are not cide inputs were made in at least 13 sites, in Germany, routinely collected for suites of compounds in such a The Netherlands, Switzerland, and the United Kingdom way that they may be exploited within this new ap- (Table VIII). In all cases, beneficial nontarget inverte- proach as a decision-making aid. brate densities were higher in areas where the total Table VII, adapted from van Straalen and van Rijn regime of pesticide input had been reduced. In the (1998), summarizes the differences in ranking of toxic- larger scale studies (e.g., the Boxworth study, UK), with ity that result if pesticide toxicity to soil organisms and 5.6- to 15.7-ha treatment area sizes, some beneficial chemical persistence (half-life) in soil are integrated to species were rendered locally extinct for the full 5- predict the time when recovery could take place by year treatment phase of the project, and recovery was organisms. A compound with high intrinsic toxicity, subsequently slow. The level of impact on individual such as chlorpyrifos, has a lower ranking once its lim- species was shown to be a function of life history attri- ited persistence is taken into account, whereas benomyl butes that affected pesticide exposure and capacity of climbs higher up the rankings because of its persistence. that organism to reinvade the treated area. Predatory Analytical procedures of this form are beginning to capacity was inhibited in the highest pesticide regimes, forge a link between the large amounts of laboratory- and there was evidence that this contributed to higher obtained toxicological data that exist and the field, pest densities in some years. Although similar data have where functioning communities are exposed to the been obtained for the invertebrate community of rice toxin, rather than individual species. systems in the tropics, data sets of this level of complex- ity are rare in the investigation of pesticide impacts in A. Farm-Scale Observations of agroecosystems. These investigations have revealed the subtler impact Ecotoxicological Impact of second- and third-generation active ingredients that A number of research projects investigating the ecology followed the organochlorines. They reinforce the need of farming systems were initiated throughout the 1980s to measure ecological impacts on scales that reflect and 1990s in Europe (Holland et al., 1994). Pesticide agricultural practice and pesticide use in the real world impacts were investigated in all of these studies, and and that are tuned to the scale of dispersive movement comparisons between conventional and reduced pesti- of nontarget taxa. They have also triggered considerable PESTICIDES, USES AND EFFECTS OF 521

TABLE VIII Summary of Date from Farming System Experiment in the United Kingdom (Boxworth, SCARAB, TALISMAN, RISC, LIFE), Germany (INTEX), The Netherlands (Nagele), and Switzerland (Third Way): Results of Integrated Farming, with Reduced Pesticide Inputs, Compared with the Conventional Levels of Usea

Beneficial Birds and Soil Soil Project mammals Earthworms microorganisms minerals

Boxworth ϩ o SCARAB ϩ oo TALISMAN ϭ RISC o LIFE ϩϩϭϭ Lautenbach ϩϩ ϭ INTEX ϩϭ Netherlands ϩϩ ϩ Third Way ϩϩϩ

a Key: ϩ, increase; ϭ, no change; o, variable result over the period of the study.

interest in the mechanisms that underlie long-term supply reduction or alteration, variation in sensitivity depletions, even local extinction of certain species. Both between species, and the synergistic effects of exposure scale of treatment and the mode and rate of dispersal to multiple compounds. of arthropods influence rates of population recovery following pesticide use, and the proximity of local refu- gia from which recovery can occur, and landscape fea- C. Aquatic Systems tures conducive to movement and colonization are im- Similar arguments may be applied to the investigation portant factors underlying extinction risk. Modeling of pesticide effects on aquatic organisms. The recent may provide an appropriate tool for testing our under- decision in the United States to reduce the requirements standing of invertebrate population processes at the for ecological data from multispecies test systems in agroecosystem level, but it does not substitute for the the regulatory process has been criticized because it need to undertake a far greater number of manipulative will reduce the probability of detecting biologically sig- experiments and monitoring programs that examine nificant effects (Taub, 1997). These effects include indi- the spatial dynamics of nontarget organisms in sprayed rect trophic-level impacts, compensatory shifts within farming systems. a trophic level, responses that are associated with sea- sonal trends in populations, chemical transformations effected by organisms in the exposed system, and im- B. Avian Impacts pacts that result from long persistence of either the The requirement for large-scale, field-based monitoring parent product or toxic breakdown products. and experimentation is not restricted to terrestrial non- In conclusion, there is now abundant evidence that target invertebrates. Avian toxicologists have long rec- pesticide impacts can evolve at the agroecosystem scale ognized that field-based studies provide unique and and that this requires the development of appropriately indispensable data for interpretation of pesticide effects scaled monitoring or experimental systems. Toxicologi- on birds (Taub, 1997). Many of the most important cal data are of fundamental value in the initial evalua- effects of pesticides on birds, including eggshell thin- tion of pesticides, but in their real-world applications, ning as a result of the bioconcentration of organochlo- pesticides may also elicit ecological effects that reverber- rines through food chains, were originally detected and ate through the system, long after the chemical residues documented as a result of field-based observations. have become undetectable. Laboratory-based, single- These effects also include endocrine disruption, food species tests are limited in their predictive power for 522 PESTICIDES, USES AND EFFECTS OF impacts in the field, and further development of the methodology that could also be explained to con- theory and methodology associated with ecological ef- sumers. fects is required. See Also the Following Articles D. Tools for Pesticide Management AGRICULTURE INVASIONS • AGRICULTURE, It is questionable whether we apply our knowledge INDUSTRIALIZED • ECOTOXICOLOGY • HERBICIDES • about pesticides effectively at any stage following the INSECTICIDE RESISTANCE regulatory permission to use a product in a specified way. Given the need to combine knowledge of chemi- cal properties, fate and behavior, environmental attri- Bibliography butes such as soil type, toxicology, and ecology, the Bellows, T. S., and Fisher, T. W. (1999). Handbook of Biological challenge is considerable. In each of these disciplinary Control. Academic Press, San Diego. areas, however, there are considerable databases of Benbrook, C. M. (1996). Pest Management at the Crossroads. Consum- ers Union, New York. knowledge and predictive models that can be used Calow, P. (1998). Handbook of Ecotoxicology, Vols. 1 and 2. Blackwell to interpret how a pesticide will behave in a given Sci., Oxford. set of field conditions. Conway, G. R., and Pretty, J. (1991). Unwelcome Harvest: Agriculture Attempts have been made to summarize clusters of and Pollution. Earthscan Publications, London. pesticide properties in databases that may be used to Croft, B. A. (1990). Arthropod Biological Control Agents and Pesticides. Wiley, New York. compare the environmental and ecological risks posed Farm Chemicals Handbook (2000). Meister Publishing Co. Wil- by lists of candidate compounds for specific uses. These loughby, Ohio. databases are not specifically tuned to local conditions; Greig-Smith, P. W., Frampton, G. K., and Hardy, A. R. (Eds.) (1992). they do, however, combine many factors, including Pesticides, Cereal Farming and the Environment. H. M. Stationery risks to wildlife, in the rankings that they generate, and Office, London. Hartley, G. S., and Graham Bryce, I. J. (1980). Physical Principles of enhance the capacity of the end user to make more Pesticide Behavior. Academic Press, San Diego. informed decisions about particular uses. The most sig- Holland, J. M., Frampton, G. K., Cilgi, T., and Wratten, S. D. (1994). nificant development in this field is the proposal to Arable acronyms analysed: A review of integrated arable farming derive Environmental Impact Quotients (EIQ) for com- systems research in W. Europe. Ann. Appl. Biol. 125, 399–438. pounds from established databases of pesticide proper- Kogan, M. (Ed.) (1986). Ecological Theory and Integrated Pest Manage- ment Practice. Wiley, New York. ties (Kovach et al., 1992). The quotient combines farm- Kovach, J., Petzoldt, C., Degni, J., and Tette, J. (1992). A method to worker effects (built from acute and chronic toxicity measure the environmental impact of pesticides. New York’s Food and plant surface half-life) with consumer effects (built Life Sci. Bull. No. 139. from systemicity, soil and leaf surface persistence, and Matthews, G. A. (1992). Pesticide Application Methods, 2nd ed. Long- potential for groundwater contamination) and ecologi- man, New York. Marco, G. J., Hollingworth, R. M., and Durham, W. (1987). Silent cal effects (built from aquatic and terrestrial ecotoxicol- Spring Revisited. Am. Chem. Soc., Washington, D.C. ogy). There is considerable scope for toxicologists to Taub, F. B. (Ed.) (1997). Invited Feature: Are ecotoxicological studies develop approaches such as this from first principles relevant to pesticide registration decisions? Ecol. Appl. 7, 1083– in order to make data available in a form that can be 1132. used to assist decisions in the field. Guided by EIQs, Van Straalen, N. M., and van Rijn, J. P. (1998). Ecotoxicological risk assessment of soil fauna recovery from pesticide application. Rev. growers and their advisors could then plan pest control Environ. Contam. Toxicol. 154, 83–141. tactics that attempt to minimize nontarget impacts and Ware, G. W. (1999). The Pesticide Book, 5th ed. Thomson Publica- track their progress with a rigorous and quantitative tions, Washington, D.C.