L1190 CH13 pgs Page 623 Friday, July 2, 1999 5:54 PM chapter thirteen Ecological and environmental effects 13.1Movement of pesticides in the environment Introduction The widespread use and disposal of pesticides by farmers, institutions, and the general public provide many possible sou rces of pesticides in the environment. After release into the environment, pesticides may have many different fates. Pesticides that are sprayed can move through the air and may eventually end up in other parts of the environment, such as in soil or water. Pesticides applied directly to the soil may be washed off the soil into nearby bodies of surface water or may percolate through the soil to lower soil layers and groundwater. Pesticides injected into the soil may also be subject to the latter two fates. The application of pesticides directly to bodies of water for weed control, or indirectly as a result of leaching from boat paint, runoff from soil, or other routes, may lead not only to the build-up of pesticides in water, but may also contribute to air levels through evaporation. This incomplete list of possibilities suggests that the movement of pesticides in the environment is very complex with transfers occurring continually among differ- ent environmental compartments. In some cases, these exchanges occur not only between areas that are close together (such as a local pond receiving some of the herbicide application on adjacent land) but may also involve transportation of pes- ticides over long distances. The worldwide distribution of DDT and the presence of pesticides in bodies of water far from their primary use areas are good examples of the vast potential for such movement. While all of the above possibilities exist, this does not mean that all pesticides travel long distances or that all compounds are threats to groundwater. To under- stand which ones are of most concern, it is necessary to understand how pesticides move in the environment and what characteristics must be considered in evaluating contamination potential. Two things may happen to pesticides once they are released into the environment. They may be broken down, or degraded, by the action of sunlight, water or other chemicals, or microorganisms such as bacteria. This degra- dation process usually leads to the formation of less harmful breakdown products, but in some instances can produce more toxic products. The second possibility is that the pesticide will be very resistant to degradation by any means and thus remain unchanged in the environment for a long period of time. The ones that are most rapidly broken down have the shortest time to move through the environment or to produce adverse effects in people or other o rganisms. The ones that last the longest, the so-called “persistent pesticides,” can move over © 2000 CRC Press LLC L1190 CH13 pgs Page 624 Friday, July 2, 1999 5:54 PM long distances and can build up in the environment, leading to greater potential for adverse effects. Properties of pesticides In addition to resistance to degradation, there are a number of other properties of pesticides that determine their behavior and fate. One is how volatile they are or, in other words, how easily they evaporate. The ones that are most volatile have the greatest potential to evaporate into the atmosphere and, if persistent, to move long distances. Another important property is solubility in water or how easily they dissolve in water. If a pesticide is very soluble in water, it is more easily carried off with rainwater as runoff or through the soil as a potential groundwater contaminant (leaching). In addition, the water-soluble pesticide is more likely to stay mixed in the surface water where it can have adverse effects on fish and other organisms. If the pesticide is very insoluble in water, it usually tends to stick to soil and also to settle to the bottom of bodies of surface water, making it less available to organisms. Environmental characteristics From a knowledge of these and other characteristics, it is possible to predict in a general sense how a pesticide will behave. Unfortunately, more precise prediction is not possible because the environment itself is very complex. There are, for example, huge numbers of soil types that vary with respect to the percentage of sand, organic matter, metal content, acidity, etc. All of these soil characteristics influence the behav- ior of a pesticide so that a pesticide that might be anticipated to contaminate ground- water in one soil may not do so in another. Similarly, surface waters vary in their properties, such as acidity, depth, temper- ature, clarity (suspended soil particles or biological organisms), flow rate, and general chemistry. These properties and others all can affect pesticide movement and fate. Everyone who is familiar with the difficulty of forecasting weather knows it is partly due to p roblems in p redicting air flow patterns. As a result, determination of pesticide distribution in the atmosphere is subject to great uncertainty. With such g reat complexit y, scientists cannot determine exactly what will happen to a particular pesticide once it has entered the environment. However, they can divide pesticides into general categories with regard to, for example, persistence and potential for groundwater contamination. They can also provide some idea as to where the released pesticide will most likely be found at highest levels. Thus, it is possible to gather information that can help make informed decisions about what pesticides to use in which situations and what possible risks are being faced due to a particular use. Movement of pesticides in soil Table 13.1 lists some of the more commonly used pesticides, with an estimate of their persistence in soil. In this table, persistence is measured as the time it takes for half of the initial amount of a pesticide to break down. Thus, if a pesticide’s half-life is 30 days, half will be left after 30 days, one quarter after 60 days, one eighth after 90 days, and so on. It might seem that a short half-life would mean a pesticide would not have a chance to move far in the environment. This is generally true. However, if it is also very soluble in water and the conditions are right, it can move rapidly through certain soils. As it moves away from the surface, it moves away from the © 2000 CRC Press LLC L1190 CH13 pgs Page 625 Friday, July 2, 1999 5:54 PM agents that are degrading it, such as sunlight and bacteria. As it gets deeper into the soil, it degrades more slowly and thus has a chance to get into groundwater. The measures of soil persistence in the table only describe pesticide behavior at or near the surface. The downwa rd movement of nonpersistent pesticides is not an unlikely scenario, and several pesticides with short half-lives, such as aldicarb, have been widely found in groundwater. In contrast, very persistent pesticides may have other properties that limit their potential for movement throughout the environment. Many of the chlorinated hydrocarbon pesticides a re very resistant to breakdown but are also very water insoluble and tend not to move down through the soil into g roundwater. They can, however, become problems in other ways since they remain on the surface for a long time where they may be subject to rff and possible evaporation. Even ifuno they are not very volatile, the tremendously long time that they persist can lead, over time, to measurable concentrations moving through the atmosphere and accu- mulating in remote areas. Table 13.1 Pesticide Persistence in Soils Low persistence Moderate persistence High Persistence (half-life < 30 days) (half-life 30–100 days) (half-life > 100 days) Aldicarb Aldrin Glyphosate Bromacil Captan Atrazine Heptachlor Chlordane Dalapon Carbaryl Linuron Lindane Dicamba Carbofuran Parathion Paraquat Malathion Diazinon Phorate Picloram Methyl-parathion Endrin Simazine TCA Oxamyl Fonofos Terbacil Trifluralin Role of living organisms So far, the discussion has focused on air, soil, and water. However, living organ- isms may also play a significant role in pesticide distribution. This is particularly important for pesticides that can accumulate in living creatures. An example of accumulation is the uptake of a very water-insoluble pesticide, such as chlordane, by a creature living in water. Since this pesticide is stored in the organism, the pesticide accumulates and levels increase over time. If this organism is eaten by a higher organism which also stores this pesticide, levels can reach much higher values in the higher organism than is present in the water in which it lives. Levels in fish, for example, can be tens to hundreds of thousands of times greater than ambient water levels of the same pesticide. This type of accumulation has a specific name. It is called “bioaccumulation.” In this regard, it should be remembered that humans are at the top of the food chain and so may be exposed to these high levels when they eat food animals that have bioaccumulated pesticides and other organic chemicals. It is not only fish but also domestic farm animals that can be accumulators of pesticides, and so care must be taken in the use of pesticides in agricultural situations. Summary The release of pesticides into the environment may be followed by a very com- plex series of events that can transport the pesticide through the air or water, into © 2000 CRC Press LLC L1190 CH13 pgs Page 626 Friday, July 2, 1999 5:54 PM the ground, or even into living organisms. The most important route of distribution and the extent of distribution will be different for each pesticide. It will depend on the formulation of the pesticide (what it is combined with) and how and when it is released. Despite this complexity, it is possible to identify situations that can pose concern and to try to minimize them. However, there are significant gaps in the knowledge of pesticide movement and fate in the environment, and so it is best to minimize unnecessary release of pesticides into the environment. The fewer pesti- cides that are unnecessarily released, the safer our environment will be. 13.2Bioaccumulation Defining bioaccumulation An important process by which chemicals can affect living organisms is through bioaccumulation. Bioaccumulation means an increase in the concentration of a chem- ical over time in a biological organism compared to the chemical’s concentration in the environment. Compounds accumulate in living things any time they are taken up and stored faster than they are broken down (metabolized) or excreted. Under- standing the dynamic process of bioaccumulation is very important in protecting human beings and other organisms from the adverse effects of chemical exposure, and it has become a critical consideration in the regulation of chemicals. A number of terms are used in conjunction with bioaccumulation. Uptake describes the entrance of a chemical into an organism — such as by breathing, swallowing, or absorbing it through the skin — without regard to its subsequent storage, metabolism, or excretion by that organism. Storage, a term sometimes confused with bioaccumulation, means the temporary deposit of a chemical in body tissue or in an organ. Storage is just one facet of chemical bioaccumulation. (The term also applies to other natural processes, such as the storage of fat in hibernating animals or the storage of starch in seeds.) Bioconcentration is the specific bioaccumulation process by which the concen- tration of a chemical in an organism becomes higher than its concentration in the air or water around the organism. Although the process is the same for both natural and man-made chemicals, the term bioconcentration usually refers to chemicals foreign to the organism. For fish and other aquatic animals, bioconcentration after uptake through the gills (or sometimes the skin) is usually the most important bioaccumulation process. Biomagnification describes a process that results in the accumulation of a chem- ical in an organism at higher levels than are found in its own food. It occurs when a chemical becomes more and more concentrated as it moves up through a food chain — the dietary linkages from single-celled plants to increasingly larger animal species. A typical food chain includes algae eaten by a waterflea, eaten by a minnow, eaten by a trout, and finally consumed by an osprey (or human being). If each step results in increased bioaccumulation, that is, biomagnification, then an animal at the top of the food chain, through its regular diet, may accumulate a much greater concentration of chemical than was present in organisms lower in the food chain. Biomagnification is illustrated by a study of DDT that showed that where soil levels were 10 parts per million (ppm), DDT reached a concentration of 141 ppm in earthworms and 444 ppm in robins. Through biomagnification, the concentration of a chemical in the animal at the top of the food chain may be high enough to cause death or adverse effects on behavior, reproduction, or disease resistance and thus © 2000 CRC Press LLC L1190 CH13 pgs Page 627 Friday, July 2, 1999 5:54 PM endanger that species, even though contamination levels in the air, water, or soil are low. Fortunately, bioaccumulation does not always result in biomagnification. The bioaccumulation process Bioaccumulation is a normal and essential process for the growth and nurturing of organisms. All animals, including humans, daily bioaccumulate many vital nutri- ents, such as Vitamins A, D, and K, trace minerals, and essential fats and amino acids. What concerns toxicologists is the bioaccumulation of substances to levels in the body that can cause harm. Because bioaccumulation is the net result of the interaction of uptake, storage, and elimination of a chemical, these parts of the process will be examined further. Uptake Bioaccumulation begins when a chemical passes from the environment into an organism’s cells. Uptake is a complex process that is still not fully understood. Scientists have learned that chemicals tend to move, or diffuse, passively from a place of high concentration to one of low concentration. The force or pressure for diffusion is called the chemical potential, and it works to move a chemical from outside to inside an organism. A number of factors may increase the chemical potential of certain substances. For example, some chemicals do not mix well with water. They are called lipophilic, meaning “fat loving”, or hydrophobic, meaning “water hating.” In either case, they tend to move out of water and into the cells of an organism, where there are lipophilic microenvironments. Storage The same factors affecting the uptake of a chemical continue to operate inside an organism, hindering a chemical’s return to the outer environment. Some chemicals are attracted to certain sites, and by binding to proteins or dissolving in fats, they are temporarily stored. If uptake slows or is not continued, or if the chemical is not very tightly bound in the cell, the body can eventually eliminate the chemical. One factor important in uptake and storage is water solubilit y, which is the ability of a chemical to dissolve in water. Usually, compounds that are highly water soluble have a low potential to bioaccumulate and do not readily enter the cells of an organism. Once inside the organism, they are easily removed unless the cells have a specific mechanism for retaining them. Heavy metals like mercury and certain other water-soluble chemicals are the exceptions because they bind tightly to specific sites within the body. When binding occurs, even highly water-soluble chemicals can accumulate. This is illustrated by cobalt, which binds very tightly and specifically to sites in the liver and accumulates there despite its water solubility. Similar accumulation processes occur for mercury, copper, cadmium, and lead. Many fat-loving (lipophilic) chemicals pass into organism’s cells through the fatty layer of cell membranes more easily than water-soluble chemicals. Once inside the organism, these chemicals may move through numerous membranes until they are stored in fatty tissues and begin to accumulate. The storage of toxic chemicals in fat reserves serves to detoxify the chemical by removing it from contact with other organs. However, when fat reserves are utilized © 2000 CRC Press LLC L1190 CH13 pgs Page 628 Friday, July 2, 1999 5:54 PM to provide energy for an o rganism, the materials sto red in the fat may be remobilized within the organism and may again be potentially toxic. If appreciable amounts of a toxicant are stored in fat, and fat reserves are quickly used, significant toxic effects may be seen from the remobilization of the chemical. Elimination Another factor affecting bioaccumulation is whether an organism can break down and/or excrete a chemical. The biological breakdown of chemicals is called metabolism. This ability varies among individual organisms and species and also depends on the chemical’s characteristics. Chemicals that dissolve readily in fat but not in water tend to be more slowly eliminated by the body and thus have a greater potential to accumulate. Many metabolic reactions alter a chemical into more water-soluble metabolites, which are more readily excreted. However, there are exceptions. Natural pyrethrins, insecticides that are derived from the chrysanthemum plant, are highly fat-soluble pesticides, but they are easily degraded and do not accumulate. The insecticide chlorpyrifos, which is less fat soluble but more poorly degraded, tends to bioaccumulate. Factors affecting metab- olism often determine whether a chemical achieves its bioaccumulation potential in a given organism. A dynamic equilibrium When a chemical enters the cells of an organism, it is distributed and then excreted, stored, or metabolized. Excretion, storage, and metabolism decrease the concentration of the chemical inside the organism, increasing the potential of the chemical in the outer environment to move into the organism. During constant environmental exposure to a chemical, the amount of a chemical accumulated inside the organism and the amount leaving reach a state of dynamic equilibrium. To understand this concept of dynamic equilibrium, imagine a tub filling with water from a faucet at the top and draining out through a pipe of smaller size at the bottom. When the water level in the tub is low, little pressure is exerted on the outflow at the bottom of the tub. As the water level rises, the pressure on the outflow increases. Eventuall y, the amount of water flowing out will equal the amount flowing in, and the level of the tub will not change. If the input or outflow is changed, the water in the tub adjusts to a different level. So it is with living organisms. An environmental chemical will at first move into an organism more rapidly than it is stored, degraded, and excreted. With constant exposure, the concentration inside the organism gradually increases. Eventually, the concentration of the chemical inside the o rganism will reach an equilibrium with the concentration of the chemical outside the organism, and the amount of chemical entering the organism will be the same as the amount leaving. Although the amount inside the organism remains constant, the chemical continues to be taken up, stored, degraded, and excreted. If the environmental concentration of the chemical increases, the amount inside the organism will increase until it reaches a new equilibrium. Exposure to large amounts of a chemical for a long period of time, however, may overwhelm the equilibrium (for example, overflowing the tub) and potentially cause harmful effects. Likewise, if the concentration in the environment dec reases, the amount inside the organism will also decline. If the organism moves to a clean environment, in which there is no exposure, then the chemical eventually will be eliminated f rom the body. © 2000 CRC Press LLC L1190 CH13 pgs Page 629 Friday, July 2, 1999 5:54 PM Bioaccumulation factors This simplified explanation does not take into account all of the many factors that affect the ability of chemicals to be bioaccumulated. Some chemicals bind to specific sites in the body, prolonging their stay, whereas others move freely in and out. The time between uptake and eventual elimination of a chemical directly affects bioaccumulation. Chemicals that are immediately eliminated, for example, do not bioaccumulate. Similarly, the duration of exposure is also a factor in bioaccumulation. Most exposures to chemicals in the environment vary continually in concentration and duration, sometimes including periods of no exposure. In these cases, an equilibrium is never achieved and the accumulation is less than expected. Bioaccumulation varies between individual organisms as well as between spe- cies. Large, fat, long-lived individuals or species with low rates of metabolism or excretion of a chemical will tend to bioaccumulate more than small, thin, short-lived organisms. Thus, an old lake trout may bioaccumulate much more than a young bluegill in the same lake. Summary Bioaccumulation results from a dynamic equilibrium between exposure from the outside environment and uptake, excretion, storage, and degradation within an organism. The extent of bioaccumulation depends on the concentration of a chemical in the environment, the amount of chemical coming into an organism from the food, air, or water, and the time it takes for the organism to acquire the chemical and then excrete, store, and/or degrade it. The nature of the chemical itself, such as its solu- bility in water and fat, affects its uptake and storage. Equally important is the ability of the organism to degrade and exc rete a particular chemical. When exposure ceases, the body gradually metabolizes and excretes the chemical. Bioaccumulation is a normal process that can result in injury to an organism only when the equilibrium between exposure and bioaccumulation is overwhelmed. Sometimes, bioaccumulation can be a protective mechanism in which the body accumulates needed chemicals. 13.3Ecological effects Introduction Chemicals released into the environment may have a variety of adverse ecolog- ical effects. Ranging from fish and wildlife kills to forest decline, ecological effects can be long-term or short-lived changes in the normal functioning of an ecosystem, resulting in biological, economic, social, and aesthetic losses. These potential effects are an important reason for the regulation of pesticides, toxic wastes, and other sources of pollution. What is an ecosystem? An ecosystem is the physical environment, along with the organisms (biota) inhabiting that space. Some examples of ecosystems include: a farm pond, a moun- tain meadow, and a rain forest. An ecosystem follows a certain sequence of processes and events through the days, seasons, and years. These processes include not only the birth, growth, repro- © 2000 CRC Press LLC L1190 CH13 pgs Page 630 Friday, July 2, 1999 5:54 PM duction, and death of biota in that particular ecosystem, but also the interactions between species and physical characteristics of the geological environment. From these processes, the ecosystem gains a recognizable structure and function, and matter and ene rgy are cycled and flow through the system. Over time, better adapted species will dominate. Sometimes, entire new species may be introduced and pe rhaps greatly alter the ecosystem. The organization of ecosystems The basic level of ecological organization is the individual: a single plant, or insect, or bird. The definition of ecology is based on the interactions of organisms with their environment. In the case of an individual, it would entail the relation- ships between that individual and numerous physical (rain, sun, wind, tempera- ture, nutrients, etc.) and biological (plants, insects, diseases, animals, etc.) factors. The next level of organization is the population. Populations are no more than collections of individuals of the same species within an area or region. We can see populations of humans, birch trees, or sunfish in a pond. Population ecology is concerned with the interaction of the individuals with each other and with their environment. The next, more complex level of organization is the community. Communities are made up of different populations of interacting plants, animals, and mic roorgan- isms also within some defined geographic area. Different populations within a com- munity interact more among themselves than with populations of the same species in other communities. Therefore, there are often genetic differences between the members of two different communities. The populations in a community have evolved together, so that members of that community provide resources (such as nutrition and shelter) for each other. The next level of organization is the ecosystem. An ecosystem consists of different communities of organisms associated within a physically defined space. For example, a forest ecosystem consists of animal and plant communities in the soil, forest floor, and forest canopy, along the stream bank and bottom, and in the stream. A stream bottom community will contain various fungi and bacteria living on dead leaves and animal wastes, protozoans and microscopic invertebrates feed- ing on these microbes, and larger invertebrates (worms, crayfish) and vertebrates (turtles, catfish). Each community functions somewhat separately, but is linked to the others by the forest, rainfall, and interactions between communities. For exam- ple, the stream community is heavily dependent upon leaves produced in the surrounding trees falling into the stream that feeds the microbes and other inver- tebrates. As another example, the rainfall and groundwater flow in a surrounding forest community greatly affects the amount and quality of water entering the stream or lake system. Terrestrial ecosystems can be grouped into units of similar nature, termed biomes (such as a deciduous forest, grassland, coniferous forest, etc.), or into a geographic unit, termed landscapes, containing several different types of ecosystems. Aquatic ecosystems are commonly categorized on the basis of whether the water is moving (streams, river basins) or still (ponds, lakes, large lakes), and whether the water is fresh, salty (oceans), or brackish (estuaries). Landscapes and biomes (and large lakes, river basins, and oceans) are subject to global threats of pollution (acid deposition, stratospheric ozone depletion, air pollution, the greenhouse effect) and human activ- ities (soil erosion, deforestation). © 2000 CRC Press LLC L1190 CH13 pgs Page 631 Friday, July 2, 1999 5:54 PM Adverse effects on ecosystems While many natural forces — drought, fire, flood, frost, or species migration — can affect it, an ecosystem will usually continue to function in a recognizable way. For instance, a pond ecosystem may go through flood or drought but continues to be a pond. This natural resilience of ecosystems enables them to resist change and recover quickly from disruption. On the other hand, toxic pollutants and other nonnatural phenomena can over- whelm the natural stability of an ecosystem and result in irreversible changes and serious losses, as illustrated by the following examples. •Decline of forests, due to air pollution and acid deposition •Loss of fish production in a stream, due to death of invertebrates from copper pollution •Loss of timber growth, due to nutrient losses caused by mercury poisoning of microbes and soil insects •Decline and shift in age of eagle and hawk (and other top predator) popula- tions, due to the effects of DDT in their food supply on egg survival •Losses of numbers of species (diversity) in ship channels subjected to repeated oil spills •Loss of commercially valuable salmon and endangered species (bald eagle, osprey) from forest applications of DDT Each of these pollutant-caused losses has altered ecosystem processes and com- ponents and thus affected the aesthetic and commercial value of the ecosystem. Usually, adverse ecological effects take place over a long period of time or even at some distance from the point of chemical release. For example, DDT, though banned for use in the U.S. for over 20 years, is still entering the Great Lakes ecosystem through rainfall and dust from sources halfway around the world. The long-term effects and overall impacts of new and existing chemicals on ecosystems can only be partially evaluated by current laboratory testing procedures. Nevertheless, through field studies and careful monitoring of chemical use and biological outcome, it is possible to evaluate the short- and long-term effects of pesticides and other chemicals. Adverse ecological effects on communities Scientists are most concerned about the effects of chemicals and other pollutants on communities. Short-term and temporary effects are much more easily measured than long-term effects of pollutants on ecosystem communities. Understanding the impacts requires knowledge of the time course and variability of these short-term changes. Pollutants may adversely affect communities by disrupting their normal struc- ture and delicate inte rdependencies. The structure of a community includes its phys- ical system, usually created by the plant life and geological processes, as well as the relationships between its populations of biota. For example, a pollutant may eliminate a species essential to the functioning of the entire community; it may p romote the dominance of undesirable species (weeds, trash fish); or it may simply decrease the numbers and variety of species present in the community. It may also disrupt the dynamics of the food webs in the community by breaking existing dietary linkages between species. Most of these adverse effects © 2000 CRC Press LLC L1190 CH13 pgs Page 632 Friday, July 2, 1999 5:54 PM in communities can be measured through changes in productivity in the ecosystem. Under natural stresses (e.g., unusual temperature and moisture conditions), the community may be unable to tolerate effects of a chemical otherwise causing no harm. An important facet of biological communities is the number and intensity of interactions between species. These interactions make the community greater than simply the sum of its parts. The community as a whole is stronger than its popula- tions, and the ecosystem as a whole is more stable than its communities. A seriously altered interaction may adversely affect all the species dependent on it. Even so, some ecosystem properties or functions (such as nutrient dynamics) can be altered by chemicals without apparent effects on populations or communities. Thus, an important part of research in ecological effects is concerned with the relative sensi- tivity of ecosystems, communities, and populations to chemicals and to physical stresses. Consider the effects of spraying an orchard with an insecticide when bees and other beneficial insects may be present and vulnerable to the toxicant. This practice is both economically and ecologically unsound, since it would deprive all plants in the area of pollinators and disrupt the dynamic control of plant pests by their natural enemies. Advanced agricultural practices, such as integrated pest management (IPM), avoid these adverse effects through appropriate timing and selection of sprays in conjunction with nonchemical approaches to insect control. The effects of chemicals on communities can be measured through laboratory model ecosystem (microcosm) studies, through intermediate-sized model systems (mesocosms, engineered field systems, open-top plant chambers, field pens), and through full-field trials. Thus, data gathered about effects of chemicals on processes and species can be evaluated in various complex situations that reflect the real world. Adverse effects on species Most information on ecological effects has been obtained from studies on single species of biota. These tests have been performed in laboratories under controlled conditions and chemical exposures, usually with organisms reared in the laboratory representing inhabitants of natural systems. Most tests employ short-term, single exposures (acute toxicity assays), but long-term ( chronic) exposures are used as well. Although such tests reveal which chemicals are relatively more toxic and which species are relatively more vulnerable to their effects, these tests do not disclose much about either the important interactions noted above or the role of the range of natural conditions faced by organisms in the environment. Generally, the effects observed in these toxicity tests include reduced rates of survival or increased death rates, reduced growth and altered development, reduced reproductive capabilities, including birth defects, changes in body sys- tems, including behavior, and genetic changes. Any of these effects can influence a species’ ability to adapt and respond to other environmental stresses and com- munity interactions. Environmental toxicology studies performed on species in the laboratory provide the basis for much of the current regulation of pollutants and have allowed major improvements in environmental quality. However, these tests yield only a few clues as to effects on more complex systems. Long-term studies and monitoring of eco- logical effects of new and existing chemicals released into the environment are needed to develop an understanding of potential adverse ecological effects and their consequences. © 2000 CRC Press LLC