James R. Pratt

The scientific basis of bioassays

The ultimate goal of ecotoxicological testing is to predict ecological effects of chemicals and other stressors. Since damage should be avoided rather than corrected after it occurs, the predictive value of such tests is crucial. A modest base of evidence shows that, in some cases, extrapolations from bioassays on one species to another species are reasonably accurate and, in other cases, misleading. Extrapolations from laboratory bioassays to response in natural systems at the population level are effective if the environmental realism of the bioassay is sufficiently high. When laboratory systems are poor simulations of natural systems, gross extrapolation errors may result. The problem of extrapolating among levels of biological organization has not been given the serious attention it deserves, and currently used methodologies have been chosen for reasons other than scientific validity. As the level of biological organization increases, new properties are added (e.g., nutrient cycling, energy transfer) that are not readily apparent at the lower levels. The measured responses (or end points) will not be the same at all levels of biological organization, making the validation of predictions difficult. Evidence indicates that responses of ecologically complex laboratory systems correspond to predicted and documented patterns in stressed ecosystems. The difficulties of improving the ecological evidence used to predict adverse effects are not insurmountable since the essence of predictive capability is the determination of effects thresholds at all levels of organization. The dilemma between basing predictive schemes on either traditional or holistic methods can only be solved by facing scientific and ethical questions regarding the adequacy of evidence used to make decisions of environmental protection.

The Relationship Between Ecosystem Health and Delivery of Ecosystem Services

Ecosystem services is a term applied to any functional attribute of natural systems that is easily perceived by policy makers as beneficial to human society. If a society were highly environmentally literate, it would probably accept the assertion that every ecosystem function is, in the long term, beneficial to human society. However, because environmental literacy is less robust than it should be for the present decisions society must make, it would be best to use only those services that are likely to be persuasive at the present level of literacy. A biologically impoverished natural system delivers services of poorer quality and dramatically reduced quantity and may even perform some functions (such as concentrating persistent toxic substances) that are harmful to human health. As one reviewer noted, a non-impoverished system may also concentrate toxic substances. However, it seems probable that biotic impoverishment may lead to reduced functional capabilities, which, in this case, would mean reduced ability to transform obnoxious wastes into something less so. This attribute, which ecologists regard as an ecosystem function, would be regarded by laypersons as an ecosystem service which otherwise might have to be carried out in waste treatment plants or other treatment systems. However, the correspondence of ecosystem health and the delivery of environmental services is poorly documented. The rapid rate of ecological destruction and the concomitant rapid increase in human population make a drastic reduction in ecosystem services per capita inevitable by the year 2000 and in the period immediately thereafter when the human population is expected to exceed 10 billion.

Evaluation of joint toxicity of chlorine and ammonia to aquatic communities

Abstract Periphytic communities on artificial substrates were exposed to chlorine and ammonia, alone and in combinations. The species richness of protozoans decreased with increasing toxicant concentrations. Species richness was reduced by 20% in 2.7 μg/l chlorine, 15.4 μg/l un-ionized ammonia, and a combination of 1.2 μg/l chlorine and 16.8 μg/l ammonia. Interaction between toxicants was significant and effects of mixtures were less-than-additive, especially at higher concentrations. Multiple regression was used to derive a response surface model accounting for 73.4% of the variation in species richness. Algal biomass and community metabolism measures were less sensitive to stress and showed different patterns of joint action.

A simple, cost-effective multispecies toxicity test using organisms with a cosmopolitan distribution

Difficulties in making accurate, ecosystem-level predictions of environmental effects of chemicals, mixtures, and effluents based solely on the results of tests on single species have necessitated the development of more environmentally realistic, predictive testing methods. This paper describes a multispecies, community-level toxicity test based on the colonization of artificial substrates by microbial species. Tests examined the colonization of initially barren polyurethane foam artificial substrates by Protozoa from a species source colonized in a natural system. Differences in colonization were examined in microecosystems amended with low levels of cadmium, a very toxic heavy metal, and TFM, an organic biocide used against larval sea lamprey. Tests examined differences in colonization over 28 days. For cadmium, effect levels were estimated to be near 1 μg 1−1, in the low range of effect levels determined from chronic single species tests. For TFM, effect levels were estimated to be between 1 and 10 ppm, overlapping the concentrations used in environmental applications. The colonization response, which depends on naked microbial cells reproducing and migrating through toxicant amended water to new substrates, is very sensitive. Tests based on colonization can be adapted to use species from a target receiving system or can use species from a designated natural source. Field validation of these tests can employ nearly identical methods to those used in laboratory studies to assess the accuracy of predictions based on test system data.

Field evaluation of predictions of environmental effects from a multispecies-microcosm toxicity test

The predictive validity of a multispecies-microcosm toxicity test was evaluated. Predictions of biological response to a complex effluent were made from dose-response curves in laboratory tests and compared to observed effects in the receiving system. No effects on protozoan or macroinvertebrate communities were observed at the field site with effluent concentrations less than the chronic value of 1.7% effluent determined in laboratory tests. In addition, the microcosm test accurately predicted the magnitude of decreases in species richness in protozoan and macroinvertebrate communities in the receiving system at the first downstream site. Predictions of environmental effects for stations farther downstream were generally less accurate and too high, perhaps due to lack of persistence in the toxicity of the effluent. Stimulation of total biomass and algal growth were observed in both laboratory and field tests, but laboratory tests greatly overestimated the magnitude of enrichment responses in the receiving system.

Trends in ecotoxicology

Abstract The field of environmental toxicology has undergone a startling evolution. Toxicologists working at the organism level have become ecotoxicologists measuring ecological variables to assess toxicity — or have they? The existing paradigms in toxicology focus on the responses of individuals, not populations, communities, or ecosystems. For example, the ‘dose response’ for ecological variables might better be stated as a ‘concentration-effect’ relationship. Toxicology paradigms are based on the concept of biological similarities among organisms: protecting sensitive reactions (end points) for the most sensitive species will protect others. An ecotoxicological paradigm would accept the great uncertainty present in the stress responses of complex systems with numerous interacting subsystems, thus requiring the testing of ecological surrogates at several levels of biological organization. The major questions in ecotoxicology follow from the need to make accurate and cost-effective predictions of the fate and effects of chemicals in the environment. For example, can tests at higher levels of biological organization be carried out in a repeatable and scientifically defensible manner? To what degree can extrapolation be made from cellular and molecular systems to effects on ecological systems? What ecological end points can be measured in the laboratory and validated in the field? Do toxicants act as selective forces altering the structure of populations and communities? Can ecosystems recover from toxic stress and to what degree? Despite the importance of these questions, the ecotoxicology ‘industry’ is burdened by toxicology. The rate of development of the field of ecotoxicology will have to continue at least as fast as it has over the past 40 years if it is to resolve the neglected but important areas of environmental management.

Developing a Sampling Strategy

Sampling decisions must emphasize not only data collection and analysis, but also data use in decisions made for protection and management of aquatic ecosystems. Although data gathering is often the main focus of an investigation, it only provides the opportunity for generating information. The quality of this information is dependent upon the method of data acquisition and analysis, and the effectiveness of the decision made depends on the entire process-not only sampling. The basic problem with analyzing aquatic ecosystems is their complexity which may not be adequately displayed if the sampling program is not carefully designed. Furthermore, even the most effectively designed program may not achieve the desired objectives if the sampling program design does not recognize the way the information will be used. This paper discusses the limitation of common experimental designs and sampling methods including the use of structural and functional measures, the sampling of natural and artificial substrates, and use of appropriate statistical tests. Certain sampling regimes, including sampling over a single annual cycle, may underestimate ecosystem variability. The use of artificial substrates for collections may be misleading if the behavior of the substrate over time is not understood. Nevertheless, artificial substrates may show greater replicability and reliability than collections from naturally heterogeneous substrates. Generators of information should understand the uses that will be made of the data and that the limitations of the data should be understood by those who must make decisions with it. A simple checklist is provided for use of investigators to ensure adequate preparation of hypotheses, selection of sampling methods, and use of statistical tests.

Effect of Seasonal Changes on Protozoans Inhabiting Artificial Substrates in a Small Pond

Summary Effects of seasonal variation on the structure of protozoan communities were investigated by comparing interactive, equilibrium communities that had colonized polyurethane foam artificial substrates. Substrates were colonized near the surface and bottom of a 1 m deep, eutrophic pond and sampled at weekly or bi-weekly intervals over an annual cycle. No seasonal differences were apparent. Numbers of species were relatively constant except during periods of heavy rainfall or ice melt. Species numbers were significantly, negatively correlated with dilution of the water column. Similarity between samples decreased with increasing time between samples; however, samples taken as much as 30 weeks apart retained a small, residual similarity. Residual similarity was interpreted to be a core community of species. Cluster analysis revealed a generally orderly transition in species composition over time. Stable species numbers in these communities and the rapid change and recovery of species numbers during perturbations make these communities especially valuable in assessing acute impacts on freshwater ecosystems.

Variation in morphology, ecology, and toxicological responses of Colpoda inflata (stokes) collected from five biogeographic realms

Summary Recent studies have revealed low genetic variation within soil isolates of Colpoda inflata from several biogeographic realms, prompting us to question whether such isolates were equally similar with respect to morphological and ecological variables. We also compared the sensitivity of these isolates to acute exposure to three heavy metals (copper, zinc and cadmium), since toxicological response may reflect differences in morphological or ecological parameters. Multivariate analysis of twelve morphological parameters revealed substantial overlap among the six isolates. Isolates from USA and Canada and isolates from China and Kenya tended to cluster together, respectively. Isolates from Mexico and Russia appeared to be intermediate between these two groups. Isolates from China exhibited the greatest growth rate in contrast to the lowest shown by isolates from USA and Canada. Growth rates following exposure to copper, did not differ among the six isolates, however, the Kenya isolate appeared to be the most sensitive to zinc and cadmium. Aside from the Kenya isolate, variation among the other five isolates was relatively small although they were isolated from soils from four biogeographic realms. Our results indicate that morphological, ecological and toxicological variation within C. inflata isolates is sufficiently low, especially among those from the Northern hemisphere, to allow the use of native populations of this species in screening tests for toxicity assessment.

Restoring ecosystem health and integrity during a human population increase to ten billion

Human population growth and the improving condition of human populations in developing countries affect ecological health and integrity. Agricultural development co-opts increasing amounts of global primary production, degrading lands, and reducing species richness. The development of human populations and associated increasing demands for energy assures disposal for increasing amounts of waste, further damaging local ecosystems. Global climate change resulting from diffuse pollutants will affect even the most pristine ecosystems. The human challenge is to maintain ecological integrity and restore ecosystems in the face of accelerating development. The present level of ecosystem protection in not sufficient. Only integrated means of assessing recovery potential and acting to restore ecological productivity can assure continued availability of ecosystem services ranging from free production of food and fiber by plants and animals to final waste assimilation. Restoring ecosystems presumes that species sources are available and that adequate management is in place to monitor and manage recovery. Today, even in the most advanced societies, management is fragmented by non-integrative thinking and the failure to realize that the human scale of political decision-making and management is inappropriate to assure ecosystem restoration. Only by adopting radically new ideas integrating management and ecosystem science can ecological integrity be maintained.