Multispecies Toxicity Tests Research Articles

Toxicity of Herbicide Mixtures to Tropical Freshwater Microalgae Using a Multispecies Test.

Agriculture within the Great Barrier Reef catchment area has contributed to pesticide contamination of adjacent freshwater ecosystems that flow into the Great Barrier Reef World Heritage Area. A novel multispecies toxicity test was used to assess the toxicity of diuron and hexazinone, 2 herbicides commonly detected within the Great Barrier Reef catchment area, to a community of 3 tropical freshwater microalgae: Monoraphidium arcuatum, Nannochloropsis-like sp., and Pediastrum duplex. Diuron was the most toxic herbicide, with 10% inhibition concentration (IC10) values of 4.3, 7.1, and 29 µg/L for P. duplex, M. arcuatum, and Nannochloropsis-like sp., respectively, followed by hexazinone, with IC10 values of 15, 18, and 450 µg/L, respectively Toxicity testing on 2 commercial formulations (Barrage, 13.2% hexazinone and 48.6% diuron; Diurex, 90% diuron) showed that additives in the commercial formulations did not significantly increase the toxicity of diuron. Direct toxicity assessments were carried out on water samples from the herbicide-contaminated Sandy Creek, which discharges to the Great Barrier Reef lagoon, and a clean reference site, Tully Gorge in the Tully River. Toxicity was observed in several Sandy Creek samples. Artificial herbicide mixtures were assessed in synthetic soft water and natural freshwaters, with toxic responses being observed at environmentally relevant concentrations. The present study successfully applied a novel multispecies tropical microalgal toxicity test, indicating that it is an effective tool for the assessment of herbicide toxicity in both natural and synthetic freshwaters. Environ Toxicol Chem 2021;40:473-486. © 2020 SETAC.

Development and application of a multispecies toxicity test with tropical freshwater microalgae

Microalgae are commonly used in ecotoxicity testing due to their ease of culturing and rapid cell division rates. These tests generally utilise a single species of algae; however, microalgae occur in the environment as complex communities of multiple species. To date, routine multispecies toxicity tests using tropical microalgae have not been available. This study investigated four tropical freshwater microalgal species for use in a chronic multispecies toxicity test based on the population growth (cell division) rate: Pediastrum duplex, Monoraphidium arcuatum, Nannochloropsis-like sp. and Chlorella sp. 12. Flow cytometric analysis identified the different fluorescence and light scattering properties of each algal species and quantified each species within multispecies mixtures. Following optimisation of test media nutrients and pH, a toxicity testing protocol was developed with P. duplex, M. arcuatum and Nannochloropsis-like sp. There were no significant differences in growth rates of each alga when tested over 72 h as single species or in multispecies mixtures. Atrazine and imazapic, two herbicides with different modes of action, were used to assess the sensitivity of the multispecies toxicity test. Atrazine was toxic to all species with 72-h IC10 values of 7.2, 63 and 280 μg/L for P. duplex, M. arcuatum and Nannochloropsis-like sp. respectively, while imazapic was not toxic to any species at concentrations up to 1100 μg/L. The toxicity of atrazine and imazapic to each microalgal species in the multispecies toxicity test was the same as that determined from single-species toxicity tests indicating that the presence of these microalgae in a mixture did not affect the toxicity of these two herbicides. This study is the first to develop a multispecies tropical microalgal toxicity test for application in freshwaters. This time- and cost-effective tool can be utilised to generate data to assist environmental decision making and to undertake risk assessments of contaminants in tropical freshwater environments.

Effect of algal surface area and species interactions in toxicity testing bioassays

Single and multispecies algal bioassays were assessed using copper toxicity with three green algae (Scenedesmus subspicatus, Scenedesmus quadricauda and Ankistrodesmus angustus) and one blue-green algae species (Oscillatoria prolifera). Single and multispecies toxicity tests were conducted based on cell density as per standard toxicity testing, and on equivalent surface area. A higher copper sulfate toxicity was registered for O. prolifera, followed by S. subspicatus, S. quadricauda, and A. angustus in single-species toxicity tests based on cell density. Single species toxicity tests based on surface area showed increased copper toxicity with increasing algal surface area except for A. angustus. In multispecies control bioassays, the growth of A. angustus was inhibited in the presence of other species in surface area-based tests. As compared to single species bioassays, O. prolifera, and S. quadricauda showed a decreased sensitivity to copper sulfate in both cell density and surface area based multispecies tests. However, for the algae species with the smallest surface area, S. subspicatus, 96h-EC50 value decreased in multispecies bioassays based on surface area as compared to the single species test, while it increased in multispecies bioassays based on cell density. The difference in S. subspicatus sensitivity to copper between tests based on cell density and surface area supports the need to adopt multispecies toxicity testing based on surface area to avoid the confounding effect on copper toxicity of increased biomass for metal binding. 96h-EC50 values for all species combined in the multispecies test based on cell density and on surface area were significantly different from 96h-EC50 values obtained in single species bioassays. These results demonstrate that single-species bioassays may over- or underestimate metal toxicity in natural waters.

Comparative effects of seawater acidification on microalgae: Single and multispecies toxicity tests

In order to gain knowledge about the potential effects of acidification in aquatic ecosystems, global change research based on microalgae as sentinel species has been often developed. However, these studies are limited to single species tests and there is still a research gap about the behaviour of microalgal communities under this environmental stressor. Thus, the aim of this study was to assess the negative effects of CO2 under an ecologically realistic scenario. To achieve this objective, two types of toxicity tests were developed; i) single toxicity tests and ii) multispecies toxicity tests, in order to evaluate the effects on each species as well as the interspecific competition. For this purpose, three microalgae species (Tetraselmis chuii, Phaeodactylum tricornutum and Nannochloropsis gaditana) were exposed to two selected pH levels (7.4, 6.0) and a control (pH 8.0). The pH values were choosen for testing different scenarios of CO2 enrichment including the exchange atmosphere-ocean (pH 7.4) and natural or anthropogenic sources of CO2 (pH 6.0). The effects on growth, cell viability, oxidative stress, plus inherent cell properties (size, complexity and autofluorescence) were studied using flow cytometry (FCM). Results showed that T. chuii was the most resistant species to CO2 enrichment with less abrupt changes in terms of cell density, inherent cell properties, oxidative stress and cell viability. Although P. tricornutum was the dominant species in both single and multispecies tests, this species showed the highest decrease in cell density under pH 6.0. Effects of competence were recorded in the multispecies control (pH 8) but this competence was eclipsed by the effects of low pH. The knowledge of biological interactions made by different microalgae species is a useful tool to extrapolate research data from laboratory to the field.

Is Caenorhabditis elegans representative of freshwater nematode species in toxicity testing?

Multi-species toxicity tests were conducted using a broad range of freshwater nematode species to assess interspecific differences in sensitivity to chemical stress and to compare the toxicity to that on the standard test organism Caenorhabditis elegans. The lethal effects of nine different chemical treatments, including metals and polycyclic aromatic hydrocarbons (PAHs) in single and mixture application, were determined for nematodes exposed for 48h to spiked aqueous solutions. The investigated freshwater nematodes exhibited distinct differences in their sensitivity. Ranking of the susceptibility of 27 species to chemical stress showed that the effects were largely independent of the tested chemical compounds. Overall, the responses of C. elegans were well within the range of those of freshwater nematode species, being slightly less tolerant to metals, but more tolerant to PAHs than the average freshwater species response. Therefore, this study justified the use of C. elegans as representative model for freshwater nematode species in toxicity testing.

Multispecies toxicity test for silver nanoparticles to derive hazardous concentration based on species sensitivity distribution for the protection of aquatic ecosystems

With increasing concerns about the release of silver nanoparticles (AgNPs) into the environment and the risks they pose to ecological and human health, a number of studies of AgNP toxicity to aquatic organisms have been conducted. USEPA and EU JRC have published risk assessment reports for AgNPs. However, most previous studies have focused on the adverse effects of AgNPs on individual species. Hazardous concentration (HC) of AgNPs for protection of aquatic ecosystems that are based on species sensitivity distributions (SSDs) have not yet been derived because sufficient data have not been available. In this study, we conducted multispecies toxicity tests, including acute assays using eight species from five different taxonomic groups (bacteria, algae, flagellates, crustaceans and fish) and chronic assays using six species from four different taxonomic groups (algae, flagellates, crustaceans and fish). Using the results of these assays, we used a SSD approach to derive an AgNP aquatic HC5 (Hazard concentrations at the 5% species) of 0.614 μg/L. To our knowledge, this is the first report of a proposed HC of AgNPs for the protection of aquatic ecosystems that is based on SSDs and uses chronic toxicity data.

Assessment of the biocompatibility of three-dimensional-printed polymers using multispecies toxicity tests.

Additive manufacturing was adopted in multiple fields of life sciences. It is also becoming a popular tool for rapid prototyping of microfluidic and biomedical devices. Limited studies have been performed to investigate the biological implications of using 3D printed polymers. Here we assessed the biocompatibility of seven commercially available polymers, using a battery of standardized bioassays for chemical risk assessment. Our data show that leachates from photopolymers substrata appear to be very toxic to vertebrates and several invertebrate indicator organisms. These results demonstrate significant consequences for the use of selected photopolymers in the fabrication of bio-devices.

Temporal changes in the sensitivity of coastal Antarctic zooplankton communities to diesel fuel: A comparison between single‐ and multi‐species toxicity tests

Despite increasing human activity and risk of fuel spills in Antarctica, little is known about the impact of fuel on Antarctic marine fauna. The authors performed both single- and multi-species (whole community) acute toxicity tests to assess the sensitivity of an Antarctic coastal zooplankton community to the water-accommodated fraction of Special Antarctic Blend diesel. Single-species tests using abundant copepods Oncaea curvata, Oithona similis, and Stephos longipes allowed comparisons of sensitivity of key taxa and of sensitivity estimates obtained from traditional single-species and more novel multi-species tests. Special Antarctic Blend diesel caused significant mortality and species compositional change in the zooplankton community within 4 d to 7 d. The sensitivity of the community also increased across the summer sampling period, with decreasing 7-d median lethal concentration (LC50) values for total petroleum hydrocarbons (TPH): 1091 µg TPH/L in early January 2011, 353 µg TPH/L in mid January 2011, and 186 µg TPH/L in early February 2011. Copepods showed similar sensitivities to Special Antarctic Blend diesel in single-species tests (7-d LC50s: O. curvata, 158 µg TPH/L; O. similis, 176 µg TPH/L; S. longipes, 188 µg TPH/L). The combined use of single- and multi-species toxicity tests is a holistic approach to assessing the sensitivity of key species and the interactions and interdependence between species, enabling a broader understanding of the effects of fuel exposure on the whole zooplankton community.

Field research for the authorisation of pesticides.

On request of the Dutch government a committee of the Health Council of the Netherlands has reviewed the role that results of field research in its broadest sense (i.e., including multi-species toxicity tests in the laboratory, research on model ecosystems et cetera) can play in ecotoxicological risk assessment for the authorisation of pesticides. The Committee believes that field research can provide valuable additional data about the exposure of non-target organisms and the resultant effects at population, community and ecosystem level. However, it frequently is unclear how these data might be used in reaching a decision about authorisation. To solve this problem, it is necessary to specify what is understood by "unacceptable damage". Both more clearly formulated protection goals of the government and a better understanding of the ecological significance of effects are needed to clarify this. Furthermore, the Committee points out that the statistical power of field trials must be sufficient to allow for the detection of changes that might be regarded as ecologically relevant. Finally, it recommends keeping a finger on the pulse in relation to authorised pesticides by monitoring their presence in environmental compartments and by investigating their role in suddenly occurring mortality among conspicuous animal species, such as birds, fish and honeybees. This kind of research forms a safety net for substances that have been wrongly authorised.

Design and Analysis of Multispecies Toxicity Tests for Pesticide Registration

The community conditioning hypothesis describes ecological structures as historical, nonequilibrial, and by definition complex. Indeed, the historical nature of ecological structures is seen as the primary difference between single-species toxicity tests and multispecies test systems. Given the complex properties of ecological structures, multispecies toxicity tests need to be designed accordingly with appropriate data analysis tools. Care must be taken to ensure that each replicate shares an identical history, or divergence will rapidly occur. Attempting to realize homogeneity by linear cross inoculation or waiting for an equilibrium state to occur assumes properties that ecological structures do not have. Data analysis must also incorporate the dynamic and hyperdimensional nature of ecological structures. Univariate analysis of individual variables denies the fundamental character of ecological structures as complex systems. A variety of methods, such as correspondence analysis, nonmetric multidimensional scaling, and nonmetric clustering and association analysis, are available to search for patterns and to test their relationships to experimental treatments. Visualization techniques including Space–Time Worms and redundancy analysis are also critical in attempting to understand the dynamic nature of these structures. Reliance upon the traditional analysis methods, such as ANOVA and the estimation of LOECs (lowest observable effects concentrations) or NOECs (no observable effects concentrations), comparable to those of single-species toxicity tests, is to be blind to the unique and complex nature of multispecies toxicity tests. Fundamental design criteria for multispecies toxicity tests, data analysis, and interpretation are presented.

DESIGN AND ANALYSIS OF MULTISPECIES TOXICITY TESTS FOR PESTICIDE REGISTRATION

The community conditioning hypothesis describes ecological structures as historical, nonequilibrial, and by definition complex. Indeed, the historical nature of eco- logical structures is seen as the primary difference between single-species toxicity tests and multispecies test systems. Given the complex properties of ecological structures, mul- tispecies toxicity tests need to be designed accordingly with appropriate data analysis tools. Care must be taken to ensure that each replicate shares an identical history, or divergence will rapidly occur. Attempting to realize homogeneity by linear cross inoculation or waiting for an equilibrium state to occur assumes properties that ecological structures do not have. Data analysis must also incorporate the dynamic and hyperdimensional nature of ecological structures. Univariate analysis of individual variables denies the fundamental character of ecological structures as complex systems. A variety of methods, such as correspondence analysis, nonmetric multidimensional scaling, and nonmetric clustering and association analysis, are available to search for patterns and to test their relationships to experimental treatments. Visualization techniques including Space-Time Worms and redundancy analysis are also critical in attempting to understand the dynamic nature of these structures. Reliance upon the traditional analysis methods, such as ANOVA and the estimation of LOECs (lowest observable effects concentrations) or NOECs (no observable effects concentrations), com- parable to those of single-species toxicity tests, is to be blind to the unique and complex nature of multispecies toxicity tests. Fundamental design criteria for multispecies toxicity tests, data analysis, and interpretation are presented.

The community conditioning hypothesis and its application to environmental toxicology

AbstractIn this paper we present the community conditioning hypothesis, “ecological communities retain information about events in their history.” This hypothesis, which was derived from the concept of nonequilibrium community ecology, was developed as a framework for understanding the persistence of dose‐related responses in multispecies toxicity tests. We present data from three standardized aquatic microcosm (SAM) toxicity tests using the water‐soluble fractions from turbine fuels (Jet‐A, JP‐ 4, and JP‐8). In all three tests, the toxicants depressed the Daphnia populations for several weeks, which resulted in algal blooms in the dosed microcosms due to lower predation rates. These effects were short‐lived, and by the second and third months of the experiments, the Daphnia populations appeared to have recovered. However, multivariate analysis of the data revealed dose/response differences that reappeared during the later part of the tests, often due to differences in other consumers (rotifers, ostracods, ciliates), or algae that are not normally consumed (filamentous green algae and bluegreen “algae”). Our findings are consistent with ecological theories that describe communities as the unique product of their etiologies. The implications of this to environmental toxicology are that almost all environmental events leave lasting effects, whether or not we have observed them.

TREATABILITY, TOXICITY AND BIODEGRADABILITY TEST METHODS

1. This review confirms that treatability and biodegradability test methods have been cited extensively in the literature. It is clear that the method selected depends on the specific objectives of the test, i.e. the determination of whether a substance is toxic, biodegradable or treatable. Factors that have to be considered when selecting the test methods are the cost of performing the test, the time and resources involved, and the accuracy required. It often appears that more extensive simulation studies are required after initial screening tests have been performed. 2. Many of the enzyme and bacterial growth tests which have been developed for monitoring or screening of toxicants and their persistence in water and wastewaters have been reviewed. Most of these tests are rapid, inexpensive, and reproducible. Most of the biochemical and microcalorimetric approaches, although promising, are still in their infancy as regards toxicity testing. Therefore, biological testing still appears to be most suitable for routine assessment. 3. Micro-organisms are particularly suitable for use in toxicity testing of chemicals as they are inexpensive to culture, have rapid growth rates, and usually provide reproducible results (Vaishnav & Korthals, 1990). Many bioassays have been developed to evaluate the toxicity and treatability of municipal and industrial effluents. Numerous single species tests have been recommended by several authors (Dutka et al., 1983; Beaubien et al. 1986). Such approaches are mainly based on the belief that, by selecting the most sensitive species and by using appropriate factors to allow for variability not included in the test, the highest levels of biological organization will be adequately protected. Single species tests are now quite well established, and when properly used, are easy to analyse and quantify. However, it has been pointed out (Levin, 1984) that the results obtained from single species tests cannot easily be applied to natural field conditions because the test organisms are extensively laboratory acclimated; also the test conditions provide for optimized growth and survival, a situation unlikely to be found in the field. Moreover, a fundamental problem with this approach is that it assumes that the ecosystem is a collection of single species exposed to toxicants under constant conditions (Cairns, 1982). Multi-species toxicity tests, that is the use of mixed cultures or communities of micro-organisms for a testing protocol, are found to be generally much less sensitive than single species tests (Dutka & Kwan, 1984).(ABSTRACT TRUNCATED AT 400 WORDS)

Multispecies toxicity tests using indigenous organisms: Predicting the effects of complex effluents in streams

A study was conducted to determine if contaminant-induced changes in macroinvertebrate communities in laboratory stream microcosms could be used to predict responses of these organisms in a natural stream receiving the same contaminant. Test organisms were transferred to the artificial streams in rock-filled containers previously colonized for 30 days upstream of the effluent outfall. The microcosms were exposed for 20 days to concentrations of the effluent that reflected those at field sites where macroinvertebrates were collected.

Diversity indices, community comparison indices and canonical discriminant analysis: Interpreting the results of multispecies toxicity tests

Canonical discriminant analysis, diversity indices and community comparison indices were evaluated to determine their utility in quantifying macroinvertebrate response to a complex effluent in laboratory microcosms. The Shannon and Simpson diversity indices and the following community comparison indices were analyzed: (1) Renkonen's percentage similarity; (2) Bray-Curtis index; (3) average χ 2 index; (4) Stander's SIMI index; (5) Pinkham-Pearson index; and (6) Canberra metric index. Statistical inferences were made with the diversity measures using an ANOVA in conjunction with Duncan's test. A permutation or randomization procedure was used to test the hypothesis of no treatment effect based on the community comparison indices. The canonical discriminant analysis was primarily influenced by the drop in mayfly densities in the higher dose microcosms and indicated that the high-dose microcosms were different from the other microcosms. The Shannon and Simpson diversity measures indicated that both the medium- and high-dose microcosms were significantly different ( P ⩽ 0.05) from the control microcosm, but this response was due solely to the increase in density of chironomids. When the diversity indices were calculated without chironomids, they failed to reflect adverse effects on mayflies in the medium-dose microcosms. The statistical inferences for all community comparison indices were similar and indicated that the high dose microcosms were significantly ( P ⩽ 0.06) different from the control. However, the Bray-Curtis index provided the most meaningful condensation of data.

Establishing and maintaining laboratory-based microcosms of riffle insect communities: their potential for multispecies toxicity tests

The purpose of this study was to determine which of the following artificial stream designs would be most logistically simple yet effective in maintaining riffle insects during a 30 d bioassay: 1) static and no current (S-NC); 2) flow-through and no current (FT-NC); 3) static with current (S-C); or 4) flow-through with current (FT-C). Flow-through and current, when provided, were 12 ml min−1 and 30 cm sec−1, respectively. Streams were covered by emergence traps, and daylight equivalent lights provided a natural photoperiod. The four stream designs were evaluated in triplicate based on changes in insect species-abundances after 30 d. Test organisms were transferred to the artificial streams in rock-filled containers previously colonized for 30 d in a third-order mountain stream riffle. Additional colonized substrates were sampled immediately to provide an estimate of initial densities placed in the artificial streams. Hess samples were taken directly from the source riffle to evaluate how well the artificial substrates reflected species-abundances on the natural substrate. Adults were collected from the artificial streams every 48–72 h to determine the percentage of initial densities that emerged. After 30 d (7 Aug–6 Sept, 1986), all organisms remaining in the streams were censused. Designs were evaluated using combined densities of adults and young.

Effects of atrazine on freshwater microbial communities.

A multispecies toxicity test system using naturally derived microbial communities on polyurethane foam substrates was used to evaluate the toxic effects of the herbicide atrazine. Both structural (e.g., protozoan species number, biomass) and functional (e.g., colonization rate, oxygen production) community responses were measured. Oxygen production and the ability of communities to sequester magnesium and calcium were the most sensitive measures of toxic stress due to atrazine (maximum allowable toxicant concentrations [MATCs]=17.9 μg/L). Dissolved oxygen was 33% lower, and there was 15% less calcium and magnesium in communities at and above 32.0 μg/L atrazine compared to controls. Species richness and estimates of biomass (total protein and chlorophyll a) were less sensitive (MATCs=193) to atrazine. At the highest atrazine concentration (337 μg/L), species numbers were 30% lower than controls, and protein and chlorophyll a content of communities were reduced by 38 and 91%, respectively. Low levels of atrazine (3.2–32.0 μg/L) resulted in a 46% increase in species numbers and a greater concentration of total protein and chlorophyll a (41 and 57%, respectively). Results compared well with other estimates of chronic toxicity for effects of atrazine on aquatic communities. Reported MATCs ranged from 70.7 to 3,400 μg/L. The results from this test emphasize the importance of monitoring both structural and functional measures of community integrity in toxicity testing with multispecies.

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.

A Provisional Multispecies Toxicity Test Using Indigenous Organisms

Abstract A multispecies toxicity test is described that uses indigenous microorganisms. The test is suitable for both laboratory and field, is inexpensive, replicates easily, and uses extremely inexpensive materials. An additional advantage is the use of an important ecological rate process as an end point; therefore the test is superior to test using lethality as an end point. The test can be carried out using organisms collected from a site of interest or from a specific ecological resource area. Site-specific or synthetic dilution water may be used. The major drawback is a requirement for significant taxonomic ability. However, more general chemical measures such as ATP biomass, chlorophyll biomass, or heterotrophic index may substitute for species identification. Although this test has been used in a variety of freshwater ecosystems in the United States and has been validated to a limited degree in the People's Republic of China, a wider data base is required before it can be generally used.

EVALUATING THE OPTIONS FOR WATER QUALITY MANAGEMENT1

ABSTRACT: The agricultural revolution occurred because the un‐managed environment was not providing food in either the quantity or quality that society desired. The “environmental revolution” is developing because the unmanaged environment is clearly not capable of assimilating societal wastes without being seriously degraded. Effective environmental management will require regional and site‐specific modification of general principles and practices that can be used at a national or international level. An environmental management system can be operated in the same manner as any industrial quality control system with three basic components: (a) sensors at appropriate locations, (b) rapid generation and feedback of information, and (c) a quality control group capable of taking immediate effective action when system performance is outside predetermined boundary conditions. This discussion focuses primarily on three areas: (a) management options available to regulate intrusion of societal wastes into natural systems, (b) types of methods available for predicting and validating effects on natural systems, and (c) modifications of present legislation that would permit the most flexibility in selecting from the various management options. Also considered are multispecies toxicity tests using species with cosmopolitan distribution in test systems with a high degree of environmental realism. Among the many values of such tests is the ability to exchange information from all parts of the world effectively because the test organisms are not restricted to a particular geographic region.