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Experiments with field soils confirm the hypothesis that metal availability can decrease as a result of aging, especially for metals with a small ionic radius. Although aging also seems to affect metal uptake, it should be noted that some organisms are able to regulate their internal metal concentra- tions within a narrow range, especially for essential elements.

Deficiency of essential metals as well as metal toxicity to plants and invertebrates seem to be liromium B , copper C , n uncontaminated full a De Groot et al. Janssen related to the environmental availability of these metals. Unfortunately, aging effects are often confounded by differences in soil properties between freshly spiked and historically contaminated soils. Environmental parameters such as temperature, moisture content, drying and rewetting cycles, and pH affect the rate of aging, whereas pH seems to be the sole important parameter affecting the extent of aging.

Soil Sci Soc Am J Alexander M Aging, bioavailability, and overestimation of risk from environmen- tal pollutants. Environ Sci Technol Almas A, Singh BR, Salbu B Mobility of cadmium and zinc in soil influ- enced by equilibration time, temperature, and organic matter. J Environ Qual Almas A, Salbu B, Singh BR Changes in partitioning of cadmium- and zinc- 65 in soil as affected by organic matter addition and temperature.

J Soil Sci Aust J Soil Res Barrow NJ Testing a mechanistic model. The effects of time and temperature on the reaction of zinc with a soil. Barrow NJ Effect of time and temperature on the sorption of cadmium, zinc, cobalt, and nickel by a soil. Modeling the extent and rate of reaction. Boawn LC Residual availability of fertilizer zinc. Soil Sci Soc Am Proc Brennan RE Reaction of zinc with soil affecting its availability to subterranean clover.

Effect of soil properties on the relative effectiveness of applied zinc. The relationship between critical concentrations of extractable zinc and properties of Australian soils responsive to applied zinc. Effect of soil type and time. Effect of incubation temperature. Aust J Agric Res Brown AL Zinc relationships in Aiken clay loam. Adsorption and diffusion of metals.

Mater Res Soc Symp Proc Arch Environ Contam Toxicol Soil Biol Biochem Christensen TH a Cadmium soil sorption at low concentrations: Effect of time, cadmium load, pH, and calcium. Water Air Soil Pollut Christensen TH b Cadmium soil sorption at low concentrations: Reversibility, effect of changes in solute composition, and effect of soil aging.

Comans RNJ Adsorption, desorption and isotopic exchange of cadmium on illite: Appl Soil Ecol 5: Geochim Cosmochim Acta Elgabaly MM Mechanisms of zinc fixation by colloidal clays and related miner- als.

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Z Pflanzenemahr Bodenkd Harter RD Effect of soil pH on adsorption of lead, copper, zinc, and nickel. Hooda PS, Alloway BJ Changes in operational fractions of trace metals in two soils during two years of reaction time following sewage sludge treatment.

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Int J Envi- ron Anal Chem Kuo S Concurrent sorption of phosphate and zinc, cadmium, or calcium by a hydrous ferric oxide. Physical, Chemical and Biological Interactions. Environ Toxicol Chem Lock K, Janssen CR b Ecotoxicity of zinc in spiked artificial soils versus contami- nated field soils. Lock K, Janssen CR c Test designs to assess the influence of soil characteristics on the toxicity of copper and lead to the oligochaete Enchytraeus albidus. Lock K, Janssen CR The effect of aging on the toxicity of zinc for the potworm Enchytraeus albidus exposed in artificial soils.

Eur J Soil Sci Environ Sci Tecbnol Commun Soil Sci Plant Anal Ma YB, Uren NC a Tbe effects of temperature, time and cycles of drying and rewetting on tbe extractability of zinc added to a calcareous soil. Aust 1 Soil Res Martin HW, Kaplan DI Temporal changes in cadmium, tballium and vanadium mobility in soil and pbytoavailability under field conditions. Clays Clay Miner McGrath SP, Cegarra J Chemical extractability of heavy metals during and after long-term applications of sewage sludge to soil.

Padmanabham M Adsorption-desorption behaviour of copper II at the goethite- solution interface. Ecotoxicol Environ Saf Posthuma L, Notenboom J Toxic effects of heavy metals in three worm species exposed in artificially contaminated soil substrates and contaminated field soils. National Institute of Public Health 20 K. J Colloid Interface Sci Isotomidae to copper under different soil copper contamination histories in relation to risk assessment. Anne- lida , using neutral-red retention assay. Appl Soil Ecol 3: Spurgeon DJ, Hopkin SP Effects of variations of the organic matter content and pH of soils on the availability and toxicity of zinc to the earthworm Eisenia fetida.

Street JJ, Sabey , Lindsay WL Influence of pH, phosphorus, cadmium, sewage sludge, and incubation time on the solubility and plant uptake of cadmium. J Environ Qual 7: Clays Clay Miner 9: Isotopic exchange equilibria and the application of tracer techniques. Xiang HE, Banin A Long-term transformations and redistribution of potentially toxic heavy metals in arid-zone soils incubated: Manuscript received September 6; accepted September 11, Rev Environ Contam Toxicol Use and Misuse of Algal Toxicity Data: Regulatory Context 25 III.

Test Methods 26 A. Environmental Availability and Physicochemical Eactors 27 C. Biological Availability and Biological factors 34 IV. Introduction Although algae were used as early as in toxicity tests Allen and Nelson , it was not until the s that a standardized assay with freshwater algae was developed. The aim of this method was to determine the algal growth potential and algal productivity of natural waters and effluents: As a result, most current regulatory methods, including the selection of test species, culture, and test methods, rely heavily on this origi- Communicated by George W.

Heijerick nal test procedure. For example, most algal bioassays in recent years have been performed predominantly with S. Although most standard algal assays used for regulatory purposes seem very similar in design and protocol, subtle differences in all aspects of the toxicity test design may lead to a large variability in test results.

For example, the composition of the culture and test medium, which may vary considerably among test protocols, not only can determine the bio- availability of the test substance but also can affect the physiological state of the test organism before and during the bioassay and thus influence the test result. It has been shown that using starved algae as inoculum for toxicity assays can lead to higher toxicity, probably as a result of the poorer physiological condition of the algae or increased toxicant uptake.

Increased nutrient concentra- tions, on the other hand, appear to reduce the uptake of certain substances Horn- strom For example, Sanders observed a decreased uptake of arse- nic when algae were exposed to higher phosphorus concentrations. Although the need for a relatively simple algal toxicity test as part of a battery of tests for regulatory toxicity testing of substances and wastes is obvi- ous, it should be equally clear that we need to understand the meaning of the results and that we should be aware of the limitations in applying these results in environmental risk assessments Nalewajko and Olaveson All too of- ten, these types of data are used for regulatory purposes other than those for which they were developed.

Several authors, comparing different algal toxicity test procedures, have iden- tified potential uses and limitations of these methods and have come to similar conclusions. Lewis provides an overview of currently used toxicity tests with freshwater algae and discusses the potential implications of differences in culture techniques, nutrient media, test species and sensitivity, test concentra- tions, condition and duration, effects measurements, reproducibility, and use of results.

Similarly, Nalewajko and Olaveson critically reviewed all aspects of algal toxicity testing and concluded that an ecophysiological approach is required to increase the ecological relevance of algal toxicity tests. They empha- sized the need for increased understanding of the relationship between the physi- cochemical characteristics of the environment and the physiological dynamics of algae.

Hornstrom made a survey of the different aspects of batch algal test methods that are poorly described in existing international protocols, leading to high variability in test results.

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Based on this review, he proposed an alterna- tive test method that also considers prevailing environmental conditions in oli- gotrophic lakes. Several authors have indicated that these procedures or aspects of these procedures might not be suitable for testing metals and metal compounds; this includes the physical, chemical, and biological aspects of the test methods. Current standard methods for assessing metals suffer from a number of weaknesses from both environmen- tal e.

The aim of this review is to evaluate and discuss the different parameters that may affect the outcome of freshwater algal toxicity tests for metals and, where possible, to suggest solutions or modifications to the existing test proto- cols. This presentation should help to generate realistic metal toxicity data that can be used and incorporated in realistic risk assessment approaches and envi- ronmental management purposes.

Note that the marine environment is not dis- cussed here; such reviews have been presented by Eletcher , Thursby et al. Regulatory Context Laboratory algal toxicity tests may be used as screening toxicity tests, but in many cases the results are used as estimates of ecotoxic concentrations. Their use as toxicity screens is more justified than their application to predicting envi- ronmental impact Lewis OECD and ISO state that the effects data from algal tests should not be used to predict environmental impact but only to provide the likelihood of effect or no effect.

Table 1 summarizes the main test conditions of these four internationally recognized standard test procedures. The overall caution expressed in these guidelines and by several other authors Lewis ; Nalewajko and Olaveson regarding appropriate application of laboratory algal toxicity data is not reflected in general regulatory practice.

Most toxicity data contribute to data compilations that are then used for hazard and risk assessments. Eor example, the currently used European Union EU sys- tem for classifying chemical substances for their potential hazard to the aquatic 26 C. Overview of existing standard test protocols for toxicity tests with algae.

Adapted from Lewis Similarly, labora- tory algal toxicity data are used in the EU risk assessment procedures for new and existing substances to derive Predicted No Effect Concentration EC, These types of data are also used to derive water quality objectives in both the United States and Europe Lewis Consequently it is surprising that, despite the numerous applications and the importance of this type of test, the standard protocols currently used do not adequately consider or control the various physicochemical and biological pa- rameters that can affect the accuracy of the results.

The use of some toxicity data could, therefore, have undesirable repercussions on conclusions and envi- ronmental management programs when based on erratic or nonrepresentative test results. General Most standard algal toxicity tests are similar in technique: A control and five test concentrations are used with a minimum of three replicates. Test vessels are placed on a rotary or oscillatory shaker or may be hand shaken daily.

The tests are conducted under conditions of controlled tem- perature, light, and initial pH. Algal biomass or other endpoints determined or estimated at several intervals during the test or at the end of the assay are then used to calculate the effects of the toxicant on algae. Comparison and discussion of the general experimental conditions for widely used freshwater algal assays are given in Nyholm and Kallqvist , Lewis , and Nalewajko and Olaveson Below, a brief comparison is given of the general experimen- tal conditions in standard toxicity tests with algae e. Issues that are specifically important for testing metals and metal compounds are discussed in greater detail.

As indicated, as- pects affecting both environmental and biological availability of metals are pre- sented. To initiate a toxicity test, algal cultures in log growth phase are needed. In most of the standard protocols considered in this review, very little guidance is given on the exact culturing techniques required to estab- lish the test organisms in the log growth phase. However, this phase is of crucial importance to ensure the optimal and, perhaps more important in a regulatory context, reproducible growth and physiological condition of the organisms. Im- portant factors for optimal growth include culture type, growth medium and nutrient concentrations, light conditions, temperature, and pH.

Although the ef- fects of these factors on toxicity test results are discussed in detail, it should be emphasized that pretest culturing variations can influence test results for the same physiological reasons as discussed next. In comparison to the studies examining factors affecting toxicity test results in the actual assay, little information is available on the effect of pretest cultur- ing conditions.

However, variation in culturing techniques of the algae before toxicity testing might well be an important factor affecting the wide variability of algal toxicity test results. Copper, for example, was found to be more toxic toward green algae under phosphorus limitation than under nitrogen limitation conditions Hall et al. Although these limitations refer to the actual test conditions, the type of limitation in the preculture medium could also be reflected in the outcome of algal tests.

Until now, this possible source of test variation has not been examined. Most guidelines propose batch culture methods, although continuous culture techniques e. In chemostat cultures, the test medium is being renewed during the expo- sure period and determines, together with a known limiting nutrient, the growth rate of the culture Lederman and Rhee Heijerick In the continuous chemostat culture, algae were stressed by nutrient limitation; subsequent Cu exposure demonstrated an increased sensitivity of the algae.

Cells originating from a nutrient-rich batch culture that were exposed to a single pulse of Cu were less sensitive, however. The observation that algae are substan- tially more sensitive to Cu when exposed in chemostat cultures may raise con- cerns about the applicability to the natural environment of toxicity test results obtained from simple batch culturing.

Problems associated with growth in batch cultures have been discussed in the context of basic algal physiology Klaine and Ward and in the context of algal toxicity testing Nyholm and Kall- qvist Culture and Test Media. Algae are normally cultured and exposed to the test substance in a nutrient-enriched medium. A large number of culture and test media for both freshwater and marine algae have been described Guilard and Ryther ; Harrison et al.

Most media used in standard protocols are prepared by adding prescribed amounts of macro- and micronutri- ents to distilled, filtered, or deionized water.

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The test medium, possibly with minor adjustments, is used as the culture medium. However, in most publica- tions little or no information is given on the type of medium that has been used to culture algae. Unlike the media prescribed for toxicity testing, culture media are less well defined. It is clear that the type of culture medium will be reflected in the general health of the algal culture and might affect the physiological state of the algae and the outcome of toxicity tests. The importance of this factor cannot be ascertained as no literature is available.

The effect of test medium composition on algal sensitivity has been studied extensively. Stauber and Florence , for example, examined the toxicity of Cu and Zn to the marine diatom Nitszchia closterium and that of Cu and Pb to the freshwater alga Chlorella pyrenoidosa in two different media. Similarly, the toxicity of copper and zinc toward N. It is well recognized that test medium composition is a major factor affecting toxicity Eloranta ; Millington et al. These authors identified pH, chelator presence, and major cat- ion composition as important factors influencing toxicity.

Although the initial pH of standard algal tests is given in the respective guidelines, varying from 7. This change is a consequence of the interaction of three factors: Microalgae use primarily dissolved CO 2 as their car- bon source. In standard batch assays, the biomass density may quickly reach a level where the demand for CO 2 by the growing algal population exceeds the transfer rate of CO 2 from the gas phase to the liquid phase.

This utilization of biocarbonate leads to the formation of Off ions and thus to an increase in pH. As the biological uptake rate of dissolved CO 2 is saturated at very low CO 2 concentrations, exponential algal growth continues until the bicarbonate source is exhausted, or until the pH rises to levels that adversely affect the algae.

As population growth is reduced, pH may return to its initial value or may, through alkalinity-changing reactions e. A full description of the mechanism is given in Nyholm and Kallqvist Based on a large number of reported algal studies performed in static circumstances with no aera- tion and with high algal densities, these authors concluded that the algal popula- tions probably were growth limited and experienced high pHs. They found that in the static test pH had increased from 7. Population growth was clearly limited in the static test, exhibiting a linear growth after only 2 d.

Considering the importance of even small pH changes on the speciation and toxicity of many metals, the observed differences caused by these simple opera- tional variables may, and probably do, contribute to the variability of the stan- dard algal toxicity results obtained for metals. Indeed, Peterson et al.

The opposite phenomenon, however, has been reported by many authors. Steeman-Nielsen and Kamp-Nielsen and Hargreaves and Whitton reported an increase of Cu toxicity with increasing pH for the algae Chlorella pyrenoidosa and Hormidium rivulare, respectively. There is growing evidence that this might be explained by the fact that hydrogen ions competitively exclude metal ions from binding to cell-surface ligands and hence inhibit metal uptake Campbell and Stokes ; Parent and Campbell ; Peterson et al.

Recently, Heijerick et al. This physiological effect of pH was reported earlier by Crist et al. For copper they reported a decrease of the hr EC50 from 35 to 1. From the foregoing examples it is clear that pH control and carbon supply are, even in the current standard guidelines, factors that should be adequately monitored or controlled during the test.

An exception might be the use of MOPS 3-[A-morpholino]propanesulfonic acid , which is reported to be completely noncomplexing for metals Kandeged- ara and Rorabacher and which is recommended by USEPA be- cause it does not change the toxicity of nontoxic effluents or the toxicity of toxic effluents and sediment pore waters.

De Schamphelaere et al. Consequently, additional guid- ance in the present standard procedures is required to minimize pH as a source of variability. As low initial algal biomass and exposure periods of d are already well defined and adequate in most standard procedures, strictly defining adequate mass transfer conditions for CO2, by using continuous shaking or aera- tion, might be a considerable step forward in controlling pH changes in routine algal assays.

In conclusion, it is clear that metal toxicity toward algae cannot be separated from the pH of the test medium. To obtain a constant pH, several methods could be applied such as frequent adjust- ments of the pH with a nontoxic acid, through the use of a noncomplexing and nontoxic buffer such as MOPS De Schamphelaere et al.

Although pH can be controlled with these techniques, one still might question the ecologi- cal relevance of Climited test conditions. The composition of the nutrient medium has been shown to affect the toxicity of chemicals such as pentachlorophenol and brominated organic Algal Toxicity Tests 31 compounds Smith et al. Vasseur and Pandard , however, reported that the medium composition did not affect metal toxicity toward S. The effect of one constituent, EDTA, has been investigated more than others. Low concentrations of EDTA are needed to complex trace metal micronutrients e.

However, EDTA will also complex and reduce the toxicity of metal test substances if used in these media. If chelators are omitted, algal growth may be nutrient limited significantly during the test and log growth may be delayed or not attained Lewis In their investigation into species-dependent variation of copper toxicity, Blanck et al. It is clear that the presence of strong chelators such as EDTA will affect metal bioavailability and toxicity and should be taken into account when com- paring metal toxicity data obtained in different test media. Nutrients and Other Medium Characteristics. In a batch culture, providing light absorption or CO 2 mass transfer is not limiting, exponential growth will prevail at a constant rate until the limiting nutrient has been taken up.

Growth may still continue until the intracellular reserves have been used up Nyholm and Kallqvist In comparison with phosphorus limitation, algal growth is more rapidly suppressed under nitrogen-limiting conditions.

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An in-depth study of the influence of the mineral composition of the medium on growth of plank- tonic algae was reported by Chu Comparisons of the nutrient composi- tion of the standard algal culture and test media are given by Millington et al. According to these authors, although differences in composition do occur, in general these media are rather similar in both the type of nutrients and their quantity.

Despite the apparent similarities among standard media, Adams and Dobbs found that medium composition had a signifi- cant effect on the toxicity of aminotriazole to S. Similarly, Mil- 32 C. Heijerick lington et al. In the tests with S. For Scenedesmus subspicatus, an identical maximum difference was observed, whereas for Chlorella vulgaris medium composition influenced toxicity values by a factor of Metal toxicity to marine and freshwater algae may be regulated to some extent by macronutrient availability Bates et al.

There are several reports of decreased toxicity in response to increases in P concentrations Harding and Whitton ; Meijer ; Monahan ; Li ; Say and Whitton A possible explanation for these observations, based on the liter- ature, is given by Hall et al. High P concentrations in the medium result in elevated cellular P concentrations, in excess of immediate cell require- ments, and are stored in polyphosphate bodies Aitchison and Butt ; Rhee , Polyphosphate bodies have been reported to act as a site for intra- cellular detoxification of metals Pettersson et al.

Enhanced cellular P levels may consequently lead to increased algal detoxification capacity and thus lower observed metal toxicity; this was also suggested by the findings of Twiss and Nalewajko , indicating that internal polyphosphate plays a passive role in protecting Scenedesmus acutus from Cu. The role of nutrient limitation on Cu toxicity to algae was investigated by Hall et al. In the first study, these authors observed that both Chlamydomonas geitleri and Chlorella vulgaris were more sensitive to Cu effects in batch cultures under P limitation than under N limitation.

C ratio of 0. Similarly, in the N-limited cultures, a decrease from 2. For Chlamydomonas geitleri, growth rates decreased from 2. As well as explaining some of the variability in the copper algal toxicity reported in literature, the observed sensitivity differences in nutri- ent-limited algae might also have ecological implications. Quantities of micronutrients in test and culture media used in standard guide- lines can vary considerably.

Copper concentrations are 3. The influence of these trace elements on the sensitivity of algae to environmental contaminants has not been examined in depth. This fac- Algal Toxicity Tests 33 tor may be especially important in toxicity assessments of metal and metal com- pounds, as it has been reported that preexposure to metals during culturing can affect the sensitivity of algae in metal toxicity tests.

Muyssen and Janssen acclimated S. Com- pared to nonacclimated algae, acclimated S. An increased growth rate was not observed for C. Other authors Coleman et al. There are other observations of adap- tation to metal levels in culture. Stokes and Dreier demonstrated a loss of Cu tolerance in a Cu-tolerant isolate of Scenedesmus sp. Kuwabara and Leland found that Cu toxicity to S. Einally, Ahluwalia and Kaur found that 0. In conclusion, there are clear indications that nutrients and trace elements affect the sensitivity of algae to metals.

For trace elements, the concentrations of these elements in the culture medium should be considered when evaluating toxicity data, especially those results that are used for water quality criteria derivations and risk assessments. Temperature and light need to be controlled during algal toxic- ity tests because they can significantly affect algal growth Gaur and Singh Current standard algal tests have exposure periods ranging from 3 to 4 d. Longer exposure periods using batch procedures should be avoided as algal growth may become nutrient limited or changes in the bioavailability of the contaminant e.

Few data are available on the effect of these variables on metals toxicity toward algae. Only Mayer et al. Temperature only influenced the results indirectly by interacting with light increase of the saturation intensity at higher temperature. Nalewajko and Olaveson reported that selection of the test species is the most important step in the performance of algal toxicity assays.

Based on the arguments presented here, the present authors tend to agree with this statement, although species selection should depend on the purpose of the toxicity test. The algal species recommended in various standard methods are given in Table 2. Many of these were chosen because of their availability and ease of culture and, to a lesser extent, because of their ecological relevance and sensitiv- ity to toxicants Lewis The species most frequently used is the green alga Selenastrum capricornutum Prlntz renamed Pseudokirchneriella subcapitata; Hindak Other less commonly used species include the green algae Chlo- rella vulgaris, Scenedesmus quadricauda, and Scenedesmus subspicatus, and some diatoms, cyanobacteria, and chrysophytes.

The predominance of Selena- strum as the standard test species can be attributed in part to its use in the AAP hottle tests described in the Introduction Leischman et al. The infrequent use of diatoms, cyanobacteria, and chrysophytes in toxicity tests is due to the difficulties encountered in maintaining cultures, lack of commercial sources, and difficulty in obtaining sufficient growth during the 3- to 4-d test period. From the point of view of ecological relevance, impor- tant for certain uses of algal toxicity data, S.

Overview of algal species used in common standard algal methods. Cyanophyta Microcystis aeruginosa Kutzing Anabaena flos-aquau Lyng. Navicula pelliculosa Grunow Nitzschia sp. Algal Toxicity Tests 35 distributed in the environment as perceived. For example, Riemer re- ported that although the genus is widely distributed in U. Greeson noted that, of genera of freshwater algae present in the U. Selenastrum was not considered dominant but is classified as commonly occurring. More important, reliance on one species for risk assessment may over- or underpredict toxicity to other species that exhibit different toxicokinetics.

The majority of freshwater microalgae used in toxicity testing belong to one of eight possible classes. As this classification is made on the external and internal characteristics of the algal cell, it should be clear that all these classes, genera, or species might very well have different responses to contaminant uptake and ensuing toxicity Bold and Wynne This variation may be particularly important in species for which exclusion of metals is the only operative mechanism of metal resis- tance, as demonstrated by Flawkins and Griffiths for four species of marine phytoplankton exposed to Cu.

Nalewajko and Olaveson further reviewed the ecology of natural algal assemblages in the context of species representativeness of standard algal toxicity tests. It should be emphasized that no validation studies have been performed that examine the potential of any algal species as surrogate test species in laboratory or field studies. Perhaps the most important argument for increasing the number of species routinely used in algal assays is provided by the extensively reported intra- and interspecies differences in sensitivity of algae toward environmental contami- nants Blanck et al.

From the current literature it is unclear whether the reported differences in sensitivity among various taxa, and indeed within individual species, are real or artifacts caused by differences in culturing conditions, media composition, or other test abiotic variables. Next to these factors, the extent to which the physio- logical state of the algae during and before the assay affects the results is rarely considered or studied.

Examples of interspecific differences in algal sensitivity are summarized in Lewis In toxicity tests with copper sulfate, Fitzgerald and Faust compared sensitivity of Microcystis aeruginosa and Chlorella pyrenoidosa and observed a difference of a factor of Similarly, USEPA reported a toxicity difference between 80 and when comparing results from Cu assays with the frequently used regulatory species Chlorella pyrenoidosa, Scenedesmus quadricauda, Selenastrum capricomutum, and Chlamydomonas sp.

Bringmann and Kiihn noted a sensitivity difference of , , and 37 for Micro- cystis aeruginosa and Scenedesmus exposed to sodium dichromate, nickel chlo- ride, and copper sulfate. Using four green and blue-green species, Vocke et al. Heijerick found differences of , 4, 7, and for As, Cd, Hg, and Se. Based on the Zn toxicity data reported by Les and Walker and Van Ginneken , an eightfold difference in sensitivity was calculated between S. For cadmium, 3-d NOECs are reported ranging from 8. They demonstrated that a species-dependent variation in algal sensitivity, based on d ECioo values, may exceed three orders of magnitude depending on the chemical tested.

The ECiooS observed for copper sulfate ranged from 0. The authors further concluded that no generally sensitive algal species could be identified. However, based on the distribution of sensitivity toward the 19 chemicals, some algae seemed to be more extreme in their response to chemicals.

Monodus subterraneus, Raphidonema longistra, and Synech- ococcus leopoliensis, on the other hand, were very sensitive to some and very insensitive to other compounds. These observations are clearly in contradiction with the conclusions of Roberts et al. It should be noted that the latter authors only tested three algal species and three chemicals. In general, the observation of large differences in interspecies sensitivity sup- ports the suggestion of various authors Blanck et al.

Which algal species to be used in a test battery has not been suggested, but it is obvious that selected algal species should be representative for the area of concern. Page vi - Bulletin are also reviewed but are published by photo-offset to provide the latest results without delay. The individual editors of these three publications comprise the Joint Coordinating Board of Editors with referral within the Board of manuscripts submitted to one publication but deemed by major emphasis or length more suitable for one of the others.

Page v - International concern in scientific, industrial, and governmental communities over traces of xenobiotics in foods and in both abiotic and biotic environments has justified the present triumvirate of specialized publications in this field: These three international publications are integrated and scheduled to provide the coherency essential for nonduplicative and current progress in a field Archives of Environmental Contamination and Toxicology vol.

Page viii - These reviews are either general or specific, but properly they may lie in the domains of analytical chemistry and its methodology, biochemistry, human and animal medicine, legislation, pharmacology, physiology, regulation, and toxicology; certain affairs in the realm of food technology concerned specifically with pesticide and other food-additive problems are also appropriate subject matter. Page v - Bulletin of Environmental Contamination and Toxicology vol.